m101b Receptors & Synaptic Transmission
Where are active zones positioned in the NMJ?
Across from the corners of the receptor laden postsynaptic crests
If we reintroduce (what?) protein into these RIM-1/2 double knockout animals, the presence of voltage activated calcium channels at the active zone is restored
Alpha isoform of the RIM-1 protein
enzymes that catalyze the hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP)
GTPase
This figure shows NMDA receptor currents. Which subunits would lead to the least amount of calcium entry into the cell?
GluN2A, current decays fastest 2-3, 15
The tetanus toxin is taken up predominantly by what kind of neurons that do what?
Glycinergic inhibitory interneurons that aid in the proper coordination and termination of motor commands
Loading the NT into the vesicle as its final form does what?
Greatly speeds up the rate at which a vesicle can be used to release NT
Type of AGS that bind Galpha-GDP subunits interfering Gbg trimerization
Group 2, GDIs, guanine nucleotide dissociation inhibitors
Type of AGS that bind to Gbg protein complex and mediate GTP independent dissociation from the Galpha trimerization, thus activating the Gbg protein complex
Group 3, Gbg binding proteins
when the GPCR receptor is activated by its preferred ligand, it acts as a what?
Guanine nucleotide exchange factor (GEF)
Before joining the endosome, the vesicle is uncoated by what set of proteins?
HSC 70 and auxilin
When Miledi injected calcium into the pre-synaptic axon of the squid giant synapse, without presynaptic depolarization, what happened?
Immediately subsequent to the presynaptic calcium injection, depolarization in the POSTsynaptic neuron occured
Calcium channels co-locate with vesicles where?
In the active zone
Where are some synaptic vesicles pre-positioned at the plasma membrane and wait for a signal to release?
In the active zone
AMPA receptors assemble where?
In the endoplasmic reticulum
Is ion specificity higher in voltage or ligand activated ion channels?
In voltage activated channels which usually are only permeable to one ion
Is the NT loaded into the vesicle as its final form or as a precursor that requires processing?
NT is loaded into the vesicle as its final form
The key amino acid residues responsible for generating a cation selectivity filter in the Alpha7 ACh receptor exists toward which end of the pore?
the intracellular end of the pore
can intracellular stores in the endoplasmic reticulum trigger release in other situations?
yes
has nicotine been shown to occupy the same sites as acetylcholine?
yes
What is the calcium hypothesis?
Says that strong presynaptic depolarization generates calcium influx, which leads to quantal NT release.
Activated Munc13 does what?
Sets syntaxin in its 'open' conformation so that synaptobrevin could come together with snap25 and syntaxin
Synapses with only NMDA receptors are said to be what?
Silent bc they need depolarization from AMPA receptor activation to activate
When acetylcholine or another activating ligand like nicotine binds into the pocket, the loop C gate does what?
swings shut
What are the two secretory pathways used by cells?
The regulated secretory pathway and the constitutive secretory pathway
Chemical synaptic transmission is an adaptation of what pathway?
The regulatory secretory pathway used by most cells
Both synaptotagmin and complexin directly associate with (what?) at diff stages of NT release?
The snare complex (the core release machinery
Describe the zippering of SNARE complexes that occurs during SNARE-catalyzed membrane fusion
There are 3 helices anchored in the plasma membrane (t-SNARE) that assemble with the 4th helix anchored in the vesicle membrane (v-SNARE) to form the trans-SNARE complexes, or SNAREpins. Assembly (zippering) of the SNAREpins pulls the two membranes together forcing them to fuse. Once fusion has occured, there is no longer a force pulling them together and the SNAREs are in the low energy cis-SNARE complex. 1-3, 37
does a comparison of the active zone size, vesicle pool size, or number of putatively docked vesicles for the wild type and munc13 knockout condition show differences? If so in which areas?
There are no differences in any of those areas
Adding magnesium to the external solution of the NMJ affected the muscular responses how?
There were no muscular responses at all or only ones the size of a single spontaneous release when the motor neuron was stimulated
Do water molecules occupy the full extent of the pore in pentameric ligand activated ion channels?
Yes
are nicotinic acetylcholine receptors found in the postsynaptic sarcolemma of the muscle fiber at all vertebrate neuromuscular junctions?
Yes
does the activating or inactivating ligand of a GPCR receptor embedded in a membrane have to penetrate into the plasma membrane to bind and affect the receptor's activity?
Yes
is the ACh receptor wide enough to allow water to accompany ions through the pore?
Yes
Is alpha-LTX mediated fusion abolished in Munc18 knockouts?
Yes 1-3, 43
Is the coming together of the vesicular and plasma-membrane SNAREs RIM dependent?
Yes bc RIM is needed to activate Munc13 which sets syntaxin in its open conformation
Can a GPCR receptor be active regardless of an activating ligand being bound?
Yes it is just energetically unlikely
Most ligands and drugs that act on GPCRs embedded in the plasma membrane must be what?
lipophilic
the time it takes from the transmitter to be released, diffuse across the cleft and bind with receptors on the postsynaptic membrane is referred to as what?
synaptic delay
Upon calcium entry, what acts as the calcium sensor to trigger synchronous release?
synaptotagmin
what is the primary determiner of the intracellular response to G protein-coupled receptor activation by neurotransmitters?
the G-protein
Amino acid residues in transmembrane domains 3 and 5 form direct contacts with what?
the G-protein in the active state
The two permissive mutations shown in green performed without the insertion to generate 236' affect the channel how?
the channel will conduct cations 2-2, 27
When no ligand is bound to the receptor, the receptor energetically prefers what state?
the closed (deactivated) state over the desensitized state
These RGS proteins facilitate what?
the conversion of GTP to GDP
When activated, the G alpha S subunit binds to the what?
the enzyme adenylyl cyclase 2-5, 10
Precursor molecules in both secretory pathways are packaged into vesicles where?
In the golgi apparatus
The vesicular snare (synaptobrevin) comes together with two targets (snap-25 and syntaxin) where?
In the plasma membrane of the active zone
How does redundancy work at the NMJ where each skeletal muscle fiber is innervated by only a single motor axon?
In this case there is a redundancy in active zones within the synapse
Is it possible that an acetylcholine receptor can be made from all one type of subunit?
Yes, these are homomeric receptors
Can different subunits mix and match to generate receptors that have slightly different properties?
Yes, this allows for great heterogeneity
Does presynaptic depolarization lead directly to calcium entry?
Yes, via voltage activated calcium channels
Is there an acute immediate need for extracellular calcium at the time of the action potential?
Yes, within one millisecond prior of the presynaptic AP firing
Is presynaptic depolarization (apart from APs) enough to induce synaptic release?
Yes, you don't necessarily need an AP, injecting depolarizing currents is enough
When GPCRs dimerize can the functioning of one or both receptors be affected?
Yes; Changes to a receptor's response sensitivity to a particular concentration of a ligand, as well as changes to second messenger signaling via G proteins have been observed as well
will an activated G-protein coupled receptor activate many more than just one G alpha subunit?
Yes; this leads to signal amplification
Does a binding pocket form at the Beta 2-beta 2 interface?
No
Does ablation of RIM destroy normal synaptic formation?
No
Does knockout of Munc13 impact fusion?
No
If the alpha RIM-1 protein lacks the PDZ domain, is the co-localization of voltage activated calcium channels still rescued?
No
Is every G alpha subunit associated with adenylyl cyclase signaling?
No
do postganglionic axons extend to skeletal muscles?
No
is a single active zone in the NMJ more reliable than at any other synapse?
No
Will the Beta2-alpha4 interface form a binding pocket?
No 2-2, 18
Are neurons intrinsically active?
Yes
Are proteins from all four G alpha subunit families, in addition to most of the G Beta and Gamma isoforms, found in the brain?
Yes
What activates Munc13? How?
RIM, by interfering with Munc13 homodimerization
Binds to Rab 3/27 to keep vesicles near calcium channels
RIM; Rab interacting molecules
Interact with RIM to hold vesicles to the membrane to allow for priming
Rab 3 and Rab 27
Adaptor proteins like AP2 and AP180 mark the synaptic vesicle for what?
Recycling
A pathway/process of exocytosis in which soluble proteins and other substances are initially sorted in secretory vesicles for later release in response to a signal
Regulated secretory pathway
Which proteins facilitate G alpha protein's GTPase activity, shortening the time it takes for the G alpha subunit to turn itself off?
Regulators of G-protein signaling (RGS)
Potential at which there is no net flow of ions
Reversal potential of the channel
What do the lines and their shapes connecting the different states represent?
-The lines connecting the states represent the transition energy required to pass between the two states. -The hump in each line is representative of the energy barrier between the two states, a taller hump means more energy is required and the transition between these two states is less likely and thus would take place less often. 2-2,22
What was some of the evidence that led scientists to first believe nervous activity was through electrical synapses?
-galvani's experiment of electricity causing muscle twitches in the frog -EEG recorded electrical brain activity -electrical transmission would be a simpler mode of communication between neurons -the synaptic delay of vagal stimulation was too long
To be classified as a GPCR, what does the protein need to have?
-seven 25 to 35 amino acid stretches that show a high degree of hydrophobicity; 7 transmembrane domains -must show the ability to interact with heterotrimeric G proteins
What are the three groups of proteins in the family of active zone players?
-the snare complex or snare pin -the exocytosis gatekeepers -RIM coordinating complex
What are the two types of chemical synaptic transmission?
1. Synchronous evoked or AP dependent synaptic release, occurs when an AP invades the presynaptic terminal 2. Spontaneous, no AP fired but individual quanta of NT released in spontaneous pattern
What are the 5 required processes for chemical synaptic transmission?
1. the synthesis of NT 2. release of NT 3. recognition of the NT message 4. Conversion of the chemical message back into electrical signaling 5. clearing the NT to stop the message
What are the 2 essential adaptions in synaptic transmission from the regulated secretory pathway?
1. the vesicles are smaller with simplified contents 2. the vesicles are recycled in the local endosome rather than coming from the GA
Full activation of the NMDA receptor requires the binding of how many molecules, each of glutamate and glycine or D serine.
2
Normally how many glutamate molecules must bind to the AMPA receptor to activate it?
2 2-3, 7
what type of receptor is this?
2-3, 13 NMDA
In the ach/nicotine alpha-beta interface binding region, each subunit offers how many loops that come together to form the binding pocket?
3
Nicotinic ach receptor subunits are composed of how many transmembrane domains?
4
What makes up the partial snare complex?
4 partially intertwined alpha helices, two from snap 25 and one each from syntaxin and synaptobrevin, and a complexin protein comes in
How many subunit types are there for AMPA receptors?
4; GluA1-A4
The G-protein coupled receptors in the human genome form how many families?
5 families
How do WT and munc13 KO synapses differ?
:In their synaptic transmission, munc13 KO affects priming not docking or fusion
Does the pentameric ligand-activated ion channel family include receptors that are cationic or anionic permeable?
:It inlcudes both types of receptors within the family
On the presynaptic side of the motor neuron at the NMJ how many active zones are there?
:Multiple; more than one
Is this a NMJ or postganglionic varicosity? How can you tell?
:NMJ bc it has deep invaginations and folds in the sarcolemma and the active zones are lined up with the receptor dense areas of the crests (1-4, 29) Postganglionic varicosity bc it lacks the detailed structure of deep invaginations in the postsynaptic membrane and tightly controlled apposition of presynaptic active zones with postsynaptic receptor densities
Are glycine or D serine released by the presynaptic neuron at the glutamatergic synapses in which they exist?
:NO, they are just present there, hence they are called coagonists instead of ligands
Can a neuron be both pre and postsynaptic?
:Yes just not at the same synapse
where proteins are refreshed or repaired as necessary; endocytosed vesicle is brought here
:local endosome
Because of its interaction with the guanine dissociation inhibitor, while the G-alpha protein is inactive and cannot bind to and innactivate what?
:the G beta/gamma subunit
Ligand activated ion channels tend to be selective only for the (WHAT?) of the ion
:the charge of the ion, so they tend to be permeable to some degree to most relevant cations, et
Is this a receptor or a subunit?
A single subunit of a nicotinic ach receptor 2-2, 13
Which disease causes slow degradation and death of motor neurons in the spinal cord and brainstem, as well as neurons of the primary motor cortex.
ALS aka Lou Gehrig's Disease
what type of glutamate activated ion channels display rapid almost complete desensitization shortly after binding glutamate?
AMPA (2-3, 10)
For the central nervous system and almost exclusively in the forebrain, the postsynaptic responses at these synapses result from the activation of what two types of ligand activated ion channel receptors?
AMPA receptors and NMDA receptors that often appear at synapses together
an electron dense material spread throughout the synaptic cleft between the presynaptic motor axon and the postsynaptic muscle fiber
Acetylcholinesterase
organophosphates block what? prolonged contraction
Acetylcholinesterase 1-4, 21
what ends the message to contract the muscle fiber?
Acetylcholinesterase within the synaptic cleft breaking down acetylcholine into acetate and choline
Activation of the acetylcholine activated ion channels in the sarcolemma generates what?
An end plate potential in the muscle fiber (this is a transient depolarization that triggers the initiation of an AP
What is the active zone?
Area in the presynaptic axon usually found on the axonal terminal where the presynaptic neuron releases the NT message from vesicles into the synaptic cleft
The phosphorylation of the intracellular C terminal tail encourages the binding of (what?) to the receptor.
Arrestin
Is the magnesium ion in the NMDA channel pore at hyper or depolarized values?
At hyperpolarized values (near the neuron's resting potential
What supports removal of clathrin and prepares readying the synaptic vesicle for endosomal entry?
Auxilin and HSC-70
Why does a channel when bound transition from closed to open in the beginning even though the Desensitized state is the lowest energy one?
Bc there are high-energy barriers to overcome to reach the D state while the required energy to reach O' is smaller (smaller hump) and O' is still preferred over closed
why will most acetylcholine receptors be in a closed state and tend to stay in a closed state when no acetylcholine is bound?
Because large energy barriers exist between this state and any of the other states
Botulinum and tetanus toxins produce the same result in a cell, so why are their resulting phenotypes completely different?
Because they act on different neurons, the toxins are taken up by different types of neurons
Class of agents for GPCRs that promote (in equal proportions) both activation of the GPCR's guanine nucleotide exchange function as well as the B-arrestin pathway that eventually leads to receptor internalization
Biased agonist
The inactive non-signaling state of the GPCR can be stabilized by what?
Binding antagonists or a class of molecules called inverse agonists
Type of AGS that facilitates Galpha exchange of GDP for GTP
GEF; guanine nucleotide exchange factors, Group 1
What does a calcium chelator such as BAPTA do?
Binds to free molecules of calcium to prevent them from binding to their target sites
What ion or ions is this channel permeable to?
Both Na and K since changes in extracellular Na and K concentrations causes the IV curve to shift 2-1, 19
Knockout of Munc13 profoundly reduces what type of neurotransmission?
Both evoked (synchronous) and spontaneous
In mammals, complexin present at the synapse affects spontaneous and AP dependent release how?
Both types of release are enhanced
How does neostigmine help MG?
By inhibiting acetylcholinesterase it raises the concentration of acetylcholine in the synaptic cleft, allowing for more effective activation of the postsynaptic acetylcholine receptors not yet destroyed by the immune system
This kinase phosphorylates the GPCR's intracellular what?
C terminal Tail
What are the two calcium binding zones on synaptotagmin?
C2A and C2B}
what causes synaptotagmin to change conformation and bind to the partial snare complex near the vicinity of the complexin binding?
Calcium binding to C2A and C2B
What is a molecule that is an inverse agonist of the GPCR receptor that inactivates it?
Carazalol
What does curare do?
Causes a weaking or paralysis of a muscle by competing with ACh at the NMJ; doesn't allow contraction
Which receptor class mediates the majority of cellular responses to external stimuli?
GPCR
which receptors are 7-transmembrane domain monomers?
GPCR
Synapse where NTs are secreted and activate receptors on the postsynaptic neuron
Chemical synapse
Applies the brake on NT release OR facilitates NT release (currently still being debated)
Complexin
Apex of each sarcolemma fold
Crest
NMDA receptors require (what?) to relieve Mg2+ block of the ion channel following glutamate activation
Depolarization
Describe Ramon y Cajal's law of dynamic polarization
Describes how a neuron uses its dendrites to take inputs from other neurons, processes that info and if it decides to, passes it onto postsynaptic neurons at its axon terminals
What is the long-term preferred state of the Ach receptor if ACh is present long enough?
Desensitized state
Describe the response of an individual nicotinic acetylcholine receptor to acetylcholine
Despite the continual presence of ACh in the solution, the single channel flickers on and off as it binds and unbinds ACh in a thermodynamically random manner. 2-1, 16
What is referred to as a receptor's stoichiometry?
Differences in the specific combinations of multiple independent protein subunits that come together to form the subunit
RIM binds with Rab 3 and Rab 27 GTP-binding proteins during which phase of NT release?
Docking
holding the synaptic vesicle at the active zone once it is delivered there, this is done through interlocking of proteins that are bound in the plasma and vesicle membranes respectively
Docking
What are the three phases of NT release?
Docking, Priming and Fusion
The protein (what?) then comes in, wraps itself around the stock and acts as molecular scissors severing the Clathrin-coated synaptic vesicle from the rest of the plasma membrane
Dynamin
What pinches off the lipid stalk from the clathrin-coated synaptic vesicle?
Dynamin
The post-junctional folds in the sarcolemma immediately opposed to the motor axon terminal do what?
Effectively increase the membrane surface area exposed to the synaptic cleft by a factor of two to eight depending upon the species of animal
What is the last protein to bind to the complex during GPCR inactivation before it is edocytosed?
Extracellular signal regulated kinase (ERK)
the G-protein coupled receptor is phosphorylated when it encounters what?
GPCR kinase
Which class of NT receptors are metabotropic receptors?
GPCRs
What are so-called orphan G-protein-coupled receptors?
GPCRs that have not yet been linked to endogenous ligands; we don't know what molecules in the body activate them
AMPA and NMDA receptors are made up of how many distinct genetically encoded subunits that come together in the endoplasmic reticulum to form a functional receptor?
Four, they are tetrameric
what technique consists of physically breaking apart ,that is fracturing, a biological sample frozen at extremely low temperatures?
Freeze fracture
Calcium binding to C2A and C2B regions of synaptotagmin triggers what?
Fusion
Process that detects calcium influx when the AP occurs, allowing the full SNARE complex to form and the vesicle fuses with the membrane
Fusion
The process whereby the synaptic vesicle and plasma membrane become one and release the neurotransmitter is known as what?
Fusion
While G-protein-coupled receptors themselves do not have ion channels, their activation can modulate the function of ion channels through what?
G Beta Gamma signaling
Adenylyl cyclase is considered an effector protein of which G subunit?
G alpha S subunit
Which proteins eventually turn themselves off by promoting hydrolysis of the GTP that is bound to them to GDP?
G alpha protein
Are G alpha or beta/gamma proteins weak GTPases?
G alpha proteins
which proteins are a molecular timer that sets limits on how long signaling can occur?
G alpha proteins
Which G subunits regulate a number of effectors at the cell surface, including adenylyl cyclase isoforms, Kir3 and voltage-gated calcium channels, phospholipase Cβ isoforms, and PI3K isoforms?
G beta/gamma
the receptor with the ligands still bound activates other inactive (GDP or GTP?) bound Alpha subunits of heterotrimeric G-proteins activating them as well.
GDP
What does carazalol do?
Inhibits activation of the GPCR receptor
Which class of NT receptors are ligand activated ion channels?
Ionotropic receptors
What are the two classes of NT receptors?
Ionotropic receptors and G-protein-coupled-receptors
How does alpha-Bungarotoxin paralyze an animal and cause respiratory failure?
It binds to the acetylcholine receptor at the same place acetylcholine would, preventing acetylcholine from binding and activating skeletal muscles including the diaphragm 1-4,15
what does alpha-LTX do?
It can stimulate calcium independent synaptic vesicle exocytosis
What happens when you apply alpha-LTX at munc13 deficient synapses?
It causes strong synaptic release
Knocking out complexin in fruit flies affects spontaneous transmission how? how about synchronous transmission?
It enhances spontaneous transmission but reduces synchronous AP dependent release}
Is synaptotagmin bound to the plasma or vesicle membrane?
It's bound to the synaptic vesicle membrane
Is the synaptic cleft greater in NMJ or central synapses?
Larger in NMJ than central synapses (30 nm opposed to 20 nm
when a G beta, gamma bound calcium channel is activated by depolarization, will the channel pass more or less calcium with greater depolarization?
Less
molecules that are oily or greasy and difficult to dissolve in water; hydrophobic
Lipophilic
Glutamatergic presynaptic terminals emanate in a distributed fashion across the NS forming both local and distant projections that depend on (what?) for NT release
Local astrocyte assisted glutamate production
the types of ions the receptor channel is permeable to and the local membrane potential of the postsynaptic density plasma membrane in which the ion channel is embedded.
Loop C
Does a biased agonist cause the activity it prefers at lower or higher concentrations?
Lower concentrations, at higher concentrations both activities will be promoted at different levels by the drug 2-4, 19
Would this be a mammalian or invertebrate synapse?
Mammalian bc complexin is enhancing both types of synaptic release and in invertebrates it only enhances spontaneous not AP evoked release 1-3, 35
Are NT-activated receptors more like Na+/Ca2+ channels or K+ channels? why?
More like K+ channels bc they are composed of multiple independently genetically encoded subunits
Can the application of alpha-LTX cause any synaptic vesicles to be released in the absence of Munc18?
No
Botulinum is taken up by what types of neurons?
Motor neurons (1-3, 30)
NMDA receptors containing GluN2B subunits have much longer lasting responses to activation, would this lead to more or less calcium entry into the cell?
Much more Ca2+ entry into the cell
Syntaxin requires an ineraction with (what?) to be placed into the 'open' coformation prior to the formation of the partial snare complex?
Munc13
Hypothesized that this protein: mediates lipid mixing during vesicle membrane, plasma membrane fusion, catalyzes or nucleates snare complex formation in the active zone, organizes the snare complex around the fusion site.
Munc18
Disease where receptors in the muscles that control the eyelids and eye movements, as well as facial muscles controlling expressions, chewing, swallowing and speaking, are a particular target, especially early in the disease. -an autoimmune disorder where the body produces antibodies against the acetylcholine receptors in the muscle, designating them for attack by the body's immune system.
Myasthenia Gravis
If the NMJ is almost unrecognizable with the synaptic cleft approximately three times wider than normal and little evidence of sarcolemma folds, what disease does the patient most likely have?
Myasthenia Gravis 1-4,23
Glycine or D serine are coagonists for which receptor?
NMDA glutamate-activated receptor
Local astrocyte assisted glutamate production
NMDA receptor
a specialized synapse between the motor neuron axon and skeletal muscle fiber, a chemical synapse which uses the neurotransmitter acetylcholine
NMJ, aka motor end plate
Do the plasma membranes of two neurons forming a synapse ever touch?
NO
If you activate a channel and change the amount of a single ion type in the extracellular solution and the new curve overlays the old curve, is the channel permeable to that ion?
NO
Is the NT (the ligand) the 'gate' in ligand activated ion channel receptors?
NO, it is instead the activating signal, the physical structure that holds back the flow of ions when the channel is closed is part of the channel protein
Does knocking out Munc13 prevent docking?
NO, just prevents priming
Does a cDKO or RIM 1 and 2 affect the number of synaptic vesicles in the neuron?
NO, just the amount docked in the active zone
Are addictive properties of nicotine thought to be via acetylcholine receptors in the NMJ?
NO, they are thought to be via acetylcholine receptors in the brain
Class of agents that opposes activation of the receptor by binding to the same receptor sites a full or partial agonist would, thereby blocking binding of full or partial agonists to the receptor.
Neutral antagonist
These receptors mediate postsynaptic responses in skeletal muscles at the NMJ in vertebrates and also other forms of these receptors in the brain mediate nicotine addiction and attention.
Nicotinic acetylcholine receptors
Receptors in the NMJ that pass relatively more Na+ in than K+ out to lead to muscle fiber excitation when activated
Nicotinic acetylcholine receptors 1-4,14
Are metabotropic nicotinic ach receptors that are activated by ach also activated by nicotine?
No
Is the binding to and activation of adenylyl cyclase by the G alpha subunit an amplifying step?
No because there is a one-to-one correspondence of the G alpha subunit with an adenylyl cyclase molecule
are all synaptic vesicles docked?
No only a few of them are
Are the phenotypes resulting from botulinum and tetanus toxins the same?
No they are entirely different
Do response properties always correlate across different activating ligands between receptors with different stoichiometries?
No, diff stoichiometries can have similar responses to one type of ligand (ACh) but completely unalike responses to another ligand 2-2,9
Are there any morphological differences in the active zones between a WT and a munc13 KO?
No, the munc13 KO synapse appears to be completely normal, no differences in the number or location of vesicles
Do the new vesicles bud off the endosome already filled?
No, they bud off ready to be filled but not filled yet
Are postganglionic axons highly myelinated?
No, they often lack myelin, have much slower conduction velocities
Do Acetylcholine receptors respond to acetate and choline?
No, thus signalling ends when this breakdown of acetylcholine occur
Does removing extracellular calcium at the NMJ affect the presynaptic motor neuron's AP?
Not at all
How many effector molecules can each of the activated G protein subunits go on to activate?
One or multiple
Describe an electrical synapse
One where neurons are in electrical continuity with one another via interlocking proteins with large channels that allow the exchange of ions and other molecules
Class of agents that produce weaker than maximum receptor activity at saturating concentrations for GPCRs
Partial agonists
Which NT-receptor family includes nicotinic acetylcholine receptors, gaba and glycine receptors, and two kinds of serotonin activated ion channels?
Pentameric family, where five subunits come together
after the synaptic vesicle fuses with the active zone plasma membrane, it moves out of the active zone via the (what?) region and is then retrieved via what?
Perisynaptic .... endocytosis
Region near a synapse, just outside the active zone
Perisynaptic zone
Where synaptic vesicles are recovered through endocytosis, just outside the active zone
Perisynaptic zone
an action potential propagates along the sarcolemma and throughout the t-tubule system, leading to release of calcium from where?
Sarcoplasmic reticulum
what catalyzes the production of inositol triphosphate, or IP3 for short, and diacylglycerol, also known as DAG, which leads to the release of intracellular calcium and activation of protein kinase C?
Phospholipase C
Is RIM plasma or vesicle membrane bound?
Plasma membrane
fibers from the ganglion to the effector organ, these neurons are directly responsible for changes in the activity of the target organ via biochemical modulation and neurotransmitter release
Postganglionic fibers/neurons
Sits opposite the active zone, electron dense region of the postsynaptic neuron
Postsynaptic density
Is it the pre or postsynaptic neuron that determines the response to a NT?
Postsynaptic neuron
Nicotinic acetylcholine receptors are permeable to what?
Potassium and sodium
What are the three parts of the tripartite?
Presynaptic and postsynaptic neuron and the partner astrocyte
what prepares the vesicle for triggering of calcium-dependent fusion with the plasma membrane to cause neurotransmitter release?
Priming
What does tetanus result in?
Prolonged or unending contraction of skeletal muscles
Botulinum and tetanus toxins act as what?
Proteases
Which symbol represents the inactive low affinity state when an activating ligand referred to as an agonist is bound.
R'
Which symbol represents the activated agonists bound state characterized by substantial global rearrangement of helices and side chains on the intracellular side of the receptor that exposes the G-protein binding pocket?
R'' 2-4,17
State when the G-protein does bind in the binding pocket, a new conformation state represented by (what?) occurs
R* 2-4, 17
a distinct G-protein signaling conformation of a receptor which can be achieved upon full engagement and activation of the GPCR G Alpha Beta, Gamma complex.
R*G
While it is the intrinsic GTPase function of the G alpha subunit itself that catalyzes the hydrolysis, when (what?) proteins bind to G alpha proteins, they stabilize the transition state when G Alpha nucleotide hydrolysis occurs.
RGS proteins
What genes in the RIM family of proteins are used by the cell to generate RIMs that participate in the RIM- Rab 3, Rab 27 interaction between the synaptic vesicle and the active zone of the plasma membrane?
RIM 1 and RIM 2
Proteins in this group are intimately involved in supporting the three phases of docking, priming and fusion by coordinating the key players in each of these steps
RIM coordinating complex
The Erev for ligand activated ion channels is equal to what?
Some weighted function of the reversal potentials where the weightings depend upon the relative permeability to different ions
Are the G-protein coupled receptor and its associated heterotrimeric G proteins semi-autonomous entities?
Yes
what determines the number of ligand binding sites for acetylcholine?
Subunit types and quantities
what hydrolyzes GTP back to GDP turning off the G alpha protein?
Surrounding regulators of G-protein signaling (RGS)
Where two neurons come in very close proximity to communicate with one another
Synapse
What proteins make up the snare complex or the snare pin?
Synaptobrevin, Snap-25 and syntaxin
Binds to 5 calcium ions, which is necessary for vesicle fusion, has many isoforms
Synaptotagmin
What are the two proteins making up the second group in the family of active zone players called the exocytosis gatekeepers?
Synaptotagmin and complexin
Which NT-activated ion channel family is made up of cation permeable ion channels that are sensitive to glutamate; the AMPA and NMDA channels are ubiquitous mediators of excitatory signaling in the central nervous system.
Tetrameric family; made up of four individual subunits
Which ion channel family's members mediate the vast majority of excitatory signaling in the central nervous system?
Tetrameric ligand activated ion channels
Is the NMJ or central synapse greater in area in humans?
The NMJ by 100 to 1000x greater in area
What particular region of the RIM protein is the point of interaction between RIM and the voltage activated calcium channels?
The PDZ domain
By adding presynaptic TTX in the giant squid axoaxonic synapse, was the presynaptic or postsynaptic AP more greatly affected?
The postsynaptic AP is more dramatically affected
Are there multiple binding sites for all stochiometries of nicotinic ach receptors?
Yes
The plasma membrane region of the presynaptic terminal can be subdivided functionally into what two parts?
The active zone and the perisynaptic zone
Which subunit offers loops A, B and C?
The alpha subunit 2-2, 20
what supporting cell often times removes neurotransmitter from the synaptic cleft?
The astrocyte by its end feet that's around the synapse
What plays a critical role in regulating extracellular potassium in the synapse?
The astrocytes
Which subunit offers loops D, E and F on the minus or negative side?
The beta subunit
What does the yellow triangle signal?
The binding of an activating ligand 2-4, 17
All 3 mutations together affect the channel how?
The channel will conduct anions like chloride but not pass sodium or potassium cations 2-3, 27
what is taken up by the motor axon via the its transporter protein and re-synthesized into acetylcholine?
The choline
Describe what the 'safety factor' is in the NMJ
The fact that 3 to 5 times as much NT is released than is required to cause muscle fiber contraction, it provides certainty that neuromusclular transmission remains effective under stressful physiological conditions
When we say the NS accounts for the high unreliability of chemical synaptic transmission through redundancy, what are we referring to?
The fact that many presynaptic neurons must reliably act together in unison to cause a postsynaptic neuron to fire, so there are many presynaptic neurons acting on one postsynaptic neuron
Once the synaptic vesicle fuses with the active zone plasma membrane, it is recycled through where?
The local endosome
Release of calcium from the sarcoplasmic reticulum transiently increases the concentration of calcium in where?
The muscle fiber cytoplasm
The method that is used to clear and effectively end the NT depends on what?
The neurotransmitter
Which electron micrograph is showing the cDKO of genes RIM1 and 2? How can you tell?
The one on the left because without RIM 1 and 2 the cell cannot generate RIM proteins that participate in the RIM Rab 3 and 27 interaction that holds the synatptic vesicle membrane close to the plasma membrane (no docking without RIM 1 and 2 1-3, 25
Which freeze fracture frame shows a stimulated presynaptic plasma membrane? 1-3,38
The one on the right bc it shows larger pockmarks where vesicles have fused with the membrane; note also this shows the close co-location of vesicles and voltage activated calcium channels
Where can the transporter proteins responsible for NT uptake be found?
They can be in the perisynaptic region of the presynaptic terminal, in the end feet of the astrocyte surrounding the synapse, or both. 1-4, 8
Can Acetylcholine Receptors flicker open briefly when bound or unbound?
They can flicker open both when bound and unbound, the flicker open energy state is represented by O* in a notional energy landscape
How were the vesicles that first picked up HRP different from the vesicles that were ready for release?
They had an electron dense coating on the outside and were far away from the active zone
During endosomal recycling, were the first vesicles that initially picked up HRP from the synaptic cleft found to be far or near from the active zone?
They were far from the active zone (1-4, 4)
What is the primary purpose of the AP?
Trigger synaptic transmission
Which NT-receptor family is sensitive to activation by purines such as ATP
Trimeric family, 3 subunits come together
The axon terminals of these postganglionic axons have characteristic bead shaped swellings known as what?
Varicosities
What structures contain multiple active zones so that large amounts of neurotransmitters are released to stimulate the adjacent smooth muscle, cardiac muscle, or glands that are the target.
Varicosities of postganglionic axons
How does the G beta/gamma subunit get turned off?
When the G alpha is bound to GDP its signaling stops and its able to trimerize with the G beta/gamma protein complex which turns the G beta/gamma subunit off in the process
What is the postsynaptic density?
Where the NT receptors and their associated signaling molecules are embedded in the cell membrane of the postynaptic neuron
What method allows you to see detailed protein strucutre including the subunits?
X-ray crystallography
Will the alpha4-beta2 interface form a binding pocket?
YES
After the G protein-coupled receptor facilitates the exchange of GDP bound to the G alpha subunit for a GTP, is the G-protein signaling process decoupled from the G protein-coupled receptor?
Yes
The primary effect of knocking out the rim one and rim two proteins at the synapses is what?
a dramatic reduction in the number of vesicles considered to be docked
What is the signal to release?
a sudden and local rise in intracellular calcium at the site of the synaptic vesicle.
When the NT binds to a GPCR receptor, the receptor becomes activated and triggers a biochemical signaling cascade by activating what?
a three protein complex, referred to as a heterotrimeric G-protein that is associated with it.
Nestled in between two of the alpha 4 to beta-2 subunit interfaces are what?
acetylcholine binding sites
an enzyme that speeds the degradation of acetylcholine into acetate and choline
acetylcholinesterase
The coated vesicle is then transported away from the plasma membrane via (what?) on its way to the endosome.
actin
channel opens in response to ligand binding
activation
What is at the apex of each fold, or crest, of the sarcolemma?
an abundance of acetylcholine activated ion channel receptors
the activated acetylcholine receptor generates what kind of postsynaptic potential?
an excitatory postsynaptic potential or EPSP.
Both botulinum and tetanus toxins act as proteases and produce what same result?
arrest of synaptic transmission
The activated (what?) serves to nucleate the same clathrin AP2 complex used for synaptic vesicle endocytosis.
arrestin
Why is the receptor called a nicotinic acetylcholine receptor?
because the drug nicotine activates this kind of acetylcholine receptor
When GTP is hydrolyzed to GDP, the Alpha subunit does what?
becomes inactive and binds a beta-gamma subunit, reconstituting an inactive heterotrimeric G-protein
what pathway eventually leads to GPCR receptor internalization?
beta arrestin pathway
Where does complexin insert itself in the partial snare complex?
between synaptobrevin and syntaxin
Under hyperpolarized conditions when an NMDA receptor is activated, magnesium ions immediately rush in to do what?
block the pore of the channel
The diuretic cyclothymic has the unusual property that it does what?
blocks desensitization in AMPA type glutamate activated ion channels 2-3, 10
Does the size of the response, the decay of the response, or both, vary for the different receptor stoichiometries?
both
Fusion starts with what?
calcium entry into the active zone
Any AMPA receptor lacking a gluA2 type subunit will also be what?
calcium permeable
The closing of the loop C gate does what?
causes a conformational change in the protein that causes opening of the pore to allow cations to permeate the pore
Inhibition of motor neurons by Cl- mediated currents gave evidence for chemical or electrical synaptic transmission?
chemical
The isolated heart preparation with the one innervated vagus nerve heart and other not, showed what?
chemical communication since the two hearts were connected by solution but only one heart was innervated by the vagus nerve. when the vagus nerve was stimulated, both hearts ended up slowing thier heart rate, the innervated one slowed first and then the non innervated one, this showed evidence of chemical molecules being released at the synapse
AP2 and AP180 bind to (WHAT?) and interact with other proteins to build (WHAT?) triscalia, which bind to the plasma membrane that was formerly part of the vesicle membrane.
clathrin 1-4, 6
What does cDKO stand for?
conditional double knockout
When glycinergic inhibitory interneuron synapses are no longer functional, what results?
continual muscle excitation (tetanus)
rise in cytoplasmic calcium leads to (WHAT?) of the muscle fiber via actin and myosin.
contraction
The enzyme adenylyl cyclase mediates the production of what?
cyclic AMP from ATP
While bound to an active G alpha S subunit, adenylyl cyclase will catalyze the production of many molecules of what?
cyclic AMp
Which side of the GPCR receptor opens to create a binding pocket for the C terminal helix of a compatible G-protein Alpha subunit once the agonist binds?
cytoplasmic side (intracellular
Channel stops conducting when ligand dislocates from receptor
deactivation
Channel stops conducting, despite continued presence of the activating ligand
desensitization
the binding pocket of the GPCR is formed principally by which transmembrane domains
domains 3, 5, 6, and 7, with the extracellular loops that connect these helices also playing a part
Each central synapse has how many active zones?
each central synapse only has a single active zone
What are the two primary methods of ending the NT message?
enzymatic breakdown and uptake
Does carazalol bind on the intra or extracellular end of the GPCR?
extracellular
The binding pocket for AMPA receptors is in the extensive (what?) of the receptor.
extracellular domain
Acetylcholine and neuropeptides rely upon enzymes present (where?) to speed the degradation of the neurotransmitter into inert chemicals.
extracellularly, for example in the synaptic cleft
When this class of agents bind to a G protein coupled receptor, they promote the receptor achieving its active conformation and maximal guanine nucleotide exchange factor activity.
full agonists
Knockout of Munc18 obliterates events of which phase?
fusion
For NMDA receptors, there is a dramatic difference in the kinetics of the receptor current depending upon what?
gluN2 subunit composition
Crystal structures suggest that the dimers of NMDA receptors are hetero or homodimers?
heterodimers
The rim RAB 3 and RAB 27 interaction does what?
holds the synaptic vesicle membrane close to the plasma membrane to allow for priming to occur
Ionotropic glutamate synapses are the most abundant synapses where?
in the CNS
What does hydrophobicity indicate?
indicates the preference of these amino acids to be sequestered/isolated in lipids like the plasma membrane; higher hydrophobicity- wants to be more in the plasma membrane
the conversion to an anionic selectivity filter in the alpha7 ach receptor cannot happen without what insertion?
insertion of prolene, P236'
Method in which a tiny patch of membrane is pulled off the neuron and the cytoplasmic side of the receptor is exposed to the outside of the electrode
inside-out patch recording
A negative sign on the current during volt clamp means the net balance of positive charge flows in or out of the neuron?
into the neuron 2-1, 18 AB
(What?) are the class of drugs that would most commonly be considered to have antagonistic behavior against G-protein-coupled receptors.
inverse agonists
Class of agents (drugs) for GPCRs that reduce receptor activity to below baseline levels
inverse agonists
Does nicotine activate the ionotropic or metabotropic nicotinic ach receptors?
ionotropic
What does it mean if a channel is heteromeric?
it is made up of more than one type of subunit
How does the NMJ account for low probability of NT release following a single AP?
multiple active zones in the motor axon; there are so many active zones in the single motor axon so that it is guaranteed that some of them will release acetylcholine each and every time an action potential invades the motor axon terminal.
a common treatment for the muscle weakness that results from Myasthenia Gravis; it is an acetylcholinesterase inhibitor
neostigmine
are all ligand activated ion channels neurotransmitter receptors?
no
How does adding organophosphates affect muscle contraction?
organophosphates block acetylcholinesterase, leaving acetylcholine in the synaptic cleft, causing the muscle fiber to remain in a state of prolonged contraction called tetanus.
A positive sign on the current during volt clamp means the net charge flows in or out of the neuron?
out of the neuron 2-1,18 D
Method in which a tiny patch of membrane is pulled off the neuron and the extracellular side of the receptor is exposed to the outside of the electrode
outside out patch recording
What does botulism cause?
paralysis and weakness affecting both skeletal and smooth muscle function
The G alpha q/11 family works through what effector molecule?
phospholipase C
Activation of protein kinase A can lead to what?
phosphorylation of many downstream targets
a cyclic AMP dependent protein kinase, activated when two cAMP molecules combine to the catalytic subunit
protein kinase a
Areas of high electron density in electron micrographs usually signal the presence of large amounts of what?
proteins
Many other neurotransmitters, for example, Glutamate, gaba or glycine, Norepinephrine, Dopamine and Serotonin are removed from the synaptic cleft via what?
proteins called transporters
How does the NS acount for chemical synaptic transmission being highly unreliable?
redundancy
Muscle fiber membrane
sarcolemma
what refers to how likely a receptor is to activate in a given concentration of it's activating ligand.
sensitivity of the receptor
a separate genetically encoded protein.
subunit
some of these very same types of transporters responsible for NT uptake, which can also be found in the synaptic vesicle membrane, are also important in what?
the loading of neurotransmitter into the synaptic vesicle
Rather than returning directly to the pool of vesicles that were ready for release, the vesicles with the electron dense coating that initially picked up HRP appeared to become part of what?
the local endosome 1-4, 4
the muscle fibers ability to sense acetylcholine was localized to what area?
the motor end plate.
a method sensitive enough to record from single ligand activated ion channels
the patch clamp method
If a prolene is inserted inbetween the glycine at position 236 and glutamate position 237, called insertion P236', and is done by itself, what happens to the alpha7 ach pore?
the pore becomes non-conducting.
A receptor's stoichiometry affects what?
the response properties of the receptor to its ligand
the kinetics of activation, desensitization and deactivation refer to what?
the size and shape of the response of the channel current
Whether the electrical signal is excitatory or inhibitory depends upon what?
the types of ions the receptor channel is permeable to and the local membrane potential of the postsynaptic density plasma membrane in which the ion channel is embedded.
What is the crucial difference between the regulated and the constitutive secretory pathways?
the vesicle being released via the regulated secretory pathway requires a signal to trigger release whereas in the constitutive process, vesicles are released on arrival at the cell membrane, no extra signal required
Since you don't know exactly how many of each subunit make up the channel, since it can vary, what do the responses represent?
these responses represent a weighted average of the different possible combinations of the two subunit types. 2-2, 8
Man-made drugs based on curare are used to do what?
to block neuro-muscular activity, for example, during surgery and intubation
the silent synapses (just NMDA no AMPA receptors) are thought to play an important role in what?
:the expression of long-term potentiation 2-3, 13
NMDA receptors are known for their permeability to what? what else are they permeable to?
:to calcium, but they are also permeable to sodium and potassium
Synaptotagmin acts as what?
A calcium sensor
activating the alpha subunit at the same time causes its dissociation from the beta gamma subunit dimer, this leads to what?
Activation of the beta gamma subunit dimer
The surface of the presynaptic plasma membrane that sits opposite the electron dense region of the postsynaptic neuron
Active zone
What connects the clathrin to the vesical membrane?
Adaptor proteins
When does the ligand get removed from the GPCR receptor?
After it is endocytosed but before it is reinserted into the plasma membrane
the absence of RIM proteins appears to greatly reduce or enhance the presence of voltage activated calcium channels at the presynaptic terminal?
Greatly reduce
regulators of G-protein signaling serve as what?
GTPases
Which family of G alpha subunits is antagonistic to Galpha,s and reduced adenylyl cyclase activity?
Galpha,i family 2-5, 10
Which subunit renders AMPA type glutamate receptors impermeable to calcium?
GluA2
Which subunits provide the glutamate binding sites in NMDA receptors?
GluN2
Is cyclic AMP binding to the regulatory subunit of protein kinase A an amplifying step?
No bc it is two to one, so this is not an amplifying step
Will the ligand activated ion channel's reversal potential be the same as the reversal potential for any of the ions to which it is permeable?
No bc ligand activated ion channels are not as ion selective as voltage activated ones, permeable to multiple ions
Which NMJ has more severe MG? How can you tell? 1-4, 24
The one on the right bc the neuromuscular junction is almost unrecognizable with the synaptic cleft approximately three times wider than normal and little evidence of sarcolemma folds
once calcium binds, synaptotagmin binds to what?
The partial snare complex
In some presynaptic terminals, NT receptors that modulate synaptic release can also be found in which zone?
The perisynaptic zone
Injecting a calcium chelator affected the pre and postsynaptic action potentials how?
The presynaptic AP was not affected at all but the postsynaptic AP completely does not occur
Explain how AMPA receptor subunits assemble
They assemble as dimers of dimers, two subunits come together to form a dimer and then this dimer joins another to make a fully functional receptor 2-3, 8
In a postsynaptic density, do each of the nicotinic ACh receptors flicker on and off in the presence of neurotransmitters?
Yes, the NTs bind and unbind from individual receptors but together they produce a smooth response
Are fusion and the completion of zippering of snare complexes coupled?
Yes
Are tetramers of GPCRs possible?
Yes
Can G-protein-coupled receptors join together in dimers of like or different receptors?
Yes
Do NT-activated ion channels differ by the structure of their subunits?
Yes
Do NT-activated ion channels differ in how many subunits come together to make a functional receptor?
Yes
Do adjacent subunits both contribute to the binding pocket in nicotinic ach receptors?
Yes
Do all three phases of NT release take place in the active zone?
Yes
Do nmda receptors also come together in a dimer of dimers configuration?
Yes
Do the G alpha, G beta/gamma subunits independently signal their downstream effectors?
Yes
Does a synapse in the CNS have the same protein players and active zone design as a NMJ onto skeletal muscle or an autonomic varicosity synapse?
Yes
Does complexin have an important role in modulating the likelihood of vesicle fusion with the plasma membrane that results in neurotransmitter release?
Yes
Does subunit composition affect size of ion flow through nicotinic acetylcholine receptors?
Yes
Is RIM a family of proteins?
Yes
Is cyclic AMP a second messenger?
Yes
Is each subunit of the G-protein genetically encoded separately?
Yes
Is rab a family of proteins?
Yes
Is the GPCR a single protein?
Yes
Is the alpha subunit layout highly conserved across isoforms?
Yes
Is the machinery used for neurotransmitter release the same across all types of synapses?
Yes
When the GPCR and the C terminal tail complex are endocytosed to stop the receptors ability to signal, is the ligand still bound to it?
Yes
Will any given biased agonist be better at promoting one or the other type of activity?
Yes
is the pentameric ligand-activated ion channel pore structure conserved?
Yes its highly conserved
Can a receptor go from closed to desensitized without ever opening?
Yes, a receptor can transition directly from one state to any of the other states but it is unlikely to do so
are NMDA type glutamate activated ion channels often co-located with AMPA receptors? why or why not?
Yes, bc the AMPA receptor activation can provide the depolarization needed for NMDA receptors to activate
Does there seem to be a threshold effect in the presynaptic depolarization leading to postsynaptic response?
Yes, below 50 mV presynaptic depolarization there is no postsynaptic response and after 50mV you quickly go up to the maximum postsynaptic response (1-2, 10)
Is presynaptic calcium alone sufficient to cause NT release?
Yes, depolarization of the presynaptic axon is not required
Does subunit stoichiometry affect the size and shape of the response?
Yes, different relative amounts of each subunit can affect the channels current/response 2-3, 10
Can AMPA receptor dimers be both homo or heteromeric?
Yes, dimers can be made up of two of the same AMPA receptor subunits or two different ones
Does the nervous system have endogenous behavior?
Yes, is active on its own
Lack of synaptic transmission in motor neurons means what?
loss of motor function
When synaptotagmin binds to the partial snare complex near the vicinity of the complexin binding, complexin's interaction with synaptobrevin and syntaxin changes as a result. This likely does what?
lowers the energy required to initiate completion of the partial snare complex, resulting in fusion
a single G beta gamma protein complex binds to the intracellular n, c and domain 1-2 linker portions of some voltage activated calcium channels that do what?
mediate synaptic vesicle release 2-5, 17
The GPCR acting as a GEF means it does what?
mediates G alpha's exchange of GDP for GTP; catalyzes the exchange of a molecule of guanosine diphosphate (GDP) that is attached to the alpha subunit of the heterotrimeric G-protein for a molecule of guanosine triphosphate (GTP)
Pentameric Ligand-activated ion channel pore is formed by what?
the M2 transmembrane domain from each of the 5 subunits that faces into the channel pore
The exchange of GDP for GTP activates what?
the alpha subunit
Nicotine (acetylcholine mimetic) binding occurs at what parts of the channels?
the alpha-beta interfaces
The interaction between the calcium channel and a single G beta gamma subunit leads to inactivation of what?
the calcium channel in a voltage dependent manner
Most molecules that activate or inhibit activation of G-protein coupled receptors bind in this pocket formed by the what?
transmembrane domains; this pocket is at the level of the transmembrane domains 2-4, 23
Functional NMDA receptors are comprised of which subunits?
two GluN1 and two GluN2 subunits
The close co-location of release competent synaptic vesicles with voltage activated calcium channels is maintained by what?
two proteins from the rim coordinating complex: RIM and RIM-binding protein
Are Rab 3 and Rab 27 GTP-binding proteins plasma or vesicle membrane bound?
vesicle membrane bound
When are subunit types considered to be structural?
when they can be part of a receptor but not participate in ligand binding
Are all AMPA receptors also permeable to sodium and potassium?
yes
Do G-protein-coupled receptors that do not have any ligand or agonists bound to it have a certain level of basal guanine nucleotide exchange factor activity?
yes
Do both the alpha and beta/gamma subunits activate and dissociate from the receptor and activate various effector molecules?
yes
Do the same transmembrane domains that participate in the binding of the activating ligand also have their residues line the binding pocket for the C terminal helix for compatible G proteins?
yes
Is spontaneous release calcium-dependent?
yes
Within a family, are the G alpha proteins thought to interact with similar effector proteins?
yes
is the synchronous response the stimulated response?
yes
Was the observed synaptic delay at the NMJ an acceptable amount?
yes, it was much faster than the cardiac vagal synaptic delay