neuroscience chapter 4

. Which statement about voltage-gated ion channels is true? a. Without sodium channels, no current flows out b. Without potassium channels, no current flows in c. Na+ channels open after a short delay d. K+ channels close after a short delay e. Na+ and K+ channels can work independently of one another

. Na+ and K+ channels can work independently of one another

. Which technique would you use to study the effects of the extracellular environment on ion channel activity? a. Conventional voltage clamp b. Whole-cell patch clamp c. Inside-out patch clamp d. Outside-out patch clamp e. Cell-attached patch clamp

. Outside-out patch clamp

. Which ligand-gated ion channel is regulated primarily by an intracellular signal? a. Glutamate receptor b. The potassium-activated calcium channel c. The glutamate receptor d. The cAMP- and cGMP-gated ion channels e. The acid-sensing ion channels

. The cAMP- and cGMP-gated ion channels

Which statement regarding the diversity of ion channels is false? a. With only six different types, potassium channels are the least diverse channel type. b. There are at least 10 different sodium channels in humans. c. Sodium channels that do not inactivate have been found. d. There are least 10 different types of calcium channels. e. Calcium channels serve diverse functions such as influencing action potential shape and mediating the release of neurotransmitters.

. With only six different types, potassium channels are the least diverse channel type.

The technique that provides the most direct information about the physical, three-dimensional structure of ion channels is a. the sequencing of the channel's amino acids. b. physiological measurement of ion selectivity. c. X-ray crystallography. d. fluorescence imaging of channel subunit dynamics. e. high-performance liquid chromatography.

. X-ray crystallography.

. The calcium ATPase a. is much simpler than the sodium-potassium pump because it has only three transmembrane regions. b. pumps 15 calcium ions for each molecule of ATP consumed. c. uses the same intracellular domain for both nucleotide binding and ion translocation. d. pumps calcium in a cyclical process that utilizes energy from ATP. e. is unique among transporters in that its pumping action involves no conformational changes.

. pumps calcium in a cyclical process that utilizes energy from ATP.

. A surprising result that emerged from the molecular and genetic analysis of ion channels was the a. size of the individual ion channels. b. voltage-dependence of the ion channels. c. time-dependence of the ion channels. d. discovery of differences in ionic selectivity. e. sheer number of different ion channels.

. sheer number of different ion channels

Compare the responses of voltage-gated Na+ and K+ channels to depolarization.

: Both types of channels open in response to depolarization; however, depolarization inactivates Na+ channel for a period of time. In contrast, K+ channels are not inactivated.

1. What is patch clamping? Explain how it can be used to show that properties of voltage-sensitive Na+ and K+ channels are responsible for the action potential.

: Patch clamping is a technique in which a recording pipet is used to grip a cell membrane and record the electrical potential or flow of ions through one ion channel. The patch clamp method allows experimental control of the membrane potential, and it can be used to characterize the voltage dependence of membrane currents. It allows measuring minute electrical currents such as those originating from a single ion channel.

Which experimental approaches can be used to determine which ions can pass through a particular ion channel?

: X-ray crystallography, toxins, patch clamping.

. Which property is characteristic of Na+ channels but not K+ channels? a. Ion permeability b. Ion selectivity c. Voltage sensitivity d. Ability to inactivate e. Ability to bind neurotoxins

Ability to inactivate

What is the mechanism of action of the different active transporters? Explain the differences between the following types of active transporters: ATPase pumps, antiporters, and co-transporters. Provide an example of each.

All active transporters must be able to move ions across the membrane against their concentration gradient. The ATPase pump moves ions across the membrane using energy derived from ATP hydrolysis. Example: Na+/K+ ATPase pump. An ion exchanger moves ions by using energy derived from electrochemical gradient of other ions. There are two types of ion exchangers: antiporters and co-transporters. Antiporters transport ions in opposite directions. Example: Na+/H+ exchanger. Co-transporters transport ions in the same direction. Example: Na+/K+/Cl- co-transporter.

. Which statement is a common, defining feature of membrane-bound active ion transporters? a. All are electrogenic. b. All transport two or more different ions. c. All catalyze the conversion of ATP to ADP. d. All are able to move at least one ion against its concentration gradient. e. All move sodium across the membrane.

All are able to move at least one ion against its concentration gradient.

. In what way are ion channels similar to active transporters? a. Both are proteins. b. Both actively move ions from one side of the membrane to the other. c. Both create ion concentration gradients. d. Both maintain ion concentration gradients. e. Both enable selective ion permeability.

Both are proteins.

Which technique is illustrated in the figure, and what can it be used to measure? a. Whole-cell patch clamp; measures potentials from the entire cell b. Whole-cell patch clamp; measures the current that flows through a single ion channel c. Cell-attached patch clamp; measures potentials from the entire cell d. Cell-attached patch clamp; measures the current that flows through a single ion channel e. Outside-out patch clamp; measures the current that flows through a single ion channel

Cell-attached patch clamp; measures the current that flows through a single ion channel

Which toxin is not correctly paired with its mechanism of action? a. a-toxin—slows the inactivation of Na+ channels b. Tetrodotoxin—blocks the pore of Na+ channels c. Charybdotoxin—blocks K+ channels d. Dendrotoxin—slows the activation of K+ channels e. Batrachotoxin—halts inactivation of Na+ channels

Dendrotoxin—slows the activation of K+ channels

. Which of the following was observed in studies measuring the efflux of radioactive sodium from the squid giant axon? a. Dramatic increase of efflux during a brief train of action potentials b. Sharp drop in efflux when intracellular potassium was removed c. Dependence of efflux upon the presence of ATP d. Decrease of efflux when ATP synthesis was increased e. No recovery when potassium or ATP was restored.

Dependence of efflux upon the presence of ATP

Which statement accurately describes the difference between bacterial and mammalian channels that are selectively permeable to K+? a. Mammalian channels have four subunits. b. Bacterial K+ channels have four pore loops. c. Mammalian K+ channels have four additional structures that act as voltage sensors. d. Bacterial K+ channels do not have a selectivity filter. e. There is no difference between bacterial and mammalian K+ channels.

Mammalian K+ channels have four additional structures that act as voltage sensors.

. In which way do potassium channels in the squid giant axon differ from sodium channels? a. The potassium channels pass only a few ions per second. b. The potassium channels show little voltage dependence. c. The summing of the individual potassium channels does not reconstruct the macroscopic current. d. Once the potassium channels open in response to a voltage step command, they tend to remain open. e. The potassium channels open in response to hyperpolarization of the membrane.

Once the potassium channels open in response to a voltage step command, they tend to remain open.

Which evidence supports the assertion that the macroscopic Na+ current is the sum of many microscopic Na+ currents? a. The probability of a Na+ channel opening increases as the membrane is hyperpolarized. b. The averaged collective response of single channels resembles the time course of the macroscopic current. c. Opening and closing of Na+ channels is concentration-dependent. d. Tetrodotoxin blocks macroscopic, but not microscopic, currents. e. All of the above

The averaged collective response of single channels resembles the time course of the macroscopic current.

There are nearly 100 genes for K+ channels. What value might there be in such variation?

The value of a large number of genes, which fall into several distinct groups of channel proteins, is that several different K+ channel proteins can be produced from them, each different from one another in function, permitting variation in cell function, such as the different signaling properties found among neurons.

List five major stimulus types that can gate (open or close) various kinds of ion channels.

Voltage, ligand, mechanical force, temperature, and light

Briefly describe how each of the following experimental approaches and tools can be used to study ion channels: X-ray crystallography Expression of mRNA in Xenopus oocyte Patch clamping Mutagenesis Toxins

X-ray crystallography: provides information about the structure of the channel proteins. Expression of mRNA in Xenopus oocyte: can be used to express a specific type of channel in the cell in order to study its function. Patch clamping: can be used to evaluate current flowing through a single channel. Mutagenesis: an be used to evaluate channel function in a genetically modified organism and compare the function to that in a genetically intact organism. Toxins: used to modify or suppress the function of certain ion channels during studies.

Which structural features of Cl- channels account for a) ion selectivity, b) voltage sensitivity, and c) ion conductance?

a) Positive charges in the pores that coordinate the negative ions as they move from one side of the membrane to the other b) Voltage-dependent movement of a negatively charged amino acid c) Two separate pores, each surrounded by one of two identical subunits

. Which structural features of K+ channels account for: a) ion selectivity, b) voltage sensitivity, and c) ion conductance?

a) Selectivity filter: pore loops create a pore too small for larger ions but too large for smaller ions to be stabilized. b) Voltage sensor c) Pore

What would occur if the ATPase pumps in a neuron stopped functioning? a. Concentration gradients would not be maintained across the membrane b. At rest, sodium would continuously depolarize the cell c. At rest, potassium would continuously depolarize the cell d. During the action potential, the sodium channel would not inactivate e. During the action potential, the voltage-gated ion channels would remain closed

a. Concentration gradients would not be maintained across the membrane

. What is the net charge transported by one cycle of the Na+/ K+ ATPase pump? a. One positive charge leaves the cell b. Two positive charges leave the cell c. Three positive charges leave the cell d. One positive charge enters the cell e. There is no net change in charge

a. One positive charge leaves the cell

Which intervention will disrupt the function of the Na+/K+ ATPase pump? a. Removal of extracellular K+ b. Removal of extracellular Na+ c. Removal of extracellular ATP d. Removal of cytoplasmic Ca2+ e. Application of tetrodotoxin

a. Removal of extracellular K+

Ion channels that are involved in generation of action potentials open or close in response to a. voltage. b. neurotransmitters. c. second messengers. d. mechanical stimulation. e. temperature.

a. voltage.

The proteins that establish ionic gradients are called a. passive transporters. b. active transporters. c. voltage-gated ion channels. d. ligand-gated ion channels. e. permeability transition pores.

active transporters.

. Structures that form the voltage sensors of K+ channels a. are embedded in the cell membrane. b. extend into the intracellular space. c. extend into the extracellular space. d. are embedded in the cell membrane but extend into the extracellular space when the membrane is depolarized. e. are located within the channel pore.

are embedded in the cell membrane.

Which ion is transported down its concentration gradient by transporters? a. H+ b. Na+ c. K+ d. Cl- e. Ca2+

b, na+

. Which channel(s) is(are) implicated in inherited forms of epilepsy? a. Ca2+ and Na+ only b. K+, Ca2+, and Na+ c. K+ and Ca2+ only d. K+ only e. Ca2+ only

b. K+, Ca2+, and Na+

. Which substance binds only at the extracellular domain of a ligand-gated ion channel? a. H+ b. Neurotransmitter c. Ca2+ d. cAMP e. cGMP

b. Neurotransmitter

The TRP ion channel family includes channels responsive to a. complex sequences of voltage commands. b. heat and cold. c. intracellular cyclic nucleotides. d. hyperpolarization. e. ultraviolet light.

b. heat and cold.

. The paddle-like, charged transmembrane domains of potassium channels may a. serve as a plug or inactivation gate. b. be the primary voltage sensors. c. confer ion selectivity to the channel. d. enable the aggregation of channel subunits into functional channels. e. dehydrate the ions as they cross the membrane

be the primary voltage sensors.

Which transporter plays a key role in maintaining the concentration gradients of ions in the brain that are critical for generating electrical signals? a. SERCA b. PMCA c. Na+/K+ ATPase pump d. Na+/Ca2+ exchanger e. Na+/K+/Cl- co-transporter

c. Na+/K+ ATPase pump

. What do microscopic and macroscopic Na+ currents have in common? a. They flow through a single ion channel b. They flow through multiple ion channels c. They flow through a large area of neuronal membrane d. They represent a flow of many ions e. They have a magnitude of 1-10 pA

d. They represent a flow of many ions

. Animal toxins have been discovered that a. block sodium channels. b. prolong the open state of sodium channels. c. alter the voltage-dependence of sodium channels. d. block potassium channels. e. All of the above

e, all of the above

. Based on the observations made by Hodgkin and Huxley, one can expect ion channels to a. allow ions to move across the membrane quickly. b. work with the electrochemical gradients to pass ions. c. exist in distinct variants, allowing different types of ions to pass. d. respond to changes in the membrane potential. e. All of the above

e, all of the above

In the operation of sodium-potassium ATPase, a. there is an obligatory coupling of sodium efflux and potassium influx. b. this transporter (or "pump") is electrogenic. c. phosphorylation and dephosphorylation respectively, are associated with the sodium and potassium transport steps. d. the pump transports two potassium ions for every three sodium ions. e. All of the above

e, all of the above

10. The K+ channel is made up of _______, each of which contains helical membrane-spanning domains with a _______ between them. a. two subunits; pore loop b. four domains; pore loop c. four subunits; pore loop d. two subunits; pore e. two domains; selectivity filter

four subunits; pore loop

The current flowing through individual ion channels a. was visualized with the advent of the voltage clamp in 1956. b. exhibits the same time course across all individual sodium channels. c. reflects the passage of thousands of ions per millisecond. d. has a different voltage dependence than the macroscopic ionic current has. e. has a different reversal potential than the macroscopic ionic current has.

reflects the passage of thousands of ions per millisecond.

A K+ inward rectifier channel has a. two transmembrane domains, four pore loops, and a voltage sensor. b. two transmembrane domains and a pore loop, but no voltage sensor. c. two transmembrane domains, a pore loop, and a voltage sensor. d. six transmembrane domains and a pore loop, but no voltage sensor. e. six transmembrane domains, a pore loop, and a voltage sensor.

two transmembrane domains and a pore loop, but no voltage sensor.