Chapter 5a Membrane Dynamics Continued
Figure on slide 43
...
What are the main cardiac effects of digoxin are?
1.decrease conduction of electrical impulses through AV node 2. increase force of contraction via inhibition of Na/K ATPase pump
What is produced per cycle of the Na+/K+ ATPase?
3 Na+ into the ECF, 2 K+ into the ICF, and one ATP to occur.
What other names can Digoxin be marketed by?
Digoxin marketed under the trade names Lanoxin, Digitek, and Lanoxicaps
Is Ouabain still used for the treatment of the human heart?
No
What type of transporter is SGLT an example of?
Sodium dependent symport carrier.
What is saturation?
Transport maximum (Tm) - point at which increases in concentration do not result in increased movement of a substance through a carrier protein
What is transcytosis?
Unidirectional movement of substances across endothelium lining capillaries. -utilizes caveolae -(can move vitamins (B12, folate, albumin) from blood stream into interstitial space
What is endocytosis?
an active process that can be nonselective or highly selective. membrane surface idents and pinches off a piece to form a vesicle
What is Non-selective-Potocytosis?
(i.e. cell drinking), or way to move small (<1 kDa) molecules into cell) uses caveolae
Figure 5-27. How does transcytosis work? 1. Plasma proteins are concentrated where? What happens? 2. How do vesicles cross the cell? 3. Vesicle contents are released where?
1. In the caveolae and undergo endocytosis and form vesicles 2. Cross the cell with the help from the cytoskeleton 3. Contents are released into ISF by exocytosis
What are two types of endocytosis?
1. Non-selective-Potocytosis 2. Selective - Receptor-mediated endocytosis
What are the steps of phagocytosis?
1. Phagocytic white blood cell encounters a bacterium that binds to the cell membrane 2. phagocyte uses its cytoskeleton to push its cell membrane around the bacterium creating a large vesicle (the phagosome) 3. Phagosome containing the bacterium separates from the cell membrane and moves into the cytoplasm. 4. The phagosome fuses with lysosomes containing digestive enzymes 5. Bacterium is killed and digested within the vesicle
What are the types of vesicular transport?
1. Phagocytosis 2. Endocytosis 3. Transcytosis 4. Exocytosis
What are three characteristics of carrier-mediated transport?
1. Specificity 2. Competition 3. Saturation -shared by both channel and carrier
How does Receptor-Mediated Endocytosis and Exocytosis work? *Figure 5-24* 1-7= RME 8-9=exocytosis
1. extracellular ligand to be brought into the cell binds to membrane receptor 2. Receptor-ligand migrates to clatherin-coated pit 3. Endocytosis: The membrane draws inward, pinched itself off from the membrane and forms a vesicle. 4. Endocytic vesicle loses the clatherin coat 5. Receptors and ligands separate leaving the ligand in the endosome. 6. Ligands go to lysosomes or golgi for processing 7. Transport vesicle with receptors moves to the cell membrane 8. Transport vesicle and cell membrane fuse (membrane cycling) 9. Exocytosis: the vesicle membrane in then incorporated back into the cell membrane.
Know the two graphs on slides
46 and 47.
An increase in the level of Na in myocytes causes a rise in what? How?
A rise in the level of calcium ions. -intracellular Na slows down extrusion of Ca by Na/Ca exchange pump (relies on the high Na gradient!) (causes the contraction to last a long time) -increases length of Phase 4 and Phase 0 of cardiac action potential and leads to slower, more prolonged (stronger) contractions - Increased amounts Ca are then stored in SR and released by each action potential, leading to increased contractility of heart
A pump is also known as an? What type of pump if the Na/K pump?
ATPase -P-type ATPase
Energy is transported into the cell as what? Where is it stored?
As energy that is stored in chemical bonds of nutrients such as glucose.
Are caveolae abundant?
Caveolae are a highly abundant but enigmatic feature of mammalian cells.
What is phagocytosis?
Cell engulfs bacterium or other particle into phagosome (most)
How does increased force of contraction via inhibition of Na/k ATPase pump have a cardiac effect?
Digoxin binds extracellular site of α-subunit Na/K ATPase pump on heart cells (myocytes), slows activity
what is the Na/K pump made of?
Dimeric protein with two different subunits. Alpha subunits and beta subunits. Inactive ATPase enzymatic activity is on the alpha subunit while the beta subunits are glycosated (have oligosaccharides, used for cell identity to self))
What is Ouabain's long history in France and Germany?
In France, Germany, IV ouabain has long history of use for treatment of heart failure, some advocate use by mouth in angina pectoris and myocardial infarction (dying of heart muscle due to the lack of O2.)
How does the yolk sac form?
Initially a clathrin coated pit forms. The cargo receptors extend through the membrane and interact with cargo molecules in the cytoplasm. In this case the cells are chicken oocytes and the cargo receptors are interacting with particles containing protein and lipids that will be incorporated into the yolk. As the process continues, the vesicles rounds up and pinches off.
Sodium-potassium pump steps:
Initially the pump is open to the ICF. It has a high affinity for Na+ and a low affinity to K+. *1.* 3 sodium ions are taken into the cell. This is the *first recognition*. *2.* ATP binds to the pump and undergoes ATP hydrolysis. ATP goes to ADP and inorganic phosphate. ADP is released into the cytoplasm and Pi binds to the pump which preserves energy from ATP hydrolysis. (*Activation of ATPase, or ATP phosphorylates the alpha subunit*) *3.* The *first translocation* occurs and is powered by energy from ATP hydrolysis. Now has a low affinity for Na+, and a high affinity for K+. *4.*The pump open to the outside and releases the three Na into the ECF. *first release* *5.* Two accepted K+ ions accepted from the outside *2nd recognition* *6.* Pi is released from the pump. This dephospho-rylation triggers a conformational change. *2nd translocation* *7.* *2nd release* of K+ ions into the ICF. The pump now returns back to its original shape.
What causes the inhibition of the Na/K pump? Inhibition of the Na/K pump will cause an increase in what? What will occur?
Intracellular calcium which will inhibit the Na/Ca transporter by destroying the Na concentration gradient. This will then cause an increase in intracellular calcium which can prolong the contractile process.
The Na/K pump is an example of what type of activity?
Intrinsic activity
Ouabain binding to the hormone of the Na/K ATPase pump can do what?
It can activate various pathways.
How do rodents and non-rodents used Ouabain?
Non-rodent specied pump is stimulated by low concentrations of Ouabain (nM range) while rodents have different isomers of the Na/K pump which some will be sensitive to Ouabain while others will not.
Is there any evidence that Ouabain is better than digoxin?
Only anecdotal evidence for improved efficacy of ouabain relative to digoxin in small number patients.
Why are only 2 K+ ions pumped?
Only two because they are larger and the shape change of the pump will change the selectivity of the amino acids.
How does Ouabain perform its function?
Ouabain blocks Na+/K+-ATPase in higher concentrations which are attainable in vitro or with intravenous dosage
How is Ouabain used by scientists?
Ouabain used by scientists for in-vitro-studies to block the sodium pump (Na-K-ATPase).
what is an example of secondary active transport? How does it work? *Figure 5-18*
SGLT transporter. (sodium glucose lumenal transporter) 1. Na bind to the carrier. 2. The Na binding creates a site for glucose 3. Glucose binding changes carrier conformation 4. Na released into cytosol and glucose follows. -Favorable Na+ gradient 'drives' unfavorable Glu movement
How have other people used Ouabain in the past?
Several African tribes use ouabain (from Strophanthus) as principal ingredient in arrow poisons (since 3rd century BC!)
What is Ouabain's signaling first mediated by?
Signaling first mediated by L-type voltage-dependent Ca channel and a store-operated channel (SOC)
What is probably the most important transport protein pump in animal cells? Why?
The Sodium/Potassium pump because it maintains the concentration gradients of Na+ and K+ across the cell membrane.
The diverse functions of caveolae such as ______, may be linked to what?
The apparently diverse functions of caveolae, including *mechanosensing and lipid regulation*, might be linked to their ability to respond to plasma membrane changes, a property that is dependent on their specialized lipid composition and biophysical properties.
what do caveolae form and can also function in?
They form remarkably stable membrane domains at the plasma membrane but can also function as carriers in the exocytic and endocytic pathways.
The Na/K pump will change their what?
They will change their shape to open to the ICF and the ECF
Caveolae are very large or small?
Very large, larger than a protein.
The separation of ions causes what?
a storage of energy that can be harnessed for work
What is specificity?
both carrier and channel proteins will only transport a specific substance -only 1 substance, or a closely related group of them
What can Ouabain be used to treat? Is it very common?
can be used to treat atrial fibrillation (too rapid beating of the atrium) & congestive heart failure. -Digoxin is more commonly used
Some cell types like neurons may completely lack what?
caveolae
Transcytosis (capillary exchange) occurs through what? What are they?
caveolae. -(Latin for little caves) small (50-100 nm) invaginations of plasma membrane in many vertebrate cell types (endothelial cells, adipocytes, etc.)
What is competition?
closely-related substances will compete for access to the same carrier or channel protein
What is exocytosis?
essentially reversal of endocytosis (no clathrin needed for exocytosis) -Intracellular vesicles move to the cell membrane and fuse with it, then releasing their contents into the ECF.
What is the structure of caveolae and where are they rich in? Why are they important?
flask-shaped structures rich in proteins, lipids (cholesterol & sphingolipids) -important in signal transduction, endocytosis, oncogenesis, the uptake of pathogenic bacteria and certain viruses
How does a sodium/potassium pump get its energy?
from ATPase. These enzymes hydrolyze ATP to ADP and inorganic phosphate releasing usable energy in the process.
Metabolism: What happens to the chemical bond energy?
it is converted into high-energy bonds of ATP through the process of metabolism.
What is transepithelial transport made of? What are the different structures in in?
it is made up polarized cells of transporting epithelia. -apical membrane: faces the lumen -tight junction:prevents movements of substances between cells -transporting epithelial cell -basolateral membrane: faces the ECF
Overall SGLT works because...
it rapidly pulls glucose from the cell and into the bloodstreams to be utilized. The Na/K pump will drive the Na gradient
What will low concentrations of Ouabain do?
low concentrations ouabain has the opposite effect (stimulates Na-K-ATPase), a biphasic response, not a property of digoxin
What is Ouabain (g-strophanthib)? Where is it found?
poisonous cardiac glycoside - affect Na/K pump -found in the ripe seeds of African plants Strophanthus gratus and Acokanthera ouabaio
How does transepithelial transport work?
polarized epithelia have different transport proteins on apical and basolateral membranes. This will allow for selective directional transport across the epithelium. -absorption -secretion
What is digoxin? how is it used?
purified cardiac glycoside extracted from foxglove plant, Digitalis lanata - Its corresponding aglycone is digoxigenin - Digoxin widely used to atrial fibrillation, atrial flutter and sometimes heart failure
How is the sodium-potassium pump arranged?
so that it will pump 3 Na+ out of the cell and 2 K+ into the cell
What is the general site of Ouabain interference?
the extracellular surface of the plasma membrane. This will block potassium binding.
What causes the shape change of the Na+/K+ ATPase?
the phosphorylation and the dephospho-rylation causing the conformation change and the binding sites affinity for ions.
primary active transport: the energy in high-energy phosphate bond of ATP is used for what?
to move K and Na against their concentration gradient. Which will create potential energy stored in the ion concentration gradients.
secondary active transport: the energy of the Na transport can be used how?
to move other molecules across their cell membrane against their concentration gradient .
what is the physiological purpose of the Receptor-Mediated Endocytosis and Exocytosis process?
to terminate hormone signaling
What is secretion?
transport from ECF to lumen
What is absorption?
transport from lumen to the ECF
hormones that circulate in your body that bind to hormone receptors will?
trigger a certain event. -taking in a hormone into an endosome will stop hormone signaling
what is Selective - Receptor-mediated endocytosis?
used clatherin coated pits not caveolae
how does decreased conduction electrical impulses through AV node have a cardiac effect?
via effects on vagus nerve (increase parasympathetic activity) - thus used as anti-arrhythmic agent to control heart rate during atrial fibrillation or atrial flutter
