Cardiac stuff

Question 1

What two channels are unique to nodal cardiac cells? What channel does nodal cardiac cell not have?

Answer 1

L-type calcium channel
Na+ “funny” channel

Doesn’t have usual sodium channel

Question 2

What is the difference in the behavior of potassium channels in skeletal and cardiac muscle?

Answer 2

skeletal muscle: depolarization = open K+ channels

cardiac muscle: depolarization = close K+ channels

Question 3

Describe the sequence of channel activity (4) that occurs in SA node firing.

Answer 3

1. Na+(F) channels open and sodium enters cell
2. Ca2+(T) channels open and sodium enters cell
   Threshold is reached
3. Ca2+(L) channels open and membrane potential shoots up
4. K+ channels open and potassium leaves the cell, membrane repolarizes downward

Question 4

Which channel is it that gives the nodal cells their pacemaker potential?

Answer 4

funny sodium channel

Question 5

What is special about Purkinje fibers, channel-wise?

Answer 5

If needed, Purkinje fibers can do funny sodium channels and provide a pacemaker potential

Question 6

How is increased contractility related to calcium influx?

Answer 6

faster influx of calcium = faster rise of contractile force
more calcium influx = stronger force
faster efflux (resequestration) of calcium = quicker relaxation

Question 7

What are two sources of calcium influx when action potential is received?

Answer 7

extracellular calcium, sarcoplasmic reticulum calcium

Question 8

What are two methods for getting calcium back out of the cardiac cell into the extracellular fluid?

Answer 8

1. A calcium ATP-ase pump in the cell membrane. Uses up an ATP and pumps out a CA2+
2. Sodium-calcium exchange pump in the cell membrane. Sodium enters cell down its concentration gradient (created by other pumps in the membrane using ATP) and calcium is pumped out of the cell.

Question 9

There are two pumps in the cardiac cell membrane that pump calcium out of the cell and into the extracellular fluid. What is one other way that calcium is removed from the intracellular fluid in order to maintain the very low levels of calcium in the cell between action potentials?

Answer 9

Resequester calcium back into the sarcoplasmic reticulum via a calcium ATP-ase associated with a protein called phospholamban. When phospholamban is phosphorylated, calcium can come back into the SR.

Question 10

Where do calcium channel blockers work?

Answer 10

At the L-type calcium channels in the T-tubules of cardiac cells. These channels are blocked and the influx of calcium into the cell is reduced.

Question 11

What is the effect of calcium channel blockers on the contractility of the heart?

Answer 11

CCBs reduce the rate and the force of contractility.

Question 12

Where do cardiac glycosides work?

Answer 12

At the sodium-potassium ATP-ase pump that maintains the sodium gradient of the cell (the gradient that powers one of the pumps that removes calcium from inside the cell).

Question 13

What is the effect of cardiac glycosides on the contractility of the heart?

Answer 13

Increase in contractility

Question 14

Example of cardiac glycoside?

Answer 14

digoxin