Cardiac Muscle Action Potential

[ElphinStar]

A question from my Body Systems Physiology heart practical...

 

True or False:

 

'Action potentials in contractile ventricular muscle cells exhibit a different electronic profile, relative to cells of the SA node, due to a stable resting membrane potential, and the opening of voltage gated Ca2+ gates and delayed opening of K+ gates, during the AP.'

 

Any help would be greatly appreciated!

[CharonY]

K, where precisely do you have problems with it?

[ElphinStar]

The 'stable RMP' part - I thought ventricular muscle had unstable contraction?

 

I THINK the other part about Ca2+ and K+ is true.. but generally a little lost.

[CharonY]

Ok, if you compare the resting potential of these cell types, what is the typical difference between those two? Think of automaticity.

[ElphinStar]

Do you mean that cardiac muscle can depolarize spontaneously, whereas smooth muscle can't?

[CharonY]

That is one difference and the other is the consequence of relying on Ca2+ to depolarize. What is the kinetics of Ca2+ vs Na+ influx on AP? So if you drew a typical cardiac AP compare it to SA, what differences would you expect?

 

 

It may be easier if you think about the different phases and where the differences of SA node cells are.

Edited March 6, 2012 by CharonY

[ElphinStar]

The cardiac AP would have stages; Na+ in (rapidly) where it depolarises, K+ and Cl- out, Ca2+ in and K+ out (delayed), then K+ out (rapid) where it repolarises.

 

SA node AP; Ca2+ in depolarising, K+ out repolarising, Ca2+ in and Na2+ in.

 

So Na+ entry causes depolarisation of cardiac muscle, whereas Ca2+ entry causes it in SA node?

[CharonY]

Right, now how fast are Ca2+ channels relative to the Na+ ones?

[ElphinStar]

I think the Ca2+ channels are slower than Na+?