Sodium channels activation and inactivation

[Polycherry]

We learn in physio that during depolarization phase in the membrane, more sodium channels open as the membrane potential increases i.e., less negative. This is a kind of positive feedback in the action potential and explains the threshold of depolarization(an epsp) required for action potential.
So in short as the membrane potential becomes less negative. Sodium channels tend to open.


On the other hand, we have this very famous graph in katzung on how ' ready' the sodium channels are, to fire, in phase 3,4 of the cardiac action potential. Fig 14.4 11ed. (regarding after depolarizations)
It says, as the membrane potential reduces, i.e., more negative, more the sodium channels are ready to fire.

This seems very much contradicting with the 1st case

So i kinda came up with an explanation. Which i don't know if is true and that's where i need your help
So here it goes!

Case 1 was mainly about resting to active state of sodium channels (decided by m gates)
Case 2 was mainly about inactivating to resting state of sodium channels (decided by h gates)


So if this explanation is to be true, m gates should open on depol and h on hyperpol is it correct????


After all this, even if i assume my explanation is correct, it contradicts the explanation for reduced Vmax of phase 0 given here

http://www.ncbi.nlm.nih.gov/pmc/articlerender.fcgi?artid=1413606

This article shows the similar katzung 14.4 graph and changes the y axis from 'channels available' to 'vmax of phase0'
Defying my explanation of sodium channels opening favored by less negative potentials..

Hope you understand my doubt.

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[worldbeater]

So if this explanation is to be true, m gates should open on depol and h on hyperpol is it correct????

For this, sodium channels are used for depolarization. It's a gated ion channel, with an "m" as the first step and "h" used as the second step. They work in sequence and both are used for depolarization.

m is used first and it is known as the slow depolarization channel, h is used as the second and is known as the fast depolarization channel. The way we were taught to remember is "move home"

Not sure about the rest of your question(s).