At the peak of the AP of contractile myocardiocytes just before _

Question

A, the Na+ channels open
B, the ca2+ channels close
C, the Na+ channels close, causing the membrane voltage to remain elevated.
D, the channels close causing the membrane voltage to fall slightly
E, opening of k+ channels causing k+ efflux that drops the membrane voltage slightly

Answer 1

At the peak of the action potential (AP) of contractile myocytes, the correct answer is:

C, the Na+ channels close, causing the membrane voltage to remain elevated.

Here's a brief explanation of the reasoning:

1. During phase 0 of the action potential, voltage-gated Na+ channels open, causing depolarization and the membrane potential to rapidly rise.
2. At the peak of the action potential, Na+ channels begin to close, which contributes to the maintenance of a depolarized state for a short time.
3. Subsequently, during phase 1 and 2 (the plateau phase), Ca2+ channels open to sustain depolarization, while K+ channels start to open slowly.

However, since the statement specifically mentions the peak of the AP, focusing on the closing of Na+ channels is the most relevant point, and the voltage does remain high before transitioning to the next phases.