Question

which of the following pairs concerning action potentials in cardiac muscle is mismatched? multiple choice opening of na+ channels - depolarization closing of ca²+ channels - plateau phase opening of k+ channels - rapid repolarization closure of na+ channels - early repolarization opening of ca²+ channels - plateau phase

Explanation:

The plateau phase of the cardiac - muscle action potential is maintained by the opening of calcium ($Ca^{2+}$) channels and the slow closing of potassium ($K^{+}$) channels. Closing of $Ca^{2+}$ channels would not be associated with the plateau phase but rather with the transition to repolarization. Opening of $Na^{+}$ channels causes depolarization, opening of $K^{+}$ channels causes rapid repolarization, closure of $Na^{+}$ channels is related to early repolarization, and opening of $Ca^{2+}$ channels is related to the plateau phase.

Answer:

Closing of $Ca^{2+}$ channels - plateau phase