The plateau in the action potential of cardiac muscle result

The plateau in the action potential of cardiac muscle results from the action of ___. A) NA^+ outflow B) K^+ inflow C) Cl^- inflow D) Ca^2+ inflow E) Ca^2+ outflow

Solution

Answer:

The plateau in the action potential of cardiac muscle results from the action of C) Ca²⁺ inflow.

Plateau is the relatively stable period when cardiac muscle cells are depolarized and contracting due to opening of the voltage-gated slow Ca⁺⁺ channels which permits prolonged influx of Ca⁺⁺ ions into the general cytoplasm. This in turn triggers the opening of ordinary voltage-gated Ca⁺⁺ channels in the smooth ER which permits an additional influx of Ca⁺⁺ ions into the general cytoplasm. Not only that, but it also activates chloride channels which allow Cl to enter the cell. The movement of all of these ions results in the membrane potential remaining relatively constant.