Question

Compare and contrast the role of L-type calcium channels contributing to an action potential in cardiac contractile cells and in cardiac autorhythmic cells.

A) In contractile cells, L-type calcium channels initiate depolarization, while in autorhythmic cells, they contribute to repolarization.

B) L-type calcium channels play a primary role in depolarization in both contractile and autorhythmic cells.

C) In contractile cells, L-type calcium channels contribute to repolarization, while in autorhythmic cells, they initiate depolarization.

D) L-type calcium channels function similarly in both contractile and autorhythmic cells, contributing to depolarization.

Answer 1

In cardiac contractile cells, b. L-type calcium channels are responsible for depolarization and repolarization, while in cardiac autorhythmic cells, they contribute to repolarization. The calcium channels in contractile cells maintain a plateau phase, while in autorhythmic cells, they close after depolarization.

Step-by-step explanation:

b. Cardiac contractile cells and cardiac autorhythmic cells have different roles for L-type calcium channels in contributing to an action potential.

In contractile cells, L-type calcium channels are responsible for depolarization. When stimulated by an action potential, voltage-gated channels rapidly open, causing a rapid influx of positively charged ions and raising the membrane potential.

This depolarization is followed by a plateau phase, during which slow calcium channels allow calcium ions to enter the cell and maintain the depolarization. Finally, repolarization occurs when the calcium channels close and potassium channels open, allowing potassium ions to exit the cell.

In autorhythmic cells, L-type calcium channels contribute to repolarization. These cells have a prepotential depolarization phase, during which sodium ion channels slowly allow a normal influx of sodium ions, causing the membrane potential to rise slowly.

At a certain point, calcium ion channels open, allowing calcium ions to enter the cell and further depolarize it. However, when the membrane potential reaches around +5 mV, the calcium channels close, and potassium channels open, resulting in repolarization.