What is the mechanism of action of calcium channel blockers?

Calcium channel blockers primarily work by blocking the influx of calcium ions into the cells of the heart and the smooth muscle cells of blood vessel walls. By preventing calcium from entering these cells, they lead to a decrease in intracellular calcium concentration, which then reduces cardiac contractility and dilates blood vessels. This results in lowered blood pressure and reduced workload on the heart.

Specifically, in the heart, calcium is essential for the contraction of cardiac muscle. By inhibiting calcium entry, these medications decrease the force of heart muscle contraction and slow down heart rate, which is beneficial in conditions like hypertension and certain arrhythmias. In the vascular smooth muscle, relaxation occurs, leading to vasodilation and subsequent reduction in blood pressure.

In contrast to this correct mechanism, the other options do not accurately represent the action of calcium channel blockers. They do not influence heart rate in a direct stimulatory manner, nor do they have a role in insulin production or serotonin reuptake. This distinction underscores the unique role that calcium channel blockers play in cardiovascular pharmacology.