What is the mechanism of action of calcium channel blockers?

The mechanism of action of calcium channel blockers centers on their ability to block the entry of calcium ions into myocardial (heart muscle) and vascular smooth muscle cells. Calcium plays a critical role in muscle contraction, including that of the heart and blood vessels. By inhibiting calcium entry through voltage-gated calcium channels, these medications reduce contractility of cardiac muscle and promote vasodilation in blood vessels. This leads to lower blood pressure, reduced myocardial oxygen demand, and improved blood flow, particularly beneficial in conditions like hypertension and angina.

The importance of this mechanism is highlighted by the fact that the decrease in intracellular calcium levels leads to relaxation of both the cardiac and vascular muscles. This relaxation can alleviate the workload on the heart and improve oxygen delivery to the myocardium, which is crucial during episodes of chest pain or stress on the heart.

The other choices do not reflect the primary and well-documented way in which calcium channel blockers work. While they do have effects that can relax blood vessels, that is part of the broader mechanism rather than a standalone action. Additionally, their role as autonomic agents is not their primary action, as they do not directly affect the autonomic nervous system in the way that specialized autonomic drugs do.