What is the mechanism by which calcium channel blockers exert their effect?

Calcium channel blockers primarily exert their therapeutic effects by counteracting the actions of calcium within vascular smooth muscle, leading to vasodilation. These medications block the influx of calcium ions through L-type calcium channels on the cell membranes of smooth muscle cells. Calcium plays a critical role in the contraction of these muscles; therefore, when the entry of calcium is inhibited, it results in relaxation of the smooth muscle and dilation of blood vessels.

This vasodilation effect reduces peripheral vascular resistance and lowers blood pressure, making calcium channel blockers useful in treating conditions such as hypertension and angina. The decreased availability of calcium also allows for greater coronary artery dilation, thereby improving blood flow to the heart muscle.

In contrast, increasing calcium in vascular smooth muscle would lead to enhanced contraction, which is the opposite of what calcium channel blockers aim to achieve. Similarly, while these medications can have effects on renal function, they do not primarily inhibit sodium reabsorption in the kidneys. Lastly, rather than stimulating the heart rate, certain calcium channel blockers may actually reduce heart rate, particularly those that selectively affect cardiac tissue or are non-dihydropyridine types. Thus, option B correctly describes the mechanism of action of calcium channel blockers in promoting vasodilation.