Channel blockers - calcium

A Calcium channel is just one that allows calcium ions to go through or as the text books say “displays selective permeability to calcium ions”.

Calcium channel blockers (CCBs) , for example, are a class of drugs and natural substances that disrupt the calcium (Ca²⁺) through calcium channels.  Because every cell has channels,  calcium channel blockers can have an effect on numerous cells in the body, such as cardiac muscle, i.e. heart, smooth muscles of blood vessels, the stomach, the intestines or neurons.

The blocking action of a channel blocker decreases intracellular calcium leading to a reduction in muscle contraction. In the heart, for example, a decrease in calcium available for each beat results in a decrease in cardiac contractility.

In blood vessels, a decrease in calcium results in less contraction of the vascular smooth muscle and therefore an increase in arterial diameter [vasodilation].  CCBs do not work on venous smooth muscle.  Vasodilation decreases total peripheral resistance, while a decrease in cardiac contractility decreases cardiac output. Since blood pressure is determined by cardiac output and peripheral resistance, blood pressure drops.  So the overall effect of CCBs is to reduce blood pressure!

In theory.