calcium-channel blocker
any of a class of drugs, the prototype of which is verapamil, used in the treatment of hypertension and abnormal heart rhythms (arrhythmias). Calcium-channel blockers inhibit the flow of calcium ions into the smooth-muscle cells of blood vessels and the cells of heart muscle, which need calcium to contract. They act by binding to calcium channels on the surface of depolarized muscle-cell membranes, causing a decrease in transmembrane calcium transmission and prolonged relaxation of the muscles. Verapamil has been studied as a potential mood stabilizer, with equivocal results in the treatment of mania.