The physiological and pharmacological significance of cardiovascular T-type, voltage-gated calcium channels.

An influx of calcium ions into cells, made possible by the opening of specific, voltage-gated channels, triggers muscular contraction and several other physiological processes. Two types of calcium channels, L-type and T-type, are found in the cardiovascular system. These two types of channels differ considerably in their electrical and chemical characteristics and in their distribution in tissue. The L-type calcium channel is responsible for normal myocardial contractility and for vascular smooth muscle contractility. In contrast, T-type calcium channels are not normally present in the adult myocardium, but are prominent in conducting and pacemaking cells. They are thought to help regulate vascular tone, signal conduction, cardiac pacemaking, and the secretion of certain intercellular transmitters. T-Type channels also seem to have an important role in normal growth processes and in the tissue remodeling that occurs in pathologic processes such as cardiac hypertrophy. Traditional calcium antagonists act on L-type channels. Mibefradil is a recently characterized calcium antagonist and the first that is selective for T-type calcium channels. This unique property may lead to major applications in cardiovascular medicine.