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.
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