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The L-type voltage-gated Ca2+ channel
There are at least 5 types of voltage-gated Ca2+ channel. However, it is the L-type voltage-gated Ca2+ channel that is the site of action of the inhibitors of Ca2+ influx that are used as antihypertensive agents. This channel is particularly important in regulating the contraction of cardiac and smooth muscle. It opens to allow Ca2+ influx during the action potential of cardiac and smooth muscle cells.The channel is a large and elaborate protein that comprises four domains. Each domain contains six membrane-spanning α-helices (click to see a diagram of the channel structure).
One of the α-helices in each domain contains many basic (positively charged) amino acids and helps to form the voltage sensor of the channel. When the cell membrane becomes depolarised, the cell interior becomes less negative. This allows the voltage sensor to move towards the outer surface of the cell membrane thereby opening the channel pore.
The L-type voltage-gated Ca2+ channel comprises several subunits (click for subunit details).
