Abstract
Currently available calcium antagonists act primarily on L-type calcium channels. Composed of 5 subunits, this ion channel is markedly more complicated than the potassium and sodium channels. Most of the data that have emerged over the past year have concerned the α subunit. The secondary structure of this subunit includes 4 repeating motifs; each motif contains 6 membrane-spanning helices, designated S 1 through S 6. The dihydropyridine (e.g., nifedipine) binding site is most likely situated primarily in motif 4 and the phenylalkylamine (e.g., verapamil) binding site is on motif 4 in an intracellular region. The benzothiazepine (e.g., diltiazem) binding site is also located on the α 1 subunit, but its precise location has not been determined. The transmembrane helices S 5 and S 6 of each motif have been proposed as the “wall” of the actual ion channel.
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