Different voltage-dependent inhibition by dihydropyridines of human Ca2+ channel splice variants.

Voltage-dependent inhibition by 1,4-dihydropyridines is a characteristic property of L-type Ca2+ channels. Six out of 50 exons of the channel alpha 1C subunit gene are subjected to alternative splicing, thus generating channel isoform diversity. Using Xenopus oocytes as an expression system, we have found that transmembrane segment IIIS2 of human alpha 1C subunit is involved in the control of voltage dependence of dihydropyridine action. This segment is genetically regulated through alternative splicing of exons 21/22. Site-directed mutagenesis points to two amino acids in IIIS2, which determine the difference of the splice variants in their sensitivities to dihydropyridines. This finding provides new insight into molecular mechanisms of Ca2+ channel inhibition by this important class of drugs.