Mechanism of Dihydropyridine Interaction with Critical Binding Residues of L-type Ca2+ Channel α1 Subunits

Abstract

We investigated the mechanism of interaction of individual L-type channel amino acid residues with dihydropyridines within a dihydropyridine-sensitive α1A subunit (α1ADHP). Mutation of individual residues in repeat III and expression in Xenopus oocytes revealed that Thr1393 is not required for dihydropyridine interaction but that bulky side chains (tyrosine, phenylalanine) in this position sterically inhibit dihydropyridine coordination. In position 1397 a side chain carbonyl group was required for high antagonist sensitivity. Agonist function required the complete amide group of a glutamine residue. Val1513 and Met1512 side chains were required for agonist (Val1513) and antagonist (Val 1516, Met1512) sensitivity. Replacement of Ile 1504 and Ile1507 by α1A phenylalanines was tolerated. Substitution of Thr1393 by phenylalanine or Val 1516 by lanine introduced voltage dependence of antagonist action into α1ADHP, suggesting that these residues form part of a mechanism mediating voltage dependence of dihydropyridine sensitivity. Our data provide important insight into dihydropyridine binding to α1A DHP which could facilitate the development of α1A-selective modulators. By modulating P/Q-type Ca2+ channels such drugs could serve as new anti-migraine therapeutics.