Mechanism of Dihydropyridine Interaction with Critical Binding

We investigated the mechanism of interaction of individual L-type channel amino acid residues with dihydropyridines within a dihydropyridine-sensitive a1A subunit (a1ADHP). Mutation of individual residues in repeat III and expression in Xenopus oocytes revealed that Thr 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. Val and Met side chains were required for agonist (Val) and antagonist (Val, Met) sensitivity. Replacement of Ile and Ile by a1A phenylalanines was tolerated. Substitution of Thr by phenylalanine or Val by alanine introduced voltage dependence of antagonist action into a1ADHP, suggesting that these residues form part of a mechanism mediating voltage dependence of dihydropyridine sensitivity. Our data provide important insight into dihydropyridine binding to a1ADHP which could facilitate the development of a1A-selective modulators. By modulating P/Q-type Ca channels such drugs could serve as new anti-migraine therapeutics.