Mechanism of dihydropyridine interaction with critical binding residues ofL-type Ca2+ channel alpha 1 subunits

We investigated the mechanism of interaction of individual L-type channel a mino acid residues with dihydropyridines within a dihydropyridine-sensitive alpha 1A subunit (alpha 1A(DHP)). Mutation of individual residues in repea t III and expression in Xenopus oocytes revealed that Thr(1393) is not requ ired for dihydropyridine interaction but that bulky side chains (tyrosine, phenylalanine) in this position sterically inhibit dihydropyridine coordina tion. In position 1397 a side chain carbonyl group was required for high an tagonist sensitivity. Agonist function required the complete amide group of a glutamine residue. Val(1516) and Met(1512) side chains were required for agonist (Val(1516)) and antagonist (Val(1516) Met(1512)) sensitivity, Repl acement of Ile(1504) and Ile(1507) by alpha 1A phenylalanines was tolerated . Substitution of Thr(1393) by phenylalanine or Val(1516) by alanine introd uced voltage dependence of antagonist action into alpha 1A(DHP), suggesting that these residues form part of a mechanism mediating voltage dependence of dihydropyridine sensitivity. Our data provide important insight into dih ydropyridine binding to alpha 1A(DHP) which could facilitate the developmen t of alpha 1A-selective modulators. By modulating P/Q-type Ca2+ channels su ch drugs could serve as new anti-migraine therapeutics.