Molecular studies on the voltage dependence of dihydropyridine action on L-type Ca2+ channels - Critical involvement of tyrosine residues in motif IIIS6 and IVS6

The interaction site(s) of dihydropyridine (DHP) antagonists and agonists have been identified by site-directed mutagenesis and localized on motifs IIIS5, IIIS6, and IVS6 of L-type voltage gated calcium channels, In this study, we investigated the voltage-dependent action of DHPs with mutants of the IIIS6 and IVS6 segments of a cardiac calcium channel, Tyrosine residues in both motifs (Tyr(1178) and Tyr(1489)) strongly contributed to the action of DHP agonists and antagonists. When these two sites mere mutated, the communication between the voltage sensor and the DHP interaction site(s) was substantially impaired. In contrast, mutants of a nearby Ile (Ile(1182)) had much less influence on DHP agonist and antagonist interaction, and the voltage dependence of DHP antagonists was very similar to that of the wild type. The effect of a mutating of Ile(1182), on agonist or antagonist action, however, depended strongly on the type of amino acid change, When Ile(1182) was substituted with alanine, small changes were noted for DHP agonist and antagonist action, Changing this site into phenylalanine, however, significantly decreased the action of the DHP antagonist. These data show that Ile(1182) can preferentially interact with DHP antagonists, but has a lesser contribution in agonist interaction. Thus, even though the agonist and antagonist interaction sites for DHPs with L-type calcium channels may overlap, some amino acids in this site may exhibit a preference for either DHP enantiomers.