Serine residue in the IIIS5-S6 linker of the L-type Ca2+ channel alpha(1C)subunit is the critical determinant of the action of dihydropyridine Ca2+ channel agonists

The dihydropyridine (DHP)-binding site has been identified within L-type Ca 2+ channel alpha (1C) subunit. However, the molecular mechanism underlying modulation of Ca2+ channel gating by DHPs has not been clarified. To search for novel determinants of high affinity DHP binding, we introduced point m utations in the rat brain Ca2+ channel alpha (1C) subunit (rbCII or Ca(v)1. 2c) based on the comparison of amino acid sequences between rbCII and the a scidian L-type Ca2+ channel alpha (1) subunit, which is insensitive to DHPs . The alpha (1C) mutants (S1115A, S1146A, and A1420S) and rbCII were transi ently expressed in BHK6 cells with beta (1a) and alpha (2)/delta subunits. The mutation did not affect the electrophysiological properties of the Ca2 channel, or the voltage- and concentration-dependent block of Ca2+ channel currents produced by diltiazem and verapamil. However, the S1115A channel was significantly less sensitive to DHP antagonists. Interestingly, in the S1115A channel, DHP agonists failed to enhance whole-cell Ca2+ channel curr ents and the prolongation of mean open time, as well as the increment of NP o. Responsiveness to the non-DHP agonist FPL-64176 was also markedly reduce d in the S1115A channel. When S1115 was replaced by other amino acids (S111 5D, S1115T, or S1115V), only S1115T was slightly sensitive to S-(-)-Bay K 8 644. These results indicate that the hydroxyl group of Ser(1115) in IIIS5-S 6 linker of the L-type Ca2+ channel alpha (1C) subunit plays a critical rol e in DHP binding and in the action of DHP Ca2+ channel agonists.