Two amino acid residues in the IIIS5 segment of L-type calcium channels differentially contribute to 1,4-dihydropyridine sensitivity

The transmembrane segment IIIS5 of the L-type calcium channel alpha(1) subunit participates in the formation of the 1,4 dihydropyridine (DHP) interaction domain (Grabner, M,, Wang, Z., Hering, S., Striessnig, J., and Glossmann, H. (1996) Neuron 16, 207-218), We applied mutational analysis to identify amino acid residues within this segment that contribute to DHP sensitivity. DHP agonist and antagonist modulation of Ba2+ inward currents was assessed after coexpression of chimeric and mutant calcium channel alpha(1) subunits with alpha(2) delta and beta(1a) subunits in Xenopus oocytes. Whereas DHP antagonists required Thr-1066, DHP agonist modulation crucially depended on the additional presence of Gln-1070 (numbering according to alpha(1C-a)), which also further increased the sensitivity to DHP antagonists, Asp-955, which is found at the corresponding position in the calcium channel alpha(1S) subunit from carp skeletal muscle, displayed functional similarity to Gln-1070 with respect to DHP interaction, We conclude that these residues (Thr-1066 plus Gln-1070 or Asp-955), which are located in close vicinity on the same side of the putative a-helix of transmembrane segment IIIS5, form a crucial DHP binding motif.