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  • Title: Key roles of Phe1112 and Ser1115 in the pore-forming IIIS5-S6 linker of L-type Ca2+ channel alpha1C subunit (CaV 1.2) in binding of dihydropyridines and action of Ca2+ channel agonists.
    Author: Yamaguchi S, Zhorov BS, Yoshioka K, Nagao T, Ichijo H, Adachi-Akahane S.
    Journal: Mol Pharmacol; 2003 Aug; 64(2):235-48. PubMed ID: 12869628.
    Abstract:
    Voltage-dependent L-type Ca2+ channels are modulated by the binding of Ca2+ channel antagonists and agonists to the pore-forming alpha1c subunit (CaV 1.2). We recently identified Ser1115 in IIIS5-S6 linker of alpha1C subunit as a critical determinant of the action of 1,4-dihydropyridine agonists. In this study, we applied alanine-scanning mutational analysis in IIIS5-S6 linker of rat brain alpha1C subunit (rbCII) to illustrate the role of pore-forming IIIS5-S6 linker in the action of Ca2+ channel modulators. Ca2+ channel currents through wild-type (rbCII) or mutated alpha1C subunits, transiently expressed in BHK6 cells with beta1a and alpha2/delta subunits, were analyzed. The replacement of Phe1112 by Ala (F1112A) significantly impaired the sensitivity to Ca2+ channel agonists (S)-(-)-Bay k 8644 and FPL-64176, and modestly to 1,4-dihydropyridine (DHP) antagonists. The low sensitivity of F1112A and S1115A to DHP antagonists was consistent with the reduced binding affinity for [3H](+)PN200-110. The replacement of Phe1112 by Tyr, but not by Ala, restored the long openings produced by FPL-64176, thus indicating the critical role of aromatic ring of Phe1112 in the Ca2+ channel agonist action. Interestingly, double-mutant Ca2+ channel (F1112A/S1115A) failed to discriminate between Ca2+ channel agonist (S)-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-[trifluoromethyl] phenyl)-3-pyridine carboxylic acid methyl ester (Bay k 8644) and antagonist (R)-(+)-Bay k 8644 and was blocked by the two enantiomers in an identical manner. These results indicate that both Phe1112 and Ser1115 in linker IIIS5-S6 are required for the action of Ca2+ channel agonists. A model of the DHP receptor is proposed to visualize possible interactions of Phe1112, Ser1115, and other DHP-sensing residues with a typical DHP ligand nifedipine.
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