Transfer of high sensitivity for benzothiazepines from L-type to class A (BI) calcium channels

To investigate the molecular basis of the calcium channel block by diltiazem, we transferred amino acids of the highly sensitive and stereoselective L-type (alpha(1S) or alpha(1C)) to a weakly sensitive, nonstereoselective class A (alpha(1A)) calcium channel. Transfer of three amino acids of transmembrane segment IVSG of L-type alpha into the alpha(1A) subunit (I1804Y, S1808A, and M1811I) was sufficient to support a use-dependent block by diltiazem and by the phenylalkylamine (-) gallopamil after expression in Xenopus oocytes, An additional mutation F1805M increased the sensitivity for (-)-gallopamil but not for diltiazem, Our data suggest that the receptor domains for diltiazem and gallopamil have common but not identical molecular determinants in transmembrane segment IVS6. These mutations also identified single amino acid residues in segment IVS6 that are important for class A channel inactivation.