A Mutation Affecting Dihydropyridine-Sensitive Current Levels and Activation Kinetics inDrosophilaMuscle and Mammalian Heart Calcium Channels

The Dmca1D gene encodes a Drosophila calcium channel α 1 subunit. We describe the first functional characterization of a mutation in this gene. This α 1 subunit mediates the dihydropyridine-sensitive calcium channel current in larval muscle but does not contribute to the amiloride-sensitive current in that tissue. A mutation, which changes a highly conserved Cys to Tyr in transmembrane domain IS1, identifies a residue important for channel function not only in Drosophila muscle but also in mammalian cardiac channels. In both cases, mutations in this Cys residue slow channel activation and reduce expressed currents. Amino acid substitutions at this Cys position in the cardiac α 1 subunit show that the size of the side chain, rather than its ability to form disulfide bonds, affects channel activation.