CALCIUM CHANNELS FROM CYPRINUS-CARPIO SKELETAL-MUSCLE

The complete amino acid sequence of the L-type calcium channel alpha-1 subunit from the carp (Cyprinus carpio) white skeletal muscle was deduced by cDNA cloning and sequence analysis. The open reading frame encodes 1852 amino acids (M(r) 210,060). A 155-amino acid COOH-terminal sequence (after the fourth internal repeat) is evolutionarily preserved (90% homology) and may represent an important functional domain of L-type calcium channels. The photolabeled, membrane-bound, and purified carp alpha-1 subunits have masses of 211 and 190 kDa. The purified channel could not be phosphorylated by cAmP-dependent protein kinase. Two glycoproteins (alpha-2 subunits) are associated with the alpha-1 subunit and change their apparent masses from 235 and 220 kDa to 159 kDa upon reduction of disulfide bonds. Nucleic acid hybridization with alpha-2 cDNA revealed an 8.0-kilobase transcript in carp skeletal muscle. Evidence for a copurification of subunits similar in size to mammalian beta or gamma subunits was not obtained.