Evidence for the existence of a cardiac specific isoform of the α₁ subunit of the voltage dependent calcium channel

Biochemical, pharmacological and electrophysiological evidence implies the existence of tissue specific isoforms of the L-type VDCC. The α₁ and α₂ subunits of the skeletal muscle calcium channel have been previously cloned and their amino acid sequence deduced. Here we report the isolation and sequencing of a partial cDNA that encodes a heart specific isoform of the α₁ subunit. The amino acid sequence deduced from this part cDNA clone shows 64.7% similarity with the skeletal muscle α₁ subunit. Northern analysis reveals 2 hybridizing bands, 8.5 and 13 kb, in contrast to one 6.5 kb band in the skeletal muscle. Selective inhibition of mRNA expression in Xenopus oocytes by complementary oligodeoxynucleotides derived from the heart clone provides further evidence that the cDNA corresponds to an essential component of the VDCC. These data further support the existence of tissue-specific isoforms of the L-type VDCC.