Evidence for the existence of a cardiac specific isoform of the alpha 1 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 alpha 1 and alpha 2 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 alpha 1 subunit. The amino acid sequence deduced from this part cDNA clone shows 64.7% similarity with the skeletal muscle alpha 1 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 oligodeoxy-nucleotides 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.