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A study resorted to libraries obtained from ordinary human heart mRNA to isolate a distinct structural variant of the cardiac L-type voltage-dependent calcium channel alpha-1 subunit cDNA. Masked homology with other calcium channel alpha1 subunits is observed for the obtained amino acid sequence. A shortened N-terminus, a distinct C-terminal insertion and both versions of an optionally spliced motif IV S3 area were some of the differences from the rabbit heart alpha1. A single hybridizing mRNA species of 9.4 kb was observed. Native-like pharmacology and channel characteristics were formed in single-channel studies, and in Xenopus oocytes, the cloned alpha-1 subunit was expressed.

The rat aorta alpha-1 subunit, which isa component of the voltage-dependent calcium channel, is present in two isoforms, differing only in the third membrane-spanning region of the fourth motif (IVS3). Characterization of clones containing the genes encoding these variant subunits showed that the diversity arises from alternative splicing of a primary transcript containing a single pair of adjacent exons each encoding aunique sequence for the IVS3 region. Both variant forms are expressed in fetal and newborn rat heart, but only a single isoform predominates in the adult.