Differential translation of the alpha-1 isoforms of L-type calcium channel in rat brain and other tissues.

Abstract

L-Type voltage operated calcium channel plays an important role in the contraction-relaxation of muscle cells. The alpha-1 subunit of this pentameric protein performs catalytic functions. Multiple mRNA isoforms of this subunit are generated by alternative splicing. For example, an exon encoding 11 amino acids (aa) between the third and fourth transmembrane domains produces two mRNA isoforms in gastrointestinal (GI) tract. The corresponding exon in brain encodes 15 aa. Whether the alpha-1 mRNA isoforms are translated into the corresponding isozymes remain unknown. To address this issue and to characterize the exon in brain, isozymes specific anti-peptide polyclonal antibodies were raised. Both the antibodies reacted with a protein of Mr 180 kDa in the heart and GI-tract, while no reaction was obtained in the kidney or liver. Brain expressed the isoform containing the same exon encoding 11 amino acids present in GI-tract, but the corresponding isozymes were of Mr 145-150 kDa. These findings suggest a tissue-specific translation of the alpha-1 isozymes.