Expression of multiple CaV1.2 transcripts in rat tissues mediated by different promoters.

The expression of two different transcripts for Ca(V)1.2 in rat tissues mirrors that which has previously been described for human tissue, in that expression of transcripts expressing exon 1a is predominant only in heart, whereas expression of transcripts expressing exon 1b is greater in smooth muscle rich tissues such as aorta and intestine. Transcripts expressing exon 1b also predominate in brain and in diaphragm. Western blots indicate that the N-terminus coded for by exon 1b is present in much of the protein in all these tissues except heart. The promoter just upstream of exon 1b has been cloned, sequenced and utilized to drive expression of luciferase in smooth muscle A7r5 cells, cardiac HL-1 cells, skeletal muscle L6 cells and neuronal PC12 cells. The nucleotide sequence of the promoter exhibits 80% identity with the equivalent promoter previously identified in humans and 94% identity with the sequence of the equivalent region of the mouse genome. Evidence in favor of still another promoter upstream of exon 2 has been uncovered.

A new promoter for alpha1C subunit of human L-type cardiac calcium channel Ca(V)1.2.

The cardiac Ca channel known as alpha1C or Ca(V)1.2 is shown to express a new longer first exon equivalent to that formerly reported in rabbit heart or rat aorta. Ribonuclease protection assay indicates that this exon is found in the majority of Ca(V)1.2 transcripts in human heart RNA. The presence of this exon also suggests that expression of this transcript is driven by a promoter immediately upstream of this exon and its 5' untranslated region. The putative promoter exhibits 69% homology to its rat counterpart and displays functional promoter activity when transfected into heart cells in culture in luciferase-expressing constructs.