Protein and gene expression of Ca2+ channel isoforms in murine colon: effect of inflammation.

L-Type voltage-dependent Ca2+ channels (L-VDCC) mediate calcium influx in response to membrane depolarization and regulate intracellular processes such as contraction, secretion, neurotransmission, and gene expression. Colonic inflammation significantly attenuates calcium currents in smooth muscle; however, the basis for this remains unclear. In this study we examined the protein and mRNA expression of two isoforms of Ca(v)1.2, encoded by either exon la or 1b. Both isoforms were detected by Western blots, immunohistochemistry and RT-PCR in smooth muscle cells. Neither the protein nor mRNA expression measured by real-time PCR of either isoforms was affected in colonic myocytes from dextran sulfate sodium-treated mice. In whole-cell voltage-clamp experiments, the amplitude of the calcium currents were decreased by almost 70% by inflammation. The calcium channel currents were attenuated by 50 +/- 3% by the c-src kinase specific inhibitor, PP2, in control cells but only 19 +/- 7% in cells from inflamed mice. These studies suggest that decreased calcium channel currents following colonic inflammation are not due to decreased expression but may result from altered regulation by the non-receptor cellular tyrosine kinase, c-src kinase.