A role for Ca(v)1.3 in rat intestinal calcium absorption

Active Ca(2+) absorption through epithelial Ca(2+) channels TRPV5/6 in duodenum is activated by hyperpolarisation. However, when diet and Ca(2+) are plentiful, digestion products cause depolarisation. We therefore used homology-based PCR from a rat jejunal mucosal cDNA preparation to reveal the presence of the neuroendocrine L-type isoform Ca(v)1.3alpha(1). Immunocytochemical labelling and immunoblotting localised Ca(v)1.3 alpha(1) protein in apical membrane from proximal jejunum to mid ileum. Perfusion studies in vivo with 1.25 mM luminal Ca(2+) revealed L-type channel activity. Inhibition of glucose absorption with phloridzin strongly inhibited 45Ca(2+) absorption; absorption was inhibited by nifedipine and Mg(2+) and activated by Bay K 8644, none of which affect TRPV5/6. At 10mM Ca(2+), nifedipine inhibited 45Ca(2+) absorption with a time course similar to that at 1.25 mM Ca(2+): absorption was therefore channel-mediated rather than paracellular. We suggest that in times of dietary sufficiency, Ca(v)1.3 may mediate a significant route of Ca(2+) absorption into the body.