Functional Expression and Characterization of a Voltage-Gated CaV1.3 (a1D) Calcium Channel Subunit from an Insulin-Secreting

L-type calcium channels mediate depolarization-induced calcium influx in insulin-secreting cells and are thought to be modulated by G protein-coupled receptors (GPCRs). The major fraction of L-type a1-subunits in pancreatic b-cells is of the neuroendocrine subtype (CaV1.3 or a1D). Here we studied the biophysical properties and receptor regulation of a CaV1.3 subunit previously cloned from HIT-T15 cells. In doing so, we compared this neuroendocrine CaV1.3 channel with the cardiac L-type channel CaV1.2a (or a1C-a) after expression together with a2d- and b3-subunits in Xenopus oo-cytes. Both the current voltage relation and voltage dependence of inactivation for the neuroendocrine CaV1.3 channel were shifted to more negative po-tentials compared with the cardiac CaV1.2 channel. In addition, the CaV1.3 channel activated and inac-tivated more rapidly than the CaV1.2a channel. Both subtypes showed a similar sensitivity to the dihydropyridine (1)isradipine. More interestingly, the CaV1.3 channels were found to be stimulated by ligand-bound Gi/Go-coupled GPCRs whereas a neuronal CaV2.2 (or a1B) channel was inhibited. The observed receptor-induced stimulation of CaV1.3 channels could be mimicked by phorbol-12-myris-tate-13-acetate and was sensitive to inhibitors of protein kinases, but not to the phosphoinositol-3-kinase-inhibitor wortmannin, pointing to serine/ threonine kinase-dependent regulation. Taken to-gether, we describe a neuroendocrine L-type CaV1.3 calcium channel that is stimulated by Gi/Go-coupled GPCRs and differs significantly in distinct biophysical characteristics from the cardiac sub-type (CaV1.2a), suggesting that the channels have different roles in native cells. (Molecular Endocri-nology 15: 1211–1221, 2001