Distinct calcium channel isoforms mediate parathyroid hormone and chlorothiazide-stimulated calcium entry in transporting epithelial cells

Some cells express multiple calcium channel isoforms that are likely to have distinct functions. The present study used molecular cloning and antisense techniques to identify calcium channel isoforms mediating calcium entry in mouse distal convoluted tubule (DCT) cells. The DCT is the major site of hormone-and diuretic-regulated calcium transport in the kidney. Cellular calcium absorption involves entry through apical membrane calcium channels that are sensitive to dihydropyridine-type calcium channel antagonists. Partial cDNA clones corresponding to one isoform of the calcium channel alpha(1) pore-forming subunit, alpha(1C), and one isoform of the calcium channel beta accessory subunit, beta 3, were isolated by RT-PCR. Full-length transcripts were detected by Northern blot analysis in immortalized DCT cells. Antisense oligonucleotides complementary to the alpha(1C) sequence inhibited the rise of intracellular calcium ([Ca2+](i)) induced by the thiazide diuretic, chlorothiazide (CTZ), but not that induced by parathyroid hormone (PTH). However, antisense oligonucleotides complementary to the beta 3 sequence inhibited both CTZ- and PTH-induced rises of [Ca2+](i). beta 3 antisense oligonucleotides also inhibited the membrane hyperpolarization induced by CTZ but not that triggered by PTH. Thus, members of the voltage-gated calcium channel family are expressed in DCT cells, where they are responsible for hormone-and drug-induced calcium uptake. The results suggest that DCT cells contain multiple calcium channels with distinct roles in the regulation of cellular calcium.