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 t o have distinct functions. The present study used molecular cloning an d antisense techniques to identify calcium channel isoforms mediating calcium entry in mouse distal convoluted tubule (DCT) cells. The DCT i s the major site of hormone-and diuretic-regulated calcium transport i n the kidney. Cellular calcium absorption involves entry through apica l 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(1 C), and one isoform of the calcium channel beta accessory subunit, bet a 3, were isolated by RT-PCR. Full-length transcripts were detected by Northern blot analysis in immortalized DCT cells. Antisense oligonucl eotides complementary to the alpha(1C) sequence inhibited the rise of intracellular calcium ([Ca2+](i)) induced by the thiazide diuretic, ch lorothiazide (CTZ), but not that induced by parathyroid hormone (PTH). However, antisense oligonucleotides complementary to the beta 3 seque nce inhibited both CTZ- and PTH-induced rises of [Ca2+](i). beta 3 ant isense oligonucleotides also inhibited the membrane hyperpolarization induced by CTZ but not that triggered by PTH. Thus, members of the vol tage-gated calcium channel family are expressed in DCT cells, where th ey are responsible for hormone-and drug-induced calcium uptake. The re sults suggest that DCT cells contain multiple calcium channels with di stinct roles in the regulation of cellular calcium.