Pathways involved in PTH-induced rise in cytosolic Ca2+ concentration of rat renal proximal tubule.

Parathyroid hormone (PTH) raises cytosolic Ca2+ concentration ([Ca2+]i) in isolated or cultured renal proximal tubule cells. The pathways through which this action is mediated are not fully delineated. This study explored these pathways utilizing fura 2. [Ca2+]i of freshly prepared renal proximal tubular cells increased from 150 +/- 3.6 to 281 +/- 9.0 nM after the exposure to 10(-7) M angiotensin II, which served as a positive control. Both PTH-(1-84) and PTH-(1-34) produced a dose-dependent rise in [Ca2+]i. The effects of both moieties were similar up to 10(-7) M, but with higher doses the rise in [Ca2+]i with PTH-(1-84) was greater (P < 0.01) than with PTH-(1-34). This effect of the hormone occurred in the presence or absence of calcium in the media, but the rise in [Ca2+]i was significantly greater in the presence of calcium. The PTH-induced rise in [Ca2+]i was markedly inhibited by PTH antagonist [Nle8,18,Tyr34]bPTH-(7-34)-NH2 (bPTH is bovine PTH), verapamil, or nifedipine. 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, increased [Ca2+]i of cells, but its effect was less than PTH. Staurosporine abolished the TPA effect and partially inhibited that of PTH. A G protein activator raised [Ca2+]i, whereas a G protein inhibitor and pertussis toxin partially blocked the effect of PTH. Sodium or chloride channel blockers or sodium-free media did not modify the effect of PTH.(ABSTRACT TRUNCATED AT 250 WORDS)