Effects of PTH on intracellular calcium of MDCK cells in culture

Abstract

Intracellular calcium [Ca2+](i) exerts multiple functions in renal epithelia and is regulated by several hormonal factors, among them parathyroid hormone (PTH). The effect of PTH on [Ca2+](i) was investigated in Madin-Darby canine (MDCK) kidney cells in culture. Changes in [Ca2+](i) were monitored fluorometrically with the Ca2+-sensitive probe fura 2/AM, at 37 degrees C. The addition of PTH, in three cumulative doses, led to a significant and sustained raise in [Ca2+](i), in a medium with 1.36 mM [Ca2+](e). When Ca2+ was subtracted from the extracellular medium, [Ca(2+)0](e), the addition of PTH caused discrete changes on [Ca2+](i), suggesting that the hormone-induced alteration in [Ca2+](i) depend not only on [Ca2+](e), but also on intracellular stores of the ion. Nifedipine (NF) and verapamil (VP) partially blocked the PTH-induced increase in [Ca2+](i), when calcium was present in the medium, suggesting that dihydropyridine sensible-type channels are present in the plasma membrane (PM). PTH showed no effect on [Ca2+](i) in MDCK cells previously treated with 2 mu M thapsigargine (TP) in [Ca(2+)0](e) conditions but the hormone led to further fluctuations in [Ca2+](i) when [Ca2+](e) was restored to normal values. VP did not interfere with the sharp increase in [Ca2+](i) induced in cells depleted from Ca2+, which were reincubated in a normal Ca2+ medium, showing that calcium-release-activated channels (CRAC) may be also present in PM. Our results support the view that MDCK cells are responsive to PTH, and that both voltage-induced calcium channels (Ca2+-VOC) and CRAC are present in the PM of MDCK cells.