Vitamin D3 accelerates PTH-dependent calcium transport in distal convoluted tubule cells

This study examined the interaction of 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] and parathyroid hormone (PTH) on Ca2+ uptake, intracellular Ca2+ ([Ca2+]i) and membrane voltage in transformed mouse distal convoluted tubule (DCT) cells. 1,25(OH)2D3 increased PTH-dependent 45Ca2+ uptake by 2 h and was maximally stimulated at 5 h over the range of 10(-11) to 10(-9) M 1,25(OH)2D3. [Ca2+]i was measured in single cells grown on cover slips and loaded with fura-2. In control cells [Ca2+]i averaged 109 nM and was not changed by acute addition of 1,25(OH)2D3 (10(-7) M) alone or by pretreatment with 1,25(OH)2D3 for 5 h. The magnitude of the bPTH-(1-34)-stimulated increase of [Ca2+]i was similar in control cells and in cells pretreated with 1,25(OH)2D3. In cells pretreated with 1,25(OH)2D3 the latency before [Ca2+]i increased, following addition of PTH, was reduced from 8.6 min to 3.5 +/- 0.9 min (P < 0.01). 1,25(OH)2D3 alone had no effect on 45Ca2+ uptake but shortened the time course of PTH-dependent 45Ca2+ uptake. The inactive vitamin D analogue, 25-hydroxyvitamin D3 (10(-7) M) (with or without PTH), did not affect 45Ca2+ uptake. Inhibition of transcription with 5-6-dichloro-1-beta-D- ribofuranosylbenzimidazole abolished the effect of 1,25(OH)2D3, but not that of PTH. Treatment with 1,25(OH)2D3 also decreased the latency but not the magnitude of membrane hyperpolarization induced by PTH. Nifedipine abolished PTH-induced increases of [Ca2+]i and 45Ca2+ entry in cells pretreated with 1,25(OH)2D3.(ABSTRACT TRUNCATED AT 250 WORDS)