Effect of 1,25-dihydroxyvitamin D3 on cytosolic calcium in dispersed parathyroid cells

Abstract

We examined the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on cytosolic calcium ([Ca](i)) of dispersed bovine parathyroid cells, using the fluorescent dye indo-1. The addition of 10-8 M 1,25-(OH)2D3 caused an increase in [Ca](i) by 23.4 ± 2.7% over a 10 minute period. There was a significant increase in [Ca](i) within two minutes of the addition of 1,25-(OH)2D3. 1,25-(OH)2D3 increases [Ca](i) in a dose-dependent manner and this occurred with as little as 10-10 M. Neither 10-7 M 25-(OH)D3 nor 10-7 M 24, 25-(OH)2D3 caused a significant increase in [Ca](i). Chelation of extracellular calcium with EGTA blocked the 1,25-(OH)2D3-induced increase in [Ca](i), suggesting that the increase was mainly from extracellular calcium. Neither 10-5 M verapamil nor 10-4 M diltiazem blocked the 1,25-(OH)2D3-induced increase in [Ca](i). The present data suggest that 1,25-(OH)2D3 might modify membrane permeability to calcium independent of voltage-dependent calcium channels sensitive to verapamil or diltiazem. The rapid effect of 1,25-(OH)2D3 raises the possibility that its mechanism is independent of genome activation, perhaps attributable to direct interaction with components of the parathyroid cell plasma membrane.