SINGLE CELL ANALYSIS OF CHANGES IN CYTOSOLIC CALCIUM INDUCED BY VITAMIN-D3 METABOLITES IN CULTURED RAT MESANGIAL CELLS

The acute effects of 1,25-Dihydroxy-vitamin D3 [1,25(OH)2D3] on the concentration of cytoplasmic ionized calcium [Ca2+] of cultured rat mesangial cells were studied at the single cell level by microspectrofluorometry of fura-2-loaded cells. Addition of 1,25(OH)2D3 produced an immediate increase of [Ca2+]. This rise in [Ca2+] was sustained and similar to that caused by the Ca2+ channel agonist BAY K 8644. Comparable changes were also observed in cultured human mesangial cells. The effects of the hormone (10-10 - 10-7 M) were dose-dependent (62% and 285%). Only 30-40% of the cells responded to stimulation with 1,25(OH)2D3. 250HD3 also increased Ca2+ whereas 24,25(OH)2D3 and laOHD3 were inactive. Addition of 1 mM CoCl2 or 2-5 μM nifedipine largely blocked the effects of 1,25(OH)2D3 suggesting the involvement of Ca2+ channel activation in the rapid 1,25(OH)2D3-induced increase in mesangial cell [Ca2+]. 45Ca uptake studies are consistent with this interpretation. © 1991 Academic Press, Inc.