NONGENOMIC ACTIONS OF 1,25-DIHYDROXY-VITAMIN-D(3) IN CULTURED MUSCLE-CELLS - STIMULATION OF CA2+ UPTAKE

Recent studies involve 1,25-dihydroxy vitamin D3[1,25(OH)2D3] as an im portant modulator of muscle function. The hormone acts partially throu gh a receptor-mediated genomic route, analogously to classic steroid h ormones. However, the sterol also affects muscle calcium fluxes by a m echanism independent of genome activation. Here we have characterized the rapid, non-genomic effects of 1,25(OH)2D3 on calcium up ake in cul tured chick embryo myoblasts. The hormone stimulated Ca-45 uptake with in 1 min (50% above control values), effects that were time [1-10 min. ] and dose [10(-11) M - 10(-7) M] dependent. The effects of 1,25(OH)2D 3 were mimicked by the Ca2+ channel agonist BAY K8644 and effectively suppressed by the Ca2+ channel antagonist nifedipine. Cell membrane de polarization with high K+, similarly to the hormone, elicited a rapid increase in Ca2+ uptake. The effect of 1,25(OH)2D3, on Ca2+ influx was dependent on the presence of exracellular calcium, since it was aboli shed by prior addition of EGTA and was restored upon the addition of 1 mM Ca2+. These results suggest the modulation of competent calcium ch annels in embryonic muscle cells by 1,25(OH)2D3.