1,25(OH)2-vitamin D3 stimulation of phospholipases C and D in muscle cells involves extracellular calcium and a pertussis-sensitive G protein.

The steroid hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] activates in chick myoblasts the breakdown of phosphoinositides by phospholipase C and the hydrolysis of phosphatidylcholine by phospholipase D. Extracellular Ca2+ requirement and GTP-binding protein mediation of 1,25(OH)2D3-dependent activation of phospholipases C and D were investigated in cells prelabelled with [3H]glycerol or [3H]arachidonic acid. Generation of diacylglycerol by phospholipase C and phosphatidylethanol by phospholipase D were shown to be dependent on extracellular calcium, since both responses were suppressed by EGTA and the Ca(2+)-channel blockers nifedipine and verapamil, and were mimicked by the calcium ionophore A23187. The G-protein activators guanosine 5'-O-(3-thiotriphosphate) and AlF4- strongly enhanced diacylglycerol and phosphatidylethanol release in myoblasts while guanosine 5'-O-(2-thiodiphosphate), which inhibits G-protein-mediated signals, abolished 1,25(OH)2D3-dependent diacylglycerol and phosphatidylethanol release. Bordetella pertussis toxin pretreatment suppressed the hormone action. These results suggest that 1,25(OH)2D3-stimulation of phosphoinositide-specific phospholipase C and phospholipase D in chick myoblasts is mediated by a pertussis-sensitive GTP-binding protein(s) and the influx of extracellular calcium.