High extracellular calcium attenuates adipogenesis in 3T3-L1 preadipocytes.

We studied the effect of extracellular Ca(2+) concentration (Ca(2+)) on adipocyte differentiation. Preadipocytes exposed to continuous Ca(2+) higher than 2.5 mmol/l accumulated little or no cytoplasmic lipid compared to controls in 1.8 mmol/l Ca(2+). Differentiation was monitored by Oil Red O staining of cytoplasmic lipid and triglyceride assay of accumulated lipid, by RT-PCR analysis of adipogenic markers, and by the activity of glycerol-3-phosphate dehydrogenase (GPDH). Elevated Ca(2+) inhibited expression of peroxisome proliferator-activated receptor gamma, CCAAT/enhancer binding protein alpha, and steroid regulatory binding element protein. High Ca(2+) significantly inhibited differentiation marker expression including adipocyte fatty acid binding protein, and GPDH. The decrease in Pref-1 expression that accompanied differentiation also was prevented by high Ca(2+). Treatment of 3T3-L1 cells with high Ca(2+) did not significantly affect cell number or viability and did not trigger apoptosis. Levels of intracellular Ca(+2) remained unchanged in various Ca(2+). Treatment of 3T3-L1 with pertussis toxin (PTX) partially restored lipid accumulation and increased differentiation markers in cells treated with 5 mmol/l Ca(2+). 'Classical' parathyroid cell Ca(2+) sensing receptors (CaSR) were not detected either by RT-PCR or by Western blotting. These results suggest that continuous exposure to high Ca(2+) inhibits preadipocyte differentiation and that this may involve a G-protein-coupled mechanism mediated by a novel Ca(2+) sensor or receptor.