Chelation of intracellular calcium prevents mesangial cell proliferative responsiveness

Mesangial cell transformation into a proliferative phenotype, observed in many glomerular diseases, occurs in response to growth factors and cytokines. This study tests the hypothesis that intracellular calcium is necessary for stimulation of mesangial cell proliferative responsiveness to a variety of growth factors. Furthermore, these experiments tested whether nonspecific calcium entry via a calcium ionophore was sufficient to elicit the same response. Rat primary mesangial cells (passages 5 to 10) were growth-arrested for 48 h in 0.5% fetal bovine serum (FBS), then stimulated with 0.1 microM endothelin-1, 1.9 microM platelet-derived growth factor (PDGF)-BB, 0.5% FBS, or 0.1 microM ionomycin, with or without the intracellular calcium chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid (BAPTA). Calcium signaling was measured in Fura-2-loaded cells on coverslips by dual-wavelength spectrofluorometry and in Fluo-3-loaded cells by confocal fluorescence laser microscopy. [3H]-Thymidine incorporation was measured after 12 to 24 h of stimulation with each test agent. Expression of c-fos mRNA was analyzed by Northern blot. All test agents stimulated a significant increase in cytosolic and nuclear calcium, which were both effectively inhibited with BAPTA. All agents stimulated a significant increase in [3H]-thymidine incorporation and enhanced c-fos mRNA expression (no detectable c-fos mRNA was observed in quiescent cells). BAPTA prevented the enhanced [3H]-thymidine incorporation stimulated by endothelin-1 and PDGF, and partial inhibition of FBS-stimulated incorporation with BAPTA was observed. BAPTA inhibited c-fos expression observed in response to these agents. Phorbol ester induction of c-fos mRNA in the absence of raised cytosolic or nuclear calcium was also suppressed by BAPTA. Cell viability as measured by thiazolyl blue and trypan blue was not altered by BAPTA. It is concluded that normal regulation of intracellular calcium is necessary for mesangial cell proliferative responsiveness.