Abstract: | In cultured porcine aortic smooth muscle cells,sphingosylphosphorylcholine (SPC), ATP, or bradykinin (BK) induced arapid dose-dependent increase in the cytosolicCa2+ concentration([Ca2+]i)and also stimulated inositol 1,4,5-trisphosphate(IP3) generation. Pretreatmentof cells with pertussis toxin blocked the SPC-induced IP3 generation and[Ca2+]iincrease but had no effect on the action of ATP or BK. In addition, SPCstimulated the mitogen-activated protein kinase (MAPK) and increasedDNA synthesis, whereas neither ATP nor BK produced such effects. Boththe SPC-induced MAPK activation and DNA synthesis were pertussis toxinsensitive. SPC-induced MAPK activation was blocked by treatment ofcells with the phospholipase C inhibitor, U-73122, or the intracellularCa2+-ATPase inhibitor,thapsigargin, but not by removal of extracellular Ca2+. Lysophosphatidic acidinduced cellular responses similar to SPC in a pertussistoxin-sensitive manner in terms of[Ca2+]iincrease, IP3 generation, MAPKactivation, and DNA synthesis. Platelet-derived growth factor (PDGF)also induced a[Ca2+]iincrease, MAPK activation, and DNA synthesis in the same cells; however, the PDGF-induced MAPK activation was not sensitive to pertussis toxin and changes in[Ca2+]i.SPC-induced MAPK activation was inhibited by pretreatment of cells withstaurosporine, W-7, or calmidazolium. Our results suggest that, inporcine aortic smooth muscle cells, MAPK is not activated by theincrease in[Ca2+]iunless a pertussis toxin-sensitive G protein is simultaneously stimulated, indicating the role ofCa2+ in pertussis toxin-sensitiveG protein-mediated MAPK activation. |