Thrombin increases cytoplasmic Ca2+ and stimulates formation of prostaglandin E2 in the osteoblastic cell line MC3T3-El.

Using microfluorometric analysis in individual, fura-2 loaded cells, we found that thrombin (0.1-10 U/ml) caused a dose-dependent (EC50 approximately 0.5 U/ml), rapid (within seconds), transient increase in cytoplasmic Ca2+ in the osteoblastic cell line MC3T3-El. The thrombin induced rise in cytoplasmic Ca2+ was not dependent on extracellular Ca2+ and was unaffected by indomethacin. In MC3T3-El cells, thrombin (0.3-10 U/ml) caused a rapid and dose-dependent (EC50 approximately 0.5 U/ml) stimulation of PGE2 formation. The calcium ionophore A23187 (2 mumol/l) also rapidly stimulated an increase in cytoplasmic Ca2+ and the formation of PGE2 in MC3T3-El cells. These data indicate that thrombin mobilizes Ca2+ from intracellular stores and that Ca2+ may serve as a second messenger in thrombin induced stimulation of PGE2 biosynthesis in osteoblasts.