BOMBESIN AND THROMBIN AFFECT DISCRETE POOLS OF INTRACELLULAR CALCIUM THROUGH DIFFERENT G-PROTEINS

In mouse NIH 3T3 cells, the mitogens bombesin and thrombin induced Ca2 + release from intracellular stores. Ca2+ release induced by bombesin was inhibited by the Ca2+-ATPase inhibitor thapsigargin, while Ca2+ re lease induced by thrombin was unaffected by this agent. The Ca2+-relea se response to bombesin was not affected by pertussis toxin, but the r esponse to thrombin was abolished by the toxin. Stable transfectants o verexpressing the G-protein subunit type alpha(q) showed an accentuate d response to bombesin, indicating that the bombesin receptor was coup led to a G(q)-like G-protein. Together, these results show that the tw o mitogenic receptors are coupled to distinct G-proteins that affect f unctionally different pools of Ca2+. Organization of signalling pathwa ys in this manner may allow cells to differentially encode information from different signals.