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⁺ release induced by thrombin was unaffected by this agent. The Ca²⁺-release response to bombesin was not affected by pertussis toxin, but the response to thrombin was abolished by the toxin. Stable transfectants overexpressing the G-protein subunit type α_q showed an accentuated response to bombesin, indicating that the bombesin receptor was coupled to a G_q-like G-protein. Together, these results show that the two mitogenic receptors are coupled to distinct G-proteins that affect functionally different pools of Ca²⁺. Organization of signalling pathways in this manner may allow cells to differentially encode information from different signals.