ACCENTUATION BY PERTUSSIS TOXIN OF THE 5-HYDROXYTRYPTAMINE-INDUCED POTENTIATION OF ATP-EVOKED RESPONSES IN RAT PHEOCHROMOCYTOMA CELLS

We previously demonstrated that 5-hydroxytryptamine (5-HT) enhances th e cationic current activated by extracellular ATP in rat pheochromocyt oma PC12 cells. We report here that pertussis toxin (PTX) modulates th is 5-HT-dependent enhancement in these cells. 5-HT potentiated ATP-evo ked intracellular Ca2+ concentration ([Ca](i)) rise and dopamine relea se over a concentration range from 1 to 100 mu M. When cells were pre- treated with PTX, this potentiation was accentuated. Pretreatment with PTX also accentuated the 5-HT-dependent enhancement of the ATP-activa ted current. These results suggest that the enhancement by 5-HT of the ATP-evoked responses is negatively regulated by a mechanism mediated through PTX-sensitive GTP-binding protein,