Enhancement of Hormonal Stimulation in Intact Cells

The ability of prostaglandin El (PGE1) and cholera toxin to increase cyclic AMP levels is potentiated g-fold when normal rat kidney (NRK) cells are treated with picolinic acid or histidinol, or grown in isoleucine-deficient medium. The response to (-)-isoproterenol is increased a-fold in NRK cells treated with picolinic acid but not in cells subjected to isoleucine deprivation. The increase in agonist responsiveness is time-dependent, reaches its maximum at 40 h, and is quickly reversed following removal of picolinic acid or addition of medium with normal amounts of isoleucine. The cholera toxin response is also increased about ?-fold in simian virus 40-transformed NRK cells and Moloney sarcoma virus-transformed NRK cells treated with picolinic acid. GTP-stimulated, but not fluoride-stimulated, adenylate cyclase activities are increased in membranes from NRK cells treated with picolinic acid or starved for isoleucine, indicating that the increased response is due, at least in part, to a specific potentiation of GTPdependent functions of the adenylate cyclase system. The results demonstrate that GTP-dependent events in hormonal stimulation of adenylate cyclase can be altered in intact cells to modulate hormonal enhancement of cyclic AMP production.