Abstract

Many cells develop an adaptive increase in the capacity of adenylate cyclase to synthesize cyclic AMP (cAMP) after prolonged (hours or days) exposure to drugs which initially inhibit enzyme activity. Recent evidence suggests that adaptive increases in cAMP responses can be induced within minutes by inhibitory drugs. We have investigated the kinetics for induction and decay of this phenomenon in mouse neuroblastoma x rat glioma hybrid cells. The muscarinic cholinergic agonist carbachol induced an increase in prostaglandin E1-stimulated cAMP accumulation within 2 min of pretreatment with carbachol; the increase was 70 to 100% above control values after exposure to carbachol for 30 min. Enhanced cAMP responsiveness decayed with a half-life of about 8 min after removal of carbachol. Pretreatment with carbachol for 30 hr led to an enhanced cAMP response which decayed in two components, a rapid component and an additional, more stable component which persisted for at least 2 hr after withdrawal of carbachol. Pertussis toxin prevented these effects of carbachol. Prevention of carbachol-induced inhibition of cAMP accumulation below basal concentrations with a phosphodiesterase inhibitor did not prevent the ability of carbachol to acutely induce augmented prostaglandin E1-stimulated cAMP accumulation. Mouse neuroblastoma x rat glioma hybrid cells exhibit an enhanced cAMP response after both acute and chronic exposure to a muscarinic cholinergic agonist although these processes decay with different time courses. The signal for this acutely induced adaptation does not appear to be the decrease in cellular cAMP concentration resulting from inhibition of adenylate cyclase but does require a pertussis toxin-sensitive substrate.