Modification of receptor-mediated inhibition of adenylate cyclase in NG108-15 neuroblastoma X glioma cells by n-ethylmaleimide.

Previous studies with membranes from rat heart (Mol. Pharmacol. 21: 570-580, 1982) and human platelets (J. Biol. Chem. 257: 2829-2833, 1982) have suggested that inhibition of adenylate cyclase by occupation of hormone receptors is blocked by pretreatment of membranes with relatively low concentrations of N-ethylmaleimide (NEM). Using membranes derived from NG108-15 neuroblastoma X glioma cells as a model system, we have examined the effect of NEM on the interaction of three inhibitory receptors with adenylate cyclase. Pretreatment of membranes with 100 to 216 microM NEM resulted in a loss of the capacity of agonists to inhibit adenylate cyclase through muscarinic cholinergic and opiate receptors and a loss of GTP-sensitive high-affinity binding of agonists to both of these receptors. Under the same conditions, stimulation of adenylate cyclase by prostaglandin E1 was unchanged. In contrast to the total loss of capacity to inhibit adenylate cyclase by muscarinic and opiate receptor activation, the inhibition of adenylate cyclase by activation of alpha-2 adrenergic receptors was only partially blocked by maximally effective concentrations of NEM. Similarly, GTP-sensitive high-affinity binding of epinephrine to alpha-2 receptors still occurred in NEM (316 microM)-treated membranes. Whereas only a decrease in the efficacy of muscarinic and opiate receptor agonists for inhibition of adenylate cyclase occurred as a result of NEM treatment, pretreatment of membranes with 316 microM NEM resulted in a 30-fold decrease in the potency of epinephrine for inhibition of adenylate cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)