Catecholamine-induced desensitization involves an uncoupling of beta-adrenergic receptors and adenylate cyclase

Incubation of 1321N1 astrocytoma cells for 15 min with 1 microM (-)-isoproterenol resulted in a 50-65% loss of isoproterenol-stimulated adenylate cyclase activity. No decrease occurred in basal adenylate cyclase activity or in the density of beta-adrenergic receptors as assessed by (125I)-hydroxybenzylpindolol binding. Concentration-effect studies indicated that the apparent affinity of isoproterenol for inhibition of (125I)-hydroxbenzylpindolol binding was decreased by approximately 10-fold in membranes prepared from cells that had been exposed to 1 umM isoproterenol for 15 min. In the presence of GTP there was a shift to the right of the concentration-effect curve for isoproterenol in control membranes. GTP had little effect on the apparent affinity of isoproterenol in desensitized membranes. In desensitized cells that were subsequently washed free of catecholamine, the decrement in isoproterenol-stimulated adenylate cyclase activity and the decrease in the capacity of isoproterenol to inhibit 125IHYP binding returned to control levels within 15 min. These data are consistent with the hypothesis that an early event in the process of desensitization in 1321N1 cells involves a reversible uncoupling of beta-adrenergic receptors and adenylate cyclase.