Anesthetic Barbiturates Enhance Gsα-Dependent Cyclic AMP Production in S49 Mouse Lymphoma Cells

Abstract: Cyclic AMP (cAMP) regulates many important physiological processes. Barbiturates influence cAMP regulation, possibly through effects on G proteins. This study used intact S49 mouse lymphoma cells to characterize the role of G proteins in the effect of barbiturates on cAMP regulation. cAMP accumulation was determined in intact S49 WT (wild-type) and S49 cyc^? cells (the G_sα-deficient mutant) by measuring the conversion of [³H]-ATP to [³H]cAMP in cells preloaded with [³H]adenine. Pentobarbital enhanced cAMP accumulation in WT cells in the absence (basal) or presence of isoproterenol but had no effect on the EC₅₀ for isoproterenol. This effect was dose dependent with a 50–60% enhancement at 2 mM pentobarbital. Pentobarbital did not affect forskolin-stimulated cAMP accumulation in WT cells. In cyc^? cells, basal and forskolin-stimulated cAMP accumulation were stimulated only at the highest concentration of pentobarbital used (2 mM). Pentobarbital did not affect the inhibition of cAMP accumulation by somatostatin in WT cells, and pertussis toxin treatment of WT cells did not affect the action of pentobarbital on cAMP accumulation. Pentobarbital did not affect isoproterenol-stimulated adenylyl cyclase activity in whole-cell homogenates or membranes prepared from WT cells. The S-(?)-isomer of pentobarbital enhanced isoproterenol-stimulated cAMP accumulation more than the R-(+)-isomer. Phenobarbital and barbituric acid did not enhance isoproterenol-stimulated cAMP accumulation, whereas the anesthetic barbiturates hexobarbital, pentobarbital, and thiopental all enhanced activity. These results suggest that pentobarbital enhances cAMP accumulation in intact WT cells by a mechanism that is dependent on G_sα but independent of G_i. The properties of barbiturates that are responsible for the enhancement of cAMP accumulation may be related to the properties that are responsible for producing sedation and anesthesia.