DIFFERENT SUBUNIT REQUIREMENTS FOR VOLATILE AND NONVOLATILE ANESTHETICS AT GAMMA-AMINOBUTYRIC-ACID TYPE-A RECEPTORS

The ability of volatile (halothane and isoflurane) and nonvolatile (al phaxalone and pentobarbital) general anesthetics to modulate radioliga nd binding to gamma-aminobutyric acid (GABA)(A) receptors was examined in an immortalized cell line (WSS-1) expressing rat alpha 1 and gamma 2 subunits. Volatile anesthetics enhance [H-3]flunitrazepam binding t o WSS-1 cells in a concentration-dependent manner, with potencies and efficacies comparable to those found with native GABA(A) receptors. Tr ansfection of these cells with cDNAs encoding rat beta 2 or beta 3 sub units had a significant influence on anesthetic efficacy but not poten cy in this assay. Thus, transfection with the beta 2 subunit reduced t he efficacy of both isoflurane and halothane, whereas transfection wit h the beta 3 subunit increased the efficacy of isoflurane but not halo thane, compared with values obtained in WSS-1 cells. In contrast, alph axalone (an anesthetic steroid) had no effect, whereas at high concent rations pentobarbital (an anesthetic barbiturate) produced a modest in hibition of [H-3]flunitrazepam binding to GABAA receptors in WSS-1 cel ls. Transfection of WSS-1 cells with cDNAs encoding either beta 2 or b eta 3 subunits resulted in a concentration-dependent enhancement of [H -3]flunitrazepam binding by these nonvolatile anesthetics. Moreover, p entobarbital was significantly more potent in enhancing [H-3]flunitraz epam binding to WSS-1 cells transfected with the beta 2 subunit, compa red with the beta 3 subunit. The difference in subunit requirements be tween volatile and nonvolatile anesthetics for enhancement of [H-3]-fl unitrazepam binding indicates that these classes of agents affect GABA (A) receptor function at distinct loci. These studies also provide evi dence that the beta subunit is required for these nonvolatile anesthet ics to positively modulate GABA(A) receptors.