Title: Isoflurane Potentiation of GABAA Receptors is Reduced but not Eliminated by the β3(N265M) Mutation
Legend: Left – Rapid solution exchange methods were used to record from recombinant GABAA receptors were expressed in HEK293 cells. Right – Isoflurane concentration-dependent modulation of the EC10 response to GABA was attenuated by the b3-N265M point mutation. This finding differs from the complete insensitivity of mutant receptors to etomidate and propofol (not shown). 
Citation: Lor, C., M. Perouansky, and R.A. Pearce, Isoflurane Potentiation of GABAA Receptors Is Reduced but Not Eliminated by the beta3(N265M) Mutation. Int J Mol Sci, 2020. 21(24).
Abstract: Background – Mice carrying the GABAA receptor β3(N265M) point mutation, which renders receptors incorporating β3-subunits insensitive to many general anesthetics, have been used experimentally to link modulation of different receptor subtypes to distinct behavioral endpoints. Remarkably, however, the effect of the mutation on the susceptibility to modulation by isoflurane (a standard reference agent for inhalational vapors) has never been tested directly. Therefore, we compared the modulation by isoflurane of expressed α5β3(N265M)γ2L receptors with their wild type counterparts. Methods – Using whole-cell electrophysiological recording and rapid solution exchange techniques, we tested the effects of isoflurane at concentrations ranging from 80 μM to 320 μM on currents activated by 1 μM GABA. We measured drug modulation of wild-type α5β3γ2L GABAA receptors and their counterparts harboring the β3(N265M) mutation. Results – Currents elicited by GABA were enhanced two- to four-fold by isoflurane, in a concentration-dependent manner. Under the same conditions, receptors incorporating the β3(N265M) mutation were enhanced by approximately 1.5- to two-fold; i.e., modulation by isoflurane was attenuated by approximately one-half. Direct activation by isoflurane was also present in mutant receptors but also attenuated. Conclusions – In contrast to the complete insensitivity of β3(N265M) mutant receptors to etomidate and propofol, the mutation has only a partial effect on receptor modulation by isoflurane. Therefore, the persistence of isoflurane effects in mutant mice does not exclude a possible contribution of β3-GABAA receptors.
About the Lab: Research in the Pearce laboratory is focused on the mechanisms by which general anesthetics alter brain function. We are particularly interested in understanding how modulation of GABAA receptors impairs memory – a fundamental endpoint of anesthesia. For our studies we utilize expressed recombinant receptors and hippocampal brain slices to investigate the roles of specific subunit combinations and cell types in the control of learning and memory.