Stereoselective actions of halothane at GABA A receptors

Isoflurane anesthesia exhibits stereoselectivity, and a corresponding stereoselectivity ((+)->(−)-isomer) has been reported at GABA A receptors in vitro. The objective of the present study was to determine if the positive modulatory actions of halothane at GABA A receptors exhibited a similar stereoselectivity. Both ( R)- and ( S)-halothane ((+)- and (−)- isomers, respectively) enhanced [ 3H ]flunitrazepam binding to brain membranes in a concentration dependent manner without a significant difference in either potency (EC 50) or efficacy ( E max). While both ( R)- and ( S)-halothane enhanced [ 3H ]muscimol binding, the potency of the (+)-isomer was slightly greater than the corresponding (−)-isomer (0.91±0.17 versus 1.45±0.04% atmospheres, respectively ( P