Inhibitory effects of anesthetics and ethanol on muscarinic receptors expressed in Xenopus oocytes.

Anesthetics (and ethanol) are known to produce amnesia as well as immobilization. Recent identification of a nonimmobilizing (nonanesthetic) agent (F6 or 1,2-dichlorohexafluorocyclobutane) that impairs learning and memory suggests that distinct mechanisms may be responsible for these two actions of anesthetic agents. Muscarinic receptors are believed to play a role in memory and learning, and we asked if a specific subtype of these receptors is affected by anesthetics as well as the new nonanesthetic. We investigated the effects of halothane, a novel halogenated anesthetic compound F3 (1-chloro-1,2,2-trifluorocyclobutane) and ethanol on acetylcholine-induced current mediated by a muscarinic m1 receptor expressed in Xenopus oocytes. We also studied the effects of halogenated nonanesthetic compounds, F6 and F8 (2,3-chlorooctafluorobutane) on muscarinic m1 receptors. Halothane, F3, F6 and ethanol inhibited muscarinic m1 receptor-induced Ca2+-dependent Cl- currents at pharmacologically relevant concentrations. F8 had no effect on acetylcholine-induced muscarinic m1 receptor function. The protein kinase C inhibitor, bisindolylmaleimide I (GF109203X), enhanced the acetylcholine-induced current and the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), inhibited this current. GF109203X abolished the inhibitory effects of halothane, F3 and ethanol on muscarinic m1 receptors but had no effect on actions of F6. These results demonstrate that anesthetics and a nonanesthetic inhibit the function of muscarinic m1 receptors and suggest activation of protein kinase C as the mechanism of action of anesthetics and ethanol on these receptors.