Propofol Inhibits Muscarinic Acetylcholine Receptor-Mediated Signal Transduction in Xenopus Oocytes Expressing the Rat M1 Receptor

Abstract

The effects of propofol, 2,6-diisopropylphenol, an intravenous general anesthetic, on signal transduction mediated by the rat M1 muscarinic acetylcholine (ACh) receptor (M1 receptor) were examined in electrophysiological studies by analyzing receptor-stimulated, Ca2+-activated Cl--current responses in the Xenopus oocyte expression system. In oocytes expressing the M1 receptor, ACh induced the Ca2+-activated C1- current, in a dose-dependent manner (EC50= 114 nM). Propofol (5-50 microM) reversibly and dose-dependently inhibited induction of the Ca2+-activated Cl- current by ACh (100 nM) (IC50=5.6 microM). To determine a possible site affected by propofol in this signal transduction, we tested the effects of this anesthetic (10 microM) on the activation of current by injection of CaCl2 and aluminum fluoride (AlF4-). Propofol did not affect activation of the current by the intracellular injected Ca2+, or activation of the current by the intracellular injected AlF4-. These results indicate that propofol does not affect G protein, the inositol phosphate turnover, release of Ca2+ from Ca2+ store or the Ca2+-activated Cl- channel. Propofol apparently inhibits the M1 receptor-mediated signal transduction at the receptor site and/or the site of interaction between the receptor and associated G protein.

Site of Action of the General Anesthetic Propofol in Muscarinic M1 Receptor-Mediated Signal Transduction

“…All statistics were generated using StatView 5.0 (SAS Institute, Cary, NC), and p values less than 0.05 were considered statistically significant. the M1 receptor, application of ACh induced no significant current (Matsumoto et al, 1998;Nagase et al, 1999). As shown in Fig.…”

“…Two-electrode voltage-clamp studies revealed that propofol inhibits the acetylcholine-induced Ca 2ϩ activated Cl Ϫ current in oocytes expressing M1 receptors. Propofol did not affect activation of the current by an intracellular injection of CaCl 2 or aluminum fluoride (AlF 4 Ϫ ) (Nagase et al, 1999), thus indicating that the target site of propofol may be the upstream of G protein coupled with the M1 receptor, that is, binding site of the receptor or interaction site between the receptor and G protein. It is also debated whether propofol inhibits GDP-GTP exchange on G protein, because activation of G protein with AlF 4 Ϫ does not require the GDP-GTP exchange (Gilman, 1987).…”

“…We reported effects of propofol, which is now a widely used intravenous anesthetic, on M1 receptor-mediated signal transduction in oocytes (Nagase et al, 1999). Two-electrode voltage-clamp studies revealed that propofol inhibits the acetylcholine-induced Ca 2ϩ activated Cl Ϫ current in oocytes expressing M1 receptors.…”

“…Oocyte preparation and two-electrode voltage-clamp method have been described elsewhere (Nagase et al, 1999). Female X. laevis toads were immersed in ice until unresponsive to painful stimulus.…”

“…In a previous study, effects of propofol on ACh-induced M1 receptor-mediated signal transduction were studied using a 10-min application of propofol in oocytes expressing the M1 receptor (Nagase et al, 1999), because a relatively long period of application of propofol was required for inhibition. To obtain comparable data, we applied propofol for 10 min in the present study, although a 2-min application of propofol (100 nM) completely inhibited the activation of current with ACh (data not shown).…”