The effects of anesthetics and ethanol on alpha2 adrenoceptor subtypes expressed with G protein-coupled inwardly rectifying potassium channels in Xenopus oocytes.

A wide range of physiological effects are mediated by alpha2-adrenoceptors (ARs) through their association with G protein-coupled inwardly rectifying potassium (GIRK) channels. Although alpha2-ARs are divided into three subtypes (alpha2A-C), a pharmacological distinction among the subtypes is difficult to establish because of the lack of a selective agonist and antagonist; therefore, little is known about the effects of anesthetics on the alpha2-AR subtypes. We expressed each subtype together with GIRK1/GIRK2 subunits in Xenopus oocytes and observed alpha2-AR-mediated GIRK1/GIRK2 currents to test the effects of ethanol, halothane, and several IV anesthetics at clinical concentrations. UK 14,304, a selective alpha2-AR agonist, evoked GIRK1/GIRK2 currents in every subtype. None of the IV anesthetics, which included pentobarbital, propofol, ketamine, and alphaxalone, influenced UK 14,304-evoked potassium currents in any of the receptor subtypes. Ethanol enhanced the UK 14,304-evoked potassium currents, whereas halothane inhibited the currents. However, these effects were not significantly different from those on the baseline-GIRK1/GIRK2 current, suggesting that neither ethanol nor halothane acts directly on the alpha2-AR subtypes. Although none of the drugs examined had any effect on the alpha2-ARs, the physiological actions of the alpha2-ARs mediated by the GIRK1/GIRK2 channels may be affected by ethanol and halothane.