title: The inhibitory effects of alphaxalone on M1 and M3 muscarinic receptors expressed in Xenopus oocytes.
abstract: Alphaxalone is a neurosteroid anesthetic, but its mechanisms of action are not completely understood. Muscarinic receptors are involved in a variety of neuronal functions in the brain and autonomic nervous system, and much attention has been paid to them as targets of anesthetics. In this study, we investigated the effects of alphaxalone on M(1) and M(3) muscarinic receptors using the Xenopus oocyte expression system. Alphaxalone inhibited acetylcholine-induced currents in oocytes expressing M(1) receptors at clinically relevant concentrations. Alphaxalone also suppressed acetylcholine-induced currents in oocytes expressing M(3) receptors. The half-maximal inhibitory concentration values for the inhibition of M(1)- and M(3)-mediated currents were 1.8 +/- 0.6 micro M and 5.3 +/- 1.0 micro M, respectively. GF109203X, a selective protein kinase C inhibitor, had little effect on the inhibition of acetylcholine-induced currents by alphaxalone in oocytes expressing these receptors. Alphaxalone inhibited the specific binding of [(3)H]quinuclidinyl benzilate to oocytes expressing M(1) or M(3) receptors. These findings suggest that alphaxalone at clinically relevant concentrations inhibits the function of M(1) and M(3) receptors through a protein kinase C-independent mechanism by interfering with the [(3)H]quinuclidinyl benzilate binding sites on the receptors.
  
  
  CONCLUSIONS
  Alphaxalone, a neurosteroid anesthetic, inhibited the function of muscarinic M(1) and M(3) receptors and the specific binding of [(3)H]quinuclidinyl benzilate ([(3)H]QNB) to oocytes expressing these receptors. These findings suggest that alphaxalone inhibits these receptors by interfering with the QNB binding sites.
authors.affiliation: Department of *Anesthesiology and †Physiology, University of Occupational and Environmental Health, School of Medicine, Kitakyushu; and ‡Department of Pharmacology, Nagasaki University Graduate School of Biomedical Sciences, Japan.
authors.forename: Munehiro
authors.initials: M
authors.lastname: Shiraishi
authors.forename: Kouichiro
authors.initials: K
authors.lastname: Minami
authors.forename: Izumi
authors.initials: I
authors.lastname: Shibuya
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Uezono
authors.forename: Junichi
authors.initials: J
authors.lastname: Ogata
authors.forename: Takashi
authors.initials: T
authors.lastname: Okamoto
authors.forename: Osamu
authors.initials: O
authors.lastname: Murasaki
authors.forename: Muneshige
authors.initials: M
authors.lastname: Kaibara
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ueta
authors.forename: Akio
authors.initials: A
authors.lastname: Shigematsu
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D018727:Muscarinic Antagonists / Q000378:metabolism / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism*; D011277:Pregnanediones / Q000494:pharmacology*; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D000777:Anesthetics; D018118:Chloride Channels; D018727:Muscarinic Antagonists; D011277:Pregnanediones; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate; C006477:alphaxalone; D000109:Acetylcholine