Halothane inhibits signaling through m1 muscarinic receptors expressed in Xenopus oocytes.
BACKGROUND
Interactions between volatile anesthetics and muscarinic acetylcholine receptors have been studied primarily in binding assays or in functional systems derived from tissues or cells, often containing multiple receptor subtypes. Because interactions with muscarinic signaling systems may explain some effects and side effects of anesthetics and form a model for anesthetic-protein interactions in general, the author studied anesthetic inhibition of muscarinic signaling in an isolated system.


METHODS
mRNA encoding the m1 muscarinic receptor subtype was prepared in vitro and expressed in Xenopus oocytes. Effects of halothane on methylcholine-induced intracellular Ca2+ release was measured. Angiotensin II receptors were expressed to evaluate anesthetic effects on intracellular signaling.


RESULTS
m1 Receptors expressed in oocytes were functional, and could be inhibited by atropine and pirenzepine. Halothane depressed m1 muscarinic signaling in a dose-dependent manner: half-maximal inhibition of 10(-7) M methylcholine was obtained with 0.3 mM halothane. The effect was reversible and could be overcome by high concentrations of muscarinic agonist. Angiotensin II signaling was unaffected by 0.34 mM halothane.


CONCLUSIONS
m1 Muscarinic signaling is inhibited by halothane, and lack of halothane effect on angiotensin signaling indicates that the intracellular signaling systems of Xenopus oocytes are unaffected. Therefore, the most likely site of halothane action is the receptor and/or G protein. Oocytes provide a versatile system for detailed investigation into the molecular mechanism of anesthetic-protein interactions.
Department of Anesthesiology, University of Virginia, Charlottesville 22908.
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Durieux
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004594:Electrophysiology; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D006221:Halothane / Q000494:pharmacology*; D066298:In Vitro Techniques; D008967:Molecular Biology; D018727:Muscarinic Antagonists; D009865:Oocytes; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011976:Receptors, Muscarinic / Q000235:genetics; D011994:Recombinant Proteins; D015398:Signal Transduction / Q000187:drug effects; D014981:Xenopus
D018727:Muscarinic Antagonists; D012333:RNA, Messenger; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D019204:GTP-Binding Proteins; D002118:Calcium; D006221:Halothane