Anesthetics inhibit acetylcholine-promoted guanine nucleotide exchange of heterotrimeric G proteins of airway smooth muscle.
BACKGROUND
Anesthetics inhibit airway smooth muscle contraction in part by a direct effect on the smooth muscle cell. This study tested the hypothesis that the anesthetics halothane and hexanol, which both relax airway smooth muscle in vitro, inhibit acetylcholine-promoted nucleotide exchange at the alpha subunit of the Gq/11 heterotrimeric G protein (Galphaq/11; i.e., they inhibit muscarinic receptor-Galphaq/11 coupling).


METHODS
The effect of halothane (0.38 +/- 0.02 mm) and hexanol (10 mm) on basal and acetylcholine-stimulated Galphaq/11 guanosine nucleotide exchange was determined in membranes prepared from porcine tracheal smooth muscle. The nonhydrolyzable, radioactive form of guanosine-5'-triphosphate, [S]GTPgammaS, was used as the reporter for Galphaq/11 subunit dissociation from the membrane to soluble fraction, which was immunoprecipitated with rabbit polyclonal anti-Galphaq/11 antiserum.


RESULTS
Acetylcholine caused a significant time- and concentration-dependent increase in the magnitude of Galphaq/11 nucleotide exchange compared with basal values (i.e., without acetylcholine), reaching a maximal difference at 100 microm (35.9 +/-2.9 vs. 9.8 +/-1.2 fmol/mg protein, respectively). Whereas neither anesthetic had an effect on basal Galphaq/11 nucleotide exchange, both halothane and hexanol significantly inhibited the increase in Galphaq/11 nucleotide exchange produced by 30 microm acetylcholine (by 59% and 68%, respectively).


CONCLUSIONS
Halothane and hexanol interact with the receptor-heterotrimeric G-protein complex in a manner that prevents acetylcholine-promoted exchange of guanosine-5(')-triphosphate for guanosine-5'-diphosphate at Galphaq/11. These data are consistent with the ability of anesthetics to interfere with cellular processes mediated by heterotrimeric G proteins in many cells, including effects on muscarinic receptor-G-protein regulation of airway smooth muscle contraction.
Sakihara
Chie
C
Department of Anesthesiology, Mayo Foundation, Rochester, Minnesota 55905, USA.
Perkins
William J
WJ
Warner
David O
DO
Jones
Keith A
KA
D000109:Acetylcholine / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D000777:Anesthetics / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006221:Halothane / Q000494:pharmacology; D000441:Hexanols / Q000494:pharmacology; D066298:In Vitro Techniques; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D011233:Precipitin Tests; D013552:Swine; D014132:Trachea / Q000187:drug effects / Q000378:metabolism
D000777:Anesthetics; D018685:Anesthetics, Inhalation; D006150:Guanine Nucleotides; D000441:Hexanols; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D019205:GTP-Binding Protein alpha Subunits, Gs; D000109:Acetylcholine; D006221:Halothane