Anesthetics inhibit membrane receptor coupling to the Gq/11 heterotrimeric G protein in airway smooth muscle.
BACKGROUND
Some anesthetics relax airway smooth muscle in part by inhibiting acetylcholine-induced increases in Ca2+ sensitivity, an effect associated with inhibition of guanosine nucleotide exchange at the alpha subunit of the Gq/11 (Galphaq/11) heterotrimeric G protein. This study tested the hypothesis that these anesthetic effects are not unique to the muscarinic receptor but are a general property of the heptahelical receptors that increase Ca2+ sensitivity in airway smooth muscle.


METHODS
Anesthetic effects on agonist-induced increases in Ca2+ sensitivity were measured in porcine airway smooth muscle strips permeabilized with S. aureus alpha-toxin. Anesthetic effects on basal (without agonist stimulation) and agonist-promoted Galphaq/11 guanosine nucleotide exchange were determined in crude membranes prepared from porcine airway smooth muscle. The nonhydrolyzable, radioactive form of guanosine 5'-triphosphate was used as the reporter for nucleotide exchange at Galphaq/11.


RESULTS
Acetylcholine, endothelin-1, and histamine caused a concentration-dependent increase in Ca2+ sensitivity. Halothane (0.67 +/- 0.07 mM) and hexanol (10 mM) significantly inhibited the increase in Ca2+ sensitivity induced by each agonist. Each agonist also caused a time- and concentration-dependent increase in Galphaq/11 nucleotide exchange. Neither anesthetic had an effect on basal Galphaq/11 nucleotide exchange, whereas halothane and hexanol significantly inhibited the increase in Galphaq/11 nucleotide exchange promoted by each agonist.


CONCLUSIONS
These data suggest that inhibition of agonist-promoted guanosine nucleotide exchange at Galphaq/11 by some anesthetics may be a general property of heptahelical receptors involved cellular processes mediated by Galphaq/11, including muscarinic, endothelin-1, and histamine receptor activation of Ca2+ sensitivity.
Nakayama
Tetsuzo
T
Department of Anesthesiology, Mayo Foundation, Rochester, Minnesota 55905, USA.
Hayashi
Masao
M
Warner
David O
DO
Jones
Keith A
KA
D000109:Acetylcholine / Q000494:pharmacology; D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1 / Q000494:pharmacology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006632:Histamine / Q000494:pharmacology; D013552:Swine; D014132:Trachea / Q000187:drug effects* / Q000378:metabolism
D000777:Anesthetics; D019332:Endothelin-1; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006632:Histamine; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D000109:Acetylcholine; D002118:Calcium