The sensitivity of G protein-activated K+ channels toward halothane is essentially determined by the C terminus.
G protein-activated K(+) channels (GIRKs or Kir3.x) are targets for the volatile anesthetic, halothane. When coexpressed with the m(2) acetylcholine (ACh) receptor in Xenopus oocytes, agonist-activated GIRK1(F137S)- and GIRK2-mediated currents are inhibited by halothane, whereas in the absence of ACh, high concentrations of halothane induce GIRK1(F137S)-mediated currents. To elucidate the molecular mechanism of halothane action on GIRK currents of different subunit compositions, we constructed deletion mutants of GIRK1(F137S) (GIRK1(Delta363*)) and GIRK2 (GIRK2(Delta356)) lacking the C-terminal ends, as well as chimeric GIRK channels. Mutated GIRK channels showed normal currents when activated by ACh but exhibited different pharmacological properties toward halothane. GIRK2(Delta356) showed no sensitivity against the inhibitory action of halothane but was activated by halothane in the absence of an agonist. GIRK1(Delta363*) was activated by halothane more efficiently. Currents mediated by chimeric channels were inhibited by anesthetic concentrations that were at least 30-fold lower than those necessary to decrease GIRK2 wild type currents. Glutathione S-transferase pulldown experiments did not show displacement of bound Gbetagamma by halothane, indicating that halothane does not interfere with Gbetagamma binding. Single channel experiments revealed an influence of halothane on the gating of the channels: The agonist-induced currents of GIRK1 and GIRK2, carried mainly by brief openings, were inhibited, whereas higher concentrations of the anesthetic promoted long openings of GIRK1 channels. Because the C terminus is crucial for these effects, an interaction of halothane with the channel seems to be involved in the mechanism of current modulation.
Milovic
Sergej
S
Medical University of Vienna, Department of Anesthesia and Intensive Care Medicine (B), Währinger Gürtel 18-20, A-1090 Vienna, Austria.
Steinecker-Frohnwieser
Bibiane
B
Schreibmayer
Wolfgang
W
Weigl
Lukas G
LG
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005260:Female; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D017353:Gene Deletion; D005982:Glutathione Transferase / Q000378:metabolism; D006221:Halothane / Q000494:pharmacology*; D051379:Mice; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010957:Plasmids / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D017434:Protein Structure, Tertiary; D018075:RNA, Complementary / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors; D014982:Xenopus laevis
D018685:Anesthetics, Inhalation; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D018075:RNA, Complementary; D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase; D006221:Halothane