Effect of halothane on galphai-3 and its coupling to the M2 muscarinic receptor
| Autor: | Sumedha G. Penheiter, Shuyan Wang, Alan R. Penheiter, David O. Warner, Joshua D. Spencer, Keith A. Jones, Fang Jin, John H. Streiff |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
Magnetic Resonance Spectroscopy
GTP' G protein Gi alpha subunit GTPgammaS GTP-Binding Protein alpha Subunits Gi-Go Transfection chemistry.chemical_compound Heterotrimeric G protein Muscarinic acetylcholine receptor Chlorocebus aethiops Escherichia coli Medicine Animals Humans Receptor Muscarinic M2 business.industry Cell Membrane Acetylcholine Guanine Nucleotides Recombinant Proteins G beta-gamma complex Anesthesiology and Pain Medicine Biochemistry chemistry Anesthetics Inhalation COS Cells Biophysics Guanosine Triphosphate business Halothane Baculoviridae medicine.drug |
| Zdroj: | Anesthesiology. 103(5) |
| ISSN: | 0003-3022 |
| Popis: | Background Halothane is an effective bronchodilator and inhibits airway smooth muscle contraction in part by inhibiting intracellular signaling pathways activated by the M2 muscarinic receptor and its cognate inhibitory heterotrimeric guanosine-5'-triphosphate (GTP)-binding protein (G protein), Gi. This study hypothesized that halothane inhibits nucleotide exchange at the alpha isoform-3 subunit of Gi (Galphai-3), but only when regulated by the M2 muscarinic receptor. Methods GTP hydrolysis by Galphai-3 and the Galphai-3beta1gamma2HF heterotrimer expressed in Spodoptera frugiperda cells was measured using a phosphohydrolase assay with [gammaPi]-labeled GTP. Anesthetic binding to Galphai-3 was measured by saturation transfer difference nuclear magnetic resonance spectroscopy. Galphai-3 nucleotide exchange was measured in crude membranes prepared from COS-7 cells transiently coexpressing the M2 muscarinic receptor and Galphai-3. A radioactive analog of GTP, [S]GTPgammaS, was used as a reporter for Galphai-3 nucleotide exchange. Results Although spectroscopy demonstrated halothane binding to Galphai-3, this binding had no effect on [gammaPi]-labeled GTP hydrolysis by the Galphai-3beta1gamma2HF heterotrimer expressed in Spodoptera frugiperda cells, nor basal Galphai-3 nucleotide exchange measured in crude membranes when the muscarinic receptor agonist acetylcholine was omitted from the assay. Conversely, halothane caused a concentration-dependent inhibition of Galphai-3 nucleotide exchange with acetylcholine included in the assay. Conclusion These data indicate that despite halothane binding to Galphai-3, halothane has no direct inhibitory effect on the intrinsic activity of the Galphai-3beta1gamma2HF heterotrimer but inhibits M2 muscarinic receptor regulation of the heterotrimer. This novel effect is consistent with the ability of halothane to inhibit airway smooth muscle contraction and bronchoconstriction induced by acetylcholine. |
| Databáze: | OpenAIRE |
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