Etomidate and Etomidate Analog Binding and Positive Modulation of γ-Aminobutyric Acid Type A Receptors
| Autor: | Celena Ma, Keith W. Miller, Douglas E. Raines, Megan McGrath, Mansi Tolia, Selwyn S. Jayakar, Jonathan B. Cohen, Zhiyi Yu, Xiaojuan Zhou |
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| Rok vydání: | 2018 |
| Předmět: |
0301 basic medicine
030102 biochemistry & molecular biology business.industry GABAA receptor Stereochemistry Substituent Aminobutyric acid gamma-Aminobutyric acid 03 medical and health sciences chemistry.chemical_compound 0302 clinical medicine Anesthesiology and Pain Medicine chemistry 030202 anesthesiology Etomidate Competitive antagonist Medicine Binding site business Receptor medicine.drug |
| Zdroj: | Anesthesiology. 129:959-969 |
| ISSN: | 0003-3022 |
| DOI: | 10.1097/aln.0000000000002356 |
| Popis: | Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Naphthalene-etomidate, an etomidate analog containing a bulky phenyl ring substituent group, possesses very low γ-aminobutyric acid type A (GABAA) receptor efficacy and acts as an anesthetic-selective competitive antagonist. Using etomidate analogs containing phenyl ring substituents groups that range in volume, we tested the hypothesis that this unusual pharmacology is caused by steric hindrance that reduces binding to the receptor’s open state. Methods The positive modulatory potencies and efficacies of etomidate and phenyl ring–substituted etomidate analogs were electrophysiology defined in oocyte-expressed α1β3γ2L GABAA receptors. Their binding affinities to the GABAA receptor’s two classes of transmembrane anesthetic binding sites were assessed from their abilities to inhibit receptor labeling by the site-selective photolabels 3[H]azi-etomidate and tritiated R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid. Results The positive modulatory activities of etomidate and phenyl ring–substituted etomidate analogs progressively decreased with substituent group volume, reflecting significant decreases in both potency (P = 0.005) and efficacy (P < 0.0001). Affinity for the GABAA receptor’s two β+ − α– anesthetic binding sites similarly decreased with substituent group volume (P = 0.003), whereas affinity for the receptor’s α+ – β–/γ+ – β– sites did not (P = 0.804). Introduction of the N265M mutation, which is located at the β+ − α– binding sites and renders GABAA receptors etomidate-insensitive, completely abolished positive modulation by naphthalene-etomidate. Conclusions Steric hindrance selectively reduces phenyl ring–substituted etomidate analog binding affinity to the two β+ − α– anesthetic binding sites on the GABAA receptor’s open state, suggesting that the binding pocket where etomidate’s phenyl ring lies becomes smaller as the receptor isomerizes from closed to open. |
| Databáze: | OpenAIRE |
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