Kinetics of recovery from opioids at wild-type and mutant mu opioid receptors expressed in xenopus oocytes.
To investigate a previous observation that classical antagonists behave as agonists at mutant H297N and H297Q mu opioid receptors, we compared the kinetics of recovery from opioids at wild-type and mutant mu receptors expressed in voltage-clamped Xenopus oocytes. The cDNA for the potassium channel GIRK1 was coinjected into the oocytes with that of the mu receptors to transduce agonist binding into a coupled electrophysiological response. The kinetics of recovery were estimated by brief test pulses of the agonist normorphine given at a frequency of 0.67 or 1 per min. After treatment with a variety of agonists, the receptors recovered from desensitization at rates that depended on the agonist, but there was little difference between mutant and wild-type receptors. Antagonists, however, induced agonist-like currents and demonstrated faster recovery at the mutant receptors. These results suggest that His-297 may comprise part of an antagonist subsite. This conclusion, when coupled with the steric theory that intrinsic activity depends on independent binary equilibration of a drug between agonist and antagonist subsites, could unify the paired observations that antagonists become agonists and recover faster at the mutant than at the wild-type receptors. Synapse 38:254-260, 2000. Published 2000 Wiley-Liss, Inc.
Spivak
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Cellular Neurobiology Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland 21224, USA. cspivak@intra.nida.nih.gov
Beglan
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D000818:Animals; D009154:Mutation / Q000187:drug effects / Q000502:physiology; D009292:Narcotic Antagonists / Q000737:chemistry / Q000493:pharmacokinetics*; D009294:Narcotics / Q000819:agonists / Q000737:chemistry / Q000493:pharmacokinetics*; D009865:Oocytes; D017450:Receptors, Opioid, mu / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus
D009292:Narcotic Antagonists; D009294:Narcotics; D017450:Receptors, Opioid, mu