Activation of G-proteins in the mouse pons/medulla by beta-endorphin is mediated by the stimulation of mu- and putative epsilon-receptors.
The activation of mu-, delta- and kappa1-opioid receptors by their respective agonists increases the binding of the non-hydrolyzable GTP analog guanosine-5'-(gamma-thio)-triphosphate (GTPgammaS) to G proteins. Beta-endorphin is an endogenous opioid peptide which binds nonselectively to mu-, delta- and putative epsilon-opioid receptors. The present experiment was designed to determine which opioid receptors are involved in the stimulation of [35S]GTPgammaS binding induced by beta-endorphin in the mouse pons/medulla. The mouse pons/medulla membranes were incubated in an assay buffer containing 50 pM [35S]GTPgammaS, 30 microM GDP and various concentrations of beta-endorphin. Beta-endorphin (0.1 nM-10 microM) increased [35S]GTPgammaS binding in a concentration-dependent manner, and 10 microM beta-endorphin produced a maximal stimulation of approximately 260% over baseline. This stimulation of [35S]GTPgammaS binding by beta-endorphin was partially attenuated by the mu-opioid receptor antagonist beta-funaltrexamine (beta-FNA), but not by the delta-opioid receptor antagonist naltrindole (NTI) or the kappa1-opioid receptor antagonist nor-binaltorphimine (nor-BNI). Beta-endorphin stimulated [35S]GTPgammaS binding by about 80% in the presence of 10 microM beta-FNA, 30 nM NTI and 100 nM nor-BNI. The same concentrations of these antagonists completely blocked the stimulation of [35S]GTPgammaS binding induced by 10 microM [D-Ala2,NHPhe4,Gly-ol]enkephalin, [D-Pen(2,5)]enkephalin and U50,488H, respectively. Moreover, the residual stimulation of [35S]GTPgammaS binding induced by beta-endorphin in the presence of the three opioid receptor antagonists was significantly attenuated by 100 nM of the putative epsilon-opioid receptor partial agonist beta-endorphin (1-27). These results indicate that the stimulation of [35S]GTPgammaS binding induced by beta-endorphin is mediated by the stimulation of both mu- and putative epsilon-opioid receptors in the mouse pons/medulla.
Mizoguchi
H
H
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA.
Narita
M
M
Nagase
H
H
Tseng
L F
LF
D000818:Animals; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000493:pharmacokinetics; D006153:Guanosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D011149:Pons / Q000187:drug effects / Q000502:physiology*; D011957:Receptors, Opioid / Q000502:physiology*; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000502:physiology*; D013462:Sulfur Radioisotopes; D001615:beta-Endorphin / Q000494:pharmacology*
D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D013462:Sulfur Radioisotopes; C043460:epsilon receptor; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009271:Naltrexone; D001615:beta-Endorphin; C024524:beta-funaltrexamine; D019204:GTP-Binding Proteins; C055382:naltrindole