Antagonistic property of buprenorphine for putative epsilon-opioid receptor-mediated G-protein activation by beta-endorphin in pons/medulla of the mu-opioid receptor knockout mouse.
beta-Endorphin is a non-selective opioid peptide which binds mu-, delta- and putative epsilon (beta-endorphin-sensitive non-mu-, non-delta- and non-kappa(1)-)-opioid receptors. We have previously reported that beta-endorphin-produced G-protein activation is mediated by the stimulation of both mu- and putative epsilon-opioid receptors. The present study was designed to further characterize this putative epsilon-opioid receptor-mediated G-protein activation in the pons/medulla membrane obtained from mice lacking mu-opioid receptor, using a guanosine-5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS)-binding assay. beta-Endorphin and the mu-opioid receptor agonist [D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin (DAMGO) increased the [(35)S]GTPgammaS binding in a concentration-dependent manner (0.001-10 microM), and at 10 microM beta-endorphin and DAMGO produced approximately 250 and 120% increases of [(35)S]GTPgammaS binding in the pons/medulla membrane obtained from wild-type mice, respectively. In the pons/medulla membrane obtained from mu-opioid receptor knockout mice, beta-endorphin-stimulated [(35)S]GTPgammaS binding was only partially attenuated and a more than 100% increase by 10 microM beta-endorphin still remained, while DAMGO failed to produce any increase in [(35)S]GTPgammaS binding. The residual increase in [(35)S]GTPgammaS binding by 10 microM beta-endorphin in mu-opioid receptor knockout mice was partially but significantly attenuated by the putative epsilon-opioid receptor partial agonist beta-endorphin (1-27), but not by the delta-opioid receptor antagonist naltrindole or the kappa(1)-receptor antagonist norbinaltorphimine. Furthermore, buprenorphine significantly attenuated the residual increase in [(35)S]GTPgammaS binding by 10 microM beta-endorphin in mu-opioid receptor knockout mice. The present results indicate that beta-endorphin activates G-protein by stimulation of putative epsilon-opioid receptors in the condition lacking the mu-opioid receptor, and buprenorphine acts as an antagonist for putative epsilon-opioid receptors in this condition.
Mizoguchi
H
H
Department of Anesthesiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
Wu
H-E
HE
Narita
M
M
Hall
F S
FS
Sora
I
I
Uhl
G R
GR
Nagase
H
H
Tseng
L F
LF
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D002047:Buprenorphine / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D005260:Female; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists; D009294:Narcotics / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology; D011149:Pons / Q000187:drug effects / Q000378:metabolism; D011869:Radioligand Assay; D011957:Receptors, Opioid / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000172:deficiency* / Q000187:drug effects / Q000235:genetics; D012249:Rhombencephalon / Q000187:drug effects / Q000378:metabolism*; D013462:Sulfur Radioisotopes; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D001615:beta-Endorphin / Q000037:antagonists & inhibitors / Q000378:metabolism*
C114628:NTI compound; D009292:Narcotic Antagonists; D009294:Narcotics; D010446:Peptide Fragments; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D013462:Sulfur Radioisotopes; C043460:epsilon receptor; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C051843:binaltorphimine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002047:Buprenorphine; D009271:Naltrexone; D001615:beta-Endorphin; D019204:GTP-Binding Proteins