Mu-opioid ([3H]DAGO) binding in slices of rat brain: inhibition by sodium ions, guanyl-5'-yl imidodiphosphate and by the adrenergic neurotoxins DSP4 and xylamine.
We have characterized and quantified the specific binding of the mu-agonist [3H] DAGO to 300 microM slices of hypothalamus and cerebral cortex. The receptors have many of the opioid characteristics previously demonstrated in homogenate assays. Binding is reversible, saturable, stereospecific and of high affinity. The delta-opioids DTLET and DSLET are 36- and 30-fold respectively, less effective than DAGO in competing for the binding site. Assays can be routinely performed in the presence of physiological concentrations of sodium, though in TRIS buffer the affinity and the number of receptors is increased. Protection of the ligand against proteolytic degradation is unnecessary. Unexpectedly, we observed that GppNHp inhibits [3H] DAGO binding to brain slices. This suggests an allosteric modification of the mu-receptor in the membranes of intact cells. The mu-receptors are also blocked by the adrenergic neurotoxins DSP4 and xylamine. This re-emphasizes our contention that care should be exercised in the use of these drugs. The technique is simple, rapid and involves minimal disruption of tissue. It should provide new opportunities for the study of cell surface opioid receptor subtypes in intact tissue.
D000818:Animals; D001596:Benzylamines / Q000494:pharmacology*; D001921:Brain / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology*; D008297:Male; D009498:Neurotoxins / Q000494:pharmacology; D009588:Nitrogen Mustard Compounds / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology*; D013566:Sympathomimetics / Q000494:pharmacology; D014316:Tritium
D001596:Benzylamines; D004745:Enkephalins; D009498:Neurotoxins; D009588:Nitrogen Mustard Compounds; D011480:Protease Inhibitors; D013566:Sympathomimetics; D014316:Tritium; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D006165:Guanylyl Imidodiphosphate; D010042:Ouabain; C026131:xylamine; D006160:Guanosine Triphosphate; D012964:Sodium; C012102:DSP 4