SOLUBILIZATION OF HIGH-AFFINITY, GUANINE NUCLEOTIDE-SENSITIVE MU-OPIOID RECEPTORS FROM 7315C CELL-MEMBRANES

High-affinity mu-opioid receptors have been solubilized from 7315c cel l membranes. Occupancy of the membrane-associated receptors with morph ine before their solubilization in the detergent 3-[(3-cholamidopropyl ) dimethyl]-l -propane sulfonate was critical for stabilization of the receptor. The solubilized opioid receptor bound [H-3]etorphine with h igh affinity (K(D)) = 0.304 +/- 0.06 nM; B(max) = 154 +/- 33 fmol/mg o f protein). Of the membrane-associated [H-3]etorphine binding sites, 4 0 +/- 5% were recovered in the solubilized fraction. Both mu-selective and nonselective enkephalins competed with [H-3]etorphine for the sol ubilized binding sites; in contrast, delta- and K-opioid enkephalins f ailed to compete with [H-3]etorphine for the solubilized binding sites at concentrations of < 1 muM. The mu-selective ligand [H-3][D-Ala2,N- Me-Phe4,Gly5-ol]enkephalin also bound with high affinity (K(D) = 0.79 nM; B(max) = 108 +/- 17 fmol/mg of protein) to the solubilized materia l. Of the membrane-associated [H-3][D-Ala2,N-Me-Phe4,Gly5-ol]enkephali n binding sites, 43 +/- 3% were recovered in the solubilized material. Guanosine 5'-O-(3-thiotriphosphate), GTP, and guanosine 5'-O-(2-thiod iphosphate), but not adenylylimidodiphosphate, diminished [H-3][D-Ala2 ,N-Me-Phe4,Gly5-ol]enkephalin binding in a concentration-dependent man ner. Finally, mu-opioid receptors from rat brain membranes were also s olubilized in a high-affinity, guanine nucleotide-sensitive state if m embrane-associated receptors were occupied with morphine before and du ring their solubilization with the detergent 3-[(3-cholamidopro-pyl)di methyl]-1-propane sulfonate.