3H][D-Ala 2,NMePhe 4,Gly-ol 5]-enkephalin (mu-opioid) binding in beige-J mice

Abstract

Tritiated [D-Ala 2,NMePhe 4,Gly-ol 5]-enkephalin [ 3H]DAGO) was used to examine mu-opioid receptor number and mu-ligand binding in brain synaptic membranes (P 2 fraction) from C57BL/6J-bg J/bg J (beige-J) mice, a strain with combined deficiencies in immunological function (resembling Chediak-Higashi syndrome) and analgesic response to mu-opioid agonists such as morphine and DAGO. As controls, white mice, beige-J littermates (normally responsive to mu-opioid agonists), and a known mu-deficient strain (CXBK) were also examined. Neither the K D (0.47 to 0.49 nM) nor the B max (153 to 168 fmol/mg protein) determined for beige-J mice was significantly different from values determined for littermates or white mice. In contrast, the B max of CXBK mice (66 fmol/mg protein) was clearly less than that of the other strains. The analgesic defect of beige-J mice, therefore, is not likely due to an insufficient number of mu-opioid receptors, as it presumably is in CXBK mice. Carbachol (200 μg/ml), which partly corrects the analgesic defect of beige-J mice, had no effect on [ 3H]DAGO binding either acutely in vitro or chronically ex vivo after administration to beige-J mice for three weeks. Hence, the analgesic defect of beige-J mice appears to be due to some defect in the mu-opioid receptor-effector coupling mechanism or to some endogenous substance that inhibits binding of mu-opioid ligands to otherwise functional receptors.