Abbreviations used: ECL, enhanced chemiluminescence; NorBNI, norbinaltorphimine; SDS-PAGe, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TBS, Tris-buffered saline; TBST, TBS with 0.05% Tween 20; WGA, wheat germ agglutinin.
Abstract: Antipeptide antibodies against the κ-opioid receptor were used to test whether acute or chronic exposure to κ agonists altered the phosphorylation state of the κ-opioid receptor. Immunoprecipitation of the κ receptor from guinea pig hippocampal slices preincubated in [32P]orthophosphoric acid revealed a basal phosphorylation of the κ-opioid receptor. The amount of 32P incorporation into the receptor was increased following a 75-min treatment with the κ agonist U50,488H. This effect was blocked by the selective κ receptor antagonist norbinaltorphimine. The time course of this change in the phosphorylation state of the receptor correlated with a desensitization of the electrophysiological response to κ agonists measured in the dentate gyrus of hippocampal slices. The phosphorylation state of the κ-opioid receptor was also elevated in brain slices from guinea pigs made tolerant to U50,488H by 5 days of continuous exposure and then maintained in κ agonist to avoid acute opiate withdrawal. The results of this study show that the κ-opioid receptor was phosphorylated in an agonist-dependent manner in brain slices taken from untreated and U50,488H-tolerant animals.