OPIOID BINDING TO RAT AND GUINEA-PIG NEURAL MEMBRANES IN THE PRESENCE OF PHYSIOLOGICAL CATIONS AT 37-DEGREES-C

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 233  (3) , 722-728
Abstract
.mu., .delta. and .kappa. opioid binding sites in 4 types of neural membranes were identified under conditions which included physiological concentrations of ions and an incubation temperature of 37.degree. C. Binding parameters determined under these conditions should be more directly comparable with physiological experiments than parameters obtained under conditions of low ionic concentration and at low temperature. By using either a radioligand which is selective for a single type of opioid binding site or a relatively nonselective radioligand in the presence of an unlabeled selective ligand, binding to single populations of sites was isolated. Saturation and displacement data were analyzed with the aid of a computerized nonlinear curve fitting program. [3H]Tyr-D-Ala-Gly-(Me)Phe-Gly-ol bound to a single population of sites with the characteristics of .mu. receptors, as determined by saturation and displacement analysis. Binding to the .mu. site represented 70% of the total specific opioid binding in the rat brain, but only 20-30% in guinea pig tissues. [3H][D-Ala2-D-Leu5]enkephalin bound almost equally well to .mu. and .delta. sites, but the .delta. site could be examined by the inclusion of unlabeled Tyr-D-Ala-Gly-(Me-Phe-Gly-ol in the incubations. [3H]Ethylketocyclazocine bound .mu. and .kappa. sites, and Tyr-D-Ala-Gly-(Me)Phe-Gly-ol was also used to block the .mu. component in experiments in .kappa. binding was studied. Binding to .kappa. sites represented 50-60% of the total in guinea pig tissues, but less than 20% in rat brain.