ELECTRON-SPIN RESONANCE STUDY OF SYNAPTOSOME OPIATE RECEPTOR - KINETICS OF STEREOSPECIFIC BINDING OF SPIN LABELED MORPHINE

Morphine, spin labeled on the 3- or 6-position was used as the opiate ligand in a study of the time course of stereospecific opiate binding to intact synaptosomes isolated from non-cerebellar rat brain. The broadening of ESR lines induced by immobilization of the ligand on binding was used to determine the concentration of bound opiate. The stereospecificity of the reaction was measured by comparing ligand binding in the presence of 100-fold molar excesses of dextrorphan or levorphanol. Using both static and flow techniques, the binding process was continuously monitored at times greater than 4.8 s after mixing spin labeled morphine with synaptosomes. For this ligand and receptor preparation, binding takes place primarily during a delayed, abrup process whose rate and time of onset are temperature dependent and reflect the presence of added opiate agonist or antagonist.