Electron spin resonance study of the synaptosome opiate receptor: kinetics of stereospecific binding of spin labeled morphine

Abstract

Morphine, spin labeled on the 3- or 6-position has been 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 electron spin resonance lines induced by immobilization of the ligand on binding has been used to determine the concentration of bound opiate. The stereospecificity of the reaction was measured by comparing ligand binding in the presence of thousand-fold molar excesses of dextrorphan or levorphanol. Using both static and flow techniques, the binding process has been continuously monitored at times greater than 4.8 s after mixing spin labeled morphine with synaptosomes. It is shown that for this ligand and receptor preparation, binding takes place primarily during a delayed, abrupt process whose rate and time of onset are temperature dependent and reflect the presence of added opiate agonist or antagonist.

The excitation of mammalian central neurones by amino acids.

“…Two results suggest that none do: (a) the excitation elicited by glutamate but not by the more potent agonists DLH and cis-ADCP is preferentially antagonized by GDEE while the converse is true for DAA which spares the glutamate-induced excitations, and (b) the time courses of onset of excitation for the cyclic amino acids are very much longer than are those for glutamate and aspartate. Although it is possible that the long latency to onset of effect of some of these compounds indicates that a conformational change has been induced in the receptor by them, analogous to the situation for some opiate binding processes (Copeland & de Barre, 1976), taken in conjunction with the data derived from the use of antagonists, the concept that different populations of receptors are involved seems probable. In this connexion too it may be noted that Engberg, Flatman & Lambert (1975) and Altmann, Bruggencate, Pickelmann & Steinberg (1976) have reported that the conductance changes elicited in motoneurones by DLH and by glutamate are not identical.…”