THE ROLE OF MICROVISCOSITY CHANGES OF SYNAPTIC-MEMBRANES IN INACTIVATION OF LIGAND-BINDING TO RAT-BRAIN MEMBRANE-BOUND OPIOID RECEPTORS

We investigated the microviscosity changes in the environment of the ESR probes 5,6-benzo-2,2,4,4-tetramethyl-1,2,3,4-tetrahydro-gamma-carbolin-3oxyl (probe I) and 2,2,6,6-tetramethyl-4-capryloyloxypiperidine-1-oxyl (probe II) during the incubation of rat brain synaptosomes in solution (37-degrees-C) in the presence of effectors: linoleic, arachidonic, potassium salt of 4-hydroxy-3,5-di-tret-butylphenylpropionic acid (phenoxane). The decrease in microviscosity of the environment of probe II in 1 h was more pronounced than on that of probe I. Linoleic, arachidonic, palmitic acids and ionol (all 10(-4) M) significantly reduced the rate of microviscosity decrease of both probes, while phenoxane slightly increased it. The rate constants of opioid receptors inactivation and microviscosity decrease in the presence of effectors were compared. The inactivation of opioid receptors in solution is suggested to be mediated by the increase of lipid bilayer fluidity.