Variations in incubation temperature can markedly differentiate opiate receptor binding of agonists and antagonists. In the presence of sodium increasing incubation temperatures from 0° to 30° reduces receptor binding of 3H-naloxone by 50% while tripling the binding of the agonist 3H-dihydromorphine. Lowering incubation temperature from 25° to 0° reduces the potency of morphine in inhibiting 3H-naloxone binding by 9-fold while not affecting the potency of the antagonist nalorphine. At temperatures of 25° and higher the number of binding sites for opiate antagonists is increased by sodium and the number of sites for agonists is decreased by sodium with no changes in affinity. By contrast, in the presence of sodium lowering of incubation temperature to 0° increases opiate receptor binding of the antagonist naloxone by enhancing its affinity for binding sites even though the total number of binding sites are not changed.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Pharmacology, Toxicology and Pharmaceutics(all)