The temperature dependence of the dissociation constant for the interaction of an opioid δ selective ligand and its receptor was evaluated in three tissues. The change in free energy of this interaction was similar in mouse brain, mouse spinal cord, and NG 108-15 mouse neuroblastoma-rat glioma hybrid cells (ΔG(o)' = -13.44, -13.34, and -13.66 kcal · mol-1, respectively). However, the reaction was endothermic and occurred with an increase in entropy in mouse brain and NG 108-15 cells, but it was exothermic and occurred with a negligible change in entropy in mouse spinal cord. These data are consistent with the existence of multiple subtypes of opioid δ receptor, and they further suggest that the opioid δ receptor recently cloned from the NG 108-15 cell line is of the brain subtype. Subtypes of opioid δ receptors may mediate analgesia, but not side-effects, of opiates and thus could be targets for future drug design.
|Number of pages
|Proceedings of the National Academy of Sciences of the United States of America
|Published - Dec 6 1994
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