Molecular Pharmacology, Vol 20, 263-268, Copyright © 1981 by the American Society for Pharmacology and Experimental Therapeutics

Opiate Receptors in the Rat Brain

Specific Labeling of Multiple Membrane Components with [³H]Etorphine?

¹ Laboratoire de Pharmacologie et de Toxicologie Fondamentales, Centre National de la Recherche Scientifique, 31078 Toulouse Cedex, France

A crude membrane fraction (CMF) from rat brain is labeled with [³H]etorphine (2 x 10^-9 M) in the absence (total binding, -L) and in the presence (nonspecific binding, +L) of 2 x 10^-6 M levorphanol. The ³H-labeled CMF (±L) is solubilized with 1% (w/v) cholic acid (sodium salt) and centrifuged. The high-speed (100,000 x g) supernatant is analyzed by molecular exclusion chromatography on Sephadex G-25, Sephadex G-100, and Sepharose 6B. A comparison of the radioactivity profiles reveals, in addition to the previously identified 500,000 mol wt species [Puget et al., F. E. B. S. Lett. 122:199-202 (1980)] lower molecular weight, tritium-labeled entities distinct from monomolecular [³H]etorphine. These small complexes are readily separated from free radioligand upon dialysis in the cold. They appear to be opiate-specific, since they are not observed in ³H-labeled CMF (+L) soluble extracts.