Selective labeling of kappa 2 opioid receptors in rat brain by [125I]IOXY: interaction of opioid peptides and other drugs with multiple kappa 2a binding sites.
Recent studies from our laboratory resolved two subtypes of the kappa 2 binding site, termed kappa 2a and kappa 2b, using guinea pig, rat, and human brain membranes depleted of mu and delta receptors by pretreatment with the site-directed acylating agents BIT (mu-selective) and FIT (delta-selective). 6 beta-Iodo-3,14-dihydroxy-17-cyclopropylmethyl-4,5 alpha-epoxymorphinan (IOXY), an opioid antagonist that has high affinity for kappa 2 sites, was radioiodinated to maximum specific activity (2200 Ci/mmol) and purified by high pressure liquid chromatography and used to characterize multiple kappa 2 binding sites. The results indicated that [125I]IOXY, like [3H]bremazocine, selectively labels kappa 2 binding sites in rat brain membranes pretreated with BIT and FIT. Using 100 nM [D-Ala2-MePhe4,Gly-ol5]enkephalin to block [125I]IOXY binding to the kappa 2b site, two subtypes of the kappa 2a binding site were resolved, both in the absence and presence of 50 microM 5'-guanylyimidodiphosphate. Viewed collectively, these results provide further evidence for heterogeneity of the kappa opioid receptor, which may provide new targets for drug design, synthesis, and therapeutics.
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Clinical Psychopharmacology Section, National Institute on Drug Abuse, NIH, Baltimore, MD 21224.
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Partilla
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de Costa
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Rice
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Rothman
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D000818:Animals; D001921:Brain / Q000378:metabolism; D004723:Endorphins / Q000378:metabolism*; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D009019:Morphinans; D011869:Radioligand Assay; D051381:Rats; D017473:Receptors, Opioid, kappa / Q000187:drug effects*; D012965:Sodium Chloride / Q000494:pharmacology
D004723:Endorphins; D007457:Iodine Radioisotopes; D009019:Morphinans; D017473:Receptors, Opioid, kappa; C075927:6-iodo-3,14-dihydroxy-17-(cyclopropylmethyl)-4,5-epoxymorphinan; D012965:Sodium Chloride