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*COCAINE
*SODIUM CHLORIDE

Vol. 282, Issue 3, 1228-1241, 1997

In Vitro Characterization of Cocaine Binding Sites in Human Hair

Robert E. Joseph, Jr., Wei-Jen Tsai, Li-I Tsao, Tsung-Ping Su and Edward J. Cone

Chemistry and Drug Metabolism Section, Clinical Pharmacology Branch (R.E.J., E.J.C.), Neurochemistry Unit, Molecular Pharmacology Section, Neuroscience Branch (W.J.T., L.I.T., T.P.S.), Division of Intramural Research, Addiction Research Center, National Institute on Drug Abuse, NIH, Baltimore, Maryland

In vitro studies were performed to characterize [3H]cocaine binding to dark and light ethnic hair types. In vitro binding to hair was selective, was reversible and increased linearly with increasing hair concentration. Scatchard analyses revealed high-affinity (6-112 nM) and low-affinity (906-4433 nM) binding in hair. Competition studies demonstrated that the potencies of 3beta -(4-bromophenyl)tropane-2beta -carboxylic acid methyl ester, and 5-(4-chlorophenyl)-2,5-dihydro-3H-imidazol[2,1-alpha ]isoindole-5-ol and 2beta -carbomethoxy-3beta -(4-fluorophenyl)tropane were similar to or less than that of (-)-cocaine. The potency of (-)-cocaine was 10-fold greater than that of (+)-cocaine at inhibiting radioligand specific binding to hair. Multivariate analysis indicated that significantly greater nonspecific and specific radioligand binding occurred in dark hair than in light hair. Multivariate analysis also demonstrated a significant ethnicity × sex effect on specific and nonspecific binding to hair. Greater radioligand binding occurred in male Africoid hair than in female Africoid hair and in all Caucasoid hair types. Melanin was considered the most likely binding site for cocaine in hair. Typically, the concentration of melanin is much greater in dark than in light hair. Scatchard analysis indicated that dark hair had a 5- to 43-fold greater binding capacity than light hair. Differences in radioligand binding between hair types appeared to be due to differences in the density of binding sites formed by melanin in hair.

Copyright © by The American Society for Pharmacology and Experimental Therapeutics


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