The examination and quantitation of tissue cytosolic receptors for 2,3,7,8-tetrachlorodibenzo- p-dioxin using hydroxylapatite

Abstract

An assay using hydroxylapatite has been developed for the examination and quantitation of cytosolic receptors for 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). This method, as compared to others, has a relatively high ratio of specific to nonspecific binding of [ 3H]TCDD and is relatively rapid. The total number of specific binding sites and equilibrium dissociation constants ( K D) for [ 3H]TCDD were determined in hepatic cytosol from Sprague-Dawley rats and C57BL 6J , DBA 2J , and B6D2F 1 J mice. With the exception of the cytosol from DBA 2J mice in which little specific binding was observed, high-affinity, specific binding was obtained in all cases. The rat hepatic cytosol demonstrated the highest affinity for [ 3H]TCDD with a K D of 0.12 n m. The total amount of specific [ 3H]TCDD binding in hepatic cytosol from B6D2F 1 J mice was found to be intermediate between that of the C57BL 6J and DBA 2J parents. Ligand competition studies suggest the specificity of binding of various compounds to the receptor species from Sprague-Dawley rats is similar to that observed with the hepatic cytosol from C57BL 6J mice. These data support the hypothesis that, as in mice, the particular cytosol binding species in rats is the receptor that may mediate the induction of aryl hydrocarbon hydroxylase activity.