Figure 6. AhR ligand binding ability of harmine and harmol.

A, Guinea pig hepatic cytosol (2 mg/mL) or B, C57BL/6 mouse hepatic cytosols (2 mg/mL) were incubated with [³H]-TCDD (2 nM) alone (total binding), [³H]-TCDD (2 nM) and TCDF (200 nM, 100-fold excess of competitor, nonspecific binding), or [³H]-TCDD (2 nM) in the presence of increasing concentrations of harmine or harmol (1 and 25 μM) and the samples analyzed by the hydroxyapatite assay as described under Material and methods. Values were adjusted for nonspecific binding and expressed as % specific binding relative to the absence of a competitor ligand. Values are presented as the mean ± S.E.M. (n = 9). (*) P < 0.05 compared with [³H]-TCDD.