Figure 3.

Mean competition curves showing α₁-adrenoceptor antagonist inhibition of [¹²⁵I]HEAT binding in membranes from SMG-C10 cells. For each concentration of antagonist, [¹²⁵I]HEAT binding is expressed as percent of specific binding in the absence of drugs. The competition curves were fit to one- and two-site binding models and mean K_i values (Table 1) were determined from the curve fits. Competition curves for the non-subtype selective antagonist prazosin and the α_1D-subtype selective antagonist BMY 7378 fit best to a one-site binding model. In contrast, competition curves for 5-methylurapidil (5-MU) fit significantly better to a two-site model (p < 0.05 using an F test; Table 1) indicating that both α_1A- and α_1B-adrenoceptors are present in SMG-C10 cells. Each curve is the mean ± S.E.M. of 4-5 individual experiments, each using different SMG-C10 cell cultures.