Fig. 3.
SKF83959 binds with high affinity to PTX-resistant D2 receptors only in the presence of D1 receptors. Competition of [3H]raclopride binding by SKF83959 or SKF83822 is shown. Data from three to eight independent experiments conducted in duplicate were normalized and fit to one-site or two-site analysis. (a) Comparison of binding on membranes from D2HEK cells and D1–D2HEK cells reveals a high-affinity binding site for SKF83959 only in D1–D2 cells (KH, 2.4 ± 0.8 nM; %KH, 19 ± 1.5). (b) High-affinity binding of SKF83959 to D2 receptors in D1–D2HEK cells was only slightly affected by pretreatment with PTX (KH, 1.9 ± 1.3 nM; %KH, 11 ± 3.3). (c) Incubation of D1–D2HEK membranes with quinpirole (10 nM) eliminated high-affinity binding of SKF83959. (d) Incubation of D1–D2HEK membranes with SCH23390 (10 nM) did not reduce affect high-affinity binding of SKF83959. (e) Competition binding of [3H]raclopride by SKF83822 indicated high-affinity binding of the agonist to D2 receptors in D1–D2HEK cells that was eliminated by pretreatment of cells with PTX.