Fig. 2.
Affinity of CM572 at sigma-1 and sigma-2 receptors. Affinity of CM572 for sigma-1 and sigma-2 receptors was determined by competition binding in rat liver membranes. Assays were carried out as described in Materials and Methods, using [3H](+)-pentazocine to label sigma-1 receptors and [3H]DTG in the presence of unlabeled (+)-pentazocine to label sigma-2 receptors. Ki values were determined by analysis of competition curves using GraphPad Prism 6 and previously determined radioligand Kd values ([3H](+)-pentazocine Kd, 7.5 nM; [3H]DTG Kd, 17.9 nM; Hellewell et al., 1994). The Ki value for CM572 at sigma-2 receptors was determined to be 14.6 ± 6.9 nM. At sigma-1 receptors, CM572 produced less than complete displacement, with 10 µM inhibiting radioligand binding by approximately 50% (Ki ≥ 10 µM). Values for sigma-2 are the average of four independent experiments ± S.D., and values for sigma-1 are results of two independent experiments. Each experiment was carried out in duplicate. Figure shown is a composite of the averaged experiments.