POSSIBLE EXPRESSION OF A SIGMA(1) SITE IN RAT PHEOCHROMOCYTOMA (PC12)CELLS

To examine the functional interaction between the sigma binding sites and nicotinic acetylcholine receptors, we investigated the effects of various sigma receptor ligands on nicotine-evoked Ca2+ uptake in diffe rentiated PC12 cells. The IC50 values of sigma receptor ligands tested in this uptake study did not correlate with their K-i values in the [ H-3]1,3-di(2-tolyl)guanidine ([H-3]DTG) binding to guinea pig brain re ported by Rothman et al. (1991). To clarify further the binding charac teristics of the sigma binding sites on PC12 cells, we examined the ef fects of sigma receptor ligands on -2-[4-methoxy-3-(2-phenylethoxy)phe nyl]-ethylamine HCl ([H-3]NE-100) binding to PC12 membranes. The K-i v alues of the various drugs tested for [H-3]NE-100 binding site closely correlated with their K-i values for the DTG site-1 reported by Rothm an et al. (1991). This study showed that PC12 cells express sigma(1)-l ike sites and the inhibitory effect of sigma receptor ligands on the n icotine-evoked Ca2+ uptake was not directly coupled with either the si gma(1) or sigma(2) sites.