Characteristics of binding of [³H]NE-100, a novel sigma-receptor ligand, to guinea-pig brain membranes

Abstract

We examined the characteristics of binding of radiolabeled N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride ([³H] NE-100), a highly potent and selective sigma-receptor ligand, to guinea-pig brain membranes. [³H]NE-100 showed saturable and reversible binding to sigma binding sites. A dissociation constant (K_d) and maximal numbers of binding sites (B _max) obtained from Scatchard plot analysis were 1.2 ± 0.1 nM and 1049.3 ± 115.1 fmol/mg protein (n = 3), respectively. NE-100 was the most potent inhibitor of [³H]NE-100 binding among several structurally dissimilar sigma-receptor ligands, including haloperidol and ( + )-pentazocine. ( + )-Benzomorphanes had more than a 10-fold potent inhibitory activity over (−)-benzomorphanes, with regard to [³H]NE-100 binding. The binding of [³H]NE-100 was not influenced by histaminergic, dopaminergic, adrenergic, serotonergic cholinergic or glutaminergic agents at 10⁻⁷ M. GTP-γ-S and phenytoin also did not affect the binding of [³H]NE-100. A higher [³H]NE-100 binding was observed in the cerbellum and medulla oblongata. Except for the nuclear fraction, the highest level of [³H]NE-100 binding to subcellular fractions was observed in microsomal fractions. These results suggest that NE-100 selectively binds, with a high affinity, to sigma-1 binding sites in guinea-pig brain membranes, as an “antagonist”.