The human sigma site, which resembles that in NCB20 cells, may correspond to a low-affinity site in guinea pig brain.

1,3-di(2-[5-3H]tolyl)Guanidine ([3H]DTG) was found to bind to a single saturable population of binding sites in human cerebral cortex and NCB20 cells, a second low-affinity site was apparent in guinea pig brain. Displacement studies were performed to determine the pharmacology of the [3H]DTG binding site in these 3 membrane preparations. In human cortical tissue and NCB20 cell membranes the (+)-stereoisomers of benzomorphans displaced binding with Hill coefficients close to one, displayed similar affinity and did not give the biphasic displacement curve characteristic of guinea pig membranes. The pIC50 of the low-affinity component of the sigma binding site in guinea pig brain correlates best with the affinity of drugs for the binding site in human cortex.