Efflux of rubidium in rat cortical synaptosomes is blocked by sigma and dextromethorphan binding site ligands

Large concentrations of potassium were used to stimulate the release of rubidium-86 from preloaded cortical synaptosomes, so that the pharmacological sensitivity of this efflux could be examined. Potassium channel blockers, 4-aminopyridine and tetraethylammonium, inhibited the evoked release of rubidium. Sigma ligands, e.g. pentazocine, cyclazocine, rimcazole, 1,3-di(2-tolyl)guanidine (DTG) and haloperidol, as well as the antitussives, carbetapentane, caramiphen and dextromethorphan, significantly reduced potassium-stimulated efflux of rubidium. By contrast, 3-hydroxyphenyl-propylpiperidine (3-PPP), 5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten-5,10-imine (MK-801), phencyclidine (PCP), ketamine and D-2-amino-5-phosphonovalerate (D-AP5) were all inactive. This suggests that inhibition of potassium-stimulated efflux of rubidium is correlated with activity at the sigma and/or dextromethorphan binding sites rather than at the N-methyl-D-aspartate (NMDA)/PCP receptor-channel complex.