[3H]DTG and [3H](+)-3-PPP label pharmacologically distinct sigma binding sites in guinea pig brain membranes

The interaction of various compounds with sigma binding sites was examined in membranes prepared from whole guinea pig brain. Whereas [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine labeled a single population of binding sites exhibiting a Kd of 43 nM, [3H]1,3-di-o-tolylguanidine bound to two sites having Kds of 35 and 212 nM, and to a greater maximum number of sites than [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine. Haloperidol, 1,3-di-o-tolylguanidine, BMY 14802, and (-)-pentazocine each displayed nearly equal affinity for binding sites labeled by [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and [3H]1,3-di-o-tolylguanidine, whereas (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine was 3 times more potent in inhibiting [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine than [3H]1,3-di-o-tolylguanidine binding. In contrast, (+)-SKF 10,047, (+)-cyclazocine and (+)-pentazocine exhibited more than 9-fold higher affinity for [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine than [3H]1,3-di-o-tolylguanidine binding sites. Dextromethorphan was 15-fold more potent against [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine than [3H]1,3-di-o-tolylguanidine, inhibited [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine binding in a biphasic manner, and inhibited [3H]haloperidol and [3H](+)-SKF 10,047 binding with potencies similar to those obtained against [3H]1,3-di-o-tolylguanidine and [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine, respectively. Phenytoin increased [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and [3H](+)-SKF 10,047 binding, but did not enhance [3H]1,3-di-o-tolylguanidine or [3H]haloperidol binding. However, the potency of dextromethorphan to inhibit [3H]1,3-di-o-tolylguanidine binding was increased in the presence of phenytoin.(ABSTRACT TRUNCATED AT 250 WORDS)