Rat liver and kidney contain high densities of sigma 1 and sigma 2 receptors: characterization by ligand binding and photoaffinity labeling.

Rat liver and kidney were investigated for the presence of sigma (sigma) receptor subtypes by radioligand binding with three highly selective sigma probes and by photoaffinity labeling using [3H]azido-di-o-tolylguanidine ([3H]azido-DTG). [3H](+)-Pentazocine, a highly selective sigma 1 probe, bound to sites in liver membranes with Kd = 7.5 nM and Bmax3 = 2929 fmol/mg protein. [3H](+)-Pentazocine binding sites in kidney had Kd = 23.3 nM and Bmax = 229 fmol/mg protein. [3H]1,3-Di-o-tolylguanidine ([3H]DTG) and [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ([3H](+)-3-PPP) label both sigma 1 and sigma 2 receptors. Parameters for [3H]DTG in the liver were Kd = 17.9 nM and Bmax = 11,895 fmol/mg protein. Similar parameters were observed for [3H](+)-3-PPP, Kd = 51.9 nM and Bmax = 11,070 fmol/mg protein. [3H]DTG bound to rat kidney with Kd = 45.8 nM and Bmax = 1190 fmol/mg protein. The observation that either [3H]DTG or [3H](+)-3-PPP and [3H](+)-3-PPP labeled a higher number of sites relative to [3H](+)-pentazocine suggested that liver and kidney contain both subtypes of sigma receptor. This was confirmed by competition studies vs. [3H](+)-pentazocine and [3H]DTG (in the presence of dextrallorphan to mask sigma 1 sites). In both tissues, [3H](+)-pentazocine labeled sites with high affinity for haloperidol and enantioselectivity for (+)-benzomorphans over (-)-benzomorphans. [3H]DTG + dextrallorphan labeled sites in both tissues which also had high affinity for haloperidol, but which had the characteristic sigma 2 property of low affinity for (+)-benzomorphans and enantioselectivity for (-)-benzomorphans over the corresponding (+)-isomer. Similar results were obtained with [3H](+)-3-PPP + dextrallorphan. Several novel aryl diamines, such as 1S,2R-cis-N-[2-(3,4-dichlorophenylethyl]-N-methyl-2- (1-pyrrolidinyl)cyclohexylamine (BD737) and N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (BD1008), bound to both sites with high affinity. Photoaffinity labeling with 10 nM [3H]azido-DTG resulted in specific labeling of polypeptides of 25 kDa and 21.5 kDa. Dextrallorphan (100 nM or 500 nM) completely blocked labeling of the 25 kDa polypeptide, but had no effect on labeling of the lower molecular weight protein. (+)-10,11-Dihydro-5-methyl-5H-dibenzo[a,d]cyclohepten-5,10- imine((+)-MK-801) had no effect on labeling of either polypeptide. These data are consistent with the notion that the 25 kDa and 21.5 kDa proteins represent sigma 1 and sigma 2 receptors, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)