Discrepancies in characterization of sigma sites in the mouse central nervous system.
The characteristics of [3H](+)-pentazocine and [3H]1,3-di(2-tolyl) guanidine (DTG) binding to mouse whole brain, cortex, cerebellum and spinal cord membranes were investigated in radioreceptor assays. [3H](+)-Pentazocine bound to a single, high affinity site (Kd = 1.2-1.6 nM) with increasing density along the neuraxis from the cortex (Bmax = 543 fmol/mg protein) to the spinal cord (Bmax = 886 fmol/mg protein). Hot saturation studies resolved the presence of one binding site for [3H]DTG showing no tissue variations in terms of density (Bmax = 1075-1264 fmol/mg protein) or affinity (Kd = 16.6-22.3 nM). Incubation with 100 nM (+)-pentazocine revealed two classes of high affinity [3H]DTG labeled binding sites corresponding to sigma 1 and sigma 2 subtypes. A preponderance of sigma 2 sites was revealed in all investigated tissues. Different pharmacological profiles were demonstrated for the sigma 2 sites in mouse whole bain compared to mouse spinal cord. However, competition studies indicated that the whole brain and spinal [3H](+)-pentazocine labeled sigma 1 binding sites exhibited similar pharmacological properties. The density of [3H](+)-pentazocine labeled sigma 1 population was found not to match that of [3H]DTG labeled sigma 1 site throughout the mouse central nervous system. The presence of low affinity [3H]DTG labeled sites was demonstrated in cold saturation experiments. Equilibrium binding data for the low affinity [3H]DTG binding site resulted in an increasing density (Bmax = 1973-11,369 fmol/mg protein) with a decreasing affinity (Kd = 242-943 nM) in mouse cortex through the spinal cord.
Kovács
K J
KJ
Department of Veterinary Pathobiology, University of Minnesota, St. Paul 55108, USA.
Larson
A A
AA
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D002490:Central Nervous System / Q000187:drug effects / Q000378:metabolism*; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology; D066298:In Vitro Techniques; D008024:Ligands; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009294:Narcotics / Q000378:metabolism; D010423:Pentazocine / Q000378:metabolism; D011869:Radioligand Assay; D017480:Receptors, sigma / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism
D006146:Guanidines; D008024:Ligands; D009294:Narcotics; D017480:Receptors, sigma; C050232:1,3-ditolylguanidine; D010423:Pentazocine