title: Sigma-2 receptors are specifically localized to lipid rafts in rat liver membranes.
abstract: We have previously shown that sigma-2 receptors are relatively difficult to solubilize (Eur. J. Pharmacol. 304 (1996) 201), suggesting possible localization in detergent-resistant lipid raft domains. Rat liver membranes were treated on ice with 1% Triton X-100 or 20 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), and the extract subjected to centrifugation on a discontinuous gradient of 5%, 38%, and 40% sucrose. Gradient fractions were analyzed for sigma-1 receptors using [3H]+-pentazocine and for sigma-2 receptors using [3H]1,3-di-o-tolylguanidine ([3H]DTG), in the presence of dextrallorphan. Flotillin-2 was assessed by immunoblotting as a marker for lipid rafts. Sigma-2 receptors were found to discretely co-localize with flotillin-2 in lipid raft fractions. However, sigma-1 receptors were found throughout the gradient. Rafts prepared in CHAPS had sigma-2 receptors with normal pharmacological characteristics, whereas those in Triton X-100-prepared rafts had about seven-fold lower affinity for [3H]DTG and other ligands. Thus, sigma-2 receptors are resident in membrane lipid rafts, whereas sigma-1 receptors appear in both raft and non-raft membrane domains. Lipid rafts may play an important role in the mechanism of sigma-2 receptor-induced apoptosis.
authors.affiliation: Unit on Receptor Biochemistry and Pharmacology, Laboratory of Medicinal Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 8, Rm. B1-23 8 Center DR MSC 0815 Bethesda, MD 20892, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gebreselassie
authors.forename: Wayne D
authors.initials: WD
authors.lastname: Bowen
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000473:pathology*; D002793:Cholic Acids / Q000737:chemistry / Q000494:pharmacology; D042783:Endothelial Cells / Q000737:chemistry; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting / Q000379:methods; D007977:Levallorphan / Q000494:pharmacology; D008099:Liver / Q000166:cytology*; D008110:Liver Extracts / Q000737:chemistry; D008297:Male; D021962:Membrane Microdomains / Q000737:chemistry / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification; D009316:National Institutes of Health (U.S.); D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000302:isolation & purification; D017830:Octoxynol / Q000737:chemistry / Q000494:pharmacology; D010423:Pentazocine / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017480:Receptors, sigma / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology*; D014316:Tritium; D014481:United States; D000097605:Sigma-1 Receptor
chemical_list: D002793:Cholic Acids; D006146:Guanidines; D007977:Levallorphan; D008110:Liver Extracts; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D017830:Octoxynol; D010423:Pentazocine; D017480:Receptors, sigma; D014316:Tritium; D000097605:Sigma-1 Receptor; C106354:flotillins; C106107:sigma-2 receptor; C044130:dextrallorphan; C050232:1,3-ditolylguanidine; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate