Sigma-2 receptors are specifically localized to lipid rafts in rat liver membranes

• Published in: European journal of pharmacology 2004-06, Vol.493 (1), p.19-28
• Main Authors: Gebreselassie, Daniel, Bowen, Wayne D.
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Biological and medical sciences; Cell Membrane - chemistry; Cell Membrane - pathology; Cholic Acids - chemistry; Cholic Acids - pharmacology; Endothelial Cells - chemistry; Guanidines - pharmacology; Humans; Immunoblotting - methods; Levallorphan - pharmacology; Lipid raft; Liver; Liver - cytology; Liver Extracts - chemistry; Male; Medical sciences; Membrane Microdomains - chemistry; Membrane Microdomains - physiology; Membrane Proteins - chemistry; Membrane Proteins - isolation & purification; National Institutes of Health (U.S.); Nerve Tissue Proteins - chemistry; Nerve Tissue Proteins - isolation & purification; Octoxynol - chemistry; Octoxynol - pharmacology; Pentazocine - pharmacology; Pharmacology. Drug treatments; Radioligand Assay; rat; Rats; Rats, Sprague-Dawley; Receptors, sigma - chemistry; Receptors, sigma - isolation & purification; Receptors, sigma - physiology; Sigma receptor; Sigma-1 Receptor; Sphingolipid; Tritium; United States
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/j.ejphar.2004.04.005

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.