ULTRASTRUCTURE OF THE 5-HYDROXYTRYPTAMINE(3) RECEPTOR

We have determined the ultrastructure of 5-hydroxytryptamine(3) (5-HT3 ) serotonin receptors purified from NG108-15 mouse neuroblastoma x rat glioma cells by electron microscopic examination of receptor particle s embedded in uranyl acetate stain and metal replicas of rapidly froze n receptors. The 5-HT, receptor can be modelled as a cylinder 11 nm in length and 8 nm in diameter with a closed end and a central cavity 3 nm in diameter. Analysis of the rotational symmetry of single receptor particles indicates that the 5-HT3 receptor is composed of five subun its arranged symmetrically around a central cavity. Together with evid ence obtained for related proteins in other studies using ultrastructu ral, biochemical, or electrophysiological methods, our observations su ggest that all members of the ligand-gated ion channel superfamily may possess a pentameric quaternary structure.