The distribution of the two fluorescent phospholipid analogs across acetylcholine receptor (AChR)-rich membranes from Torpedo marmorata has been studied by a combination of nonradiative fluorescence resonance energy transfer using fluorescent lipid probes and quenching of their fluorescence with Co2+ and 2,4,6-trinitrobenzenesulfonic acid. The fluorescent lipid analogs were supplied to the AChR-rich membrane or liposome suspension by simply injecting ethanol solutions of the probes into the medium. The efficiency of the fluorescence energy transfer between NBD-labeled phosphatidylcholine and rhodamine-labeled ethanolamine glycerophospholipids was measured in model membranes prepared in such a way that the probes could be targeted at the same or opposite halves of the bilayer, and the results were compared with those obtained for native AChR-rich membranes. It is shown that NBD-PC and Rho-PE can be efficiently (95%) incorporated into AChR-rich membranes and liposomes. On the basis of the comparison with model liposomes, the energy transfer experiments suggest a preferential exofacial location of the parental phospholipids in the native AChR-rich membrane. Fluorescence quenching with Co2+ and TNBS showed these two phospholipid analogs to be located predominantly in the outer leaflet of the bilayer in AChR-rich membranes. From the Co2+ quenching of the lipid analogs, it was also possible to calculate the surface potential of the outer leaflet of the membrane as being on the order of -15 mV.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.