Effect of cholesterol on lateral diffusion of fluorescent lipid probes in native hippocampal membranes

Cholesterol is an abundant lipid of mammalian membranes and plays a crucial role in membrane organization, dynamics, function and sorting. The role of cholesterol in membrane organization has been a subject of intense investigation that has largely been carried out in model membrane systems. An extension of these studies in natural membranes, more importantly in neuronal membranes, is important to establish a relationship between disease states and changes in membrane physical properties resulting from an alteration in lipid composition. We have monitored the lateral diffusion of lipid probes, DiIC(18)(3) and FAST DiI which are similar in their intrinsic fluorescence properties but differ in their structure, in native and cholesterol-depleted hippocampal membranes using the fluorescence recovery after photobleaching (FRAP) approach. Our results show that the mobility of these probes is in general higher in hippocampal membranes depleted of cholesterol. Interestingly, the increase in mobility of these probes does not linearly correlate with the extent of cholesterol depletion. These results assume significance in the light of recent reports on the requirement of cholesterol to support the function of the G-protein coupled serotonin(1A) receptor present endogenously in hippocampal membranes.