MEMBRANE HETEROGENEITY IN ISOLATED RAT HEPATOCYTES AND LIVER PLASMA-MEMBRANE SUBFRACTIONS - A COMPARATIVE-STUDY USING DPH AND ITS CATIONIC DERIVATIVE TMA-DPH

The fluorescence decay of 1,6-diphenyl-1,3,5-hexatriene (DPH) and of t rimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) has been s tudied in hepatocytes isolated from rat liver and in isolated plasma m embrane subfractions (cLPM, canalicular membranes and bLPM, basolatera l membranes) using frequency domain fluorometry. The decay has been an alyzed either by using a model of discrete exponential components or a model that assumes a continous distribution of lifetime values in ord er to study different aspects of membrane heterogeneity. The results o btained by the two analyses are practically superimposable but the dis tributional approach allows an evaluation of membrane heterogeneity th rough the width of the distribution that has shown particularly signif icant differences when freshly hepatocytes are compared with in vitro aged hepatocytes. Moreover, the comparison of the distributional analy sis of the two probes has shown in cLPM a tendency to higher values of the main lifetime component and a narrower distribution width with re spect to bLPM. These results indicate changes of membrane domain organ ization that have been discussed in relation with the specific lipid c omposition that characterizes the two membrane subfractions. Our resul ts indicate that frequency domain fluorometry may be used to study mem brane heterogeneity in intact cells and isolated membranes.