PROPERTIES OF A PHOSPHATIDYLCHOLINE DERIVATIVE OF DIPHENYL HEXATRIENE(DPH-PC) IN LYMPHOCYTE MEMBRANES - A COMPARISON WITH DPH AND THE CATIONIC DERIVATIVE TMA-DPH USING STATIC AND DYNAMIC FLUORESCENCE

Using static and dynamic fluorescence we studied the fluorescence prop erties of a phosphatidylcholine analog of 1,6-diphenyl-1,3,5-hexatrien e (DPH-PC) incorporated in lymphocyte plasma membranes with respect to DPH and its cationic derivative trimethylammoniumphenyl)-6-phenyl-1,3 ,5-hexatriene (TMA-DPH), in order to study if phospholipid derivatives of DPH may be used to investigate structural and physicochemical prop erties of specific membrane lipid domains. DPH-PC and TMA-DPH showed s imilar fluorescence polarization values that were significantly higher with respect to DPH, suggesting a localization of the fluorescent por tion of DPH-PC in a more ordered region of the membrane which was prob ably due to the electrostatic interactions between phospholipid head-g roups. The localization of the fluorescent moiety of DPH-PC near the m embrane surface was also supported by the study of the fluorescence de cay of the three probes using frequency-domain fluorometry. The main l ifetime component of DPH-PC was rather similar to that of TMA-DPH (6.7 4 versus 6.24, ns) but considerably lower with respect to DPH (10.52, ns), in agreement with data obtained from exponential analysis. In lym phocyte membranes obtained from concanavalin A treated cells, a signif icant decrease of fluorescence polarization has been shown with DPH an d its phosphatidylcholine derivative, but not with TMA-DPH. In liposom es obtained from total lipids extracted from lymphocyte membranes, a d ecrease of fluorescence polarization has been observed only with DPH. Our results suggest that DPH-PC localizes the fluorescent portion of i ts molecule in membrane micro-environments of different properties wit h respect to those probed by DPH and TMA-DPH. The use of DPH-phospholi pid derivatives and other DPH-probes may represent an useful tool to s tudy plasma membrane heterogeneity in biological membranes.