Developmental changes in synaptic membrane fluidity: a comparison of 1,6-Diphenyl-1,3,5-hexatriene (DPH) and 1-[4-(Trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH)

Cortical synaptic plasma membranes were prepared from rats 3, 7, 10, 14, 21, 28 and 120 days of age. Developmental changes in the fluidity of these membranes were assessed using fluorescence polarization techniques. 1,6-Diphenyl-1,3,5-hexatriene (DPH), a probe of the membrane interior, showed a marked developmental increase in polarization, suggesting a developmental decrease in fluidity. The magnitude of the change from day 3 to the adult was the equivalent of lowering the temperature 7 °C. The developmental change in DPH polarization was maintained in liposomes (multilamellar vesicles) prepared from membrane total lipid extracts. In contrast to DPH, 1-[4-(trimethylamino)phenyl]6-phenyl-1,3,5-hexatriene (TMA-DPH), a probe of the membrane surface reported no significant developmental effect on polarization for intact membranes; however, TMA-DPH did report a significant increase in polarization for the total lipid extract liposomes. For the intact membranes, both cis- and trans-parinarate, fluorescent probes of the mid-region of the acyl chains, reported significant developmental increases in polarization. The role of gangliosides in the developmental regulation of fluidity was examined. Gangliosides did not appear to play a role in the developmental changes, but they do have a significant effect (increased polarization) on the membrane surface as reported by TMA-DPH. Fluorescence lifetime and heterogeneity analyses were performed for DPH. There was a small but significant increase in probe lifetime during development. Thus, polarization measurements alone underestimated the increases in membrane order. In an attempt to amplify the differences in membrane organization between the developing and adult membranes, we examined the effects of the membrane perturbant ethanol, on DPH polarization at the different ages. No developmental effect on the ethanol-induced fluidization of synaptic membranes was observed.