Abstract
Fluorescence anisotropy measurements to determine membrane fluidity have been generally performed with diphenylhexatriene (DPH) on purified membrane samples. This probe could not be used satisfactorily with intact cells, because it did not present any specificity for a particular type of membrane and labelled all the hydrophobic regions of the cell. We have recently focussed our attention on the cationic derivative of DPH, trimethylamino-diphenylhexatriene (TMA-DPH). This molecule displays excellent photophysical properties in hydrophobic media: lifetime 6 ns (DPH 8 ns), quantum yield 0.55 (DPH 0.75), and is not fluorescent in water.1’2 In comparison with DPH and the other fluorescent probes previously used in membrane fluidity determinations it was given evidence3,4 by fluorescence micrography and by fluorescence intensity measurements, to have two particularly favorable features : (i) it is incorporated in membranes very rapidly (ii) when it is interacted with intact cells, it is retained specifically in the plasma membranes for periods of typically 30 min. before being internalized.
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