MEMBRANE FLUIDITY MEASURED BY FLUORESCENCE POLARIZATION USING AN EPICS V-CELL SORTER

We have characterized the measurement of fluorescence polarization on single cells using an EPICS V cell sorter. A critical analysis is made of the balancing and calibration of the system. The system is highly linear for polarization measurements. Cellular membranes were labeled with 1,6-diphenyl-1,3,5-hexatriene (DPH) to measure membrane fluidity. Fluorescence polarization histograms had coefficients of variation as low as 7%. Cells labeled with DPH after 24 hr incubation in medium lacking serum showed a significantly higher fluorescence polarization than cells in medium containing serum. The fluorescence polarization measured at 15.degree. C was 0.311 compared to 0.270 at 25.degree. C for cells labeled with DPH, verifying that temperature affects the membrane fluidity as measured by flow cytometry.