SPIN-LABEL ESR STUDY OF THE INFLUENCE OF FLUORIDE ON ERYTHROCYTE-MEMBRANE FLUIDITY

The fluidity of intact human erythrocyte membrane and the effect of fluoride on fluidity were studied by using two kinds of fatty acid spin labels and measuring the time and temperature dependence of order parameter S and rotational correlation time tau(c). The time dependance of S or tau(c) indicated that there is an effect of time in the course of the F- action on the cell membrane. The plot of S vs. temperature for I [12, 3] showed an abrupt discontinuity at 29.0-degrees-C in untreated and 36.0-degrees-C in F--treated but for I [1, 14] showed no discontinuity. Plots of tau(c) vs. temperature for I [12, 3] and I [1, 14] showed a point of phase transition at 38.0-degrees-C and 40.0-degrees-C in untreated and at 36.6-degrees-C and 44.6-degrees-C in F--treated, which indicated that a difference in fluidity exists between the surface and the interior of the lipid bilayer, and that the above fluidity difference is changed by F- exposure. It is concluded that F- has little effect on membrane fluidity but, when combining with a factor of time or temperature, has a marked effect on it.