Aluminum-altered membrane dynamics in human red blood cell white ghosts

Fluorescence polarization of the hydrophobic membrane probe 1,6-diphenyl hexatriene was used to investigate alterations in membrane dynamics caused by micromolar concentrations of aluminum. Metal titration onto resealed white ghost membranes showed a progressive increase in steady-state fluorescence anisotropy of the probe in the presence of aluminum which was twice the value obtained upon titration of calcium. As calculated from steady-state fluorescence data in the presence and absence of 20 microM aluminum, a temperature dependent lipid order parameter indicated increased lipid packing. Motional dynamics of the probe molecule on the nanosecond time scale showed severe constraints in the presence of 20 microM aluminum as indicated by decreased rotational rate, decreased cone angle, and increased values of time resolved limiting anisotropy. Physiological consequences of altered membrane dynamics are also discussed.