Effects of cadmium and calcium on the fluidity of plasma membranes.

The fluidity of plasma membranes was assessed by steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), a fluorescent probe. The presence of increasing concentrations of calcium (Ca) (0.5-4 mM), cadmium (Cd) (50-500 microM), or both decreased the motional freedom of the fluorescent probe molecules in plasma membranes derived from both human erythrocytes and rat hepatocytes. The effects of Cd were 3-10 times greater than those of Ca. Increasing concentrations of Cd in the presence of Ca increased the anisotropy parameter, which plateaued at lower Cd concentrations. The presence of Ca diminished the overall effects of Cd on these membranes.