Rat hepatocyte plasma membranes isolated from Morris hepatoma 7288C, normal and regenerating liver were labelled with the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. 2. Steady-state fluorescence polarisation measurements indicated an increased fluidity of the membranes in the early stages of regeneration, returning to normal levels after 48 hr. 3. There was a decrease in hepatoma plasma membrane fluidity compared to normal hepatocytes. Changes in fluorescence polarisation with temperature (Arrhenius studies) indicate an increase in the lower critical temperature for the membrane lipid thermotropic transition of hepatoma compared to normal liver plasma membranes. 4. These changes in membrane lipid fluidity alter the activation of some intrinsic and extrinsic membrane bound enzymes.
