Physical Properties of Membranes and Membrane Lipids from the Fiber Cell of the U18666A-Cataractous Rat

Abstract

Steady state fluorescence anisotropy of parinaric acid probes was used to examine lipid motion in membranes and membrane lipids from U18666A-induced cataractous rat lenses. Cortical and nuclear fractions were examined separately. The drug treatment resulted in an increase in the sterol/phospholipid ratio in the nucleus and a decrease in this ratio in the cortex. Fluorescence anisotropy of trans parinaric acid (tPnA) suggested that membranes from the cortex of cataractous lenses were more ordered than the cortical membranes from control or treated-but-clear lenses. Membranes from the nucleus of control lenses were more ordered than membranes from the cortex of controls. Nuclear membranes from cataractous lenses were slightly less ordered than nuclear membrane from control or treated-but-clear lenses. Similar experiments using liposomes prepared with membrane lipid from lens cortex showed that membrane lipids from treated lenses, control lenses, and treated-but-clear lenses had similar fluorescence anisotropy profiles, suggesting that cortical lipids had similar order. Conversely, fluorescence anisotropy of parinaric acid probes in liposomes prepared from nuclear fractions showed a slight increase in lipid order from control to treated-but-clear to cataractous preparations. These results are interpreted to indicate the presence of an alteration in lipid-protein interactions in cortical membranes in the cataractous lenses; this results in more ordered membranes at the physiological temperature in these lenses. The increase in the order of cortical membranes from cataractous lenses is dependent on the presence of membrane proteins rather than lipids, since it is not seen in the liposome preparations (which are protein-free). The effects of this higher order on membrane protein function might include loss of permeability through the gap junction protein and increased susceptibility of this major lens membrane protein to proteolysis.