PARTIAL CHARACTERIZATION OF THE INHIBITORY EFFECT OF LIPID-PEROXIDATION ON THE OUABAIN-INSENSITIVE NA-ATPASE OF RAT-KIDNEY CORTEX PLASMA-MEMBRANES

The present work evaluates the effect of lipid peroxidation on the ouabain-insensitive Na-ATPase of basolateral plasma membranes from rat kidney proximal tubular cells as an indirect way to study the lipid dependence of this enzyme. An inverse relationship between lipid peroxidation and Na-ATPase activity was found. This effect was due neither to a change in the optimal K(m) of the system for Na+ nor for the substrate Mg : ATP, nor the optimal pH value of the medium. The optimal temperature value, however, was shifted toward a higher value. There was also an increase of the apparent energy of activation in the region of temperatures above the transition point (20-degrees-C) with increase in lipid peroxidation. Peroxidized membranes incubated with phosphatidylcholine from soybean restored their Na-ATPase activity. On the other hand. the Na-ATPase activity was sensitive to oleoly lysophosphatidylcholine. These results suggest that lipid peroxidation might be affecting the Na-ATPase activity through either an increase of peroxidized phospholipids, which might change the membrane fluidity of the lipid microenvironment of the ATPase molecules, or through a direct effect of lysophospholipids released during the lipid peroxidation.