Effect of Ethanol on Na<SUP>&#8290;</SUP>-P<SUB>i</SUB> Uptake in Opossum Kidney Cells Role of Membrane Fluidization and Reactive Oxygen Species

Effect of Ethanol on Na<SUP>&#8290;</SUP>-P<SUB>i</SUB> Uptake in Opossum Kidney Cells Role of Membrane Fluidization and Reactive Oxygen Species

<P> This study was undertaken to examine the effect of ethanol on Na<SUP>&#8290;</SUP>-dependent phosphate (Na<SUP>&#8290;</SUP>-P<SUB>i</SUB>) uptake in opossum kidney (OK) cells, an established renal proximal tubular cell line. Ethanol inhibited Na<SUP>&#8290;</SUP>-dependent component of phosphate uptake in a dose-dependent manner with I<SUB>50</SUB> of 8.4%, but it did not affect Na<SUP>&#8290;</SUP>-independent component. Similarly, ethanol inhibited Na<SUP>&#8290;</SUP>-dependent uptakes of glucose and amino acids (AIB, glycine, alanine, and leucine). Microsomal Na<SUP>&#8290;</SUP>-K<SUP>&#8290;</SUP>-ATPase activity was not significantly altered when cells were treated with 8% ethanol. Kinetic analysis showed that ethanol increased K<SUB>m</SUB> without a change in V<SUB>max</SUB> of Na<SUP>&#8290;</SUP>-P<SUB>i</SUB> uptake. Inhibitory effect of <I>n</I>-alcohols on Na<SUP>&#8290;</SUP>-P<SUB>i</SUB> uptake was dependent on the length of the hydrocarbon chain, and it resulted from the binding of one molecule of alcohol, as indicated by the Hill coefficient (n) of 0.8-1.04. Catalase significantly prevented the inhibition, but superoxide dismutase and hydroxyl radical scavengers did not alter the ethanol effect. A potent antioxidant DPPD and iron chelators did not prevent the inhibition. Pyrazole, an inhibitor of alcohol dehydrogenase, did not attenuate ethanol-induced inhibition of Na<SUP>&#8290;</SUP>-P<SUB>i</SUB> uptake, but it prevented ethanol-induced cell death. These results suggest that ethanol may inhibit Na<SUP>&#8290;</SUP>-P<SUB>i</SUB> uptake through a direct action on the carrier protein, although the transport system is affected by alterations in the lipid environment of the membrane.