Hydroxyl Radical Participation in the In Vitro Effects of Gram-Negative Endotoxin on Cardiac Sarcolemmal Na, K-ATPase Activity

Abstract

The effect of in vitro exposure of sarcolemmal membrane (SL) vesicles to Gram-negative endotoxin lipopolysaccharides (LPS) was studied. LPS decreased the Na, K-ATPase activity of SL vesicles; this effect was inhibited by hydroxyl radical (·OH) scavengers such as dimethylthiourea and dimethyl sulfoxide, but not by superoxide dismutase, a scavenger of superoxide anion radicals or by the hydrogen peroxide scavenger catalase. ESR spin-trapping with 5, 5-dimethyl-l-pyrroline N-oxide verified the generation of ·OH from LPS itself under the conditions used; ·OH gener ated from LPS was not affected by deferoxamine, a powerful iron chelator. The Na, K-ATPase activity was reduced by an ·OH radical generating system consisting of dihydroxyfumarate and Fe³⁺-ADP. Furthermore, exposure of SL vesicles to LPS caused an increase in malondialdehyde formation. It can be concluded that LPS damages cardiac SL by an oxygen free radical mechanism by the generation of ·OH, due to inhibition of Na, K-ATPase activity and peroxidation of lipids, and that the effect of LPS is not dependent on the presence of contaminating iron.