PROTECTION BY PYRUVATE AGAINST INHIBITION OF NA+,K+-ATPASE BY A FREE-RADICAL GENERATING-SYSTEM CONTAINING T-BUTYLHYDROPEROXIDE

Global tissue damage due to oxygen-derived free radicals has been implicated in several pathological processes including exposure to ionizing radiation, and postischemic reperfusion of the heart or kidney. Recently pyruvate, a hydroperoxide scavenger, has been shown to protect against functional damage during postischemic reperfusion of the heart and in acute renal failure. In the present study, pyruvate was found to protect against inactivation of partially purified guinea pig renal and rat cardiac Na+,K+-ATPase which occurred when microsomal membranes were assayed for 1 hr at 37 degrees C (pH 7.5) in the presence of a free radical generating system (FRGS) containing 0.3 mM t-butylhydroperoxide and horseradish peroxidase. The presence of the FRG system inhibited the guinea pig renal Na+,K+-ATPase activity by 48.2+/-4.8% (N=10, P<.05) and the presence of 0.2 to 20 mM pyruvate partially protected the Na+,K+-ATPase. At 5 mM pyruvate Na+,K+-ATPase was inhibited by only 18.8+/-2.5% (N=10, P<.05) but increasing the pyruvate concentration gave no further protection. Equimolar concentrations of glucose, mannitol or lactate were without effect. The protection appeared to require an alpha-keto acid since alpha- but not beta-ketoglutarate was also effective and the mechanism is most probably the scavenging of t-BHO2. The results of the present study therefore support the hypothesis that, if free radical damage to native Na+,K+-ATPase does contribute to global tissue injury in certain pathological processes, pyruvate, in addition to being a powerful metabolic effector of recovery, may also protect against oxidative damage.