[Analysis of thermodenaturation of Na,K-ATPase in the rat myocardial sarcolemma and possible role of damage of this enzyme in the pathogenesis of arrhythmias].

Activity of Na+, K+-ATPase and kinetics of the enzyme thermodenaturation were estimated in preparations of heavy sarcolemma isolated from rat myocardium. Emotional-painful stress (EPS) decreased the enzymatic activity by 20%, whereas the rate of the enzyme thermodenaturation was increased 2-3-fold. A thermodynamic analysis enabled to find a decrease in the energy of activation of the process after the stressory effects as well as alterations in entalpy and entropy under conditions of practically constant changes in free energy; this suggests the possible conformational transformations in the Na+, K+-ATPase molecules in EPS, resembling the state of denaturation. Lipid peroxidation was essential for the decrease in the enzyme thermostability. Activation of lipid peroxidation in the sarcolemma native membranes was accompanied by impairments typical for EPS. Preadministration of an antioxidant ionol before stress protected both the activity and thermostability of Na+, K+-ATPase. Adaptation to EPS by means of multiple short-term stressory actions prevented also the enzyme impairment. Mechanisms of the stress arrhythmogenic effect are discussed.