Abstract
The activities of Na +K +-stimulated ATPase, a membrane bound enzyme, from the hearts of control hamsters and genetically myopathic hamsters with a moderate degree of heart failure (BIO 14.6) were determined. The specific activity of the Na +K + ATPase in the failing hearts was higher than the control preparations at different steps of isolation. The enzyme activity of the failing heart was also observed to be elevated under different assay conditions obtained by changing the concentrations of Na +, K +, H +, and Mg 2+ ATP. The value for the maximal velocity of reaction for the Na +K + ATPase from the failing heart was markedly higher than the control but the K m values were not different from each other. The enzyme preparations from the control and failing hearts exhibited similar allosteric nature of activation kinetics. The inhibitory responses of the Na +K + ATPase from the failing hearts to both ouabain and calcium were also similar to those of the control. The increase in Na +K + ATPase activity in the myopathic hamster heart may be due to some adaptive change in the cell membrane in this model of heart failure.
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