Cardiac ischemia causes inhibition of the Na/K ATPase by a labile cytosolic compound whose production is linked to oxidant stress

Fuller, W. , Parmar, V., Eaton, P., Bell, J. R. and Shattock, M. J. (2002) Cardiac ischemia causes inhibition of the Na/K ATPase by a labile cytosolic compound whose production is linked to oxidant stress. Cardiovascular Research, 57(4), pp. 1044-1051. (doi:10.1016/S0008-6363(02)00810-6) (PMID:12650882)

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Objective: Intracellular Na rises rapidly during cardiac ischemia and this has been attributed to the combination of increased influx of Na via sodium–proton exchange and decreased activity of the Na/K ATPase. The aim of these studies was to investigate the effects of ischemia on Na/K ATPase function in Langendorff-perfused rat hearts. Methods: Na/K ATPase activity was determined by measuring ouabain-sensitive phosphate generation from ATP by cardiac homogenates. Results: Global ischemia (15 and 30 min) caused a substantial reduction in Na/K ATPase function despite high substrate availability in the assay. When sarcolemmal membranes were purified away from the cytosol a profound activation of the Na/K ATPase was revealed following ischemia, indicating that the inhibition was due to the cytosolic accumulation of an inhibitor of Na/K ATPase. The half-life of the inhibitor in cardiac homogenates was 10±3 min at room temperature. Perfusion with the antioxidant MPG (1 mmol/l) reduced the accumulation of this inhibitor, however MPG was without effect on Na/K ATPase function when added directly to the Na/K ATPase activity assay. While the inhibitor reduced the activity of cardiac and brain forms of the Na/K ATPase in bioassay experiments, no effect was observed on the renal and skeletal muscle forms of the enzyme. Conclusions: An unstable cardiac and brain-specific inhibitor of the Na/K ATPase whose production is linked to oxidant stress, accumulates intracellularly during ischemia. Intracellular Na is a primary determinant of electro-mechanical recovery on reperfusion, so inhibition of the Na/K ATPase by this compound may be crucial in determining recovery from ischemia.

Item Type:Articles
Additional Information:This work was supported by grants from the British Heart Foundation and the Wellcome Trust.
Glasgow Author(s) Enlighten ID:Fuller, Dr Will
Authors: Fuller, W., Parmar, V., Eaton, P., Bell, J. R., and Shattock, M. J.
College/School:College of Medical Veterinary and Life Sciences > Institute of Cardiovascular and Medical Sciences
Journal Name:Cardiovascular Research
ISSN (Online):1755-3245

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