Function of the sodium-potassium pump and its corticosteroid regulation as factors limiting cardiac adaptation to severe physical exertion
Kyrge, P.K.
Kardiologiia 16(9): 15-21
1976
ISSN/ISBN: 0022-9040 PMID: 138013 Document Number: 106238
Experiments were carried out on male Wistar rats in order to clarify the leading biochemical mechanism responsible for an increase in the functional capacity of the heart. The obtained results indicate that the function of the Na,K-pump in myocardial sarcolemma is rather stable and deteriorates only during extreme exertion. The alteration of the Na,K-pump function due to a decrease in Na,K-ATP-ase activity leads to a decrease in the Na gradient and an accumulation of water in the cells which in turn reduces the capacity of the Na-Ca exchange mechanism and the rate of Ca removal from the myofibrils. Hence, the decrease in the working capacity of the heart during excessive physical exercises is primarily connected with the exhaustion of the ions active transport mechanism rather than the mechanism of aerobic energy production. In accordance with this conclusion, the functional stability of the myocardial Na,K-pump increased in our experiments with regular training, whereas the capacity to regenerate ATP via oxidative phosphorylation did not change, as demonstrated by Holloszy et al. Experiments in adrenalectomized animals, with or without administration of gluco- and mineralocorticoids, has revealed that an adequate supply of glucocorticoids to the heart is important in maintaining the function of the myocardial Na,K-pump and thereby in the working capacity of the heart during severe physical exertion.