The function of Na+,K+-ATPase and its importance for drug action
The primary function of Na+,K+ -ATPase in cardiac and other excitable tissues is to maintain the resting, excitable state. In addition, the intracellular Ca2+ concentration is markedly affected by the balance between Na+,K+-ATPase activity (capacity of the sodium pump) and Na+ influx rate. The sodium pump in cardiac muscle has a substantial reserve capacity under normal conditions; however, a relatively modest sodium pump inhibition or an increase in Na+ influx rate elevates [Na+]i and therefore intracellular Ca2+ via Na+/Ca2+ exchange. The subsequent loading of the sarcoplasmic reticulum by Cat+ and an enhanced Ca2+ release upon membrane excitation appear to be responsible for the positive inotropic effect of a Na+,K+-ATPase inhibitor.
KeywordsInflux Rate Cardiac Glycoside Reserve Capacity Positive Inotropic Effect Sodium Pump
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