ABSTRACT
The Na,K-adenosine triphosphatase (Na,K-ATPase), also known as the sodium pump or sodium-potassium pump, is a membrane-associated enzyme responsible for maintaining the high internal K concentration and low internal Na concentration characteristic of most animal cells. It couples the hydrolysis of ATP to the transport of Na and K across the plasma membrane against their respective electrochemical gradients. For each ATP hydrolyzed the Na,K-ATPase normally expels three Na ions and takes in two K ions. As outlined in Figure 1, the Na,KATPase is fundamental to several diverse cellular functions. These functions include: (a) regulation of cellular volume; (b) maintenance of the high internal K concentration required for several intracellular enzymes; (c) generation of the transmembrane Na gradient necessary for the uphill transport of sugars, amino acids and ions; (d) maintenance of the ion gradients essential for the membrane potential and the excitability of the membrane; and (e) the transport of Na across the epithelia. Generally up to one-third of an animal cell’s energy requirement is consumed in fueling the Na,K-ATPase. In electrically active tissues or tissues involved in salt transport up to 70% of the cell’s total energy requirement may be used by the pump.
