ABSTRACT
The sodium- and potassium-activated adenosinetriphosphatase (Na,K-ATPase) is a ubiquitous and vital enzyme of animal cell plasma membranes. Clearly, a perturbation of steady state Na,K-ATPase expression by gene amplification will have interesting consequences for cell physiology. The levels of expression and activity of the Na,K-ATPase must be tightly controlled in most cells to maintain cellular homeostasis. A different kind of regulation of the Na,K-ATPase operating via endogenous factors interacting directly with the enzyme at the external surface of the cell may also be of considerable physiological importance. Na,K-ATPase expression has also been reported to be under developmental control or to be controlled by hormones including aldosterone, corticosteroids, thyroid hormones, and insulin. The first evidence that the increased Na,K-ATPase expression seen in C+ is due to gene amplification was the correlation of unstable resistance with the presence of minute chromosomes.
