The efficiency of (Na+ + K+)-ATPase in tumorigenic cells

The efficiency of (Na+ + K+)-ATPase (i.e. the amount of K+ pumped per ATP hydrolyzed) in intact tumorigenic cells was estimated in this study. This was accomplished by simultaneously measuring the rate of ouabain-sensitive K+ uptake and oxygen consumption in tumorigenic cell suspensions during the reintroduction of K+ to K+-depleted cells. The ATP turnover was then estimated by assuming 5.6-6 ATP/O2 as the stoichiometry of NADH-linked respiration in these cells. In the three cell lines tested (hamster and chick embryo cells transformed with Rous sarcoma virus and Ehrlich ascites cells), the K+/ATP ratio was approximately 2, the same value as that found in normal tissues. Furthermore, only 20% of the total ATP production of these cells was used by (Na+ + K+)-ATPase.