Na-K pump and Na-K-ATPase: disparity of their temperature sensitivity

As previously observed in red blood cells, ouabain-sensitive K influx of kidney cells grown in culture for 3 days was much less inhibited by cooling that Na-K-ATPase of the same cells. (At 5 degrees C K influx was 9.7% of that at 38 degrees C, Na-K-ATPase, 1--2%.) Resealed ghosts of erythrocytes of ground squirrels were made containing 24Na and ATP, and the Na efflux and ATP hydrolysis were measured simultaneously. Under these conditions there was no difference in the reduction of activity with cooling, and the amount of reduction was close to that of active K transport in intact cells. The high sensitivity to temperature, characteristic of broken membranes, could not be induced in intact cells or resealed ghosts by eliminating either the Na/K gradient or the ATP gradient nor by chelation of cellular and extracellular Ca. It could not be eliminated in broken membranes by protection with ATP or Mg. Structural reorganization of membrane during lysis may cause the increase in temperature sensitivity of Na-K-ATPase.