Cell cycle dependent changes in potassium transport

K transport has been investigated during progression of cultured Ehrlich ascites tumor cells through the cell cycle. Using a double thymidine block technique, Ehrlich cells carried in continuous culture have been synchronized, as verified by simultaneous monitoring of cell number, cell volume, 3 H‐thymidine incorporation and mitotic index. Unidirectional influx, efflux and cell content of K have been monitored throughout the cell cycle. The nature of the pump mediated, ouabain‐sensitive K flux and the furosemide‐sensitive component of K flux, presumably representing K‐K exchange, have also been evaluated. In early S period the ouabain sensitive component, representing the Na‐K pump, comprises 52% of the total unidirectional K influx. During S period the pump activity increases to a maximum of 65% of the unidirectional K influx and subsequently declines during G 2 period to a minimum of 40% in mid G 2 . During M and early S the activity again rises. As the ouabain sensitive component becomes maximal in late S period, the furosemide sensitive component diminishes from approximately 30% of the total influx to approximately 10%. The same pattern is observed in the G 2 period. As the pump component diminishes, the furosemide sensitive component increases. Furosemide sensitive K efflux has also been monitored and the pattern is equivalent to that observed in the influx studies. No change in net K flux is observed in the presence of furosemide. This indicates that the furosemide sensitive component represents an exchange component for K. These results are consistent with the conclusion that the alterations in exchange and pump fluxes are physiological events associated with progression of the cell cycle.