Evidence for a New Mechanism of Respiratory Stimulation and Proton Ejection in Ehrlich Ascites Tumour Cells dependent on Potassium Ions

OVER the past decade, evidence has accumulated that fragments of cellular membranes exhibit ATPase activity which is dependent on sodium ions and inhibited by ouabain, and which is probably involved in the active transport of sodium and potassium ions1. Another type of cation transport, characterized by an insensitivity to ouabain and coupled directly to the energy transfer system of the respiratory chain, has been demonstrated in isolated mitochondria. Interest in this system has been concerned primarily with the transport of divalent cations, and their exchange with hydrogen ions2, but it is now obvious that a similar mechanism can operate for the transport of monovalent cations, provided that the mitochondria are treated with certain polypeptide antibiotics. Valinomycin specifically promoted the uptake of potassium, rubidium and caesium ions3,4, whereas gramicidin also activated uptake of sodium and lithium ions by isolated mitochondria5.