¹ From the Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia, and Department of Biology, Brookhaven National Laboratory, Upton, Long Island

Studies have been conducted on the movements of sodium and potassium into and out of the Ehrlich ascites tumor cell. Under steady state conditions, at 22°C., in the absence of an exogenous source of glucose, the cell flux for both potassium and sodium averaged 0.8 µM10⁷ cells/hr, or 3.0 pM/cm.²/sec. The cell can accumulate potassium and extrude sodium against electrochemical gradients for both ions. It is possible under the experimental conditions reported to separate the transport systems for these two ions. Thus, it has been shown that under conditions of low temperature with a diminished metabolism, net fluxes for the two ions are different. Also, following periods of 24 hours at 2°C., an exogenous source of glucose enhances the accumulation of potassium sevenfold while sodium extrusion is uninfluenced by the presence of glucose. Similarly potassium exchange rates are temperature-dependent, with Q₁₀ values as high as 5, while exchange rates for sodium are temperature-insensitive, with Q₁₀ values of 1.2 to 1.6. Glycolysis has been eliminated as an energy source for the transport processes since these processes go on in the absence of an exogenous source of glucose. It is estimated that a maximum of 0.3 per cent of the energy derived from the total oxidative metabolism of glucose would be required to support independent transport of potassium and sodium.

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