Effect of Extracellular Potassium on the Transport of Sodium and Potassium in Rat Thymocytes

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Abstract
The effect of extracellular K on the transport of Na and K in rat thymocytes was studied in vitro. A significant increase in the rate constant for total and ouabain-sensitive Na efflux was demonstrated at an extracellular K concentration of 1 mmol/l as compared with that at either 0 or 2 mmol/l. At K concentrations below 3 mmol/l ouabain-sensitive Na influx was observed, suggesting Na-Na exchange catalyzed by the Na pump. Both total and ouabain-insensitive K efflux rose with external K. A small ouabain-sensitive K efflux was observed at all levels of external K studied. Total and ouabain-insensitive K influx increased with external K, but did not appear to saturate. Ouabain-sensitive K influx reached a maximum at an external K concentration of 2 mmol/l then decreased with increasing external K.