i8 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



now responds to each substance differently and the characteristic features of 

 incorporation aid in the distinction between the two processes. 



Table 14 shows that the uptake of potassium, rubidium and cesium from 

 the saline solution continues during prolonged exposure of the cells to the 

 cation. No uptake of sodium was observed beyond that quantity expected in 

 the water space of the cell. With the addition of glucose, a rapid additional 



Table 14. Effect of glucose upon uptake of potassium, rubidium, cesium and sodium 



* Potassium, rubidium, cesium, and sodium concentrations were 0.13, 0.026, 0.08, and 

 6.2 mg/ml medium respective!}-. 



Table 15. Wash losses during metabolism 



* Medium: 50 ml cSsSc NaCl and 10 ml Na2HP04 buffer solution. No growth occurs in 

 this medium even when glucose is added. 



t 1.6 mg radiorubidium in 60 ml medium. 



t 4.9 mg radiocesium in 60 ml medium. The specific radioactivity of the cesium was much 

 greater than that of the rubidium. 



uptake of potassium, rubidium and cesium was observed. The addition of 

 glucose had no effect on the uptake of sodium. Clearly, during metabolism the 

 cell is able to distinguish among the four ions — a distinction not observable 

 when the uptake is nonmetabolic. 



d) Wash losses during metabolism. The metabolic uptake of potassium, 

 rubidium and cesium is large as compared with the nonmetabolic uptake when 

 the ion concentration is low. Table 15 shows that the nongrowing, metabolizing 

 cell removes both rubidium and cesium from the medium and binds these 

 materials so that subsequent washing in saline solution does not remove the 



