4© ELECTROLYTES IN BIOLOGICAL SYSTEMS 



Influence of Metabolism on Exchange Rate of Potassium Ion 



In studying the mechanisms of cation regulation in living cells it is desirable 

 to determine the rate and extent of exchange of the ions in question between 

 the cell and its environment. The use of radioactive potassium has demonstrated 

 that a dynamic equilibrium normally prevails between the potassium of a 

 variety of living cells and that of their environments. According to the studies 

 of Raker et al. (32) on the human erythrocyte and Fenn et al. (11) on muscle, 

 all the potassium of these cells appears to be exchangeable. 



Ulva lactuca is well suited for such investigations because of the ready inter- 

 change possible between the cells and the surrounding sea water. Accordingly 

 K*2 was used to determine the influence of illumination and temperature on 

 the rate and extent of potassium ion exchange (37). 



Table 3. Effect of illumination and temperature on rate of potassium ion exchange 



IN ULVA lactuca 

 Conditions Time for 75% exchange hr. 



Light 30°C 0.4 



Dark 3o°C 1.8 



Light 20°C 2.2 



Dark 2o°C 3 • 2 



The specific activities were calculated according to the following equation: 



.^ . . . counts/min X loo mg 



bpecmc Activity = =; — :r—, 



mLq K/ioo gm 



The rate of exchange, as indicated by the time required for the cellular 

 specific activity to reach 75% that of the sea water (75% exchange), was 

 much faster in the illuminated samples and those at the higher temperature 

 (table 3). Since under all of these conditions the algal specific activity, K*^ 

 cellular/K^^ cellular, reaches equality with that of the sea water K^ sea water/ 

 K^' sea water the complete exchangeability of the cellular potassium is indi- 

 cated. It may be noted that the rate of exchange of potassium in illuminated 

 Ulva is many times more rapid than in human erythrocytes and slowly ferment- 

 ing yeast and not too different from strongly fermenting yeast (32, 19). 



Role of Metabolism in Cation Regulation 



In the following section evidence will be discussed which indicates an energetic 

 coupling of cation regulation to metabolism and the presence of separate 

 mechanisms for the active transport of both Na and K cations against their 

 concentration gradients. In order to modify the prevailing cellular metabo- 

 lism the following agents were used: /) light and dark, 2) the metabolic in- 

 hibitors monoiodoacetate, phenylurethane and 4,6-dinitro-o-cresol, j) the 

 addition along with iodoacetate of carbohydrate intermediates, the normal 



