76 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



associated with the markedly diminished cellular concentration of K+ and 

 perhaps with a drop in cellular pH. 



At the time of writing, data on K+ leakage are incomplete, but certain con- 

 clusions can be drawn. The leakage of K+ is accompanied by an inflow of H+ 

 from the medium. Both ions are moving with the concentration gradient, 

 which probably supplies the driving force. The leakage rate is very dependent 

 on extracellular pH. There is a minimum leakage at pH 4.5 with an increased 

 rate up to pn 6.0 (no data are as yet available above pH 6.0) and down to pH 

 2.0. The rates are remarkably high at low values of pH. 



The metabolizing cell can take up K+ despite the pronounced outward leak- 

 age, because the inward transport system is so effective. It has already been 



Fig. 6. K"*" leakage by yeast into a K^-free medium as a function of pH, with and without 

 lucose. 



pointed out that at pn 4.5 a steady state exists at 5 X io~* m/1. K+, in which 

 the leakage rate is equal to the rate of inflow. The leakage rate is about 12 mivi/kg 

 hr. of cells. Thus the rate of inflow must be at least 12 mn/kg hr. at this re- 

 markably low concentration of K"*". At higher concentrations of K+ the rate of 

 inflow approaches 360 mM/kg hr. The actual rates of inflow may be even higher, 

 because in addition to correcting for the outflow of K+ measured by leakage into 

 a K+-free medium there may be an additional correction for outflow of K+ 

 associated with a K+-K+ exchange when the medium contains appreciable 

 concentrations of K+. The extent of the latter phenomenon can be determined 

 by isotope studies. The relationship between K+ concentration and K+ inflow 

 appears to follow an asymptotic curve on the basis of preliminary data, with 

 one half maximal rate at a K+ concentration of about 3 X io~^ m/1. However, 

 a great deal more experimental data on rates of inflow and outflow are required 



