I40 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



treated human red cells, we will consider only the K flux ratio analysis, varia- 

 tion of K flux with concentration, and competition between K and cesium in 

 S-S cells incubated in N2 (sickle shape). 



Flux ratio analysis. The distribution ratio and transport rate of chloride in 

 S-S cells is indistinguishable from normal. Thus, the ratio of inward to outward 

 rate constant for K diffusion in this system is also 1.2. Table i shows that the 

 observed K rate constant ratio far exceeds this value. However, as in the 

 case with normal human red cells, we may assume that the whole of the K 

 outflux is by diffusion. On the basis of this assumption, the calculated value for 

 D'k , the inward rate constant for diffusion, is .072 for sickled cells (table 2). 

 The value of cMk , the inward K transport rate by carrier, is 3.32. Both of 

 these values considerably exceed those derived from observations on S-S cells 

 in the disk shape and on normal cells. 



Variation oj flux with concentration. Figure 3 shows the variation of K influx 

 with concentration of K in the medium for sickled and disk-shaped S-S cells. 

 The values for D'k and JMk for sickled cells obtained from this curve are 

 .084 and 3.45 respectively, in good agreement with the values obtained from 

 the flux ratio analysis. 



Competition between K and Cs. Evidence indicates that Cs enters the sickled 

 cell by at least two routes, only one of which involves competition with K. If 

 one assumes that transport via the non-competitive pathway is entirely by 

 diffusion, it is possible to calculate a value for D V-s of .043 in the sickled S-S 

 cell, somewhat smaller than the value for D'k of .093 in the same subject. 



Conclusions About Cation Transport in Human Red Cells. The following 

 synthesis of K and Na transport in normal human red cells accounts for most 

 of the experimental data reviewed. K outflux and Na influx occur almost 

 entirely by slow diffusion, possibly through many aqueous pores in the cell 

 membrane which contain a high concentration of fixed positive charges or 

 possibly through a few negatively charged pores of small area. INIaizels (60) 

 argues that cation diffusion in the human red cell membrane occurs through a 

 lipoid layer. He bases this conclusion on the fact that D'^a exceeds D'k while 

 the hydrated Na ion is larger than hydrated K. However, such selectivity 

 could also be shown by a watery ion exchange membrane since some resins 

 are known to have a selective affinity for Na over K (3). 



K influx and Na outflux are mediated almost entirely by specific chemical 

 reactions. These reactions are linked to glycolysis, but the organic reactants 

 involved are completely unknown. There is some evidence that the reactions 

 involved in K influx are linked to those required for Na outflux (24, 34, 35), as 

 seems to be the case in squid nerve (42). Conclusive proof of the existence of 

 such oriented chemical reactions must await the identification of the membrane 

 components which react with Na and K respectively. The steady state con- 

 centrations of K and Na in the cell are determined by the relation between 



