D. C. TOSTESON 



131 



and o, outward, and subscripts are m, medium, and c, cells. In the calculation 

 of the rate constants we have used the figure 2.0 for K flux and 3.0 for Na 

 flux both expressed as mM/(l. RBC) X (hr.). Thus, for human red cells sus- 

 pended in plasma, 'Ick , the inward rate constant for potassium is .44 while 

 'kxa is .021. On the other hand, "Ick is .014 while °kNa is .30. The asymmetric 

 character of the red cell surface is thus clearly evident. The outside of the 

 membrane prefers K to Na by a factor of about 21, while the inside prefers 

 the Na to K by a factor of about 21 (100). 



Flux ratio analysis. Table i indicates that the ratio of inward to outward 

 rate constant is much higher than would be predicted for diffusion in the case 

 of K, but much lower than the theoretical value for Na. It is, however, possible 

 that the transport of both ions in the direction of their decreasing electro- 

 chemical potential gradient, i.e. outward transport of K and inward transport 

 of Na, is entirely by diffusion. According to this assumption, K influx and Na 



Table i. Rate constants for cation transport in red cells 



outflux are accomplished largely by one or more chemical reactions. This 

 hypothesis contrasts with that of Solomon (100) who proposed that four 

 carrier processes were involved in cation transport in human red cells; one 

 each for K influx, Na influx, K outflux and Na outflux. We will now proceed 

 to examine the simpler model outlined above which requires only two oriented 

 chemical reaction systems. If K outflux were wholly by diffusion, D'k , the 



inward rate constant for K diffusion, would equal W^ °^k. ■ When calculated 



from the value for "kn in table i, D'k = .017 (table 2). By comparison, 

 D'jja = 'kxa — .020. If we assume that the total K influx, 'Mr , is made up of 

 a concentration independent carrier component, c^Ir , and a concentration 

 dependent component, D'K[K]ni , we may write. 



'Mk = cMk + D'k[K], 



(8) 



Having evaluated D'k by the flux ratio analysis we may calculate cMr to be 



