D. C. TOSTESON 143 



tions which transports K into and Na out of the human cell but which is not 

 present in the dog cell. One objection to this hypothesis is that if K and Na 

 move by diffusion alone in the dog cell, colloid osmotic hemolysis of the cell 

 should result (98, 121). However, this process would occur only very slowly 

 due to the low rate of cation diffusion. Furthermore, it might be prevented 

 completely by a low external concentration of nonpermeable solute. 



Duck Red Cells 



In contrast to non-nucleated mammalian red cells, bird cells possess a 

 nucleus and an appreciable oxidative metabolism. The red cells of the duck 

 contain about no him/I. K and about 8 mM/1. Na.The ratio [Cl]m/[Cl]c is about 

 .75 at pH 7.5 and the CI exchange rate measured with CP* is complete within 

 I to 2 minutes. Therefore, the same arguments regarding the existence of 

 electro-chemical potential gradients for Na and K across the cell membrane 

 which were outlined for human cells also apply to duck cells. They consume 

 glucose at about the same rate as human cells in both O2 and N2 (though the 

 product is CO2 and H2O in O2 and lactate in N2). However, K transport is 

 four to five times faster than in human cells. For this reason, it was chosen 

 as a convenient system for the study of the role of metabolically linked chemical 

 reactions in the transport of K (108, in). 



Flux Ratio Analysis. Inward and outward rate constants for K transport in 

 duck red cells suspended in Geiman's medium containing glucose and 10% 

 plasma at pH 7.5 at 3o°C are shown in table i. The rate constants are ap- 

 preciably higher than in human red cells. The ratio of inward to outward K 

 rate constant is much higher than the measured [Cl]m/[Cl]c , indicating that 

 diffusion cannot be the major pathway of transport. Both the values of the 

 rate constants and the ratio are greater for cells incubated in N2 than in cells 

 incubated in O2 . The values for D'k calculated from these rate constant ratios 

 are .053 in O2 and .067 in N2 (table 2). The corresponding values of cMk are 

 6.3 in O2 and 7.7 in N2 . When duck cells are incubated in N2 rather than O2 , 

 they rapidly gain water and K. This ca. 10% increase in cell volume is complete 

 within 15 minutes, and thereafter the cells maintain a new steady state for 

 many hours. The measurements of K transport in N2 described in this section 

 were made during this steady state. 



Variation of Flux With Concentration. Figure 5 shows the relation of K in- 

 flux with [K],n for duck cells incubated in O2 and N2 . The values for cMr 

 and D'k are 4.6 and .21 for cells incubated in O2 . This value for D'k maybe 

 compared with the value .053 obtained for the flux ratio analysis. In the case 

 of duck red cells incubated in N2 , the values for cMr and D'k are 8.4 and o 

 respectively. Thus, inward K transport by chemical reaction is considerably 

 faster in N2 than in O2 . Furthermore, the apparent ^Michaelis-Menton con- 



