D. C. TOSTESON 1 47 



incubation in air. Addition of KCl-NaCl mixtures so as to make the plasma 

 hypertonic also resulted in considerable net accumulation of K by the cells. 

 One percent ethanol caused net loss of K from the cells incubated in plasma, 

 but did not prevent accumulation of K from media made hypertonic with 

 NaCl-KCl. 



K transport in duck red cells thus differs from that in human red cells in 

 several important respects. First, the assumption that K outflux is entirely by 

 diffusion is probably not valid. One reason for this conclusion is that K out- 

 flux is markedly decreased when the cells are allowed to incubate for many 

 hours in X2 in the absence of glucose. This slowing down of K outtlux occurs 

 without a comparable increase in the resistance of the membrane to the pene- 

 tration (presumably by diflfusion) of ethylene glycol. Furthermore, the marked 

 discrepancy between the value of D'k calculated from ilux ratio and concen- 

 tration curve analyses also argues against the idea that K outiiux is entirely 

 by diffusion. Therefore, specific chemical reactions may be involved in K out- 

 flux as well as influx in duck cells. 



Secondly, there are several distinctive features of the K influx process in 

 duck red cells which may give important information regarding the specific 

 chemical reactions involved. The acceleration of K influx in N2 suggests that 

 there are one or more reactions associated with glycolysis which are involved 

 in K transport. A clue to the specific reactions concerned is provided by the 

 effects of lAA and NaF on glycolysis and K transport. 



lAA probably blocks glycolysis by inhibiting triosephosphate dehydrogenase, 

 an — SH enzyme which catalyzes the oxidation of 3-phosphoglyceraldehyde to 

 1,3 diphosphoglyceric acid in the presence of inorganic phosphate (30). The 

 coenzyme of this reaction is diphospho-pyridinenucleotide. This is the only 

 known reaction in the glycolytic scheme in which inorganic phosphate is 

 esterified. Since it has been shown that P^- labelled inorganic phosphate first 

 appears in human red cells as ATP and 2,3 diphosphoglyceric acid (28, 86), it 

 is possible that this enzyme is involved in the transport of phosphate across 

 the cell membrane. (The nucleoside phosphorylase reaction is also known to 

 occur in red cells so that other routes of primary esterification are also pos- 

 sible.) Clarkson and Maizels (11) have demonstrated the presence of a powerful 

 apyrase on the outer surface of human red cells. Rapid hydrolysis of easily ' 

 hydrolysable organic phosphates in the medium occurred even during active 

 glycolysis when the easily hydrolysable fraction in the cell was maintained in 

 the steady state. This does not, of course, rule out the existence of all phos- 

 phorylative reactions on the cell surface. lAA blocks phosphate influx in 

 human (27, 66) and, presumably, in duck red cells. Since lAA also inhibits K 

 influx, it is reasonable to suspect that K influx is associated with the esterifica- 

 tion of inorganic phosphate. This deduction is compatible with the observa- 

 tions of Stanbury and Mudge (102), who found that liver mitochondria cannot 



