D. C. TOSTESON I37 



organic phosphate, probably by inhibiting hexokinase (56). Since variations in 

 pH could also affect the charge distribution and geometry of diffusion pathways 

 for ions, this classification of pn effects is obviously somewhat arbitrary. 

 Parpart et al. (76) found that net K loss from human red cells cold stored in 

 the presence of glucose was minimal at pn 6.8. Reduction of pH from 7.5 to 

 7.0 does not affect K influx or outflux (87), but does reduce both Na outflux 

 and influx (35, 100). The importance of controlling pH in experiments in which 

 the effect of alterations in metabolism on cation transport is under study has 

 recently been pointed out (31). 



Acetylcholine appears to reduce K loss from human red cells suspended in 

 isotonic NaHCO? (51). This effect is reversed by the addition of physostig- 

 mine. Acetylcholine also seems to promote a small (5-10%) increase in the K 

 concentration in cells suspended in isotonic NaCl or NaHCOg containing 35 

 mM/1. KCl at pH 8.0 in). Physostigmine also appears to inhibit this effect. 

 Lindvig et al. (51) conclude that cholinesterase activity is required for the 

 maintenance of normal K and Na distribution in human red cells, but Parpart 

 and Hoffman (77) have suggested that the effect of acetylcholine is due to the 

 reduction in pH produced by addition of the compound. Cholinesterase in- 

 hibitors (physostigmine and diisopropyl fluorophosphate) reduce K influx 

 without affecting outflux, but this effect requires ten times more inhibitor 

 than is required to completely block cholinesterase activity (104). Physostig- 

 mine has been shown to accumulate in human red cells (5). Compounds which, 

 among other things, inhibit choline acetylase (2-methyl-i,4-napthoquinone 

 and methylene blue) increase K outflux without appreciable effect on K influx 

 (104). In contrast with earlier reports (50), recent careful attempts have failed 

 to reveal evidence of choline acetylase activity in normal human red cells (96). 

 Thus, the relevance of the acetylcholine-acetyl cholinesterase system to Na 

 and K transport in normal human red cells is, at present, in doubt. 



The relation between potassium and amino acid transport has received 

 considerable attention (6-9). Human red cells contain about 1.6 times more 

 glycine and alanine and 3 times as much glutamate per kg of cell water as 

 does the plasma (9). When the concentration of these amino acids in the 

 plasma is raised about two-fold, the cell concentration also increases so that 

 the distribution ratio of the amino acids between cell and plasma water re- 

 mains greater than unity. This accumulation of amino acid by human red 

 cells is not inhibited by anoxia, cyanide, pyruvate, phloretin or elevated 

 plasma potassium concentration (9). Human red cells do not take up a,y- 

 diamino butyric acid, a compound which is accumulated so strongly by mouse 

 ascitic tumor cells that most of the cell potassium is replaced (8). Pyridoxal 

 produces a small net loss of K with replacement by Na but indole acetic acid 



