THE SELECTIVE ABSORPTION OF POTASSIUM BY ANIMAL 



CELLS. 



I. Conditions Controlling Absorption and Retention of 



Potassium. 



By PHILIP H. MITCHELL and J. WALTER WILSON. 



(From the Biological Laboratory of Brown University.) 



(Received for publication, July 9, 192L) 



The accumulation of potassium with little or no sodium in the 

 cell living in a medium richer in sodium than in potassium is so wide- 

 spread a phenomenon as to be considered a general attribute of living 

 cells. In the few exceptions on record the distribution of sodium 

 between cells and tissue fluids has not been satisfactorily investigated. 

 The mechanism governing potassium selection has not been explained. 

 Loeb (1) as early as 1906, stated, "we may take it for granted that, 

 at least, potassium forms a non-dissociable constituent of the proto- 

 plasm of a number of tissues of animals and plants. " The view that 

 much of the potassium of the cell is not dissociated seems generally 

 accepted. Robertson (2), for example, uses the selective action of 

 cells for potassium as one of the proofs of the dissociation of pro- 

 tein salts so as to hold inorganic constituents as a part of protein 

 ions without the formation of free inorganic ions. Such a theory 

 explains very well the retention of accumulations of potassium in 

 the cells but it gives no clew as to why potassium is ' ' selected "ins tead of 

 sodium nor, in the face of the apparent impermeability of normal 

 cells to electrolytes, does it explain how potassium makes its way into 

 growing cells. Our investigations bear on such aspects of the problem. 



It seemed of first importance to find some of the limiting conditions 

 for the retention of potassium. The work of Loeb (3), showing the 

 so called salt effect as necessary for both the inward and outward 

 diffusion of potassium from the fertilized eggs of Fundiilus, does 

 not apply to such a structure as a muscle cell. It does show that the 

 presence of a certain amount of salt or of acidity or both is necessary 



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