THE SELECTIVE ABSORPTION OF POTASSIUM BY ANIMAL 



CELLS. 



II, THE CAUSE OF POTASSIUM SELECTION AS INDICATED BY 

 THE ABSORPTION OF RUBIDIUM AND CESIUM. 



By PHILIP H. MITCHELL, J. WALTER WILSON, and RALPH E. STANTON. 

 {From the Biological Laboratory of Brown University.) 



(Received for publication, July 9, 1921.) 



That the peculiarities of the physiological behavior of potassium 

 may be related to its ionic mobility has been suggested by Bayliss 

 (1). Loeb (2) has referred its peculiarities to its electronic structure; 

 i.e., to the outside ring of electrons and its atomic number. These, 

 in accord with modern views, would determine hydration. Hydration, 

 according to Jones (3), is responsible for the difference in ionic veloci- 

 ties of members of the group of alkali metals. The arrangement of 

 outer electrons and the atomic number then may be regarded as 

 determining the relative ionic mobility. This is the general expla- 

 nation as set forth by Mines (4) and others as to why ionic mobilities 

 have a complex relationship to ionic volumes. The fact that potas- 

 sium is generally selected in preference to sodium by a great variety 

 of living cells is especially notable among its several peculiarities. 

 Is there any evidence to show that the difference in the migration 

 velocities of potassium and sodium are concerned in this so called 

 "selective action" ? 



Among the comparative ionic conductances of the univalent metal- 

 lic ions, together with the ammonium ion which has similar beha\'ior, 

 we note certain relations. The figures below are taken from Landolt 

 (5) and refer to ionic conductances at 18°C. 



141 



