i6o 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



species of ions, since a more general equation taking into account permeabilities 

 to other ions has given better agreement for giant axons (20); however, diffi- 

 culties still remain, particularly the indifference of E to modifications in the 

 intracellular ion concentration (19). 



An especially serious difficulty became evident exactly 20 years ago when no 

 change in [K], could be detected under conditions of metabolic inhibition (12) 

 which lead to a large decrease in E (17) and which, even if equation i were only 

 roughly correct, would be expected to produce a substantial decrease in [K]i. 

 However, recognition that measurements of resting potential are usually made 

 in a moist chamber with the nerves mounted in air led to the realization that 

 small losses of intracellular potassium must cause an appreciable increment in 

 [K]o (42, 54). Since E is dependent on relative changes in potassium, and [K]o 



Table i. Decreases ( — ) or increases (+) in resting potential (e), intracellular 



POTASSIUM [k],- and INTRACELLULAR SODIUM [na]; IN FROG NERVE UNDER 

 different ENVIRONMENTAL CONDITIONS 



The number of symbols indicates the intensity of the change only for the anoxia series, 

 being relative to that with anoxia alone. 



is small, little decrease in [K]i would cause a large change in E, chiefly by 

 alteration of [K]o. For example, in a frog nerve with half its aqueous content in 

 the interstitial spaces and half in the fibers, a ten-fold increase in [K]o from 

 2 to 20 /xM/ml would be achieved by a decline in [K]i from about 150 to 132 

 juM/ml, with a change in E of the order of 60 millivolts due chiefly to the in- 

 crement in [K]o. 



With the development of techniques for following the much smaller potassium 

 shifts now expected, the anticipated magnitude of potassium movement was 

 found (13, 43) and complete agreement established between the direction of 

 intracellular potassium concentration changes and E. Table i shows quali- 

 tatively the nature of the correlations which have been established, chiefly for 

 intact frog nerve; the opposite movement of sodium, which usually accom- 

 panies potassium transfer, also is evident (44, 45). 



The table provides evidence that maintenance of the polarized state, reten- 



