ABRAHAM M. SHANES 



163 



give the appearance of exchange. The possibility of the latter situation was 

 indicated in our early studies when the anoxic emergence of potassium was 

 found to continue without sodium uptake in a low sodium medium (44, 45). 

 More recently we have observed potassium to be reabsorbed without a corre- 

 sponding loss of sodium. This occurs in NaCl-treated toad nerves which have 

 been returned to normal Ringer's, as may be seen in table 2. NaCl exposure 

 causes the nerves to gain sodium which is equal to the loss of potassium when 

 account is taken of the 5% gain in weight; the potassium deficit is partly 

 restored upon return to Ringer's with no significant change in the sodium 

 content. Such independence of sodium and potassium movement is also sug- 

 gested by data from other biological systems (35), including those described 

 earlier in this symposium, so that the observations on nerve reflect a more 

 general pattern. The now well-known experiments of Hodgkin and his asso- 



Table 2. Contents of sodium and potassium of paired desheathed toad nerves after 

 a) 40 hours in ringer's, b) 1 6 hours in nacl, and c) 16 hours in 



NACL FOLLOWED BY 24 HOURS IN RINGEr's 



All values referred to the wet weight. Eight preparations gave the data for A, and eleven 

 each for B and c. 



ciates appear to establish separate transfer of sodium and potassium ions during 

 the squid axon impulse as well, processes regarded as 'passive' (21, 25). 



Our more recent measurements on the unidirectional fluxes of sodium and 

 potassium in toad nerve provide further evidence for the possibility of inde- 

 pendent movement by these ions. Thus, sodium outflux is unaffected by meta- 

 bolic inhibition, e.g., with dinitrophenol, iodoacetate, eserine or anoxia, or a 

 combination of these, whereas potassium influx is reduced to about a third by 

 oxygen lack, particularly in the presence of iodoacetate. 



The data indicate, therefore, that in nerve specific metabolic reactions under 

 resting conditions can contribute energy, at the moment in an unspecified 

 manner, to at least two mechanisms, one of which excludes sodium while the 

 other retains or restores potassium in the axoplasm. Interference with contin- 

 uous energy turnover leads to ionic shifts such that equation i provides the 

 order of magnitude for associated changes in resting potential under conditions 

 of restricted diffusion. I shall now consider relationships which may exist be- 

 tween metabolic processes, ion distribution and resting potentials. 



