ABRAHAM M. SHANES 1 59 



sliuclure and function in single verlebrale nerve fibers (55, 56) represent a 

 subslantial contribution in this direction. 



METABOLISM, RESTING POTENTIAL AND ELECTROLYTES 



Progress in the past decade in our understanding of electrolytes in peripheral 

 nerve has been largely a consequence of a growing conviction that the bioelec- 

 trical phenomena characteristic of this tissue can be understood primarily in 

 terms of the ions, particularly sodium and potassium. This had, of course, been 

 suspected and proposed when Arrhenius, Ostwald, Nernst, Planck, Bernstein, 

 Overton, and other early outstanding investigators were making their important 

 contributions. While it is one thing to propose and another to provide experi- 

 mental proof, we cannot detract from the early accomplishments; important 

 concepts which underly present somewhat more involved hypotheses, which 

 still are not completely satisfactory, were developed when technical methods 

 and physical chemistry were in their early stages of development. 



In any case, nerve electrolytes cannot be discussed without the resting poten- 

 tial since their movement and distribution must of necessity be affected by it. 

 Major analytical findings in recent years have been a consequence in large 

 part of efforts to explain the origin of bioelectrical phenomena. This approach 

 began with the discovery, verified in many other systems, that the resting 

 potential varies inversely with the logarithm of the extracellular potassium 

 level over a wide range of higher potassium concentrations, but is indifferent, 

 or almost so, to the sodium content of the medium. This focused attention on 

 the considerable amount of potassium known to be present in cells, since studies 

 with inanimate membranes reveal that a boundary which permits potassium 

 to move much more freely than other ions, when interposed between two 

 solutions containing different concentrations of potassium salt, likewise gives 

 rise to a potential difference — a concentration potential — which varies as the 

 logarithm of potassium concentration on either side of the boundary. In other 

 words, nerve (and muscle) fibers were early regarded as being surrounded by 

 a membrane highly selective for potassium ions but impermeable, or nearly so, 

 to other ions. Thus, the resting potential, £„, in millivolts at room temperature 

 (2o°C), ideally would depend on intracellular [K]i and extracellular concentra- 

 tion [K]o as follows if activities and concentrations are equated: 



E. = 58 log ([K]i/[K]o) (/) 



Exact measurements of E„ and [K]i were not possible until recently with the 

 introduction of giant axons and with the development of microelectrodes and 

 application of microanalytical techniques; these have shown that equation i is 

 only an approximation of the situation (20), the actual resting potential, E, 

 in general being lower than predicted from this equation. This is ordinarily 

 attributed to non-ideality of the fiber membrane, that is, a leakiness to other 



