Electrolyte distribution in mammalian central nervous system

Abstract

Evidence concerning the distribution of electrolytes in mammalian central nervous system is reviewed. Studies of the electrical properties of central nervous neurons suggest that these neurons contain high concentrations of K and are bathed in a medium containing preponderantly Na. Chemical analyses show that the whole tissue contains large amounts of Na as well as K, on the average 58 meq of Na/kg fresh weight and 100 meq of K/kg of fresh weight. Evidence fron electron microscopy indicates that the bulk of these electrolytes must be distributed between neurons and glial cells, the brain being filled with cellular elements with only 100- 200-A, spaces between. Moreover, axons may be embedded in the cytoplasm of glial cells. This evidence leads to alternative hypotheses: first, that Na and K are homogeneously distributed throughout the cells, the small spaces between the cells functioning as an extracellular space to preserve the electrochemical gradient at membranes, and, second, that glial cells or a fraction of the glial cells act as the functional extraneuronal space to preserve the electrochemical gradients. The consequence of the second hypothesis is that the glial cells acting in this capacity should be high Na cells. Experimental data of 2 types are presented. The first demonstrates that extracts of brain acidic lipid contain cation with Na predominating over K. This indicates that the Na and K of the brain are not homogeneously distributed but that there must be formed elements with high Na concentrations. Secondly, the meq of Na: meq of K of 10 glial cell tumors is found to exceed 1.0 with an average value of 1.8. While this finding must be applied with caution, it is consistent with the hypothesis that some or all of the glial cells may be high Na cells.