Na AND K CONTENT OF GLIAL CELLS AND NEURONS DETERMINED BY FLAME PHOTOMETRY IN THE CENTRAL NERVOUS SYSTEM OF THE LEECH

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Abstract
In previous studies indirect methods of measurement have shown that neuroglial cells in the central nervous system of the leech are high K cells. The possibility remained that appreciable amounts of Na might also be present in a bound form rather than free in solution. This has been tested by measuring the Na and K composition of the nerve cord directly by flame photometry. Na and K content of the cord was determined under two experimental conditions. (a) The extracellular space was filled with Ringer fluid. Under such conditions the K:Na ratio in the total cord was 1.1:1.0. If all the Na and K is assigned to the total water, determined by weight, the sum of their concentrations in the entire cord is 135 mEq/l, practically isotonic with leech blood or leech Ringer solution. (b) The extracellular space was filled with sucrose by bathing the cord for several minutes in sucrose-Ringer solution. Due to the loss of Na from the extracellular spaces the K:Na ratio became 8:1. At the same time the total K content remained practically unchanged. Therefore, relatively little Na can be present inside cells in the nerve cord. Since the volumes of glial cells and neurons are approximately equal in the leech nervous system it is concluded that in glia as well as in neurons K is the predominant intracellular cation. The total extracellular space was calculated from the Na that was lost when the cord was washed for 2 1/2 min. in sucrose-Ringer solution. The calculated values agreed with measurements made by microscopy.