Activities of Sodium and Potassium Ions in Epithelial Cells of Small Intestine

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Science  17 Mar 1972:
Vol. 175, Issue 4027, pp. 1261-1264
DOI: 10.1126/science.175.4027.1261


Intracellular molar Na+ activity (aNa), measured with cation-selective glass microelectrodes, in epithelial cells of isolated bullfrog small intestine immersed at 26°C in a sodium sulfate Ringer solution containing mannitol was 0.0144 ± 0.0031 (average value plus or minus standard deviation). The corresponding K+ activity (aK) was 0.0854 ± 0.0060. Combination of these values with previous estimates of intracellular Na+ and K+ concentrations under identical conditions indicated that a substantial fraction of the cellular Na+ is in an osmotically inactive state. When the cells were exposed to a Ringer solution in which 26 millimoles of mannitol per liter were replaced by 3-O-methyl glucose, highly significant decreases in aK and aNa were observed. The decrease in aK was proportionately larger than the corresponding decrease in aNa.