Abstract
In the case of transmembrane ion distribution, the pump-leak hypothesis postulates the operational immobilization of a fraction of intracellular potassium and of extracellular sodium as the result of the activity of a ouabain-sensitive Na +/K + ATPase. Respiratory trees of Isostichopus badionotus Selenka were exposed to five sea water concentrations: 17.5, 21.0, 26.25, 35.0 and 42‰ S in the presence and absence of ouabain. In ouabain-treated tissues cell potassium concentration and content were lower and cell sodium concentration and content were higher than in control cells; chloride was unaffected. Total intracellular monovalent ion content was not modified by ouabain. Control and ouabain-treated cells responded as perfect osmometers to variations in sea water concentration implying that intracellular organic osmolyte content also remained unchanged despite changes in sea water concentration. If the Na +/K + pump is inhibited, more cell potassium will be free to leave the cells and more extracellular sodium will be free to enter them, explaining the effect of the glycoside on cell cations.
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