A transmembrane sodium cycle in astrocytes

This study demonstrates that the Na+-K+ pump of mouse astrocytes in primary cultures is stimulated by increases of intracellular Na+. The data presented show that the coupling ratio of the pump varies as a function of intracellular Na+ but not of extracellular K+. A furosemide-sensitive K+ net uptake activated by increased external K+ was partly ouabain-sensitive and found to be dependent upon the Na+ driving force. These findings and those of other authors indicating that an increase of intracellular K+ of glial cells did not involve a concomitant decrease in intracellular Na+ are explained by a transmembrane Na+ cycle. Na+ would enter the cells by providing the driving force for the KCl carrier and would be pumped out by the Na+-K+ pump. The proposed Na+ cycle would function as a coupler and synchronizer of the Na+-K+ and KCl pump under conditions of physiologically elevated external K+.

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