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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D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D005665:Furosemide / Q000494:pharmacology; D007473:Ion Channels / Q000378:metabolism*; D051379:Mice; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D007473:Ion Channels; D010042:Ouabain; D005665:Furosemide; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium