Energy-dependent cell volume maintenance in UC-11MG human astrocytomas.
Swelling of astrocytes in the brain is a major cause of the morbidity and mortality associated with stroke and head trauma. Using a human astrocytoma cell line (UC-11MG) as a model system, we studied cell volume changes caused by ATP depletion under conditions mimicking hypoxia. ATP levels were reduced to less than 10% of control using the metabolic inhibitors KCN or antimycin in combination with glucose deprivation. This was sufficient to eliminate ouabain-sensitive 86Rb+ uptake, indicating the Na+-K+-adenosinetriphosphatase was not operating. Furosemide-sensitive 86Rb+ uptake was reduced by approximately 60%, indicating Na+-K+-2Cl- cotransport was also sensitive to ATP loss. ATP depletion resulted in a 30-40% reduction of cell volume within 60 min. ATP depletion also resulted in a net loss of intracellular K+. This loss of K+ could be blocked by Ba2+, indicating the K+ loss was through a conductive channel. When the net K+ loss was blocked by Ba2+, the volume decrease was also prevented. The cells remained viable throughout the time period as judged by exclusion of ethidium bromide by 99% of the cells and recovery of ATP levels to 75% of control within 60 min. We conclude that ATP depletion, following inhibition of glycolysis and oxidative phosphorylation, causes astrocytes to shrink because of a more rapid loss of K+ than uptake of Na+. Thus it appears that ATP depletion alone is not sufficient to account for the rapid phase of astrocytic swelling observed during cerebral ischemia.
Lomneth
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Department of Biochemistry and Molecular Biology, University of Cincinnati Medical School, Ohio 45267-0522.
Gruenstein
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D001254:Astrocytoma; D001693:Biological Transport, Active; D002460:Cell Line; D002470:Cell Survival; D004734:Energy Metabolism; D006801:Humans; D007477:Ions; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D010101:Oxygen Consumption; D011188:Potassium / Q000378:metabolism; D011190:Potassium Cyanide / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D007477:Ions; C032456:antimycin; D010042:Ouabain; D000968:Antimycin A; D000255:Adenosine Triphosphate; D012413:Rubidium; D011190:Potassium Cyanide; D011188:Potassium