Effect of external cation concentration and metabolic inhibitors on membrane potential of human glial cells.
1. The effect on membrane potential (Em) of low external [K+]o, [Na+]o and [Ca2+]o and of metabolic inhibitors was studied in cultured human glial cells (U-787CG) and human glioma cells (Tp-483MG and U-251MG). Whole cells were voltage or current clamped with the tight-seal recording technique. 2. Em was -76 and -80 mV in glial and glioma cells (mean values in U-787CG and U-251MG, respectively) in a reference external solution with 3.0 mM K+. K(+)-free external solution caused a rapid and reversible depolarization of these cells by about 26 and 42 mV (respectively). 3. Block of K+ channels with 1 mM Ba2+ in external solution rapidly depolarized the cells (U-251MG) by about 35 mV. 4. Na(+)-free solutions caused a delayed depolarization by 40-50 mV, which was slowly reversible (in 2 min). 5. Ouabain (1 mM) depolarized the cells by about 4 mV. It did not prevent the effect of K(+)-free solution. 6. Ca(2+)-free external solution rapidly depolarized the cells to Em about -17 mV. The combination of either Na(+)-K(+)-free or Na(+)-Ca(2+)-free solution transiently repolarized the cell, which indicated that the K+ selectivity of the membrane was decreased in both K(+)- and Ca(2+)-free solutions. 7. Metabolic inhibitors (carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP) and 2,4-dinitrophenol (DNP)) rapidly and reversibly depolarized the cells. This effect was not prevented by intracellular perfusion of a strong Ca(2+)-buffering solution. 8. Voltage clamp revealed only minor changes (< 20%) in the leak conductance (g) of cells that were depolarized by the above-mentioned solutions. 9. Positive polarizing current elicited (in some cells) a regenerative depolarization. The threshold for depolarization was less in low external [K+]o. 10. It is concluded (a) that the resting potential of these glial cells depends on ion channels that are K+ selective only in the presence of external Ca2+ and K+ and (b) that this K+ selectivity may require that Em is near the reversal potential for potassium (EK), and (c) that the action of metabolic inhibitors (DNP and FCCP) is different from that in neurones.
Brismar
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Department of Clinical Neurophysiology, Karolinska Hospital, Stockholm, Sweden.
Collins
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D019297:2,4-Dinitrophenol; D001254:Astrocytoma / Q000473:pathology; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D002478:Cells, Cultured; D004140:Dinitrophenols / Q000494:pharmacology; D004553:Electric Conductivity / Q000187:drug effects; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009457:Neuroglia / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014475:Uncoupling Agents / Q000494:pharmacology*
D002412:Cations; D004140:Dinitrophenols; D014475:Uncoupling Agents; D001464:Barium; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D010042:Ouabain; D012964:Sodium; D019297:2,4-Dinitrophenol; D011188:Potassium; D002118:Calcium