Regulation of intracellular sodium in cultured rat hippocampal neurones
1. We studied regulation of intracellular Na+ concentration ([Na+]i) in cultured rat hippocampal neurones using fluorescence ratio imaging of the Na+ indicator dye SBFI (sodium-binding benzofuran isophthalate). 2. In standard CO2/HCO3(-)-buffered saline with 3 mM K+, neurones had a baseline [Na+]i o...
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Published in | The Journal of physiology Vol. 499; no. Pt 3; pp. 573 - 587 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
England
The Physiological Society
15.03.1997
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Subjects | |
Online Access | Get full text |
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Summary: | 1. We studied regulation of intracellular Na+ concentration ([Na+]i) in cultured rat hippocampal neurones using fluorescence
ratio imaging of the Na+ indicator dye SBFI (sodium-binding benzofuran isophthalate). 2. In standard CO2/HCO3(-)-buffered
saline with 3 mM K+, neurones had a baseline [Na+]i of 8.9 +/- 3.8 mM (mean +/- S.D.). Spontaneous, transient [Na+]i increases
of 5 mM were observed in neurones on 27% of the coverslips studied. These [Na+]i increases were often synchronized among nearby
neurones and were blocked reversibly by 1 microM tetrodotoxin (TTX) or by saline containing 10 mM Mg2+, suggesting that they
were caused by periodic bursting activity of synaptically coupled cells. Opening of voltage-gated Na+ channels by application
of 50 microM veratridine caused a TTX-sensitive [Na+]i increase of 25 mM. 3. Removing extracellular Na+ caused an exponential
decline in [Na+]i to values close to zero within 10 min. Inhibition of Na+,K(+)-ATPase by removal of extracellular K+ or ouabain
application evoked a [Na+]i increase of 5 mM min-1. Baseline [Na+]i was similar in the presence or absence of CO2/HCO3-; switching
from CO2/HCO3(-)-free to CO2/HCO3(-)-buffered saline, however, increased [Na+]i transiently by 3 mM, indicating activation
of Na(+)-dependent Cl(-)-HCO3- exchange. Inhibition of Na(+)-K(+)-2Cl- cotransport by bumetanide had no effect on [Na+]i.
4. Brief, small changes in extracellular K+ concentration ([K+]o) influenced neuronal [Na+]i only weakly. Virtually no change
in [Na+]i was observed with elevation or reduction of [K+]o by 1 mM. Only 30% of cells reacted to 3 min [K+]o elevations of
up to 5 mM. In contrast, long [K+]o alterations (> or = 10 min) to 6 mM or greater slowly changed steady-state [Na+]i in the
majority of cells. 5. Our results indicate several differences between [Na+]i regulation in cultured hippocampal neurones
and astrocytes. Baseline [Na+]i is lower in neurones compared with astrocytes and is mainly determined by Na+,K(+)-ATPase,
whereas Na(+)-dependent Cl(-)-HCO3- exchange, Na(+)-HCO3- cotransport or Na(+)-K(+)-2Cl- cotransport do not play a significant
role. In contrast to glial cells, [Na+]i of neurones changes only weakly with small alterations in bath [K+]o, suggesting
that activity-induced [K+]o changes in the brain might not significantly influence neuronal Na+,K(+)-ATPase activity. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.1997.sp021951 |