Glial depolarization evokes a larger potassium accumulation around oligodendrocytes than around astrocytes in gray matter of rat spinal cord slices
✍ Scribed by Alexandr Chvátal; Miroslava Anděrová; Drahomír Žiak; Eva Syková
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 285 KB
- Volume
- 56
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
The cell membrane of astrocytes and oligodendrocytes is almost exclusively permeable for K ؉ . Depolarizing and hyperpolarizing voltage steps produce in oligodendrocytes, but not in astrocytes, decaying passive currents followed by large tail currents (I tail ) after the offset of a voltage jump. The aim of the present study was to characterize the properties of I tail in astrocytes, oligodendrocytes, and their respective precursors in the gray matter of spinal cord slices. Studies were carried out on 5-to 11-day-old rats, using the wholecell patch clamp technique. The reversal potential (V rev ) of I tail evoked by membrane depolarization was significantly more positive in oligodendrocytes (؊31.7 ؎ 2.58 mV, n ؍ 53) than in astrocytes (؊57.9 ؎ 2.43 mV, n ؍ 21), oligodendrocyte precursors (؊41.2 ؎ 3.44 mV, n ؍ 36), or astrocyte precursors (؊52.1 ؎ 1.32 mV, n ؍ 43). Analysis of the I tail (using a variable amplitude and duration of the deand hyperpolarizing prepulses as well as an analysis of the time constant of the membrane currents during voltage steps) showed that the I tail in oligodendrocytes arise from a larger shift of K ؉ across their membrane than in other cell types. As calculated from the Nernst equation, changes in V rev revealed significantly larger accumulation of the extracellular K ؉ concentration ([K ؉ ] e ) around oligodendrocytes than around astrocytes. The application of 50 mM K ؉ or hypotonic solution, used to study the effect of cell swelling on the changes in [K ؉ ] e evoked by a depolarizing prepulse, produced in astrocytes an increase in [K ؉ ] e of 201% and 239%, respectively. In oligodendrocytes, such increases (22% and 29%) were not found. We conclude that K ؉ tail currents, evoked by a larger accumulation of K ؉ in the vicinity of the oligodendrocyte membrane, could result from a smaller extracellular space (ECS) volume around oligodendrocytes than around astrocytes. Thus, in addition to the clearance of K ؉ from the ECS performed by astrocytes, the presence of the K ؉ tail currents in oligodendrocytes indicates that they might also contribute to efficient K ؉ homeostasis.