Loading…
Activity-dependent extracellular K+ accumulation in rat optic nerve: the role of glial and axonal Na+ pumps
We measured activity-dependent changes in [K + ] o with K + -selective microelectrodes in adult rat optic nerve, a CNS white matter tract, to investigate the factors responsible for post-stimulus recovery of [K + ] o . Post-stimulus recovery of [K + ] o followed a double-exponential time course with...
Saved in:
Published in: | The Journal of physiology 2000-02, Vol.522 (3), p.427-442 |
---|---|
Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
Summary: | We measured activity-dependent changes in [K + ] o with K + -selective microelectrodes in adult rat optic nerve, a CNS white matter tract, to investigate the factors responsible for
post-stimulus recovery of [K + ] o .
Post-stimulus recovery of [K + ] o followed a double-exponential time course with an initial, fast time constant, Ï fast , of 0.9 ± 0.2 s (mean ± s.d. ) and a later, slow time constant, Ï slow , of 4.2 ± 1 s following a 1 s, 100 Hz stimulus. Ï fast , but not Ï slow , decreased with increasing activity-dependent rises in [K + ] o . Ï slow , but not Ï fast , increased with increasing stimulus duration.
Post-stimulus recovery of [K + ] o was temperature sensitive. The apparent temperature coefficients ( Q 10 , 27â37°C) for the fast and slow components following a 1 s, 100 Hz stimulus were 1.7 and 2.6, respectively.
Post-stimulus recovery of [K + ] o was sensitive to Na + pump inhibition with 50 μM strophanthidin. Following a 1 s, 100 Hz stimulus, 50 μM strophanthidin increased Ï fast and Ï slow by 81 and 464%, respectively. Strophanthidin reduced the temperature sensitivity of post-stimulus recovery of [K + ] o .
Post-stimulus recovery of [K + ] o was minimally affected by the K + channel blocker Ba 2+ (0.2 m m ). Following a 10 s, 100 Hz stimulus, 0.2 m m Ba 2+ increased Ï fast and Ï slow by 24 and 18%, respectively.
Stimulated increases in [K + ] o were followed by undershoots of [K + ] o . Post-stimulus undershoot amplitude increased with stimulus duration but was independent of the peak preceding [K + ] o increase.
These observations imply that two distinct processes contribute to post-stimulus recovery of [K + ] o in central white matter. The results are compatible with a model of K + removal that attributes the fast, initial phase of K + removal to K + uptake by glial Na + pumps and the slower, sustained decline to K + uptake via axonal Na + pumps. |
---|---|
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1111/j.1469-7793.2000.00427.x |