The Journal of Neuroscience, May 1, 2003, 23(9):3826
Aberrant Chloride Transport Contributes to Anoxic/Ischemic White
Matter Injury
Sameh A.
Malek,
Elaine
Coderre, and
Peter K.
Stys
Ottawa Health Research Institute, Ottawa Hospital, University of
Ottawa, Canada K1Y 4K9
Rundown of ionic gradients is a central feature of white matter
anoxic injury; however, little is known about the contribution of
anions such as Cl
. We used the in
vitro rat optic nerve to study the role of aberrant Cl transport in anoxia/ischemia. After 30 min of
anoxia (NaN3, 2 mM), axonal membrane
potential (Vm) decreased to 42 ± 11%
of control and to 73 ± 11% in the presence of tetrodotoxin (TTX)
(1 µM). TTX + 4,4'-diisothiocyanatostilbene-2,2'
disulfonic acid disodium salt (500 µM), a broad spectrum
anion transport blocker, abolished anoxic depolarization (95 ± 8%). Inhibition of the K-Cl cotransporter (KCC) (furosemide 100 µM) together with TTX was also more effective than TTX
alone (84 ± 14%). The compound action potential (CAP) area
recovered to 26 ± 6% of control after 1 hr anoxia. KCC blockade (10 µM furosemide) improved outcome (40 ± 4%), and
TTX (100 nM) was even more effective (74 ± 12%). In
contrast, the Cl channel blocker niflumic acid (50 µM) worsened injury (6 ± 1%). Coapplication of TTX
(100 nM) + furosemide (10 µM) was more
effective than either agent alone (91 ± 9%). Furosemide was also
very effective at normalizing the shape of the CAPs. The KCC3a isoform
was localized to astrocytes. KCC3 and weaker KCC3a was detected in
myelin of larger axons. KCC2 was seen in oligodendrocytes and within
axon cylinders. Cl gradients contribute to resting
optic nerve membrane potential, and transporter and channel-mediated
Cl fluxes during anoxia contribute to injury,
possibly because of cellular volume changes and disruption of axo-glial
integrity, leading to propagation failure and distortion of fiber
conduction velocities.
Key words:
anoxia; ischemia; axon; chloride; K-Cl
cotransporter; KCC
Copyright © 2003 Society for Neuroscience 0270-6474/03/2393826-11$05.00/0
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