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 -. Previous studies have shown that Na+-blockade during anoxia was in adequate in preserving K+-loss. We hypothesized that run down of the K+-gradient during anoxia/Na+-channel inhibition proceeds in conjunction with an anion and more specifically 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 2mM), axonal membrane potential (V m) decreased to 42 +/- 11% of control, and to 73 +/- 11% in the presence of TTX (1 muM). TTX + DIDS 500muM (a broad spectrum anion transport blocker) abolished anoxic depolarization (95 +/- 8%). Inhibition of the K-Cl cotransporter (KCC) (furosemide 100muM) together with TTX was also more effective than TTX alone (84 +/- 14%). Compound action potential (CAP) area recovered to 26 +/- 6% of control after 1 h anoxia. KCC blockade (furosemide 10muM) improved outcome (40 +/- 4%) and TTX (100nM) was even more effective (74 +/- 12%). In contrast, the Cl- channel blocker niflumic acid (50 muM) worsened injury (6 +/- 1%). Co-application of TTX (100 nM) + furosemide (10 muM) 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 of during anoxia contribute to injury, possibly due cellular volume changes and disruption of axo-glial integrity, leading to propagation failure and distortion of fiber conduction velocities.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/26419 |
| Date | January 2003 |
| Creators | Malek, Sameh A |
| Contributors | Stys, P. K., |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 102 p. |
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