Acute ischemic injury of astrocytes is mediated by Na-K-Cl cotransport and not Ca2+ influx at a key point in white matter development.
Cerebral palsy is a common birth disorder that frequently involves ischemic-type injury to developing white matter (WM). Dead glial cells are a common feature of this injury and here we describe a novel form of acute ischemic cell death in developing WM astrocytes. Ischemia, modeled by the withdrawal of oxygen and glucose, evoked [Ca2+]i increases and cell death in astrocytes in post-natal day 10 (P10) rat optic nerve (RON). Removing extracellular Ca2+ prevented increases in [Ca2+]i but increased the amount of cell death. Astrocytes showed rapid [Na+]i increases during ischemia and cell death was reduced to control levels by substitution of extracellular Na+ or Cl- or by perfusion with bumetanide, a selective Na-K-Cl cotransport (NKCC) blocker. Astrocytes showed marked swelling during ischemia in the absence of extracellular Ca2+, which was blocked by bumetanide. Raising the extracellular osmolarity to limit water uptake reduced ischemic astrocyte death to control levels. Ultrastructural examination showed that post-ischemic astrocytes had lost their processes and frequently were necrotic, effects partially prevented by bumetanide. At this point in development, therefore, NKCC activation in astrocytes during ischemia produces an osmo-regulatory challenge. Astrocytes can subsequently regulate their cell volume in a Ca2+-dependent fashion but this will require ATP hydrolysis and does not protect the cells against acute cell death.
Department of Neurology, University of Washington, Seattle, Washington, USA.
Robert
R
Thomas
Michael G
MG
Salter
Scott
S
Wilke
Annalise
A
Husen
Natalie
N
Allcock
Mary
M
Nivison
Aisha N
AN
Nnoli
Robert
R
Fern
D000208:Acute Disease; D000818:Animals; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology*; D001693:Biological Transport, Active; D002545:Brain Ischemia / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D020318:Rats, Long-Evans; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*
D028021:Sodium-Potassium-Chloride Symporters; D002118:Calcium