¹Department of Cell Physiology & Pharmacology, University of Leicester, Leicester, UK

Correspondence: Dr R Fern, Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, University Road, Leicester LE1 9HN, UK. E-mail: rf34@leicester.ac.uk

Received 17 April 2007; Revised 17 July 2007; Accepted 9 August 2007; Published online 3 October 2007.

Abstract

Astrocytes are fundamentally important to the maintenance and proper functioning of the central nervous system. During the period of development when myelination is occurring, white matter astrocytes are particularly sensitive to ischemic injury and their failure to regulate glutamate during ischemic conditions may be an important factor in excitotoxic injury. Here, we have identified key mechanisms of injury that operate on the processes of immature white matter astrocytes during oxygen-glucose deprivation (OGD) using GFAP-GFP mice. Oxygen-glucose deprivation produced a parallel loss of astrocyte processes and somata, assessed by both the retention of GFP fluorescence within these structures and by quantitative electron microscopy. Oxygen-glucose deprivation-induced process loss was Ca²⁺ independent and had two distinct mechanisms. Substituting either extracellular Na⁺ or Cl^-, or perfusion with the Na–K–Cl co-transport blocker bumetanide, provided protection up to 40 mins of OGD but not beyond that point. HCO₃^- substitution or perfusion with 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid provided complete protection of the processes up to 60 mins of OGD. Zero-Na⁺/zero-K⁺ conditions provided complete protection from OGD-induced injury of processes and somata at all time points. We conclude that acute ischemic-type injury of immature astrocytes follows a cytotoxic ion influx mediated in part by Na–K–Cl co-transport and in part by Na⁺- and K⁺-dependent HCO₃^- transport, a mechanism that is common to both cell processes and somata. This work provides a basis on which preventative strategies may be developed to protect white matter astrocytes from ischemic injury in susceptible individuals.