Intracellular calcium and cell death during ischemia in neonatal rat white matter astrocytes in situ

The major pathological correlate of cerebral palsy is ischemic injury of CNS white matter. Histological studies show early injury of glial cells and axons. To investigate glial cell injury, I monitored intracellular Ca2+ and cell viability in fura-2-loaded neonatal rat white matter glial cells during ischemia. Fura-2 fixation combined with immunohistochemistry revealed that fura-2-loaded cells were GFAP+/O4(-) and were therefore a population of neonatal white matter astrocytes. Significant ischemic Ca2+ influx was found, mediated by both L- and T-type voltage-gated Ca2+ channels. Ca2+ influx via T-type channels was the most important factor during the initial stage of ischemia and was associated with significant cell death within 10-20 min of the onset of ischemia. The Na+-Ca2+ exchanger acted to remove cytoplasmic Ca2+ throughout the ischemic and recovery periods. Neither the release of Ca2+ from intracellular stores nor influx via glutamate-gated channels contributed to the rise in intracellular Ca2+ during ischemia. Ischemic cell death was reduced significantly by removing extracellular Ca2+ or by blocking voltage-gated Ca2+ channels. The exclusively voltage-gated Ca2+ channel nature of the Ca2+ influx, the role played by T-type Ca2+ channels, the protective effect of the Na+-Ca2+ exchanger, and the lack of significant Ca2+ release from intracellular stores are features of ischemia that have not been reported in other CNS cell types.