To determine the role of
calcium homeostasis in ischemic neuronal death, the authors used an in vitro model of
oxygen-
glucose deprivation in neuronal cell lines. Exposure of human
neuroblastoma SH-SY5Y cells to 10-to 16-hour
oxygen-
glucose deprivation decreased viability to 50% or less, and longer exposure times killed almost all cells. The death following 10-to 16-hour
oxygen-
glucose deprivation was not manifested until 24 to 72 hours after exposure. Deprivation of both
glucose and
oxygen together was required for expression of toxicity at these exposure times.
Dantrolene, which blocks the release of endoplasmic reticulum Ca2+ stores, partially protected SH-SY5Y cells from
oxygen-
glucose deprivation toxicity. The addition of
dantrolene during the deprivation phase alone produced the maximal
drug effect; no further protection was obtained by continued
drug exposure during the recovery phase. Prevention of Ca2+ influx by chelation or channel blockade or the chelation of cytosolic Ca2+ did not inhibit
oxygen-
glucose deprivation toxicity. In contrast, increasing extracellular Ca2+ or stimulating Ca2+ influx did inhibit toxicity.
Calcium measurements with
fura-2 acetoxymethylester revealed that
oxygen-
glucose deprivation caused a significant reduction in
thapsigargin-releasable endoplasmic reticular stores of Ca2+. These studies suggest that an important component of the neuronal toxicity in
cerebral ischemia is due to disruption of
calcium homeostasis, particularly to the depletion of intracellular Ca2+ stores.