EFFECT OF CA2+ ON IN-VITRO ASTROCYTE INJURY

Current literature suggests that a massive influx of Ca2+ into the cel ls of the CNS induces cell damage associated with traumatic brain inju ry (TBI). Using an in vitro model for stretch-induced cell injury deve loped by our laboratory, we have investigated the role of extracellula r Ca2+ in astrocyte injury. The degree of injury was assessed by measu rement of propidium iodide uptake and release of lactate dehydrogenase . Based on results of in vivo models of TBI developed by others, our i nitial hypothesis was that decreasing extracellular Ca2+ would result in a reduction in astrocyte injury. Quite unexpectedly, our results in dicate that decreasing extracellular Ca2+ to levels observed after in vivo TBI increased astrocyte injury. Elevating the extracellular Ca2content to twofold above physiological levels (2 mM) produced a reduct ion in cell injury. The reduction in injury afforded by Ca2+ could not be mimicked with Ba2+, Mn2+, Zn2+, or Mg2+, suggesting that a Ca2+-sp ecific mechanism is involved. Using Ca-45(2+), we demonstrate that inj ury induces a rapid influx of extracellular Ca2+ into the astrocyte, a chieving an elevation in total cell-associated Ca2+ content two- to th reefold above basal levels. Pharmacological elevation of intracellular Ca2+ levels with the Ca2+ ionophore A231 87 or thapsigargin before in jury dramatically reduced astrocyte injury. Our data suggest that, con trary to popular assumptions, an elevation of total cell-associated Ca 2+ reduces astrocyte injury produced by a traumatic insult.