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Keywords:

  • calcium paradox;
  • antisense;
  • nitric oxide;
  • ascorbic acid

Abstract

In some cells, Ca2+ depletion induces an increase in intracellular Ca2+ ([Ca2+]i) after reperfusion with Ca2+-containing solution, but the mechanism for the reperfusion injury is not fully elucidated. Using an antisense strategy we studied the role of the Na+-Ca2+ exchanger in reperfusion injury in cultured rat astrocytes. When astrocytes were perfused in Ca2+-free medium for 15–60 min, a persistent increase in [Ca2+]i was observed immediately after reperfusion with Ca2+-containing medium, and the number of surviving cells decreased 3–5 days latter. The increase in [Ca2+]i was enhanced by low extracellular Na+ ([Na+]o) during reperfusion and blocked by the inhibitors of the Na+-Ca2+ exchanger amiloride and 3,4-dichlorobenzamil, but not by the Ca2+ channel antagonists nifedipine, Cd2+ and Ni2+. Treatment of astrocytes with antisense, but not sense, oligodeoxynucleotide to the Na+-Ca2+ exchanger decreased Na+–Ca2+ exchanger protein level and exchange activity. The antisense oligomer attenuated reperfusion-induced increase in [Ca2+]i and cell toxicity. The Na+-Ca2+ exchange inhibitors 3,4-dichlorobenzamil and ascorbic acid protected astrocytes from reperfusion injury partially, while the stimulators sodium nitroprusside and 8-bromo-cyclic GMP and low [Na+]o exacerbated the injury. Pretreatment of astrocytes with ouabain and monensin caused similar delayed glial cell death. These findings suggest that Ca2+ entry via the Na+–Ca2+ exchanger plays an important role in reperfusion-induced delayed glial cell death.