INVOLVEMENT OF NA-CA2+ EXCHANGER IN REPERFUSION-INDUCED DELAYED CELL-DEATH OF CULTURED RAT ASTROCYTES()

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 a n antisense strategy we studied the role of the Na+-Ca2+ exchanger in reperfusion injury in cultured rat astrocytes. When astrocytes were pe rfused in Ca2+-free medium for 15-60 min, a persistent increase in [Ca 2+](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+] (0)) during reperfusion and blocked by the inhibitors of the Na+-Ca2exchanger amiloride and 3,4-dichlorobenzamil, but not by the Ca2+ chan nel antagonists nifedipine, Cd2+ and Ni2+. Treatment of astrocytes wit h antisense, but not sense, oligodeoxynucleotide to the Na+-Ca2+ excha nger decreased Na+-Ca2+ exchanger protein level and exchange activity. The antisense oligomer attenuated reperfusion-induced increase in [Ca 2+](i) and cell toxicity. The Na+-Ca2+ exchange inhibitors 3,4-dichlor obenzamil and ascorbic acid protected astrocytes from reperfusion inju ry partially, while the stimulators sodium nitroprusside and 8-bromo-c yclic GMP and low [Na+](0) exacerbated the injury. Pretreatment of ast rocytes with ouabain and monensin caused similar delayed glial cell de ath. These findings suggest that Ca2+ entry via the Na+-Ca2+ exchanger plays an important role in reperfusion-induced delayed glial cell dea th.