Pharmacological evidence that the activation of the Na + ‐Ca 2+ exchanger protects C6 glioma cells during chemical hypoxia

In C6 glioma cells exposed to chemical hypoxia a massive release of lactate dehydrogenase (LDH) occurred at 3 and 6 h, coupled with an increased number of propidium‐iodide positive dead cells. Extracellular Na + removal, which activates the Na + ‐Ca 2+ exchanger as a Na + efflux pathway and prevents Na + entrance, significantly reduced LDH release and the number of propidium iodide positive C6 cells. During chemical hypoxia, in the presence of extracellular Na + ions, a progressive increase of [Ca 2+ ] i occurred; in the absence of extracellular Na + ions [Ca 2+ ] i was enhanced to a greater extent. The blockade of the Na + ‐Ca 2+ exchanger by the amiloride derivative 5‐(N‐4‐chlorobenzyl)‐2′,4′‐dimethylbenzamil (CB‐DMB), lanthanum (La 3+ ) and the Ca 2+ chelator EGTA, completely reverted the protective effect exerted by the removal of Na + ions on C6 glioma cells exposed to chemical hypoxia. The inhibition of the Na + ‐Ca 2+ antiporter enhanced chemical hypoxia‐induced LDH release when C6 glioma cells were incubated in the presence of physiological concentrations of extracellular Na + ions (145 m M ), suggesting that the blockade of the Na + ‐Ca 2+ antiporter during chemical hypoxia can lead to increased cell damage. Collectively, these results suggest that activation of the Na + ‐Ca 2+ exchanger protects C6 glioma cells exposed to chemical hypoxia, whereas its pharmacological blockade can exacerbate cellular injury. British Journal of Pharmacology (1997) 121 , 303–309; doi: 10.1038/sj.bjp.0701092