A concerted role of Na+-K+-Cl- cotransporter and Na+/Ca2+ exchanger in ischemic damage

Na+-K+-Cl- cotransporter isoform 1 (NKCC1) and Na+/Ca2+ exchanger isoform 1 (NCX1) were expressed in cortical neurons. Three hours of oxygen and glucose deprivation (OGD) significantly increased expression of full-length NCX1 protein (similar to 116 kDa), which remained elevated during 1 to 21 h reoxygenation (REOX) and was accompanied with concurrent cleavage of NCX1. Na+/Ca2+ exchanger isoform 1 heterozygous (NCX1(+/-)) neurons with similar to 50% less of NCX1 protein exhibited similar to 64% reduction in NCX-mediated Ca2+ influx. Expression of NCX1 and NKCC1 proteins was reduced in double heterozygous (NCX1(+/-)/NKCC1(+/-)) neurons. NCX-mediated Ca2+ influx was nearly abolished in these neurons. Three-hour OGD and 21-h REOX caused similar to 80% mortality rate in NCX1(+/+) neurons and in NCX1(+/-) neurons. In contrast, NKCC1(+/-) neurons exhibited similar to 45% less cell death. The lowest mortality rate was found in NCX1(+/-)/NKCC1(+/-) neurons (similar to 65% less neuronal death). The increased tolerance to ischemic damage was also observed in NCX1(+/-)/NKCC1(+/-) brains after transient cerebral ischemia. NCX1(+/-)/NKCC1(+/-) mice had a significantly reduced infarct volume at 24 and 72 h reperfusion. In conclusion, these data suggest that NKCC1 in conjunction with NCX1 plays a role in reperfusion-induced brain injury after ischemia.