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 (∼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 ∼50% less of NCX1 protein exhibited ∼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 ∼80% mortality rate in NCX1^+/+ neurons and in NCX1 ^+/- neurons. In contrast, NKCC1^+/- neurons exhibited ∼45% less cell death. The lowest mortality rate was found in NCX1 ^+/-/NKCC1^+/- neurons (∼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.