A Na+/Ca2+ Exchanger Isoform, NCX1, Is Involved in Retinal Cell Death After N-methyl-D-aspartate Injection and Ischemia-reperfusion

We investigated the expression of Na+/Ca2+ exchanger (NCX) and the functional role of NCX in retinal damage by using NCX1-heterozygous deficient mice (NCX1(+/-)) and SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy] phenoxy]-5-ethoxyaniline), a selective NCX inhibitor in vivo. We also examined the role of NCX in oxygen-glucose deprivation (OGD) stress with a retinal ganglion cell line (RGC-5) cell culture in vitro. The expression of NCX1 was confirmed and entirely localized in retina by immunoblotting and immunohistochemistry, respectively. NCX1(+/-) mice possessed significant protection against retinal damage induced by intravitreal injection of N-methyl-D-aspartate (NMDA). SEA0400 at 3 and 10 mg/kg significantly reduced NMDA- or high intraocular pressure-induced retinal cell damage in mice. Furthermore, SEA0400 reduced the number of TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling)-positive cells and the expression of phosphorylated mitogen-activated protein kinases (ERK1/2, JNK, p38) induced by NMDA injection. In RGC-5, SEA0400 at 0.3 and 1 mu M significantly inhibited OGD-induced cell damage. OGD-induced cell damage was aggravated by ouabain (a Na+,K+-ATPase inhibitor) at 100 mu M, and this increased damage was significantly reduced by SEA0400 at 1 mu M. In conclusion, these results suggest that NCX1 may play a role in retinal cell death induced by NMDA and ischemia-reperfusion. (C) 2008 Wiley-Liss, Inc.