The Na+-Ca2+ exchanger is essential for embryonic heart development in mice

The cardiac Na+-Ca2+ exchanger 1 (NCX1) is thought to be the major calcium extrusion mechanism and to play an important role in the regulation of intr acellular calcium in the heart. The Na+-Ca2+ exchanger is particularly abun dant in the heart, although it is found in a variety of other tissues. To i nvestigate the role of NCX1, we have generated NCX1-deficient mice. Mice he terozygous for the NCX1 mutation showed no discernable phenotype, grew norm ally, and were fertile; however, no viable homozygote was observed among 17 5 offspring obtained from intercrosses of heterozygotes. All the homozygous mutant mice died in utero before E10.5. Morphological analysis indicated t hat homozygotes of NCX1 mutation at E9.5 died with an underdeveloped heart with a dilated pericardium. Microscopic analysis of these embryos showed my ocardial cell loss due to apoptosis. The apoptosis was first observed in E8 .5 mutant heart. Areas outside the heart appeared normal in the mutant embr yos at E8.5. In contrast, at E9.0, various regions of mutant embryos showed extensive cell loss. These results suggest that mutant embryos die owing t o cardiac abnormalities caused by apoptotic cell loss, indicating that NCX1 is essential for normal development of the heart.