Targeted disruption of Na+/Ca2+ exchanger gene leads to cardiomyocyte apoptosis and defects in heartbeat.
Ca(2+), which enters cardiac myocytes through voltage-dependent Ca(2+) channels during excitation, is extruded from myocytes primarily by the Na(+)/Ca(2+) exchanger (NCX1) during relaxation. The increase in intracellular Ca(2+) concentration in myocytes by digitalis treatment and after ischemia/reperfusion is also thought to result from the reverse mode of the Na(+)/Ca(2+) exchange mechanism. However, the precise roles of the NCX1 are still unclear because of the lack of its specific inhibitors. We generated Ncx1-deficient mice by gene targeting to determine the in vivo function of the exchanger. Homozygous Ncx1-deficient mice died between embryonic days 9 and 10. Their hearts did not beat, and cardiac myocytes showed apoptosis. No forward mode or reverse mode of the Na(+)/Ca(2+) exchange activity was detected in null mutant hearts. The Na(+)-dependent Ca(2+) exchange activity as well as protein content of NCX1 were decreased by approximately 50% in the heart, kidney, aorta, and smooth muscle cells of the heterozygous mice, and tension development of the aortic ring in Na(+)-free solution was markedly impaired in heterozygous mice. These findings suggest that NCX1 is required for heartbeats and survival of cardiac myocytes in embryos and plays critical roles in Na(+)-dependent Ca(2+) handling in the heart and aorta.
Wakimoto
K
K
Advanced Medical Research Department and Discovery Research Laboratory, Tanabe Seiyaku Co. Ltd., 3-16-89 Kashima, Yodogawa-ku, Osaka 532-8505, Japan.
Kobayashi
K
K
Kuro-O
M
M
Yao
A
A
Iwamoto
T
T
Yanaka
N
N
Kita
S
S
Nishida
A
A
Azuma
S
S
Toyoda
Y
Y
Omori
K
K
Imahie
H
H
Oka
T
T
Kudoh
S
S
Kohmoto
O
O
Yazaki
Y
Y
Shigekawa
M
M
Imai
Y
Y
Nabeshima
Y
Y
Komuro
I
I
D000818:Animals; D017209:Apoptosis; D001145:Arrhythmias, Cardiac / Q000235:genetics*; D005091:Exons; D006321:Heart / Q000502:physiology*; D017403:In Situ Hybridization; D051379:Mice; D008817:Mice, Mutant Strains; D009206:Myocardium / Q000166:cytology*; D010920:Placenta / Q000737:chemistry; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000737:chemistry / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics* / Q000502:physiology; D015017:Yolk Sac / Q000737:chemistry
D019408:Platelet Endothelial Cell Adhesion Molecule-1; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1