Na(+)-Ca(2+) exchanger overexpression predisposes to reactive oxygen species-induced injury.
OBJECTIVE
In heart failure (HF), the generation of reactive oxygen species (ROS) is enhanced. It was shown that failing cardiac myocytes are more susceptible to ROS-induced damage, possibly due to increased expression of the sarcolemmal Na-Ca exchanger (NCX).


METHODS
We investigated the consequences of increased expression levels of NCX in adult rabbit ventricular cardiomyocytes (via adenovirus-mediated gene transfer, Ad-NCX1-GFP) with respect to tolerance towards ROS. After 48-h incubation, cells were monitored for morphological changes on an inverted microscope. ROS were generated via hydrogen peroxide (H(2)O(2)) (100 micromol/l) and Fe(3+)/nitrilotriacetate (Fe(3+)/NTA, 100/200 micromol/l) for 4 min and cell morphology was followed over 30 min. [Na(+)](i) and [Ca(2+)](i) in native cells were measured using SBFI-AM and Indo1-AM, respectively.


RESULTS
In native myocytes, exposure to ROS induced hypercontracture. This was accompanied by a 1.3-fold increase in diastolic Indo1 fluorescence ratio (P<0.05). Overexpression of NCX significantly enhanced development of hypercontracture. After 15 min, the percentage of cells that had undergone hypercontracture (F(hyper)) was 85+/-4% vs. only 44+/-10% in control cells (P<0.05). Inhibition of NCX-mediated Ca(2+) entry with KB-R7943 (5 micromol/l) reduced F(hyper) to 33+/-11% (P<0.05). [Na(+)](i) was increased 2.9-fold 1 min prior to hypercontracture (P<0.05).


CONCLUSIONS
ROS-induced hypercontracture is due to Ca(2+) entry via NCX which could be triggered by a concomitant substantial increase in [Na(+)](i). Elevated NCX levels predispose to ROS-induced injury, a mechanism likely contributing to myocyte dysfunction and death in heart failure.
Wagner
Stefan
S
Department of Cardiology and Pneumology, Georg-August-University Göttingen, Robert-Koch-Str 40, D-37075 Göttingen, Germany.
Seidler
Tim
T
Picht
Eckard
E
Maier
Lars S
LS
Kazanski
Victor
V
Teucher
Nils
N
Schillinger
Wolfgang
W
Pieske
Burkert
B
Isenberg
Gerrit
G
Hasenfuss
Gerd
G
Kögler
Harald
H
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D005822:Genetic Vectors / Q000008:administration & dosage; D006146:Guanidines / Q000494:pharmacology; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D006861:Hydrogen Peroxide / Q000009:adverse effects*; D007424:Intracellular Fluid / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D011817:Rabbits; D012508:Sarcolemma / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D014161:Transduction, Genetic / Q000379:methods
D000889:Anti-Arrhythmia Agents; D006146:Guanidines; D019831:Sodium-Calcium Exchanger; D013450:Sulfones; C110374:sodium-calcium exchanger 1; C093373:cariporide; D012964:Sodium; D006861:Hydrogen Peroxide; D002118:Calcium