Na+-Ca2+ 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-NCXI-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 (H2O2) (100 mumol/l) and Fe3+/nitrilotriacetate (Fe3+/NTA, 100/200 mumol/l) for 4 min and cell morphology was followed over 30 min. [Na+](i) and [Ca2+](i) in native cells were measured using SBFI-AM and Indo l-AM, respectively. Results: In native myocytes, exposure to ROS induced hypercontracture. This was accompanied by a 1.3-fold increase in diastolic Indo l 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 Ca2+ entry with KB-R7943 (5 mumol/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 Ca2+ 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. (C) 2003 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.