Biochemical and Biophysical Research Communications
Role of Na+–Ca2+ exchanger in myocardial ischemia/reperfusion injury: evaluation using a heterozygous Na+–Ca2+ exchanger knockout mouse model
Section snippets
Materials and methods
NCX KO mice. NCX knockout (KO) mice were generated as described previously [7]. Male heterozygous KO mice and wild type (WT) littermates 12 weeks old were used. All animal experiments were performed according to the Guide for the Care and Use of Laboratory Animals (NIH Publication No. 85-23, revised 1996).
Electrophysiology. Ventricular cells were prepared from adult mice hearts by standard enzymatic digestion [8]. Whole-cell membrane currents were recorded by the patch-clamp method and the
NCX current density and Western blot analysis
We previously reported that the protein content of NCX in NCX KO mice hearts was ∼50% of that in WT mice hearts [13]. To elucidate the functional activity, we examined NCX current densities from −40 to 40 mV in WT (n=9) and NCX KO ventricular cells (n=6) (Fig. 1). The densities of the reverse mode of NCX at 40 mV in ventricular cells of KO mice (0.57 ± 0.07 pA/pF) were approximately half (55.4%) compared with those of WT mice (1.04 ± 0.14 pA/pF). These results suggest that the functional activity as
Discussion
Myocardial cell injury is induced by a combination of mechanical and chemical stresses during ischemia [14]. Reoxygenation after extended periods of ischemia rapidly induces hypercontracture of cardiomyocytes [15] and aggravates the pre-existing injury [16]. The hypercontracture represents a major cause of acute lethal cell injury in the reperfused myocardium [17], [18]. It has been hypothesized that an increase in intracellular Ca2+ levels of cardiomyocytes through NCX induces the
Acknowledgements
We thank to Y. Reien for the current density analysis and R. Kobayashi, E. Fujita, M. Watanabe, M. Iida, and A. Ohkubo for technical assistance. This work was supported in part by grants from Japanese Ministry of Education, Science, Sports and Culture, and Japan Health Sciences Foundation.
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