Cardiomyocytes from postinfarction failing rat hearts have improved ischemia tolerance

Sharikabad MN, Aronsen JM, Haugen E, Pedersen J, Moller AS, Mork HK, Aass HC, Sejersted OM, Sjaastad I, Brors O. Cardiomyocytes from postinfarction failing rat hearts have improved ischemia tolerance. Am J Physiol Heart Circ Physiol 296: H787-H795, 2009. First published January 9, 2009; doi:10.1152/ajpheart.00796.2008.-Altered myocardial Ca2+ and Na+ handling in congestive heart failure (CHF) may be expected to decrease the tolerance to ischemia by augmenting reperfusion Ca2+ overload. The aim of the present study was to investigate tolerance to hypoxia-reoxygenation by measuring enzyme release, cell death, ATP level, and cell Ca2+ and Na+ in cardiomyocytes from failing rat hearts. CHF was induced in Wistar rats by ligation of the left coronary artery during isoflurane anesthesia, after which cardiac failure developed within 6 wk. Isolated cardiomyocytes were cultured for 24 h and subsequently exposed to 4 h of hypoxia and 2 h of reoxygenation. Cell damage was measured as lactate dehydrogenase (LD) release, cell death as propidium iodide uptake, and ATP by firefly luciferase assay. Cell Ca2+ and Na+ were determined with radioactive isotopes, and free intracellular Ca2+ concentration ([Ca2+](i)) with fluo-3 AM. CHF cells showed less increase in LD release and cell death after hypoxia-reoxygenation and had less relative reduction in ATP level after hypoxia than sham cells. CHF cells accumulated less Na+ than sham cells during hypoxia (117 vs. 267 nmol/mg protein). CHF cells maintained much lower [Ca2+](i) than sham cells during hypoxia (423 vs. 1,766 arbitrary units at 4 h of hypoxia), and exchangeable Ca2+ increased much less in CHF than in sham cells (1.4 vs. 6.7 nmol/mg protein) after 120 min of reoxygenation. Ranolazine, an inhibitor of late Na+ current, significantly attenuated both the increase in exchangeable Ca2+ and the increase in LD release in sham cells after reoxygenation. This supports the suggestion that differences in Na+ accumulation during hypoxia cause the observed differences in Ca2+ accumulation during reoxygenation. Tolerance to hypoxia and reoxygenation was surprisingly higher in CHF than in sham cardiomyocytes, probably explained by lower hypoxia-mediated Na+ accumulation and subsequent lower Ca2+ accumulation in CHF after reoxygenation.