Cardiomyocytes from postinfarction failing rat hearts have improved ischemia tolerance

1 Clinical Chemistry Department and 2 Institute for Experimental Medical Research, Ullevål University Hospital, Oslo; 3 Center for Heart Failure Research, University of Oslo, Oslo; and 4 Department of Cardiology, Ullevål University Hospital, Oslo, Norway Submitted 31 July 2008 ; accepted in final form 23 December 2008 Altered myocardial Ca 2+ and Na + handling in congestive heart failure (CHF) may be expected to decrease the tolerance to ischemia by augmenting reperfusion Ca 2+ overload. The aim of the present study was to investigate tolerance to hypoxia-reoxygenation by measuring enzyme release, cell death, ATP level, and cell Ca 2+ 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 Ca 2+ and Na + were determined with radioactive isotopes, and free intracellular Ca 2+ concentration ([Ca 2+ ] 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 [Ca 2+ ] i than sham cells during hypoxia (423 vs. 1,766 arbitrary units at 4 h of hypoxia), and exchangeable Ca 2+ 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 Ca 2+ 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 Ca 2+ 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 Ca 2+ accumulation in CHF after reoxygenation. calcium; congestive heart failure; sodium Address for reprint requests and other correspondence: M. N. Sharikabad, Dept. of Clinical Chemistry, Ullevål Univ. Hopital, 0407 Oslo, Norw