Submitted on January 18, 2007
Accepted on July 18, 2007
COX-2-dependent and potentially cardioprotective effects of
negative inotropic substances released after ischemia
Katrin Birkenmeier1, Alexander Staudt2*, Wolf-Hagen Schunck3, Irka Janke1, Corina Labitzke1, Thomas Prange1, Christiane Trimpert1, Thomas Krieg2, Martin Landsberger4, Verena Stangl5, and Stephan B. Felix2
1 Innere Medizin B, Kardiologisches Forschungslabor, Universitatsklinikum Greifswald, Greifswald, Germany
2 Innere Medizin B, Universitatsklinikum Greifswald, Greifswald, Germany
3 Max-Delbruck-Zentrum, Berlin, Greifswald, Germany
4 Innere Medizin B, AG Molekulare Kardiologie, Universitatsklinikum Greifswald, Greifswald, Germany
5 Medizinische Klinik mit Schwerpunkt Kardiologie und Angiologie, Universitatsmedizin Berlin, Charite Campus Mitte, Berlin, Germany
* To whom correspondence should be addressed. E-mail: staudt{at}uni-greifswald.de.
Objective: During reperfusion, cardiodepressive factors are released from isolated rat hearts after ischemia. The present study analyzes the mechanisms by which these substances mediate their cardiodepressive effect.
Methods: After 10 min of global stop-flow ischemia, rat hearts were reperfused and coronary effluent was collected over a period of 30 s. We tested the effect of this post-ischemic effluent on systolic cell shortening and Ca++ metabolism, by application of fluorescence microscopy of field-stimulated rat cardiomyocytes stained with fura-2AM. Cells were pre-incubated with various inhibitors: e.g., the COX inhibitor indomethacin, the COX-2 inhibitors NS-398 and lumiracoxib, the COX-1 inhibitor SC-560, and the potassium (ATP) channel blocker glibenclamide. Lysates of cardiomyocytes and extracts from whole rat hearts were tested for expression of COX-2 in Western blot.
Results: In contrast to non-ischemic effluent (control), post-ischemic effluent induced a reduction of Ca++ transient und systolic cell shortening in the rat cardiomyocytes (p<0.001 vs. control). After pre-incubation of cells with indomethacin, NS-398 and lumiracoxib, the negative inotropic effect was attenuated. SC-560 did not influence the effect of post-ischemic effluent. The inducibly expressed COX-2 was detected in cardiomyocytes prepared for fluorescence microscopy. The effect of post-ischemic effluent was eliminated in applications of glibenclamide. Furthermore post-ischemic effluent significantly reduced the intracellular diastolic and systolic calcium increase (p<0.01 vs. control).
Conclusion: The cardiodepressive effect of post-ischemic effluent is COX-2-dependent and protective against Ca++ overload in the cells.
