Attenuation of myocardial ischemia/reperfusion injury in mice with myocyte-specific overexpression of endothelial nitric oxide synthase.
OBJECTIVE
The role of nitric oxide (NO) in myocardial ischemia/reperfusion injury remains controversial as both NO donors and NO synthase (NOS) inhibitors have shown to be protective. We generated transgenic (TG) mice that overexpress endothelial NOS (eNOS) exclusively in cardiac myocytes to determine the effects of high cardiac NO levels on ischemia/reperfusion injury and cellular Ca(2+) homeostasis. Wild-type (WT) mice served as controls.


METHODS
Hearts were perfused in vitro and subjected to 20 min of total no-flow ischemia and 30 min of reperfusion (n=5 per group). Left ventricular function, cGMP levels and intracellular Ca(2+) transients (Ca(2+)(i)) were determined.


RESULTS
Left ventricular pressure was reduced (maximum, -33%) and basal cardiac cGMP was increased (twofold) in TG hearts, and the changes were reversed by NOS blockade with N(G)-nitro-L-arginine methyl ester (L-NAME). Relative to baseline, recovery of reperfusion contractile function was significantly better in hearts from TG (98%) than WT (51%) mice, and L-NAME abolished this effect. Heart rate and coronary perfusion pressure were not different between groups. Systolic and diastolic Ca(2+)(i) concentrations were similar in WT and TG hearts, but Ca(2+)(i) overload during early reperfusion tended to be less in TG hearts. Kinetic analysis of pressure curves and Ca(2+)(i) transients revealed a faster left ventricular diastolic relaxation and abbreviated aequorin light signals in TG hearts at baseline and during reperfusion.


CONCLUSIONS
High levels of NO/cGMP strongly protect against ischemia/reperfusion injury, the protection is largely independent of changes in Ca(2+)(i) modulation, but relates to reduced preischemic performance. Myocyte-specific NO augmentation may aid in studies of the (patho)physiological roles of cardiac-derived NO.
Brunner
Friedrich
F
Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Universitätsplatz 2, A-8010 Graz, Austria. friedrich.brunner@kfunigraz.ac.at
Maier
Robert
R
Andrew
Penelope
P
Wölkart
Gerald
G
Zechner
Rudolf
R
Mayer
Bernd
B
D000818:Animals; D002118:Calcium / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006706:Homeostasis; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009203:Myocardial Infarction / Q000201:enzymology; D015428:Myocardial Reperfusion Injury / Q000517:prevention & control*; D032383:Myocytes, Cardiac / Q000201:enzymology* / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III
D004791:Enzyme Inhibitors; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; D006152:Cyclic GMP; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester