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Unlabelled: The role of AT2-receptors has recently been subject of considerable debate. We investigated the influence of AT2-stimulation/inhibition on myocardial endothelial NO-synthase (eNOS, NOS-III) promoter activity and eNOS protein expression. Stimulation of rat cardiomyocytes with angiotensin II (AngII) increased eNOS protein expression 3.3-fold. This was blocked by Cyclosporin A (CsA). Inhibition of the AT1-receptor did not reduce AngII-mediated eNOS protein expression, whereas AT2 stimulation increased it 2.4-fold and AT2 inhibition suppressed it. The modulatory effects of the AT2-receptor on eNOS expression was confirmed in mice with a genetic deletion of the AT2-receptor (AT2-KO). In gel shift assays two putative NF-AT sites in a 1.6 kb eNOS promoter fragment showed NF-AT binding and a supershift by NF-AT2(-c1)-specific antibodies. Stimulation of transfected cells with AngII or specific AT2-receptor agonists resulted in a significant increase in eNOS promoter activity, which was blocked by CsA, MCIP1, and mutation of an upstream NF-AT site., Conclusion: 1) AngII-stimulation of the myocardium, both in vivo and in vitro, is accompanied by increased expression of eNOS. 2) This effect is mediated by the calcineurin pathway and is induced by the AT2-receptor. 3) These results define a calcineurin/NF-AT/eNOS pathway as downstream effector of AT2-receptor activation in the myocardium.

Background: Various molecular mechanisms are operative in altering the sarcomeric function of the heart under increased hemodynamic workload. Expression of the atrial isoform (ALC-1) of the essential myosin light chain, a shift from alpha-myosin heavy chain (MHC) to beta-MHC, increased phosphorylation of the regulatory myosin light chains and increased troponin I (TnI) phosphorylation have been reported to modulate cardiac contractility in rodents., Methods: TO ASSESS A POSSIBLE CONTRIBUTION OF THESE SARCOMERIC PROTEINS TO CARDIAC PERFORMANCE IN HUMAN MYOCARDIAL HYPERTROPHY, TWO DIFFERENT FORMS OF CARDIAC HYPERTROPHY WERE INVESTIGATED: 19 patients with hypertropic obstructive cardiomyopathy (HOCM) and 13 patients with aortic stenosis (AS) with marked left ventricular hypertrophy and normal systolic function., Results: There was no change in MHC gene expression, regulatory myosin light chain or TnI phosphorylation status in normal heart (NH), HOCM and AS patients. However, patients with hypertrophied myocardium expressed ALC-1 that was not detectable in NH. ALC-1 protein expression correlated positively with the left ventricular ejection fraction. In patients with hypertrophied myocardium, there was a mean ALC-1 protein expression of 12.7+/-3% (range 3.6% to 32%)., Conclusion: In humans, ALC-1 expression is in vivo a powerful molecular mechanism of the sarcomere to maintain or improve myocardial contractility under increased hemodynamic demands.