Arginase modulates myocardial contractility by a nitric oxide synthase 1-dependent mechanism

Abstract

Cardiac myocytes contain two constitutive NO synthase (NOS) isoforms with distinct spatial locations, which allows for isoformspecific regulation. One regulatory mechanism for NOS is substrate (L-arginine) bioavailability. We tested the hypothesis that arginase (Arg), which metabolizes L-arginine, constrains NOS activity in the cardiac myocyte in an isoform-specific manner. Arg activity was detected in both rat heart homogenates and isolated myocytes. Although both Arg I and II mRNA and protein were present in whole heart, Arg II alone was found in isolated myocytes. Arg inhibition with S-(2-boronoethyl)-L-cysteine (BEC) augmented Ca 2؉ -dependent NOS activity and NO production in myocytes, which did not depend on extracellular L-arginine. Arg II coimmunoprecipited with NOS1 but not NOS3. Isolation of myocyte mitochondrial fractions in combination with immuno-electron microscopy demonstrates that Arg II is confined primarily to the mitochondria. Because NOS1 positively modulates myocardial contractility, we determined whether Arg inhibition would increase basal myocardial contractility. Consistent with our hypothesis, Arg inhibition increased basal contractility in isolated myocytes by a NOS-dependent mechanism. Both the Arg inhibitors N-hydroxynor-L-arginine and BEC dose-dependently increased basal contractility in rat myocytes, which was inhibited by both nonspecific and NOS1-specific NOS inhibitors N G -nitro-L-arginine methyl ester and S-methyl-L-thiocitrulline, respectively. Also, BEC increased contractility in isolated myocytes from WT and NOS3 but not NOS1 knockout mice. We conclude that mitochondrial Arg II negatively regulates NOS1 activity, most likely by limiting substrate availability in its microdomain. These findings have implications for therapy in pathophysiologic states such as aging and heart failure in which myocardial NO signaling is disrupted. mitochondria ͉ L-arginine pools ͉ spatial confinement

Arginase Inhibition by Ethylacetate Extract ofCaesalpinia sappanLignum Contributes to Activation of Endothelial Nitric Oxide Synthase

“…Furthermore, reciprocal regulation of NOS by arginase has been demonstrated in cells and organs in which NO is an important signaling molecule, including the endothelium, cardiac myocytes, penis, airway, skin, and inflammatory cells [4][5][6]10,16,[29][30][31]. It was demonstrated that arginase II activity is upregulated in atherosclerosis-prone mice and is associated with impaired endothelial NO production, endothelial dysfunction, vascular stiffness, and ultimately, aortic plaque development.…”

“…Arginase, which shares L-arginine as a substrate with eNOS, hydrolyzes L-arginine to ornithine and urea as part of the urea cycle. It is well recognized that arginase modulates NOS activity by regulating intracellular L-arginine bioavailability [4][5][6]. Thus, the balance between arginase and eNOS activities partly regulates vascular endothelial NO production.…”

Arginase II Knockout Mouse Displays a Hypertensive Phenotype Despite a Decreased Vasoconstrictory Profile

“…Instead, our findings clearly demonstrate for the first time a hypertensive phenotype in these mice when BP was assessed in the conscious animal by telemetry or under anesthesia by arterial catheterization. Despite recent findings that suggest that arginase II inhibition may be suitable therapy for heart failure, 25 we also demonstrated cardiac diastolic dysfunction and left ventricular hypertrophy in the arginase II KO mice as early as 15 weeks of age, suggesting that a lack of arginase II is not sufficient to preserve cardiac function in the face of sustained pressure overload. In comparison with the eNOS KO mice, where the MAP of 12-to 16-week-old mice was 15 mm Hg higher than the C57BL/6 strain, 26 the arginase II KO mice demonstrate a Ϸ25 mm Hg greater BP than age-matched C57BL/6 mice, suggesting a more fundamental role for arginase II than for eNOS in BP regulation.…”

L-Arginine Metabolism in the Lung: Reciprocal Regulation of the NOS and Arginase Pathways

“…Thus, there is potential for competing subcellular colocalization between these isozyme families to contribute to their respective enzyme activities. Both arginase 1 and 2 have been implicated in regulating NOS1 activity through the depletion of intracellular L-arginine [64,65]. In cultured endothelial cells arginase 2 has been demonstrated to regulate the activity of NOS3, and this regulation has been shown to take place within non-freely exchangeable Larginine pools [66,67].…”