20 research outputs found
Histamine can be Formed and Degraded in the Human and Mouse Heart
Histamine is metabolized by several enzymes in vitro and in vivo. The relevance of this
metabolism in the mammalian heart in vivo is unclear. However, histamine can exert
positive inotropic effects (PIE) and positive chronotropic effects (PCE) in humans via H2-
histamine receptors. In transgenic mice (H2-TG) that overexpress the human H2 receptor in
cardiomyocytes but not in wild-type littermate mice (WT), histamine induced PIE and PCE
in isolated left or right atrial preparations. These H2-TG were used to investigate the
putative relevance of histamine degrading enzymes in the mammalian heart. Histidine, the
precursor of histamine, increased force of contraction (FOC) in human atrial preparations.
Moreover, histamine increased the phosphorylation state of phospholamban in human
atrium. Here, we could detect histidine decarboxylase (HDC) and histamine itself in
cardiomyocytes of mouse hearts. Moreover, our data indicate that histamine is subject
to degradation in the mammalian heart. Inhibition of the histamine metabolizing enzymes
diamine oxidase (DAO) and monoamine oxidase (MAO) shifted the concentration response
curves for the PIE in H2-TG atria to the left. Moreover, activity of histamine metabolizing
enzymes was present in mouse cardiac samples as well as in human atrial samples. Thus,
drugs used for other indication (e.g. antidepressants) can alter histamine levels in the heart.
Our results deepen our understanding of the physiological role of histamine in the mouse
and human heart. Our findings might be clinically relevant because we show enzyme
targets for drugs to modify the beating rate and force of the human heart
Mechanisms of Systolic Cardiac Dysfunction in PP2A, PP5 and PP2AxPP5 Double Transgenic Mice
As part of our ongoing studies on the potential pathophysiological role of serine/threonine phosphatases (PP) in the mammalian heart, we have generated transgenic mice with cardiac muscle cell-specific overexpression of PP2Acα (PP2A) and PP5 (PP5). For further studies we crossbred PP2A and PP5 mice to obtain PP2AxPP5 double transgenic mice (PP2AxPP5, DT) and compared them with littermate wild-type mice (WT) serving as a control. The mortality of DT mice was greatly enhanced vs. other genotypes. Cardiac fibrosis was noted histologically and mRNA levels of collagen 1α, collagen 3α and fibronectin 1 were augmented in DT. DT and PP2A mice exhibited an increase in relative heart weight. The ejection fraction (EF) was reduced in PP2A and DT but while the EF of PP2A was nearly normalized after β-adrenergic stimulation by isoproterenol, it was almost unchanged in DT. Moreover, left atrial preparations from DT were less sensitive to isoproterenol treatment both under normoxic conditions and after hypoxia. In addition, levels of the hypertrophy markers atrial natriuretic peptide and B-type natriuretic peptide as well as the inflammation markers interleukin 6 and nuclear factor kappa B were increased in DT. PP2A enzyme activity was enhanced in PP2A vs. WT but similar to DT. This was accompanied by a reduced phosphorylation state of phospholamban at serine-16. Fittingly, the relaxation times in left atria from DT were prolonged. In summary, cardiac co-overexpression of PP2A and PP5 were detrimental to animal survival and cardiac function, and the mechanism may involve dephosphorylation of important regulatory proteins but also fibrosis and inflammation
Protein phosphatase 2A improves cardiac functional response to ischemia and sepsis
Reversible protein phosphorylation is a posttranslational modification of regulatory proteins involved in cardiac signaling pathways. Here, we focus on the role of protein phosphatase 2A (PP2A) for cardiac gene expression and stress response using a transgenic mouse model with cardiac myocyte-specific overexpression of the catalytic subunit of PP2A (PP2A-TG). Gene and protein expression were assessed under basal conditions by gene chip analysis and Western blotting. Some cardiac genes related to the cell metabolism and to protein phosphorylation such as kinases and phosphatases were altered in PP2A-TG compared to wild type mice (WT). As cardiac stressors, a lipopolysaccharide (LPS)-induced sepsis in vivo and a global cardiac ischemia in vitro (stop-flow isolated perfused heart model) were examined. Whereas the basal cardiac function was reduced in PP2A-TG as studied by echocardiography or as studied in the isolated work-performing heart, the acute LPS- or ischemia-induced cardiac dysfunction deteriorated less in PP2A-TG compared to WT. From the data, we conclude that increased PP2A activity may influence the acute stress tolerance of cardiac myocytes
Vascular smooth muscle and nitric oxide synthase
ABSTRACT The concept of endothelium-derived relaxing factor (EDRF) put forward in 1980 by Furchgott and Zawadzki implies that nitric oxide (NO) produced by NO synthase (NOS) in the endothelium diffuses to the underlying vascular smooth muscle, where it modulates vascular tone as well as vascular smooth muscle cell (VSMC) proliferation by increasing cGMP formation with subsequent activation of cGMP-dependent protein kinase. According to this concept, VSMC do not express NOS by themselves. This attractive, simple scheme is now under considerable debate. To address this issue, we designed this study with the use of a novel supersensitive immunocytochemical technique of signal amplification with tyramide and electron microscopic immunogold labeling complemented with Western blotting, as in our recent studies demonstrating NOS in the myocardial and skeletal muscles. We provide the first evidence that, in contrast to the currently accepted view, VSMC in various blood vessels express all three NOS isoforms depending on the blood vessel type. These findings suggest an alternative mechanism by which local NOS expression may modulate vascular functions in an endothelium-independent manner.