STIM1 plays a crucial role in Ca(2+) homeostasis, particularly in replenishing the intracellular Ca(2+) store following its depletion. In cardiomyocytes, the Ca(2+) content of the sarcoplasmic reticulum must be tightly controlled to sustain contractile activity. The presence of STIM1 in cardiomyocytes suggests that it may play a role in regulating the contraction of cardiomyocytes. The aim of the present study was to determine how STIM1 participates in the regulation of cardiac contractility. Atomic force microscopy revealed that knocking down STIM1 disrupts the contractility of cardiomyocyte-derived HL-1 cells. Ca(2+) imaging also revealed that knocking down STIM1 causes irregular spontaneous Ca(2+) oscillations in HL-1 cells. Action potential recordings further showed that knocking down STIM1 induces early and delayed afterdepolarizations. Knocking down STIM1 increased the peak amplitude and current density of T-type voltage-dependent Ca(2+) channels (T-VDCC) and shifted the activation curve toward more negative membrane potentials in HL-1 cells. Biotinylation assays revealed that knocking down STIM1 increased T-VDCC surface expression and co-immunoprecipitation assays suggested that STIM1 directly regulates T-VDCC activity. Thus, STIM1 is a negative regulator of T-VDCC activity and maintains a constant cardiac rhythm by preventing a Ca(2+) overload that elicits arrhythmogenic events.

Increased blood glucose concentrations promote reactions between glucose and proteins to form advanced glycation end-products (AGE). Circulating AGE in the blood plasma can activate the receptor for advanced end-products (RAGE), which is present on both endothelial and vascular smooth muscle cells (VSMC). RAGE exhibits a complex signaling that involves small G-proteins and mitogen activated protein kinases (MAPK), which lead to increased nuclear factor kappa B (NF-κB) activity. While RAGE signaling has been previously addressed in endothelial cells, little is known regarding its impact on the function of VSMC. Therefore, we hypothesized that RAGE signaling leads to alterations in the mechanical and functional properties of VSMC, which could contribute to complications associated with diabetes. We demonstrated that RAGE is expressed and functional in the A7r5 VSMC model, and its activation by AGE significantly increased NF-κB activity, which is known to interfere with the contractile phenotype of VSMC. The protein levels of the contraction-related transcription factor myocardin were also decreased by RAGE activation with a concomitant decrease in the mRNA and protein levels of transgelin (SM-22α), a regulator of VSMC contraction. Interestingly, we demonstrated that RAGE activation increased the overall cell rigidity, an effect that can be related to an increase in myosin activity. Finally, although RAGE stimulation amplified calcium signaling and slightly myosin activity in VSMC challenged with vasopressin, their contractile capacity was negatively affected. Overall, RAGE activation in VSMC could represent a keystone in the development of vascular diseases associated with diabetes by interfering with the contractile phenotype of VSMC through the modification of their mechanical and functional properties.

The aim of this study was to identify the role of chymase in the conversion of exogenously administered Big endothelin-1 in the mouse in vivo. Real-time polymerase chain reaction analysis detected mRNA of mucosal mast cell chymases 4 and 5, endothelin-converting enzyme 1a, and neutral endopeptidase 24.11 in pulmonary, cardiac, and aorta homogenates derived from C57BL/6J mice, with the latter tissue expressing the highest levels of both chymase isoforms. Furthermore, hydrolysis of a fluorogenic peptide substrate, Suc-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin, was sensitive to the chymase inhibitors Suc-ValPro-PheS)-Gly-X-Phe-al, where X can be the amino acid Leu, Val, or Ile) (100 M) in supernatants extracted from the same tissue homogenates. In anesthetized mice, Big endothelin-1, endothelin-1 (1-31), and endothelin-1 triggered pressor responses (ED 50 s, 0.67, 0.89, and 0.16 nmol/kg) that were all reduced or potentiated by selective endothelin ET A or ET B receptor antagonists,, each at 1 mg/kg. The pressor responses to big endothelin-1 were significantly reduced by the neutral endopeptidase inhibitor thiorphan (DL-3-mercapto-2-benzylpropanoylglycine) (1 mg/kg) or the endothelin-converting enzyme inhibitorIn contrast, the responses to endothelin-1 (1-31) were abolished by thiorphan but unaffected by CGS 35066. In addition, Suc-Val-Pro-Phe P (OPh) 2 (20 -40 mg/kg) reduced, by more than 60%, the hemodynamic response to big endothelin-1 but not to endothelin-1 (1-31) and endothelin-1. Finally, intravenous administration of big endothelin-1 induced Suc-Val-Pro-Phe P -(OPh) 2 -sensitive increases in plasma-immunoreactive levels of endothelin-1 (1-31) and endothelin-1. The present study suggests that chymase plays a pivotal role in the conversion and cardiovascular properties of big endothelin-1 in vivo. , 2003). It is noteworthy that tissues derived from mice knockdown for both ECE-1 and ECE-2, which are nonviable past late gestational stages, still contain two thirds of mature endothelin peptides found in wild-type congeners, thus suggesting an important role for other pro- The authors of the present manuscript declare that there are no financial links, including consultancies with manufacturers of material or devices described in the article, and no links to the pharmaceutical industry or regulatory agencies or any other potential conflicts of interest.Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.108.142992. -788, N-[N-[N-[(2,6-dimethyl-1-piperidinyl) ABBREVIATIONS: ECE, endothelin-converting enzyme; ET, endothelin; phosphoramidon, N-(␣-rhamno-pyranosyl-oxy-hydroxy-phosphinyl)-Leu-

Over the last decade, it has been established that G-protein-coupled receptors (GPCRs) signal not only through canonical G-protein-mediated mechanisms, but also through the ubiquitous cellular scaffolds β-arrestin-1 and β-arrestin-2. Previous studies have implicated β-arrestins as regulators of actin reorganization in response to GPCR stimulation while also being required for membrane protrusion events that accompany cellular motility. One of the most critical events in the active movement of cells is the cyclic phosphorylation and activation of myosin light chain (MLC), which is required for cellular contraction and movement. We have identified the myosin light chain phosphatase Targeting Subunit (MYPT-1) as a binding partner of the β-arrestins and found that β-arrestins play a role in regulating the turnover of phosphorylated myosin light chain. In response to stimulation of the angiotensin Type 1a Receptor (AT1aR), MLC phosphorylation is induced quickly and potently. We have found that β-arrestin-2 facilitates dephosphorylation of MLC, while, in a reciprocal fashion, β-arrestin 1 limits dephosphorylation of MLC. Intriguingly, loss of either β-arrestin-1 or 2 blocks phospho-MLC turnover and causes a decrease in the contraction of cells as monitored by atomic force microscopy (AFM). Furthermore, by employing the β-arrestin biased ligand [Sar1,Ile4,Ile8]-Ang, we demonstrate that AT1aR-mediated cellular motility involves a β-arrestin dependent component. This suggests that the reciprocal regulation of MLC phosphorylation status by β-arrestins-1 and 2 causes turnover in the phosphorylation status of MLC that is required for cell contractility and subsequent chemotaxic motility.

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