"iDoctor – Medical Blog"

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 13 January 2012

Dursun Gündüz, Muhammad Aslam, Uwe Krieger, Lutz Becker, Mathias Grebe, …

ATP can differentially affect the micro- and macrovascular endothelial barrier. It has been shown that it can both increase and/or decrease macromolecule permeability of microvascular endothelial cells and microvessels,in vivo. We hypothesised that the barrier stabilising effect is mediated by ATP itself via P2 receptors, while barrier-disrupting effect is mediated by its metabolite adenosine via adenosine receptors.The effect of ATP, ADP, AMP and adenosine on barrier function were studied in cultured rat coronary microvascular endothelial monolayers (RCEC)in vitro, as well as in rat mesentery vessels, and in rat heartsin vivo. ATP and ADP showed a biphasic effect on permeability of RCEC monolayers with a reduction followed by a later increase in albumin permeability. The permeability decreasing effect of ATP was enhanced by ecto-nucleotidase inhibitor ARL67156 while permeability increasing effect was enhanced by apyrase, an extracellular ecto-nucleotidase. Moreover, the permeability increasing effect was abrogated by adenosine receptor antagonists, 8-phenyltheophylline (8-PT) and DMPX. Adenosine and adenosine receptor agonists 5′-(N-ethylcarboxamido)-adenosine (NECA), CGS21680, and R-PIA enhanced albumin permeability which was antagonised by 8-PT, A1, and A2but not by A3receptor antagonists. Likewise, immunofluorescence microscopy of VE-cadherin and actin showed that NECA induces a disturbance of intercellular junctions. Pre-incubation of ATP antagonised the effects of NECA on permeability, actin cytoskeleton and intercellular junctions. Similar effects of the applied substances were observed in rat mesentery artery by determining the vascular leakage using intravital microscopy as well as in rat hearts by assessing myocardial water contentsin vivo. In conclusion, the study demonstrates that in RCEC, ATP, ADP, and its metabolite adenosine play opposing roles on endothelial barrier function.

Highlights

► P2Y and adenosine A2receptor activation exert opposite effect on coronary vessels. ► ATP reduces coronary microvascular endothelial permeability via P2Y receptors. ► Adenosine increases coronary microvascular endothelial permeability via A2receptors. ► ATP functionally antagonises adenosine-induced coronary microvascular leakage.

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 12 January 2012

Chaoming Zhou, Samantha L. Cavolo, Edwin S. Levitan

The Kv4.3 transient outward current (Ito) channel, which produces early repolarization in human cardiomyocytes, is downregulated with cardiac pathology. This is evident in cultured neonatal rat cardiomyocytes in which Angiotensin II (Ang II) acts via p38 mitogen-activated protein kinase (p38K) to increase apoptosis and induce Kv4.3 mRNA destabilization to downregulate the channel protein. However, it is not understood how p38K activation, which is activated transiently for minutes, induces downstream effects hours later. Here we show that there is a second phase of p38K activation. Inhibiting this delayed p38K activation eliminated Kv4.3 mRNA destabilization. Furthermore, inhibiting endosome generation left the transient activation of p38K intact, but blocked delayed p38K activation and the Kv4.3 effect. CamKII was also found to be required for delayed p38K activation and Kv4.3 mRNA destabilization. Finally, CamKII methionine oxidation and activation are biphasic, with the delayed phase requiring endosomes. Hence, in addition to participating in channel traffic, cardiomyocyte endosomes control channel mRNA expression by mediating delayed oxidative CamKII-p38K signaling.

Highlights

► Angiotensin II induces biphasic CamKII and p38 kinase activation in cardiomyocytes. ► Delayed oxidative activation of these kinases requires endosomes. ► Endosome-dependent kinase signaling regulates Kchannel mRNA expression.

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 12 January 2012

Debra G. Wheeler, Matthew E. Joseph, Shouvik D. Mahamud, William L. Aurand, Peter J. Mohler, …

CD39 (Ectonucleoside Triphosphate Diphosphohydrolase-1; ENTPD-1) rapidly hydrolyzes ATP and ADP to AMP; AMP is hydrolyzed by ecto-5’-nucleotidase (CD73) to adenosine, an anti-thrombotic and cardiovascular protective mediator. While expression of human CD39 in a murine model of myocardial ischemia/reperfusion (I/R) injury confers cardiac protection, the translational therapeutic potential of these findings require further testing in a large animal model. To determine if transgenic expression of CD39 reduces infarct size in a swine model of myocardial ischemia/reperfusion injury. Transgenic pigs expressing human CD39 (hCD39) were generated via somatic cell nuclear transfer and characterized. Expression of hC39 in cardiac tissue was confirmed by immunoblot and immunohistochemistry. Myocardial I/R injury was induced by intracoronary balloon inflation in the left anterior descending (LAD) artery for 60 min followed by three hours of reperfusion. The ischemic area was delineated by perfusion with 5% Phthalo Blue and the myocardial infarct size was determined by triphenyl tetrazolium chloride (TTC) staining. During ischemia, the rate-pressure product was significantly lower in control versus hCD39-Tg swine. Following reperfusion, compared to littermate control swine, hCD39-Tg animals displayed a significant reduction in infarct size (hCD39-Tg: 17.2 ± 4.3 %vs. Control: 44.7 ± 5.2 %,P = 0.0025). Our findings demonstrate for the first time that the findings in transgenic mouse models translate to large animal transgenic models and validate the potential to translate CD39 into the clinical arena to attenuate human myocardial ischemia/reperfusion injury.

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 11 January 2012

Elizabeth Murphy, Cam Patterson

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 9 January 2012

Jonathan D. Cheek, Elaine E. Wirrig, Christina M. Alfieri, Jeanne F. James, Katherine E. Yutzey

Studies of human diseased aortic valves have demonstrated increased expression of genetic markers of valve progenitors and osteogenic differentiation associated with pathogenesis. Three potential mouse models of valve disease were examined for cellular pathology, morphology, and induction of valvulogenic, chondrogenic, and osteogenic markers.Osteogenesis imperfecta murine(Oim) mice, with a mutation inCol1a2,have distal leaflet thickening and increased proteoglycan composition characteristic of myxomatous valve disease.Periostinnull mice also exhibit dysregulation of the ECM with thickening in the aortic midvalve region, but do not have an overall increase in valve leaflet surface area.Klothonull mice are a model for premature aging and exhibit calcific nodules in the aortic valve hinge-region, but do not exhibit leaflet thickening, ECM disorganization, or inflammation.Oim/oimmice have increased expression of valve progenitor markersTwist1,Col2a1,Mmp13,Sox9andHapln1, in addition to increasedCol10a1andAsporinexpression, consistent with increased proteoglycan composition.Periostinnull aortic valves exhibit relatively normal gene expression with slightly increased expression ofMmp13andHapln1. In contrast,Klothonull aortic valves have increased expression ofRunx2, consistent with the calcified phenotype, in addition to increased expression ofSox9,Col10a1, andosteopontin. Together these studies demonstrate thatoim/oimmice exhibit histological and molecular characteristics of myxomatous valve disease andKlothonull mice are a new model for calcific aortic valve disease.

Highlights

► Osteogenesis imperfecta mice have myxomatous valve disease. ► Klotho null mice have calcific aortic valve disease without inflammation. ► Mouse models have differential expression of valve progenitor, cartilage and bone genes. ► Myxomatous and calcific valve disease in mice can occur without myofibroblast activation.

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 8 January 2012

William M. Chilian, Gerd Heusch

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 8 January 2012

Iris C.R.M. Kolder, Michael W.T. Tanck, Connie R. Bezzina

Sudden cardiac death (SCD) is a prevalentcauseof death in Western societies. Genome-wide association studies (GWAS) conducted over the last few years have uncovered common genetic variants modulating risk of SCD. Furthermore, GWAS studies uncovered several loci impacting on heart rate and ECG indices of conduction and repolarization, as measures of cardiac electrophysiological function and likely intermediate phenotypes of SCDrisk. We here review these recent developments and their implications for the identification of novel molecular pathways underlying normal electrophysiological function and susceptibility to SCD.

Highlights

► A heritable component modulates electrophysiological traits and susceptibility to SCD. ► GWAS uncovered common genetic variants at multiple loci modulating ECG indices. ► GWAS has started to uncover common genetic variants impacting on SCD risk. ► Further work is required to understand the mechanisms associated with these loci. ► Much of the heritability of these traits remains unexplained.

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 8 January 2012

William M. Chilian, Gerd Heusch

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 3 January 2012

Eirini Kefaloyianni, Li Bao, Michael J. Rindler, Miyoun Hong, Tejaskumar Patel, …

Since ion channels move electrical charge during their activity, they have traditionally been studied using electrophysiological approaches. This was sometimes combined with mathematical models, for example with the description of the ionic mechanisms underlying the initiation and propagation of action potentials in the squid giant axon by Hodgkin and Huxley. The methods for studying ion channels also have strong roots in protein chemistry (limited proteolysis, the use of antibodies, etc.). The advent of the molecular cloning and the identification of genes coding for specific ion channel subunits in the late 1980′s introduced a multitude of new techniques with which to study ion channels and the field has been rapidly expanding ever since (e.g. antibody development against specific peptide sequences, mutagenesis, the use of gene targeting in animal models, determination of their protein structures) and new methods are still in development. This review focuses on techniques commonly employed to examine ion channel function in a electrophysiological laboratory. The focus is on the KATPchannel, but many of the techniques described are also used to study other ion channels.

Highlights

► We review methods for measuring KATPchannel in cardiac muscle ► Methods covered include electrophysiological approaches and mRNA and protein expression ► Other methods discussed include trafficking, complex formation and genetic approaches

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Available online 2 January 2012

Keith D. Garlid, Andrew P. Halestrap

The mitochondrial ATP-dependent Kchannel (mitoKATP) is widely considered by many to play a central role in cardioprotection by ischemic and pharmacological preconditioning and by ischemic postconditioning. Nevertheless, several laboratories have questioned the existence of mitoKATP. This article summarizes the evidence for and against and addresses two key questions: How strong is the evidence for the presence of a KATPchannel in mitochondria? Are the pharmacological agents used to modulate mitoKATPactivity sufficiently specific to allow the role of these channels in cardioprotection to be established?