bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of repeated episodes of reversible myocardial ischemia on myocardial blood flow and function in humans
Authors: Barnes Edward , Dutka David P. , Khan Masood , Camici Paolo G. , Hall Roger J.
Published: March 2015

Nine patients with coronary artery disease and normal left ventricular (LV) function underwent two episodes of dobutamine-induced ischemia to determine whether repeated episodes of ischemia lead to cumulative stunning. Positron emission tomography (PET) and oxygen 15-labeled H2O was used to assess myocardial blood flow (MBF) at baseline, peak stress, and after stress for each ischemic episode. Quantitative echocardiographic assessment of global ejection fraction (EF) and regional systolic function (SF) was performed at rest and regular intervals after dobutamine. SF was assessed for regions subtended by a coronary artery with a >70% diameter stenosis. Both EF and SF were more severely impaired 45 min after the second episode of stress compared with 45 min after the first (both P < 0.01), despite no difference in duration of the two dobutamine infusions or MBF at peak stress (1.72 vs. 1.69). After both episodes of ischemia, when LV function was impaired but subsequently recovered, MBF (1.15 ± 0.39 and 1.20 ± 0.43, respectively) was no different to baseline MBF (1.02 ± 0.35), confirming that repeated episodes of dobutamine-induced ischemia lead to cumulative myocardial stunning.
Tumor necrosis factor-α-induced leukocyte adhesion and microvessel permeability
Authors: Zeng Min , Zhang Hong , Lowell Clifford , He Pingnian
Published: March 2015

The objective of this study was to investigate whether leukocyte adhesion and/or emigration are critical steps in increased microvessel permeability during acute inflammation. To conduct this study, we combined autologous blood perfusion with a single microvessel perfusion technique, which allows microvessel permeability to be measured precisely after the endothelium has interacted with blood-borne stimuli. Experiments were carried out in intact venular microvessels in rat mesenteries. Firm attachment of leukocytes to endothelial cells was induced by intravenous injection of TNF-α (3.5 μg/kg) and resuming autoperfusion in a precannulated microvessel. Leukocyte emigration was facilitated by superfusion of formyl-Met-Leu-Phe-OH. Microvessel permeability was measured as hydraulic conductivity ( Lp) or the solute permeability coefficient to tetramethylrhodamine isothiocyanate-labeled α-lactalbumin before and after leukocyte adhesion and emigration in individually perfused microvessels. We found that perfusion of a microvessel with TNF-α did not affect basal microvessel permeability, but intravenous injection of TNF-α caused significant leukocyte adhesion. However, the significant leukocyte adhesion and emigration did not cause corresponding increases in either Lpor solute permeability. Thus our results suggest that leukocyte adhesion and emigration do not necessarily increase microvessel permeability and the mechanisms that regulate the adhesion process act independently from mechanisms that regulate permeability. In addition, silver staining of endothelial boundaries demonstrated that leukocytes preferentially adhere at the junctions of endothelial cells. The appearance of the silver lines indicates that the TNF-α-induced firm adhesion of leukocyte to microvessel walls did not involve apparent changes in the junctional structure of endothelial cells, which is consistent with the results of permeability measurements.
Involvement of Na+/Ca2+exchanger in endothelial NO production and endothelium-dependent relaxation
Authors: Schneider Jean-Christophe , El Kebir Driss , Chéreau Christiane , Mercier Jean-Christophe , Dall'Ava-Santucci Josette , Dinh-Xuan A. Tuan
Published: March 2015

Endothelial nitric oxide (NO) synthase (eNOS) is controlled by Ca2+/calmodulin and caveolin-1 in caveolae. It has been recently suggested that Na+/Ca2+exchanger (NCX), also expressed in endothelial caveolae, is involved in eNOS activation. To investigate the role played by NCX in NO synthesis, we assessed the effects of Na+loading (induced by monensin) on rat aortic rings and cultured porcine aortic endothelial cells. Effect of monensin was evaluated by endothelium-dependent relaxation of rat aortic rings in response to acetylcholine and by real-time measurement of NO release from cultured endothelial cells stimulated by A-23187 and bradykinin. Na+loading shifted the acetylcholine concentration-response curve to the left. These effects were prevented by pretreatment with the NCX inhibitors benzamil and KB-R7943. Monensin potentiated Ca2+-dependent NO release in cultured cells, whereas benzamil and KB-R7943 totally blocked Na+loading-induced NO release. These findings confirm the key role of NCX in reverse mode on Ca2+-dependent NO production and endothelium-dependent relaxation.
Ca2+loading and adrenergic stimulation reveal male/female differences in susceptibility to ischemia-reperfusion injury
Authors: Cross Heather R. , Murphy Elizabeth , Steenbergen Charles
Published: March 2015

To compare ischemia-reperfusion injury in males versus females under hypercontractile conditions, perfused hearts from 129J mice pretreated with 3 mmol/l Ca2+or 10−8mol/l isoproterenol ± 10−6mol/l Nω-nitro-l-arginine methyl ester (l-NAME) were subjected to 20 min of ischemia and 40 min of reperfusion while31P NMR spectra were acquired. Basal contractility increased equivalently in female versus male hearts with isoproterenol- or Ca2+treatment. Injury was equivalent in untreated male versus female hearts but was greater in isoproterenol or Ca2+-treated male than female hearts, as indicated by lower postischemic contractile function, ATP, and PCr. Endothelial nitric oxide (NO) synthase (eNOS) expression was higher in female than male hearts, neuronal NOS (nNOS) did not differ, and inducible NOS (iNOS) was undetectable. Ischemic NO production was higher in female than male hearts, andl-NAME increased injury in female isoproterenol-treated hearts. In summary, isoproterenol or high Ca2+pretreatment increased ischemia-reperfusion injury in males more than females. eNOS expression and NO production were higher in female than male hearts, and l-NAME blocked female protection. Females were therefore protected from the detrimental effects of adrenergic stimulation and Ca2+loading via a NOS-mediated mechanism.
Role of the area postrema in angiotensin II modulation of baroreflex control of heart rate in conscious mice
Authors: Xue Baojian , Gole Hope , Pamidimukkala Jaya , Hay Meredith
Published: March 2015

This study reports the effects of angiotensin II (ANG II), arginine vasopression (AVP), phenylephrine (PE), and sodium nitroprusside (SNP) on baroreflex control of heart rate in the presence and absence of the area postrema (AP) in conscious mice. In intact, sham-lesioned mice, baroreflex-induced decreases in heart rate due to increases in arterial pressure with intravenous infusions of ANG II were significantly less than those observed with similar increases in arterial pressure with PE (slope: −3.0 ± 0.9 vs. −8.1 ± 1.5 beats · min−1 · mmHg−1). Baroreflex-induced decreases in heart rate due to increases in arterial pressure with intravenous infusions of AVP were the same as those observed with PE in sham animals (slope: −5.8 ± 0.7 vs. −8.1 ± 1.5 beats · min−1 · mmHg−1). After the AP was lesioned, the slope of baroreflex inhibition of heart rate was the same whether pressure was increased with ANG II, AVP, or PE. The slope of the baroreflex-induced increases in heart rate due to decreases in arterial blood pressure with SNP were the same in sham- and AP-lesioned animals. These results indicate that, similar to other species, in mice the ability of ANG II to acutely reset baroreflex control of heart rate is dependent on an intact AP.
Threshold effects of respiratory muscle work on limb vascular resistance
Authors: Sheel A. William , Derchak P. Alexander , Pegelow David F. , Dempsey Jerome A.
Published: March 2015

The purpose of this study was to determine whether the human diaphragm, like limb muscle, has a threshold of force output at which a metaboreflex is activated causing systemic vasoconstriction. We used Doppler ultrasound techniques to quantify leg blood flow (QL) and utilized the changes in mouth twitch pressure (ΔPMT) in response to bilateral phrenic nerve stimulation to quantify the onset of diaphragm fatigue. Six healthy male subjects performed four randomly assigned trials of identical duration (8 ± 2 min) and breathing pattern [20 breaths/min and time spent on inspiration during the duty cycle (time spent on inspiration/total time of one breathing cycle) was 0.4] during which they inspired primarily with the diaphragm. For trials 1- 3, inspiratory resistance and effort was gradually increased [30, 40, and 50% maximal inspiratory pressure (MIP)], diaphragm fatigue did not occur, and QL, limb vascular resistance (LVR), and mean arterial pressure remained unchanged from control ( P > 0.05). The fourth trial utilized the same breathing pattern with 60% MIP and caused diaphragm fatigue, as shown by a 30 ± 12% reduction in PMT with bilateral phrenic nerve stimulation. During the fatigue trial, QL and LVR were unchanged from baseline at minute 1, but LVR rose 36% and QL fell 25% at minute 2 and by 52% and 30%, respectively, during the final minutes of the trial. Both LVR and QL returned to control within 30 s of recovery. In summary, voluntary increases in inspiratory muscle effort, in the absence of fatigue, had no effect on LVR and QL, whereas fatiguing the diaphragm elicited time-dependent increases in LVR and decreases in QL. We attribute the limb vasoconstriction to a metaboreflex originating in the diaphragm, which reaches its threshold for activation during fatiguing contractions.
Mitochondrial creatine kinase is critically necessary for normal myocardial high-energy phosphate metabolism
Authors: Spindler Matthias , Niebler Reinhard , Remkes Helga , Horn Michael , Lanz Titus , Neubauer Stefan
Published: March 2015

The individual functional significance of the various creatine kinase (CK) isoenzymes for myocardial energy homeostasis is poorly understood. Whereas transgenic hearts lacking the M subunit of CK (M-CK) show unaltered cardiac energetics and left ventricular (LV) performance, deletion of M-CK in combination with loss of sarcomeric mitochondrial CK (ScCKmit) leads to significant alterations in myocardial high-energy phosphate metabolites. To address the question as to whether this alteration is due to a decrease in total CK activity below a critical threshold or due to the specific loss of ScCKmit, we studied isolated perfused hearts with selective loss of ScCKmit (ScCKmit−/−, remaining total CK activity ∼70%) using31P NMR spectroscopy at two different workloads. LV performance in ScCKmit−/−hearts ( n = 11) was similar compared with wild-type hearts ( n = 9). Phosphocreatine/ATP, however, was significantly reduced in ScCKmit−/−compared with wild-type hearts (1.02 ± 0.05 vs. 1.54 ± 0.07, P < 0.05). In parallel, free [ADP] was higher (144 ± 11 vs. 67 ± 7 μM, P < 0.01) and free energy release for ATP hydrolysis (Δ GATP) was lower (−55.8 ± 0.5 vs. −58.5 ± 0.5 kJ/mol, P < 0.01) in ScCKmit−/−compared with wild-type hearts. These results demonstrate that M- and B-CK containing isoenzymes are unable to fully substitute for the loss of ScCKmit. We conclude that ScCKmit, in contrast to M-CK, is critically necessary to maintain normal high-energy phosphate metabolite levels in the heart.
Analysis of right ventricular function in healthy mice and a murine model of heart failure by in vivo MRI
Authors: Wiesmann Frank , Frydrychowicz Alex , Rautenberg Judith , Illinger Ralf , Rommel Eberhard , Haase Axel , Neubauer Stefan
Published: March 2015

Because of its complex geometry, assessment of right ventricular (RV) function is more difficult than it is for the left ventricle (LV). Because gene-targeted mouse models of cardiomyopathy may involve remodeling of the right heart, the purpose of this study was to develop high-resolution functional magnetic resonance imaging (MRI) for in vivo quantification of RV volumes and global function in mice. Thirty-three mice of various age were studied under isoflurane anesthesia by electrocardiogram-triggered cine-MRI at 7 T. MRI revealed close correlations between RV and LV stroke volume and cardiac output ( r = 0.97, P < 0.0001 each). Consistent with human physiology, murine RV end-diastolic and end-systolic volumes were significantly higher compared with LV volumes ( P < 0.05 each). MRI in mice with LV heart failure due to myocardial infarction revealed significant structural and functional changes of the RV, indicating RV dysfunction. Hence, MRI allows for the quantification of RV volumes and global systolic function with high accuracy and bears the potential to evaluate mechanisms of RV remodeling in mouse models of heart failure.
Diastolic right ventricular filling vortex in normal and volume overload states
Authors: Pasipoularides Ares , Shu Ming , Shah Ashish , Womack Michael S. , Glower Donald D.
Published: March 2015

Functional imaging computational fluid dynamics simulations of right ventricular (RV) inflow fields were obtained by comprehensive software using individual animal-specific dynamic imaging data input from three-dimensional (3-D) real-time echocardiography (RT3D) on a CRAY T-90 supercomputer. Chronically instrumented, lightly sedated awake dogs ( n = 7) with normal wall motion (NWM) at control and normal or diastolic paradoxical septal motion (PSM) during RV volume overload were investigated. Up to the E-wave peak, instantaneous inflow streamlines extended from the tricuspid orifice to the RV endocardial surface in an expanding fanlike pattern. During the descending limb of the E-wave, large-scale (macroscopic or global) vortical motions ensued within the filling RV chamber. Both at control and during RV volume overload (with or without PSM), blood streams rolled up from regions near the walls toward the base. The extent and strength of the ring vortex surrounding the main stream were reduced with chamber dilatation. A hypothesis is proposed for a facilitatory role of the diastolic vortex for ventricular filling. The filling vortex supports filling by shunting inflow kinetic energy, which would otherwise contribute to an inflow-impeding convective pressure rise between inflow orifice and the large endocardial surface of the expanding chamber, into the rotational kinetic energy of the vortical motion that is destined to be dissipated as heat. The basic information presented should improve application and interpretation of noninvasive (Doppler color flow mapping, velocity-encoded cine magnetic resonance imaging, etc.) diastolic diagnostic studies and lead to improved understanding and recognition of subtle, flow-associated abnormalities in ventricular dilatation and remodeling.
A 4-AP-sensitive current is enhanced by chronic carbon monoxide exposure in coronary artery myocytes
Authors: Barbé Christine , Dubuis Eric , Rochetaing Annie , Kreher Paul , Bonnet Pierre , Vandier Christophe
Published: March 2015

A physiological role of carbon monoxide has been suggested for coronary myocytes; however, direct evidence is lacking. The objective of this study was to test the effect of chronic carbon monoxide exposure on the K+ currents of the coronary myocytes. The effect of 3-wk chronic exposure to carbon monoxide was assessed on K+ currents in isolated rat left coronary myocytes by the use of the patch-clamp technique in the whole cell configuration. Moreover, membrane potential studies were performed on coronary artery rings using intracellular microelectrodes, and coronary blood flow in isolated heart preparation was recorded. Carbon monoxide did not change the amplitude of global whole cell K+ current, but it did increase the component sensitive to 1 mM 4-aminopyridine. Carbon monoxide exposure hyperpolarized coronary artery segments by ∼10 mV and, therefore, increased their sensitivity to 4-aminopyridine. This effect was associated with an enhancement of coronary blood flow. We conclude that chronic carbon monoxide increases a 4-aminopyridine-sensitive current in isolated coronary myocytes. This mechanism could, in part, contribute to hyperpolarization and to increased coronary blood flow observed with carbon monoxide.
Cardiac myocyte adenosine A2areceptor activation fails to alter cAMP or contractility: role of receptor localization
Authors: Kilpatrick Eric L. , Narayan Prakash , Mentzer Robert M. , Lasley Robert D.
Published: March 2015

Adenosine A2areceptors are found in coronary vascular tissue although, their presence in myocardium is subject to investigation. Although there have been numerous studies on adenosine A2areceptor agonist effects on contractility and cAMP levels in ventricular myocytes, these have yielded conflicting results. Negative pharmacological studies have even led to the conclusion that A2areceptors are not present in cardiac myocytes. The purpose of this study was to determine whether A2areceptors are expressed in rat ventricular myocytes and what physiological effects are mediated via activation of these receptors. Western blot analysis with a polyclonal antibody raised against a peptide sequence specific to the carboxy terminus of the A2areceptor revealed the presence of a band at ∼45 kDa. However, the immunoreactivity was located in the nonmembrane fraction of the cell lysate. The membrane fraction only exhibited an immunoreactive band ≥50 kDa. Treatment of isolated myocytes with the adenosine A2aagonist 2-[4-[(2-carboxyethyl)-phenyl]ethylamino]-5′- N-ethylcarboxamidoadenosine (CGS-21680) exerted no effects on cAMP levels or myocyte twitch amplitude. These results indicate that although rat ventricular myocytes appear to express adenosine A2areceptors, stimulation with an A2aagonist exerts no functional effects, possibly because of the subcellular localization of the A2areceptor.
Nitrate tolerance does not increase production of peroxynitrite in the heart
Authors: Csont Tamás , Csonka Csaba , Ónody Annamária , Görbe Anikó , Dux László , Schulz Richard , Baxter Gary F. , Ferdinandy Péter
Published: March 2015

Clinical studies have suggested that long-term nitrate treatment does not improve and may even worsen cardiovascular mortality, and the possible role of nitrate tolerance has been suspected. Nitrate tolerance has been recently shown to increase vascular superoxide and peroxynitrite production leading to vascular dysfunction. Nevertheless, nitrates exert direct cardiac effects independent from their vascular actions. Therefore, we investigated whether in vivo nitroglycerin treatment leading to vascular nitrate tolerance increases cardiac formation of nitric oxide (NO), reactive oxygen species, and peroxynitrite, thereby leading to cardiac dysfunction. Nitrate tolerance increased bioavailability of NO in the heart without increasing formation of reactive oxygen species. Despite elevated myocardial NO, neither cardiac markers of peroxynitrite formation nor cardiac mechanical function were affected by nitroglycerin treatment. However, serum free nitrotyrosine, a marker for systemic peroxynitrite formation, was significantly elevated in nitroglycerin-treated animals. This is the first demonstration that, although the systemic effects of nitroglycerin may be deleterious due to enhancement of extracardiac peroxynitrite formation, nitroglycerin does not result in oxidative damage in the heart.
Molecular conformation dictates signaling module formation: example of PKCε and Src tyrosine kinase
Authors: Song Changxu , Vondriska Thomas M. , Wang Guang-Wu , Klein Jon B. , Cao Xinan , Zhang Jun , Kang Y. James , D'Souza Stanley , Ping Peipei
Published: March 2015

Our laboratory has conducted multiple functional proteomic analyses to characterize the components of protein kinase C (PKC)ε cardioprotective signaling complexes and found that activation of PKCε induces dynamic modulation of these complexes. In addition, it is known that signal transduction within a complex involves the formation of modules, one of which has been shown to include PKCε and Src tyrosine kinase in the rabbit heart. However, the cellular mechanisms that define the assembly of PKCε modules remain largely unknown. To address this issue, the interactions between PKCε and Src were studied. We used recombinant proteins of wild-type PKCε (PKCε-WT) and open conformation mutants of the kinase (PKCε-AE5 and PKCε-AN59), the regulatory and catalytic domains of PKCε, along with glutathione-S-transferase (GST) fusion proteins of Src (GST-Src) and two domains of Src (GST-SH2 and GST-SH3). GST pulldown assays demonstrated that Src and PKCε are binding partners and that the interaction between PKCε and Src appears to involve multiple sites. This finding was supported for endogenous PKCε and Src in the murine heart using immunofluorescence-based confocal microscopy and coimmunoprecipitation. Furthermore, PKCε-WT and GST-Src interactions were significantly enhanced in the presence of phosphatidyl-l-serine, an activator of PKC, indicating that Src favors interaction with activated PKCε. This finding was confirmed when the PKCε-WT was replaced with PKCε-AE5 or PKCε-AN59, demonstrating that the conformation of PKCε is a critical determinant of its interactions with Src. Together, these results illustrate that formation of a signaling module between PKCε and Src involves specific domains within the two molecules and is governed by the molecular conformation of PKCε.
Nitric oxide production is maintained in exercising swine with chronic left ventricular dysfunction
Authors: Haitsma David B. , Merkus Daphne , Vermeulen Jefrey , Verdouw Pieter D. , Duncker Dirk J.
Published: March 2015

Left ventricular (LV) dysfunction caused by myocardial infarction (MI) is accompanied by endothelial dysfunction, most notably a loss of nitric oxide (NO) availability. We tested the hypothesis that endothelial dysfunction contributes to impaired tissue perfusion during increased metabolic demands as produced by exercise, and we determined the contribution of NO to regulation of regional systemic, pulmonary, and coronary vasomotor tone in exercising swine with LV dysfunction produced by a 2- to 3-wk-old MI. LV dysfunction resulted in blunted systemic and coronary vasodilator responses to ATP, whereas the responses to nitroprusside were maintained. Exercise resulted in blunted systemic and pulmonary vasodilator responses in MI that resembled the vasodilator responses in normal (N) swine following blockade of NO synthase with N ω-nitro-l-arginine (l-NNA, 20 mg/kg iv). However, l-NNA resulted in similar decreases in systemic (43 ± 3% in N swine and 49 ± 4% in MI swine), pulmonary (45 ± 5% in N swine and 49 ± 4% in MI swine), and coronary (28 ± 4% in N and 35 ± 3% in MI) vascular conductances in N and MI swine under resting conditions; similar effects were observed during treadmill exercise. Selective inhibition of inducible NO synthase with aminoguanidine (20 mg/kg iv) had no effect on vascular tone in MI. These findings indicate that while agonist-induced vasodilation is already blunted early after myocardial infarction, the contribution of endothelial NO synthase-derived NO to regulation of vascular tone under basal conditions and during exercise is maintained.
Differential effects of 5,6-EET on segmental pulmonary vasoactivity in the rabbit
Authors: Stephenson Alan H. , Sprague Randy S. , Losapio Jennifer L. , Lonigro Andrew J.
Published: March 2015

In the rabbit, 5,6-epoxyeicosatrienoic acid (EET) was reported both to dilate and to constrict pulmonary blood vessels. We propose that these seemingly contradictory results could be explained by differences in responses to 5,6-EET in large-conductance pulmonary arteries (PA) compared with smaller PA and resistance vessels. Thus we found that in rings of extralobar PA [>2-mm outside diameter (OD)], in which active tension had been increased with PGF2α, 5,6-EET produced relaxation in a concentration- and cyclooxygenase (COX)-dependent manner. In contrast, 5,6-EET increased tension in intralobar (1- to 2-mm OD) PA. Small extralobar PA (2- to 2.5-mm OD) exhibited intermediate responses. In the intact lung, the net effect of 5,6-EET (1 × 10−8–1 × 10−5M) was an increase in pulmonary vascular resistance (PVR) from 13.0 ± 0.5 to 47.8 ± 4.6 mmHg · 100 ml−1· min−1(EC505.9 ± 1.7 × 10−7M). The increase in PVR was accompanied by a 10-fold increase in perfusate thromboxane (TX)B2concentration. The 5,6-EET-induced increase in PVR was prevented with indomethacin (100 μM), a cyclooxygenase inhibitor, or ONO-3708 (20 μM), a TX/PGH2(TP) receptor antagonist, but not with OKY-046 (700 μM), a TX synthase inhibitor. These results demonstrate that although 5,6-EET dilates large extralobar PA segments in a COX-dependent manner, in the intact rabbit lung 5,6-EET produces constriction that requires synthesis of a COX-dependent agonist of the TP receptor other than TX.
Impact of anesthesia on cardiac function during echocardiography in mice
Authors: Roth David M. , Swaney James S. , Dalton Nancy D. , Gilpin Elizabeth A. , Ross John
Published: March 2015

Anesthetics provide sedation and immobility facilitating echocardiography in mice, but influence cardiac function. We studied the effects of intraperitoneal and inhaled anesthetic agents on echocardiographic measurements. Mice were anesthetized with intraperitoneal tribromoethanol (TBE), ketamine-midazolam (K/M), ketamine-xylazine (K/X), or inhaled isoflurane (Isf), and echocardiographic parameters were assessed at 5, 10, 15, and 20 min. In C57BL/6N mice, Isf produced high initial heart rates (HR) that decreased to levels comparable to TBE at 15–20 min (∼450 beats/min) and the most stable percent fractional shortening (%FS) and end-diastolic dimension (EDD). With TBE, %FS initially was low, but increased comparable to Isf (∼45%) at 15 min. K/M produced similar time trends but lower absolute values compared with TBE for all parameters. K/X produced cardiac depression evidenced by low HR and %FS, and increased EDD. Isf was the most reproducible in repeat studies at 12 days. In C57BL/6J compared with C57BL/6N mice, K/M produced higher HR, and %FS and TBE produced smaller EDD. In conclusion, anesthetic agent, timing of echocardiographic measurements, and genetic background are all critical variables during echocardiography in mice.
Scar and pulmonary expression and shedding of ACE in rat myocardial infarction
Authors: Gaertner Roger , Prunier Fabrice , Philippe Monique , Louedec Liliane , Mercadier Jean-Jacques , Michel Jean-Baptiste
Published: March 2015

We examined the topology of angiotensin-converting enzyme (ACE) mRNA expression, activity, and shedding in myocardial infarction-induced heart failure and sought to elucidate the source of the increased plasma ACE activity in this model. Three months after coronary ligature, lung, scar, and remaining viable left ventricular tissues were analyzed for ACE mRNA expression as well as tissue and solubilized ACE activity. ACE mRNA expression increased in the scar with respect to infarct severity, decreased in the lung, and remained unchanged in the left ventricle. ACE activity decreased in the lung and increased in the scar tissue and plasma. Shedding of ACE remained constant in the lung and increased in the scar. This study shows that ACE expression and activity is shifted from the pulmonary endothelium to the infarct scar tissue and that constancy of shedding in the lung and its increase in the scar are the source of the increased plasma ACE in congestive heart failure.
A mathematical model of phase 2 reentry: role of L-type Ca current
Authors: Miyoshi Shunichiro , Mitamura Hideo , Fujikura Kana , Fukuda Yukiko , Tanimoto Kojiro , Hagiwara Yoko , Ita Makoto , Ogawa Satoshi
Published: March 2015

Phase 2 reentry (P2R) is known to be one of the mechanisms of malignant ventricular arrhythmias, especially those associated with Brugada syndrome. However, little is known about the underlying mechanism for P2R. Our aim in this study was to simulate P2R in a mathematical model to enable us to understand its mechanism and identify a potential therapeutic target. A mathematical model of the L-type Ca current was composed according to whole cell current data from guinea pig ventricular myocytes recorded at 37°C. Our mathematical model was incorporated into the modified Luo-Rudy phase 2 model. We set a dispersion in transient outward current ( I to) density within the theoretical fiber, composed of 80 serially arranged epicardial cells with gap junctions and then observed the P2R. The dispersion in I todensity within an only 0.8-cm epicardial theoretical fiber generated P2R with our Ca channel but not with the original model. When the P2R developed in the theoretical fiber, the calculated extracellular field potential showed coved-type ST segment elevation. We succeeded in generating P2R in our model for the first time. The local epicardial P2R may contribute the genesis of coved-type ST segment elevation in the Brugada syndrome.
Microinjection of ANG II into paraventricular nucleus enhances cardiac sympathetic afferent reflex in rats
Authors: Zhu Guo-Qing , Patel Kuashik P. , Zucker Irving H. , Wang Wei
Published: March 2015

The aims of present study were to determine whether angiotensin II (ANG II) in the paraventricular nucleus (PVN) is involved in the central integration of the cardiac sympathetic afferent reflex and whether this effect is mediated by the ANG type 1 (AT1) receptor. While the animals were under α-chloralose and urethane anesthesia, mean arterial pressure, heart rate, and renal sympathetic nerve activity (RSNA) were recorded in sinoaortic-denervated and cervical-vagotomized rats. A cannula was inserted into the left PVN for microinjection of ANG II. The cardiac sympathetic afferent reflex was tested by electrical stimulation (5, 10, 20, and 30 Hz in 10 V and 1 ms) of the afferent cardiac sympathetic nerves or epicardial application of bradykinin (BK) (0.04 and 0.4 μg in 2 μl). Microinjection of ANG II (0.03, 0.3, and 3 nmol) into the PVN resulted in dose-related increases in the RSNA responses to electrical stimulation. The percent change of RSNA response to 20- and 30-Hz stimulation increased significantly at the highest dose of ANG II (3 nmol). The effects of ANG II were prevented by pretreatment with losartan (50 nmol) into the PVN. Microinjection of ANG II (0.3 nmol) into the PVN significantly enhanced the RSNA responses to epicardial application of BK, which was abolished by pretreatment with losartan (50 nmol) into the PVN. These results suggest that exogenous ANG II in the PVN augments the cardiac sympathetic afferent reflex evoked by both electrical stimulation of cardiac sympathetic afferent nerves and epicardial application of BK. These central effects of ANG II are mediated by AT1 receptors.
Pharmacological correction of hypothermic P50shift does not alter outcome from focal cerebral ischemia in rats
Authors: Wainwright Mark S. , Sheng Huaxin , Sato Yukie , Burkhard Mackensen G. , Steffen Robert P. , Pearlstein Robert D. , Warner David S.
Published: March 2015

Hypothermia decreases the arterial Po2at which hemoglobin is 50% saturated (P50), increasing hemoglobin O2-binding affinity. We used RSR13, a synthetic allosteric modifier of hemoglobin that increases P50, to study the role of altered hemoglobin O2-binding affinity in mild hypothermic neuroprotection. RSR13 (150 mg/kg iv) restored P50to normothermic values. Rats underwent 70 min of middle cerebral artery occlusion (MCAO) at 30.0, 34.0, or 37.5°C with hemoglobin saturation held at 98–100%. The 34.0°C group received RSR13 or vehicle before ischemia. After 7 days of recovery, infarct volumes were reduced in all hypothermic groups, without evidence of a detrimental effect on infarct size or neurological score as a result of P50correction. To examine for a beneficial effect of P50correction, ischemia duration was increased to 120 min in rats maintained at 34.0°C. Correction of P50by RSR13 did not alter cerebral infarct sizes or neurological scores. The decrease in P50, caused by mild hypothermia, could not be associated with infarct size or neurological deficit resulting from ischemic brain hypoxia in rats.
Involvement of inducible nitric oxide synthase in cardiac dysfunction with tumor necrosis factor-α
Authors: Funakoshi Hajime , Kubota Toru , Machida Yoji , Kawamura Natsumi , Feldman Arthur M. , Tsutsui Hiroyuki , Shimokawa Hiroaki , Takeshita Akira
Published: March 2015

Transgenic (TG) mice with cardiac-specific overexpression of tumor necrosis factor (TNF)-α develop dilated cardiomyopathy with myocardial inflammation. The purpose of this study was to investigate the role of nitric oxide (NO) in this mouse model of cardiomyopathy. Female TG and wild-type mice at the age of 10 wk were studied. The expression and activity of inducible NO synthase (iNOS) were significantly increased in the TG myocardium, whereas those of endothelial NOS were not altered. The majority of the iNOS protein was isolated in the interstitial cells. The selective iNOS inhibitor (1 S,5 S,6 R,7 R)- 7-chloro-3-imino-5-methyl-2-azabicyclo[4.1.0]heptane hydrochloride (ONO-1714) was used to examine the effects of iNOS induction on myocardial contractility. Echocardiography and left ventricular pressure measurements were performed. Both fractional shortening and the maximum rate of rise of left ventricular pressure were significantly suppressed in TG mice. Although ONO-1714 did not change hemodynamic parameters or contractility at baseline, it significantly improved β-adrenergic inotropic responsiveness in TG mice. These results indicate that induction of iNOS may play an important role in the pathogenesis of cardiac dysfunction in this mouse model of cytokine-induced cardiomyopathy.
Optimizing ventricular fibers: uniform strain or stress, but not ATP consumption, leads to high efficiency
Authors: Vendelin Marko , Bovendeerd Peter H. M. , Engelbrecht Jüri , Arts Theo
Published: March 2015

The aim of this study was to investigate the influence of fiber orientation in the left ventricular (LV) wall on the ejection fraction, efficiency, and heterogeneity of the distributions of developed fiber stress, strain and ATP consumption. A finite element model of LV mechanics was used with active properties of the cardiac muscle described by the Huxley-type cross-bridge model. The computed variances of sarcomere length (SLvar), developed stress (DSvar), and ATP consumption (ATPvar) have several minima at different transmural courses of helix fiber angle. We identified only one region in the used design space with high ejection fraction, high efficiency of the LV and relatively small SLvar, DSvar, and ATPvar. This region corresponds to the physiological distribution of the helix fiber angle in the LV wall. Transmural fiber angle can be predicted by minimizing SLvar and DSvar, but not ATPvar. If ATPvarwas minimized, then the transverse fiber angle was considerably underestimated. The results suggest that ATP consumption distribution is not regulating the fiber orientation in the heart.
Cardiovascular effects of hypocretin-1 in nucleus of the solitary tract
Authors: de Oliveira Cleusa V. R. , Rosas-Arellano M. Patricia , Solano-Flores L. Pastor , Ciriello John
Published: March 2015

Experiments were done in male Wistar rats to investigate the effects of microinjection of hypocretin-1 (Hcrt-1) into the nucleus of the solitary tract (NTS) on mean arterial pressure (MAP), heart rate (HR), and the baroreflex. In the first series, the distribution of Hcrt-1-like immunoreactivity (Ir) was mapped within the region of NTS. Hcrt-1 Ir was found throughout the NTS region, predominantly within the caudal dorsolateral (Slt), medial (Sm), and interstitial subnuclei of the NTS. In the second series, in α-chloralose or urethane-anesthetized rats, microinjection of Hcrt-1 (0.5–5 pmol) into the caudal NTS elicited a dose-dependent decrease in MAP and HR. A mapping of the caudal NTS region showed that the largest depressor and bradycardia responses elicited by Hcrt-1 were from sites in the Slt and Sm. In addition, doses >2.5 pmol at a small number of sites localized to the caudal commissural nucleus of NTS elicited pressor and tachycardia responses. Intravenous administration of the muscarinic receptor blocker atropine methyl bromide abolished the bradycardia response and attenuated the depressor response, whereas subsequent administration of the nicotinic receptor blocker hexamethonium bromide abolished the remaining MAP response. Finally, microinjection of Hcrt-1 into the NTS significantly potentiated the reflex bradycardia to activation of arterial baroreceptors as a result of increasing MAP by systemic injections of phenylephrine (2–4 μg/kg). These results suggest that Hcrt-1 in the NTS activates neuronal circuits that increases vagal activity to the heart, inhibits sympathetic activity to the heart and vasculature, and alters the excitability of NTS neuronal circuits that reflexly control the circulation.
Regional passive ventricular stress-strain relations during development of altered loads in chick embryo
Authors: Tobita Kimimasa , Schroder Elizabeth A. , Tinney Joseph P. , Garrison Jason B. , Keller Bradley B.
Published: March 2015

Mechanical load influences embryonic ventricular growth, morphogenesis, and function. However, little is known about changes in regional passive ventricular properties during the development of altered mechanical loading conditions in the embryo. We tested the hypothesis that regional mechanical loads are a critical determinant of embryonic ventricular passive properties. We measured biaxial passive right and left ventricular (RV and LV, respectively) stress-strain relations in chick embryos at Hamburger-Hamilton stages 21 and 27after conotruncal banding (CTB) to increase biventricular pressure load or left atrial ligation (LAL) to reduce LV volume load and increase RV volume load. In the RV, wall strains at end-diastolic (ED) pressure normalized whereas ED stresses increased after either CTB or LAL during development. In the left ventricle, both ED strain and stress normalized after CTB, whereas both remained reduced with significantly increased myocardial stiffness after LAL. These results suggest that the embryonic ventricle adapts to chronically altered mechanical loading conditions by changing specific RV and LV passive properties. Thus regional mechanical load has a critical role during cardiogenesis.
Hydrolysis of Ca2+-sensitive fluorescent probes by perfused rat heart
Authors: Scaduto Russell C. , Grotyohann Lee W.
Published: March 2015

Rat hearts were loaded with the fluorescent calcium indicators fura 2, indo 1, rhod 2, or fluo 3 to determine cytosolic calcium levels in the perfused rat heart. With fura 2, however, basal tissue fluorescence increased above anticipated levels, suggesting accumulation of intermediates of fura 2-AM deesterification. To examine this process, we separated the intermediates of the deesterification process using HPLC after incubation of fura 2-AM with tissue homogenates and after loading in the rat heart. Loading of hearts with fura 2-AM resulted in tissue levels of fura 2 free acid that were only 5% of the total heart dye content of all fura 2 species. The parent fura 2-AM form accumulated without accumulation of intermediate products. Similar results were obtained with indo 1-AM. Fluo 3 loaded very poorly in perfused hearts. Unlike other indictors, rhod 2 rapidly loaded in perfused hearts and was completely converted to the free acid form. To determine the subcellular localization of the free acid form of these indictors, mitochondria from indicator-loaded hearts were assayed for the free acid form. Approximately 75% of the total amount of rhod 2 in hearts could be recovered in isolated mitochondria. Subcellular localization of indo 1 and fura 2 was more evenly distributed between mitochondria and nonmitochondrial compartments. We conclude that measurement of calcium in the perfused rat heart using surface fluorescence with either indo 1 or fura 2 is complicated by an inconsistent accumulation of the parent ester and that the resulting signal cannot be easily calibrated using “in situ” methods using the free acid form. Rhod 2 does not display this shortcoming, but like other indicators, it also loads into the mitochondrial matrix.
Remodeling of cardiac fiber structure after infarction in rats quantified with diffusion tensor MRI
Authors: Chen Junjie , Song Sheng-Kwei , Liu Wei , McLean Mark , Allen J. Stacy , Tan Jie , Wickline Samuel A. , Yu Xin
Published: March 2015

Structural remodeling of myocardium after infarction plays a critical role in functional adaptation. Diffusion tensor magnetic resonance imaging (DTMRI) provides a means for rapid and nondestructive characterization of the three-dimensional fiber architecture of cardiac tissues. In this study, microscopic structural changes caused by MI were evaluated in Fischer 344 rats 4 wk after infarct surgery. DTMRI studies were performed on 15 excised, formalin-fixed rat hearts of both infarct (left anterior descending coronary artery occlusion, n = 8) and control (sham, n = 7) rats. Infarct myocardium exhibited increased water diffusivity (41% increase in trace values) and decreased diffusion anisotropy (37% decrease in relative anisotropy index). The reduced diffusion anisotropy correlated negatively with microscopic fiber disarray determined by histological analysis ( R = 0.81). Transmural courses of fiber orientation angles in infarct zones were similar to those of normal myocardium. However, regional angular deviation of the diffusion tensor increased significantly in the infarct myocardium and correlated strongly with microscopic fiber disarray ( R = 0.86). These results suggest that DTMRI may provide a valuable tool for defining structural remodeling in diseased myocardium at the cellular and tissue level.
P2X purinergic receptor channel expression and function in bovine aortic endothelium
Authors: Ramirez Angelina N. , Kunze Diana L.
Published: March 2015

We examined bovine aortic endothelial cells (BAECs) for the functional expression of P2X receptors, the ATP-gated cation channels. We identified the P2X subtypes present in BAECs using RT-PCR. mRNA was present for only three of seven family members: P2X4, P2X5, and P2X7. We then characterized agonist-activated currents in whole cell and outside-out patch recordings using 2-methyl-thio-ATP (MeSATP) as a P2X4 and P2X5 receptor agonist and 2′,3′- O-(4-benzoylbenzoyl)ATP (BzATP) as a P2X7 receptor agonist. MeSATP (10–20 μM) produced current with characteristics of P2X4 receptors. The current was an inwardly rectifying current, reversed near 0 mV, slowly desensitized, was not blocked by suramin (300 μM) or reactive blue (60 μM), and had a single channel conductance of 36 pS. BzATP (10–100 μM), on the other hand, activated a 9-pS channel with sustained activity in the continued presence of the agonist. BzATP-activated current was blocked by reactive blue (60 μM) and by suramin (∼50% block at 300 μM). We confirmed, by immunocytochemistry, the presence of P2X4 and P2X7 protein. The agonists failed, however, to induce significant uptake of the large molecule YO-PRO, indicating the lack of pore development that has been demonstrated for P2X7 and P2X4 in response to agonist in some cell types.
Functional reentry in cultured monolayers of neonatal rat cardiac cells
Authors: Iravanian Shahriar , Nabutovsky Yelena , Kong Chae-Ryon , Saha Sumita , Bursac Nenad , Tung Leslie
Published: March 2015

Previous studies of reentrant arrhythmias in the heart have been performed in computer models and tissue experiments. We hypothesized that confluent monolayers of cardiac cells can provide a simple, controlled, and reproducible experimental model of reentry. Neonatal rat ventricular cells were cultured on 22-mm-diameter coverslips and stained with the voltage-sensitive dye RH-237. Recordings of transmembrane potentials were obtained from 61 sites with the use of a contact fluorescence imaging system. An electrical field stimulus, followed by a point stimulus, induced 39 episodes of sustained reentry and 21 episodes of nonsustained reentry. Sustained reentry consisted of single-loop ( n = 18 monolayers) or figure-of-eight ( n = 4) patterns. The cycle length, action potential duration at 80% repolarization, and conduction velocity were (in means ± SE) 358 ± 33 ms, 118 ± 12 ms, and 12.9 ± 1.0 cm/s for single loop and 311 ± 78 ms, 137 ± 18 ms, and 7.8 ± 1.3 cm/s for figure-of-eight, respectively. Electrical termination by 6- to 13-V/cm field pulses or 15- to 20-V point stimuli was successful in 60% of the attempts. In summary, highly stable reentry can be induced, sustained for extensive periods of time, and electrically terminated in monolayers of cultured neonatal rat cardiac myocytes.
Electrical refractory period restitution and spiral wave reentry in simulated cardiac tissue
Authors: Xie Fagen , Qu Zhilin , Garfinkel Alan , Weiss James N.
Published: March 2015

Theoretical and experimental studies have shown that restitution of the cardiac action potential (AP) duration (APD) plays a major role in predisposing ventricular tachycardia to degenerate to ventricular fibrillation, whereas its role in atrial fibrillation is unclear. We used the Courtemanche human atrial cell model and the Luo-Rudy guinea pig ventricular model to compare the roles of electrical restitution in destabilizing spiral wave reentry in simulated two-dimensional homogeneous atrial and ventricular tissue. Because atrial AP morphology is complex, we also validated the usefulness of effective refractory period (ERP) restitution. ERP restitution correlated best with APD restitution at transmembrane potentials greater than or equal to −62 mV, and its steepness was a reliable predictor of spiral wave phenotype (stable, meandering, hypermeandering, and breakup) in both atrial and ventricular tissue. Spiral breakup or single hypermeandering spirals occurred when the slope of ERP restitution exceeded 1 at short diastolic intervals. Thus ERP restitution, which is easier to measure clinically than APD restitution, is a reliable determinant of spiral wave stability in simulated atrial and ventricular tissue.
Baroreflex modulation of muscle sympathetic nerve activity during cold pressor test in humans
Authors: Cui Jian , Wilson Thad E. , Crandall Craig G.
Published: March 2015

The purpose of this project was to test the hypothesis that baroreceptor modulation of muscle sympathetic nerve activity (MSNA) and heart rate is altered during the cold pressor test. Ten subjects were exposed to a cold pressor test by immersing a hand in ice water for 3 min while arterial blood pressure, heart rate, and MSNA were recorded. During the second and third minute of the cold pressor test, blood pressure was lowered and then raised by intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of the relationship between MSNA and diastolic blood pressure was more negative ( P < 0.005) during the cold pressor test (−244.9 ± 26.3 units · beat−1 · mmHg−1) when compared with control conditions (−138.8 ± 18.6 units · beat−1 · mmHg−1), whereas no significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. These data suggest that baroreceptors remain capable of modulating MSNA and heart rate during a cold pressor test; however, the sensitivity of baroreflex modulation of MSNA is elevated without altering the sensitivity of baroreflex control of heart rate.