bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of hydrogen peroxide on the membrane currents of sinoatrial node cells from rabbit heart
Authors: Guo Jiqing , Giles Wayne R. , Ward Christopher A.
Published: December 2017

The effects of H2O2 on pacemaker activity and underlying membrane currents were studied in isolated rabbit sinoatrial (SA) node cells using perforated patch current- and voltage-clamp methods. Short-term exposure (<10 min) of the nodal cells to H2O2 (200 μM) resulted in an initial shortening of spontaneous action potential cycle length (from 445 ± 60 to 398 ± 56 ms; P < 0.05) and a prolongation of action potential duration. H2O2(100 μM) significantly increased peak L-type Ca2+ current ( I Ca,L) from −384 ± 77 to −439 ± 84 pA (116 ± 2%, n = 6). Additionally, the persistent or non-inactivating component of I Ca,L was increased from −52 ± 3 to −88 ± 14 pA (174 ± 19%, n = 6). The hyperpolarization-activated current ( I f) was decreased from −228 ± 62 to −161 ± 72 pA after exposure to H2O2 ( n = 7). There were no changes in the delayed rectifier K+ current ( I K) ( n = 7). H2O2-induced Ca2+ currents were blocked by 2 μM nicardipine ( n = 6), 2 mM Ni2+ ( n = 2), and the protein kinase C (PKC) inhibitor bisindolylmaleimide (10−7 M; n = 4) but not by 20 μM tetrodotoxin. These results suggest that H2O2 can increase the spontaneous pacing rate in rabbit SA node cells by enhancing I Ca,L and that this effect is mediated by a PKC-dependent pathway.
Dynamics of action potential head-tail interaction during reentry in cardiac tissue: ionic mechanisms
Authors: Hund Thomas J. , Otani Niels F. , Rudy Yoram
Published: December 2017

In a sufficiently short reentry pathway, the excitation wave front (head) propagates into tissue that is partially refractory (tail) from the previous action potential (AP). We incorporate a detailed mathematical model of the ventricular myocyte into a one-dimensional closed pathway to investigate the effects of head-tail interaction and ion accumulation on the dynamics of reentry. The results were the following: 1) a high degree of head-tail interaction produces oscillations in several AP properties; 2) Ca2+-transient oscillations are in phase with AP duration oscillations and are often of greater magnitude; 3) as the wave front propagates around the pathway, AP properties undergo periodic spatial oscillations that produce complicated temporal oscillations at a single site; 4) depending on the degree of head-tail interaction, intracellular [Na+] accumulation during reentry either stabilizes or destabilizes reentry; and 5) elevated extracellular [K+] destabilizes reentry by prolonging the tail of postrepolarization refractoriness.
Vasodilator mechanisms in the coronary circulation of endothelial nitric oxide synthase-deficient mice
Authors: Lamping Kathryn G. , Nuno Daniel W. , Shesely Edward G. , Maeda Nobuyo , Faraci Frank M.
Published: December 2017

Previous studies have demonstrated that responses to endothelium-dependent vasodilators are absent in the aortas from mice deficient in expression of endothelial nitric oxide synthase (eNOS −/− mice), whereas responses in the cerebral microcirculation are preserved. We tested the hypothesis that in the absence of eNOS, other vasodilator pathways compensate to preserve endothelium-dependent relaxation in the coronary circulation. Diameters of isolated, pressurized coronary arteries from eNOS −/−, eNOS heterozygous (+/−), and wild-type mice (eNOS +/+ and C57BL/6J) were measured by video microscopy. ACh (an endothelium-dependent agonist) produced vasodilation in wild-type mice. This response was normal in eNOS +/− mice and was largely preserved in eNOS −/− mice. Responses to nitroprusside were also similar in arteries from eNOS +/+, eNOS +/−, and eNOS −/− mice. Dilation to ACh was inhibited by N G-nitro-l-arginine, an inhibitor of NOS in control and eNOS −/− mice. In contrast, trifluoromethylphenylimidazole, an inhibitor of neuronal NOS (nNOS), decreased ACh-induced dilation in arteries from eNOS-deficient mice but had no effect on responses in wild-type mice. Indomethacin, an inhibitor of cyclooxygenase, decreased vasodilation to ACh in eNOS-deficient, but not wild-type, mice. Thus, in the absence of eNOS, dilation of coronary arteries to ACh is preserved by other vasodilator mechanisms.
Preserved ventricular contractility in infarcted mouse heart overexpressing β2-adrenergic receptors
Authors: Du Xiao-Jun , Gao Xiao-Ming , Jennings Garry L. , Dart Anthony M. , Woodcock Elizabeth A.
Published: December 2017

Effects of cardiac specific overexpression of β2-adrenergic receptors (β2-AR) on the development of heart failure (HF) were studied in wild-type (WT) and transgenic (TG) mice following myocardial infarction (MI) by coronary artery occlusion. Animals were studied by echocardiography at weeks 7 to 8 and by catheterization at week 9 after surgery. Post-infarct mortality, due to HF or cardiac rupture, was not different among WT mice, and there was no difference in infarct size (IS). Compared with the sham-operated group (all P < 0.01), WT mice with moderate (<36%) and large (>36%) IS developed lung congestion, cardiac hypertrophy, left ventricular (LV) dilatation, elevated LV end-diastolic pressure (LVEDP), and suppressed maximal rate of increase of LV pressure (LV dP/d t max) and fractional shortening (FS). Whereas changes in organ weights and echo parameters were similar to those in infarcted WT groups, TG mice had significantly higher levels of LV contractility in both moderate (dP/d t max 4,862 ± 133 vs. 3,694 ± 191 mmHg/s) and large IS groups (dP/d t max4,556 ± 252 vs. 3,145 ± 312 mmHg/s, both P< 0.01). Incidence of pleural effusion (36% vs. 85%, P < 0.05) and LVEDP levels (6 ± 0.3 vs. 9 ± 0.8 mmHg, P < 0.05) were also lower in TG than in WT mice with large IS. Thus β2-AR overexpression preserved LV contractility following MI without adverse consequence.
Striated muscle-specific β1D-integrin and FAK are involved in cardiac myocyte hypertrophic response pathway
Authors: Pham Can G. , Harpf Alice E. , Keller Rebecca S. , Vu Hoa T. , Shai Shaw-Yung , Loftus Joseph C. , Ross Robert S.
Published: December 2017

Alterations in the extracellular matrix occur during the cardiac hypertrophic process. Because integrins mediate cell-matrix adhesion and β1D-integrin (β1D) is expressed exclusively in cardiac and skeletal muscle, we hypothesized that β1D and focal adhesion kinase (FAK), a proximal integrin-signaling molecule, are involved in cardiac growth. With the use of cultured ventricular myocytes and myocardial tissue, we found the following: 1) β1D protein expression was upregulated perinatally; 2) α1-adrenergic stimulation of cardiac myocytes increased β1D protein levels 350% and altered its cellular distribution; 3) adenovirally mediated overexpression of β1D stimulated cellular reorganization, increased cell size by 250%, and induced molecular markers of the hypertrophic response; and 4) overexpression of free β1D cytoplasmic domains inhibited α1-adrenergic cellular organization and atrial natriuretic factor (ANF) expression. Additionally, FAK was linked to the hypertrophic response as follows: 1) coimmunoprecipitation of β1D and FAK was detected; 2) FAK overexpression induced ANF-luciferase; 3) rapid and sustained phosphorylation of FAK was induced by α1-adrenergic stimulation; and 4) blunting of the α1-adrenergically modulated hypertrophic response was caused by FAK mutants, which alter Grb2 or Src binding, as well as by FAK-related nonkinase, a dominant interfering FAK mutant. We conclude that β1D and FAK are both components of the hypertrophic response pathway of cardiac myocytes.
c-Fos expression in the midbrain periaqueductal gray during static muscle contraction
Authors: Li Jianhua , Mitchell Jere H.
Published: December 2017

The periaqueductal gray (PAG) of the midbrain is involved in the autonomic regulation of the cardiovascular system. The purpose of this study was to determine if static contraction of the skeletal muscle, which increases arterial blood pressure and heart rate, activates neuronal cells in the PAG by examining Fos-like immunoreactivity (FLI). Muscle contraction was induced by electrical stimulation of the L7 and S1 ventral roots of the spinal cord in anesthetized cats. An intravenous infusion of phenylephrine (PE) was used to selectively activate arterial baroreceptors. Extensive FLI was observed within the ventromedial region (VM) of the rostral PAG, the dorsolateral (DL), lateral (L), and ventrolateral (VL) regions of the middle and caudal PAG in barointact animals with muscle contractions, and in barointact animals with PE infusion. However, muscle contraction caused a lesser number of FLI in the VM region of the rostral PAG, the DL, L, and VL regions of the middle PAG and the L and VL regions of the caudal PAG after barodenervation compared with barointact animals. Additionally, the number of FLI in the DL and L regions of the middle PAG was greater in barodenervated animals with muscle contraction than in barodenervated control animals. Thus these results indicated that both muscle receptor and baroreceptor afferent inputs activate neuronal cells in regions of the PAG during muscle contraction. Furthermore, afferents from skeletal muscle activate neurons in specific regions of the PAG independent of arterial baroreceptor input. Therefore, neuronal cells in the PAG may play a role in determining the cardiovascular responses during the exercise pressor reflex.
Significance of adenosine metabolism of coronary smooth muscle cells
Authors: Mattig Sabine , Deussen Andreas
Published: December 2017

A detailed understanding of adenosine metabolism of vascular smooth muscle cells (VSMC) is highly desirable to critically evaluate possible autocrine effects of adenosine in this cell species. Therefore, this study quantified intra- and extracellular adenosine flux rates, the transmembrane concentration gradient, and the adenosine surface concentration in porcine VSMC and, for comparison, aortic endothelial cells (PAEC). Cell-covered microcarrier beads packed in a chromatography column were superfused with a HEPES buffer. With the use of specific inhibitors of adenosine kinase (iodotubericidine, 10 μM), adenosine deaminase [ erythro-9-(2-hydroxy-3-nonyl)-adenine, 5 μM], ecto-5′-nucleotidase (α,β-methylene-adenosine 5′-diphosphate, 50 μM), and adenosine membrane transport ( n-nitrobenzylthioinosine, 1 μM), total production rates of 12.3 ± 2.7 and 7.5 ± 1.3 pmol · min−1· μl cell volume−1were obtained for VSMC and PAEC, respectively. Despite prevailing intracellular adenosine production (76 and 70% of total production, respectively), transmembrane concentration gradients under control conditions were directed toward the cytosol as a result of rapid intracellular adenosine rephosphorylation and continuous extracellular hydrolysis from 5′-AMP. Surface concentrations were ∼18 nM in VSMC and PAEC under control conditions and increased to ∼60 nM during partial inhibition of adenosine metabolism. Simultaneously, the transmembrane adenosine concentration gradient was reversed. We conclude that adenosine flux rates in VSMC and PAEC are quantitatively similar and that VSMC may influence the interstitial adenosine concentration under basal steady-state conditions.
Contribution of ventricular remodeling to pathogenesis of heart failure in rats
Authors: Brower Gregory L. , Janicki Joseph S.
Published: December 2017

We previously reported an approximately 50% incidence of rats with symptoms of congestive heart failure (CHF) at 8 wk postinfrarenal aorto-caval fistula. However, it was not clear whether compensatory ventricular remodeling could continue beyond 8 wk or whether the remaining animals would have developed CHF or died. Therefore, the intent of this study was to complete the characterization of this model of sustained volume overload by determining the morbidity and mortality and the temporal response of left ventricular (LV) remodeling and function beyond 8 wk. The findings demonstrate an upper limit to LV hypertrophy and substantial increases in LV volume and compliance, matrix metalloproteinase activity, and collagen volume fraction associated with the development of CHF. There was an 80% incidence of morbidity and mortality following 21 wk of chronic volume overload. These findings indicate that the development of CHF is triggered by marked ventricular dilatation and increased compliance occurring once the myocardial hypertrophic response is exhausted.
Role of protein phosphatases in regulation of cardiac inotropy and relaxation
Authors: Bokník Peter , Khorchidi Sascha , Bodor Geza S. , Huke Sabine , Knapp Jörg , Linck Bettina , Lüss Hartmut , Müller Frank Ulrich , Schmitz Wilhelm , Neumann Joachim
Published: December 2017

We studied the effects of the protein phosphatase (PP) inhibitor cantharidin (Cant) on time parameters and force of contraction (FOC) in isometrically contracting electrically driven guinea pig papillary muscles. We correlated the mechanical parameters of contractility with phosphorylation of the inhibitory subunit of troponin (TnI-P) and with the site-specific phosphorylation of phospholamban (PLB) at serine-16 (PLB-Ser-16) and threonine-17 (PLB-Thr-17). Cant (after 30 min) started to increase FOC (112 ± 4% of control, n = 10) and TnI-P and PLB-Thr-17 (120 ± 5 and 128 ± 7% of control) without any alteration of relaxation time. Cant (10 μM) started to increase PLB-Ser-16, but the relaxation was shortened at only 100 μM (from 140 ± 9 to 116 ± 12 ms, n = 9). Moreover, 100 μM Cant, 3 min after application, started to increase PLB-Thr-17, TnI-P, and FOC. Cant (100 μM) began to increase PLB-Ser-16 after 20 min. This was accompanied by shortening of relaxation time. Differences in protein kinase activation or different substrate specificities of PP may explain the difference in Cant-induced site-specific phosphorylation of PLB in isometrically contracting papillary muscles. Moreover, PLB-Thr-17 may be important for inotropy, whereas PLB-Ser-16 could be a major determinant of relaxation time.
Overexpression of FGF-2 increases cardiac myocyte viability after injury in isolated mouse hearts
Authors: Sheikh Farah , Sontag David P. , Fandrich Robert R. , Kardami Elissavet , Cattini Peter A.
Published: December 2017

We generated transgenic (TG) mice overexpressing fibroblast growth factor (FGF)-2 protein (22- to 34-fold) in the heart. Chronic FGF-2 overexpression revealed no significant effect on heart weight-to-body weight ratio or expression of cardiac differentiation markers. There was, however, a significant 20% increase in capillary density. Although there was no change in FGF receptor-1 expression, relative levels of phosphorylated c-Jun NH2-terminal kinase and p38 kinase as well as of membrane-associated protein kinase C (PKC)-α and total PKC-ε were increased in FGF-2-TG mouse hearts. An isolated mouse heart model of ischemia-reperfusion injury was used to assess the potential of increased endogenous FGF-2 for cardioprotection. A significant 34–45% increase in myocyte viability, reflected in a decrease in lactate dehydrogenase released into the perfusate, was observed in FGF-2 overexpressing mice and non-TG mice treated exogenously with FGF-2. In conclusion, FGF-2 overexpression causes augmentation of signal transduction pathways and increased resistance to ischemic injury. Thus, stimulation of endogenous FGF-2 expression offers a potential mechanism to enhance cardioprotection.
Morphological and membrane characteristics of spider and spindle cells isolated from rabbit sinus node
Authors: Wu Jianyi , Schuessler Richard B. , Rodefeld Mark D. , Saffitz Jeffrey E. , Boineau John P.
Published: December 2017

This study reports the comparative quantitative, morphological, and electrophysiological properties of two pacemaker cell types, spider and spindle-shaped cells, isolated from the rabbit sinoatrial node. Isolated nodal cells were studied with perforated and ruptured patch whole cell recording techniques. The basic spontaneous cycle length of the spider cells was 381 ± 12 ms, and the basic spontaneous cycle length of the spindle cells was 456 ± 17 ms ( n = 12, P < 0.05). The spider cells had a more positive maximum diastolic potential (−54 ± 1 mV) compared with the spindle cells (−68 ± 1mV, P < 0.05). The overshoot and action potential amplitudes were also smaller in the spider cells. The hyperpolarization-activated inward ( I f) current density, measured from their tail currents, was 15 ± 1.3 pA/pF for the spider cells and 9 ± 0.7 pA/pF for the spindle cells ( P < 0.01). I f current activation voltage was more positive in the spider cells than the spindle cells. Isoproterenol (1 μM) decreased the spontaneous cycle length of the spider cells by 28 ± 3% and the spindle cells by 20 ± 1.5% ( P < 0.05). Acetylcholine (0.5 μM) hyperpolarized the membrane potential of the spider cells to −86 ± 0.7mV and the spindle cells to −76 ± 0.8 mV ( P < 0.05). In summary, there are at least two distinct pacemaker cell types in the sinus node with different electrophysiological characteristics.
Adenosine-induced late preconditioning in mouse hearts: role of p38 MAP kinase and mitochondrial KATPchannels
Authors: Zhao Ting C. , Hines Denise S. , Kukreja Rakesh C.
Published: December 2017

We investigated the role of p38 mitogen-activated protein kinase (MAPK) phosphorylation and opening of the mitochondrial ATP-sensitive K+[(KATP)mito] channel in the adenosine A1receptor (A1AR)-induced delayed cardioprotective effect in the mouse heart. Adult male mice were treated with vehicle (5% DMSO) or the A1AR agonist 2-chloro- N6-cyclopentyladenosine (CCPA; 0.1 mg/kg ip). Twenty-four hours later, hearts were subjected to 30 min of global ischemia and 30 min of reperfusion in the Langendorff mode. Genistein or SB-203580 (1 mg/kg ip) given 30 min before CCPA treatment was used to block receptor tyrosine kinase or p38 MAPK phosphorylation, respectively. 5-Hydroxydecanoate (5-HD; 200 μM) was used to block (KATP)mitochannels. CCPA produced marked improvement in left ventricular function, which was partially blocked by SB-203580 and 5-HD and completely abolished with genistein. CCPA caused a reduction in infarct size (12.0 ± 2.0 vs. 30.3 ± 3.0% in vehicle), which was blocked by genistein (29.4 ± 2.3%), SB-203580 (28.3 ± 2.6%), and 5-HD (33.9 ± 2.4%). CCPA treatment also caused increased phosphorylation of p38 MAPK during ischemia, which was blocked by genistein, SB-203580, and 5-HD. The results suggest that A1AR-triggered delayed cardioprotection is mediated by p38 MAPK phosphorylation. Blockade of cardioprotection with 5-HD concomitant with decrease in p38 MAPK phosphorylation suggests a potential role of (KATP)mitochannel opening in phosphorylation and ensuing the late preconditioning effect of A1AR.
Intensity-controlled treadmill running in rats: V˙o 2 max and cardiac hypertrophy
Authors: Wisløff Ulrik , Helgerud Jan , Kemi Ole Johan , Ellingsen Øyvind
Published: December 2017

Physiological studies of long-term cardiovascular adaptation to exercise require training regimens that give robust conditioning effects and adequate testing procedures to quantify the outcome. We developed a valid and reproducible protocol for measuring maximal oxygen uptake (V˙o 2 max), which was reached at a 25° inclination with a respiratory exchange ratio > 1.05 and blood lactate > 6 mmol/l. The effect of intensity-controlled aerobic endurance training was studied in adult female and male rats that ran 2 h/day, 5 days/wk, in intervals of 8 min at 85–90% of V˙o 2 max and 2 min at 50–60% of V˙o 2 max, with adjustment of exercise level according to V˙o 2 maxevery week. After 7 wk, the increase inV˙o 2 max plateaued at 60–70% above sedentary controls. Ventricular weights and myocyte length were up 25–30% and 6–12%, respectively. Work economy, oxygen pulse, and heart rate were sufficiently changed to indicate substantial cardiovascular adaptation. The model mimics important human responses to training and could be used in future studies on cellular, molecular, and integrative mechanisms of improved cardiovascular function.
AT1 receptor blockers prevent sympathetic hyperactivity and hypertension by chronic ouabain and hypertonic saline
Authors: Zhang Jing , Leenen Frans H. H.
Published: December 2017

Sympathetic hyperactivity and hypertension caused by chronic treatment with ouabain or sodium-rich artificial cerebrospinal fluid (aCSF) can be prevented by central administration of an angiotensin type 1 (AT1) receptor blocker. In the present study, we assessed whether, in Wistar rats, chronic peripheral treatment with the AT1 receptor blockers losartan and embusartan can exert sufficient central effects to prevent these central effects of ouabain and sodium. Losartan or embusartan (both at 100 mg · kg−1 · day−1) were given subcutaneously once daily. Ouabain (50 μg/day) was infused subcutaneously, and sodium-rich aCSF (1.2 M Na+, 5 μl/h) was infused intracerebroventricularly, both by osmotic minipump for 13–14 days. The mean arterial pressure (MAP) at rest and in response to air stress and intracerebroventricularly injection of guanabenz (75 μg/7.5 μl), ANG II (30 ng/3 μl), and ouabain (0.5 μg/2 μl) were then measured. In control rats, chronic treatment with ouabain subcutaneously and hypertonic saline intracerebroventricularly both increased baseline MAP by 20–25 mmHg and enhanced twofold the pressor responses to air stress and depressor responses to the α2-adrenoceptor agonist guanabenz. Simultaneous treatment with losartan or embusartan fully prevented hypertension, maintained normal responses to air stress and guanabenz, and attenuated pressor responses to acute intracerebroventricular injection of ANG II and ouabain. We concluded that peripheral administration of losartan as well as embusartan can cause sufficient central effects to prevent the sympathetic hyperactivity and hypertension induced by chronic peripheral ouabain and central sodium.
Mitral inertance in humans: critical factor in Doppler estimation of transvalvular pressure gradients
Authors: Nakatani Satoshi , Firstenberg Michael S. , Greenberg Neil L. , Vandervoort Pieter M. , Smedira Nicholas G. , McCarthy Patrick M. , Thomas James D.
Published: December 2017

The pressure-velocity relationship across the normal mitral valve is approximated by the Bernoulli equation ΔP = ½ ρΔ v 2 + M · d v/d t, where ΔP is the atrioventricular pressure difference, ρ is blood density, v is transmitral flow velocity, and M is mitral inertance. Although M is indispensable in assessing transvalvular pressure differences from transmitral flow, this term is poorly understood. We measured intraoperative high-fidelity left atrial and ventricular pressures and simultaneous transmitral flow velocities by using transesophageal echocardiography in 100 beats (8 patients). We computed mean mitral inertance ( [Formula: see text] ) by [Formula: see text] = ∫(ΔP−½ · ρ v 2)d t/∫(d v/d t)d tand we assessed the effect of the inertial term on the transmitral pressure-flow relation. [Formula: see text] ranged from 1.03 to 5.96 g/cm2 (mean = 3.82 ± 1.22 g/cm2). ΔP calculated from the simplified Bernoulli equation (ΔP = ½ · ρ v 2) lagged behind (44 ± 11 ms) and underestimated the actual peak pressures (2.3 ± 1.1 mmHg). [Formula: see text] correlated with left ventricular systolic pressure ( r = −0.68, P < 0.0001) and transmitral pressure gradients ( r = 0.65, P < 0.0001). Because mitral inertance causes the velocity to lag significantly behind the actual pressure gradient, it needs to be considered when assessing diastolic filling and the pressure difference across normal mitral valves.
ETA-receptor blockade prevents matrix metalloproteinase activation late postmyocardial infarction in the rat
Authors: Podesser Bruno K. , Siwik Deborah A. , Eberli Franz R. , Sam Flora , Ngoy Soeun , Lambert Julie , Ngo Khahn , Apstein Carl S. , Colucci Wilson S.
Published: December 2017

Endothelin (ET) A (ETA) receptors activate matrix metalloproteinases (MMP). Since endothelin-1 (ET) is increased in myocardium late postmyocardial infarction (MI), we hypothesized that stimulation of ETAreceptors contributes to activation of myocardial MMPs late post-MI. Three days post-MI, rats were randomized to treatment with the ETA-selective receptor antagonist sitaxsentan ( n = 12) or a control group ( n = 12). Six weeks later, there were rightward shifts of the left ventricular (LV) end-diastolic and end-systolic pressure-volume relationships, as measured ex vivo by the isovolumic Langendorff technique. Both shifts were markedly attenuated by sitaxsentan. In LV myocardium remote from the infarct, the activities of MMP-1, MMP-2, and MMP-9 were increased in the post-MI group, and the increases were prevented by sitaxsentan treatment. Expression of tissue inhibitor of MMP-1 was decreased post-MI, and the decrease was prevented by sitaxsentan treatment. Chronic post-MI remodeling is associated with activation of MMPs in myocardium remote from the infarct. Inhibition of ETAreceptors prevents MMP activation and LV dilation, suggesting that ET, acting via the ETAreceptor, contributes to chronic post-MI remodeling by its effects on MMP activity.
Changes in cardiac contractile function and myocardial [Ca2+]i after burn trauma: NMR study
Authors: Xia Zhao-Fan , Zhao Piyu , Horton Jureta W.
Published: December 2017

Cutaneous burn trauma causes cardiac contraction and relaxation defects, but the mechanism is unclear. Previous studies suggest that burn-related changes in myocyte handling of calcium may play an important role in postburn cardiac dysfunction. With the use of a high dissociation constant ( K d) calcium indicator 1,2-bis(2-amino-5,6-difluorophenoxy)-ethane- N,N,N′, N′-tetraacetic acid (TF-BAPTA) and 19F NMR spectroscopy, this study examined the correlation between the changes in cytosolic free calcium concentration ([Ca2+]i) and cardiac function after burn trauma. Sprague-Dawley rats were given scald burn (over 40% of the total body surface area) or sham burn. Twenty-four hours later, the hearts were excised and perfused by the Langendorff method with a modified phosphate-free Krebs-Henseleit bicarbonate buffer. Left ventricular (LV) developed pressure (LVDP), calculated from peak systolic LV pressure and LV end-diastolic pressure, was assessed through a catheter attached to an intraventricular balloon. At the same time, 31P and 19F NMR spectroscopy was performed before and after TF-BAPTA loading. LVDP measured in hearts from burned rats was <40% than that measured in hearts from sham burn rats (65 ± 6 vs. 110 ± 12 mmHg, P < 0.01); [Ca2+]i was increased fourfold in hearts from the burned group compared with that measured in the sham burn group (0.807 ± 0.192 vs. 3.891 ± 0.929 μM). Loading TF-BAPTA in hearts transiently decreased LVDP by 15%. Phosphocreatine-to-Pi ratio decreased, but ATP and intracellular pH remained unchanged by either TF-BAPTA loading or burn trauma. In conclusion, burn trauma impaired cardiac contractility, and this functional defect was paralleled by a significant rise in [Ca2+]i in the heart.
Angiotensin II AT1 receptors preserve vasodilator reactivity in skeletal muscle resistance arteries
Authors: Weber David S. , Lombard Julian H.
Published: December 2017

Resistance arteries (100–150 μm) were isolated from the gracilis muscle of normotensive Sprague-Dawley rats placed on a high-salt (HS) diet (4.0% NaCl) for 3–7 days. Exposure to the HS diet eliminated vascular relaxation in response to hypoxia (Po 2reduction to 35–40 Torr) and iloprost, a stable analog of prostacyclin. Vasodilator responses were restored in arteries isolated from chronically instrumented HS rats receiving a continuous intravenous infusion of either angiotensin II (ANG II; 5–6 ng · kg−1 · min−1) or ANG II plus the AT2 receptor blocker PD-123319 (5 μg · kg−1 · min−1) for 3 days before the isolated vessel studies. In contrast, coinfusion of the AT1 receptor blocker losartan (20 μg · kg−1 · min−1) or coinfusion of both receptor blockers with ANG II eliminated the protective effect of ANG II to restore dilator responses to hypoxia and iloprost. Neither a HS diet nor ANG II infusion affected the dilation of gracilis arteries in response to direct activation of adenylyl cyclase by forskolin, suggesting that the effect of both the HS diet and the ANG II on the vasculature is mediated upstream from second messenger systems. These findings indicate that the protective effect of ANG II to maintain vasodilator reactivity in resistance arteries of rats on a HS diet is mediated via the AT1 receptor subtype.
Gap junctional communication underpins EDHF-type relaxations evoked by ACh in the rat hepatic artery
Authors: Chaytor Andrew T. , Martin Patricia E. M. , Edwards David H. , Griffith Tudor M.
Published: December 2017

Synthetic peptides homologous to the Gap 26 and Gap 27 domains of the first and second extracellular loops of the major vascular connexins (Cx37, Cx40, and Cx43) have been used to investigate the role of gap junctions in endothelium-derived hyperpolarizing factor (EDHF)-type relaxations of the rat hepatic artery. These peptides were designated 37,40Gap 26,43Gap 26, 37,43Gap 27, and 40Gap 27, according to connexin specificity. When administered at 600 μM, none of the peptides individually affected maximal EDHF-type relaxations to ACh. By contrast, at 300 μM each, paired peptide combinations targeting more than one connexin subtype attenuated relaxation by up to 50%, and responses were abolished by the triple peptide combination 43Gap 26 + 40Gap 27 + 37,43Gap 27. In parallel experiments with A7r5 cells expressing Cx40 and Cx43, neither 43Gap 26 nor40Gap 27 affected intercellular diffusion of Lucifer yellow individually but, in combination, significantly attenuated dye transfer. The findings confirm that functional cell-cell coupling may depend on more than one connexin subtype and demonstrate that direct intercellular communication via gap junctions constructed from Cx37, Cx40, and Cx43 underpins EDHF-type responses in the rat hepatic artery.
Gene transfer of superoxide dismutase isoforms reverses endothelial dysfunction in diabetic rabbit aorta
Authors: Zanetti Michela , Sato Jun'Ichi , Katusic Zvonimir S. , O'Brien Timothy
Published: December 2017

Increased production of oxygen free radicals is an important mechanism of endothelial dysfunction in diabetes mellitus. Our goal was to test whether adenovirus (Ad)-mediated gene transfer of copper/zinc (CuZn) or manganese superoxide dismutase (Mn SOD) improves relaxation of diabetic vessels. The aortas from 9 alloxan-induced diabetic mellitus (DM) and 16 control rabbits were used. Control and DM rings were transduced ex vivo with Ad vectors encoding Mn SOD (AdMn SOD), CuZn SOD (AdCuZn SOD), β-galactosidase (Adβgal), or diluents. In the absence of gene transfer, SOD activity was significantly increased in DM aortas. Transgene expression in DM AdCuZn SOD and DM AdMn SOD-transduced vessels was confirmed by Western blot analysis and by increased SOD activity (DM AdCuZn SOD, 76.2 ± 9.3; DM AdMn SOD, 65.2 ± 4.8; P < 0.05 vs. DM Adβgal; 50.9 ± 4.4 U/mg protein). Superoxide production was increased in DM Adβgal-transduced aorta and relaxations to acetylcholine were impaired in these vessels. Gene transfer of CuZn SOD and Mn SOD corrected both of these defects. Thus Ad-mediated gene transfer CuZn and Mn SOD to the diabetic aorta improves endothelium-dependent relaxation.
CytochromeP-450 metabolite of arachidonic acid mediates bradykinin-induced negative inotropic effect
Authors: Rastaldo R. , Paolocci N. , Chiribiri A. , Penna C. , Gattullo D. , Pagliaro P.
Published: December 2017

This study focused on the mechanisms of the negative inotropic response to bradykinin (BK) in isolated rat hearts perfused at constant flow. BK (100 nM) significantly reduced developed left ventricular pressure (LVP) and the maximal derivative of systolic LVP by 20–22%. The cytochrome P-450 (CYP) inhibitors 1-aminobenzotriazole (1 mM and 100 μM) or proadifen (5 μM) abolished the cardiodepression by BK, which was not affected by nitric oxide and cyclooxygenase inhibitors (35 μM NG-nitro-l-arginine methyl ester and 10 μM indomethacin, respectively). The CYP metabolite 14,15-epoxyeicosatrienoic acid (14,15-EET; 50 ng/ml) produced effects similar to those of BK in terms of the reduction in contractility. After the coronary endothelium was made dysfunctional by Triton X-100 (0.5 μl), the BK-induced negative inotropic effect was completely abolished, whereas the 14,15-EET-induced cardiodepression was not affected. In hearts with normal endothelium, after recovery from 14,15-EET effects, BK reduced developed LVP to a 35% greater extent than BK in the control. In conclusion, CYP inhibition or endothelial dysfunction prevents BK from causing cardiodepression, suggesting that, in the rat heart, endothelial CYP products mediate the negative inotropic effect of BK. One of these mediators appears to be 14,15-EET.
Patterns of wave break during ventricular fibrillation in isolated swine right ventricle
Authors: Lee Moon-Hyoung , Qu Zhilin , Fishbein Gregory A. , Lamp Scott T. , Chang Eugene H. , Ohara Toshihiko , Voroshilovsky Olga , Kil Jong R. , Hamzei Ali R. , Wang Nina C. , Lin Shien-Fong , Weiss James N. , Garfinkel Alan , Karagueuzian Hrayr S. , Chen Peng-Sheng
Published: December 2017

Several different patterns of wave break have been described by mapping of the tissue surface during fibrillation. However, it is not clear whether these surface patterns are caused by multiple distinct mechanisms or by a single mechanism. To determine the mechanism by which wave breaks are generated during ventricular fibrillation, we conducted optical mapping studies and single cell transmembrane potential recording in six isolated swine right ventricles (RV). Among 763 episodes of wave break (0.75 times · s−1· cm−2), optical maps showed three patterns: 80% due to a wave front encountering the refractory wave back of another wave, 11.5% due to wave fronts passing perpendicular to each other, and 8.5% due to a new (target) wave arising just beyond the refractory tail of a previous wave. Computer simulations of scroll waves in three-dimensional tissue showed that these surface patterns could be attributed to two fundamental mechanisms: head-tail interactions and filament break. We conclude that during sustained ventricular fibrillation in swine RV, surface patterns of wave break are produced by two fundamental mechanisms: head-tail interaction between waves and filament break.
Tetrahydrobiopterin levels regulate endothelial cell proliferation
Authors: Marinos Rebecca S. , Zhang Wei , Wu Guoyao , Kelly Katherine A. , Meininger Cynthia J.
Published: December 2017

Vascular abnormalities, including altered angiogenesis, are major factors contributing to the morbidity and mortality of diabetes. We hypothesized that impaired angiogenesis in diabetes results from decreased tetrahydrobiopterin (BH4)-dependent synthesis of nitric oxide (NO) by endothelial cells (EC). To test this hypothesis, we utilized EC from spontaneously diabetic BB (BBd) and nondiabetes-prone BB (BBn) rats to investigate the link between BH4and EC proliferation. There were significant decreases in the proliferation rate and expression of proliferating cell nuclear antigen in BBd versus BBn EC, with no evidence of apoptosis in either group. Sepiapterin (a precursor of BH4via the salvage pathway) increased BH4synthesis and enhanced proliferation of BBd EC. The stimulating effect of sepiapterin on EC proliferation was attenuated by NG-monomethyl-l-arginine, a NO synthase inhibitor. Reducing BH4concentrations in BBn EC caused a decrease in proliferation, which was attenuated by a long-acting NO donor. Our results suggest that BH4levels regulate proliferation of normal EC and that a BH4deficiency impairs NO-dependent proliferation of BBd EC.
Contrasting effects of phentolamine and nitroprusside on neural and cardiovascular variability
Authors: van de Borne Philippe , Rahnama Mohsen , Mezzetti Silvia , Montano Nicola , Porta Alberto , Degaute Jean Paul , Somers Virend K.
Published: December 2017

The relative contributions of a central neural oscillator and of the delay in α-adrenergic transmission within the baroreflex loop in the predominance of low-frequency (LF) cardiovascular variability during sympathetic activation in humans are unclear. We measured R-R interval (RR), muscle sympathetic nerve activity (MSNA), blood pressure (BP), and their variability in 10 normal subjects during sympathetic activation achieved by BP lowering with sodium nitroprusside (SNP) and α-adrenergic blockade using phentolamine. SNP and phentolamine induced comparable reductions in BP ( P > 0.25). Despite tachycardia and sympathetic activation with both SNP and phentolamine, LF variability in RR, MSNA, and BP increased during SNP and decreased during phentolamine (SNP: RR +20 ± 6%, MSNA +3 ± 5%, systolic BP +9 ± 6%, diastolic BP +7 ± 5%; phentolamine: RR −2 ± 7%, MSNA −34 ± 6%, systolic BP −16 ± 8%, diastolic BP −13 ± 4%, P< 0.05 except systolic BP, where P = 0.09). Thus LF variability is reduced when sympathetic activation is induced by α-adrenergic blockade. This suggests that α-adrenergic transmission within the baroreflex loop may contribute importantly to the predominance of LF cardiovascular variability associated with sympathetic excitation in humans.
Pyruvate improves cerebral metabolism during hemorrhagic shock
Authors: Mongan Paul D. , Capacchione John , Fontana John L. , West Shanda , Bünger Rolf
Published: December 2017

Pyruvate (PYR) improves cellular and organ function hypoxia and ischemia by stabilizing the reduced nicotinamide adenine dinucleotide redox state and cytosolic ATP phosphorylation potential. In this in vivo study, we evaluated the effects of intravenous pyruvate on neocortical function, indexes of the cytosolic redox state, cellular energy state, and ischemia during a prolonged (4 h) controlled arterial hemorrhage (40 mmHg) in swine. Thirty minutes after the onset of hemorrhagic shock, sodium PYR ( n = 8) was infused (0.5 g · kg−1 · h−1) to attain arterial levels of 5 mM. The volume and osmotic effects were matched with 10% NaCl [hypertonic saline (HTS)] ( n = 8) or 0.9% NaCl [normal saline (NS)] ( n = 8). During the hemorrhage protocol, the time to peak hemorrhage volume was significantly delayed in the PYR group compared with the HTS and NS groups (94 ± 5 vs. 73 ± 6 and 72 ± 4 min, P < 0.05). In addition to the early onset of the decompensatory phase of hemorrhagic shock, the complete return of the hemorrhage volume during decompensatory shock resulted in the death of five and four animals, respectively, in the HTS and NS groups. In contrast, in the PYR group, reinfusion of the hemorrhage volume was slower and all animals survived the 4-h hemorrhage protocol. During hemorrhage, the PYR group also exhibited improved cerebral cortical metabolic and function status. PYR slowed and reduced the rise in neocortical microdialysis levels of adenosine, inosine, and hypoxanthine and delayed the loss of cerebral cortical biopsy ATP and phosphocreatine content. This improvement in energetic status was evident in the improved preservation of the electrocorticogram in the PYR group. PYR also prevented the eightfold increase in the excitotoxic amino acid glutamate observed in the HTS group. The findings show that PYR administered after the onset of hemorrhagic shock markedly improves cerebral metabolic and functional status for at least 4 h.
Roles for platelet-activating factor and ·NO-derived oxidants causing neutrophil adherence after CO poisoning
Authors: Thom Stephen R. , Fisher Donald , Manevich Yefim
Published: December 2017

Studies were conducted with rats to investigate whether platelet activating factor (PAF) and nitric oxide (·NO)-derived oxidants played roles in the initial adherence of neutrophils to vasculature in the brain after carbon monoxide (CO) poisoning. Before CO poisoning, rats were treated with the competitive PAF receptor antagonist WEB-2170 or with the peroxynitrite scavenger selenomethionine. Both agents caused significantly lower concentrations of myeloperoxidase in the brain after poisoning, indicating fewer sequestered neutrophils. Similarly, both agents reduced the concentration of nitrotyrosine, indicating less oxidative stress due to ·NO-derived oxidants. There were no alterations in whole brain homogenate PAF concentration measured by immunoassay and bioassay, nor were there changes in phosphatidylcholine concentration. Immunohistochemical imaging showed PAF to be more heavily localized within perivascular zones after CO poisoning. Neutrophils colocalized with both PAF and nitrotyrosine in brains of rats killed immediately after CO poisoning. We conclude that qualitative changes in brain PAF are responsible for neutrophil adherence immediately after CO poisoning and that activated neutrophils trigger the initial rise in brain nitrotyrosine. Persistent PAF-mediated neutrophil adherence required production of ·NO-derived oxidants because when oxidants were scavenged, neutrophil adherence was not maintained.
Effects of chronic estrogen-receptor blockade on ovine perinatal pulmonary circulation
Authors: Parker Thomas A. , Afshar Sam , Kinsella John P. , Grover Theresa R. , Gebb Sarah , Geraci Mark , Shaul Philip W. , Cryer Chad M. T. , Abman Steven H.
Published: December 2017

Prolonged infusions of 17β-estradiol reduce fetal pulmonary vascular resistance (PVR), but the effects of endogenous estrogens in the fetal pulmonary circulation are unknown. To test the hypothesis that endogenous estrogen promotes pulmonary vasodilation at birth, we studied the hemodynamic effects of prolonged estrogen-receptor blockade during late gestation and at birth in fetal lambs. We treated chronically prepared fetal lambs with ICI-182,780 (ICI, a specific estrogen-receptor blocker, n = 5) or 1% DMSO (CTRL, n = 5) for 7 days and then measured pulmonary hemodynamic responses to ventilation with low- and high-fraction inspired oxygen (Fi O2 ). Treatment with ICI did not change basal fetal PVR or arterial blood gas tensions. However, treatment with ICI abolished the vasodilator response to ventilation with low Fi O2 [change in PVR −30 ± 6% (CTRL) vs. +10 ± 13%, (ICI), P < 0.05] without reducing the vasodilator response to ventilation with high Fi O2 [change in PVR, −73 ± 3% (CTRL) vs. −77 ± 4%, (ICI); P = not significant]. ICI treatment reduced prostacyclin synthase (PGIS) expression by 33% ( P < 0.05) without altering expression of endothelial nitric oxide synthase or cyclooxygenase-1 and -2. In situ hybridization and immunohistochemistry revealed that PGIS is predominantly expressed in the airway epithelium of late gestation fetal lambs. We conclude that prolonged estrogen-receptor blockade inhibits the pulmonary vasodilator response at birth and that this effect may be mediated by downregulation of PGIS. We speculate that estrogen exposure during late gestation prepares the pulmonary circulation for postnatal adaptation.
Adenosine linking reduced O2 to arteriolar NO release in intestine is not formed from extracellular ATP
Authors: Sauls Bryan A. , Boegehold Matthew A.
Published: December 2017

We have previously reported that adenosine formed in response to reduced arteriolar and/or tissue Po 2 preserves endothelial nitric oxide (NO) synthesis during sympathetic vasoconstriction in the rat intestine. To more precisely identify the site and mechanism of adenosine formation under these conditions, we tested the hypothesis that ATP released in response to reduced O2 levels serves as a source of adenosine. Direct application of ATP to the wall of first-order arterioles elicited dose-dependent dilations of 15–33% above resting diameter that were reduced by 71–80% by the 5′-ectonucleotidase inhibitor α,β-methyleneadenosine 5′-diphosphate (AOPCP, 4.5 × 10−5 M) and completely abolished by N G-monomethyl-l-arginine (l-NMMA, 10−4 M). Under control conditions, sympathetic nerve stimulation at 3 and 8 Hz induced arteriolar constrictions of 11 ± 1 and 19 ± 1 μm, respectively. These responses were enhanced by 58–69% in the presence ofl-NMMA or when local Po 2 was maintained at resting levels. However, in the presence of AOPCP, the enhancing effects of l-NMMA and the high O2superfusate on sympathetic constriction were preserved. These results suggest that, although exogenously applied ATP can stimulate arteriolar NO release in the intestine largely through its sequential extracellular hydrolysis to adenosine, this process does not contribute to adenosine formation and sustained NO release during sympathetic constriction in this vascular bed.
Effects of dietary phytoestrogen on global myocardial ischemia-reperfusion injury in isolated female rat hearts
Authors: Zhai Peiyong , Eurell Thomas E. , Cotthaus Robert P. , Jeffery Elizabeth H. , Bahr Janice M. , Gross David R.
Published: December 2017

We investigated the effects of phytoestrogen on global myocardial ischemia-reperfusion injury in five groups of female rats. A high-phytoestrogen group (HPE) was ovariectomized (Ovx) and fed a diet containing soybean protein and a high-isoflavone soy extract. Another Ovx group of rats was fed the same diet as the HPE group but treated with the estrogen receptor blocker ICI-182,780 (HPE + ICI). A third group of Ovx rats was fed a diet containing soybean protein alone (low-phytoestrogen content; LPE). A fourth Ovx group was fed a diet free of phytoestrogen (Ovx). The fifth group of rats was sham ovariectomized (sham). Hearts from all rats were subjected to 30 min of global, hypothermic (4°C), cardioplegic ischemia and 120 min of normothermic (37°C) reperfusion with oxygenated Krebs-Henseleit buffer. Compared with either the sham or the HPE group, the Ovx and HPE + ICI groups had significantly decreased first derivative of left ventricular pressure (dP/d t), coronary flow rate (CFR), nitrite production and mitochondrial respiratory function and significantly increased Ca2+ accumulation and myocardial histological and ultrastructural injury. The CFR of the LPE group was significantly different from that of either Ovx or HPE + ICI group but the dP/d t, nitrite production, Ca2+ accumulation, and mitochondrial function were not. Our results indicate that diets containing phytoestrogen extract play a cardioprotective role in global myocardial ischemia-reperfusion in female rats.
Effect of adenosine receptor blockade with caffeine on sympathetic response to handgrip exercise in heart failure
Authors: Notarius C. F. , Atchison D. J. , Rongen G. A. , Floras J. S.
Published: December 2017

Adenosine (Ado) increases muscle sympathetic nerve activity (MSNA) reflexively. Plasma Ado and MSNA are elevated in heart failure (HF). We tested the hypothesis that Ado receptor blockade by caffeine would attenuate reflex MSNA responses to handgrip (HG) and posthandgrip ischemia (PHGI) and that this action would be more prominent in HF subjects than in normal subjects. We studied 12 HF subjects and 10 age-matched normal subjects after either saline or caffeine (4 mg/kg) infusion during isometric [30% of maximal voluntary contraction (MVC)] and isotonic (10%, 30%, and 50%) HG exercise, followed by 2 min of PHGI. In normal subjects, caffeine did not block increases in MSNA during PHGI after 50% HG. In HF subjects, caffeine abolished MSNA responses to PHGI after both isometric and 50% isotonic exercise ( P < 0.05) but MSNA responses during HG were unaffected. These findings are consistent with muscle metaboreflex stimulation by endogenous Ado during ischemic or intense nonischemic HG in HF and suggest an important sympathoexcitatory role for endogenous Ado during exercise in this condition.