bluuebunny/crossref_metadata_2025 huggingface dataset:
Reentry in heterogeneous cardiac tissue described by the Luo-Rudy ventricular action potential model
Authors: Ten Tusscher K. H. W. J. , Panfilov A. V.
Published: March 2015

Heterogeneity of cardiac tissue is an important factor determining the initiation and dynamics of cardiac arrhythmias. In this paper, we studied the effects of gradients of electrophysiological heterogeneity on reentrant excitation patterns using computer simulations. We investigated the dynamics of spiral waves in a two-dimensional sheet of cardiac tissue described by the Luo-Rudy phase 1 (LR1) ventricular action potential model. A gradient of action potential duration (APD) was imposed by gradually varying the local current density of K+ current or inward rectifying K+ current along one axis of the tissue sheet. We show that a gradient of APD resulted in spiral wave drift. This drift consisted of two components. The longitudinal (along the gradient) component was always directed toward regions of longer spiral wave period. The transverse (perpendicular to the gradient) component had a direction dependent on the direction of rotation of the spiral wave. We estimated the velocity of the drift as a function of the magnitude of the gradient and discuss its implications.
Enhanced baroreflex sensitivity in free-moving calponin knockout mice
Authors: Masuki Shizue , Takeoka Michiko , Taniguchi Shun'Ichiro , Nose Hiroshi
Published: March 2015

Calponin is an actin binding protein in vascular smooth muscle that modifies contractile responses. However, its role in mean arterial pressure (MAP) regulation has not been clarified. To assess this, MAP and heart rate (HR) were measured in calponin knockout (KO) mice, and the results were compared with those in wild-type (WT) mice. The measurements were performed every 100 ms during a 60-min free-moving state each day for 3 days. Mice in both groups rested during ∼70% of the total measuring period. The mean HR during rest was significantly lower in KO mice than in WT mice but with no significant difference in MAP between the groups. The change in HR response (ΔHR) to spontaneous change in MAP (ΔMAP) varied in a wider range in KO mice with an 80% increase in the coefficient of variation for HR ( P < 0.05), whereas MAP in KO mice was controlled in a narrow range similar to that in WT mice. The baroreflex sensitivity (ΔHR/ΔMAP), determined from the change in HR to the spontaneous change in MAP, was twofold higher in KO mice than that in WT mice ( P < 0.01), whereas there were no significant differences in the baroreflex sensitivity determined by intravascular administration of phenylephrine and sodium nitroprusside between the two groups ( P > 0.1). The MAP response to the administrated doses of phenylephrine in KO mice was reduced to one-half of that in WT mice ( P < 0.01) but with no significant difference in the response to sodium nitroprusside between the groups. The differences in HR variability and the spontaneous baroreflex sensitivity between the two groups completely disappeared after carotid sinus denervation. These results suggest that the higher variability in HR for KO mice was caused by the increased spontaneous arterial baroreflex sensitivity, though not detected by the intra-arterial administration of the drug, and that the higher variability of HR may be a compensatory adaptation to the blunted α-adrenergic response of peripheral vessels to sympathetic nervous activity.
Inhibition of neurons in commissural nucleus of solitary tract reduces sympathetic nerve activity in SHR
Authors: Sato Monica A. , Colombari Eduardo , Morrison Shaun F.
Published: March 2015

Neurons in the commissural nucleus of the solitary tract (commNTS) play an important role in certain cardiovascular responses dependent on sympathetic vasoconstrictor activation, including the arterial chemoreceptor reflex. Electrolytic lesions of the commNTS elicit a fall in arterial pressure (AP) in spontaneously hypertensive rats (SHR). To determine whether the latter result 1) arose from elimination of commNTS neuronal activity rather than en passant axons and 2) was accompanied by a reduction in sympathetic nerve activity, we evaluated the effect of inhibition of neurons in the commNTS on basal splanchnic sympathetic nerve activity (SNA), AP, and heart rate (HR) in SHR, Wistar-Kyoto (WKY), and Sprague-Dawley (SD) rats. In chloralose-anesthetized, paralyzed, and artificially ventilated SHR, microinjection of GABA into the commNTS markedly decreased splanchnic SNA, AP, and HR. The reductions in SNA and AP following similar microinjections in WKY and SD rats were significantly less than those in SHR. Our findings suggest that tonically active neurons in the commNTS contribute to the maintenance of SNA and the hypertension in SHR. The level of tonic discharge of these commNTS neurons in normotensive WKY and SD rats may be lower than in SHR.
Alterations in mitochondrial function in a mouse model of hypertrophic cardiomyopathy
Authors: Lucas David T. , Aryal Prafulla , Szweda Luke I. , Koch Walter J. , Leinwand Leslie A.
Published: March 2015

Familial hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease characterized by varying degrees of ventricular hypertrophy and myofibrillar disarray. Mutations in cardiac contractile proteins cause HCM. However, there is an unexplained wide variability in the clinical phenotype, and it is likely that there are multiple contributing factors. Because mitochondrial dysfunction has been described in heart disease, we tested the hypothesis that mitochondrial dysfunction contributes to the varying HCM phenotypes. Mitochondrial function was assessed in two transgenic models of HCM: mice with a mutant myosin heavy chain gene (MyHC) or with a mutant cardiac troponin T (R92Q) gene. Despite mitochondrial ultrastructural abnormalities in both models, the rate of state 3 respiration was significantly decreased only in the mutant MyHC mice by ∼23%. Notably, this decrease in state 3 respiration preceded hemodynamic dysfunction. The maximum activity of α-ketogutarate dehydrogenase as assayed in isolated disrupted mitochondria was decreased by 28% compared with isolated control mitochondria. In addition, complexes I and IV were decreased in mutant MyHC transgenic mice. Inhibition of β-adrenergic receptor kinase, which is elevated in mutant MyHC mouse hearts, can prevent mitochondrial respiratory impairment in mutant MyHC mice. Thus our results suggest that mitochondria may contribute to the hemodynamic dysfunction seen in some forms of HCM and offer a plausible mechanism responsible for some of the heterogeneity of the disease phenotypes.
Hypoxia and high glucose upregulate AT1receptor expression and potentiate ANG II-induced proliferation in VSM cells
Authors: Sodhi Chhinder P. , Kanwar Yashpal S. , Sahai Atul
Published: March 2015

We examined the effect of hypoxia and high glucose (HG) on ANG II type 1 (AT1) receptor expression and proliferation in cultured vascular smooth muscle (VSM) cells. Exposure of quiescent cells to hypoxia in a serum-free DME-Ham's F-12 medium for 6–24 h induced a progressive increase in AT1 mRNA expression. Exposure of cells to 24 h of hypoxia also resulted in a significant increase in ANG II receptor binding as assessed with 125I-labeled ANG II. Treatment with ANG II (1 μM) for 24 h under normoxic conditions caused an ∼1.5-fold increase in both DNA synthesis and cell number, which was enhanced to ∼3.0-fold under hypoxic conditions. An AT1 receptor antagonist (losartan, 10 μM) blocked the ANG II-induced increase in DNA synthesis under both normoxic and hypoxic conditions. Incubations in HG medium (25 mM) for 12–24 h under normoxic conditions induced an ∼2.5-fold increase in AT1 mRNA levels, which was markedly enhanced by hypoxia to ∼5.5-fold at 12 h and ∼8.5-fold at 24 h. ANG II under HG-normoxic conditions caused a complete downregulation of AT1 expression, which was prevented by hypoxia. These results demonstrate an upregulation of AT1 receptor expression by hypoxia and HG in cultured VSM cells and suggest a mechanism for enhanced ANG II-induced VSM cell proliferation and the development of atherosclerosis in diabetes.
Interaction of myogenic mechanisms and hypoxic dilation in rat middle cerebral arteries
Authors: Liu Yanping , Harder David R. , Lombard Julian H.
Published: March 2015

The goal of this study was to determine how myogenic responses and vascular responses to reduced Po 2 interact to determine vascular smooth muscle (VSM) transmembrane potential and active tone in isolated middle cerebral arteries from Sprague-Dawley rats. Stepwise elevation of transmural pressure led to depolarization of the VSM cells and myogenic constriction, and reduction of the O2concentration of the perfusion and superfusion reservoirs from 21% O2 to 0% O2 caused vasodilation and VSM hyperpolarization. Myogenic constriction and VSM depolarization in response to transmural pressure elevation still occurred at reduced Po 2. Arterial dilation in response to reduced Po 2 was not impaired by pressure elevation but was significantly reduced at the lowest transmural pressure (60 mmHg). However, the magnitude of VSM hyperpolarization was unaffected by transmural pressure elevation. This study demonstrates that myogenic activation in response to transmural pressure elevation does not override hypoxic relaxation of middle cerebral arteries and that myogenic responses and hypoxic relaxation can independently regulate vessel diameter despite substantial changes in the other variable.
Dopamine-1 receptor stimulation impairs intestinal oxygen utilization during critical hypoperfusion
Authors: Guzman Jorge A. , Rosado Ariosto E. , Kruse James A.
Published: March 2015

Effects of a dopamine-1 (DA-1) receptor agonist on systemic and intestinal oxygen delivery (D˙o 2)-uptake relationships were studied in anesthetized dogs during sequential hemorrhage. Control ( group 1) and experimental animals ( group 2) were treated similarly except for the addition of fenoldopam (1.0 μg · kg−1 · min−1) in group 2. Both groups had comparable systemic criticalD˙o 2(D˙o 2crit), but animals in group 2 had a higher gut D˙o 2crit(1.12 ± 1.13 vs. 0.80 ± 0.09 ml · kg−1 · min−1, P < 0.05). At the mucosal level, a clear biphasic delivery-uptake relationship was not observed in group 1; thus oxygen consumption by the mucosa may be supply dependent under physiological conditions. Group 2 demonstrated higher peak mucosal blood flow and lack of supply dependency at higher mucosalD˙o 2 levels. Fenoldopam resulted in a more conspicuous biphasic relationship at the mucosa and a rightward shift of overall splanchnic D˙o 2crit despite increased splanchnic blood flow. These findings suggest that DA-1 receptor stimulation results in increased gut perfusion heterogeneity and maldistribution of perfusion, resulting in increased susceptibility to ischemia.
Cerebral microvascular changes in permeability and tight junctions induced by hypoxia-reoxygenation
Authors: Mark Karen S. , Davis Thomas P.
Published: March 2015

Cerebral microvessel endothelial cells that form the blood-brain barrier (BBB) have tight junctions (TJ) that are critical for maintaining brain homeostasis and low permeability. Both integral (claudin-1 and occludin) and membrane-associated zonula occluden-1 and -2 (ZO-1 and ZO-2) proteins combine to form these TJ complexes that are anchored to the cytoskeletal architecture (actin). Disruptions of the BBB have been attributed to hypoxic conditions that occur with ischemic stroke, pathologies of decreased perfusion, and high-altitude exposure. The effects of hypoxia and posthypoxic reoxygenation in cerebral microvasculature and corresponding cellular mechanisms involved in disrupting the BBB remain unclear. This study examined hypoxia and posthypoxic reoxygenation effects on paracellular permeability and changes in actin and TJ proteins using primary bovine brain microvessel endothelial cells (BBMEC). Hypoxia induced a 2.6-fold increase in [14C]sucrose, a marker of paracellular permeability. This effect was significantly reduced (∼58%) with posthypoxic reoxygenation. After hypoxia and posthypoxic reoxygenation, actin expression was increased (1.4- and 2.3-fold, respectively). Whereas little change was observed in TJ protein expression immediately after hypoxia, a twofold increase in expression was seen with posthypoxic reoxygenation. Furthermore, immunofluorescence studies showed alterations in occludin, ZO-1, and ZO-2 protein localization during hypoxia and posthypoxic reoxygenation that correlate with the observed changes in BBMEC permeability. The results of this study show hypoxia-induced changes in paracellular permeability may be due to perturbation of TJ complexes and that posthypoxic reoxygenation reverses these effects.
Ventricular remodeling induced by retinoic acid supplementation in adult rats
Authors: de Paiva Sergio Alberto Rupp , Zornoff Leonardo Antonio Mamede , Okoshi Marina Politi , Okoshi Katashi , Matsubara Luiz Shiguero , Matsubara Beatriz Bojikian , Cicogna Antonio Carlos , Campana Alvaro Oscar
Published: March 2015

Retinoic acid (RA) plays a role in regulating cardiac geometry and function throughout life. The aim of this study was to analyze the cardiac effects of RA in adult rats. Wistar rats were randomly allocated to a control group ( n = 18) receiving standard rat chow and a group treated with RA ( n = 14) receiving standard rat chow supplemented with RA for 90 days. All animals were evaluated by echocardiography, isolated papillary muscle function, and morphological studies. Whereas the RA-treated group developed an increase in both left ventricular (LV) mass and LV end-diastolic diameter, the ratio of LV wall thickness to LV end-diastolic diameter remained unchanged when compared with the control group. In the isolated papillary muscle preparation, RA treatment decreased the time to peak developed tension and increased the maximum velocity of isometric relengthening, indicating that systolic and diastolic function was improved. Although RA treatment produced an increase in myocyte cross-sectional area, the myocardial collagen volume fraction was similar to controls. Thus our study demonstrates that small physiological doses of RA induce ventricular remodeling resembling compensated volume-overload hypertrophy in rats.
Voltage-sensitive dye mapping in Langendorff-perfused rat hearts
Authors: Nygren A. , Kondo C. , Clark R. B. , Giles W. R.
Published: March 2015

An imaging system suitable for recordings from Langendorff-perfused rat hearts using the voltage-sensitive dye 4-[β-[2-(di- n-butylamino)-6-naphthyl]vinyl]pyridinium (di-4-ANEPPS) has been developed. Conduction velocity was measured under hyper- and hypokalemic conditions, as well as at physiological and reduced temperature. Elevation of extracellular [K+] to 9 mM from 5.9 mM caused a slowing of conduction velocity from 0.66 ± 0.08 to 0.43 ± 0.07 mm/ms (35%), and reduction of the temperature to 32°C from 37°C caused a slowing from 0.64 ± 0.07 to 0.46 ± 0.05 mm/ms (28%). Ventricular activation patterns in sinus rhythm showed areas of early activation (breakthrough) in both the right and left ventricle, with breakthrough at a site near the apex of the right ventricle usually occurring first. The effects of mechanically immobilizing the preparation to reduce motion artifact were also characterized. Activation patterns in epicardially paced rhythm were insensitive to this procedure over the range of applied force tested. In sinus rhythm, however, a relatively large immobilizing force caused prolonged PQ intervals as well as altered ventricular activation patterns. The time-dependent effects of the dye on the rat heart were characterized and include 1) a transient vasodilation at the onset of dye perfusion and 2) a long-lasting prolongation of the PQ interval of the electrocardiogram, frequently resulting in brief episodes of atrioventricular block.
Dietary n-3 PUFAs affect the blood pressure rise and cardiac impairments in a hyperinsulinemia rat model in vivo
Authors: Rousseau Delphine , Héliès-Toussaint Cécile , Moreau Daniel , Raederstorff Daniel , Grynberg Alain
Published: March 2015

The cardiovascular consequences of eicosapentaenoic acid (EPA)- and docosahexaenoic acid (DHA)-specific intake were evaluated in vivo in a hyperinsulinemia (HI) model induced by dietary fructose intake. Wistar rats were fed a diet containing (or not for control) either EPA or DHA. The rise in blood pressure (BP), heart rate, and ECG were continuously monitored using an intra-abdominal telemetry system. The myocardial phospholipid fatty acid profile was significantly affected by DHA intake but less by EPA intake. The data indicated a reduced rise in BP in both DHA and EPA HI groups compared with controls. This result was confirmed by tail-cuff measurement after 5 wk [133.3 ± 1.67 and 142.5 ± 1.12 mmHg in n-3 polyunsaturated fatty acid (PUFA) and control groups, respectively], whereas n-3 PUFA did not affect BP in non-HI rats (116.3 ± 3.33 mmHg). The heart rate was lower in the HI DHA group than in the other two dietary HI groups. Moreover, DHA induced a significantly shorter QT interval. It is concluded that the cardioactive component of fish oils is DHA through a mechanism that may involve the cardiac adrenergic system.
Effects of hypoxia on heme oxygenase expression in human chorionic villi explants and immortalized trophoblast cells
Authors: Appleton S. D. , Marks G. S. , Nakatsu K. , Brien J. F. , Smith G. N. , Graham C. H. , Lash G. E.
Published: March 2015

Although hypoxia induces heme oxygenase (HO)-1 protein and mRNA expression in many cell types, hypoxia has also been shown to decrease HO-1 mRNA and protein expression. We tested the hypothesis that 24-h preexposure to hypoxia in human placental preparations suppresses HO protein expression and enzymatic function. Immortalized HTR-8/SVneo first-trimester trophoblast cells and explants of normal human chorionic villi (CV) from term placentas were cultured for 24 h in 1%, 5%, or 20% O2. HO protein levels were determined by Western blot analysis, and microsomal HO activity was measured. HO-2 protein content was decreased by 17% and 5% in human trophoblast cells after 24-h exposure to 1% and 5% O2, respectively, versus 20% O2. In contrast, HO-2 protein content in CV explants was unaffected by changes in oxygenation. HO-1 protein content, which was barely detectable in both biological systems, was not affected by changes in oxygenation. Similarly, HO enzymatic activity was unchanged in both preparations after 24-h exposure to 1%, 5%, or 20% O2. The above data do not support the hypothesis that hypoxia in the human placenta suppresses both HO protein content and HO protein function. The present observations reinforce the necessity to determine both HO protein expression and function.
Effects of aging on vasoconstrictor and mechanical properties of rat skeletal muscle arterioles
Authors: Muller-Delp Judy , Spier Scott A. , Ramsey Michael W. , Lesniewski Lisa A. , Papadopoulos Anthony , Humphrey J. D. , Delp Michael D.
Published: March 2015

Exercise capacity and skeletal muscle blood flow during exercise are reduced with advancing age. This reduction in blood flow capacity may be related to increased reactivity of skeletal muscle resistance vessels to vasoconstrictor stimuli. The purpose of this study was to test the hypothesis that aging results in increased vasoconstrictor responses of skeletal muscle resistance arterioles. First-order (1A) arterioles (90–220 μm) from the gastrocnemius and soleus muscles of young (4 mo) and aged (24 mo) Fischer-344 rats were isolated, cannulated, and pressurized via hydrostatic reservoirs. Vasoconstriction in response to increases in norepinephrine (NE; 1 × 10−9–1 × 10−4M) and KCl (20–100 mM) concentrations and increases in intraluminal pressure (10–130 cmH2O) were evaluated in the absence of flow. Responses to NE and KCl were similar in both soleus and gastrocnemius muscle arterioles from young and aged rats. In contrast, active myogenic responses to changes in intraluminal pressure were diminished in soleus and gastrocnemius arterioles from aged rats. To assess whether alterations in the mechanical properties of resistance arterioles underlie altered myogenic responsiveness, passive diameter responses to pressure and mechanical stiffness were evaluated. There was no effect of age on the structural behavior (passive pressure-diameter relationship) or stiffness of arterioles from either the soleus or gastrocnemius muscles. These results suggest that aging does not result in a nonspecific decrease in vasoconstrictor responsiveness of skeletal muscle arterioles. Rather, aging-induced adaptations of vasoreactivity of resistance arterioles appear to be limited to mechanisms that are uniquely involved in the signaling of the myogenic response.
H2O2opens mitochondrial KATPchannels and inhibits GABA receptors via protein kinase C-ε in cardiomyocytes
Authors: Zhang Hong Yan , McPherson Bradley C. , Liu Huiping , Baman Timir S. , Rock Peter , Yao Zhenhai
Published: March 2015

Oxygen radicals and protein kinase C (PKC) mediate ischemic preconditioning. Using a cultured chick embryonic cardiomyocyte model of hypoxia and reoxygenation, we found that the oxygen radicals generated by ischemic preconditioning were H2O2. Like preconditioning, H2O2selectively activated the ε-isoform of PKC in the particulate compartment and increased cell viability after 1 h of hypoxia and 3 h of reoxygenation. The glutathione peroxidase ebselen (converting H2O2to H2O) and the superoxide dismutase inhibitor diethyldithiocarbamic acid abolished the increased H2O2and the protection of preconditioning. PKC activation with phorbol 12-myristate 13-acetate increased cell survival; the protection of preconditioning was blocked by εV1–2, a selective PKC-ε antagonist. Similar to preconditioning, the protection of PKC activation was abolished by mitochondrial KATPchannel blockade with 5-hydroxydecanoate or by GABA receptor stimulation with midazolam or diazepam. In addition, PKC, mitochondrial ATP-sensitive K+(KATP) channels, and GABA receptors had no effects on H2O2generated by ischemic preconditioning before prolonged hypoxia and reoxygenation. We conclude that H2O2opens mitochondrial KATPchannels and inhibits GABA receptors via activating PKC-ε. Through this signal transduction, preconditioning protects ischemic cardiomyocytes.
The renin-angiotensin-aldosterone system excites hypothalamic paraventricular nucleus neurons in heart failure
Authors: Zhang Zhi-Hua , Francis Joseph , Weiss Robert M. , Felder Robert B.
Published: March 2015

The paraventricular nucleus (PVN) of the hypothalamus has critical homeostatic functions, including the regulation of fluid balance and sympathetic drive. It has been suggested that altered activity of this nucleus contributes to the progression of congestive heart failure (HF). We hypothesized that forebrain influences of the renin-angiotensin-aldosterone system augment the activity of PVN neurons in HF. The rate of PVN neurons ( n = 68) from rats with ischemia-induced HF was higher than that of PVN neurons ( n = 42) from sham-operated controls (8.7 ± 0.8 vs. 2.7 ± 0.3 spikes/s, P < 0.001, HF vs. SHAM). Forebrain-directed intracarotid artery injections of the angiotensin type 1 receptor antagonist losartan, the angiotensin-converting enzyme inhibitor captopril, and the mineralocorticoid receptor antagonist spironolactone all significantly ( P < 0.05) reduced PVN neuronal activity in HF rats. These findings demonstrate that the renin-angiotensin-aldosterone system drives PVN neuronal activity in HF, likely resulting in increased sympathetic drive and volume accumulation. This mechanism of neurohumoral excitation in HF is accessible to manipulation by blood-borne therapeutic agents.
Acute exercise enhances vasorelaxation by modulating endothelial calcium signaling in rat aortas
Authors: Jen Chauying J. , Chan Hung-Pin , Chen Hsiun-Ing
Published: March 2015

The role of endothelial calcium signaling in exercise-enhanced ACh-induced vasorelaxation was examined using male Wistar rats (8∼10 wk old) that were divided into control and exercise groups. The exercised animals ran on a treadmill with progressive increments of speed until exhaustion. After decapitation, aortic rings were dissected and loaded with fura 2-AM. After being mounted on a tissue flow chamber, vessels were precontracted with phenylephrine, and ACh-induced endothelial calcium elevation and vasorelaxation were determined simultaneously under an epifluorescence microscope equipped with ratio imaging capability. Our results showed that 1) there was logarithmic correlation between endothelial calcium elevation and vasorelaxation; 2) acute exercise enhanced ACh-induced endothelial calcium elevation and vasorelaxation without altering their relationship; 3) pretreatment with Nω-nitro-l-arginine markedly reduced ACh-induced vasorelaxation in both groups but suppressed the calcium response only in the exercise group; and 4) the exercise effect on endothelial calcium elevation was abolished by Ca2+-free buffer or gadolinium. In conclusion, acute exercise increases ACh-induced vasorelaxation by increasing the endothelial calcium influx and the calcium-dependent nitric oxide release.
Phospholemman modulates Na+/Ca2+exchange in adult rat cardiac myocytes
Authors: Zhang Xue-Qian , Qureshi Anwer , Song Jianliang , Carl Lois L. , Tian Qiang , Stahl Richard C. , Carey David J. , Rothblum Lawrence I. , Cheung Joseph Y.
Published: March 2015

Previous studies have shown that overexpression of phospholemman (PLM) affected contractile function and Ca2+homeostasis in adult rat myocytes. We tested the hypothesis that PLM modulated Na+/Ca2+exchanger (NCX1) activity. PLM was overexpressed in adult rat myocytes by adenovirus-mediated gene transfer. After 72 h, the half-time of relaxation from caffeine-induced contracture, an estimate of forward NCX1 activity, was prolonged 1.8-fold ( P < 0.003) in myocytes overexpressing PLM compared with control myocytes overexpressing green fluorescent protein alone. Reverse NCX1 current (3 Na+out:1 Ca2+in) was significantly ( P < 0.0001) lower in PLM myocytes, especially at more positive voltages. Immunofluorescence demonstrated colocalization of PLM and NCX1 to the plasma membrane and t-tubules. Resting membrane potential, action potential amplitude and duration, myocyte size, and NCX1 and calsequestrin protein levels were not affected by PLM overexpression. At 5 mM extracellular [Ca2+] ([Ca2+]o), the depressed contraction amplitudes in PLM myocytes were increased towards normal by cooverexpression with NCX1. At 0.6 mM [Ca2+]o, the supranormal contraction amplitudes in PLM myocytes were reduced by cooverexpression with NCX1. We conclude that PLM modulated myocyte contractility partly by inhibiting Na+/Ca2+exchange.
Age-dependent increase in hydrogen peroxide production by cardiac monoamine oxidase A in rats
Authors: Maurel Agnès , Hernandez Carole , Kunduzova Oksana , Bompart Guy , Cambon Claudie , Parini Angelo , Francés Bernard
Published: March 2015

Oxidative stress is one of the factors involved in age-related impairment of cardiac function. In the present study, we investigated the role of the catecholamine-degrading enzyme monoamine oxidase (MAO) in H2O2production in the hearts of young, adult, and old rats. MAO-dependent H2O2production, measured by a chemiluminescence-based assay, increased with age, reaching the maximum in 24-mo-old rats (7.5-fold increase vs. 1-mo-old rats). The following observations indicate that the age-dependent increase in H2O2generation was fully related to the MAO-A isoform: 1) at all the ages tested, chemiluminescence production was inhibited by the MAO-A inhibitor clorgyline but not by the MAO-B inhibitor RO-19 6327; 2) enzyme assay, Western blot, and semiquantitative RT-PCR analysis showed an age-dependent increase in cardiac MAO-A activity, immunodetection, and mRNA expression, respectively; and 3) the MAO-B isoform was undetectable by enzyme assay and Western blot analysis. These results suggest that MAO-A could be a major source of H2O2in the aging heart.
Ischemic preconditioning alters real-time measure of O2 radicals in intact hearts with ischemia and reperfusion
Authors: Kevin Leo G. , Camara Amadou K. S. , Riess Matthias L. , Novalija Enis , Stowe David F.
Published: March 2015

Reactive oxygen species (ROS) are believed to be involved in triggering cardiac ischemic preconditioning (IPC). Decreased formation of ROS on reperfusion after prolonged ischemia may in part underlie protection by IPC. In heart models, these contentions have been based either on the effect of ROS scavengers to abrogate IPC-induced preservation or on a measurement of oxidation products on reperfusion. Using spectrophotofluorometry at the left ventricular wall and the fluorescent probe dihydroethidium (DHE), we measured intracellular ROS superoxide (O[Formula: see text]·) continuously in isolated guinea pig heart and tested the effect of IPC and the O[Formula: see text]· scavenger manganese(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) on O[Formula: see text]· formation throughout the phases of preconditioning (PC), 30-min ischemia and 60-min reperfusion (I/R). IPC was evidenced by improved contractile function and reduced infarction; MnTBAP abrogated these effects. Brief PC pulses increased O[Formula: see text]· during the ischemic but not the reperfusion phase. O[Formula: see text]· increased by 35% within 1 min of ischemia, increased further to 95% after 20 min of ischemia, and decreased slowly on reperfusion. In the IPC group, O[Formula: see text]· was not elevated over 35% during index ischemia and was not increased at all on reperfusion; these effects were abrogated by MnTBAP. Our results directly demonstrate how intracellular ROS increase in intact hearts during IPC and I/R and clarify the role of ROS in triggering and mediating IPC.
ET-1 increases distensibility of acutely loaded myocardium: a novel ETAand Na+/H+exchanger-mediated effect
Authors: Leite-Moreira Adelino F. , Brás-Silva Carmen , Pedrosa Carla A. , Rocha-Sousa Amândio A.
Published: March 2015

This study investigated, in rabbit papillary muscles ( n = 61) and human auricular strips ( n = 7), effects of endothelin-1 (ET-1; 0.1–10 nM) on diastolic myocardial properties. ET-1 (1 nM) was also given in the presence of selective ETAor ETBantagonism, nonselective ETA/ETBantagonism, and Na+/H+exchanger inhibition. Effects of 6.3 mM Ca2+were also studied. ET-1 dose dependently increased inotropism. In contrast to baseline, in the presence of ET-1, resting tension (RT) decreased, after an isometric twitch, 3.4 ± 1.4, 6.9 ± 1.5, and 12.5 ± 3.1% with 0.1, 1, and 10 nM, respectively, reflecting an increase in myocardial distensibility. ET-1 effects were abolished with selective ETAas well as with nonselective ETA/ETBantagonism, whereas they were still present with ETBantagonism. Na+/H+exchanger inhibition abolished ET-1 effects on distensibility, whereas it only partially inhibited positive inotropic effect. Ca2+increased inotropism to a similar extent to ET-1 (1 nM) but did not affect distensibility. ET-1 therefore increased diastolic distensibility of acutely loaded human and nonhuman myocardium. This effect is mediated by ETAreceptors, requires Na+/H+exchanger activation, and cannot be elicited by Ca2+.
Acetaminophen and low-flow myocardial ischemia: efficacy and antioxidant mechanisms
Authors: Merrill Gary F.
Published: March 2015

In the current study, the cardioprotective efficacy of 0.35 mmol/l acetaminophen administered 10 min after the onset of a 20-min period of global, low-flow myocardial ischemia was investigated. Matched control hearts were administered an equal volume of Krebs-Henseleit physiological buffer solution (vehicle). In separate groups of hearts, the concentration-dependent, negative inotropic properties of hydrogen peroxide and the ability of acetaminophen to attenuate these actions, as well as the effects of acetaminophen on ischemia-reperfusion-mediated protein oxidation, were studied. Acetaminophen-treated hearts regained a significantly greater fraction of baseline, preischemia control function during reperfusion than vehicle-treated hearts. For example, contractility [rate of maximal developed pressure in the left ventricle (±dP/d t max)] after 10 min of reperfusion was 109 ± 24 and 42 ± 9 mmHg/s ( P < 0.05), respectively, in the two groups. The corresponding pressure-rate products were 1,840 ± 434 vs. 588 ± 169 mmHg · beats · min−1 ( P < 0.05). Acetaminophen attenuated peroxynitrite-mediated chemiluminescence in the early minutes of reperfusion (e.g., at 6 min, corresponding values for peak light production were ∼8 × 106 counts/min for vehicle vs. <4 × 106counts/min for acetaminophen, P < 0.05) and the negative inotropic effects of exogenously administered hydrogen peroxide (e.g., at 0.4 mmol/l hydrogen peroxide, pressure-rate products were ∼1.0 × 104 and 3.8 × 103 mmHg · beats · min−1in acetaminophen- and vehicle-treated hearts, respectively, P < 0.05). Ischemia-mediated protein oxidation was reduced by acetaminophen. The ability of acetaminophen to attenuate the damaging effects of peroxynitrite and hydrogen peroxide and to limit protein oxidation suggest antioxidant mechanisms are responsible for its cardioprotective properties during postischemia-reperfusion.
Receptor and non-receptor-dependent mechanisms of cardioprotection with adenosine
Authors: Peart Jason , Willems Laura , Headrick John P.
Published: March 2015

The relative roles of mitochondrial (mito) ATP-sensitive K+ (mitoKATP) channels, protein kinase C (PKC), and adenosine kinase (AK) in adenosine-mediated protection were assessed in Langendorff-perfused mouse hearts subjected to 20-min ischemia and 45-min reperfusion. Control hearts recovered 72 ± 3 mmHg of ventricular pressure (50% preischemia) and released 23 ± 2 IU/g lactate dehydrogenase (LDH). Adenosine (50 μM) during ischemia-reperfusion improved recovery (149 ± 8 mmHg) and reduced LDH efflux (5 ± 1 IU/g). Treatment during ischemia alone was less effective. Treatment with 50 μM diazoxide (mitoKATP opener) during ischemia and reperfusion enhanced recovery and was equally effective during ischemia alone. A3 agonism [100 nM 2-chloro- N 6-(3-iodobenzyl)-adenosine-5′- N-methyluronamide], A1 agonism ( N 6-cyclohexyladenosine), and AK inhibition (10 μM iodotubercidin) all reduced necrosis to the same extent as adenosine, but less effectively reduced contractile dysfunction. These responses were abolished by 100 μM 5-hydroxydecanoate (5-HD, mitoKATP channel blocker) or 3 μM chelerythrine (PKC inhibitor). However, the protective effects of adenosine during ischemia-reperfusion were resistant to 5-HD and chelerythrine and only abolished when inhibitors were coinfused with iodotubercidin. Data indicate adenosine-mediated protection via A1/A3 adenosine receptors is mitoKATP channel and PKC dependent, with evidence for a downstream location of PKC. Adenosine provides additional and substantial protection via phosphorylation to 5′-AMP, primarily during reperfusion.
Acute and chronic head-down tail suspension diminishes cerebral perfusion in rats
Authors: Wilkerson M. Keith , Colleran Patrick N. , Delp Michael D.
Published: March 2015

10.1152/ajpheart.00727.2001.—The purpose of this study was to test the hypothesis that regional brain blood flow and vascular resistance are altered by acute and chronic head-down tail suspension (HDT). Regional cerebral blood flow, arterial pressure, heart rate, and vascular resistance were measured in a group of control rats during normal standing and following 10 min of HDT and in two other groups of rats after 7 and 28 days of HDT. Heart rate was not different among conditions, whereas mean arterial pressure was elevated at 10 min of HDT relative to the other conditions. Total brain blood flow was reduced from that during standing by 48, 24, and 27% following 10 min and 7 and 28 days of HDT, respectively. Regional blood flows to all cerebral tissues and the eyes were reduced with 10 min of HDT and remained lower in the eye, olfactory bulbs, left and right cerebrum, thalamic region, and the midbrain with 7 and 28 days of HDT. Total brain vascular resistance was 116, 44, and 38% greater following 10 min and 7 and 28 days of HDT, respectively, relative to that during control standing. Vascular resistance was elevated in all cerebral regions with 10 min of HDT and remained higher than control levels in most brain regions. These results demonstrate that HDT results in chronic elevations in total and regional cerebral vascular resistance, and this may be the underlying stimulus for the HDT-induced smooth muscle hypertrophy of cerebral resistance arteries.
Assessment of spatial inhomogeneities in intima media thickness along an arterial segment using its dynamic behavior
Authors: Meinders Jan M. , Kornet Lilian , Hoeks Arnold P. G.
Published: March 2015

To assess locally deviating structural and mechanical properties of arterial walls, the spatial variance in end-diastolic intima media thickness (IMT) and the change in IMT during the cardiac cycle (ΔIMT) were determined along a short segment of the common carotid artery (15.86 mm), at 16 positions simultaneously. Intrasubject spatial inhomogeneities along the artery were revealed by a spatial variance significantly larger than the temporal variance over several beats. If differences between positions were confirmed, the extent of the inhomogeneity was obtained by comparison of IMT and ΔIMT at each position with their spatial medians ± the least-significant difference. Because no intersubject comparisons were necessary, a single session of several measurements was sufficient to assess inhomogeneities in the arterial wall properties of a subject, making the method independent of biological variability between subjects. The method was evaluated on 47 presumed healthy subjects (age range 21–75 yr). In 22 subjects, spatial inhomogeneities in ΔIMT occurred ( P < 0.05). In young subjects, ΔIMT was locally decreased, i.e., in systole inhomogeneities were less compressed than their surrounding tissue. In older subjects, ΔIMT was locally increased, i.e., the inhomogeneity was locally more compressed than its surrounding wall tissue.
Calcium- and superoxide anion-mediated mitogenic action of substance P on cardiac fibroblasts
Authors: Kumaran C. , Shivakumar K.
Published: March 2015

Substance P is released from nerve endings in the heart under pathological conditions like ischemia, but its action on cardiac cells has not been investigated. This study tested the hypothesis that substance P is mitogenic to adult cardiac fibroblasts and delineated the underlying mechanism(s). Substance P, acting via neurokinin-1 (NK-1) receptors, stimulated cellular hyperplasia over a range of 1–10 μmol/l. It elicited no change in net collagen production, total protein synthesis, or cell protein content but increased45Ca uptake and superoxide generation. EGTA, N-acetyl-cysteine, and superoxide dismutase attenuated the hyperplastic response to substance P. A combination of substance P and EGTA enhanced superoxide generation without an increase in DNA synthesis, showing that an increase in superoxide production does not result in hyperplasia when extracellular Ca2+is chelated. Together, the data suggest that substance P may activate, via NK-1 receptors, a hyperplastic but not hypertrophic response in adult cardiac fibroblasts and that alterations in redox state and Ca2+homeostasis may act in concert to mediate its mitogenic action.
Endogenous carbon monoxide is an endothelial-derived vasodilator factor in the mesenteric circulation
Authors: Naik Jay S. , O'Donaughy Theresa L. , Walker Benjimen R.
Published: March 2015

Chronic hypoxia (CH) is associated with both blunted agonist-induced and myogenic vascular reactivity, possibly due to an enhanced production of heme oxygenase (HO)-derived carbon monoxide (CO). However, the cellular location of the HO responsible for these effects has not been clearly established. Therefore, we examined the response to administration of the substrate for HO, heme-l-lysinate (HLL), in endothelium-intact and endothelium-denuded small mesenteric arteries from CH male Sprague-Dawley rats. Mesenteric arteries were isolated and mounted on glass cannulas, pressurized to 60 mmHg, and superfused with physiological saline solution. All experiments were performed in the presence of 100 μM Nω-nitro-l-arginine. The vasodilator response to HLL or exogenous CO was examined. HLL experiments were performed in the presence and absence of the HO inhibitor zinc protoporphyrin IX (ZnPPIX). HLL administration resulted in a dose-dependent vasodilator response that was abolished in the presence of ZnPPIX or by endothelial removal. Exogenous CO produced a vasodilator response that was independent of an intact endothelium. Cellular localization of HO was verified through immunohistochemistry in sections of the gut and aorta from CH and control animals. Staining for HO-1, HO-2, and endothelial nitric oxide synthase was confined to the endothelium. Thus we conclude that CO is a product of HO located within the endothelium.
Ectopic pacing at physiological rate improves postanoxic recovery of the developing heart
Authors: Rosa A. , Maury J.-P. , Terrand J. , Lyon X. , Kucera P. , Kappenberger L. , Raddatz E.
Published: March 2015

Recently, rapid and transient cardiac pacing was shown to induce preconditioning in animal models. Whether the electrical stimulation per se or the concomitant myocardial ischemia affords such a protection remains unknown. We tested the hypothesis that chronic pacing of a cardiac preparation maintained in a normoxic condition can induce protection. Hearts of 4-day-old chick embryos were electrically paced in ovo over a 12-h period using asynchronous and intermittent ventricular stimulation (5 min on-10 min off) at 110% of the intrinsic rate. Sham ( n = 6) and paced hearts ( n= 6) were then excised, mounted in vitro, and subjected successively to 30 min of normoxia (20% O2), 30 min of anoxia (0% O2), and 60 min of reoxygenation (20% O2). Electrocardiogram and atrial and ventricular contractions were simultaneously recorded throughout the experiment. Reoxygenation-induced chrono-, dromo-, and inotropic disturbances, incidence of arrhythmias, and changes in electromechanical delay (EMD) in atria and ventricle were systematically investigated in sham and paced hearts. Under normoxia, the isolated heart beat spontaneously and regularly, and all baseline functional parameters were similar in sham and paced groups (means ± SD): heart rate (190 ± 36 beats/min), P-R interval (104 ± 25 ms), mechanical atrioventricular propagation (20 ± 4 mm/s), ventricular shortening velocity (1.7 ± 1 mm/s), atrial EMD (17 ± 4 ms), and ventricular EMD (16 ± 2 ms). Under anoxia, cardiac function progressively collapsed, and sinoatrial activity finally stopped after ∼9 min in both groups. During reoxygenation, paced hearts showed 1) a lower incidence of arrhythmias than sham hearts, 2) an increased rate of recovery of ventricular contractility compared with sham hearts, and 3) a faster return of ventricular EMD to basal value than sham hearts. However, recovery of heart rate, atrioventricular conduction, and atrial EMD was not improved by pacing. Activity of all hearts was fully restored at the end of reoxygenation. These findings suggest that chronic electrical stimulation of the ventricle at a near-physiological rate selectively alters some cellular functions within the heart and constitutes a nonischemic means to increase myocardial tolerance to a subsequent hypoxia-reoxygenation.
Reduced perivascular Po2 increases nitric oxide release from endothelial cells
Authors: Nase G. P. , Tuttle J. , Bohlen H. G.
Published: March 2015

Many studies have suggested that endothelial cells can act as “oxygen sensors” to large reductions in oxygen availability by increasing nitric oxide (NO) production. This study determined whether small reductions in oxygen availability enhanced NO production from in vivo intestinal arterioles, venules, and parenchymal cells. In vivo measurements of perivascular NO concentration ([NO]) were made with NO-sensitive microelectrodes during normoxic and reduced oxygen availability. During normoxia, intestinal first-order arteriolar [NO] was 397 ± 26 nM ( n = 5), paired venular [NO] was 298 ± 34 nM ( n = 5), and parenchymal cell [NO] was 138 ± 36 nM ( n = 3). During reduced oxygen availability, arteriolar and venular [NO] significantly increased to 695 ± 79 nM ( n = 5) and 534 ± 66 nM ( n = 5), respectively, whereas parenchymal [NO] remained unchanged at 144 ± 34 nM ( n = 4). During reduced oxygenation, arteriolar and venular diameters increased by 15 ± 3% and 14 ± 5%, respectively: NG-nitro-l-arginine methyl ester strongly suppressed the dilation to lower periarteriolar Po2. Micropipette injection of a CO2 embolus into arterioles significantly attenuated arteriolar dilation and suppressed NO release in response to reduced oxygen availability. These results indicated that in rat intestine, reduced oxygen availability increased both arteriolar and venular NO and that the main site of NO release under these conditions was from endothelial cells.
Complementary role of extracellular ATP and adenosine in ischemic preconditioning in the rat heart
Authors: Ninomiya Hideki , Otani Hajime , Lu Kejie , Uchiyama Takamichi , Kido Masakuni , Imamura Hiroji
Published: March 2015

Although adenosine is an important mediator of ischemic preconditioning (IPC), its relative contribution to IPC remains unknown. Because adenosine is formed through the hydrolysis of ATP, the present study investigated the role of ATP and adenosine in IPC. Isolated and buffer-perfused rat hearts underwent IPC by three cycles of 5-min ischemia and 5-min reperfusion before 25 min of global ischemia. The rate-pressure product (RPP) 30 min after reperfusion was taken as an endpoint of functional protection. Interstitial fluid (ISF) adenine nucleotides and adenosine were measured by cardiac microdialysis techniques. Inhibition of IPC-induced recovery of RPP was partial by the adenosine receptor antagonist 8-( p-sulfophenyl)theophylline (SPT; 100 μM) or by the structurally distinct P2Y purinoceptor antagonists suramin (300 μM) or reactive blue (RB; 10 μM) but was additive when SPT was given with suramin or RB. The P2X antagonist pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid tetrasodium (50 μM) had no effect on functional protection. The improved functional recovery was not significantly affected by an ecto-5′-nucleotidase inhibitor, α,β-methylene adenosine diphosphate (AMP-CP; 100 μM), alone but was inhibited by AMP-CP plus SPT, suramin, or RB. ISF ATP and adenosine increased temporarily by 10-fold during IPC. AMP-CP augmented the increase in ISF ATP associated with the decrease in ISF adenosine. There was a reciprocal correlation between the ISF concentration of ATP and adenosine in preconditioned hearts. In addition, there was a significant correlation between ISF adenosine and ATP and the inhibitory potency of SPT and suramin or RB against functional protection conferred by IPC. These results suggest that extracellular ATP and adenosine play a complementary role in IPC through P2Y purinoceptors and adenosine receptors, respectively.