bluuebunny/crossref_metadata_2025 huggingface dataset:
Isolated ventricular myocytes from copper-deficient rat hearts exhibit enhanced contractile function
Authors: Wold Loren E. , Saari Jack T. , Ren Jun
Published: December 2017

Dietary copper deficiency leads to cardiac hypertrophy, cardiac fibrosis, derangement of myofibrils, and impaired cardiac contractile and electrophysiological function. The purpose of this study was to determine whether impaired cardiac function from copper deficiency is due to depressed contractile function at the single myocyte level. Male Sprague-Dawley rats were fed diets that were either copper adequate (5.59–6.05 μg copper/g body wt; n = 11) or copper deficient (0.29–0.34 μg copper/g body wt; n = 11) for 5 wk. Ventricular myocytes were dispersed and mechanical properties were evaluated using the SoftEdge video-based edge-detection system. Intracellular Ca2+ transients were examined using fura 2-acetoxymethyl ester. Myocytes were electrically stimulated to contract at 0.5 Hz. Properties evaluated included peak shortening (PS), time to peak shortening (TPS), time to 90% relengthening (TR90), and maximal velocities of shortening and relengthening (±d L/d t). Myocytes from the copper-deficient rat hearts exhibited significantly enhanced PS values associated with shortened TR90 measurements compared with those from copper-adequate rat hearts. The ±d L/d t values were enhanced and the intracellular Ca2+ transient decay rate was depressed in myocytes from copper-deficient rats. These data indicate that impaired cardiac contractile function that is seen in copper-deficient whole hearts might not be due to depressed cardiac contractile function at the single cell level but rather to other mechanisms such as cardiac fibrosis.
Purkinje and ventricular contributions to endocardial activation sequence in perfused rabbit right ventricle
Authors: Cates Adam W. , Smith William M. , Ideker Raymond E. , Pollard Andrew E.
Published: December 2017

Interactions between peripheral conduction system and myocardial wave fronts control the ventricular endocardial activation sequence. To assess those interactions during sinus and paced ventricular beats, we recorded unipolar electrograms from 528 electrodes spaced 0.5 mm apart and placed over most of the perfused rabbit right ventricular free wall endocardium. Left ventricular contributions to electrograms were eliminated by cryoablating that tissue. Electrograms were systematically processed to identify fast (P) deflections separated by >2 ms from slow (V) deflections to measure P-V latencies. By using this criterion during sinus mapping ( n = 5), we found P deflections in 22% of electrograms. They preceded V deflections at 91% of sites. Peripheral conduction system wave fronts preceded myocardial wave fronts by an overall P-V latency magnitude that measured 6.7 ± 3.9 ms. During endocardial pacing ( n = 8) at 500 ms cycle length, P deflections were identified on 15% of electrodes and preceded V deflections at only 38% of sites, and wave fronts were separated by a P-V latency magnitude of 5.6 ± 2.3 ms. The findings were independent of apical, basal, or septal drive site. Modest changes in P-V latency accompanied cycle length accommodation to 125-ms pacing (6.8 ± 2.6 ms), although more pronounced separation between wave fronts followed premature stimulation (11.7 ± 10.4 ms). These results suggested peripheral conduction system and myocardial wave fronts became functionally more dissociated after premature stimulation. Furthermore, our analysis of the first ectopic beats that followed 12 of 24 premature stimuli revealed comparable separation between wave fronts (10.7 ± 5.5 ms), suggesting the dissociation observed during the premature cycles persisted during the initiating cycles of the resulting arrhythmias.
Matrix metalloproteinase expression and activity in isolated myocytes after neurohormonal stimulation
Authors: Coker Mytsi L. , Jolly Jennifer R. , Joffs Cassandra , Etoh Takuma , Holder Jennifer R. , Bond Brian R. , Spinale Francis G.
Published: December 2017

Changes in myocardial matrix metalloproteinase (MMP) activity and expression have been associated with left ventricular (LV) remodeling. A recent study demonstrated that LV myocytes synthesize and release MMPs, which suggests that LV myocytes may participate in myocardial remodeling. However, extracellular stimuli that may potentially influence LV myocyte MMP production remains to be defined. In the present study MMP activity and expression were measured in porcine LV myocyte preparations (105 total cells; n = 6) following incubation (6 h) with endothelin-1 (ET-1;50 pM), angiotensin II (ANG II; 1 μM), or the β-receptor agonist isoproterenol (Iso; 10 nM). LV myocyte-conditioned media were then subjected to gelatin zymography and an MMP-2 antibody capture assay. MMP zymographic gelatinase activity and MMP-2 content were increased by over 40% in LV myocyte-conditioned media after incubation with ET-1 or ANG II ( P < 0.05). Exposure to the phorbol ester phorbol 12-myristate 13-acetate (PMA; 50 ng/ml) resulted in a 30% increase in zymographic gelatinase activity and a 63% increase in MMP-2 content ( P < 0.05), suggesting that protein kinase C activation may be an intracellular mechanism for MMP induction. With the use of a confocal microscopy, membrane type-1 MMP (MT1-MMP) was localized to porcine LV myocytes, and immunoblotting for MT1-MMP using LV myocyte extracts revealed that after exposure to Iso, ET-1, ANG II, or PMA ( P < 0.05), MT1-MMP abundance increased over 50%. Thus stimulation of specific neurohormonal systems that are relevant to LV remodeling influences LV myocyte MMP synthesis and release.
Menadione mimics the infarct-limiting effect of preconditioning in isolated rat hearts
Authors: Yue Yuankun , Krenz Maike , Cohen Michael V. , Downey James M. , Critz Stuart D.
Published: December 2017

The role of mitochondrial free radicals in the cardioprotective effect of ischemic preconditioning was examined in isolated buffer-perfused rat hearts. Infarct size in control rat hearts subjected to 30 min of regional ischemia and 120 min of reperfusion was 32.6 ± 3.4% of the risk zone. Ischemic preconditioning (3 cycles of 5-min global ischemia/5-min reperfusion) before the same regional ischemia and reperfusion protocol significantly reduced infarct size to 2.6 ± 0.8% of the risk zone. Perfusion with menadione (3.0 μM), a generator of mitochondrial free radicals, in lieu of preconditioning ischemia significantly reduced infarction to 10.9 ± 2.7%. N-2-mercaptopropionylglycine (1.0 mM), a free radical scavenger, blocked the protection of menadione, significantly increasing infarction to 23.5 ± 1.1%. Myxothiazol (0.6 μM), a site III mitochondrial inhibitor, blocked the protection of menadione and significantly increased infarction to 25.2 ± 3.8%. The infarct-limiting effect of menadione was attenuated to 19.7 ± 1.5% of the risk zone by 10 μM SB203580, a p38 mitogen-activated protein kinase (MAPK) inhibitor. Furthermore, menadione significantly increased p38 MAPK phosphorylation to a level 5.6-fold over basal. These results indicate that free radicals that originate within mitochondria can activate p38 MAPK and protect hearts against infarction.
Effect of a selective aldosterone receptor antagonist in myocardial infarction
Authors: Delyani John A. , Robinson Eric L. , Rudolph Amy E.
Published: December 2017

Myocardial infarction (MI) initiates adaptive tissue remodeling, which is essential for heart function (such as infarct healing) but is also important for maladaptive remodeling (for example, reactive fibrosis and left ventricular dilation). The effect of aldosterone receptor antagonism on these processes was evaluated in Sprague-Dawley rats using eplerenone, a selective aldosterone receptor antagonist. Infarct healing and left ventricular remodeling were evaluated at 3, 7, and 28 days after MI by determination of the diastolic pressure-volume relationship of the left ventricle, the infarct-thinning ratio, and the collagen-volume fraction. Eplerenone did not affect reparative collagen deposition as was evidenced by a similar collagen volume fraction in the infarcted myocardium between eplerenone and vehicle-treated groups at 7 and 28 days post-MI. In addition, the thinning ratio, which is an index of infarct expansion, was comparable between the eplerenone and vehicle-treated animals at 7 and 28 days post-MI. A protective effect of eplerenone was demonstrated at 28 days post-MI, where reactive fibrosis in the viable myocardium was reduced in eplerenone-treated animals compared with vehicle-treated animals. Thus aldosterone receptor antagonism does not retard infarct healing but rather protects against maladaptive responses after MI.
Fluvastatin inhibits O 2 − and ICAM-1 levels in a rat model with aortic remodeling induced by pressure overload
Authors: Katoh Makoto , Kurosawa Yukie , Tanaka Keiko , Watanabe Ayako , Doi Hisayoshi , Narita Hiroshi
Published: December 2017

Upregulation of intercellular adhesion molecule-1 (ICAM-1) expression is suggested to play an important role in the pathogenesis of vascular remodeling. The aim of the present study was to investigate the effects of the 3-hydroxy-3-methylglutaryl (HMG) CoA reductase inhibitor fluvastatin on superoxide anion (O[Formula: see text]) production and ICAM-1 expression in a rat model with vascular remodeling induced by pressure overload. Two weeks after aortic banding, marked increases in O[Formula: see text] production and ICAM-1 protein levels were observed in the aorta. O[Formula: see text]formation and ICAM-1 immunoreactivity were mainly increased in the endothelium and adventitia of the aorta in banded rats. Oral administration of fluvastatin prevented both these changes and the development of perivascular fibrosis and increased the expression of endothelial nitric oxide synthase. Cholesterol and lipid peroxide levels in serum did not change in the banded rats. Thus the beneficial effects of fluvastatin seen in this study as well as its cholesterol-lowering effect may contribute to attenuate the atherosclerotic process.
Quantitative analysis of intratumoral infusion of color molecules
Authors: McGuire Sarah , Yuan Fan
Published: December 2017

Intratumoral infusion has a potential for improving distribution of drugs. To optimize the infusion, we developed a novel technique to quantify the distribution volume of color molecules (Vd) in solid tumors. Evans blue-labeled albumin was infused locally with the use of a needle into a rat fibrosarcoma ex vivo under different pressures. After the infusion, tumor tissues were sectioned serially into thin slices. The blue area in each slice was quantified with the use of the newly developed technique. The Vd was calculated based on the blue area and the slice thickness. Our data showed that infusion pressure and volume (Vi) had significant effects on Vd. The median of Vd/Vi decreased from 2.99 to 1.79 when infusion pressure was increased from 50 to 163 cmH2O, presumably due to retardation of convective transport. In addition, the coefficient of variation in Vd/Vi was increased from 0.13 at 50 cmH2O to 0.64 at 163 cmH2O. The dependence of Vd/Vi and its variation on infusion pressure suggests that 1) infusion-induced tissue deformation is unpredictable and 2) both the unpredictability and the interstitial retardation of convective transport increase with infusion pressure.
Nitric oxide limits coronary vasoconstriction by a shear stress-dependent mechanism
Authors: Stepp David W. , Merkus Daphne , Nishikawa Yasuhiro , Chilian William M.
Published: December 2017

Increases in shear stress promote coronary vasodilation by stimulating the production of nitric oxide (NO). Whether shear stress-induced NO production also limits vasoconstriction in the coronary microcirculation in vivo is unknown. Accordingly, we measured microvascular diameter and flow velocity in the beating heart along with estimated blood viscosity to calculate shear stress during vasoconstriction with endothelin or vasopressin. Measurements were repeated in the presence of N G-monomethyl-l-arginine (l-NMMA) to inhibit NO production and BQ-788 to block NO-linked endothelin type B receptors. BQ-788 did not augment steady-state constriction to endothelin, suggesting that NO production via activation of this receptor is inconsequential. l-NMMA potentiated constriction to both agonists, particularly in small arteries (inner diameter >120 μm). Shear stresses in small arteries were elevated during constriction and further elevated during constriction after l-NMMA. These observations suggest that NO production limits vasoconstriction in the coronary microcirculation and that the principal stimulus for this governance is elevated shear stress. The degree of shear stress moderation of constriction is heterogeneously distributed, with small arteries displaying a higher degree of shear stress regulation than arterioles. These results provide the strongest evidence to date that shear stress-mediated production of NO exerts a “braking” influence on constriction in the coronary microcirculation.
Angiotensin II modulates catecholamine release into interstitial fluid of canine myocardium in vivo
Authors: Farrell Diane M. , Wei Chih-Chang , Tallaj José , Ardell Jeffrey L. , Armour J. Andrew , Hageman Gilbert R. , Bradley Wayne E. , Dell'Italia Louis J.
Published: December 2017

This study tested the hypothesis that exogenous infusion of angiotensin II (ANG II) leads to the release of catecholamines [norepinephrine (NE) and epinephrine (EPI)] into the cardiac interstitial fluid (ISF) space of dogs with adrenals intact (AI) ( n = 7) and with adrenals clamped (AC) ( n = 5). LV ISF samples were collected at 3-min intervals during administration of ANG II (100 μM ANG II at 1 ml/min for 10 min) to right atrial neurons via their local arterial blood supply and during electrical stimulation of the stellate ganglia of open-chest anesthetized dogs. In AI dogs, ANG II caused ISF NE to increase fivefold ( P < 0.05) without a significant increase in coronary sinus (CS) NE. Electrical stimulation (5 ms, 4 Hz, 8–14 V, and 10 min) of the stellate ganglia caused a similar increase in ISF NE ( P < 0.05), accompanied by a sevenfold increase in CS NE ( P < 0.05). ISF EPI increased greater than sixfold during ANG II infusion ( P < 0.05) and during stellate stimulation. However, during ANG II infusions, aorta plasma EPI levels increased fourfold in AI dogs, whereas in AC dogs, CS NE and EPI levels were unaffected during ANG II infusions. Nevertheless, baseline ISF NE and EPI did not differ and increased to a similar extent during ANG II infusions in AI versus AC dogs. Thus exogenously administered ANG II increases the amount of NE liberated into the ISF independent of the adrenal contribution, the amount matching that induced by electrical stimulation of all cardiac sympathetic efferent neurons. In contrast, NE spillover into the CS occurred only during electrical stimulation of stellate ganglia. NE release and uptake mechanisms within the myocardium are differently affected, depending on how the final common pathway of the sympathetic efferent nervous system is modified.
Negative wave reflections in pulmonary arteries
Authors: Hollander Ellen H. , Wang Jiun-Jr , Dobson Gary M. , Parker Kim H. , Tyberg John V.
Published: December 2017

The pulmonary arterial branching pattern suggests that the early systolic forward-going compression wave (FCW) might be reflected as a backward-going expansion wave (BEW). Accordingly, in 11 open-chest anesthetized dogs we measured proximal pulmonary arterial pressure and flow (velocity) and evaluated wave reflection using wave-intensity analysis under low-volume, high-volume, high-volume + 20 cmH2O positive end-expiratory pressure (PEEP), and hypoxic conditions. We defined the reflection coefficient R as the ratio of the energy of the reflected wave (BEW [−]; backward-going compression wave, BCW [+]) to that of the incident wave (FCW [+]). We found that R = −0.07 ± 0.02 under low-volume conditions, which increased in absolute magnitude to −0.20 ± 0.04 ( P < 0.01) under high-volume conditions. The addition of PEEP increased R further to −0.26 ± 0.02 ( P < 0.01). All of these BEWs were reflected from a site ∼3 cm downstream. During hypoxia, the BEW was maintained and a BCW appeared ( R = +0.09 ± 0.03) from a closed-end site ∼9 cm downstream. The normal pulmonary arterial circulation in the open-chest dog is characterized by negative wave reflection tending to facilitate right ventricular ejection; this reflection increases with increasing blood volume and PEEP.
Erythrocyte margination and sedimentation in skeletal muscle venules
Authors: Bishop Jeffrey J. , Nance Patricia R. , Popel Aleksander S. , Intaglietta Marcos , Johnson Paul C.
Published: December 2017

Previous studies in skeletal muscle of the dog and cat have shown that venous vascular resistance changes inversely with blood flow and may be due mainly to red blood cell aggregation, a phenomenon present in these species. To determine whether red blood cell axial migration and sedimentation contribute to this effect, we viewed either vertically or horizontally oriented venules of the rat spinotrapezius muscle with a horizontally oriented microscope during acute arterial pressure reduction. With normal (nonaggregating) rat blood, reduction of arterial pressure did not significantly change the relative diameter of the red blood cell column with respect to the venular wall. After induction of red blood cell aggregation in the rat by infusion of Dextran 500, red blood cell column diameter decreased up to 35% at low pseudoshear rates (below ∼5 s−1); the magnitude was independent of venular orientation. In vertically oriented venules, the plasma layer was symmetrical, whereas in horizontally oriented venules, the plasma layer formed near the upper wall. We conclude that, although red blood cell axial migration and sedimentation develop in vivo, they occur only for larger flow reductions than are needed to elicit changes in venous resistance.
Structural adaptation of microvascular networks: functional roles of adaptive responses
Authors: Pries A. R. , Reglin B. , Secomb T. W.
Published: December 2017

Terminal vascular beds continually adapt to changing demands. A theoretical model is used to simulate structural diameter changes in response to hemodynamic and metabolic stimuli in microvascular networks. Increased wall shear stress and decreased intravascular pressure are assumed to stimulate diameter increase. Intravascular partial pressure of oxygen (Po2) is estimated for each segment. Decreasing Po2is assumed to generate a metabolic stimulus for diameter increase, which acts locally, upstream via conduction along vessel walls, and downstream via metabolite convection. By adjusting the sensitivities to these stimuli, good agreement is achieved between predicted network characteristics and experimental data from microvascular networks in rat mesentery. Reduced pressure sensitivity leads to increased capillary pressure with reduced viscous energy dissipation and little change in tissue oxygenation. Dissipation decreases strongly with decreased metabolic response. Below a threshold level of metabolic response flow shifts to shorter pathways through the network, and oxygen supply efficiency decreases sharply. In summary, the distribution of vessel diameters generated by the simulated adaptive process allows the network to meet the functional demands of tissue while avoiding excessive viscous energy dissipation.
Na+/H+exchange inhibition prevents endothelial dysfunction after I/R injury
Authors: Gumina Richard J. , Moore Jeannine , Schelling Pierre , Beier Norbert , Gross Garrett J.
Published: December 2017

Whereas inhibition of the Na+/H+exchanger (NHE) has been demonstrated to reduce myocardial infarct size in response to ischemia-reperfusion injury, the ability of NHE inhibition to preserve endothelial cell function has not been examined. This study examined whether NHE inhibition could preserve endothelial cell function after 90 min of regional ischemia and 180 min of reperfusion and compared this inhibition with ischemic preconditioning (IPC). In a canine model either IPC, produced by one 5-min coronary artery occlusion (1 × 5′), or the specific NHE-1 inhibitor eniporide (EMD-96785, 3.0 mg/kg) was administered 15 min before a 90-min coronary artery occlusion followed by 3 h of reperfusion. Infarct size (IS) was determined by 2,3,5-triphenyl tetrazolium chloride staining and expressed as a percentage of the area-at-risk (IS/AAR). Endothelial cell function was assessed by measurement of coronary blood flow in response to intracoronary acetylcholine infusion at the end of reperfusion. Whereas neither control nor IPC-treated animals exhibited a significant reduction in IS/AAR or preservation of endothelial cell function, animals treated with the NHE inhibitor eniporide showed a marked reduction in IS/AAR and a significantly preserved endothelial cell function ( P < 0.05). Thus NHE-1 inhibition is more efficacious than IPC at reducing IS/AAR and at preserving endothelial cell function in dogs.
Coordinate regulation of endothelin and adrenomedullin secretion by oxidative stress in endothelial cells
Authors: Saito Takatoshi , Itoh Hiroshi , Chun Tae-Hwa , Fukunaga Yasutomo , Yamashita Jun , Doi Kentaro , Tanaka Tokuji , Inoue Mayumi , Masatsugu Ken , Sawada Naoki , Sakaguchi Satsuki , Arai Hiroshi , Mukoyama Masashi , Tojo Katsuyoshi , Hosoya Tatsuo , Nakao Kazuwa
Published: December 2017

To elucidate the significance of oxidative stress in the modulation of endothelial functions, we examined the effects of H2O2on the expression of two endothelium-derived vasoactive peptides, endothelin (ET) and adrenomedullin (Am), and their interaction. H2O2dose dependently suppressed ET secretion and ET-1 mRNA expression in bovine carotid endothelial cells (ECs). Menadion sodium bisulfate, a redox cycling drug, also decreased ET secretion in a dose-dependent manner. Catalase, a H2O2reductase, and dl-α-tocopherol (vitamin E) significantly inhibited H2O2-induced suppression of ET secretion. Downregulation of ET-1 mRNA under oxidative stress was regulated at the transcriptional level. In contrast, H2O2increased Am secretion (and its mRNA expression) accompanied by the augmentation of cAMP production. Am, as well as 8-bromo-cAMP and forskolin decreased ET secretion in a dose-dependent fashion. Furthermore, an anti-Am monoclonal antibody that we developed abolished H2O2-induced suppression of ET secretion at 6–24 h after the addition of H2O2. H2O2increased the intracellular Ca2+concentration ([Ca2+]i). Moreover, treatment with ionomycin, a Ca2+ionophore, and thapsigargin, an inhibitor of endoplasmic reticulum ATPase, decreased ET secretion dose dependently for 3 h. These results suggest that the production of ET was decreased via activation of the Am-cAMP pathway and by the elevation of [Ca2+]iunder oxidative stress. These findings elucidate the coordinate expression of two local vascular hormones, ET and Am, under oxidative stress, which may protect against vascular diseases.
Efficiency, efficacy, and adverse effects of adenovirus- vs. liposome-mediated gene therapy in cardiac allografts
Authors: Sen Luyi , Hong Yoo-Sun , Luo Haimin , Cui Guanggen , Laks Hillel
Published: December 2017

Virus- and nonvirus-mediated immunosuppressive cytokine gene therapy prolongs cardiac allograft survival in various nonfunctional heart transplant animal models, but its cardiac adverse effects have not been addressed. Recently, we developed a functional heterotopic heart transplant model in rabbits. For the first time, we were able to systematically compare the efficiency, efficacy, and adverse effects of optimized adenovirus- and liposome-mediated ex vivo interleukin (IL)-10 gene transfer in functional donor hearts. The efficiency of liposome-mediated gene transfer was greatly improved in physiologically functioning donor hearts and was only three- to fourfold lower than adenovirus-mediated gene transfer. The efficacy of liposome-mediated IL-10 gene transfer was much higher than that mediated by adenovirus. Significant negative inotropic and arrhythmogenic adverse effects on transplanted hearts were observed due to viral cytotoxicity and immunogenesis, which greatly abated the therapeutic efficacy of this first generation adenovirus-mediated gene therapy.
Microfocal X-ray CT imaging and pulmonary arterial distensibility in excised rat lungs
Authors: Karau Kelly L. , Johnson Roger H. , Molthen Robert C. , Dhyani Anita H. , Haworth Steven T. , Hanger Christopher C. , Roerig David L. , Dawson Christopher A.
Published: December 2017

The objective of this study was to develop an X-ray computed tomographic method for measuring pulmonary arterial dimensions and locations within the intact rat lung. Lungs were removed from rats and their pulmonary arterial trees were filled with perfluorooctyl bromide to enhance X-ray absorbance. The lungs were rotated within the cone of the X-ray beam projected from a microfocal X-ray source onto an image intensifier, and 360 images were obtained at 1° increments. The three-dimensional image volumes were reconstructed with isotropic resolution using a cone beam reconstruction algorithm. The vessel diameters were obtained by fitting a functional form to the image of the vessel circular cross section. The functional form was chosen to take into account the point spread function of the image acquisition and reconstruction system. The diameter measurements obtained over a range of vascular pressures were used to characterize the distensibility of the rat pulmonary arteries. The distensibility coefficient α [defined by D(P) = D(0)(1 + αP), where D(P) is the diameter at intravascular pressure (P)] was ∼2.8% mmHg and independent of vessel diameter in the diameter range (about 100 to 2,000 mm) studied.
Phosphorylation-dependent modulation of cardiac calcium current by intracellular free magnesium
Authors: Pelzer Siegried , La Chicuong , Pelzer Dieter J.
Published: December 2017

We compared the effects of cytosolic free magnesium (Mg[Formula: see text]) on L-type Ca2+current ( ICa,L) in patch-clamped guinea pig ventricular cardiomyocytes under basal conditions, after inhibition of protein phosphorylation, and after stimulation of cAMP-mediated phosphorylation. Basal ICa,Ldensity displayed a bimodal dependence on the concentration of Mg[Formula: see text]([Mg2+]i; 10−6–10−2M), which changed significantly as cell dialysis progressed due to a pronounced and long-lasting rundown of ICa,Lin low-Mg2+dialysates. Ten minutes after patch breakthrough, ICa,Ldensity (at +10 mV) in Mg[Formula: see text]-depleted cells ([Mg2+]i∼1 μM) was elevated, increased to a maximum at ∼20 μM [Mg2+]i, and declined steeply at higher [Mg2+]i. Treatment with the broad-spectrum protein kinase inhibitor K252a (10 μM) reduced ICa,Ldensity and abolished these effects of Mg[Formula: see text] except for a negative shift of ICa,L-voltage relations with increasing [Mg2+]i. Maximal stimulation of cAMP-mediated phosphorylation occluded the Mg[Formula: see text]-induced stimulation of ICa,Land prevented inhibitory effects of the ion at [Mg2+]i<1 mM but not at higher concentrations. These results show that the modulation of ICa,Lby Mg[Formula: see text] requires protein kinase activity and likely originates from interactions of the ion with proteins involved in the regulation of protein phosphorylation/dephosphorylation. Stimulatory effects of Mg[Formula: see text] on ICa,Lseem to increase the cAMP-mediated phosphorylation of Ca2+channels, whereas inhibitory effects of Mg[Formula: see text] appear to curtail and/or reverse cAMP-mediated phosphorylation.
Regulation of myocardial fatty acid oxidation by substrate supply
Authors: Longnus Sarah L. , Wambolt Richard B. , Barr Rick L. , Lopaschuk Gary D. , Allard Michael F.
Published: December 2017

We tested the hypothesis that myocardial substrate supply regulates fatty acid oxidation independent of changes in acetyl-CoA carboxylase (ACC) and 5′-AMP-activated protein kinase (AMPK) activities. Fatty acid oxidation was measured in isolated working rat hearts exposed to different concentrations of exogenous long-chain (0.4 or 1.2 mM palmitate) or medium-chain (0.6 or 2.4 mM octanoate) fatty acids. Fatty acid oxidation was increased with increasing exogenous substrate concentration in both palmitate and octanoate groups. Malonyl-CoA content only rose as acetyl-CoA supply from octanoate oxidation increased. The increases in octanoate oxidation and malonyl-CoA content were independent of changes in ACC and AMPK activity, except that ACC activity increased with very high acetyl-CoA supply levels. Our data suggest that myocardial substrate supply is the primary mechanism responsible for alterations in fatty acid oxidation rates under nonstressful conditions and when substrates are present at physiological concentrations. More extreme variations in substrate supply lead to changes in fatty acid oxidation by the additional involvement of intracellular regulatory pathways.
Effect of aging on the ability of preconditioning to protect rat hearts from ischemia-reperfusion injury
Authors: Schulman Daniel , Latchman David S. , Yellon Derek M.
Published: December 2017

Ischemic preconditioning (IP) reduces infarct size in young animals; however, its impact on aging is underinvestigated. The effect of variations in IP stimuli was studied in young, middle-aged, and aged rat hearts. Isolated hearts underwent 35 min of regional ischemia and 120 min of reperfusion. Hearts with IP were subjected to either one ischemia-reperfusion cycle (5 min of ischemia and 5 min of reperfusion per cycle) or three successive cycles before 35 min of regional ischemia. Additional studies investigated the effects of pharmacological preconditioning in aged hearts using the adenosine A1 receptor agonist 2-chloro- N 6-cyclopentyladenosine, the protein kinase C analog 1,2-dioctanoyl- sn-glycerol, and the mitochondrial ATP-sensitive potassium (KATP)-channel opener diazoxide. Infarct sizes indicated that the aged rat heart could not be preconditioned via ischemic or pharmacological means. The middle-aged rat heart had a blunted IP response compared with the young adult (only an increased IP stimulus caused a significant reduction in infarct size). These results suggest that there are defects within the IP signaling cascade of the aged heart. Clinical relevance is important if we are to use any IP-like mimetics to the benefit of an aging population.
Superoxide levels and function of cerebral blood vessels after inhibition of CuZn-SOD
Authors: Didion Sean P. , Hathaway Christopher A. , Faraci Frank M.
Published: December 2017

The goal of this study was to examine the role of endogenous copper/zinc (CuZn)-superoxide dismutase (SOD) on superoxide levels and on responses of cerebral blood vessels to stimuli that are mediated by nitric oxide (acetylcholine) and cyclooxygenase-dependent mechanisms (bradykinin and arachidonic acid). Levels of superoxide in the rabbit basilar artery were measured using lucigenin-enhanced chemiluminescence (5 μM lucigenin). Diethyldithiocarbamate (DDC; 10 mM), an inhibitor of CuZn-SOD, increased superoxide levels by ∼2.4-fold ( P < 0.05) from a baseline value of 1.0 ± 0.2 relative light units · min−1 · mm−2(means ± SE). The diameter of cerebral arterioles (baseline diameter, 99 ± 3 μm) was also measured using a closed cranial window in anesthetized rabbits. Topical application of DDC attenuated responses to acetylcholine, bradykinin, and arachidonate, but not nitroprusside. For example, 10 μM arachidonic acid dilated cerebral arterioles by 40 ± 5 and 2 ± 2 μm under control conditions and after DDC, respectively ( P < 0.05). These inhibitory effects of DDC were reversed by the superoxide scavenger 4,5-dihydroxy-1,3-benzenedisulfonic acid (10 mM). Arachidonate increased superoxide levels in the basilar artery moderately under normal conditions and this increase was greatly augmented in the presence of DDC. These findings suggest that endogenous CuZn-SOD limits superoxide levels under basal conditions and has a marked influence on increases in superoxide in vessels exposed to arachidonic acid. The results also suggest that nitric oxide- and cyclooxygenase-mediated responses in the cerebral microcirculation are dependent on normal activity of CuZn-SOD.
Functional expression of a GFP-tagged Kv1.5 α-subunit in mouse ventricle
Authors: Li Huilin , Guo Weinong , Xu Haodong , Hood Rebecca , Benedict Andrew T. , Nerbonne Jeanne M.
Published: December 2017

The experiments here were undertaken to determine the feasibility of increasing the cell surface expression of voltage-gated ion channels in cardiac cells in vivo and to explore the functional consequences of ectopic channel expression. Transgenic mice expressing a green fluorescent protein (GFP)-tagged, voltage-gated K+(Kv) channel α-subunit, Kv1.5-GFP, driven by the cardiac-specific α-MHC promoter, were generated. In recent studies, Kv1.5 has been shown to encode the micromolar 4-aminopyridine (4-AP)-sensitive delayed rectifier K+current ( IK,slow) in mouse myocardium. Unexpectedly, Kv1.5-GFP expression is heterogeneous in the ventricles of these animals. Although no electrocardiographic abnormalities were evident, expression of Kv1.5-GFP results in marked decreases in action potential durations in GFP-positive ventricular myocytes. In voltage-clamp recordings from GFP-positive ventricular myocytes, peak outward K+currents are significantly higher, and their waveforms are distinct from those recorded from wild-type cells. Pharmacological experiments revealed a selective increase in a micromolar 4-AP-sensitive current, similar to the 4-AP-sensitive component of IK,slowin wild-type cells. The inactivation rate of the “overexpressed” current, however, is significantly slower than the Kv1.5-encoded component of IK,slowin wild-type cells, suggesting differences in association with accessory subunits and/or posttranslational processing.
Effect of adenosine receptor blockade on pial arteriolar dilation during sciatic nerve stimulation
Authors: Meno Joseph R. , Crum Alison V. , Winn H. Richard
Published: December 2017

In the present study, we report the effects of adenosine receptor antagonists on pial vasodilatation during contralateral sciatic nerve stimulation (SNS). The pial circulation was observed through a closed cranial window in α-chloralose-anesthetized rats. In artificial cerebrospinal fluid (CSF), SNS resulted in a 30.5 ± 13.2% increase in pial arteriolar diameter in the hindlimb somatosensory cortex. Systemic administration of the selective adenosine A2A receptor antagonist, 4-(2-{7-amino-2-[2-furyl][3,2,4]triazolol[2,3-a][1,3,5]triazin-5-yl-amino} ethyl)phenol (ZM-241385), significantly ( P < 0.05, n = 6) attenuated the SNS-induced vasodilatation. Systemic administration of 8-( p-sulfophenyl)theophylline (8SPT), a nonselective antagonist that is blood-brain barrier (BBB) impermeable, had no effect on vasodilatation to SNS. In contrast, systemic theophylline, which readily penetrates the BBB, nearly abolished the SNS-induced vasodilatation ( P < 0.01; n = 7). Topical superfusion of 8SPT significantly ( P < 0.01; n = 6) attenuated vasodilatation during SNS. Topical superfusion of 8- cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective adenosine A1 receptor antagonist, significantly potentiated SNS-induced vasodilatation ( P < 0.01; n ≥ 5). Hypercarbic vasodilatation and somatosensory-evoked potentials were not affected by any of the compounds tested. Our findings suggest that luminal endothelial adenosine receptors are not involved in the arteriolar response to SNS, as demonstrated by a lack of effect with systemic 8SPT. Furthermore, the adenosine A2A receptor subtype appears to be involved in the dilator response to SNS. Finally, the neuromodulatory action of adenosine, via the A1 receptor subtype, significantly influences SNS-induced vasodilatation. Thus the present study provides further evidence for a role of adenosine in the regulation of CBF during somatosensory stimulation.
Gender affects sympathetic and hemodynamic response to postural stress
Authors: Shoemaker J. Kevin , Hogeman Cynthia S. , Khan Mazhar , Kimmerly Derek S. , Sinoway Lawrence I.
Published: December 2017

We tested the hypothesis that differences in sympathetic reflex responses to head-up tilt (HUT) between males ( n = 9) and females ( n = 8) were associated with decrements in postural vasomotor responses in women. Muscle sympathetic nerve activity (MSNA; microneurography), heart rate, stroke volume (SV; Doppler), and blood pressure (Finapres) were measured during a progressive HUT protocol (5 min at each of supine, 20°, 40°, and 60°). MSNA and hemodynamic responses were also measured during the cold pressor test (CPT) to examine nonbaroreflex neurovascular control. SV was normalized to body surface area (SVi) to calculate the index of cardiac output (Qi), and total peripheral resistance (TPR). During HUT, heart rate increased more in females versus males ( P < 0.001) and SVi and Qi decreased similarly in both groups. Mean arterial pressure (MAP) increased to a lesser extent in females versus males in the HUT ( P < 0.01) but increases in TPR during HUT were similar. MSNA burst frequency was lower in females versus males in supine ( P < 0.03) but increased similarly during HUT. Average amplitude/burst increased in 60° HUT for males but not females. Both males and females demonstrated an increase in MAP as well as MSNA burst frequency, mean burst amplitude, and total MSNA during the CPT. However, compared with females, males demonstrated a greater neural response (ΔTotal MSNA) due to a larger increase in mean burst amplitude ( P < 0.05). Therefore, these data point to gender-specific autonomic responses to cardiovascular stress. The different MSNA response to postural stress between genders may contribute importantly to decrements in blood pressure control during HUT in females.
Losartan prevents contractile dysfunction in rat myocardium after left ventricular myocardial infarction
Authors: Daniëls Marcel C. G. , Keller Rebecca S. , de Tombe Pieter P.
Published: December 2017

We studied the effects of chronic losartan (Los) treatment on contractile function of isolated right ventricular (RV) trabeculae from rat hearts 12 wk after left ventricular (LV) myocardial infarction (MI) had been induced by ligation of the left anterior descending artery at 4 wk of age. After recovery, one-half of the animals were started on Los treatment (MI+Los; 30 mg · kg−1 · day−1per os); the remaining animals were not treated (MI group). Rats without infarction or Los treatment served as controls (Con group). MI resulted in increases in LV and RV weight and unstressed LV cavity diameter; these were partially prevented by Los treatment. The active peak twitch force-sarcomere length relation was depressed in MI compared with either Con or MI+Los. Likewise, maximum Ca2+saturated twitch force was depressed in MI, whereas twitch relaxation and twitch duration were prolonged. Myofilament function, as measured in skinned trabeculae, was not significantly different among the Con, MI, and MI+Los groups. We conclude that Los prevents contractile dysfunction in rat RV trabeculae after LV MI. Our results suggest that the beneficiary effect of Los treatment results not from improved myofilament function but rather from improved myocyte Ca2+homeostasis.
Role of Cl− current in endothelin-1-induced contraction in rabbit basilar artery
Authors: Dai Yun , Zhang John H.
Published: December 2017

Cl− efflux induces depolarization and contraction of smooth muscle cells. This study was undertaken to explore the role of Cl− channels in endothelin-1 (ET-1)-induced contraction in rabbit basilar artery. Male New Zealand White rabbits ( n = 26), weighing 1.8–2.5 kg, were euthanized by an overdose of pentobarbital. The basilar arteries were removed for isometric tension recording. ET-1 produced a concentration-dependent contraction of the rabbit basilar artery in the normal Cl− Krebs-Henseleit bicarbonate buffer (123 mM Cl−). The ET-1-induced contraction was reduced by the following manipulations: 1) inhibition of Na+-K+-2Cl− cotransporter with bumetanide (3 × 10−5 and 10−4 M), 2) bicarbonate-free solution to disable Cl−/HCO[Formula: see text] exchanger, and 3) preincubation of rings with the Cl− channel blockers niflumic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid, and indanyloxyacetic acid 94. The ET-1-induced contraction was enhanced by substitution of extracellular Cl− (10 mM) with methanesulfonic acid (113 mM). Cl− channels are involved in ET-1-induced contraction in the rabbit basilar artery.
Signaling pathway for nitric oxide generation with simulated ischemia in flow-adapted endothelial cells
Authors: Wei Zhihua , Al-Mehdi Abu B. , Fisher Aron B.
Published: December 2017

Ischemia in the intact ventilated lung (oxygenated ischemia) leads to endothelial generation of reactive oxygen species (ROS) and nitric oxide (NO). This study investigated the signaling pathway for NO generation with oxygenated ischemia in bovine pulmonary artery endothelial cells (BPAEC) that were flow adapted in vitro. BPAECs were cultured in an artificial capillary system and subjected to abrupt cessation of flow (ischemia) under conditions where cellular oxygenation was maintained. Immunoblotting and dichlorofluorescein/triazolofluorescein fluorescence were used to assess extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylation and ROS/NO generation, respectively. ERK1/2 phosphorylation significantly increased during ischemia, whereas total ERK1/2 did not change. ERK1/2 phosphorylation was suppressed by an inhibitor of tyrosine phosphorylation (genestein), cholesterol-binding reagents (filipin or cyclodextrin), or inhibitors of ROS (diphenyleneiodonium, N-acetylcysteine, or catalase), suggesting a role for both membrane cholesterol and ROS in ERK1/2 activation. Ischemia resulted in a 1.8-fold increase in NO generation that was suppressed by inhibitors of ERK1/2 activation (PD-98059 or U-0126). A calmodulin inhibitor (calmidizolium) or removal of Ca2+ from the medium also blocked NO generation, indicating that endothelial NO synthase (eNOS) is the activated isoform. These results indicate ischemia induces NO generation (possibly through a membrane cholesterol-sensitive flow sensor), the ERK1/2 cascade mediates signaling from the sensor to eNOS, and ROS are required for ERK activation.
Central mineralocorticoid receptor blockade improves volume regulation and reduces sympathetic drive in heart failure
Authors: Francis Joseph , Weiss Robert M. , Wei Shun-Guang , Johnson Alan Kim , Beltz Terry G. , Zimmerman Kathy , Felder Robert B.
Published: December 2017

The mineralocorticoid (MC) receptor antagonist spironolactone (SL) improves morbidity and mortality in patients with congestive heart failure (CHF). We tested the hypothesis that the central nervous system actions of SL contribute to its beneficial effects. SL (100 ng/h for 28 days) or ethanol vehicle (VEH) was administered intracerebroventricularly or intraperitoneally to rats with CHF induced by coronary artery ligation (CL) and to SHAM-operated controls. The intracerebroventricular SL treatment prevented the increase in sodium appetite and the decreases in sodium and water excretion observed within a week of CL in VEH-treated CHF rats. Intraperitoneal SL also improved volume regulation in the CHF rats, but only after 3 wk of treatment. Four weeks of SL treatment, either intracerebroventricularly or intraperitoneally, ameliorated both the increase in sympathetic drive and the impaired baroreflex function observed in VEH-treated CHF rats. These findings suggest that activation of MC receptors in the central nervous system plays a critical role in the altered volume regulation and augmented sympathetic drive that characterize clinical heart failure.
No involvement of nitric oxide in the limitation of β-adrenergic inotropic responsiveness during ischemia
Authors: Post Heiner , Schulz Rainer , Gres Petra , Heusch Gerd
Published: December 2017

We tested whether or not endogenous nitric oxide (NO) attenuates β-adrenergic inotropic responsiveness during normoperfusion or moderate myocardial ischemia. In 13 anesthetized pigs with a cannulated left anterior descending (LAD) coronary artery, the maximal contractile responses to intracoronary dobutamine and calcium were assessed during normoperfusion and at the end of a 90-min period of moderate ischemia (50% reduction in coronary arterial inflow) without ( group 1, n = 6) and with ( group 2, n = 7) prior inhibition of NO synthesis [30 mg/kg iv Nω-nitro-l-arginine (l-NNA)]. Contractile function was assessed by a regional work index (sonomicrometry, micromanometry, mm · mmHg). In groups 1 and 2 during normoperfusion, the maximal increase of the work index was greater with calcium than with dobutamine. At the end of ischemia in group 1, the baseline work index was decreased by ∼50%, and the subsequent maximal increase of the work index with dobutamine, but not with calcium, was reduced compared with normoperfusion. In group 2 during normoperfusion, l-NNA did not alter the maximal increases of the work index with dobutamine or calcium. At the end of ischemia, the baseline work index was reduced by 64%, and the subsequent maximal increases of the work index with both dobutamine and calcium were reduced compared with normoperfusion; however, the response to calcium was still greater than that to dobutamine. We conclude that endogenous NO does not limit β-adrenergic inotropic responsiveness in normoperfused or moderately ischemic porcine myocardium.
Roles of norepinephrine and ATP in sympathetically evoked vasoconstriction in rat tail and hindlimb in vivo
Authors: Johnson Christopher D. , Coney Andrew M. , Marshall Janice M.
Published: December 2017

In anesthetized rats, we characterized the contributions of norepinephrine (NE) and ATP to changes in tail and hindlimb (femoral) vascular resistances (TVR and FVR, respectively) evoked by three patterns of sympathetic stimulation: 1) couplets (2 impulses at 20 Hz), 2) short trains (20 impulses at 20 Hz), and 3) a natural irregular pattern previously recorded from a sympathetic fiber innervating the rat tail artery. All stimuli evoked greater changes in TVR than FVR. Judging from the effects of the α-adrenoceptor antagonist phentolamine, the purinergic receptor antagonist suramin, or α,β-methylene ATP (which desensitizes P2X receptors), we propose that NE has a major role in the constriction evoked by the couplet, as well as by the short train and by the low- and high-frequency components of the natural pattern, but that considerable synergy occurred between the actions of ATP and NE. This contrasts with previous in vitro studies that indicated that ATP dominates vascular responses evoked by sympathetic stimulation with a few impulses at low frequency and that NE dominates responses to longer trains or at high frequencies.
Angiotensin II inhibits and alters kinetics of voltage-gated K+channels of rat arterial smooth muscle
Authors: Hayabuchi Y. , Standen N. B. , Davies N. W.
Published: December 2017

The vasoconstrictor angiotensin II (ANG II) inhibits several types of K+channels. We examined the inhibitory mechanism of ANG II on voltage-gated K+(KV) currents ( IKV) recorded from isolated rat arterial smooth muscle using patch-clamp techniques. Application of 100 nM ANG II accelerated the activation of IKVbut also caused inactivation. These effects were abolished by the AT1receptor antagonist losartan. The protein kinase A (PKA) inhibitor Rp-cyclic 3′,5′-hydrogen phosphothioate adenosine (100 μM) and an analog of diacylglycerol, 1,2-dioctanyoyl-rac-glycerol (2 μM), caused a significant reduction of IKV. Furthermore, the combination of 5 μM PKA inhibitor peptide 5–24 (PKA-IP) and 100 μM protein kinase C (PKC) inhibitor peptide 19–27 (PKC-IP) prevented the inhibition by ANG II, although neither alone was effective. The ANG II effect seen in the presence of PKA-IP remained during addition of the Ca2+-dependent PKC inhibitor Gö6976 (1 μM) but was abolished in the presence of 40 μM PKC-ε translocation inhibitor peptide. These results demonstrate that ANG II inhibits KVchannels through both activation of PKC-ε and inhibition of PKA.