bluuebunny/crossref_metadata_2025 huggingface dataset:
Ablation of mitral annular and leaflet muscle: effects on annular and leaflet dynamics
Authors: Timek Tomasz A. , Lai David T. , Dagum Paul , Tibayan Frederick , Daughters George T. , Liang David , Berry Gerald J. , Miller D. Craig , Ingels Neil B.
Published: March 2015

Mitral annular (MA) and leaflet three-dimensional (3-D) dynamics were examined after circumferential phenol ablation of the MA and anterior mitral leaflet (AML) muscle. Radiopaque markers were sutured to the left ventricle, MA, and both mitral leaflets in 18 sheep. In 10 sheep, phenol was applied circumferentially to the atrial surface of the mitral annulus and the hinge region of the AML, whereas 8 sheep served as controls. Animals were studied with biplane video fluoroscopy for computation of 3-D mitral annular area (MAA) and leaflet shape. MAA contraction (MAACont) was determined from maximum to minimum value. Presystolic MAA (PS-MAACont) reduction was calculated as the percentage of total reduction occurring before end diastole. Phenol ablation decreased PS-MAACont (72 ± 6 vs. 47 ± 31%, P = 0.04) and delayed valve closure (31 ± 11 vs. 57 ± 25 ms, P = 0.017). In control, the AML had a compound sigmoid shape; after phenol, this shape was entirely concave to the atrium during valve closure. These data indicate that myocardial fibers on the atrial side of the valve influence the 3-D dynamic geometry and shape of the MA and AML.
Cytochrome P-450 metabolites but not NO, PGI2, and H2O2 contribute to ACh-induced hyperpolarization of pressurized canine coronary microvessels
Authors: Tanaka Mitsuaki , Kanatsuka Hiroshi , Ong Boon-Hooi , Tanikawa Toshinori , Uruno Akira , Komaru Tatsuya , Koshida Ryoji , Shirato Kunio
Published: March 2015

The endothelium-dependent hyperpolarization of cells has a crucial role in regulating vascular tone, especially in microvessels. Nitric oxide (NO) and prostacyclin (PGI2), in addition to endothelium-derived hyperpolarizing factor (EDHF), have been reported to hyperpolarize vascular smooth muscle in several organs. Studies have reported the hyperpolarizing effects of these factors are increased by a stretch in large coronary arteries. EDHF has not yet been identified and cytochrome P-450 metabolites and H2O2 are candidates for EDHF. With the use of the membrane potential-sensitive fluorescent dye bis-(1,3-dibutylbarbituric acid)trimethione oxonol [DiBAC4(3)], we examined whether NO, PGI2, cytochrome P-450 metabolites, and H2O2 contribute to ACh-induced hyperpolarization in pressurized coronary microvessels. Canine coronary arterial microvessels (60–356 μm internal diameter) were cannulated and pressurized at 60 cmH2O in a vessel chamber perfused with physiological salt solution containing DiBAC4(3). Fluorescence intensity and diameter were measured on a computer. There was a linear correlation between changes in the fluorescence intensity and membrane potential. ACh significantly decreased the fluorescence intensity (hyperpolarization) of the microvessels without any inhibitors. Endothelial damage caused by air perfusion abolished the ACh-induced decrease in fluorescence intensity. The inhibitors of NO synthase and cyclooxygenase did not affect the ACh-induced decreases in the fluorescence intensity. The addition of 17-octadecynoic acid, a cytochrome P-450 monooxygenase inhibitor, to those inhibitors significantly attenuated the ACh-induced decreases in fluorescence intensity, whereas catalase, an enzyme that dismutates H2O2 to form water and oxygen, did not. Furthermore, catalase did not affect the vasodilation produced by ACh. These results indicate that NO and PGI2 do not contribute to the ACh-induced hyperpolarization and that the cytochrome P-450 metabolites but not H2O2 are involved in EDHF-mediated hyperpolarization in canine coronary arterial microvessels.
Ketamine blocks Ca2+-activated K+ channels in rabbit cerebral arterial smooth muscle cells
Authors: Han Jin , Kim Nari , Joo Hyun , Kim Euiyong
Published: March 2015

Although ketamine and Ca2+-activated K+ (KCa) channels have been implicated in the contractile activity regulation of cerebral arteries, no studies have addressed the specific interactions between ketamine and the KCa channels in cerebral arteries. The purpose of this study was to examine the direct effects of ketamine on KCa channel activities using the patch-clamp technique in single-cell preparations of rabbit middle cerebral arterial smooth muscle. We tested the hypothesis that ketamine modulates the KCa channel activity of the cerebral arterial smooth muscle cells of the rabbit. Vascular myocytes were isolated from rabbit middle cerebral arteries using enzymatic dissociation. Single KCa channel activities of smooth muscle cells from rabbit cerebral arteries were recorded using the patch-clamp technique. In the inside-out patches, ketamine in the micromolar range inhibited channel activity with a half-maximal inhibition of the ketamine conentration value of 83.8 ± 12.9 μM. The Hill coefficient was 1.2 ± 0.3. The slope conductance of the current-voltage relationship was 320.1 ± 2.0 pS between 0 and +60 mV in the presence of ketamine and symmetrical 145 mM K+. Ketamine had little effect on either the voltage-dependency or open- and closed-time histograms of KCa channel. The present study clearly demonstrates that ketamine inhibits KCa channel activities in rabbit middle cerebral arterial smooth muscle cells. This inhibition of KCa channels may represent a mechanism for ketamine-induced cerebral vasoconstriction.
Heart failure and greater infarct expansion in middle-aged mice: a relevant model for postinfarction failure
Authors: Gould Kenneth E. , Taffet George E. , Michael Lloyd H. , Christie Robert M. , Konkol Debra L. , Pocius Jennifer S. , Zachariah Justin P. , Chaupin Damian F. , Daniel Sherita L. , Sandusky George E. , Hartley Craig J. , Entman Mark L.
Published: March 2015

Young mice tolerate myocardial loss after coronary artery ligation (CAL) without congestive heart failure (CHF) signs or mortality. We predicted a CHF phenotype after CAL in aged mice. Left coronary artery ligation produced permanent myocardial infarcts (MI). Mortality was higher in male 14-mo-old C57BL/6N mice (Older mice) than in 2-mo-old mice (Young mice) (16 of 25 Older mice died vs. 0 of 10 Young mice, P < 0.02). After 8 wk, rales, weight loss, and lethargy preceded deaths. Captopril (50 mg · kg−1 · day−1) increased Older mouse survival (6 of 22 died, P < 0.02). Captopril improved systolic function (peak aortic blood velocity) from 76 ± 6% of baseline in untreated Older mice to 93 ± 8% ( P < 0.036). At 24 h, MI comprised 28 ± 4% of the left ventricle in Young mice, surprisingly larger than that in Older mice (18 ± 2%, P < 0.011). Endocardial area underlying the infarct scar was significantly larger in Older mice than in Young mice. Captopril did not reduce expansion but markedly reduced septal hypertrophy. Aging reduces compensatory ability in mice despite smaller acute infarcts. Less effective myocardial repair, greater infarct expansion, and septal hypertrophy are seen with aging. Aging is a more relevant murine model of post-MI heart failure in patients.
Effects of acute reduction of temperature on ventricular fibrillation activation patterns
Authors: Chorro Francisco J. , Guerrero Juan , Ferrero Angel , Tormos Alvaro , Mainar Luis , Millet José , Cánoves Joaquín , Porres Juan C. , Sanchis Juan , López-Merino Vicente , Such Luis
Published: March 2015

Because of its electrophysiological effects, hypothermia can influence the mechanisms that intervene in the sustaining of ventricular fibrillation. We hypothesized that a rapid and profound reduction of myocardial temperature impedes the maintenance of ventricular fibrillation, leading to termination of the arrhythmia. High-resolution epicardial mapping ( series 1; n = 11) and transmural recordings of ventricular activation ( series 2; n = 10) were used to analyze ventricular fibrillation modification during rapid myocardial cooling in Langendorff-perfused rabbit hearts. Myocardial cooling was produced by the injection of cold Tyrode into the left ventricle after induction of ventricular fibrillation. Temperature and ventricular fibrillation dominant frequency decay fit an exponential model to arrhythmia termination in all experiments, and both parameters were significantly correlated ( r = 0.70, P < 0.0001). Termination of the arrhythmia occurred preferentially in the left ventricle and was associated with a reduction in conduction velocity (−60% in left ventricle and −54% in right ventricle; P < 0.0001) and with activation maps predominantly exhibiting a single wave front, with evidence of wave front extinction. We conclude that a rapid reduction of temperature to <20°C terminates ventricular fibrillation after producing an important depression in myocardial conduction.
Cause and effect relationship between myocardial mast cell number and matrix metalloproteinase activity
Authors: Brower Gregory L. , Chancey Amanda L. , Thanigaraj Srihari , Matsubara Beatriz B. , Janicki Joseph S.
Published: March 2015

The objectives of this study were to investigate the temporal response of left ventricular (LV) matrix metalloproteinase (MMP) activity and collagen volume fraction (CVF) induced by an aortocaval fistula and the role of cardiac mast cells in regulating MMP activity. LV tissue was analyzed for MMP activity, CVF, and mast cell number in rats euthanized at 0.5, 1, 2, 3, 5, 14, 21, 35, and 56 days. Additional rats treated with the mast cell membrane-stabilizing drug cromolyn sodium were euthanized 1, 2, and 3 days postfistula. Marked increases in MMP activity occurred rapidly and remained significantly elevated for 5 days before returning toward normal. A significant decrease in CVF occurred by day 5, but thereafter CVF rebounded to normal or above normal values. The number of myocardial mast cells also significantly increased postfistula, and there was a close association between mast cell density and MMP activity. Cromolyn treatment prevented the increase in mast cell number and MMP activity. Thus it is concluded that cardiac mast cells play a major role in the regulation of MMP activity.
Comparison of effects of two hemoglobin-based O2carriers on intestinal integrity and microvascular leakage
Authors: Baldwin Ann L. , Wiley Elizabeth B. , Alayash Abdu I.
Published: March 2015

Two “blood substitutes,” a diaspirin cross-linked human hemoglobin [bis(3,5 dibromosalicyl)fumarate, DBBF-Hb] and a bovine polymerized hemoglobin (PolyHbBv), advanced to clinical trials, are used in this study. Previously, we have shown that injection of DBBF-Hb into the rat circulation produces venular leakage and intestinal epithelial disruption. The purpose of this study was to determine whether PolyHbBv, currently approved for veterinary use in the United States, shows similar effects. In anesthetized Sprague-Dawley rats, the mesenteric microvasculature was perfused with DBBF-Hb ( n = 6), PolyHbBv ( n = 5), cyanomet Hb (CNmet-DBBF-Hb), or HEPES-buffered saline with 0.5% bovine serum albumin (HBS-BSA) (controls, n = 7) for 10 min, followed by FITC-albumin for 3 min, and then fixed for microscopy. For DBBF-Hb, the mean leak number per micrometer venule length [2.41 ± 0.33 (±SE) × 10−3] was significantly greater than for PolyHbBv (0.53 ± 0.14 × 10−3), CNmet-DBBF-Hb (0.36 ± 0.14 × 10−3), and HBS-BSA (0.12 ± 0.08 × 10−3) ( P < 0.01). Corresponding quantities for leak area were 0.10 ± 0.03, 0.010 ± 0.003, 0.005 ± 0.003, and 0.02 ± 0.02 μm2/μm. In rats injected with DBBF-Hb ( n = 8), intestinal epithelial integrity was significantly compromised compared with those injected with PolyHbBv ( n = 5) or saline ( n = 6). These results indicate that intravascular PolyHbBv produces significantly less disruption of the intestinal exchange barrier than does DBBF-Hb, probably because the heme is not so easily oxidized.
Elevated glucose impairs cAMP-mediated dilation by reducing Kv channel activity in rat small coronary smooth muscle cells
Authors: Li Hongwei , Chai Qiang , Gutterman David D. , Liu Yanping
Published: March 2015

Hyperglycemia impairs endothelium-dependent vasodilation. In this study, we examined the effect of high glucose (HG) on vascular smooth muscle function. Rat small coronary arteries were freshly isolated or incubated for 24 h with normal glucose (NG; 5.5 mmol/l) or HG (23 mmol/l). In freshly isolated arteries, dilation to isoproterenol (Iso) was reduced by 3 mmol/l 4-aminopyridine (4-AP; 44 ± 10% vs. 77 ± 4%; P < 0.05) and further reduced by 4-AP + iberiotoxin (IbTX; 100 nmol/l; 17 ± 2%). Dilation to forskolin was abolished by 4-AP (–3 ± 17 vs. 73 ± 9%). cAMP production was similar in NG and HG vessels. Dilations to Iso and forskolin were significantly reduced in HG arteries (Iso, 41 ± 5% vs. 70 ± 6%; forskolin, 40 ± 4% vs. 75 ± 4%) compared with NG arteries. A similar reduction was also observed to the dilation to papaverine. Endothelial denudation had no effect on Iso-induced dilation. In HG vessels, the reduced 4-AP-sensitive component of Iso-induced dilation was greater compared with the IbTX-sensitive component. Iso increased whole cell K+ current in NG cells but had little effect in HG cells. Similarly, 4-AP-, but not IbTX-sensitive, K+ currents were reduced in HG cells. These results suggest that HG impairs cAMP-mediated dilation primarily by reducing Kv channel function. We speculate that in addition to the endothelial dysfunction, altered smooth muscle function may also contribute to the reduced coronary vasodilation in diabetes.
MMP inhibition modulates TNF-α transgenic mouse phenotype early in the development of heart failure
Authors: Li Yun You , Kadokami Toshiaki , Wang Ping , McTiernan Charles F. , Feldman Arthur M.
Published: March 2015

Myocardial extracellular matrix remodeling regulated by matrix metalloproteinases (MMPs) is implicated in the progression of heart failure. We hypothesized that MMP inhibition may modulate extracellular matrix remodeling and prevent the progression of heart failure. The effects of the MMP inhibitor BB-94 (also known as batimastat) on MMP expression, collagen expression, collagen deposition, collagen denaturation, and left ventricular structure and function in transgenic mice with cardiac-restricted overexpression of tumor necrosis factor-α (TNF-α) (TNF1.6) were assessed. The results showed that BB-94 reduced the expression of collagens, increased insoluble collagen and the ratio of undenatured to total soluble collagen, and prevented myocardial hypertrophy and diastolic dysfunction in young TNF1.6 mice. Furthermore, the treatment significantly improved cumulative survival of TNF1.6 mice. However, MMP inhibition did not have salutary effects on ventricular size and function in old mice with established heart failure. The results suggest that MMP activation may play a critical role in changes of myocardial function through the remodeling of extracellular matrix, and MMP inhibition may serve as a potential therapeutic strategy for heart failure, albeit within a narrow window during the development of heart failure.
Carnitine inhibits arachidonic acid turnover, platelet function, and oxidative stress
Authors: Pignatelli P. , Lenti L. , Sanguigni V. , Frati G. , Simeoni I. , Gazzaniga P. P. , Pulcinelli F. M. , Violi F.
Published: March 2015

Carnitine is a physiological cellular constituent that favors intracellular fatty acid transport, whose role on platelet function and O2free radicals has not been fully investigated. The aim of this study was to seek whether carnitine interferes with arachidonic acid metabolism and platelet function. Carnitine (10–50 μM) was able to dose dependently inhibit arachidonic acid incorporation into platelet phospholipids and agonist-induced arachidonic acid release. Incubation of platelets with carnitine dose dependently inhibited collagen-induced platelet aggregation, thromboxane A2formation, and Ca2+mobilization, without affecting phospholipase A2activation. Furthermore, carnitine inhibited platelet superoxide anion (O[Formula: see text]) formation elicited by arachidonic acid and collagen. To explore the underlying mechanism, arachidonic acid-stimulated platelets were incubated with NADPH. This study showed an enhanced platelet O[Formula: see text] formation, suggesting a role for NADPH oxidase in arachidonic acid-mediated platelet O[Formula: see text] production. Incubation of platelets with carnitine significantly reduced arachidonic acid-mediated NADPH oxidase activation. Moreover, the activation of protein kinase C was inhibited by 50 μM carnitine. This study shows that carnitine inhibits arachidonic acid accumulation into platelet phospholipids and in turn platelet function and arachidonic acid release elicited by platelet agonists.
GTP cyclohydrolase 1 inhibition attenuates vasodilation and increases blood pressure in rats
Authors: Mitchell Brett M. , Dorrance Anne M. , Webb R. Clinton
Published: March 2015

GTP cyclohydrolase 1 is the rate-limiting enzyme in production of tetrahydrobiopterin, a necessary cofactor for endothelial nitric oxide synthase. We tested the hypothesis that inhibition of tetrahydrobiopterin synthesis impairs endothelium-dependent relaxation and increase blood pressure in rats. 2,4-Diamino-6-hydroxypyrimidine (DAHP), a GTP cyclohydrolase 1 inhibitor, was given in drinking water (∼120 mg · kg–1 · day–1) to male Sprague-Dawley rats for 3 days. Systolic blood pressures were measured (tail-cuff procedure) for 3 days before and each day during DAHP treatment. Blood pressure was significantly increased after DAHP treatment (122 ± 2 vs. 154 ± 3 mmHg before and after DAHP, respectively; P < 0.05). Endothelium-intact aortic segments from pentobarbital sodium-anesthetized rats were isolated and hung in organ chambers for measurement of isometric force generation. Aortas from DAHP-treated rats exhibited a decreased maximal relaxation to ACh compared with controls [% relaxation from phenylephrine (10–7 M)-induced contraction: DAHP 57 ± 6% vs. control 79 ± 4%; P < 0.05]. Relaxation responses to A-23187 were also decreased in aortas from DAHP-treated rats compared with controls. Incubation with sepiapterin (10–4 M, 1 h), which produces tetrahydrobiopterin via a salvage pathway, restored relaxation to ACh in aortas from DAHP-treated rats. Superoxide dismutase significantly increased ACh-induced relaxation in aortas from DAHP-treated rats, whereas catalase had no effect. Endothelium-independent relaxation to sodium nitroprusside in aortas from DAHP-treated rats was not different from control rats; however, nitric oxide synthase inhibition increased sensitivity to sodium nitroprusside in aortas from DAHP-treated rats. These results support the hypothesis that GTP cyclohydrolase 1 inhibition decreases relaxation and increases blood pressure in rats.
Effects of Na+/Ca2+ exchange induced by SR Ca2+ release on action potentials and afterdepolarizations in guinea pig ventricular myocytes
Authors: Spencer C. Ian , Sham James S. K.
Published: March 2015

In cardiac cells, evoked Ca2+ releases or spontaneous Ca2+ waves activate the inward Na+/Ca2+ exchange current ( INaCa), which may modulate membrane excitability and arrhythmogenesis. In this study, we examined changes in membrane potential due to INaCa elicited by sarcoplasmic reticulum (SR) Ca2+ release in guinea pig ventricular myocytes using whole cell current clamp, fluorescence, and confocal microscopy. Inhibition of INaCa by Na+-free, Li+-containing Tyrode solution reversibly abbreviated the action potential duration at 90% repolarization (APD90) by 50% and caused SR Ca2+ overload. APD90 was similarly abbreviated in myocytes exposed to the Na+/Ca2+ exchange inhibitor KB-R7943 (5 μM) or after inhibition of SR Ca2+ release with ryanodine (20 μM). In the absence of extracellular Na+, spontaneous SR Ca2+ releases caused minimal changes in resting membrane potential. After the myocytes were returned to Na+-containing solution, the potentiated intracellular Ca2+ concentration ([Ca2+]i) transients dramatically prolonged APD90 and [Ca2+]i oscillations caused delayed and early afterdepolarizations (DADs and EADs). Laser-flash photolysis of caged Ca2+ mimicked the effects of spontaneous [Ca2+]i oscillations, confirming that APD prolongation, DADs, and EADs could be ascribed to intracellular Ca2+ release. These results suggest that Na+/Ca2+ exchange is a major physiological determinant of APD and that INaCa activation by spontaneous SR Ca2+ release/oscillations, depending on the timing, can account for both DADs and EADs during SR Ca2+ overload.
Oxygen delivery to skeletal muscle fibers: effects of microvascular unit structure and control mechanisms
Authors: Lo Arthur , Fuglevand Andrew J. , Secomb Timothy W.
Published: March 2015

The number of perfused capillaries in skeletal muscle varies with muscle activation. With increasing activation, muscle fibers are recruited as motor units consisting of widely dispersed fibers, whereas capillaries are recruited as groups called microvascular units (MVUs) that supply several adjacent fibers. In this study, a theoretical model was used to examine the consequences of this spatial mismatch between the functional units of muscle activation and capillary perfusion. Diffusive oxygen transport was simulated in cross sections of skeletal muscle, including several MVUs and fibers from several motor units. Four alternative hypothetical mechanisms controlling capillary perfusion were considered. First, all capillaries adjacent to active fibers are perfused. Second, all MVUs containing capillaries adjacent to active fibers are perfused. Third, each MVU is perfused whenever oxygen levels at its feed arteriole fall below a threshold value. Fourth, each MVU is perfused whenever the average oxygen level at its capillaries falls below a threshold value. For each mechanism, the dependence of the fraction of perfused capillaries on the level of muscle activation was predicted. Comparison of the results led to the following conclusions. Control of perfusion by MVUs increases the fraction of perfused capillaries relative to control by individual capillaries. Control by arteriolar oxygen sensing leads to poor control of tissue oxygenation at high levels of muscle activation. Control of MVU perfusion by capillary oxygen sensing permits adequate tissue oxygenation over the full range of activation without resulting in perfusion of all MVUs containing capillaries adjacent to active fibers.
Basic fibroblast growth factor increases collateral blood flow in spontaneously hypertensive rats
Authors: Srivastava Sunita , Terjung Ronald L. , Yang H. T.
Published: March 2015

Ischemia-induced angiogenic response is reduced in spontaneously hypertensive rats (SHR). To study whether exogenous basic fibroblast growth factor (bFGF) infusion is effective in expanding collateral circulation in frankly hypertensive SHR, femoral arteries of male SHR (weighing ∼250 g) were kept intact (nonoccluded control; n = 9) or occluded for4h( n = 12) or for 16 days with vehicle ( n = 14) or bFGF [0.5 ( n = 17), 5.0 ( n = 13), and 50.0 ( n = 14) μg · kg–1 · day–1 for 14 days] intraarterially. Maximal collateral-dependent blood flows (BF) to the hindlimbs were determined with 85Sr- and 141Ce-labeled microspheres during running at 20 and 25 m/min (15% grade). Preexercise heart rates (∼530 beats/min) and blood pressures (BP; ∼200 mmHg) were similar across groups except in the high-dose bFGF group, where BP was reduced by ∼12% ( P < 0.05). Femoral artery occlusion for 4 h resulted in ∼95% reduction of BF in calf muscles [199 ± 18.7 (nonoccluded group) to 10 ± 1.0 ml · min–1 · 100 g–1; P < 0.001]. BF to calf muscles of the vehicle and low-dose bFGF (0.5 μg · kg–1 · day–1) groups increased to 36 ± 3.2 and 45 ± 2.0 ml · min–1 · 100 g–1, respectively ( P < 0.001). bFGF infusion at 5.0 and 50.0 μg · kg–1 · day–1 further increased ( P < 0.001) BF to calf muscles (62 ± 4.6 and 62 ± 2.2 ml · min–1 · 100 g–1, respectively). Our results show that bFGF can effectively increase BF in hypertensive rats. The reduced hypertension with high-dose bFGF suggests that a critical signal in arteriogenesis (nitric oxide bioavailability) may be restored. These findings suggest that the dulled endothelial nitric oxide synthase of SHR does not preempt collateral vessel remodeling.
Functional and metabolic adaptation of the heart to prolonged thyroid hormone treatment
Authors: Degens H. , Gilde A. J. , Lindhout M. , Willemsen P. H. M. , van der Vusse G. J. , van Bilsen M.
Published: March 2015

In heart failure, thyroid hormone (TH) treatment improves cardiac performance. The long-term effects of TH on cardiac function and metabolism, however, are incompletely known. To investigate the effects of up to 28 days of TH treatment, male Wistar rats received 3,3′,5-triiodo-l-thyronine (200 μg/kg sc per day) leading to a 2.5-fold rise in plasma fatty acid (FA) level and progressive cardiac hypertrophy (+47% after 28 days) ( P < 0.001). Ejection fraction (echocardiography) was increased (+12%; P < 0.05) between 7 and 14 days and declined thereafter. Neither cardiac FA oxidation, glycolytic capacity (homogenates) per unit muscle mass, nor mRNA levels of proteins involved in FA and glucose uptake and metabolism (Northern blots and microarray) were altered. After 28 days of treatment, mRNA levels of uncoupling proteins (UCP) 2 and 3 and atrial natriuretic factor were increased ( P < 0.05). This indicates that TH-induced hypertrophy is associated with an initial increase in cardiac performance, followed by a decline in cardiac function and increased expression of UCPs and atrial natriuretic factor, suggesting that detrimental effects eventually prevail.
Endocardial versus epicardial electrical synchrony during LV free-wall pacing
Authors: Faris Owen P. , Evans Frank J. , Dick Alexander J. , Raman Venkatesh K. , Ennis Daniel B. , Kass David A. , McVeigh Elliot R.
Published: March 2015

Cardiac resynchronization therapy has been most typically achieved by biventricular stimulation. However, left ventricular (LV) free-wall pacing appears equally effective in acute and chronic clinical studies. Recent data suggest electrical synchrony measured epicardially is not required to yield effective mechanical synchronization, whereas endocardial mapping data suggest synchrony (fusion with intrinsic conduction) is important. To better understand this disparity, we simultaneously mapped both endocardial and epicardial electrical activation during LV free-wall pacing at varying atrioventricular delays (AV delay 0–150 ms) in six normal dogs with the use of a 64-electrode LV endocardial basket and a 128-electrode epicardial sock. The transition from dyssynchronous LV-paced activation to synchronous RA-paced activation was studied by constructing activation time maps for both endo- and epicardial surfaces as a function of increasing AV delay. The AV delay at the transition from dyssynchronous to synchronous activation was defined as the transition delay (AVt). AVt was variable among experiments, in the range of 44–93 ms on the epicardium and 47–105 ms on the endocardium. Differences in endo- and epicardial AVt were smaller (–17 to +12 ms) and not significant on average (–5.0 ± 5.2 ms). In no instance was the transition to synchrony complete on one surface without substantial concurrent transition on the other surface. We conclude that both epicardial and endocardial synchrony due to fusion of native with ventricular stimulation occur nearly concurrently. Assessment of electrical epicardial delay, as often used clinically during cardiac resynchronization therapy lead placement, should provide adequate assessment of stimulation delay for inner wall layers as well.
Endothelial nitric oxide production during in vitro simulation of external limb compression
Authors: Dai Guohao , Tsukurov Olga , Chen Michael , Gertler Jonathan P. , Kamm Roger D.
Published: March 2015

External pneumatic compression (EPC) is effective in preventing deep vein thrombosis (DVT) and is thought to alter endothelial thromboresistant properties. We investigated the effect of EPC on changes in nitric oxide (NO), a critical mediator in the regulation of vasomotor and platelet function. An in vitro cell culture system was developed to simulate flow and vessel collapse conditions under EPC. Human umbilical vein endothelial cells were cultured and subjected to tube compression (C), pulsatile flow (F), or a combination of the two (FC). NO production and endothelial nitric oxide synthase (eNOS) mRNA expression were measured. The data demonstrate that in the F and FC groups, there is a rapid release of NO followed by a sustained increase. NO production levels in the F and FC groups were almost identical, whereas the C group produced the same low amount of NO as the control group. Conditions F and FC also upregulate eNOS mRNA expression by a factor of 2.08 ± 0.25 and 2.11 ± 0.21, respectively, at 6 h. Experiments with different modes of EPC show that NO production and eNOS mRNA expression respond to different time cycles of compression. These results implicate enhanced NO release as a potentially important factor in the prevention of DVT.
Increased baroreceptor response in mice deficient in monoamine oxidase A and B
Authors: Holschneider D. P. , Scremin O. U. , Roos K. P. , Chialvo D. R. , Chen K. , Shih J. C.
Published: March 2015

The recent development of mice doubly deficient for monoamine oxidase A and B (MAO-A/B, respectively) has raised questions about the impact of these mutations on cardiovascular function, in so far as these animals demonstrate increased tissue levels of the vasoactive amines serotonin, norepinephrine, dopamine, and phenylethylamine. We recorded femoral arterial pressures and electrocardiograms in adult MAO-A/B-deficient mice during halothane-nitrous oxide anesthesia as well as 30 min postoperatively. During both anesthesia and recovery, systolic, diastolic, and mean arterial pressures were 10–15 mmHg lower in MAO-A/B-deficient mice compared with normal controls ( P < 0.01). Mutants also showed a greater baroreceptor-mediated reduction in heart rate in response to hypertension after intravenous pulses of phenylephrine or angiotensin II. Tachycardia elicited in response to hypotension after nitroprusside was greater in mutants than in controls. Heart rate responsiveness to changes in arterial pressure was abolished after administration of glycopyrrolate, with no differences in this phenomenon noted between genotypes. These data suggest that prevention of hypertension may occur in chronic states of catecholaminergic/indoleaminergic excess by increased gain of the baroreflex.
Contribution of Ca2+transporters to relaxation in intact ventricular myocytes from developing rats
Authors: Bassani Rosana A. , Bassani JoséW. M.
Published: March 2015

The relative contributions of Ca2+transporters to intracellular Ca2+concentration ([Ca2+]i) decline associated with twitch relaxation were analyzed in intact ventricular myocytes from developing and adult rats. This was accomplished by estimation of individual integrated Ca2+fluxes with the use of kinetic parameters calculated from [Ca2+]imeasurements during twitches and caffeine-evoked contractures, and from myocardial passive Ca2+buffering data. Our main findings were the following: 1) twitch relaxation and [Ca2+]idecline were significantly slower during the first postnatal week than in adults, 2) inhibition of sarcoplasmic reticulum (SR) Ca2+accumulation resulted in faster [Ca2+]idecline in young cells than in adult cells, 3) the contributions of the SR Ca2+uptake and Na+/Ca2+exchange (NCX) to twitch relaxation increased from ∼75 to 92%, and decreased from 24 to 5%, respectively, from birth to adulthood, and 4) Ca2+transport by the sarcolemmal Ca2+-ATPase was apparently increased in neonates. Our data indicate that despite a marked increase in NCX contribution to cell relaxation in immature rats, the SR Ca2+-ATPase appears to be the predominant transporter responsible for relaxation-associated [Ca2+]idecline from birth to adulthood.
Sildenafil (Viagra) induces powerful cardioprotective effect via opening of mitochondrial KATPchannels in rabbits
Authors: Ockaili Ramzi , Salloum Fadi , Hawkins John , Kukreja Rakesh C.
Published: March 2015

Sildenafil citrate (Viagra) is the pharmacological agent used to treat erectile dysfunction in men. Because this drug has a vasodilatory effect, we hypothesized that such an action may induce a preconditioning-like cardioprotective effect via opening of mitochondrial ATP-sensitive K (KATP) channels. Rabbits were treated with sildenafil citrate (0.7 mg/kg iv) either 30 min (acute phase) or 24 h (delayed phase) before 30 min of ischemia and 3 h of reperfusion. Mitochondrial KATPchannel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg iv) was given 10 min before ischemia-reperfusion. Infarct size was measured by tetrazolium staining. Sildenafil caused reduction in arterial blood pressure within 2 min of treatment, which returned to nearly baseline levels 3 min later. The infarct size (% risk area, means ± SE) reduced from 33.8 ± 1.7 in control rabbits to 10.8 ± 0.9 during the acute phase (68% reduction, P < 0.05) and 19.9 ± 2.0 during the delayed phase (41% reduction, P < 0.05). 5-HD abolished protection with an increase in infarct size to 35.6 ± 0.4% and 36.8 ± 1.6% during the acute and delayed phase, respectively ( P < 0.05). Similar acute and delayed cardioprotective effects were observed when sildenafil was administered orally. Systemic hemodynamics also decreased after oral administration of the drug. However, these changes were mild and occurred slowly. For the first time, we demonstrate that sildenafil induces acute and delayed protective effects against ischemia-reperfusion injury, which are mediated by opening of mitochondrial KATPchannels.
Thr164Ile polymorphism of the human β2-adrenoceptor exhibits blunted desensitization of cardiac functional responses in vivo
Authors: Bruck Heike , Leineweber Kirsten , Ulrich Anke , Radke Joachim , Heusch Gerd , Philipp Thomas , Brodde Otto-Erich
Published: March 2015

In subjects heterozygous for Thr164Ile β2-adrenoceptor (β2AR) polymorphism, cardiac responses to β2AR agonist stimulation are blunted. In this study, we investigated agonist-induced desensitization of Thr164Ile β2ARs. For this purpose, we assessed in six subjects with heterozygous Thr164Ile β2ARs and in 10 subjects with homozygous wild-type (WT) β2ARs the effects of 2-wk oral treatment with 3 × 5 mg/day terbutaline on terbutaline infusion-induced increases in heart rate (HR) and contractility [measured as shortening of HR-corrected duration of electromechanical systole (QS2c)]. Compared with WT β2AR subjects, Thr164Ile subjects exhibited a blunted terbutaline-induced maximum increase in HR (WT 32 ± 4 beats/min, Thr164Ile 19 ± 3 beats/min, P < 0.05) and contractility (WT –54 ± 2 ms, Thr164Ile –37 ± 6 ms, P < 0.05). Two-week oral terbutaline treatment desensitized cardiac β2AR responses to terbutaline infusion (increase in HR: WT 10 ± 2 beats/min, Thr164Ile 8 ± 4 beats/min; increase in contractility: WT –22 ± 5 ms Thr164Ile: –17 ± 6 ms); however, the extent of desensitization was larger in WT than Thr164Ile β2AR subjects. Thus, after 2-wk oral terbutaline treatment cardiac, β2AR responses did not differ anymore between WT and Thr164Ile β2AR subjects. We conclude that agonist-induced desensitization of cardiac β2ARs is more pronounced in WT than Thr164Ile subjects. Thus cardiac Thr164Ile subjects appear to be somewhat protected against agonist-induced desensitization.
A finite difference model of O2 transport in aortic valve cusps: importance of intrinsic microcirculation
Authors: Filion Renee J. , Ellis Christopher G.
Published: March 2015

Recent studies have reported the presence of a microcirculation within the tissue of aortic valves. To test the hypothesis that this vascular bed is needed to satisfy the oxygen demands of the cusp tissue, a two-dimensional (2D) finite difference model of oxygen diffusion was developed. The in vivo environment was modeled for vascular and avascular cusps using thickness data from precise radiographic measurements of fresh porcine valves, and O2 diffusivity (Do2) and O2 consumption (Vo2) values from experimental data. The location and density of the cusp vasculature were determined by the model to prevent oxygen levels from falling to zero. Validation of the model was performed by simulation of the experimental measurements of cusp Do2 and Vo2. For a test cusp with uniform thickness, the model returned simulated Do2 and Vo2 measurements within 1.43% and 0.18% difference of the true parameter values, respectively. For native cusps, the simulated Do2 measurements were sensitive to thickness variations (–38 to +21% difference), whereas the Vo2 measurements were minimally affected (8% difference). An improved Do2 measurement technique was found to reduce these errors to <5% and is recommended for analysis of experimental data. In the avascular case, the model predicted large regions of hypoxic tissue, whereas in the vascular case, the model predicted vessel locations and densities similar to what was experimentally observed in porcine cusps. Overall, the in vivo model developed in this study confirmed the need for an intrinsic microcirculation in the thicker basal regions of aortic cusps.
Overexpression of A3 adenosine receptors decreases heart rate, preserves energetics, and protects ischemic hearts
Authors: Cross Heather R. , Murphy Elizabeth , Black Richard G. , Auchampach John , Steenbergen Charles
Published: March 2015

To determine whether A3 adenosine receptor (A3AR) signaling modulates myocardial function, energetics, and cardioprotection, hearts from wild-type and A3AR-overexpressor mice were subjected to 20-min ischemia and 40-min reperfusion while 31P NMR spectra were acquired. Basal heart rate and left ventricular developed pressure (LVDP) were lower in A3AR-overexpressor hearts than wild-type hearts. Ischemic ATP depletion was delayed and postischemic recoveries of contractile function, ATP, and phosphocreatine were greater in A3AR-hearts. To determine the role of depressed heart rate and to confirm A3AR-specific signaling, hearts were paced at 480 beats/min with or without 60 nmol/l MRS-1220 (A3AR-specific inhibitor) and then subjected to ischemia-reperfusion. LVDP was similar in paced A3AR-overexpressor and paced wild-type hearts. Differences in ischemic ATP depletion and postischemic contractile and energetic dysfunction remained in paced A3AR-overexpressor hearts versus paced wild-type hearts but were abolished by MRS-1220. In summary, A3AR overexpression decreased basal heart rate and contractility, preserved ischemic ATP, and decreased postischemic dysfunction. Pacing abolished the decreased contractility but not the ATP preservation or cardioprotection. Therefore, A3AR overexpression results in cardioprotection via a specific A3AR effect, possibly involving preservation of ATP during ischemia.
Preload-adjusted maximal power of right ventricle: contribution of end-systolic P-V relation intercept
Authors: Segers Patrick , Leather H. Alex , Verdonck Pascal , Sun Yuan-Yuan , Wouters Patrick F.
Published: March 2015

To assess whether preload-adjusted maximal power (PAMP), which is calculated asW˙max/V[Formula: see text] (whereW˙max is maximal power and Ved is end-diastolic volume with β = 2) is an index of right ventricular (RV) contractility, we measured RV pressure (P) and volume (V) and pulmonary artery pressure and flow in 10 dogs at baseline and after inotropic stimulation. PAMP was derived from steady-state data, whereas the slope ( E es) and intercept (Vd) of the end-systolic P-V relationship were derived from data obtained during vena caval occlusion. Inotropic stimulation increased E es (from 0.96 ± 0.25 to 1.62 ± 0.28 mmHg/ml; P < 0.001) and Vd (from −3.0 ± 17.2 to 12.4 ± 10.8 ml; P < 0.05) but not PAMP (from 0.24 ± 0.10 to 0.36 ± 0.22 mW/ml2; P = 0.09). We found a strong relationship between the optimal β-factor for preload adjustment and Vd. A corrected PAMP, PAMPc= W˙max/(Ved − Vd)2, which incorporated the Vddependency, was sensitive to the inotropic changes (from 0.23 ± 0.12 to 0.54 ± 0.17 mW/ml2; P < 0.001) with a good correlation with E es( r = 0.88; P < 0.001).
Recruitment of endothelial caveolae into mechanotransduction pathways by flow conditioning in vitro
Authors: Rizzo Victor , Morton Christine , DePaola Natacha , Schnitzer Jan E. , Davies Peter F.
Published: March 2015

The luminal surface of rat lung microvascular endothelial cells in situ is sensitive to changing hemodynamic parameters. Acute mechanosignaling events initiated in response to flow changes in perfused lung microvessels are localized within specialized invaginated microdomains called caveolae. Here we report that chronic exposure to shear stress alters caveolin expression and distribution, increases caveolae density, and leads to enhanced mechanosensitivity to subsequent changes in hemodynamic forces within cultured endothelial cells. Flow-preconditioned cells expressed a fivefold increase in caveolin (and other caveolar-residing proteins) at the luminal surface compared with no-flow controls. The density of morphologically identifiable caveolae was enhanced sixfold at the luminal cell surface of flow-conditioned cells. Laminar shear stress applied to static endothelial cultures (flow step of 5 dyn/cm2), enhanced the tyrosine phosphorylation of luminal surface proteins by 1.7-fold, including caveolin-1 by 1.3-fold, increased Ser1179phosphorylation of endothelial nitric oxide synthase (eNOS) by 2.6-fold, and induced a 1.4-fold activation of mitogen-activated protein kinases (ERK1/2) over no-flow controls. The same shear step applied to endothelial cells preconditioned under 10 dyn/cm2of laminar shear stress for 6 h and induced a sevenfold increase of total phosphotyrosine signal at the luminal endothelial cell surface enhanced caveolin-1 tyrosine phosphorylation 5.8-fold and eNOS phosphorylation by 3.3-fold over static control values. In addition, phosphorylated caveolin-1 and eNOS proteins were preferentially localized to caveolar microdomains. In contrast, ERK1/2 activation was not detected in conditioned cells after acute shear challenge. These data suggest that cultured endothelial cells respond to a sustained flow environment by directing caveolae to the cell surface where they serve to mediate, at least in part, mechanotransduction responses.
Role of endothelial MCP-1 in monocyte adhesion to inflamed human endothelium under physiological flow
Authors: Maus U. , Henning S. , Wenschuh H. , Mayer K. , Seeger W. , Lohmeyer J.
Published: March 2015

Monocyte chemoattractant protein-1 (MCP-1) is an essential chemokine involved in monocyte traffic across endo- and epithelial barriers both in vitro and in vivo. However, the contribution of endothelial MCP-1 signaling via its CCR2 receptor in monocyte adhesion to inflamed endothelium under flow is incompletely understood. A sensitive flow chamber assay was used to assess monocyte adhesion to TNF-α-activated primary human pulmonary artery endothelial cells (HPAEC) during physiological shear stress. Monocyte adhesion was markedly reduced (∼45%) when HPAEC-derived MCP-1 was either neutralized with anti-MCP-1 mAb or inhibited by translational arrest of MCP-1 mRNA transcripts with MCP-1 antisense oligomers. Corresponding efficacy was observed for blockade of monocyte CCR2 receptor function by anti-CCR2 mAb or MCP-1 antagonists (9–76 analog). The impact of endothelial MCP-1 on monocyte-HPAEC adhesion occurred via β2-integrin but not via β1-integrin adhesion pathways. In this line, pretreatment of monocytes with MCP-1 but not RANTES provoked a rapid and transient neoepitope 24 expression on β2-integrin α-chains, as analyzed by increased reporter mAb24 binding. Collectively, our data show an important cross talk of endothelial MCP-1 with monocyte CCR2 effecting monocyte firm adhesion to inflamed HPAEC under physiological flow conditions.
Microcirculatory changes during chronic adaptation to hypoxia
Authors: Saldívar Enrique , Cabrales Pedro , Tsai Amy G. , Intaglietta Marcos
Published: March 2015

Microcirculatory changes in the window chamber preparation in Syrian golden hamsters, secondary to chronic hypoxia adaptation, are presented herein. Adaptation was attained by keeping animals in a 10% oxygen environment for 1 wk and 5% the following week. The following groups were studied: group 1, adapted to chronic hypoxia and kept in a 5% oxygen environment throughout the experiment; group 2, adapted to chronic hypoxia and kept in a 21% oxygen environment 24 h before and during the experiment; and group 3, control. Adaptation caused venule enlargement and hematocrit increase (68.6 ± 2.44 in group 1, 70 ± 2.66 in group 2, and 43.27 ± 2.30 in group 3; P < 0.05). Whereas heart rate decreased in adapted animals, blood pressure remained constant. Group 1 presented alkalosis, hypocapnia, and hypoxemia. The adapted groups had decreased blood flow velocity in arterioles and veins. We found no difference in microvasculature oxygen tension between groups 2 and 3; however, the number of capillaries with flow was markedly reduced in group 1 but significantly increased in group 2. Our findings suggest that, as an adaptation to hypoxia, erythropoiesis may prove beneficial by increasing blood viscosity and shear stress, leading to vasodilatation, in addition to the increase in oxygen-carrying capacity. Calculations show that oxygen extraction in the tissue of the window chamber model was significantly lowered in adapted animals breathing 5% oxygen, but was unchanged from the control when breathing 21% oxygen, even though blood hemoglobin content was increased from 14.5 ± 0.07 g/dl at control to 21.04 ± 1.24 g/dl in the adapted animals ( P < 0.05).
Ventricular-specific expression of angiotensin II type 2 receptors causes dilated cardiomyopathy and heart failure in transgenic mice
Authors: Yan Xinhua , Price Robert L. , Nakayama Masaharu , Ito Kenta , Schuldt Adam J. T. , Manning Warren J. , Sanbe Atsushi , Borg Thomas K. , Robbins Jeffrey , Lorell Beverly H.
Published: March 2015

The angiotensin II type 2 (AT2) receptor is upregulated in the left ventricle in heart failure, but its pathophysiological roles in vivo are not understood. In the present study, AT2 receptors were expressed in transgenic (TG) mice using the ventricular-specific myosin light-chain (MLC-2v) promoter. In TG compared with nontransgenic (NTG) mice, in vivo left ventricular (LV) systolic pressure and peak +dP/d t were depressed while LV diastolic pressure was elevated ( P < 0.05). Echocardiography showed severely depressed LV fractional shortening, increased systolic and diastolic dimensions, and wall thinning ( P < 0.05). Confocal and electron microscopy studies revealed an increase in the size of myocytes and interstitial spaces as well as an increase in interstitial collagen, disruption of the Z-band, and changes in cytochrome c localization. The changes were most prominent in the highest-expressing TG line, which implies a dose-response relationship. AT2 overexpression was also directly associated with the increase of phosphorylated protein levels of PKC-α, PKC-β, and p70S6 kinase. These data demonstrate that ventricular myocyte-specific expression of AT2 receptors promotes the development of dilated cardiomyopathy and heart failure in vivo.