bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of serotonin in thromboxane A2-induced coronary chemoreflex
Authors: Wacker M. J. , Wilhelm H. L. , Gomez S. E. , Floor E. , Orr J. A.
Published: March 2015

We reported previously that the thromboxane A2(TxA2) mimetic U-46619 stimulates cardiac vagal afferent nerves, eliciting a reflex decrease in heart rate (HR) and arterial blood pressure (ABP). The present experiments were designed to test the hypothesis that TxA2evokes these changes via the release of serotonin [5-hydroxytryptamine (5-HT)] and activation of the 5-HT3receptor. Injections of the 5-HT3antagonist tropisetron (1 mg of 3-tropanyl-indole-3-carboxylate or ICS-205-930) attenuated the decreases in HR and ABP induced by left atrial injections of U-46619 (20 μg). Tropisetron administration also eliminated the U-46619-induced increase in impulse frequency in a majority of cardiac, vagal afferent units tested. Measurement of serum 5-HT levels revealed an elevation in serum 5-HT levels after U-46619 injection in those rabbits that displayed a significant HR change following injection of U-46619. These results indicate that although other factors may also contribute to these reflex responses, the release of 5-HT and stimulation of the 5-HT3receptor plays a significant role in coronary reflexes induced by TxA2.
Regional arterial stress-strain distributions referenced to the zero-stress state in the rat
Authors: Zhao Jingbo , Day Judd , Yuan Zhuang Feng , Gregersen Hans
Published: March 2015

Morphometric and stress-strain properties were studied in isolated segments of the thoracic aorta, abdominal aorta, left common carotid artery, left femoral artery, and the left pulmonary artery in 16 male Wistar rats. The mechanical test was performed as a distension experiment where the proximal end of the arterial segment was connected via a tube to the container used for applying pressures to the segment and the distal end was left free. Outer wall dimensions were obtained from digitized images of the arterial segments at different pressures as well as at no-load and zero-stress states. The results showed that the morphometric data, such as inner and outer circumference, wall and lumen area, wall thickness, wall thickness-to-inner radius ratio, and normalized outer diameter, as a function of the applied pressures, differed between the five arteries ( P < 0.01). The opening angle was largest in the pulmonary artery and smallest in thoracic aorta ( P < 0.01). The absolute value of both the inner and outer residual strain and the residual strain gradient were largest in the femoral artery and smallest in the thoracic aorta ( P < 0.01). In the circumferential and longitudinal direction, the arterial wall was stiffest in the femoral artery and in the thoracic aorta, respectively, and most compliant in the pulmonary artery. These results show that the morphometric and biomechanical properties referenced to the zero-stress state differed between the five arterial segments.
Mechanistic investigation of extracellular K+accumulation during acute myocardial ischemia: a simulation study
Authors: Rodrı́guez B. , Ferrero J. M. , Trénor B.
Published: March 2015

In this study, we have used computer simulations to study the mechanisms of extracellular K+ accumulation during acute ischemia. A modified version of the Luo-Rudy phase II action potential model was used to simulate the electrical behavior of one ventricular myocyte during 14 min of simulated ischemia. Our results show the following: 1) only the integrated effect of activation of ATP-dependent K+ current, an ischemic Na+ inward current, and inhibition of Na+-K+ pump activity in the absence of coronary flow replicates the biphasic time course of extracellular K+ concentration observed during acute ischemia; 2) the time to onset of the plateau phase and the plateau level value are determined by the rate of stimulation and by the rate of alteration of the three mechanisms. However, acidosis and reduction of extracellular volume produce only a slight anticipation of the plateau phase; and 3) cellular K+ loss is mainly due to an increase of K+ efflux via the time-independent K+ current and ATP-dependent K+ current rather than to a decrease of K+ influx.
Role of ET-1 receptor binding and [Ca2+]i in contraction of coronary arteries from DOCA-salt hypertensive rats
Authors: Giulumian Ararat D. , Molero Mariela M. , Reddy Vikram B. , Pollock Jennifer S. , Pollock David M. , Fuchs Leslie C.
Published: March 2015

Hypertension is associated with an increase in coronary artery disease, but little is known about the regulation of coronary vascular tone by endothelin-1 (ET-1) in hypertension. The present study evaluated the mechanisms mediating altered contraction to ET-1 in coronary small arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. DOCA-salt rats exhibited an increase in systolic blood pressure and plasma ET-1 levels compared with placebo rats. Contraction to ET-1 (1 × 10−11 to 3 × 10−8 M), measured in isolated coronary small arteries maintained at a constant intraluminal pressure of 40 mmHg, was largely reduced in vessels from DOCA-salt rats compared with placebo rats. To determine the role of endothelin receptor binding in the impaired contraction to ET-1,125I-labeled ET-1 receptor binding was measured in membranes isolated from coronary small arteries. Maximum binding (fmol/mg protein) and binding affinity were similar in coronary membranes from DOCA-salt rats compared with placebo rats. Changes in intracellular Ca2+ concentration ([Ca2+]i) were measured in freshly dissociated coronary small artery smooth muscle cells loaded with fura 2. ET-1 (10−9 M) produced a 30 ± 9% increase in [Ca2+]i in smooth muscle cells from placebo rats, but had no effect on cells from DOCA-salt rats (2 ± 2%). In summary, the ET-1-induced coronary artery contraction and increase in [Ca2+]i are impaired in DOCA-salt hypertensive rats, whereas endothelin receptor binding is not altered. These results suggest endothelin receptor uncoupling from signaling mechanisms and indicate that impaired [Ca2+]isignaling contributes to the decrease in ET-1-induced contraction of coronary small arteries in DOCA-salt hypertensive rats.
Enhanced myogenic tone in cerebral arteries from a rabbit model of subarachnoid hemorrhage
Authors: Ishiguro Masanori , Puryear Corey B. , Bisson Erica , Saundry Christine M. , Nathan David J. , Russell Sheila R. , Tranmer Bruce I. , Wellman George C.
Published: March 2015

Cerebral artery vasospasm is a major cause of death and disability in patients experiencing subarachnoid hemorrhage (SAH). Currently, little is known regarding the impact of SAH on small diameter (100–200 μm) cerebral arteries, which play an important role in the autoregulation of cerebral blood flow. With the use of a rabbit SAH model and in vitro video microscopy, cerebral artery diameter was measured in response to elevations in intravascular pressure. Cerebral arteries from SAH animals constricted more (∼twofold) to pressure within the physiological range of 60–100 mmHg compared with control or sham-operated animals. Pressure-induced constriction (myogenic tone) was also enhanced in arteries from control animals organ cultured in the presence of oxyhemoglobin, an effect independent of the vascular endothelium or nitric oxide synthesis. Finally, arteries from both control and SAH animals dilated as intravascular pressure was elevated above 140 mmHg. This study provides evidence for a role of oxyhemoglobin in impaired autoregulation (i.e., enhanced myogenic tone) in small diameter cerebral arteries during SAH. Furthermore, therapeutic strategies that improve clinical outcome in SAH patients (e.g., supraphysiological intravascular pressure) are effective in dilating small diameter cerebral arteries isolated from SAH animals.
Effects of amiodarone on wave front dynamics during ventricular fibrillation in isolated swine right ventricle
Authors: Omichi Chikaya , Zhou Shengmei , Lee Moon-Hyoung , Naik Ajay , Chang Che-Ming , Garfinkel Alan , Weiss James N. , Lin Shien-Fong , Karagueuzian Hrayr S. , Chen Peng-Sheng
Published: March 2015

The effects of acute amiodarone infusion on dynamics of ventricular fibrillation (VF) are unclear. Six isolated swine right ventricles (RVs) were studied in vitro. Activation patterns during VF were mapped optically, whereas action potentials were recorded with a glass microelectrode. At baseline, VF was associated with frequent spontaneous wave breaks. Amiodarone (2.5 μg/ml) reduced spontaneous wave breaks and increased the cycle length (CL) of VF from 83.3 ± 17.8 ms at baseline to 118.4 ± 25.8 ms during infusion ( P < 0.05). Amiodarone increased the reentrant wave front CL (114.4 ± 15.5 vs. 78.2 ± 19.0 ms, P < 0.05) and central core area (4.1 ± 3.8 vs. 0.9 ± 0.3 mm2, P < 0.05). Within 30 min of infusion, VF terminated ( n = 1), converted to ventricular tachycardia (VT) ( n = 1) or continued at a slower rate ( n = 4). Amiodarone flattened the APD restitution curves. We conclude that amiodarone reduced spontaneous wave breaks. It might terminate VF or convert VF to VT. These effects were associated with the flattening of APD restitution slope and increased core size of reentrant wave fronts.
Maternal cardiovascular changes during pregnancy and postpartum in mice
Authors: Wong Alan Y. H. , Kulandavelu Shathiyah , Whiteley Kathie J. , Qu Dawei , Langille B. Lowell , Adamson S. Lee
Published: March 2015

Genetically altered mice may provide useful models for exploring cardiovascular regulation during pregnancy and postpartum if changes in mice mimic humans. We found in awake ICR (CD-1) mice at 17.5 days gestation that hematocrit was reduced 18%, and the pressor response to intravenous angiotensin II was reduced ∼33%. Arterial pressure in awake mice was 12% lower in early pregnancy (3.5 days) than late pregnancy (17.5 days) and postpartum (3 and 17 days after delivery), whereas heart rate was 10–20% higher in the peripartum period (17.5 days gestation and 3 days postpartum). In late pregnancy, cardiac output under isoflurane anesthesia was 64% higher than in nonpregnant mice, due to a 37% increase in stroke volume and a 17% increase in heart rate. All changes P < 0.05. We conclude that, as in humans, mice exhibit hypotension in early pregnancy, and a blunted pressor response to angiotensin II, a decrease in hematocrit, and a marked increase in cardiac output in late pregnancy.
Endothelial cell signaling during conducted vasomotor responses
Authors: Dora Kim A. , Xia Jun , Duling Brian R.
Published: March 2015

ACh and KCl stimulate vasomotor responses that spread rapidly and bidirectionally along arteriole walls, most likely via spread of electric current or Ca2+ through gap junctions. We examined these possibilities with isolated, cannulated, and perfused hamster cheek pouch arterioles (50- to 80-μm resting diameter). After intraluminal loading of 2 μM fluo 3 to measure Ca2+ or 1 μM di-8-ANEPPS to measure membrane potential, photometric techniques were used to selectively measure changes in intracellular Ca2+ concentration ([Ca2+]i) or membrane potential in endothelial cells. Activation of the endothelium by micropipette application of ACh (10-4 M, 1.0-s pulse) to a short segment of arteriole (100–200 μm) increased endothelial cell [Ca2+]i and caused hyperpolarization at the site of stimulation. This response was followed rapidly by vasodilation of the entire arteriole (∼2-mm length). Change in membrane potential always preceded dilation, both at the site of stimulation and at distant sites along the arteriole. In contrast, an increase in endothelial cell [Ca2+]i was observed only at the application site. Micropipette application of KCl, which can depolarize both smooth muscle and endothelial cells (250 mM, 2.5-s pulse), also caused a rapid, spreading response consisting of depolarization followed by vasoconstriction. With KCl stimulation, in addition to changes in membrane potential, increases in endothelial cell [Ca2+]i were observed at distant sites not directly exposed to KCl. The rapid longitudinal spread of both hyperpolarizing and depolarizing responses support electrical coupling as the mode of signal transmission along the arteriolar length. In addition, the relatively short distance between heterologous cell types enables the superimposed radial Ca2+ signaling between smooth muscle and endothelial cells to modulate vasomotor responses.
Angiotensin II stimulates migration of retinal microvascular pericytes: involvement of TGF-β and PDGF-BB
Authors: Nadal Jose A. , Scicli G. M. , Carbini L. A. , Scicli A. Guillermo
Published: March 2015

We studied the promigratory effect of angiotensin II (ANG II) on cultured bovine retinal microvascular pericytes. ANG II stimulated migration of pericytes by 86% at 10−8M, but this effect was lost at 10−4M. Migratory responses were inhibited by the ANG II type 1 (AT1) receptor antagonist losartan but not by PD-123319, an AT2antagonist. Addition of PD-123319 to the 10−4M ANG II dose restored migratory responses. The promigratory effect of ANG II (10−7M) was reduced by 59% in absence of gradient. Although ANG II augmented the latent matrix metalloproteinase-2 (MMP-2) activity of the pericyte by 35%, it also doubled tissue inhibitors of MMPs. ANG II-induced migration was not altered by a broad-spectrum MMP inhibitor (GM6001); it was inhibited by ∼50% by antibodies against transforming growth factor (TGF)-β1/2/3and was abolished by antibodies against platelet-derived growth factor (PDGF)-BB. We conclude that ANG II induces chemotactic responses on retinal microvascular pericytes acting through the AT1receptor. This effect is opposed by the AT2receptor. ANG II-induced chemotaxis is mediated by PDGF-BB and involves TGF-β, but it is independent of MMP activity. It is also independent of vascular endothelial growth factor (VEGF) because VEGF did not stimulate pericyte migration. ANG II can contribute to the regulation of retinal neovascularization by stimulating pericyte migration.
Effects of nitric oxide on red blood cell deformability
Authors: Bor-Kucukatay Melek , Wenby Rosalinda B. , Meiselman Herbert J. , Baskurt Oguz K.
Published: March 2015

In addition to its known action on vascular smooth muscle, nitric oxide (NO) has been suggested to have cardiovascular effects via regulation of red blood cell (RBC) deformability. The present study was designed to further explore this possibility. Human RBCs in autologous plasma were incubated for 1 h with NO synthase (NOS) inhibitors [ Nω-nitro-l-arginine methyl ester (l-NAME) and S-methylisothiourea], NO donors [sodium nitroprusside (SNP) and diethylenetriamine (DETA)-NONOate], an NO precursor (l-arginine), soluble guanylate cyclase inhibitors (1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one and methylene blue), and a potassium channel blocker [triethylammonium (TEA)]. After incubation, RBC deformability at various shear stresses was determined by ektacytometry. Both NOS inhibitors significantly reduced RBC deformability above a threshold concentration, whereas the NO donors increased deformability at optimal concentrations. NO donors, as well as the NO precursor l-arginine and the potassium blocker TEA, were able to reverse the effects of NOS inhibitors. Guanylate cyclase inhibition reduced RBC deformation, with both SNP and DETA-NONOate able to reverse this effect. These results thus indicate the importance of NO as a determinant of RBC mechanical behavior and suggest its regulatory role for normal RBC deformability.
Matrix remodeling in experimental and human heart failure: a possible regulatory role for TIMP-3
Authors: Fedak Paul W. M. , Altamentova Svetlana M. , Weisel Richard D. , Nili Nafiseh , Ohno Nobuhisa , Verma Subodh , Lee Tsu-Yee J. , Kiani Chris , Mickle Donald A. G. , Strauss Bradley H. , Li Ren-Ke
Published: March 2015

In the failing heart, an imbalance in matrix metalloproteinases (MMPs) and their biological regulators, the tissue inhibitors of MMPs (TIMPs), may result in cardiac dilatation from matrix degradation. We hypothesized that a reduction of myocardial TIMP-3 is associated with adverse matrix remodeling in both human and experimental heart failure. Cardiomyopathic hamsters at age 15 wk (normal), 25 wk (compensated stage), and 35 wk (overt failure) were compared with age-matched normal controls. MMP activity (gelatinase bioassay) was increased in cardiomyopathic hearts ( P = 0.03) and peaked during the transition to overt heart failure. TIMP-3 content (immunoblot) was decreased compared with normal controls (74 ± 5% at 25 wk, 69 ± 10% at 35 wk; P = 0.001) and its reduction was associated with increased MMP activity ( r = −0.6; P = 0.004). TIMP-1 increased progressively ( P = 0.001), whereas TIMP-2, TIMP-4, and MMP protein levels were unchanged. Myocardial collagen (hydroxyproline content) increased with time during the progression to end-stage cardiac failure ( P < 0.0001). Collagen synthesis ([14C]proline uptake) was elevated in cardiomyopathy at 15 and 25 wk ( P < 0.05). The collagen cross-linking ratio (insoluble:soluble collagen) was reduced ( P = 0.003) as the left ventricle dilated. By confocal microscopy restricted to viable myocardium, collagen content was reduced ( P = 0.04) with fragmentation ( P < 0.0001) and thinning ( P = 0.003) of perimysial collagen fibers. Similarly, patients with end-stage congestive heart failure ( n = 7) compared with nonfailing controls ( n = 2) had elevated gelatinase MMP activity ( P = 0.02) associated with isolated reductions in TIMP-3 (55 ± 5% of normal; P = 0.003). Reductions of TIMP-3 parallel adverse matrix remodeling in the cardiomyopathic hamster and the failing human heart. TIMP-3 may contribute to the regulation of myocardial remodeling and its reduction may promote a transition from compensated to end-stage congestive heart failure.
Effects of gestational age on myocardial blood flow and coronary flow reserve in pressure-loaded ovine fetal hearts
Authors: Dalshaug Gregory B. , Scholz Thomas D. , Smith Oliva M. , Bedell Kurt A. , Caldarone Christopher A. , Segar Jeffrey L.
Published: March 2015

To test the hypothesis that coronary flow and coronary flow reserve are developmentally regulated, we used fluorescent microspheres to investigate the effects of acute (6 h) pulmonary artery banding (PAB) on baseline and adenosine-enhanced right (RV) and left ventricular (LV) blood flow in two groups of twin ovine fetuses (100 and 128 days of gestation, term 145 days, n = 6 fetuses/group). Within each group, one fetus underwent PAB to constrict the main pulmonary artery diameter by 50%, and the other twin served as a nonbanded control. Physiological measurements were made 6 h after the surgery was completed; tissues were then harvested for analysis of selected genes that may be involved in the early phase of coronary vascular remodeling. Within each age group, arterial blood gas values, heart rate, and mean arterial blood pressure were similar between control and PAB fetuses. Baseline endocardial blood flow in both ventricles was greater in 100 than 128-day fetuses (RV: 341 ± 20 vs. 230 ± 17 ml · min−1 · 100 g−1; LV: 258 ± 18 vs. 172 ± 23 ml · min−1 · 100 g−1, both P < 0.05). In both age groups, RV and LV endocardial blood flows increased significantly in control animals during adenosine infusion and were greater in PAB compared with control fetuses. After PAB, adenosine further increased RV blood flow in 128-day fetuses (from 416 ± 30 to 598 ± 33 ml · min−1 · 100 g−1, P < 0.05) but did not enhance blood flow in 100-day animals (490 ± 59 to 545 ± 42 ml · min−1 · 100 g−1, P > 0.2). RV vascular endothelial growth factor and Flk-1 mRNA levels were increased relative to controls ( P < 0.05) in 128 but not 100-day PAB fetuses. We conclude that in the ovine fetus, developmentally related differences exist in 1) baseline myocardial blood flows, 2) the adaptive response of myocardial blood flow to acute systolic pressure load, and 3) the responses of selected genes involved in vasculogenesis to increased load in the fetal myocardium.
Tamoxifen inhibits Na+ and K+ currents in rat ventricular myocytes
Authors: He Jianying , Kargacin Margaret E. , Kargacin Gary J. , Ward Christopher A.
Published: March 2015

Tamoxifen is an estrogen receptor antagonist used in the treatment of breast cancer. However, tamoxifen has been shown to induce QT prolongation of the electrocardiogram, thereby potentially causing life-threatening polymorphic ventricular arrhythmias. The purpose of the present study was to elucidate the electrophysiological mechanism(s) that underlie the arrhythmogenic effects of tamoxifen. We used standard ruptured whole cell and perforated patch-clamping techniques on rat ventricular myocytes to investigate the effects of tamoxifen on cardiac action potential (AP) waveforms and the underlying K+ currents. Tamoxifen (3 μmol/l) markedly prolonged AP duration, decreased maximal rate of depolarization, and decreased resting membrane potential. At this concentration, tamoxifen significantly depressed the Ca2+-independent transient outward K+ current ( Ito), sustained outward delayed rectifier K+ current ( Isus), inward rectifier K+ current ( IK1), and Na+ current ( INa) in the myocytes. Lower concentrations of tamoxifen (1 μmol/l) also decreased the resting membrane potential and significantly depressed IK1 to 79 ± 5% ( n = 5; at –120 mV) of pretreatment values. The results of this study indicate that inhibition of Ito, Isus, and IK1 by tamoxifen may underlie AP prolongation in cardiac myocytes and thereby contribute to prolonged QT interval observed in patients.
Role of hyaluronic acid glycosaminoglycans in shear-induced endothelium-derived nitric oxide release
Authors: Mochizuki Seiichi , Vink Hans , Hiramatsu Osamu , Kajita Tatsuya , Shigeto Fumiyuki , Spaan Jos A. E. , Kajiya Fumihiko
Published: March 2015

Endothelium-derived nitric oxide (NO) is synthesized in response to chemical and physical stimuli. Here, we investigated a possible role of the endothelial cell glycocalyx as a biomechanical sensor that triggers endothelial NO production by transmitting flow-related shear forces to the endothelial membrane. Isolated canine femoral arteries were perfused with a Krebs-Henseleit solution at a wide range of perfusion rates with and without pretreatment with hyaluronidase to degrade hyaluronic acid glycosaminoglycans within the glycocalyx layer. NO production rate was evaluated as the product of nitrite concentration in the perfusate and steady-state perfusion rate. The slope that correlates the linear relation between perfusion rate and NO production rate was taken as a measure for flow-induced NO production. Hyaluronidase treatment significantly decreased flow-induced NO production to 19 ± 9% of control (mean ± SD; P < 0.0001 vs. control; n = 11), whereas it did not affect acetylcholine-induced NO production (88 ± 17% of pretreatment level, P = not significant; n = 10). We conclude that hyaluronic acid glycosaminoglycans within the glycocalyx play a pivotal role in detecting and amplifying the shear force of flowing blood that triggers endothelium-derived NO production in isolated canine femoral arteries.
Attenuation of ischemic preconditioning in pigs by scavenging of free oxyradicals with ascorbic acid
Authors: Skyschally Andreas , Schulz Rainer , Gres Petra , Korth Hans-Gert , Heusch Gerd
Published: March 2015

Free oxyradicals are involved in the signal transduction of ischemic preconditioning in rats and rabbits. Data from larger mammals in which the infarct development is closer to that in humans are lacking. We have therefore investigated the impact of the radical scavenger ascorbic acid on ischemic preconditioning in pigs. In 33 anesthetized pigs, the left anterior descending coronary artery was perfused from an extracorporeal circuit. Infarct size (measured as percent area at risk) was determined by triphenyltetrazolium chloride staining. In placebo-treated animals undergoing 90 min of severe ischemia and 120 min of reperfusion, infarct size averaged 26.9 ± 3.9% (mean ± SE; n = 9). Ischemic preconditioning by 10 min of ischemia and 15 min of reperfusion reduced infarct size to 6.4 ± 2.4% ( P < 0.05 vs. placebo; n = 9). Intravenous infusion of ascorbic acid (30 min before ischemic preconditioning or ischemia; 2-g bolus followed by 25 mg/min until the end of ischemia) had no effect on infarct size per se (22.6 ± 6.5%; n = 6), but largely abolished the infarct size reduction by ischemic preconditioning (19.1 ± 5.4%; n = 9). Scavenging of free oxyradicals with ascorbic acid largely attenuates the beneficial effect of ischemic preconditioning in pigs.
Activation of cardiac ryanodine receptors by cardiac glycosides
Authors: Sagawa Toshio , Sagawa Kazuko , Kelly James E. , Tsushima Robert G. , Wasserstrom J. Andrew
Published: March 2015

This study investigated the effects of cardiac glycosides on single-channel activity of the cardiac sarcoplasmic reticulum (SR) Ca2+release channels or ryanodine receptor (RyR2) channels and how this action might contribute to their inotropic and/or toxic actions. Heavy SR vesicles isolated from canine left ventricle were fused with artificial planar lipid bilayers to measure single RyR2 channel activity. Digoxin and actodigin increased single-channel activity at low concentrations normally associated with therapeutic plasma levels, yielding a 50% of maximal effect of ∼0.2 nM for each agent. Channel activation by glycosides did not require MgATP and occurred only when digoxin was applied to the cytoplasmic side of the channel. Similar results were obtained in human RyR2 channels; however, neither the crude skeletal nor the purified cardiac channel was activated by glycosides. Channel activation was dependent on [Ca2+] on the luminal side of the bilayer with maximal stimulation occurring between 0.3 and 10 mM. Rat RyR2 channels were activated by digoxin only at 1 μM, consistent with the lower sensitivity to glycosides in rat heart. These results suggest a model in which RyR2 channel activation by digoxin occurs only when luminal [Ca2+] was increased above 300 μM (in the physiological range). Consequently, increasing SR load (by Na+pump inhibition) serves to amplify SR release by promoting direct RyR2 channel activation via a luminal Ca2+-sensitive mechanism. This high-affinity effect of glycosides could contribute to increased SR Ca2+release and might play a role in the inotropic and/or toxic actions of glycosides in vivo.
Lipopolysaccharide induces apoptosis in adult rat ventricular myocytes via cardiac AT1 receptors
Authors: Li Hai Ling , Suzuki Jun , Bayna Evelyn , Zhang Fu-Min , Dalle Molle Erminia , Clark Aaron , Engler Robert L. , Lew Wilbur Y. W.
Published: March 2015

Lipopolysaccharide (LPS) from gram-negative bacteria circulates in acute, subacute, and chronic conditions. It was hypothesized that LPS directly induces cardiac apoptosis. In adult rat ventricular myocytes (isolated with depyrogenated digestive enzymes to minimize tolerance), LPS (10 ng/ml) decreased the ratio of Bcl-2 to Bax at 12 h; increased caspase-3 activity at 16 h; and increased annexin V, propidium iodide, and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining at 24 h. Apoptosis was blocked by the caspase inhibitor benzyloxycarbonyl-valine-alanine-aspartate fluoromethylketone (Z-VAD-fmk), captopril, and angiotensin II type 1 receptor (AT1) inhibitor (losartan), but not by inhibitors of AT2 receptors (PD-123319), tumor necrosis factor-α (TNFRII:Fc), or nitric oxide ( N G-monomethyl-l-arginine). Angiotensin II (100 nmol/l) induced apoptosis similar to LPS without additive effects. LPS in vivo (1 mg/kg iv) increased apoptosis in left ventricular myocytes for 1–3 days, which dissipated after 1–2 wk. Losartan (23 mg · kg−1 · day−1 in drinking water for 3 days) blocked LPS-induced in vivo apoptosis. In conclusion, low levels of LPS induce cardiac apoptosis in vitro and in vivo by activating AT1 receptors in myocytes.
Alterations in apoptotic signaling in human idiopathic cardiomyopathic hearts in failure
Authors: Steenbergen Charles , Afshari Cynthia A. , Petranka John G. , Collins Jennifer , Martin Karla , Bennett Lee , Haugen Astrid , Bushel Pierre , Murphy Elizabeth
Published: March 2015

Dilated cardiomyopathy, a disease of unknown etiology and pathogenesis, is associated with heart failure and compensatory hypertrophy. Although cell and animal models suggest a role for altered gene expression in the transition to heart failure, there is a paucity of data derived from the study of human heart tissue. In this study, we used DNA microarray profiling to investigate changes in the expression of genes involved in apoptosis that occur in human idiopathic dilated cardiomyopathic hearts that had progressed to heart failure. We observed altered gene expression consistent with a proapoptotic shift in the TNF-α signaling pathway. Specifically, we found decreased expression of TNF-α- and NF-κB-induced antiapoptotic genes such as growth arrest and DNA damage-inducible ( GADD) 45β, Flice inhibitory protein ( FLIP), and TNF-induced protein 3 ( A20). Consistent with a role for apoptosis in heart failure, we also observed a significant decrease in phosphorylation of BAD at Ser-112. This study identifies several pathways that are altered in human heart failure and provides new targets for therapy.
Cell death during ischemia: relationship to mitochondrial depolarization and ROS generation
Authors: Levraut Jacques , Iwase Hirotaro , Shao Z.-H. , Vanden Hoek Terry L. , Schumacker Paul T.
Published: March 2015

Ischemia-reperfusion injury induces cell death, but the responsible mechanisms are not understood. This study examined mitochondrial depolarization and cell death during ischemia and reperfusion. Contracting cardiomyocytes were subjected to 60-min ischemia followed by 3-h reperfusion. Mitochondrial membrane potential (ΔΨm) was assessed with tetramethylrhodamine methyl ester. During ischemia, ΔΨmdecreased to 24 ± 5.5% of baseline, but no recovery was evident during reperfusion. Cell death assessed by Sytox Green was minimal during ischemia but averaged 66 ± 7% after 3-h reperfusion. Cyclosporin A, an inhibitor of mitochondrial permeability transition, was not protective. However, pharmacological antioxidants attenuated the fall in ΔΨmduring ischemia and cell death after reperfusion and decreased lipid peroxidation as assessed with C11-BODIPY. Cell death was also attenuated when residual O2was scavenged from the perfusate, creating anoxic ischemia. These results suggested that reactive oxygen species (ROS) were important for the decrease in ΔΨmduring ischemia. Finally, 143B-ρ0osteosarcoma cells lacking a mitochondrial electron transport chain failed to demonstrate a depletion of ΔΨmduring ischemia and were significantly protected against cell death during reperfusion. Collectively, these studies identify a central role for mitochondrial ROS generation during ischemia in the mitochondrial depolarization and subsequent cell death induced by ischemia and reperfusion in this model.
Cardiovascular regulation and expressions of NO synthase-tyrosine hydroxylase in nucleus tractus solitarius of ovine fetus
Authors: Ma Sheng-Xing , Fang Qun , Morgan Brian , Ross Michael G. , Chao Conrad R.
Published: March 2015

The purpose of this study was to examine cardiovascular responses to fourth cerebral ventricle (4V) administration of nitroglycerin (NTG) or an inhibitor of nitric oxide (NO) synthase (NOS) in the near-term ovine and to determine whether, during birth, neuronal NOS (nNOS) is induced in noradrenergic A1 neurons in the medial nucleus tractus solitarius (mNTS). In chronically instrumented fetal sheep, 4V injection of NTG (1.2 nmol), an NO donor, produced an arterial blood depressor and a moderate decrease in heart rate. Arterial blood pressure is increased by 4V administration of NG-nitro-l-arginine methyl ester (10 nmnol), an inhibitor of NOS, in fetuses. Sections of the medulla from fetuses and newborn lambs were examined by using immunolabeling with tyrosine hydroxylase (TH) antibody combined with NADPH diaphorase (NADPHd) histochemistry, a marker of nNOS activity. The NADPHd-positive cells and TH-positive cells containing NADPHd reactivity were significantly increased in the mNTS of newborns compared with the fetuses. The results suggest that during birth, there is upregulation of NADPHd/nNOS in the noradrenergic neurons of mNTS resulting in a centrally mediated reduction of fetal arterial blood pressure.
Glycolytic buffering affects cardiac bioenergetic signaling and contractile reserve similar to creatine kinase
Authors: Harrison Glenn J. , van Wijhe Michiel H. , de Groot Bas , Dijk Francina J. , Gustafson Lori A. , van Beek Johannes H. G. M.
Published: March 2015

Creatine kinase (CK) and glycolysis represent important energy-buffering processes in the cardiac myocyte. Although the role of compartmentalized CK in energy transfer has been investigated intensely, similar duties for intracellular glycolysis have not been demonstrated. By measuring the response time of mitochondrial oxygen consumption to dynamic workload jumps ( tmito) in isolated rabbit hearts, we studied the effect of inhibiting energetic systems (CK and/or glycolysis) on transcytosolic signal transduction that couples cytosolic ATP hydrolysis to activation of oxidative phosphorylation. Tyrode-perfused hearts were exposed to 15 min of the following: 1) 0.4 mM iodoacetamide (IA; n = 6) to block CK (CK activity <3% vs. control), 2) 0.3 mM iodoacetic acid (IAA; n = 5) to inhibit glycolysis (GAPDH activity <3% vs. control), or 3) vehicle (control, n = 7) at 37°C. Pretreatment tmitowas similar across groups at 4.3 ± 0.3 s (means ± SE). No change in tmitowas observed in control hearts; however, in IAA- and IA-treated hearts, tmitodecreased by 15 ± 3% and 40 ± 5%, respectively ( P < 0.05 vs. control), indicating quicker energy supply-demand signaling in the absence of ADP/ATP buffering by CK or glycolysis. The faster response times in IAA and IA groups were independent of the size of the workload jump, and the increase in myocardial oxygen consumption during workload steps was unaffected by CK or glycolysis blockade. Contractile function was compromised by IAA and IA treatment versus control, with contractile reserve (defined as increase in rate-pressure product during a standard heart rate jump) reduced to 80 ± 8% and 80 ± 10% of baseline, respectively ( P < 0.05 vs. control), and significant elevations in end-diastolic pressure, suggesting raised ADP concentration. These results demonstrate that buffering of phosphate metabolites by glycolysis in the cytosol contributes appreciably to slower mitochondrial activation and may enhance contractile efficiency during increased cardiac workloads. Glycolysis may therefore play a role similar to CK in heart muscle.
Long-term inhibition of nitric oxide synthesis increases arterial thrombogenecity in rat carotid artery
Authors: Kubo-Inoue Mayuko , Egashira Kensuke , Usui Makoto , Takemoto Masao , Ohtani Kisho , Katoh Makoto , Shimokawa Hiroaki , Takeshita Akira
Published: March 2015

Reduced activity of endothelial nitric oxide (NO) may be involved in thrombus formation on atherosclerotic plaques, a major cause of acute coronary syndrome. However, mechanisms of such increase in arterial thrombogenecity have not been fully understood. We previously reported that long-term inhibition of NO synthesis by administration of N G-nitro-l-arginine methyl ester (l-NAME) causes hypertension and activates vascular tissue angiotensin-converting enzyme (ACE) activity. We used this model to investigate the mechanism by which long-term impairment of NO activity increases arterial thrombogenecity. We observed cyclic flow variations (CFVs), a reliable marker of platelet thrombi, after the production of stenosis of the carotid artery in rats treated with l-NAME for 4 wk. The thrombin antagonist argatroban suppressed the CFVs. The CFVs were detected in rats receiving l-NAME plus hydralazine but not in rats receiving l-NAME plus an ACE inhibitor (imidapril). Treatment with the ACE inhibitor imidapril, but not with hydralazine, prevented l-NAME-induced increases in carotid arterial ACE activity and attenuated tissue factor expression. These results suggest that long-term inhibition of endothelial NO synthesis may increase arterial thrombogenecity at least in part through angiotensin II-induced induction of tissue factor and the resultant thrombin generation. These data provide a new insight as to how endothelial NO exhibits antithrombogenic properties of the endothelium.
Stabilization of mast cells by heme oxygenase-1: an anti-inflammatory role
Authors: Takamiya Rina , Murakami Makoto , Kajimura Mayumi , Goda Nobuhito , Makino Nobuya , Takamiya Yoshihiro , Yamaguchi Tokio , Ishimura Yuzuru , Hozumi Nobumichi , Suematsu Makoto
Published: March 2015

This study examined the role of bilirubin in heme oxygenase (HO)-1-mediated amelioration of mast cell (MC)-elicited inflammatory responses. Pretreatment of rats with an intraperitoneal injection of hemin, an inducer of HO-1, evolved a marked induction of the enzyme in MCs. Intravital videomicroscopy revealed that hemin pretreatment attenuated compound 48/80-elicited degranulation of MCs and resultant leukocyte adhesion in venules. Superfusion with biliverdin or bilirubin, but not with carbon monoxide (CO), another product of the HO reaction, mimicked suppressive actions of the HO-1 induction on both the cell degranulation and leukocyte adhesion elicited by the stimulus, suggesting a requirement of the enzyme reaction to generate bilirubin in the inhibitory mechanisms. Such MC-desensitizing actions of bilirubin were observed in primary-cultured MCs and reproduced irrespective of the choice of stimuli, such as compound 48/80, calcium ionophore, and anti-IgE serum. Furthermore, MC-stabilizing effects of HO-1 were reproduced by the gene transfection of the enzyme into mastocytoma cell line RBL2H3. These results suggest that bilirubin generated through HO-1 serves as an anti-inflammatory substance that desensitizes MCs and ameliorates leukocyte recruitment.
Effects of high salt intake on brain AT1 receptor densities in Dahl rats
Authors: Wang Jun Ming , Veerasingham Shereeni J. , Tan Junhui , Leenen Frans H. H.
Published: March 2015

To assess effects of dietary salt on brain AT1 receptor densities, 4-wk-old Dahl salt-sensitive (Dahl S) and salt-resistant (Dahl R) rats were fed a regular (101 μmol Na/g) or high (1,370 μmol Na/g)-salt diet for 1, 2, or 4 wk. AT1 receptors were assessed by quantitative in vitro autoradiography. AT1 receptor densities did not differ significantly between strains on the regular salt diet. The high-salt diet for 1 or 2 wk increased AT1 receptor binding by 21–64% in the Dahl S rats in the subfornical organ, median preoptic nucleus, paraventricular nucleus, and suprachiasmatic nucleus. No changes were noted in the Dahl R rats. After 4 wk on a high-salt diet, increases in AT1 receptor binding persisted in Dahl S rats but were now also noted in the paraventricular nucleus, median preoptic nucleus, and suprachiasmatic nucleus of Dahl R rats. At 4 wk on the diet, intracerebroventricular captopril caused clear decreases in blood pressure only in the Dahl S on the high-salt diet but caused largely similar relative increases in brain AT1 receptor densities in Dahl S and R on the high-salt diet versus regular salt diet. These data demonstrate that high salt intake rapidly (within 1 wk) increases AT1 receptor densities in specific brain nuclei in Dahl S and later (by 4 wk) also in Dahl R rats. Because the brain renin-angiotensin system only contributes to salt-induced hypertension in Dahl S rats, further studies are needed to determine which of the salt-induced increases in brain AT1 receptor densities contribute to the hypertension and which to other aspects of body homeostasis.
Absorption of amniotic fluid by amniochorion in sheep
Authors: Faber J. Job , Anderson Debra F.
Published: March 2015

Swallowing of amniotic fluid and lung fluid inflow were eliminated in 10 chronically instrumented fetuses. The urachus was ligated, and fetal was urine drained to the outside. At the beginning and the end of 21 experiments of 66 ± 5 (SE) h duration, all amniotic fluid was temporarily drained to the outside for volume measurement and sampling. Amniotic fluid osmolalities and oncotic pressures were experimentally controlled. Amniochorionic absorption of amniotic fluid depended strongly on the osmolality difference between amniotic fluid and fetal plasma ( P< 0.001), but at zero osmolality difference there still was a mean absorption rate of 23.8 ± 4.7 (SE) ml/h ( P < 0.001). Absorption was unaffected by the protein concentration difference between amniotic fluid and fetal plasma, but infused bovine albumin in the amniotic fluid was absorbed at a rate of 1.8 ± 0.4 g/h ( P < 0.001), corresponding to a volume flow of fluid of 33.8 ± 6.1 ml/h ( P < 0.001). Fluid absorption in the amniochorion is driven in part by crystalloid osmotic pressure, but about 25 ml/h is absorbed by a path that is permeable to protein. That path has the physiological characteristics of lymphatic drainage, although no anatomic basis is known to exist for a lymphatic system in the amniochorion.
Escherichia coliLPS-induced LV dysfunction: role of toll-like receptor-4 in the adult heart
Authors: Nemoto Shintaro , Vallejo Jesus G. , Knuefermann Pascal , Misra Arunima , Defreitas Gilberto , Carabello Blase A. , Mann Douglas L.
Published: March 2015

The precise molecular mechanisms responsible for sepsis-induced myocardial dysfunction remain undefined. Toll-like receptor-4 (TLR-4) engages lipopolysaccharide (LPS) and activates signaling pathways leading to the expression of proinflammatory cytokines implicated in myocardial dysfunction. We determined whether TLR-4 was necessary for LPS-induced myocardial dysfunction in vivo. The effects of LPS on left ventricular (LV) function were studied in mice with defective TLR-4 signaling (C3H/HeJ, TLR-4 deficient) and wild-type mice (C3HeB/FeJ). Mice ( n = 5/group) were injected with LPS or diluent, and LV function was examined by using two-dimensional echocardiography and conductance catheters. LPS significantly decreased all indexes of LV function in wild-type mice when compared with controls; LV function was not depressed in the LPS-treated TLR-4-deficient mice relative to controls. LPS increased myocardial nitric oxide synthase-2 expression and cGMP only in wild-type mice. This study suggests that TLR-4 mediates the LV dysfunction that occurs in LPS-induced shock. Therefore, TLR-4 might be a therapeutic target for attenuating the effects of LPS on the heart.
Cardiac mast cell-mediated activation of gelatinase and alteration of ventricular diastolic function
Authors: Chancey Amanda L. , Brower Gregory L. , Janicki Joseph S.
Published: March 2015

Mast cells contain proteases capable of activating matrix metalloproteinases (MMPs). However, given the relatively low density of mast cells in the myocardium (i.e., 1.5–5.3 cells/mm2), it is unknown whether these enzymes are present in sufficient quantities in the normal heart to mediate MMP activation. Accordingly, this study sought to determine whether chemically induced degranulation of cardiac mast cells (with compound 48/80) would have an effect in isolated, blood-perfused, functioning rat hearts. Mast cell degranulation produced a 15% increase in histamine levels present in the coronary efflux, a significant increase in myocardial water (i.e., edema) relative to normal values (80.1 ± 3.4% vs. 77.4 ± 1.08%, P≤ 0.03), a substantial activation of MMP-2 (126% increase relative to controls, P ≤ 0.02), and a marked decrease in myocardial collagen volume fraction (0.46 ± 0.10% vs. 0.97 ± 0.33%, P ≤ 0.001). Furthermore, although an increase in ventricular stiffness was expected due to the extent of edema resulting from mast cell degranulation, modest ventricular dilatation was observed. These findings clearly demonstrate that the number of mast cells present in normal hearts is sufficient to mediate activation of MMPs and produce extracellular matrix degradation, thereby potentially causing subsequent ventricular dilatation.
Bax ablation protects against myocardial ischemia-reperfusion injury in transgenic mice
Authors: Hochhauser Edith , Kivity Shaye , Offen Daniel , Maulik Nilanjana , Otani Hajime , Barhum Yael , Pannet Hannah , Shneyvays Vladymir , Shainberg Asher , Goldshtaub Valeri , Tobar Anna , Vidne Bernardo A.
Published: March 2015

The role of the proapototic Bax gene in ischemia-reperfusion (I/R) injury was studied in three groups of mice: homozygotic knockout mice lacking the Bax gene (Bax−/−), heterozygotic mice (Bax+/−), and wild-type mice (Bax+/+). Isolated hearts were subjected to ischemia (30 min, 37°C) and then to 120 min of reperfusion. The left ventricular developed force of Bax-deficient vs. Bax+/+ hearts at stabilization and at 120 min of reperfusion was 1,411 ± 177 vs. 1,161 ± 137 mg and 485 ± 69 vs. 306 ± 68 mg, respectively. Superior cardiac function of Bax−/− hearts after I/R was accompanied by a decrease in creatine kinase release, caspase 3 activity, irreversible ischemic injury, and the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cardiomyocytes. Electron microscopic evaluation revealed reduced damage to mitochondria and the nuclear chromatin structure in Bax-deficient mice. In the Bax+/− hearts, the damage markers were moderate. The superior tolerance of Bax knockout hearts to I/R injury recommends this gene as a potential target for therapeutic intervention in patients with severe and intractable myocardial ischemia.
Influence of coronary artery diameter on eNOS protein content
Authors: Laughlin M. H. , Turk J. R. , Schrage W. G. , Woodman C. R. , Price E. M.
Published: March 2015

The purpose of this study was to test the hypothesis that the content of endothelial nitric oxide synthase (eNOS) protein (eNOS protein/g total artery protein) increases with decreasing artery diameter in the coronary arterial tree. Content of eNOS protein was determined in porcine coronary arteries with immunoblot analysis. Arteries were isolated in six size categories from each heart: large arteries [301- to 2,500-μm internal diameter (ID)], small arteries (201- to 300-μm ID), resistance arteries (151- to 200-μm ID), large arterioles (101- to 150-μm ID), intermediate arterioles (51- to 100-μm ID), and small arterioles(<50-μm ID). To obtain sufficient protein for analysis from small- and intermediate-sized arterioles, five to seven arterioles 1–2 mm in length were pooled into one sample for each animal. Results establish that the number of smooth muscle cells per endothelial cell decreases from a number of 10 to 15 in large coronary arteries to 1 in the smallest arterioles. Immunohistochemistry revealed that eNOS is located only in endothelial cells in all sizes of coronary artery and in coronary capillaries. Contrary to our hypothesis, eNOS protein content did not increase with decreasing size of coronary artery. Indeed, the smallest coronary arterioles had less eNOS protein per gram of total protein than the large coronary arteries. These results indicate that eNOS protein content is greater in the endothelial cells of conduit arteries, resistance arteries, and large arterioles than in small coronary arterioles.