bluuebunny/crossref_metadata_2025 huggingface dataset:
Cross talk of shear-induced production of prostacyclin and nitric oxide in endothelial cells
Authors: Osanai Tomohiro , Fujita Norio , Fujiwara Naoto , Nakano Takao , Takahashi Koki , Guan Weiping , Okumura Ken
Published: December 2017

We tested the hypothesis that vessel homeostasis is maintained through the cross talk of shear-induced production of prostacyclin and nitric oxide (NO). Confluent human umbilical vein endothelial cells (HUVEC) were exposed to fluid shear stress at 15 dyn/cm2using a cone-plate device, and the concentrations of 6-keto-PGF1αand NO metabolites (nitrate and nitrite) in the medium were measured with radioimmunoassay and the Greiss method, respectively. Compared with static control, shear stress increased cumulative prostacyclin production by twofold after 90 min of exposure. Inhibition of NO synthase enhanced flow-induced prostacyclin production by twofold without affecting the baseline production. Guanylyl cyclase inhibitor enhanced flow-induced prostacyclin production to the same degree. In contrast, a stable agonist of cGMP attenuated the rapid early phase of flow-dependent prostacyclin production. Shear-induced NO metabolite production was unaffected even after indomethacin inhibited prostacyclin production. We conclude that NO shows an inhibitory effect on prostacyclin production under shear stress and that vessel homeostasis may be maintained through an increase in prostacyclin production when NO synthesis is impaired in endothelial cells.
AV blocking due to asynchronous vagal stimulation in rats
Authors: Schiereck P. , Sanna N. , Mosterd W. L.
Published: December 2017

The parasympathetic nervous system innervates the heart through two cervical vagal branches. The right vagal branch mainly influences the heart rate by the modulation of the rhythmogenesis of the sinoatrial node. The left branch predominantly influences the conduction properties of the atrioventricular (AV) node. We investigated the effect of asynchronous stimulation by the vagal nerves on the occurrence of irregularities in heart rate. In rats, the vagal nerves were isolated and cut. Different vagal stimulation patterns (continuous, pulsed) were applied. The heart was beating spontaneously under continuous vagal stimulation. In case of pulsed vagal stimulation, the atria were paced at different rates. Asynchronicity was induced by delaying the right stimulus with respect to the left stimulus (early right) or the left stimulus with respect to the right stimulus (early left). The value of the fraction of deviated R-R or P-Q intervals in the distribution in the histogram was used to characterize irregularities during a stimulation protocol (duration in case of continuous stimulation: 20 s; pulsed stimulation: 120 s). Under both stimulation patterns (continuous or pulsed), we found that early left vagal stimulation introduced a much larger fraction of deviated intervals in the R-R or P-Q histogram (in R-R: 29.1 ± 4.9%; in P-Q: 12.90 ± 1.95%) than early right vagal stimulation (in R-R: 7.4 ± 2.0%; in P-Q: 1.05 ± 0.50%) or synchronous stimulation (in R-R: 8.2 ± 3.6%; in P-Q: 2.15 ± 0.75%). We conclude that early stimulation by the left vagal nerve can introduce irregularities in heart rate, mainly due to different degrees of AV nodal blockade.
A novel right-heart catheterization technique for in vivo measurement of vascular responses in lungs of intact mice
Authors: Champion Hunter C. , Villnave Douglas J. , Tower Allen , Kadowitz Philip J. , Hyman Albert L.
Published: December 2017

The present study employed a new right-heart catheterization technique to measure pulmonary arterial pressure, pulmonary arterial wedge pressure, and pulmonary vascular resistance in anesthetized intact-chest, spontaneously breathing mice. Under fluoroscopic guidance, a specially designed catheter was inserted via the right jugular vein and advanced to the main pulmonary artery. Cardiac output was determined by the thermodilution technique, and measured parameters were stable for periods of ≤3 h. Pressure-flow curves in vivo were curvilinear, with mean pulmonary arterial pressure increasing more rapidly at low pulmonary blood flows of 5–10 ml/min and less rapidly at higher blood flow rates. The pressure-flow relationship was shifted to the left by the nitric oxide synthase inhibitor nitro-l-arginine methyl ester (l-NAME) at higher blood flow levels, whereas the cyclooxygenase inhibitor sodium meclofenamate was without effect. The increase in pulmonary arterial pressure in response to acute hypoxia (fractional inspired O2 10%) was augmented byl-NAME but unaltered by sodium meclofenamate. The present results demonstrate that the right-heart catheterization technique can be used to measure pulmonary vascular pressures and responses in the mouse. This is, to our knowledge, the first report of a right-heart catheterization technique to measure pulmonary vascular pressures and responses in the intact-chest, spontaneously breathing mouse and should prove useful for the investigation of pulmonary vascular responses in transgenic mice.
bFGF increases collateral blood flow in aged rats with femoral artery ligation
Authors: Yang H. T. , Feng Y.
Published: December 2017

We tested the hypothesis that aged animals are as responsive as the young adult animals in expanding collateral vasculature under a similar treatment of basic fibroblast growth factor (bFGF). Two age groups of male Fischer 344 rats (11 mo old; n = 32, 23 mo old; n = 43) weighing ∼385 g were subdivided into normal, acute ligation [femoral artery (FA) ligated 3 days before blood flow (BF) measurement] or ligated groups for 16 days and received recombinant human bFGF intra-arterial infusion at doses of 0, 0.5, 5, and 50 μg ⋅ kg−1⋅ day−1. BF was determined with85Sr- and141Ce-labeled microspheres during treadmill running at 15 and 20 m/min at 15% grade. Blood presure (BP) values were ∼149 and ∼163 mmHg ( p < 0.05); heart rates were ∼496 and ∼512 beats/min in the aged and young adult groups during running, respectively. Maximal collateral BF values were confirmed by no additional BF increase in the calf muscle at the higher speed. Ligation of the FA for 3 days reduced the BF reserve to the calf muscle by ∼90%. Calf muscle BF was modestly greater (10 ml ⋅ min−1⋅ 100 g−1) by 16 days in the carrier group. bFGF infusion expanded collateral BF in a dose-dependent manner with an increase of 33 and 42 ml ⋅ min−1⋅ 100 g−1( P < 0.001) in the 5 and 50 μg ⋅ kg−1⋅ day−1bFGF groups, respectively. Aged animals showed similar BF improvements as observed with the adult groups in response to ligation surgery and bFGF treatment. Our data indicate that the aged rats (∼23 mo old) remain responsive to exogenous bFGF induced in developing collateral-dependent BF as the young adult (∼11 mo old) controls. This suggests that the influence of bFGF in expanding collateral BF should not be preempted in the aged group, the population most affected by peripheral arterial insufficiency.
Regulation of myocardial blood flow response to mental stress in healthy individuals
Authors: Schöder Heiko , Silverman Daniel H. , Campisi Roxana , Sayre James W. , Phelps Michael E. , Schelbert Heinrich R. , Czernin Johannes
Published: December 2017

Mental stress testing has been proposed as a noninvasive tool to evaluate endothelium-dependent coronary vasomotion. In patients with coronary artery disease, mental stress can induce myocardial ischemia. However, even the determinants of the physiological myocardial blood flow (MBF) response to mental stress are poorly understood. Twenty-four individuals (12 males/12 females, mean age 49 ± 13 yr, range 31–74 yr) with a low likelihood for coronary artery disease were studied. Serum catecholamines, cardiac work, and MBF (measured quantitatively with N-13 ammonia and positron emission tomography) were assessed. During mental stress (arithmetic calculation) MBF increased significantly from 0.70 ± 0.14 to 0.92 ± 0.21 ml ⋅ min−1⋅ g−1( P < 0.01). Mental stress caused significant increases ( P < 0.01) in serum epinephrine (26 ± 16 vs. 42 ± 17 pg/ml), norepinephrine (272 ± 139 vs. 322 ± 136 pg/ml), and cardiac work [rate-pressure product (RPP) 8,011 ± 1,884 vs. 10,416 ± 2,711]. Stress-induced changes in cardiac work were correlated with changes in MBF ( r = 0.72; P < 0.01). Multiple-regression analysis revealed stress-induced changes in the RPP as the only significant ( P = 0.0001) predictor for the magnitude of mental stress-induced increases in MBF in healthy individuals. Data from this group of healthy individuals should prove useful to investigate coronary vasomotion in individuals at risk for or with documented coronary artery disease.
Frequency limits on aortic baroreceptor input to nucleus tractus solitarii
Authors: Liu Zhi , Chen Chao-Yin , Bonham Ann C.
Published: December 2017

The frequency of baroreceptor volleys to the central nervous system can influence the fidelity of baroreceptor signal transmission and thus may affect baroreflex regulation of blood pressure. We examined 1) the extent to which frequency-dependent depression of aortic baroreceptor signals was initiated at the first central synapse between primary baroreceptor fibers and second-order nucleus tractus solitarii (NTS) neurons; 2) whether the pattern of baroreceptor input influenced the depression; and 3) the potential relevance to baroreflex sympathoinhibition. In urethan-anesthetized rats, NTS action potential responses of neurons classified as second or higher order and averaged lumbar sympathetic nerve activity responses were simultaneously measured during 100 aortic depressor nerve stimuli delivered in constant or phasic patterns (0.8–48 Hz). Frequency-dependent depression was initiated at second-order neurons, with NTS responses decreasing to a 72% response rate at 48 Hz; the depression was greater at higher-order neurons; responses decreased to a 30% response rate. The depression was slightly but significantly greater with phasic inputs. Curve fitting suggested that synaptic depression may limit baroreflex sympathoinhibition. Thus frequency limits on baroreceptor inputs at NTS synapses may affect baroreflex function.
Mechanisms of ischemic preconditioning effects on Ca2+paradox-induced changes in heart
Authors: Kawabata Ken-Ichi , Netticadan Thomas , Osada Mitsuru , Tamura Kohji , Dhalla Naranjan S.
Published: December 2017

The effects of ischemic preconditioning (IP) on changes in cardiac performance and sarcoplasmic reticulum (SR) function due to Ca2+paradox were investigated. Isolated perfused hearts were subjected to IP (three cycles of 3-min ischemia and 3-min reperfusion) followed by Ca2+-free perfusion and reperfusion (Ca2+paradox). Perfusion of hearts with Ca2+-free medium for 5 min followed by reperfusion with Ca2+-containing medium for 30 min resulted in a dramatic decrease in the left ventricular (LV) developed pressure and a marked increase in LV end-diastolic pressure. Alterations in cardiac contractile activity due to Ca2+paradox were associated with depressed SR Ca2+-uptake, Ca2+-pump ATPase, and Ca2+-release activities as well as decreased SR protein contents for Ca2+-pump and Ca2+channels. All these changes due to Ca2+paradox were significantly prevented in hearts subjected to IP. The protective effects of IP on Ca2+paradox changes in cardiac contractile activity as well as SR Ca2+-pump and Ca2+-release activities were lost when the hearts were treated with 8-( p-sulfophenyl)-theophylline, an adenosine receptor antagonist; KN-93, a specific Ca2+/calmodulin-dependent protein kinase II (CaMK II) inhibitor; or chelerythrine chloride, a protein kinase C (PKC) inhibitor. These results indicate that IP rendered cardioprotection by preventing a depression in SR function in Ca2+paradox hearts. Furthermore, these beneficial effects of IP may partly be mediated by adenosine receptors, PKC, and CaMK II.
Beat-to-beat repolarization variability in ventricular myocytes and its suppression by electrical coupling
Authors: Zaniboni Massimiliano , Pollard Andrew E. , Yang Lin , Spitzer Kenneth W.
Published: December 2017

Single ventricular myocytes paced at a constant rate and held at a constant temperature exhibit beat-to-beat variations in action potential duration (APD). In this study we sought to quantify this variability, assess its mechanism, and determine its responsiveness to electrotonic interactions with another myocyte. Interbeat APD90 (90% repolarization) of single cells was normally distributed. We thus quantified APD90 variability as the coefficient of variability, CV = (SD/mean APD90) × 100. The mean ± SD of the CV in normal solution was 2.3 ± 0.9 (132 cells). Extracellular TTX (13 μM) and intracellular EGTA (14 mM) both significantly reduced the CV by 44 and 26%, respectively. When applied in combination the CV fell by 54%. In contrast, inhibition of the rapid delayed rectifier current with L-691,121 (100 nM) increased the CV by 300%. The CV was also significantly reduced by 35% when two normal myocytes were electrically connected with a junctional resistance ( R j) of 100 MΩ. Electrical coupling ( R j = 100 MΩ) of a normal myocyte to one producing early afterdepolarization (EAD) completely blocked EAD formation. These results indicate that beat-to-beat APD variability is likely mediated by stochastic behavior of ion channels and that electrotonic interactions act to limit temporal dispersion of refractoriness, a major contributor to arrhythmogenesis.
Alterations in relaxation to lactate and H2O2in human placental vessels from gestational diabetic pregnancies
Authors: Figueroa Reinaldo , Martinez Edilberto , Fayngersh Raisa P. , Tejani Nergesh , Mohazzab-H. Kamal M. , Wolin Michael S.
Published: December 2017

We determined whether alterations in the mechanism of relaxation to H2O2potentially contribute to the enhanced prostaglandin-mediated contractile response to H2O2and posthypoxic reoxygenation seen in human placental vessels of pregnancies with gestational diabetes mellitus (GDM). Isolated placental arteries and veins from GDM and uncomplicated full-term pregnancies were precontracted with prostaglandin F2α([Formula: see text] 35–38 Torr) and then exposed to lactate (1–10 mM), arachidonic acid (0.01–10 μM), nitroglycerin (1 nM–1 μM), forskolin (0.01–10 μM), or H2O2(1 μM–1 mM + 10 μM indomethacin). The rates of tissue H2O2metabolism by catalase and nitrite production were measured. The relaxation to lactate was reduced in GDM placental arteries and veins by 54–85 and 66–80%, and the relaxation to H2O2was inhibited by 80–94% in GDM placental veins compared with vessels from uncomplicated full-term pregnancies. H2O2caused only minimal relaxation of placental arteries. Responses to other relaxing agents were not altered in the GDM placental vessels. Diabetic vessels showed rates of nitrite production that were increased by 113–195% and rates of H2O2metabolism by catalase that were decreased by 44–61%. The loss of relaxation to H2O2and lactate (mediated via H2O2), perhaps as a result of the inhibition of catalase by nitric oxide, may explain the previously reported enhancement of prostaglandin-mediated contractile responses to H2O2and posthypoxic reoxygenation seen in GDM placental vessels.
Single-channel activity and expression of atrial L-type Ca2+channels in patients with latent hyperthyroidism
Authors: Kreuzberg U. , Theissen P. , Schicha H. , Schröder F. , Mehlhorn U. , de Vivie E. R. , Bokník P. , Neumann J. , Grohé C. , Herzig S.
Published: December 2017

Patients with “latent hyperthyroidism” (suppressed thyroid-stimulating hormone and normal circulating thyroid hormones) are at risk to develop atrial fibrillation. In animal models, hyperthyroidism is associated with increased cardiac L-type Ca2+current. Therefore, we assessed L-type channel function and expression in right atria from patients undergoing cardiac surgery. Single L-type channels were studied in the cell-attached condition. Voltage dependence of gating was similar in patients with and without latent hyperthyroidism. With use of a pulse protocol leading to maximum channel availability, single-channel activity was further analyzed. Average peak current was significantly enhanced in latent hyperthyroidism, mainly because of an increased channel availability ( P < 0.05). Protein expression was analyzed by Western blot. In latent hyperthyroidism, expression of Ca2+channel α1-subunits was increased more than threefold ( P < 0.01). In contrast, sarco(endo)plasmic reticulum Ca2+-ATPase and phospholamban levels were not significantly changed. We only observed a trend toward increased sarco(endo)plasmic reticulum Ca2+-ATPase expression ( P = 0.085). Function and expression of human atrial L-type Ca2+channels are increased in latent hyperthyroidism. These endocrine effects on the heart may be clinically relevant.
In eNOS knockout mice skeletal muscle arteriolar dilation to acetylcholine is mediated by EDHF
Authors: Huang An , Sun Dong , Smith Carolyn J. , Connetta Joseph A. , Shesely Edward G. , Koller Akos , Kaley Gabor
Published: December 2017

The mechanisms that account for acetylcholine (ACh)-induced responses of skeletal muscle arterioles of mice lacking endothelial nitric oxide (NO) synthase (eNOS-KO) were investigated. Isolated, cannulated, and pressurized arterioles of gracilis muscle from male eNOS-KO (74.1 ± 2.3 μm) and wild-type (WT, 87.2 ± 2.1 μm) mice developed spontaneous tone accounting for 63 and 61% of their passive diameter (116.8 ± 3.4 vs. 143.2 ± 2.8 μm, respectively) and dilated dose-dependently to ACh (10−9-10−7M). These dilations were significantly smaller in vessels of eNOS-KO compared with WT mice (29.2 ± 2.0 μm vs. 46.3 ± 2.1 μm, at maximum concentration) but responses to the NO donor, sodium nitrite (NaNO2, 10−6-3 × 10−5M), were comparable in the vessels of the two strains. NG-nitro-l-arginine (l-NNA, 10−4M), an inhibitor of eNOS, inhibited ACh-induced dilations by 60–90% in arterioles of WT mice but did not affect responses in those of eNOS-KO mice. In arterioles of eNOS-KO mice, dilations to ACh were not affected by indomethacin but were essentially abolished by inhibitors of cytochrome P-450, clotrimazole (CTZ, 2 × 10−6M) or miconazole (MCZ, 2 × 10−6M), as well as by either high K+(40 mM) or iberiotoxin [10−7M, a blocker of Ca2+-dependent K+channels (KCachannels)]. On the other hand, in WT arterioles CTZ or MCZ inhibited ACh-induced dilations only by ∼10% and only in the presence of l-NNA. These results indicate that in arterioles of eNOS-KO mice, endothelium-derived hyperpolarizing factor (EDHF), synthesized via cytochrome P-450, accounts entirely for the mediation of ACh-induced dilation via an increase in KCa-channel activity. In contrast, in arterioles of WT mice, endothelium-derived NO predominantly mediates ACh-induced dilation in which participation of EDHF becomes apparent only after inhibition of NO synthesis.
Inactivation of bradykinin by angiotensin-converting enzyme and by carboxypeptidase N in human plasma
Authors: Kuoppala Antti , Lindstedt Ken A. , Saarinen Juhani , Kovanen Petri T. , Kokkonen Jorma O.
Published: December 2017

Because bradykinin (BK) appears to have cardioprotective effects ranging from improved hemodynamics to antiproliferative effects, inhibition of BK-degrading enzymes should potentiate such actions. The purpose of this study was to find out which enzymes are responsible for the degradation of BK in human plasma. Human plasma from healthy donors ( n = 10) was incubated with BK in the presence or absence of specific enzyme inhibitors. At high (micromolar) concentrations, BK was mostly (>90%) degraded by carboxypeptidase N (CPN)-like activity. In contrast, at low (nanomolar) substrate concentrations, at which the velocity of the catalytic reaction is equivalent to that under physiological conditions, BK was mostly (>90%) converted into an inactive metabolite, BK-(1–7), by angiotensin-converting enzyme (ACE). BK-(1–7) was further converted by ACE into BK-(1–5), with accumulation of this active peptide. A minor fraction (<10%) of the BK was converted into another active metabolite, BK-(1–8), by CPN-like activity. The present study shows that the most critical step in plasma kinin metabolism, i.e., inactivation of BK, is mediated by ACE. Thus inhibition of plasma ACE activity would be cardioprotective by elevating the concentration of BK in the circulation.
Heterogeneous cardiac sympathetic innervation in heart failure after myocardial infarction of rats
Authors: Igawa Akihiko , Nozawa Takashi , Yoshida Naohiro , Fujii Nozomu , Inoue Minoru , Tazawa Shusaku , Asanoi Hidetsugu , Inoue Hiroshi
Published: December 2017

We examined cardiac neuronal function and β-receptor with a dual-tracer method of [131I]meta-iodobenzylguanidine (MIBG) and [125I]iodocyanopindolol (ICYP) in rat heart failure after myocardial infarction (MI). In rats with MI, left ventricular (LV) systolic function decreased, and LV dimension and right ventricular (RV) mass increased gradually. MIBG accumulations of the noninfarcted LV (remote region) and RV decreased by 15% at 1 wk compared with sham-operated rats, and these accumulations were restored by 71% and 56%, respectively, at 24 wk compared with age-matched sham rats despite sustained depletion of myocardial norepinephrine contents in these regions. ICYP accumulation of the remote region and of the RV did not decrease at any stages. Myocardial MIBG distribution was heterogeneous at 1 wk when it was lower in the peri-infarcted region than in the remote region, associated with reduced ICYP accumulation in the peri-infarcted region. The heterogeneous distribution of both isotopes disappeared at 12 wk. Thus cardiac sympathetic neuronal alteration was coupled with downregulation of β-receptors in rat heart failure after MI. The abnormal adrenergic signaling occurred heterogeneously in terms of ventricular distribution and time course after MI.
Determination of microvascular flow pattern formation in vivo
Authors: Osterloh Kurt , Gaehtgens Peter , Pries Axel R.
Published: December 2017

Blood flow in microvessels differs significantly from that of red blood cells (RBC) flowing through long, straight glass tubes in vitro. The in vivo situation is characterized by the presence of plasma favoring aggregation, by the irregular geometry of vessel segments, and by frequent branching points. Here, a method is presented to characterize flow patterns in microvascular blood flow during intravital microscopy based on Fourier analysis of recorded light intensity patterns. The interpretation of the resulting power spectra in terms of pattern size distribution was validated by model experiments employing artificial textures and by reverse transformation of idealized spectra. The determined size of RBC flow patterns in microvessels ranged from ∼8 μm in capillaries to ∼14 μm in vessels of >30 μm. With increasing shear rate above ∼100 s−1 pattern size increased, possibly reflecting formation of short-lived flow clusters. Below ∼100 s−1 an increase of pattern size with decreasing shear rate was found in experiments using local occlusion and treatment with high-molecular-weight dextran, suggesting the formation of aggregates. The dynamic process of generation and destruction of RBC flow patterns could well contribute to flow resistance in vivo in peripheral vascular beds.
Cerebral microvascular endothelial cell tube formation: role of astrocytic epoxyeicosatrienoic acid release
Authors: Munzenmaier Diane H. , Harder David R.
Published: December 2017

Cerebral microvascular endothelial cells (CMVEC) form tubes when cocultured with astrocytes (AS). Therefore, it appears that AS may be important in mediating angiogenesis in the brain. We hypothesized that AS modulate CMVEC tube formation by releasing a soluble factor. Thymidine incorporation in cultured CMVEC increased 305% when incubated with 50% conditioned AS medium for 24 h [control: 52,755 ± 4,838 counts per minute (cpm) per well, conditioned 161,082 ± 12,099 cpm/well, n = 8]. Because our laboratory has previously shown that AS can produce epoxyeicosatrienoic acids (EETs), which are known mitogens, we investigated whether release of EETs by AS is responsible for tube formation in the CMVEC-AS coculture. AS were seeded on Lab-Tek slides, CMVEC were seeded on the AS the next day, and cultures were allowed to progress for another 5 days with and without cytochrome P-450 epoxygenase blockade by 17-octadecynoic acid (17-ODYA). Tube formation in cocultures receiving 17-ODYA was significantly inhibited compared with control (93.8%). These data suggest that tube formation requires the release of EETs by AS.
Red blood cell regulation of microvascular tone through adenosine triphosphate
Authors: Dietrich Hans H. , Ellsworth Mary L. , Sprague Randy S. , Dacey Ralph G.
Published: December 2017

The matching of blood flow with metabolic need requires a mechanism for sensing the needs of the tissue and communicating that need to the arterioles, the ultimate controllers of tissue perfusion. Despite significant strides in our understanding of blood flow regulation, the identity of the O2 sensor has remained elusive. Recently, the red blood cell, the Hb-containing O2carrier, has been implicated as a potential O2 sensor and contributor to this vascular control by virtue of its concomitant carriage of millimolar amounts of ATP, which it is able to release when exposed to a low-O2 environment. To evaluate this possibility, we exposed perfused cerebral arterioles to low extraluminal O2 in the absence and presence of red blood cells or 6% dextran and determined both vessel diameter and ATP in the vessel effluent. Only when the vessels were perfused with red blood cells did the vessels dilate in response to low extraluminal O2. In addition, this response was accompanied by a significant increase in vessel effluent ATP. These findings support the hypothesis that the red blood cell itself serves a role in determining O2 supply to tissue.
Thyroid hormone-induced overexpression of functional ryanodine receptors in the rabbit heart
Authors: Jiang M. , Xu A. , Tokmakejian S. , Narayanan N.
Published: December 2017

Modifications in the Ca2+-uptake and -release functions of the sarcoplasmic reticulum (SR) may be a major component of the mechanisms underlying thyroid state-dependent alterations in heart rate, myocardial contractility, and metabolism. We investigated the influence of hyperthyroid state on the expression and functional properties of the ryanodine receptor (RyR), a major protein in the junctional SR (JSR), which mediates Ca2+release to trigger muscle contraction. Experiments were performed using homogenates and JSR vesicles derived from ventricular myocardium of euthyroid and hyperthyroid rabbits. Hyperthyroidism, with attendant cardiac hypertrophy, was induced by the injection of l-thyroxine (200 μg/kg body wt) daily for 7 days. Western blotting analysis using cardiac RyR-specific antibody revealed a significant increase (>50%) in the relative amount of RyR in the hyperthyroid compared with euthyroid rabbits. Ca2+-dependent, high-affinity [3H]ryanodine binding was also significantly greater (∼40%) in JSR from hyperthyroid rabbits. The Ca2+sensitivity of [3H]ryanodine binding and the dissociation constant for [3H]ryanodine did not differ significantly between euthyroid and hyperthyroid hearts. Measurement of Ca2+-release rates from passively Ca2+-preloaded JSR vesicles and assessment of the effect of RyR-Ca2+-release channel (CRC) blockade on active Ca2+-uptake rates revealed significantly enhanced (>2-fold) CRC activity in the hyperthyroid, compared with euthyroid, JSR. These results demonstrate overexpression of functional RyR in thyroid hormone-induced cardiac hypertrophy. Relative abundance of RyR may be responsible, in part, for the changes in SR Ca2+release, cytosolic Ca2+transient, and cardiac systolic function associated with thyroid hormone-induced cardiac hypertrophy.
Protection against endotoxemia by HSP70 in rodent cardiomyocytes
Authors: Lau Sandy S. , Griffin Tina M. , Mestril Ruben
Published: December 2017

Clinical and experimental studies have shown that myocardial dysfunction is an early event during endotoxemia or septic shock. Several reports have shown that rodents submitted to a mild heat shock become resistant to lipopolysaccharides (LPS) or sepsis. The most abundant of the heat shock proteins (HSP), the HSP70, has been postulated to be the principal mediator of the observed protection against endotoxemia. We have tested the hypothesis that a protective effect against endotoxemia is achievable by the increased presence of the HSP70 in rodent cardiomyocytes. We have found that a transgenic mouse line overexpressing the rat HSP70 gene in the heart exhibits an increased tolerance to LPS treatment {control estimated survival function [ Ŝ( t)] = 0.538, transgenic Ŝ( t) = 0.787, P < 0.05}. Interestingly, the increased presence of the HSP70 in the hearts of these mice results in a decrease in the activation of the inducible nitric oxide synthase (iNOS) after LPS treatment. We conclude that HSP70 protection against LPS is most probably mediated through the modulation of iNOS activation and the subsequent decreased synthesis of nitric oxide in cardiomyocytes.
Endothelium modulates anion channel-dependent aortic contractions to iodide
Authors: Lamb Fred S. , Barna Thomas J.
Published: December 2017

Anion currents contribute to vascular smooth muscle (VSM) membrane potential. The substitution of extracellular chloride (Cl) with iodide (I) or bromide (Br) initially inhibited and then potentiated isometric contractile responses of rat aortic rings to norepinephrine. Anion substitution alone produced a small relaxation, which occurred despite a lack of active tone and minimal subsequent contraction of endothelium-intact rings (4.2 ± 1.2% of the response to 90 mM KCl). Endothelium-denuded rings underwent a similar initial relaxation but then contracted vigorously (I > Br). Responses to 130 mM I (93.7 ± 1.9% of 90 mM KCl) were inhibited by nifedipine (10− 6 M), niflumic acid (10− 5 M), tamoxifen (10− 5 M), DIDS (10− 4 M), and[Formula: see text]-free buffer (HEPES 10 mM) but not by bumetanide (10− 5 M). Intact rings treated with N ω-nitro-l-arginine (10− 4 M) responded weakly to I (15.5 ± 2.1% of 90 mM KCl), whereas hemoglobin (10− 5 M), indomethacin (10− 6 M), 17-octadecynoic acid (10− 5 M), and 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (10− 6 M) all failed to augment the response of intact rings to I. We hypothesize that VSM takes up I primarily via an anion exchanger. Subsequent I efflux through anion channels having a selectivity of I > Br > Cl produces depolarization. In endothelium-denuded or agonist-stimulated vessels, this current is sufficient to activate voltage-dependent calcium channels and cause contraction. Neither nitric oxide nor prostaglandins are the primary endothelial modulator of these anion channels. If they are regulated by an endothelium-dependent hyperpolarizing factor it is not a cytochrome P-450 metabolite.
Regulation of contraction and relaxation by membrane potential in cardiac ventricular myocytes
Authors: Ferrier Gregory R. , Redondo Isabel M. , Mason Cindy A. , Mapplebeck Cindy , Howlett Susan E.
Published: December 2017

Control of contraction and relaxation by membrane potential was investigated in voltage-clamped guinea pig ventricular myocytes at 37°C. Depolarization initiated phasic contractions, followed by sustained contractions that relaxed with repolarization. Corresponding Ca2+ transients were observed with fura 2. Sustained responses were ryanodine sensitive and exhibited sigmoidal activation and deactivation relations, with half-maximal voltages near −46 mV, which is characteristic of the voltage-sensitive release mechanism (VSRM) for sarcoplasmic reticulum Ca2+. Inactivation was not detected. Sustained responses were insensitive to inactivation or block of L-type Ca2+ current ( I Ca-L). The voltage dependence of sustained responses was not affected by changes in intracellular or extracellular Na+ concentration. Furthermore, sustained responses were not inhibited by 2 mM Ni2+. Thus it is improbable that I Ca-L or Na+/Ca2+ exchange generated these sustained responses. However, rapid application of 200 μM tetracaine, which blocks the VSRM, strongly inhibited sustained contractions. Our study indicates that the VSRM includes both a phasic inactivating and a sustained noninactivating component. The sustained component contributes both to initiation and relaxation of contraction.
Spontaneous fluctuations in cerebral blood flow: insights from extended-duration recordings in humans
Authors: Zhang Rong , Zuckerman Julie H. , Levine Benjamin D.
Published: December 2017

To determine the dependence of cerebral blood flow (CBF) on arterial pressure over prolonged time periods, we measured beat-to-beat changes in mean CBF velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (Finapres) continuously for 2 h in six healthy subjects (5 men and 1 woman, 18–40 yr old) during supine rest. Fluctuations in velocity and pressure were quantified by the range [(peak − trough)/mean] and coefficients of variation (SD/mean) in the time domain and by spectral analysis in the frequency domain. Mean velocity and pressure over the 2-h recordings were 60 ± 7 cm/s and 83 ± 8 mmHg, associated with ranges of 77 ± 8 and 89 ± 10% and coefficients of variation of 9.3 ± 2.2 and 7.9 ± 2.3%, respectively. Spectral power of the velocity and pressure was predominantly distributed in the frequency range of 0.00014–0.1 Hz and increased inversely with frequency, indicating characteristics of an inverse power law (1/ f α). However, linear regression on a log-log scale revealed that the slope of spectral power of pressure and velocity was steeper in the high-frequency (0.02–0.5 Hz) than in the low-frequency range (0.002–0.02 Hz), suggesting different regulatory mechanisms in these two frequency ranges. Furthermore, the spectral slope of pressure was significantly steeper than that of velocity in the low-frequency range, consistent with the low transfer function gain and low coherence estimated at these frequencies. We conclude that 1) long-term fluctuations in CBF velocity are prominent and similar to those observed in arterial pressure, 2) spectral power of CBF velocity reveals characteristics of 1/ f α, and 3) cerebral attenuation of oscillations in CBF velocity in response to changes in pressure may be more effective at low than that at high frequencies, emphasizing the frequency dependence of cerebral autoregulation.
Inducible polymorphic ventricular tachyarrhythmias in a transgenic mouse model with a long Q-T phenotype
Authors: Jeron Andreas , Mitchell Gary F. , Zhou Jun , Murata Mitsunobu , London Barry , Buckett Peter , Wiviott Stephen D. , Koren Gideon
Published: December 2017

We created a mouse model with a prolonged Q-T interval and spontaneous arrhythmias by overexpressing the NH2terminus and first transmembrane segment ( Kv1.1N206Tag) of a delayed rectifier potassium channel (LQT+/ − mouse). Analyses were performed using whole cell recordings of cardiac myocytes, surface electrocardiography, and programmed electrical stimulation. Action potential duration (APD) was prolonged to the same extent and was more highly variable in myocytes derived from LQT+/ − and LQT+/+ mice than in myocytes derived from wild-type (WT) FVB mice. Under ketamine anesthesia, the Q-T interval of both LQT+/+ and LQT+/ − mice was comparably prolonged versus that of WT mice. Stimulation of the right ventricle using an intracardiac catheter induced polymorphic ventricular tachyarrhythmias in 50% of the LQT+/ − mice and 36% of the LQT+/+ mice, whereas polymorphic ventricular tachyarrhythmias were not inducible in WT mice. The analyses of LQT+/ − and LQT+/+ mice indicate that prolongation of the Q-T interval in LQT mice is associated with prolonged APD, increased dispersion of APD among cardiocytes, and inducibility of polymorphic ventricular tachycardia, providing the substrate for spontaneous arrhythmias in these animals.
Efficacy and specificity of bFGF increased collateral flow in experimental peripheral arterial insufficiency
Authors: Yang H. T. , Feng Y. , Allen Laura A. , Protter Andrew , Terjung Ronald L.
Published: December 2017

Angiogenic growth factors could prove to be useful in managing peripheral arterial insufficiency. The present study was designed to evaluate the dose response of basic fibroblast growth factor (bFGF), the efficacy of critical routes and dosing regimens, and the specificity of action in rats with peripheral arterial insufficiency. Bilateral ligation of femoral arteries greatly reduces blood flow capacity to the calf muscles but does not impair resting flow needs. Collateral blood flow to calf muscles was determined 16 days postocclusion, during treadmill running, with 85Sr and 141Ce microspheres, in blinded-randomized trials that included intra-arterial and intravenous infusions and subcutaneous injections of recombinant human bFGF. Peak blood flow of 75–80 ml ⋅ min− 1 ⋅ 100 g− 1 for calf muscle was observed at a bFGF dose of 5 μg ⋅ kg− 1 ⋅ day− 1(ia for 14 days) compared with 50 ml ⋅ min− 1 ⋅ 100 g− 1 for vehicle groups. Similar increases in collateral blood flow were observed with short-term or prolonged and continuous or intermittent delivery of bFGF by any route. Collateral blood flows were similar in corresponding muscles across both limbs. Vascular remodeling induced by bFGF required attendant vascular occlusion, inasmuch as vessels in the normal nonoccluded vascular tree were unresponsive to circulating bFGF. Improvement in collateral blood flow with exogenous bFGF is robust, amenable to short-term administration, and requires vascular occlusion to be effective.
Physiological time-series analysis using approximate entropy and sample entropy
Authors: Richman Joshua S. , Moorman J. Randall
Published: December 2017

Entropy, as it relates to dynamical systems, is the rate of information production. Methods for estimation of the entropy of a system represented by a time series are not, however, well suited to analysis of the short and noisy data sets encountered in cardiovascular and other biological studies. Pincus introduced approximate entropy (ApEn), a set of measures of system complexity closely related to entropy, which is easily applied to clinical cardiovascular and other time series. ApEn statistics, however, lead to inconsistent results. We have developed a new and related complexity measure, sample entropy (SampEn), and have compared ApEn and SampEn by using them to analyze sets of random numbers with known probabilistic character. We have also evaluated cross-ApEn and cross-SampEn, which use cardiovascular data sets to measure the similarity of two distinct time series. SampEn agreed with theory much more closely than ApEn over a broad range of conditions. The improved accuracy of SampEn statistics should make them useful in the study of experimental clinical cardiovascular and other biological time series.
Changes of β-adrenergic signaling in compensated human cardiac hypertrophy depend on the underlying disease
Authors: Schotten Ulrich , Filzmaier Karsten , Borghardt Britta , Kulka Simone , Schoendube Friedrich , Schumacher Carlos , Hanrath Peter
Published: December 2017

In human heart failure, desensitization of the β-adrenergic signal transduction has been reported to be one of the main pathophysiological alterations. However, data on the β-adrenergic system in human compensated cardiac hypertrophy are very limited. Therefore, we studied the myocardial β-adrenergic signaling in patients suffering from hypertrophic obstructive cardiomyopathy (HOCM, n = 9) or from aortic valve stenosis (AoSt, n = 8). β-Adrenoceptor density determined by [125I]iodocyanopindolol binding was reduced in HOCM and AoSt compared with nonhypertrophied, nonfailing myocardium (NF) of seven organ donors. In HOCM the protein expression of stimulatory G protein α-subunit (Gsα) measured by immunoblotting was unchanged, whereas the inhibitory G protein α-subunit (Gαi-2) was increased. In contrast, in AoSt, Gαi-2protein was unchanged, but Gsα protein was increased. Adenylyl cyclase stimulation by isoproterenol was reduced in HOCM but not in AoSt. Plasma catecholamine levels were normal in all patients. In conclusion, both forms of hypertrophy are associated with β-adrenoceptor downregulation but with different changes at the G protein level that occur before symptomatic heart failure due to progressive dilatation of the left ventricle develops and are not due to elevated plasma catecholamine levels.
Changes in ionic currents and β-adrenergic receptor signaling in hypertrophied myocytes overexpressing Gαq
Authors: Mitarai Sayaka , Reed Thomas D. , Yatani Atsuko
Published: December 2017

Transgenic overexpression of Gαq causes cardiac hypertrophy and depressed contractile responses to β-adrenergic receptor agonists. The electrophysiological basis of the altered myocardial function was examined in left ventricular myocytes isolated from transgenic (Gαq) mice. Action potential duration was significantly prolonged in Gαq compared with nontransgenic (NTG) myocytes. The densities of inward rectifier K+ currents, transient outward K+ currents ( I to), and Na+/Ca2+ exchange currents were reduced in Gαq myocytes. Consistent with functional measurements, Na+/Ca2+ exchanger gene expression was reduced in Gαq hearts. Kinetics or sensitivity of I to to 4-aminopyridine was unchanged, but 4-aminopyridine prolonged the action potential more in Gαq myocytes. Isoproterenol increased L-type Ca2+ currents ( I Ca) in both groups, with a similar EC50, but the maximal response in Gαq myocytes was ∼24% of that in NTG myocytes. In NTG myocytes, the maximal increase of I Ca with isoproterenol or forskolin was similar. In Gαq myocytes, forskolin was more effective and enhanced I Ca up to ∼55% of that in NTG myocytes. These results indicate that the changes in ionic currents and multiple defects in the β-adrenergic receptor/Ca2+ channel signaling pathway contribute to altered ventricular function in this model of cardiac hypertrophy.
Preservation of glucose metabolism in hypertrophic GLUT4-null hearts
Authors: Stenbit Antine E. , Katz Ellen B. , Chatham John C. , Geenen David L. , Factor Stephen M. , Weiss Robert G. , Tsao Tsu-Shuen , Malhotra Ashwani , Chacko V. P. , Ocampo Christopher , Jelicks Linda A. , Charron Maureen J.
Published: December 2017

GLUT4-null mice lacking the insulin-sensitive glucose transporter are not diabetic but do exhibit abnormalities in glucose and lipid metabolism. The most striking morphological consequence of ablating GLUT4 is cardiac hypertrophy. GLUT4-null hearts display characteristics of hypertrophy caused by hypertension. However, GLUT4-null mice have normal blood pressure and maintain a normal cardiac contractile protein profile. Unexpectedly, although they lack the predominant glucose transporter in the heart, GLUT4-null hearts transport glucose and synthesize glycogen at normal levels, but gene expression of rate-limiting enzymes involved in fatty acid oxidation is decreased. The GLUT4-null heart represents a unique model of hypertrophy that may be used to study the consequences of altered substrate utilization in normal and pathophysiological conditions.
Role of cGMP versus 20-HETE in the vasodilator response to nitric oxide in rat cerebral arteries
Authors: Sun Cheng-Wen , Falck John R. , Okamoto Hirotsugu , Harder David R. , Roman Richard J.
Published: December 2017

This study examined the response to nitric oxide (NO) in rat middle cerebral arteries (MCA). NO donors increased the activity of a 205-pS K+ channel recorded from vascular smooth muscle (VSM) cells isolated from MCA 10-fold. Blockade of guanylyl cyclase activity with 1 H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ, 10−5 M) did not alter the effect of NO on this channel. In contrast, adding 20-hydroxyeicosatetraenoic acid (20-HETE) to the bath (10−7 M) abolished the response to NO. NO donors also increased the diameter of serotonin-preconstricted MCA to 85% of control. Blockade of K+ channels with iberiotoxin or a high-K+ medium reduced this response by 50%. ODQ (10−5 M) reduced this response by 47 ± 3%, whereas preventing the fall of 20-HETE levels reduced the response by 59 ± 2% ( n = 5). Blockade of both pathways eliminated the response to NO donors. These results indicate that activation of K+ channels contributes 50% to vasodilator response to NO in rat MCA. This is mediated by a fall in 20-HETE levels rather than a rise in cGMP levels or a direct effect of NO.
Nitric oxide, an important regulator of perfusion-contraction matching in conscious pigs
Authors: Kudej Raymond K. , Kim Song-Jung , Shen You-Tang , Jackson John B. , Kudej Amelia B. , Yang Gui-Ping , Bishop Sanford P. , Vatner Stephen F.
Published: December 2017

We examined whether nitric oxide (NO) inhibition during moderate reduction in coronary blood flow (CBF) would affect perfusion-contraction matching. Coronary stenosis (CS) was induced in conscious pigs, which resulted in a stable 39 ± 1% reduction in CBF for 1.5 h. Ischemic zone wall thickening (IZWT) decreased by an average of 56 ± 2% during CS from 2.7 ± 0.2 mm. After reperfusion, myocardial stunning was observed, but this recovered without evidence of necrosis. After recovery and subsequent administration of systemic NO synthase inhibition ( N ω-nitro-l-arginine, 25 mg · kg−1 · day−1 × 3 days), CS for 1.5 h reduced CBF similarly but decreased IZWT significantly more, P < 0.05, by 89 ± 5%. Myocardial stunning, i.e., the decrease in IZWT at 12 h post-CS, was more severe (−65 ± 5% vs. −21 ± 3%), P < 0.05. Furthermore, CS during NO synthase inhibition resulted in multifocal subendocardial areas of necrosis in the area at risk. These data suggest that in the intact, conscious pig, NO inhibition prevents perfusion-contraction matching, resulting in intensification of post-ischemic stunning and development of subendocardial necrosis.
Neurotransmission of autonomic components of aortic baroreceptor afferents in the NTS of awake rats
Authors: Machado Benedito H. , Castania Jaci A. , Bonagamba Leni G. H. , Salgado Hélio C.
Published: December 2017

The effect of sequential blockade of N-methyl-d-aspartic acid (NMDA) receptors with dl-2-amino-5-phosphonopentanoic acid (AP-5) and non-NMDA receptors with 6,7-dinitroquinoxaline-2,3 dione (DNQX) in the nucleus tractus solitarii (NTS) on the cardiovascular responses to electrical stimulation (ES) of the aortic depressor nerve (ADN) was evaluated in awake rats. Two protocols were used. In protocol 1, bilateral microinjection of AP-5 into the NTS ( n = 7) reduced the hypotensive response to ES of the ADN; subsequent microinjection of DNQX produced additional reduction in this response. AP-5 reduced the bradycardic response, and DNQX almost abolished this response. In protocol 2, bilateral microinjection of DNQX into the NTS ( n = 6) reduced the hypotensive response, and subsequent microinjection of AP-5 significantly reduced this response. DNQX produced a significant reduction in bradycardic response, and AP-5 abolished this response. The data indicate that processing of the parasympathetic component of the NTS aortic baroreceptor afferents is mediated by both NMDA and non-NMDA receptors, whereas processing of the sympathoinhibitory component seems to be only partially mediated by ionotropic receptors.