bluuebunny/crossref_metadata_2025 huggingface dataset:
KATPchannels mediate the beneficial effects of chronic ethanol ingestion
Authors: Pagel Paul S. , Toller Wolfgang G. , Gross Eric R. , Gare Meir , Kersten Judy R. , Warltier David C.
Published: December 2017

Chronic ingestion of low doses of ethanol protects the myocardium from ischemic injury by activating adenosine receptors and protein kinase C. We tested the hypothesis that ATP-dependent potassium (KATP) channels mediate these beneficial effects. Dogs were fed with ethanol (1.5 g/kg) or water mixed with dry food twice per day for 12 wk. After they were acutely instrumented for measurement of hemodynamics, dogs received saline (vehicle) or glyburide (0.1 mg/kg iv) and were subjected to 60 min of coronary artery occlusion followed by 3 h of reperfusion. Infarct size (through triphenyltetrazolium chloride staining) was significantly ( P < 0.05) reduced to 14 ± 1% of the left ventricular area at risk in ethanol-pretreated dogs compared with controls (25 ± 2%). Glyburide alone did not affect infarct size (25 ± 3%) but abolished the protective effects of ethanol pretreatment (28 ± 3%). No differences in hemodynamics or coronary collateral blood flow (through radioactive microspheres) were observed among groups. The results indicate that KATPchannels mediate the protective effects of chronic consumption of ethanol.
Persistent but reversible coronary microvascular dysfunction after bypass grafting
Authors: Spyrou Nicos , Khan Masood A. , Rosen Stuart D. , Foale Rodney , Davies D. Wyn , Sogliani Franco , Stanbridge Rex De Lisle , Camici Paolo G.
Published: December 2017

The effect of coronary artery bypass grafting (CABG) on absolute myocardial blood flow (MBF) has not been investigated previously. MBF (ml · min−1· g−1) was measured at rest and during hyperemia (0.56 mg/kg iv dipyridamole) using H215O and positron emission tomography in eight patients with three-vessel disease before surgery and 1 and 6 mo after full revascularization. Baseline MBF was 0.87 ± 0.12 preoperatively and 1.04 ± 0.14 and 0.95 ± 0.13 at 1 and 6 mo after CABG, respectively ( P < 0.05, 6 mo vs. preoperatively). Hyperemic MBF was 1.36 ± 0.28 preoperatively and increased to 1.98 ± 0.50 and 2.45 ± 0.64 at 1 and 6 mo after CABG, respectively ( P < 0.01, 6 mo vs. preoperatively). Coronary vasodilator reserve (hyperemic/baseline MBF) increased from 1.59 ± 0.40 preoperatively to 1.93 ± 0.13 and 2.57 ± 0.49 at 1 and 6 mo, respectively ( P < 0.05, 6 mo vs. preoperatively). Minimal (dipyridamole) coronary resistance (mmHg · min · g−1· ml−1) fell progressively from 59.37 ± 14.56 before surgery to a nadir of 35.76 ± 10.12 at 6 mo after CABG ( P < 0.01 vs. preoperatively). The results of the present study confirm that CABG improves coronary vasodilator reserve progressively as a result of reduction in minimal coronary resistance. These data suggest persistent microvascular dysfunction that recovers slowly after surgery.
Evidence for functional role of εPKC isozyme in the regulation of cardiac Ca2+channels
Authors: Hu Keli , Mochly-Rosen Daria , Boutjdir Mohamed
Published: December 2017

Limited information is available regarding the effects of protein kinase C (PKC) isozyme(s) in the regulation of L-type Ca2+channels due to lack of isozyme-selective modulators. To dissect the role of individual PKC isozymes in the regulation of cardiac Ca2+channels, we used the recently developed novel peptide activator of the εPKC, εV1–7, to assess the role of εPKC in the modulation of L-type Ca2+current ( ICa,L). Whole cell ICa,Lwas recorded using patch-clamp technique from rat ventricular myocytes. Intracellular application of εV1–7 (0.1 μM) resulted in a significant inhibition of ICa,Lby 27.9 ± 2.2% ( P< 0.01, n = 8) in a voltage-independent manner. The inhibitory effect of εV1–7 on ICa,Lwas completely prevented by the peptide inhibitor of εPKC, εV1–2 [5.2 ± 1.7%, not significant (NS), n = 5] but not by the peptide inhibitors of cPKC, αC2–4 (31.3 ± 2.9%, P < 0.01, n = 6) or βC2–2 plus βC2–4 (26.1 ± 2.9%, P< 0.01, n = 5). In addition, the use of a general inhibitor (GF-109203X, 10 μM) of the catalytic activity of PKC also prevented the inhibitory effect of εV1–7 on ICa,L(7.5 ± 2.1%, NS, n= 6). In conclusion, we show that selective activation of εPKC inhibits the L-type Ca channel in the heart.
Interleukin-1β and neurogenic control of blood pressure in normal rats and rats with chronic renal failure
Authors: Ye Shaohua , Mozayeni Pantea , Gamburd Michael , Zhong Huiqin , Campese Vito M.
Published: December 2017

Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). The rise in central SNS activity is mitigated by increased local expression of neuronal nitric oxide synthase (NOS) mRNA and NO2/NO3production. Because interleukin (IL)-1β may activate nitric oxide in the brain, we have tested the hypothesis that IL-1β may modulate the activity of the SNS via regulation of the local expression of neuronal NOS (nNOS) in the brain of CRF and control rats. To this end, we first found that administration of IL-1β in the lateral ventricle of control and CRF rats decreased blood pressure and norepinephrine (NE) secretion from the posterior hypothalamus (PH) and increased NOS mRNA expression. Second, we observed that an acute or chronic injection of an IL-1β-specific antibody in the lateral ventricle raised blood pressure and NE secretion from the PH and decreased NOS mRNA abundance in the PH of control and CRF rats. Finally, we measured the IL-1β mRNA abundance in the PH, locus coeruleus, and paraventricular nuclei of CRF and control rats by RT-PCR and found it to be greater in CRF rats than in control rats. In conclusion, these studies have shown that IL-1β modulates the activity of the SNS in the central nervous system and that this modulation is mediated by increased local expression of nNOS mRNA.
Renin-angiotensin system and sympathetic nervous system in cardiac pressure-overload hypertrophy
Authors: Akers Wendell S. , Cross Andrew , Speth Robert , Dwoskin Linda P. , Cassis Lisa A.
Published: December 2017

Angiotensin II and norepinephrine (NE) have been implicated in the neurohumoral response to pressure overload and the development of left ventricular hypertrophy. The purpose of this study was to determine the temporal sequence for activation of the renin-angiotensin and sympathetic nervous systems in the rat after 3–60 days of pressure overload induced by aortic constriction. Initially on pressure overload, there was transient activation of the systemic renin-angiotensin system coinciding with the appearance of left ventricular hypertrophy ( day 3). At day 10, there was a marked increase in AT1 receptor density in the left ventricle, increased plasma NE concentration, and elevated cardiac epinephrine content. Moreover, the inotropic response to isoproterenol was reduced in the isolated, perfused heart at 10 days of pressure overload. The affinity of the β2-adrenergic receptor in the left ventricle was decreased at 60 days. Despite these alterations, there was no decline in resting left ventricular function, β-adrenergic receptor density, or the relative distribution of β1- and β2-receptor sites in the left ventricle over 60 days of pressure overload. Thus activation of the renin-angiotensin system is an early response to pressure overload and may contribute to the initial development of cardiac hypertrophy and sympathetic activation in the compensated heart.
Effects of increased pressure inside or outside ventricles on total and regional myocardial blood flow
Authors: Aldea G. S. , Mori H. , Husseini W. K. , Austin R. E. , Hoffman J. I. E.
Published: December 2017

Increasing pressures to 30 mmHg in right (RV) and left (LV) ventricles and surrounding heart (SH) in isolated, arrested, maximally vasodilated, blood-perfused dog hearts shifted pressure-flow (PF) curves rightward and increased zero flow pressure (Pzf) by an amount equal to the RV applied pressure, SH applied pressure, or two-thirds of the LV applied pressure. There were comparable increases in coronary venous pressures. Increasing LV or SH pressures decreased coronary blood flows, especially in the subendocardium. Decreases in driving pressure decreased flows in all layers, but even with driving pressure of 5 mmHg, a few subepicardial pieces had flow. We conclude with the following: 1) raising pressures inside or outside the heart shifts PF curves and raises Pzfby increasing coronary venous pressure; 2) the effects are most prominent in the subendocardial muscle layer; and 3) as driving pressures are decreased, there is a range of Pzfin the heart with the final Pzfrecorded due to the last little piece of muscle to be perfused.
Hemoglobin and red blood cells alter the response of expired nitric oxide to mechanical forces
Authors: Berg John T. , Deem Steven , Kerr Mark E. , Swenson Erik R.
Published: December 2017

Expired nitric oxide (NOe) varies with hemodynamic or ventilatory perturbations, possibly due to shear stress- or stretch-stimulated NO production. Since hemoglobin (Hb) binds NO, NOe changes may reflect changes in blood volume and flow. To determine the role of blood and mechanical forces, we measured NOe in anesthetized rabbits, as well as rabbit lungs perfused with buffer, red blood cells (RBCs) or Hb following changes in flow, venous pressure (Pv), and positive end-expiratory pressure (PEEP). In buffer-perfused lungs decreases in flow and Pv reduced NOe, but NOe rose when RBCs and Hb were present. These findings are consistent with changes in vascular NO production, whose detection is obscured in blood-perfused lungs by the more dominant effect of Hb NO scavenging. PEEP decreased NOe in all perfused lungs but increased NOe in live rabbits. The NOe fall with PEEP in isolated lungs is consistent with flow redistribution from alveolar septal capillaries to extra-alveolar vessels and decreased surface area or a direct, stretch-mediated depression of lung epithelial NO production. In live rabbits, increased NOe may reflect blood flow reduction and decreased Hb NO scavenging and/or autonomic responses that increase NO production. We conclude that blood and systemic responses render it difficult to use NOe changes as an accurate measure of lung tissue NO production.
Enhanced cAMP-induced nitric oxide-dependent coronary dilation during myocardial stunning in conscious pigs
Authors: Kudej Raymond K. , Zhang Xiao-Ping , Ghaleh Bijan , Huang Cheng-Hsuing , Jackson John B. , Kudej Amelia B. , Sato Naoki , Sato Shoko , Vatner Dorothy E. , Hintze Thomas H. , Vatner Stephen F.
Published: December 2017

The goal of the current study was to determine the effects of cAMP-mediated coronary reactivity in conscious pigs with stunned myocardium induced by 1.5 h coronary stenosis (CS) and 12 h coronary artery reperfusion (CAR). Domestic swine ( n = 5) were chronically instrumented with a coronary artery blood flow (CBF) probe, hydraulic occluder, left ventricular pressure gauge, wall-thickening crystals in the ischemic and nonischemic zones, and a coronary sinus catheter. The hydraulic occluder was inflated to induce a CS with a stable 38 ± 1% reduction in CBF for 1.5 h. Before flow reduction and during CAR, cAMP-induced coronary vasodilation was investigated by forskolin (20 nmol · kg−1 · min−1). Enhanced CBF responses [+62 ± 9%, P < 0.05, compared with pre-CS (+37 ± 3%)] were observed for forskolin at 12 h after CAR as well as for bradykinin and reactive hyperemia. With the use of a similar protocol during systemic nitric oxide (NO) synthase inhibition with Nω -nitro-l-arginine (30 mg · kg−1 · day−1 for 3 days), the enhanced CBF responses to forskolin, bradykinin, and reactive hyperemia were not observed after CS. Isolated microvessel preparations from pigs ( n = 8) also demonstrated enhanced NO production to direct stimulation of adenylyl cyclase with forskolin (+71 ± 12%) or NKH-477 (+60 ± 10%) and administration of 8-bromo-cAMP (+74 ± 13%), which were abolished by protein kinase A or NO synthase inhibition. These data indicate that cAMP stimulation elicits direct coronary vasodilation and that this action is amplified in the presence of sustained myocardial stunning after recovery from CS. This enhanced cAMP coronary vasodilation is mediated by an NO mechanism that may be involved in myocardial protection from ischemic injury.
Relation between regional function and coronary blood flow reserve in multivessel coronary artery stenosis
Authors: Bin Jian-Ping , Pelberg Robert A. , Wei Kevin , Coggins Matthew , Goodman N. Craig , Kaul Sanjiv
Published: December 2017

In the setting of chronic coronary stenoses, percent wall thickening (%WT) both at rest and during catecholamine stimulation can be abnormal despite normal resting myocardial blood flow (MBF). We hypothesized that this phenomenon is related to abnormal MBF reserve. Accordingly, 15 dogs were studied between 7 and 10 days after placement of Ameroid constrictors around the proximal coronary arteries and their major branches, at a time when collateral development had not yet occurred. %WT and MBF were measured at rest, after 0.56 mg/kg of dipyridamole, and at incremental doses of dobutamine (5–40 μg · kg−1 · min−1). Resting %WT and MBF were normal in all four sham dogs. Resting transmural MBF was normal in all segments in the 11 study dogs, despite reduced (−2 SD of normal) %WT (<30%) in 40 of 82 segments. MBF reserve was reduced (<3) in segments with reduced %WT, and a close coupling was noted between resting %WT and MBF reserve. All segments showed an increase in %WT with dobutamine up to a dose of 20 μg · kg−1 · min−1, above which those with abnormal endocardial MBF reserve showed a “biphasic” response. It is concluded that, in the presence of chronic coronary stenoses, abnormalities in resting %WT as well as inducible reduction in %WT during pharmacological stress are related to the degree of abnormal MBF reserve.
Nitroprusside induces cardiomyocyte death: interaction with hydrogen peroxide
Authors: Rabkin Simon W. , Kong Jennifer Y
Published: December 2017

We examined the hypothesis that sodium nitroprusside (SNP) produces cell death in cardiomyocytes through generation of H2O2. Embryonic chick cardiomyocytes in culture were treated with SNP, and cell viability was assessed by trypan blue, MTT assay, and fluorescent activated cell sorting (FACS) analysis. SNP for 24 h induced a significant ( P < 0.001) dose-dependent loss of cell viability. On MTT assay, the half-maximal effective concentration was 0.53 mM (confidence interval 0.45–0.59 mM). SNP-treated cardiomyocytes displayed characteristic microscopic features of apoptosis: reduced cell size, nuclear disintegration, and membrane bleb formation. FACS analysis demonstrated SNP-induced apoptosis as well as cell changes consistent with necrosis. The proportion of cells with nuclear changes of apoptosis, identified by propidium iodide (PI) staining of permeabilized cells, increased significantly ( P < 0.05) after 0.5 mM SNP for 24 h. The proportion of apoptotic cells, characterized by dual staining of intact cardiomyocytes with fluorescein diacetate and PI, was significantly ( P < 0.05) increased after treatment with 0.5 mM SNP for 24 h. SNP metabolism and NO production was suggested by the significant ( P < 0.05) increase in nitrite generation in the media with 0.5 mM SNP compared with control. SNP-mediated H2O2 production was implicated in the mechanism of SNP-induced cell death. First, SNP produced a significant ( P< 0.05) increase in H2O2 detected in the media after 6 or 24 h of SNP treatment. Second, catalase completely blocked the reduction of cell viability induced by 0.1 mM SNP and significantly ( P < 0.05) blunted the effect of 0.5 mM SNP. In contrast, the iron chelator deferoxamine did not alter SNP-induced loss of cell viability. FACS analysis showed that the combination of low concentrations of H2O2(10−8 M) that did not alter cell viability augmented SNP-induced apoptosis. In contrast, the amount of necrotic cell death was unchanged by the combination of H2O2 and SNP. H2O2 plus SNP produced a dramatic alteration in cell structure with greater membrane bleb formation, shrunken cells, and more intense cytosolic acridine orange staining and nuclear fragmentation than either agent alone. These data indicate the vulnerability of cardiomyocytes to SNP and suggest the involvement of H2O2 in the pathogenesis of SNP-induced cardiomyocyte cell death. Establishing apoptosis as a component of the type of cell death induced by SNP permitted the recognition that SNP-induced apoptosis was increased by chronic treatment with low (subtoxic) concentrations of H2O2.
Cellular and functional defects in a mouse model of heart failure
Authors: Esposito Giovanni , Santana L. F. , Dilly Keith , Cruz Jader Dos Santos , Mao Lan , Lederer W. J. , Rockman Howard A.
Published: December 2017

Heart failure and dilated cardiomyopathy develop in mice that lack the muscle LIM protein (MLP) gene (MLP−/−). The character and extent of the heart failure that occurs in MLP−/− mice were investigated using echocardiography and in vivo pressure-volume (P-V) loop measurements. P-V loop data were obtained with a new method for mice (sonomicrometry) using two pairs of orthogonal piezoelectric crystals implanted in the endocardial wall. Sonomicrometry revealed right-shifted P-V loops in MLP−/−mice, depressed systolic contractility, and additional evidence of heart failure. Cellular changes in MLP−/− mice were examined in isolated single cells using patch-clamp and confocal Ca2+ concentration ([Ca2+]) imaging techniques. This cellular investigation revealed unchanged Ca2+ currents and Ca2+ spark characteristics but decreased intracellular [Ca2+] transients and contractile responses and a defect in excitation-contraction coupling. Normal cellular and whole heart function was restored in MLP−/− mice that express a cardiac-targeted transgene, which blocks the function of β-adrenergic receptor (β-AR) kinase-1 (βARK1). These data suggest that, despite the persistent stimulus to develop heart failure in MLP−/− mice (i.e., loss of the structural protein MLP), downregulation and desensitization of the β-ARs may play a pivotal role in the pathogenesis. Furthermore, this work suggests that the inhibition of βARK1 action may prove an effective therapy for heart failure.
HIV gp120 enhances NO production by cardiac myocytes through p38 MAP kinase-mediated NF-κB activation
Authors: Kan Hong , Xie Zirong , Finkel Mitchell S.
Published: December 2017

Human immunodeficiency virus (HIV) infection is associated with a surprisingly high frequency of myocardial dysfunction. Potential mechanisms include direct effects of HIV, indirect effects mediated by cytokines, or a combination. We have previously reported that interleukin-1β (IL-1β) (500 U/ml) alone induced nitric oxide (NO) production by neonatal rat cardiac myocytes (CM). Effects of the HIV-1 envelope, glycoprotein120 (gp120), on inducible NO synthase (iNOS) in CM have not been previously reported. Unlike IL-1β, recombinant HIV-gp120 (1 μg/ml) alone failed to enhance NO production in CM (0.5 ± 0.4 vs. 0.4 ± 0.5 μmol/1.25 × 105cells/48 h, gp120 vs. control, respectively; n = 12, P = not significant). However, the addition of gp120 to IL-1β significantly enhanced iNOS mRNA expression (70 ± 1.5 vs. 26 ± 2.4 optical units, IL-1β + gp120 vs. IL-1β, respectively; n = 3), iNOS protein synthesis (42 ± 1.4 vs. 18 ± 0.8 optical units, IL-1β + gp120 vs. IL-1β, respectively; n = 3), and NO production (NO2−) (6.6 ± 0.6 vs. 4.1 ± 0.8 μmol/1.25 × 105cells/48 h, IL-1β + gp120 vs. IL-1β, respectively; n = 12, P ≤ 0.5). HIV-gp120 enhancement of IL-1β-induced NO2−production was blocked by 10 μM of SB-203580 (SB), a selective p38 protein kinase inhibitor (3.6 ± 0.2 vs. 6.6 ± 0.6 μmol/1.25 × 105cells/48 h, IL-1β + gp120 + SB vs. IL-1β + gp120, respectively; n = 12, P ≤ 0.5). HIV-gp120-enhanced p38 protein kinase activity was associated with an increase in IL-1β-stimulated NF-κB activity (184 ± 12.7 vs. 92 ± 10.7 optical units, IL-1β + gp120 vs. IL-1β, respectively; n = 3). None of these effects was seen with another recombinant HIV-1 protein, Tat. Thus HIV-gp120 enhancement of IL-1β-induced NO production is associated with p38-mediated activation of NF-κB. Direct effects of HIV-gp120 on CM may provide a previously unrecognized mechanism contributing to HIV cardiomyopathy.
Normal myocardial function in severe right ventricular volume overload hypertrophy
Authors: Ishibashi Yuji , Rembert Judith C. , Carabello Blase A. , Nemoto Shintaro , Hamawaki Masayoshi , Zile Michael R. , Greenfield Joseph C. , Cooper George
Published: December 2017

Severe left ventricular volume overloading causes myocardial and cellular contractile dysfunction. Whether this is also true for severe right ventricular volume overloading was unknown. We therefore created severe tricuspid regurgitation percutaneously in seven dogs and then observed them for 3.5–4.0 yr. All five surviving operated dogs had severe tricuspid regurgitation and right heart failure, including massive ascites, but they did not have left heart failure. Right ventricular cardiocytes were isolated from these and from normal dogs, and sarcomere mechanics were assessed via laser diffraction. Right ventricular cardiocytes from the tricuspid regurgitation dogs were 20% longer than control cells, but neither the extent (0.171 ± 0.005 μm) nor the velocity (2.92 ± 0.12 μm/s) of sarcomere shortening differed from controls (0.179 ± 0.005 μm and 3.09 ± 0.11 μm/s, respectively). Thus, despite massive tricuspid regurgitation causing overt right heart failure, intrinsic right ventricular contractile function was normal. This finding for the severely volume-overloaded right ventricle stands in distinct contrast to our finding for the left ventricle severely volume overloaded by mitral regurgitation, wherein intrinsic contractile function is depressed.
Mechanisms of respiratory sinus arrhythmia in patients with mild heart failure
Authors: El-Omar Magdi , Kardos Attila , Casadei Barbara
Published: December 2017

The high-frequency (HF) component of the heart rate variability (HRV) is regarded as an index of cardiac vagal responsiveness. However, when vagal tone is decreased, nonneural mechanisms could account for a significant proportion of the HF component. To test this hypothesis, we examined the HRV spectral power in 20 patients with mild chronic heart failure (CHF) and 11 controls before and during ganglion blockade with trimethaphan camsylate (3–6 mg/min iv). A small HF component was still present during ganglion blockade, and its amplitude did not differ between CHF patients and controls. The average contribution of nonneural oscillations to the HF component was 15% (range 1–77%) in patients with CHF and 3% (range 0.7–30%) in healthy controls ( P < 0.005). During controlled breathing at 0.16 Hz, however, it decreased to 1% (range 0.2–13%) in healthy controls and 5% (range 1–44%) in CHF patients. Our results indicate that the HF component can significantly overestimate cardiac vagal responsiveness in patients with mild CHF. This bias is improved by controlled breathing, since this maneuver increases the vagal contribution to HF without affecting its nonneural component.
Tissue engineering of functional cardiac muscle: molecular, structural, and electrophysiological studies
Authors: Papadaki M. , Bursac N. , Langer R. , Merok J. , Vunjak-Novakovic G. , Freed L. E.
Published: December 2017

The primary aim of this study was to relate molecular and structural properties of in vitro reconstructed cardiac muscle with its electrophysiological function using an in vitro model system based on neonatal rat cardiac myocytes, three-dimensional polymeric scaffolds, and bioreactors. After 1 wk of cultivation, we found that engineered cardiac muscle contained a 120- to 160-μm-thick peripheral region with cardiac myocytes that were electrically connected through gap junctions and sustained macroscopically continuous impulse propagation over a distance of 5 mm. Molecular, structural, and electrophysiological properties were found to be interrelated and depended on specific model system parameters such as the tissue culture substrate, bioreactor, and culture medium. Native tissue and the best experimental group (engineered cardiac muscle cultivated using laminin-coated scaffolds, rotating bioreactors, and low-serum medium) were comparable with respect to the conduction velocity of propagated electrical impulses and spatial distribution of connexin43. Furthermore, the structural and electrophysiological properties of the engineered cardiac muscle, such as cellularity, conduction velocity, maximum signal amplitude, capture rate, and excitation threshold, were significantly improved compared with our previous studies.
Role of KATP + channels in regulation of systemic, pulmonary, and coronary vasomotor tone in exercising swine
Authors: Duncker D. J. , Oei H. H. , Hu F. , Stubenitsky R. , Verdouw P. D.
Published: December 2017

The role of ATP-sensitive K+ (KATP +) channels in vasomotor tone regulation during metabolic stimulation is incompletely understood. Consequently, we studied the contribution of KATP + channels to vasomotor tone regulation in the systemic, pulmonary, and coronary vascular bed in nine treadmill-exercising swine. Exercise up to 85% of maximum heart rate increased body O2 consumption fourfold, accommodated by a doubling of both cardiac output and body O2 extraction. Mean aortic pressure was unchanged, implying that systemic vascular conductance (SVC) also doubled, whereas pulmonary artery pressure increased almost in parallel with cardiac output, so that pulmonary vascular conductance (PVC) increased only 25 ± 9% (both P < 0.05). Myocardial O2 consumption tripled during exercise, which was paralleled by an equivalent increase in O2 supply so that coronary venous Po 2 was maintained. Selective KATP + channel blockade with glibenclamide (3 mg/kg iv), decreased SVC by 29 ± 4% at rest and by 10 ± 2% at 5 km/h (both P < 0.05), whereas PVC was unchanged. Glibenclamide decreased coronary vascular conductance and hence myocardial O2 delivery, necessitating an increase in O2 extraction from 76 ± 2% to 86 ± 2% at rest and from 79 ± 2% to 83 ± 1% at 5 km/h. Consequently, coronary venous Po 2 decreased from 25 ± 1 to 17 ± 1 mmHg at rest and from 23 ± 1 to 20 ± 1 mmHg at 5 km/h (all values are P < 0.05). In conclusion, KATP + channels dilate the systemic and coronary, but not the pulmonary, resistance vessels at rest and during exercise in swine. However, opening of KATP + channels is not mandatory for the exercise-induced systemic and coronary vasodilation.
Modulation of cardiac Na+ current by gadolinium, a blocker of stretch-induced arrhythmias
Authors: Li Gui-Rong , Baumgarten Clive M.
Published: December 2017

Gd3+ blocks stretch-activated channels and suppresses stretch-induced arrhythmias. We used whole cell voltage clamp to examine whether effects on Na+ channels might contribute to the antiarrhythmic efficacy of Gd3+. Gd3+ inhibited Na+ current ( I Na) in rabbit ventricle (IC50 = 48 μM at −35 mV, holding potential −120 mV), and block increased at more negative test potentials. Gd3+ made the threshold for I Na more positive and reduced the maximum conductance. Gd3+ (50 μM) shifted the midpoints for activation and inactivation of I Na 7.9 and 5.7 mV positive but did not alter the slope factor for either relationship. Activation and inactivation kinetics were slowed in a manner that could not be explained solely by altered surface potential. Paradoxically, Gd3+ increased I Naunder certain conditions. With membrane potential held at −75 mV, Gd3+ still shifted threshold for activation positive, but I Na increased positive to −40 mV, causing the current-voltage curves to cross over. When availability initially was low, increased availability induced by Gd3+ dominated the response at test potentials positive to −40 mV. The results indicate that Gd3+ has complex effects on cardiac Na+channels. Independent of holding potential, Gd3+ is a potent I Na blocker near threshold potential, and inhibition of I Na by Gd3+ is likely to contribute to suppression of stretch-induced arrhythmias.
Myocardial oxygenation and high-energy phosphate levels during graded coronary hypoperfusion
Authors: Zhang Jianyi , Ugurbil Kamil , From Arthur H. L. , Bache Robert J.
Published: December 2017

This study was performed to determine the myocyte Po 2 required to sustain normal high-energy phosphate (HEP) levels in the in vivo heart. In 10 normal dogs, myocyte Po 2 values were calculated from the myocardial deoxymyoglobin resonance (Mb-δ) intensity determined with 1H-NMR spectroscopy during sequential flow reductions produced by a hydraulic occluder that decreased coronary perfusion pressure to ∼60, 50, and 40 mmHg and, finally, during total occlusion. Myocardial blood flow was measured with microspheres, and HEP levels were determined with 31P magnetic resonance spectroscopy. During control conditions, Mb-δ was undetectable. Myocardial blood flow was 1.11 ± 0.06 ml · min−1 · g−1 during basal conditions and decreased with sequential graded occlusions to 0.78 ± 0.05, 0.58 ± 0.03, and 0.38 ± 0.04 ml · min−1 · g−1, respectively; blood flow during total occlusion was 0.07 ± 0.02 ml · min−1 · g−1. Reductions of blood flow caused progressive increases of Mb-δ, which were associated with decreases of phosphocreatine (PCr), ATP, and the PCr-to-ATP ratio, as well as progressive increases of the Pi-to-PCr ratio. There was a strong linear correlation between normalized blood flow and Mb-δ ( R 2 = 0.89, P < 0.01). Reductions of HEP and Po 2 were also highly correlated (although nonlinearly); with the assumption that myoglobin was 90% saturated with O2 during basal conditions and 5% saturated during total coronary occlusion, the intracellular Po 2 values for 20% reductions of PCr and ATP were ∼4.4 and ∼0.9 mmHg, respectively. The data indicate that O2 availability plays an increasing role in regulation of oxidative phosphorylation when mean intracellular Po 2 values fall below 5 mmHg in the in vivo heart.
A partial agonist of the A1-adenosine receptor selectively slows AV conduction in guinea pig hearts
Authors: Wu Lin , Belardinelli Luiz , Zablocki Jeffrey A. , Palle Venkata , Shryock John C.
Published: December 2017

The use of full agonists of the A1-adenosine receptor (A1-ADOR) as antiarrhythmic agents is limited by their actions to cause high-grade atrioventricular (AV) block, profound bradycardia, atrial fibrillation, and vasodilation. It may be possible to avoid these undesired actions by use of partial agonists. We determined the effects of CVT-2759, a potential partial agonist of A1-ADORs, on guinea pig hearts. CVT-2759 (0.1–100 μM) increased the S-H interval of the isolated heart from 45 ± 1 to 60 ± 3 ms ( P < 0.01) with a half-maximal effect at 3.1 μM. CVT-2759 did not cause second-degree AV block. CVT-2759 significantly attenuated the actions of the full agonists N 6-cyclopentyladenosine and adenosine. CVT-2759 caused a moderate slowing of atrial rate by ≤13% and did not shorten the durations of either the atrial or the ventricular monophasic action potential. Coronary conductance was increased by CVT-2759 only at concentrations >10 μM. In contrast, CVT-2759 was a full agonist to decrease cAMP content of rat adipocytes and Fischer rat thyroid line 5 cells. Results of radioligand binding assays indicated that CVT-2759 stabilized a high-affinity, G protein-coupled state of the A1-ADOR in membranes prepared from rat adipocytes but not in membranes prepared from the guinea pig brain. The results suggest that a weak A1-ADOR agonist, such as CVT-2759, may be useful to slow AV nodal conduction and thereby ventricular rate without causing AV block, bradycardia, atrial arrhythmias, or vasodilation.
Melatonin potentiates contractile responses to serotonin in isolated porcine coronary arteries
Authors: Yang Qiong , Scalbert Elizabeth , Delagrange Philippe , Vanhoutte Paul M. , O'Rourke Stephen T.
Published: December 2017

The present study was designed to determine the effects of melatonin on coronary vasomotor tone. Porcine coronary arteries were suspended in organ chambers for isometric tension recording. Melatonin (10−10-10−5 M) itself caused neither contraction nor relaxation of the tissues. Serotonin (10−9-10−5 M) caused concentration-dependent contractions of coronary arteries, and in the presence of melatonin (10−7 M) the maximal response to serotonin was increased in rings with but not without endothelium. In contrast, melatonin had no effect on contractions produced by the thromboxane A2 analog U-46619 (10−10-10−7 M). The melatonin-receptor antagonist S-20928 (10−6 M) abolished the potentiating effect of melatonin on serotonin-induced contractions in endothelium-intact coronary arteries, as did treatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10−5 M), methylene blue (10−5 M), or NG -nitro-l-arginine (3 × 10−5 M). In tissues contracted with U-46619, serotonin caused endothelium-dependent relaxations that were inhibited by melatonin (10−7 M). Melatonin also inhibited coronary artery relaxation induced by sodium nitroprusside (10−9-10−5 M) but not by isoproterenol (10−9-10−5 M). These results support the hypothesis that melatonin, by inhibiting the action of nitric oxide on coronary vascular smooth muscle, selectively potentiates the vasoconstrictor response to serotonin in coronary arteries with endothelium.
ANG II potentiates mitogenic effect of norepinephrine in vascular muscle cells: role of FGF-2
Authors: Parenti Astrid , Brogelli Laura , Donnini Sandra , Ziche Marina , Ledda Fabrizio
Published: December 2017

We examined the possible cooperation between norepinephrine (NE) and ANG II on proliferation of cultured vascular smooth muscle cells (VSMCs) and the involved cellular mechanisms. Nanomolar NE concentrations stimulated VSMC proliferation through a prazosin-sensitive effect. The pretreatment of cells with 100 nM ANG II for 24 h significantly potentiated the NE-induced VSMC proliferation; this potentiating effect of ANG II was blocked by losartan but was unaffected by the AT2receptor antagonist PD-123177. ANG II pretreatment also potentiated the increase in inositol phosphate turnover and upregulated the cell expression of fibroblast growth factor (FGF-2) induced by NE. Anti-FGF-2 neutralizing antibodies prevented the potentiating effect of ANG II on NE-induced cell growth. Both ANG II and NE stimulated extracellular signal-related kinase (ERK1) activation, but an ANG II potentiation of the effect of NE on ERK1 activity was not detectable. Moreover, ANG II significantly increased protein synthesis but did not potentiate the hypertrophic effect of NE. These findings demonstrate that ANG II and NE cooperate in promoting VSMC growth and that FGF-2 upregulation is involved in this effect.
β-Adrenoceptor and nNOS-derived NO interactions modulate hypoglycemic pial arteriolar dilation in rats
Authors: Santizo Roberto A. , Koenig Heidi M. , Pelligrino Dale A.
Published: December 2017

We examined the relative contributions from nitric oxide (NO) and catecholaminergic pathways in promoting cerebral arteriolar dilation during hypoglycemia (plasma glucose ≅ 1.4 mM). To that end, we monitored the effects of β-adrenoceptor (β-AR) blockade with propranolol (Pro, 1.5 mg/kg iv), neuronal nitric oxide synthase (nNOS) inhibition with 7-nitroindazole (7-NI, 40 mg/kg ip) or ARR-17477 (300 μM, via topical application), or combined intravenous Pro + 7-NI or ARR-17477 on pial arteriolar diameter changes in anesthetized rats subjected to insulin-induced hypoglycemia. Additional experiments, employing topically applied TTX (1 μM), addressed the possibility that the pial arteriolar response to hypoglycemia required neuronal transmission. Separately, Pro and 7-NI elicited modest but statistically insignificant 10–20% reductions in the normal ∼40% increase in arteriolar diameter accompanying hypoglycemia. However, combined Pro-7-NI was accompanied by a >80% reduction in the hypoglycemia-induced dilation. On the other hand, the combination of intravenous Pro and topical ARR-17477 did not affect the hypoglycemia response. In the presence of TTX, the pial arteriolar response to hypoglycemia was lost completely. These results suggest that 1) β-ARs and nNOS-derived NO interact in contributing to hypoglycemia-induced pial arteriolar dilation; 2) the interaction does not occur in the vicinity of the arteriole; and 3) the vasodilating signal is transmitted via a neuronal pathway.
Carotid baroreflex pressor responses at rest and during exercise: cardiac output vs. regional vasoconstriction
Authors: Collins Heidi L. , Augustyniak Robert A. , Ansorge Eric J. , O'Leary Donal S.
Published: December 2017

The arterial baroreflex mediates changes in arterial pressure via reflex changes in cardiac output (CO) and regional vascular conductance, and the relative roles may change between rest and exercise and across workloads. Therefore, we quantified the contribution of CO and regional vascular conductances to carotid baroreflex-mediated increases in mean arterial pressure (MAP) at rest and during mild to heavy treadmill exercise (3.2 kph; 6.4 kph, 10% grade; and 8 kph, 15% grade). Dogs ( n = 8) were chronically instrumented to measure changes in MAP, CO, hindlimb vascular conductance, and renal vascular conductance in response to bilateral carotid occlusion (BCO). At rest and at each workload, BCO caused similar increases in MAP (average 35 ± 2 mmHg). In response to BCO, neither at rest nor at any workload were there significant increases in CO; therefore, the pressor response occurred via peripheral vasoconstriction. At rest, 10.7 ± 1.4% of the rise in MAP was due to vasoconstriction in the hindlimb, whereas 4.0 ± 0.7% was due to renal vasoconstriction. Linear regression analysis revealed that, with increasing workloads, relative contributions of the hindlimb increased and those of the kidney decreased. At the highest workload, the decrease in hindlimb vascular conductance contributed 24.3 ± 3.4% to the pressor response, whereas the renal contribution decreased to only 1.6 ± 0.3%. We conclude that the pressor response during BCO was mediated solely by peripheral vasoconstriction. As workload increases, a progressively larger fraction of the pressor response is mediated via vasoconstriction in active skeletal muscle and the contribution of vasoconstriction in inactive beds (e.g., renal) becomes progressively smaller.
Involvement of iNOS in postischemic heart dysfunction of stroke-prone spontaneously hypertensive rats
Authors: Abe Kohji , Tokumura Miwa , Ito Tetsuji , Murai Takashi , Takashima Akira , Ibii Nobuhiro
Published: December 2017

We investigated the possible contribution of inducible nitric oxide synthase (iNOS) to postischemic heart dysfunction and injuries in stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP, 13–14 wk of age, had significantly higher systolic blood pressure and greater heart weight than age-matched Wistar-Kyoto rats (WKY). Permanent occlusion of the left anterior descending coronary artery (LAD) caused significant and long-lasting increases in the activity and mRNA expression of myocardial iNOS in SHRSP compared with WKY. However, there was no significant difference in the LAD occlusion-induced expression of interleukin-1β mRNA between SHRSP and WKY. Hemodynamic deterioration and myocardial fibrosis were also observed in SHRSP at 4 wk after LAD occlusion. Continuous administration of 2-amino-5,6-dihydro-6-methyl-4 H-1,2-thiazin (AMT) completely blocked the LAD occlusion-induced increase in the myocardial iNOS activity of SHRSP. Moreover, postischemic heart dysfunction and injuries were also significantly ameliorated by 2-amino-5,6-dihydro-6-methyl-4 H-1,2-thiazin (AMT). These results suggest that the increased activity of myocardial iNOS plays a pivotal role in the development of postischemic cardiac dysfunction and injuries in SHRSP with the hypertensive and hypertrophic heart.
Ca2+activation of myofilaments from transgenic mouse hearts expressing R92Q mutant cardiac troponin T
Authors: Chandra Murali , Rundell Veronica L. M. , Tardiff Jil C. , Leinwand Leslie A. , de Tombe Pieter P. , Solaro R. John
Published: December 2017

The functional consequences of the R92Q mutation in cardiac troponin T (cTnT), linked to familial hypertrophic cardiomyopathy in humans, are not well understood. We have studied steady- and pre-steady-state mechanical activity of detergent-skinned fiber bundles from a transgenic (TG) mouse model in which 67% of the total cTnT in the heart was replaced by the R92Q mutant cTnT. TG fibers were more sensitive to Ca2+than nontransgenic (NTG) fibers [negative logarithm of half maximally activating molar Ca2+(pCa50) = 5.84 ± 0.01 and 6.12 ± 0.01 for NTG and TG fibers, respectively]. The shift in pCa50caused by increasing the sarcomere length from 1.9 to 2.3 μm was significantly higher for TG than for NTG fibers (ΔpCa50= 0.13 ± 0.01 and 0.29 ± 0.02 for NTG and TG fibers, respectively). The relationships between rate of ATP consumption and steady-state isometric tension were linear, and the slopes were the same in NTG and TG fibers. Rate of tension redevelopment was more sensitive to Ca2+in TG than in NTG fibers (pCa50= 5.71 ± 0.02 and 6.07 ± 0.02 for NTG and TG fibers, respectively). We concluded that overall cross-bridge cycling kinetics are not altered by the R92Q mutation but that altered troponin-tropomyosin interactions could be responsible for the increase in myofilament Ca2+sensitivity in TG myofilaments.
Role of endothelial Ni2+-sensitive Ca2+entry pathway in regulation of EDHF in porcine coronary artery
Authors: Tomioka Hiroshi , Hattori Yuichi , Fukao Mitsuhiro , Watanabe Hiroshi , Akaishi Yasuhiro , Sato Atsushi , Kim Tran Quang , Sakuma Ichiro , Kitabatake Akira , Kanno Morio
Published: December 2017

Elevation of intracellular Ca2+ concentration ([Ca2+]i) in endothelial cells is proposed to be required for generation of vascular actions of endothelium-derived hyperpolarizing factor (EDHF). This study was designed to determine the endothelial Ca2+ source that is important in development of EDHF-mediated vascular actions. In porcine coronary artery precontracted with U-46619, bradykinin (BK) and cyclopiazonic acid (CPA) caused endothelium-dependent relaxations in the presence of N G-nitro-l-arginine (l-NNA). The l-NNA-resistant relaxant responses were inhibited by high K+, indicating an involvement of EDHF. In the presence of Ni2+, which inhibits Ca2+ influx through nonselective cation channels, the BK-induced EDHF relaxant response was greatly diminished and the CPA-induced response was abolished. BK and CPA elicited membrane hyperpolarization of smooth muscle cells of porcine coronary artery. Ni2+ suppressed the hyperpolarizing responses in a manner analogous to removal of extracellular Ca2+. EDHF-mediated relaxations and hyperpolarizations evoked by BK and CPA in porcine coronary artery showed a temporal correlation with the increases in [Ca2+]i in porcine aortic endothelial cells. The extracellular Ca2+-dependent rises in [Ca2+]i in endothelial cells stimulated with BK and CPA were completely blocked by Ni2+. These results suggest that Ca2+ influx into endothelial cells through nonselective cation channels plays a crucial role in the regulation of EDHF.
Analysis of purine- and pyrimidine-induced vascular responses in the isolated rat cerebral arteriole
Authors: Horiuchi Tetsuyoshi , Dietrich Hans H. , Tsugane Shinichiro , Dacey Ralph G.
Published: December 2017

Effects of extraluminal UTP were studied and compared with vascular responses to ATP and its analogs in rat cerebral-penetrating arterioles. UTP, UDP, 2-methylthio-ATP, and α,β-methylene-ATP dilated arterioles at the lowest concentration and constricted them at high concentrations. Low concentrations of ATP dilated the vessels; high concentrations caused a biphasic response, with transient constriction followed by dilation. Endothelial impairment inhibited ATP- and UTP-mediated dilation and potentiated constriction to UTP but not to ATP. ATP- and 2-methylthio-ATP- but not UTP-mediated constrictions were inhibited by desensitization with 10−6M α,β-methylene-ATP or 3 × 10−6M pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS). PPADS at 10−4M abolished the UTP-mediated constriction and induced vasodilation in a dose-dependent manner but did not affect the dilation to ATP. These results suggest that in rat cerebral microvessels 1) ATP and 2-methylthio-ATP induce transient constriction via smooth muscle P2X1receptors in the cerebral arteriole, 2) UTP stimulates two different classes of P2Yreceptors, resulting in constriction (smooth muscle P2Y4) and dilation (possibly endothelial P2Y2), and 3) ATP and UTP produce dilation by stimulation of a single receptor (P2Y2).
Upregulation of eNOS in pregnant ovine uterine arteries by chronic hypoxia
Authors: Xiao Daliao , Bird Ian M. , Magness Ronald R. , Longo Lawrence D. , Zhang Lubo
Published: December 2017

We tested the hypothesis that chronic high-altitude (3,820 m) hypoxia during pregnancy was associated with the upregulation of endothelial nitric oxide (NO) synthase (eNOS) protein and mRNA in ovine uterine artery endothelium and enhanced endothelium-dependent relaxation. In pregnant sheep, norepinephrine-induced dose-dependent contractions were increased by removal of the endothelium in both control and hypoxic uterine arteries. The increment was significantly higher in hypoxic tissues. The calcium ionophore A23187 -induced relaxation of the uterine artery was significantly enhanced in hypoxic compared with control tissues. However, sodium nitroprusside- and 8-bromoguanosine 3′,5′-cyclic monophosphate-induced relaxations were not changed. Accordingly, chronic hypoxia significantly increased basal and A23187 -induced NO release. Chronic hypoxia increased eNOS protein and mRNA levels in the endothelium from uterine but not femoral or renal arteries. In nonpregnant animals, chronic hypoxia increased eNOS mRNA in uterine artery endothelium but had no effects on eNOS protein, NO release, or endothelium-dependent relaxation. Chronic hypoxia selectively augments pregnancy-associated upregulation of eNOS gene expression and endothelium-dependent relaxation of the uterine artery.
Reduced Na-K pump but increased Na-K-2Cl cotransporter in aorta of streptozotocin-induced diabetic rat
Authors: Michea Luis , Irribarra Verónica , Goecke I. Annelise , Marusic Elisa T.
Published: December 2017

The activities of Na-K-ATPase and Na-K-2Cl cotransporter (NKCC1) were studied in the aorta, heart, and skeletal muscle of streptozotocin (STZ)-induced diabetic rats and control rats. In the aortic rings of STZ rats, the Na-K-ATPase-dependent86Rb/K uptake was reduced to 60.0 ± 5.5% of the control value ( P < 0.01). However, Na-K-ATPase activity in soleus skeletal muscle fibers of STZ rats and paired control rats was similar, showing that the reduction of Na-K-ATPase activity in aortas of STZ rats is tissue specific. To functionally distinguish the contributions of ouabain-resistant (α1) and ouabain-sensitive (α2and α3) isoforms to the Na-K-ATPase activity in aortic rings, we used either a high (10−3M) or a low (10−5M) ouabain concentration during86Rb/K uptake. We found that the reduction in total Na-K-ATPase activity resulted from a dramatic decrement in ouabain-sensitive mediated86Rb/K uptake (26.0 ± 3.9% of control, P < 0.01). Western blot analysis of membrane fractions from aortas of STZ rats demonstrated a significant reduction in protein levels of α1- and α2-catalytic isoforms (α1= 71.3 ± 9.8% of control values, P < 0.05; α2= 44.5 ± 11.3% of control, P < 0.01). In contrast, aortic rings from the STZ rats demonstrated an increase in NKCC1 activity (172.5 ± 9.5%, P < 0.01); however, in heart tissue no difference in NKCC1 activity was seen between control and diabetic animals. Transport studies of endothelium-denuded or intact aortic rings demonstrated that the endothelium stimulates both Na-K-ATPase and Na-K-2Cl dependent86Rb/K uptake. The endothelium-dependent stimulation of Na-K-ATPase and Na-K-2Cl was not hampered by diabetes. We conclude that abnormal vascular vessel tone and function, reported in STZ-induced diabetic rats, may be related to ion transport abnormalities caused by changes in Na-K-ATPase and Na-K-2Cl activities.