bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of intracellular Ca2+and pH in positive inotropic response of cardiomyocytes to diacylglycerol
Authors: Pi Yeqing , Walker Jeffery W.
Published: December 2017

Diacylglycerol has been hypothesized to mediate the positive inotropic response of myocardium to the α-adrenergic agonists angiotensin II and endothelin. The mechanism of action of diacylglycerol was examined here in adult rat ventricular myocytes by releasing dioctanoylglycerol (diC8) intracellularly from a caged compound while monitoring Ca2+transients and pH with fluorescent indicators. DiC8caused a three- to fourfold increase in twitch amplitude and a twofold increase in the systolic Ca2+transient. No other parameter was consistently influenced by diC8, including the kinetics of Ca2+cycling, the Ca2+content of the sarcoplasmic reticulum, or the myofilament Ca2+sensitivity. DiC8also had no detectable effect on intracellular pH or Na+/H+antiport activity. Consistent with this finding, the Na+/H+exchange inhibitor N-ethylisopropyl amiloride was without effect on the positive inotropic response to diC8. The marked enhancement of systolic Ca2+by diC8suggests that the process of excitation-contraction coupling is an important and possibly preferred target of diacylglycerol-protein kinase C signaling in myocardium.
Increased myocardial lactate oxidation in lambs with aortopulmonary shunts at rest and during exercise
Authors: Beaufort-Krol Gertie C. M. , Takens Janny , Molenkamp Marieke C. , Smid Gioia B. , Meuzelaar Koos J. , Zijlstra Willem G. , Kuipers Jaap R. G.
Published: December 2017

Free fatty acids are the major fuels for the myocardium, but during a higher load carbohydrates are preferred. Previously, we demonstrated that myocardial net lactate uptake was higher in lambs with aortopulmonary shunts than in control lambs. To determine whether this was caused by an increased lactate uptake and oxidation or by a decreased lactate release, we studied myocardial lactate and glucose metabolism with13C-labeled substrates in 36 lambs in a fasting, conscious state. The lambs were assigned to two groups: a resting group consisting of 8 shunt and 9 control lambs, and an exercise group (50% of peak O2consumption) consisting of 9 shunt and 10 control lambs. Myocardial lactate oxidation was higher in shunt than in control lambs (mean ± SE, rest: 10.33 ± 2.61 vs. 0.17 ± 0.82, exercise: 38.05 ± 8.87 vs. 16.89 ± 4.78 μmol ⋅ min−1⋅ 100 g−1; P < 0.05). There was no difference in myocardial lactate release between shunt and control lambs. Oxidation of exogenous glucose, which was approximately zero at rest, increased during exercise in shunt and control lambs. The contribution of glucose and lactate to myocardial oxidative metabolism increased during exercise compared with at rest in both shunt and control lambs. We conclude that myocardial lactate oxidation is higher in shunt than in control lambs, both at rest and during exercise, and that the contribution of carbohydrates in myocardial oxidative metabolism in shunt lambs is higher than in control lambs. Thus it appears that this higher contribution of carbohydrates occurs not only in the case of pressure-overloaded hearts but also in myocardial hypertrophy due to volume overloading.
Ventricular contractility in atrial fibrillation is predictable by mechanical restitution and potentiation
Authors: Suzuki Shunsuke , Araki Junichi , Morita Terumasa , Mohri Satoshi , Mikane Takeshi , Yamaguchi Hiroki , Sano Shunji , Ohe Tohru , Hirakawa Masahisa , Suga Hiroyuki
Published: December 2017

We recently found that contractility ( E max) of an individual irregularly arrhythmic beat in electrically induced atrial fibrillation (AF) is reasonably predictable from the ratio of the preceding beat interval (RR1) to the beat interval immediately preceding RR1 (RR2) in the canine left ventricle. Moreover, the monotonically increasing relation between E max and the RR1-to-RR2 ratio (RR1/RR2) passed through or by the mean arrhythmic beat E max as well as the regular beat E max at RR1/RR2 = 1. We hypothesized that this E max-RR1/RR2 relation during irregular arrhythmia could be attributed to the basic characteristics of the mechanical restitution and potentiation. To test this, we adopted a known comprehensive equation describing the force restitution and potentiation as a function of two preceding beat intervals and simulated contractilities of irregular arrhythmic beats with randomized beat intervals on a computer. The simulated E max-RR1/RR2 relation reasonably resembled the one that we recently observed experimentally, supporting our hypothesis. We therefore conclude that the primary mechanism underlying the varying contractilities of irregular beats in AF is mechanical restitution and potentiation.
Peroxynitrite is a contractile agonist of cerebral artery smooth muscle cells
Authors: Elliott Stephen J. , Lacey David J. , Chilian William M. , Brzezinska Anna K.
Published: December 2017

On reperfusion of ischemic tissue, a prolonged phase of vasoconstriction occurs, the mechanism of which is poorly understood. However, it is known that peroxynitrite (ONOO−) is formed during reperfusion. In this study the contractile properties of ONOO−were investigated in Wistar rat middle cerebral arteries. The effects of ONOO−on vessel diameter were dose dependent. Low-dose ONOO−(10 μM) caused vessels to constrict by 15%. At an intermediate concentration of 25 μM, the effect of ONOO−was variable, whereas at the highest concentration (100 μM), vessels underwent persistent dilation and became insensitive to the endogenous vasoconstrictor 5-hydroxytryptamine. At the single cell level, ONOO−caused cerebral artery smooth muscle cells to contract. Reduced, but not oxidized, glutathione completely inhibited the contractile action of ONOO−on single cells. Vehicle and decomposed ONOO−each had minimal effect on cell length. These data show that ONOO−is a contractile agonist of middle cerebral arteries, at the single cell and whole vessel levels, suggesting that formation of ONOO−may contribute mechanistically to ischemic brain injury during stroke. Moreover, relatively high concentrations of ONOO−result in vascular paralysis.
Transmembrane potential changes caused by monophasic and biphasic shocks
Authors: Zhou Xiaohong , Smith William M. , Justice Robert K. , Wayland James L. , Ideker Raymond E.
Published: December 2017

Transmembrane potential change (Δ V m) during shocks was recorded by a double-barrel microelectrode in 12 isolated guinea pig papillary muscles. After 10 S1 stimuli, square-wave S2 shocks of both polarities were given consisting of 10-ms monophasic and 10/10-ms and 5/5-ms biphasic waveforms that created potential gradients from 1.1 ± 0.3 to 11.9 ± 0.4 V/cm. S2 shocks were applied with 30, 60- to 70-, and 90- to 130-ms S1-S2 coupling intervals so that they occurred during the plateau, late portion of the plateau, and phase 3 of the action potential, respectively. Some shocks were given across as well as along the fiber orientation. The shocks caused hyperpolarization with one polarity and depolarization with the opposite polarity. The ratio of the magnitude of hyperpolarization to that of depolarization at the three S1-S2 coupling intervals was 1.5 ± 0.3, 1.1 ± 0.2, and 0.5 ± 0.2, respectively. Δ V m during the shock was significantly greater for the monophasic than for the two biphasic shocks. The prolongation of total repolarizing time (TRT) was significantly greater for monophasic (119.8 ± 19.1%) and 10/10-ms biphasic (120.5 ± 18.2%) than for 5/5-ms biphasic (113.0 ± 12.9%) waveforms. The dispersion of the normalized TRT between instances of hyperpolarization and depolarization caused by the two shock polarities was 7.4 ± 7.1% for monophasic, 3.0 ± 4.1% for 10/10-ms biphasic, and 2.8 ± 3.1% for 5/5-ms biphasic shocks ( P < 0.05 for monophasic vs. biphasic). Shock fields along fibers produced a larger Δ V m and prolongation of TRT than those across fibers. We conclude that 1) a change in shock polarity causes an asymmetrical change in membrane polarization depending on shock timing; 2) the 5/5-ms biphasic waveform causes the smallest Δ V m, prolongs repolarization the least, and causes the smallest polarity-dependent dispersion; and 3) the changes in transmembrane potential and repolarization are influenced by fiber orientation.
Chronic regulation of arterial blood pressure by ANP: role of endogenous vasoactive endothelial factors
Authors: Melo L. G. , Veress A. T. , Ackermann U. , Sonnenberg H.
Published: December 2017

Atrial natriuretic peptide (ANP) exerts a chronic hypotensive effect due to a decrease in total peripheral resistance (TPR). This study examines if chronic ANP-dependent vasodilation is attributable to differences in the cardiovascular regulatory activity of vascular endothelium (VE), based on evidence that ANP affects synthesis/release and target cardiovascular effects of endothelin-1 (ET-1), C-type natriuretic peptide (CNP), and nitric oxide (NO). To determine if the synthetic activity of resistance vasculature VE is chronically altered by plasma ANP activity, we measured ET-1, CNP, and endothelial constitutive NO synthase (ecNOS) concentration and total NOS enzyme activity in homogenates of kidney, heart, lung, hindquarter skeletal muscle, and brain from hypotensive transgenic mice with elevated plasma ANP, hypertensive knockout mice (−/−) characterized by the absence of ANP, and the corresponding normotensive wild-type (NT, +/+) mice. Tissue distribution and abundance patterns of ET-1, CNP, ecNOS, and NOS enzyme activity were comparable between the different genotypes and did not differ significantly between mutant and control mice. Antagonism of ETA/Breceptors in −/− and +/+ mice in vivo with SB-209670 reduced arterial blood pressure (ABP) significantly and comparably in both genotypes (−27 ± 4 and −25 ± 2% change for −/− and +/+ mice, respectively) independent of any significant changes in heart rate (HR) (−6 ± 8 and −4 ± 4% change for −/− and +/+ mice, respectively). Immunoneutralization of CNP-specific guanylate cyclase-linked receptors (GC-B) with monoclonal antibodies (3G12) increased ABP slightly, but not significantly, by similar relative amounts in both −/− (10 ± 6% change) and +/+ mice (8 ± 3% change), without changing HR significantly (4 ± 1% change for both +/+ and −/− mice). Inhibition of NOS activity (by NG-nitro-l-arginine methyl ester) significantly increased ABP, but the changes were comparable between −/− (53 ± 5% change) and +/+ mice (50 ± 6% change) and occurred in the absence of significant changes in HR (−1 ± 5 and 7 ± 5% change for −/− and +/+ mice, respectively). We conclude that the differences in ABP associated with chronic variations in endogenous ANP activity are not due to alterations in synthesis or responsiveness of the cardiovascular system to the effects of ET-1, CNP, or NO.
Coronary endothelial P-selectin in pathogenesis of myocardial ischemia-reperfusion injury
Authors: Palazzo Anthony J. , Jones Steven P. , Anderson Donald C. , Granger D. Neil , Lefer David J.
Published: December 2017

We investigated in vivo coronary P-selectin expression and its pathophysiological consequences in a murine model of myocardial ischemia-reperfusion (MI/R) using wild-type and P-selectin deficient (−/−) mice. Coronary P-selectin expression [μg monoclonal antibody (MAb)/g tissue] was measured using a radiolabeled MAb method after 30 min of myocardial ischemia and 20 min of reperfusion. P-selectin expression in wild-type mice was significantly ( P< 0.01) elevated in the ischemic zone (0.070 ± 0.010) compared with the nonischemic zone (0.037 ± 0.008). Myocardial P-selectin expression was nearly undetectable in P-selectin −/− mice after MI/R. Furthermore, myocardial infarct size (% of area at risk) after 30 min of myocardial ischemia and 120 min of reperfusion was 42.5 ± 4.4 in wild-type mice and 24.4 ± 4.0 in P-selectin −/− mice ( P < 0.05). In additional experiments of prolonged myocardial ischemia (60 min) and reperfusion (120 min), myocardial infarct size was similar in P-selectin −/− mice and wild-type mice. Our results clearly demonstrate the involvement of coronary P-selectin in the development of myocardial infarction after MI/R.
Efficient protein transfection of cultured coronary venular endothelial cells
Authors: Tinsley John H. , Hawker James , Yuan Yuan
Published: December 2017

Although it is well recognized that microvascular endothelial cells play an important role in the local regulation of tissue perfusion and exchange processes, the precise effect of specific endothelial proteins on microvascular function remains to be elucidated. The lack of information is partially due to methodological limitations, because pharmacological approaches that are routinely used in conventional microcirculatory studies produce nonspecific information. The purpose of this study was to develop an efficient method of transfecting endothelial cells with proteins for functional analysis. TransIT, a polyamine reagent, proved very successful for β-galactosidase (β-Gal) protein transfection of bovine coronary venular endothelial cells, because time-course and dose-dependent experiments showed that a transfection efficiency of 88 ± 7% was possible. In control studies, β-Gal was detected in transfected cells that were trypsinized and washed, indicating that the protein was not merely adhering to the cell surface. Furthermore, transfection of a cell-impermeable peptide inhibitor of protein kinase C (PKC) resulted in a decrease in PKC activity in comparison with control cells. This approach provides a technical basis for further transfection of endothelial cell monolayers with antibodies and constitutively active or dominant-negative proteins to study the molecular control of microvascular function.
High-density epicardial mapping during current injection and ventricular activation in rat hearts
Authors: Macchi Emilio , Cavalieri Massimo , Stilli Donatella , Musso Ezio , Baruffi Silvana , Olivetti Giorgio , Ershler Philip R. , Lux Robert L. , Taccardi Bruno
Published: December 2017

The purpose of this study is to report new methods for manufacturing precision electrode arrays for recording high-resolution potential distributions from epicardial surfaces of small-animal hearts. Electrode arrays of 64 leads (8 × 8) and 121 leads (11 × 11) were constructed with a tulle substrate to which insulated, fine silver wires (60-μm diameter) were attached by knots at mesh node intervals of 540 × 720 μm. Insulation was removed at the tips of the knots. Potential distributions and waveforms were recorded from saline solutions and rat heart epicardium during ventricular paced beats and during passive current injection in the diastolic interval. Electrical responses obtained from rat epicardium compared favorably with those observed in studies of larger-animal hearts, which used arrays having greater electrode spacing, and revealed the effects of myocardial anisotropy. Epicardial potentials measured early after stimulation in the region surrounding the pacing site were interpreted in terms of potentials generated by an equivalent quadrupolar source. We conclude that electrode arrays for epicardial mapping of small hearts can be constructed with sufficient ease and precision to allow detailed study of fiber structure and electrophysiology in these hearts in normal and pathological conditions.
Letters to the Editor
Authors: Horst Gert J. Ter
Published: December 2017

The following is the abstract of the article discussed in the subsequent letter:

Worrall, Neil K., Kathy Chang, Wanda S. LeJeune, Thomas P. Misko, Patrick M. Sullivan, T. Bruce Ferguson, Jr., and Joseph R. Williamson. TNF-α causes reversible in vivo systemic vascular barrier dysfunction via NO-dependent and -independent mechanisms. Am. J. Physiol. 273 ( Heart Circ. Physiol. 42): H2565–H2574, 1997.—Tumor necrosis factor (TNF-α) and nitric oxide (NO) are important vasoactive mediators of septic shock. This study used a well-characterized quantitative permeation method to examine the effect of TNF-α and NO on systemic vascular barrier function in vivo, without confounding endotoxemia, hypotension, or organ damage. Our results showed 1) TNF-α reversibly increased albumin permeation in the systemic vasculature (e.g., lung, liver, brain, etc.); 2) TNF-α did not affect hemodynamics or blood flow or cause significant tissue injury; 3) pulmonary vascular barrier dysfunction was associated with increased lung water content and impaired oxygenation; 4) TNF-α caused inducible nitric oxide synthase (iNOS) mRNA expression in the lung and increased in vivo NO production; 5) selective inhibition of iNOS with aminoguanidine prevented TNF-α-induced lung and liver vascular barrier dysfunction; 6) aminoguanidine prevented increased tissue water content in TNF-α-treated lungs and improved oxygenation; and 7) nonselective inhibition of NOS with N G-monomethyl-l-arginine increased vascular permeation in control lungs and caused severe lung injury in TNF-α-treated animals. We conclude that 1) TNF-α reversibly impairs vascular barrier integrity through NO-dependent and -independent mechanisms; 2) nonselective NOS inhibition increased vascular barrier dysfunction and caused severe lung injury, whereas selective inhibition of iNOS prevented impaired endothelial barrier integrity and pulmonary dysfunction; and 3) selective inhibition of iNOS may be beneficial in treating increased vascular permeability that complicates endotoxemia and cytokine immunotherapy.
Endothelial nitric oxide synthase increases in left atria of dogs with pacing-induced heart failure
Authors: Khadour Fadi H. , O’Brien Darryl W. , Fu Yuling , Armstrong Paul W. , Schulz Richard
Published: December 2017

In congestive heart failure (CHF) the alterations in cardiac NO synthase (NOS) isoforms activity and expression are incompletely documented and the chamber specificity of these changes is unknown. We studied plasma nitrate-nitrite ([Formula: see text]), atrial, and ventricular NOS activities and protein expression (Western blot and densitometric analysis) in nonpaced control dogs and in dogs paced for 2 or 21 days into CHF. Plasma [Formula: see text] rose significantly after 7 and 21 days of pacing, whereas creatinine levels remained unchanged. In control dogs Ca2+-dependent NOS activity in left atria was double that of right or left ventricular activity. In paced animals the activity increased only in the atria after 21 but not 2 days of pacing. Levels of endothelial NOS (eNOS) protein were enhanced in the left atria but not ventricles after 21 days of pacing because of a greater quantity of the 150-kDa but not the 135-kDa eNOS. Ca2+-independent NOS activity was undetectable in any cardiac tissue. The specific upregulation of eNOS in the left atria suggests that NO production may be enhanced to counterbalance hypertrophy that develops during pacing-induced CHF.
High dietary salt alters arteriolar myogenic responsiveness in normotensive and hypertensive rats
Authors: Nurkiewicz Timothy R. , Boegehold Matthew A.
Published: December 2017

We evaluated arteriolar myogenic responsiveness in normotensive, salt-loaded and hypertensive rats and investigated the potential influence of luminal blood flow or shear stress on myogenic responses under each of these conditions. Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) fed low-salt (0.45%, LS) or high-salt (7%, HS) diets were enclosed in a ventilated airtight box with the spinotrapezius muscle exteriorized for intravital microscopy. Dietary salt did not affect mean arterial pressure (MAP) in WKY, whereas MAP in SHR was significantly higher and augmented by dietary salt. In all groups, box pressurization caused similar increases in MAP that were completely transmitted to the arterioles. After these pressure increases, large arteriole diameters decreased by 0–30% and intermediate arteriole diameters decreased by 21–27%. Arteriolar myogenic responsiveness was not different between WKY-LS and SHR-LS. Large arterioles in WKY-HS displayed an attenuated pressure-diameter relationship compared with that in WKY-LS. Large arterioles in SHR-HS displayed an augmented pressure-diameter relationship compared with that in SHR-LS. There were no correlations between resting flow or wall shear rate and the magnitude of initial myogenic constriction in any group or vessel type. The capacity for sustained myogenic constriction was unrelated to secondary decreases in flow (14–41%) or increases in wall shear rate (21–88%) in each group. We conclude that 1) dietary salt impairs the myogenic responsiveness of large arterioles in normotensive rats and augments the myogenic responsiveness of large arterioles in hypertensive rats, 2) hypertension does not alter arteriolar myogenic responsiveness in this vascular bed, and 3) flow- or shear-dependent mechanisms do not attenuate myogenic responses in the intact arteriolar network of normal, salt-loaded, or hypertensive rats.
Prolonged exercise causes an increase in endothelin-1 production in the heart in rats
Authors: Maeda Seiji , Miyauchi Takashi , Sakai Satoshi , Kobayashi Tsutomu , Iemitsu Motoyuki , Goto Katsutoshi , Sugishita Yasuro , Matsuda Mitsuo
Published: December 2017

Cardiac myocytes produce endothelin-1 (ET-1). ET-1 has potent positive inotropic and chronotropic effects. We investigated whether production of ET-1 in the heart is altered by prolonged exercise in rats. Rats ran on a treadmill for 45 min. Immediately after this exercise the heart and lungs were quickly removed. Control rats remained at rest during this 45-min period. Expression of preproET-1 mRNA in the heart was markedly higher in the exercised than in the control rats. The peptide level of ET-1 in the heart was also markedly higher in the exercised rats. Expression of endothelin type A- and type B-receptor mRNA and endothelin-converting enzyme mRNA in the heart did not differ between the groups. The peptide level of ET-1 and the preproET-1 mRNA level in the lungs of the exercised rats did not differ from those in the control rats. The present results show that production of ET-1 is markedly increased tissue specifically in the heart by exercise without appreciable changes in endothelin-converting enzyme and endothelin receptor expression. The present study suggests that myocardial ET-1 may participate in modulation of cardiac function during exercise.
Increased calcium loading and inotropy without greater cell death in hypoxic rat cardiomyocytes
Authors: Kondo Richard P. , Apstein Carl S. , Eberli Franz R. , Tillotson Douglas L. , Suter Thomas M.
Published: December 2017

To test whether contractile function in “hypoxic” myocytes treated with high glucose (19.5 mM) can be improved by increasing intracellular Ca2+without accelerating cell contracture or death, we challenged metabolically inhibited, paced myocytes with high extracellular Ca2+concentration ([Ca2+]o) and measured simultaneously cell shortening and intracellular Ca2+concentration ([Ca2+]i). NaCN exposure at a physiological [Ca2+]olevel (1.2 mM) caused a decline of contractile function to 58 ± 8% of the pre-NaCN value ( P < 0.001) but increased systolic and diastolic [Ca2+]iby 104 ± 17 and 37 ± 9% above baseline ( P < 0.01), respectively. Consequent doubling of [Ca2+]oto 2.4 mM, in the presence of NaCN, immediately restored contractile function, and twitch amplitude after 18 min was 123 ± 14% ( P < 0.001) of baseline pre-NaCN values, whereas systolic [Ca2+]iincreased further to 225 ± 63% ( P< 0.05) and diastolic [Ca2+]ito 73 ± 16% above baseline ( P < 0.01). This marked increase in [Ca2+]ihad no deleterious effect on myocyte diastolic function or survival. These results suggest that if adequate metabolic substrate is provided, contractile function in metabolically inhibited, hypoxic myocytes can be restored by increasing [Ca2+]iwithout causing short-term cell injury.
Metallothionein-overexpressing neonatal mouse cardiomyocytes are resistant to H2O2toxicity
Authors: Wang Guang-Wu , Schuschke Dale A. , Kang Y. James
Published: December 2017

To study cellular and molecular events of cardiac protection by metallothionein (MT) from oxidative injury, a primary neonatal cardiomyocyte culture was established from a specific cardiac MT-overexpressing transgenic mouse model. Ventricular cardiomyocytes were isolated from 1- to 3-day-old neonatal mice and cultured in an Eagle’s minimum essential medium supplemented with 20% fetal bovine serum under an atmosphere of 5% CO2-95% air at 37°C. Forty-eight hours after plating was completed, the purity of such cultures was 95% myocytes, assessed by an immunocytochemical assay. Over 80% of the cardiomyocytes beat spontaneously on the first day of culture and synchronously in a confluent monolayer after the sixth day of culture. Cellular MT concentrations in the transgenic cardiomyocytes before culturing and on the sixth day postculturing were about seven- and twofold higher than nontransgenic controls, respectively. However, there were no significant differences in cell morphology, glutathione content, and antioxidant enzymatic activities between these two types of cardiomyocytes. When these cells were challenged by H2O2, the transgenic cardiomyocytes displayed a significant resistance to the toxic effect of this oxidant, as measured by cell viability, lactate dehydrogenase leakage, and morphological alterations. In addition, the transgenic cells were highly protected from H2O2-induced lipid peroxidation. These observations demonstrate that MT protects the cultured cardiomyocytes from H2O2toxicity by preventing its interaction with macromolecules such as lipids, and this cultured primary neonatal mouse cardiomyocyte system provides a valuable tool to directly study cellular and molecular events of MT in cardiac protection against oxidative injury.
Effect of isoprenaline, carbachol, and Cs+on Na+activity and pacemaker potential in rabbit SA node cells
Authors: Choi Ho S. , Wang Dai Y. , Noble Denis , Lee Chin O.
Published: December 2017

Effects of isoprenaline, carbachol, and Cs+on intracellular Na+activity ([Formula: see text]) and spontaneous action potentials were studied in multicellular and single cell preparations isolated from rabbit sinoatrial (SA) nodes.[Formula: see text] was measured with double-barreled Na+-selective microelectrodes and the fluorescent Na+-indicator sodium-binding benzofuran isophthalate (SBFI). In spontaneously beating cells,[Formula: see text] measured with Na+-selective microelectrodes and SBFI were 4.5 ± 1.2 mM (means ± SD, n = 21) in multicellular preparations and 4.0 ± 1.1 mM ( n = 16) in single cells, respectively. Measurements of[Formula: see text] with microelectrodes showed that isoprenaline increased[Formula: see text] from 4.7 ± 1.2 to 5.5 ± 1.6 mM ( n = 16, P < 0.01) and shortened the action potential cycle length (ACL) from 338 ± 46 to 269 ± 35 ms ( n = 16, P < 0.01). However, increasing the action potential rate by pacing produced a much smaller increase in[Formula: see text]. Changes in[Formula: see text] and ACL produced by isoprenaline were blocked by Cs+. The selective hyperpolarization-activated inward current ( If) blocker ZD-7288 decreased [Formula: see text] from 5.2 ± 1.0 to 4.6 ± 1.3 mM ( n = 4, P < 0.01) and prolonged ACL from 394 ± 20 to 553 ± 68 ms ( n = 4, P < 0.01). The Ifblocker substantially inhibited the increase in[Formula: see text] produced by isoprenaline. Carbachol and Cs+decreased[Formula: see text] from 4.6 ± 1.4 to 3.9 ± 1.2 mM ( n = 15, P < 0.01) and from 4.9 ± 1.0 to 3.9 ± 1.3 mM ( n = 18, P < 0.01), respectively. In addition, carbachol and Cs+prolonged ACL from 345 ± 44 to 587 ± 100 ms ( n = 15, P < 0.01) and from 353 ± 30 to 464 ± 87 ms ( n = 18, P < 0.01), respectively. However, carbachol and Cs+almost did not change [Formula: see text] when SA node cells became quiescent in a 25.4 mM extracellular K+concentration. The results suggest that isoprenaline, ZD-7288, carbachol, or Cs+might have changed[Formula: see text] and action potential rate by possibly stimulating or inhibiting Ifcarried by Na+. Measurements of[Formula: see text] with SBFI showed that isoprenaline, carbachol, and Cs+produced [Formula: see text] changes that were similar to those measured with the microelectrodes.
Structured tree outflow condition for blood flow in larger systemic arteries
Authors: Olufsen Mette S.
Published: December 2017

A central problem in modeling blood flow and pressure in the larger systemic arteries is determining a physiologically based boundary condition so that the arterial tree can be truncated after a few generations. We have used a structured tree attached to the terminal branches of the truncated arterial tree in which the root impedance is estimated using a semianalytical approach based on a linearization of the viscous axisymmetric Navier-Stokes equations. This provides a dynamic boundary condition that maintains the phase lag between blood flow and pressure as well as the high-frequency oscillations present in the impedance spectra. Furthermore, it accommodates the wave propagation effects for the entire systemic arterial tree. The result is a model that is physiologically adequate as well as computationally feasible. For validation, we have compared the structured tree model with a pure resistance and a windkessel model as well as with measured data.
Pregnancy and steroid hormones enhance the vasodilation responses to CGRP in rats
Authors: Gangula P. R. R. , Zhao H. , Supowit S. , Wimalawansa S. , DiPette D. , Yallampalli C.
Published: December 2017

We recently reported that calcitonin gene-related peptide (CGRP) reversed the hypertension induced by nitric oxide inhibition in pregnant rats and that this effect appeared to be progesterone dependent. In the present study, we examined whether the vasodilator responses to CGRP are increased during pregnancy and whether these responses are steroid hormone dependent. Three groups of ovariectomized (Ovx) rats ( n = 4–8 rats/group) were studied 3 days after daily treatment (subcutaneous injection) with progesterone (P; 2 mg/injection, twice daily for 3 days, in 0.2 ml of sesame oil), 17β-estradiol (E; 2.5 μg/injection, twice daily for 3 days, in 0.2 ml of sesame oil), or vehicle (sesame oil). A fourth group ( n = 6 rats) of pregnant rats was studied on day 19of gestation. A fifth group of adult, nonpregnant rats ( n = 6 rats), regardless of stage of estrous cycle, was also used in this study. Mean arterial blood pressure (MAP) was continuously monitored in fully awake and free-moving instrumented rats. MAP was measured before and after administration of either saline or varying bolus doses of CGRP (9–360 pmol/kg body wt). CGRP produced a dose-dependent decrease in MAP in all rats with a significant ( P < 0.05) reduction in MAP beginning with a CGRP dose of 90 pmol/kg and with maximal effects observed at 360 pmol/kg. Decreases in MAP in response to CGRP were significantly ( P < 0.05) greater in pregnant compared with nonpregnant rats. Similarly to pregnant rats, Ovx rats given both E and P treatments produced greater decreases in MAP in response to CGRP at 90, 180, and 360 pmol/kg doses compared with both ovary-intact and Ovx nonpregnant rats, which were not different from each other. In summary, these data show that 1) the hypotensive effects of CGRP are dose dependent and 2) the hypotensive effects of CGRP are enhanced during pregnancy and in Ovx rats treated with either E or P. Therefore, we suggest that the decrease in vascular tone that is seen during pregnancy may be mediated, at least in part, by a sex steroid hormone-induced increase in the vascular sensitivity to the vasodilator effects of CGRP.
Norepinephrine-stimulated MAP kinase activity enhances cytokine-induced NO production by rat cardiac myocytes
Authors: Kan Hong , Xie Zirong , Finkel Mitchell S.
Published: December 2017

The effect of norepinephrine (NE) on cytokine-stimulated nitric oxide (NO) production by cardiac myocytes has not been previously reported. NE alone caused no significant increase in [Formula: see text] levels over vehicle. Addition of NE to interleukin-1β (IL-1β) significantly increased inducible NO synthase (iNOS) mRNA expression, iNOS protein, and [Formula: see text] production vs. IL-1β alone. Addition of the α-adrenergic blocker prazosin or the β-adrenergic blocker propranolol partially reduced the NE-mediated increase in iNOS mRNA expression and[Formula: see text] production. Addition of prazosin and propranolol together completely abolished the NE-induced increase in iNOS mRNA expression and[Formula: see text] production. NE significantly enhanced mitogen-activated protein (MAP) kinase activity that was reduced by prazosin, propranolol, and PD-98059, a selective MAP kinase kinase inhibitor. Addition of PD-98059 reduced the NE-mediated increase in iNOS mRNA expression and [Formula: see text]production. We report for the first time that NE enhances IL-1β-stimulated NO production by activation of α- and β-adrenergic receptors through a novel MAP kinase mechanism.
Ouabain- and central sodium-induced hypertension depend on the ventral anteroventral third ventricle region
Authors: Veerasingham Shereeni J. , Leenen Frans H. H.
Published: December 2017

To examine the role of the ventral anteroventral third ventricle (vAV3V) in the hypertension induced by chronic subcutaneous ouabain and intracerebroventricular hypertonic saline, neurons in this area were destroyed by microinjection of an excitotoxin, ibotenic acid. Sham-operated or lesioned Wistar rats were administered ouabain (50 μg/day) or placebo for 3 wk from subcutaneously implanted controlled release pellets or artificial cerebrospinal fluid (CSF) or CSF containing 0.8 mol/l NaCl (5 μl/h) infused intracerebroventricularly for 2 wk. At the end of the experiment, mean arterial pressure (MAP) and heart rate at rest and in response to ganglionic blockade by intravenous hexamethonium (30 mg/kg) were assessed. In rats infused with hypertonic saline, responses to air jet stress were also assessed. Baseline MAP in sham-operated rats receiving intracerebroventricular hypertonic saline or subcutaneous ouabain was significantly higher than in control rats (115 ± 1 vs. 97 ± 3 and 121 ± 3 vs. 103 ± 3 mmHg, respectively). vAV3V lesions abolished the increase in MAP elicited by chronic infusion of hypertonic saline or administration of ouabain. Sham-operated rats treated with hypertonic saline or ouabain exhibited significantly enhanced decreases in MAP to hexamethonium, but lesioned rats did not. Rats infused with hypertonic saline demonstrated enhanced responses to air jet stress that were similar in sham-operated and lesioned rats. These results demonstrate that neurons in the vAV3V are essential for the hypertension induced by intracerebroventricular hypertonic saline and subcutaneous ouabain, possibly by increasing sympathetic tone. Cardiovascular responses to air jet stress appear not to be mediated by the vAV3V.
Positive force- and [Ca2+]i-frequency relationships in rat ventricular trabeculae at physiological frequencies
Authors: Layland Joanne , Kentish Jonathan C.
Published: December 2017

The isometric force-frequency relationship of isolated rat ventricular trabeculae (diameter <250 μm) was examined at 24, 30, and 37°C at stimulation frequencies (0.1–12 Hz) encompassing the physiological range. Some muscles were microinjected with fura PE3 to monitor the diastolic and systolic intracellular concentration of Ca2+([Ca2+]i). At a near-physiological external Ca2+ concentration ([Ca2+]o) of 1 mM, a positive force-frequency relationship was demonstrated at all temperatures. The force-frequency relationship became negative at high frequencies (e.g., >6 Hz at 30°C) at 1 mM [Ca2+]oor at low frequencies at 8 mM [Ca2+]o. The twitch and Ca2+ transient became shorter as stimulation frequency increased; these changes were related to changes in systolic, rather than diastolic, [Ca2+]iand were not blocked by inhibitors of Ca2+/calmodulin-dependent protein kinase II. The positive force-frequency relationship of rat trabeculae was caused by a frequency-dependent loading of the sarcoplasmic reticulum (SR) with Ca2+. We suggest that at high frequencies, or under conditions of Ca2+ overload, this loading saturates. Processes that tend to decrease SR Ca2+ release will then predominate, resulting in a negative force-frequency relationship.
Adenosine A1receptor-mediated antiadrenergic effects are modulated by A2areceptor activation in rat heart
Authors: Norton Gavin R. , Woodiwiss Angela J. , McGinn Robert J. , Lorbar Mojca , Chung Eugene S. , Honeyman Thomas W. , Fenton Richard A. , Dobson James G. , Meyer Theo E.
Published: December 2017

Presently, the physiological significance of myocardial adenosine A2areceptor stimulation is unclear. In this study, the influence of adenosine A2areceptor activation on A1receptor-mediated antiadrenergic actions was studied using constant-flow perfused rat hearts and isolated rat ventricular myocytes. In isolated perfused hearts, the selective A2areceptor antagonists 8-(3-chlorostyryl)caffeine (CSC) and 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385) potentiated adenosine-mediated decreases in isoproterenol (Iso; 10−8M)-elicited contractile responses (+dP/d tmax) in a dose-dependent manner. The effect of ZM-241385 on adenosine-induced antiadrenergic actions was abolished by the selective A1receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (10−7M), but not the selective A3receptor antagonist 3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(±)-dihydropyridine-3,5-dicarboxylate (MRS-1191, 10−7M). The A2areceptor agonist carboxyethylphenethyl-aminoethyl-carboxyamido-adenosine (CGS-21680) at 10−5M attenuated the antiadrenergic effect of the selective A1receptor agonist 2-chloro- N6-cyclopentyladenosine (CCPA), whereas CSC did not influence the antiadrenergic action of this agonist. In isolated ventricular myocytes, CSC potentiated the inhibitory action of adenosine on Iso (2 × 10−7M)-elicited increases in intracellular Ca2+concentration ([Ca2+]i) transients but did not influence Iso-induced changes in [Ca2+]itransients in the absence of exogenous adenosine. These results indicate that adenosine A2areceptor antagonists enhance A1-receptor-induced antiadrenergic responses and that A2areceptor agonists attenuate (albeit to a modest degree) the antiadrenergic actions of A1receptor activation. In conclusion, the data in this study support the notion that an important physiological role of A2areceptors in the normal mammalian myocardium is to reduce A1receptor-mediated antiadrenergic actions.
Dispersion-based reentry: mechanism of initiation of ventricular tachycardia in isolated rabbit hearts
Authors: Robert Emmanuelle , Aya A. Guy M. , de la Coussaye Jean E. , Péray Pascale , Juan Jean-Marie , Brugada Josep , Davy Jean-Marc , Eledjam Jean-Jacques
Published: December 2017

The aim of the study was to determine whether facilitation of reentry by potassium-channel openers is related to dispersion of refractoriness and/or modification of anisotropic properties of ventricular myocardium. The dispersion of ventricular effective refractory period (VERP), longitudinal and transverse ventricular conduction velocities (θL and θT, respectively), and wavelength [λ = VERP × θ(L or T)] were studied in Langendorff-perfused left ventricular epicardium in 20 rabbits during infusion of incremental doses of levcromakalim or nicorandil. Dispersion of refractoriness was assessed using standard deviation of VERP mean (SD-VERP), dispersion index (DI; SD-VERP/mean VERP), and maximum dispersion (Dmax = VERPmax − VERPmin). Ventricular conduction velocities and anisotropic ratio were not modified, whatever the dose used. VERP and λ were significantly shortened at high concentrations of levcromakalim and nicorandil. At these doses, SD-VERP, DI, and Dmax were increased significantly. Analysis of ventricular tachycardia induction, performed using a high-resolution ventricular mapping system, confirmed that heterogeneity and shortening of VERP were factors inducing functional conduction block. Our data suggest that, in rabbit left ventricular epicardium, functional conduction block facilitating the occurrence of reentry could be initiated by shortening and, especially, by dispersion of refractoriness during infusion of potassium-channel openers.
Synchrotron microangiography reveals configurational changes and to-and-fro flow in intramyocardial vessels
Authors: Mori Hidezo , Tanaka Etsuro , Hyodo Kazuyuki , Mohammed Minhaz Uddin , Sekka Takafumi , Ito Kunihiksa , Shinozaki Yoshiro , Tanaka Akira , Nakazawa Hiroe , Abe Sumihisa , Handa Shunnosuke , Kubota Misao , Tanioka Kenkichi , Umetani Keiji , Ando Masami
Published: December 2017

In 8 dogs, in situ microangiography using synchrotron radiation visualized penetrating transmural arteries (PTAs) with a diameter of >60 μm and allowed quantitation of vessel diameters of >140 μm. Myocardial contraction reduced the vascular short-axial diameters to 87 ± 17% ( n = 62, P < 0.001, paired t-test) of the end-diastolic values and increased the longitudinal dimension to 129 ± 5% ( n = 45, P < 0.001). The diameter reduction in the subendocardial PTA segments was significantly more marked than that in the subepicardial PTA segments (60 ± 12 vs. 88 ± 12%, n=13, P < 0.001, paired t-test). Intracoronary administration of dobutamine (0.1 μg ⋅ kg−1 ⋅ min−1) increased, and in contrast, partial clamping of the coronary artery (ischemia) decreased, the configurational changes. To-and-fro blood flow was clearly observed in PTAs with visual identification of capacitive backflow, resistive forward flow during ischemia on coronary arteriography, and even under baseline conditions in coronary venography. Thus this method advances our understanding of mechanical influences on the coronary circulation.
A canine model of chronic ischemic cardiomyopathy: characterization of regional flow-function relations
Authors: Firoozan Soroosh , Wei Kevin , Linka Andre , Skyba Danny , Goodman N. Craig , Kaul Sanjiv
Published: December 2017

The controversy regarding the mechanism(s) of left ventricular (LV) dysfunction in chronic coronary artery disease is, in part, related to the lack of an appropriate animal model for this condition. We have developed such a model by placing Ameroid constrictors on proximal portions of coronary arteries in dogs who were euthanized (mean of 6 wk) after the development of severe global LV dysfunction noted on two-dimensional echocardiography. The LV end-systolic size nearly doubled ( P < 0.001) over the observation period, and the percent change in LV size from end diastole to end systole decreased by >50% ( P< 0.001). Regional dysfunction was noted in 23 of 24 myocardial beds analyzed within regions showing no gross evidence of infarction. In 10 of these beds, severe dysfunction was noted without a decrease in radiolabeled microsphere-derived myocardial blood flow (MBF). In 13 myocardial beds, decrease in function was associated with a decrease in MBF ( P < 0.001), with close coupling noted between percent wall thickening and MBF. In the beds that exhibited an ultimate decrease in MBF, the decrease in function preceded the decrease in MBF. In conclusion, we describe chronic LV dysfunction in a canine model of multivessel stenosis that closely mimics chronic ischemic LV dysfunction in humans. Whereas regional function is severely reduced in this model, MBF is varied in different segments and at different times during the observation period. These results provide new insights regarding flow-function relations in chronic ischemic LV dysfunction.
Possible obligatory functions of cyclic nucleotides in hypercapnia-induced cerebral vasodilation in adult rats
Authors: Wang Q. , Bryowsky J. , Minshall R. D. , Pelligrino D. A.
Published: December 2017

Current evidence suggests that nitric oxide (NO) and vasodilating prostanoids, possibly via the actions of cGMP and cAMP, play permissive roles in hypercapnic cerebral vasodilation. The present study examined whether cGMP and cAMP have obligatory functions in hypercapnia. Using a closed cranial window in adult rats, we measured pial arteriolar diameters and periarachnoid cerebrospinal fluid (pCSF) cyclic nucleotide levels during normo- and hypercapnia and in the presence or absence of inhibitors of neuronal NO synthase (nNOS) or cyclooxygenase (COX). Also, we measured cGMP and cAMP contents in primary neuronal and astrocyte cultures, at different levels of CO2. Hypercapnia (arterial[Formula: see text] 65 mmHg)-induced pial arteriolar dilation was accompanied by 70–80% elevations in pCSF cGMP and cAMP. Inhibition of nNOS with 7-nitroindazole (7-NI) significantly reduced both the CO2-induced arteriolar dilation (by 77%) and the pCSF cGMP and cAMP increases (by 60–70%). Inhibition of COX with indomethacin reduced arteriolar CO2reactivity (by 83%) and pCSF cyclic nucleotide increases (by 80–100%). In neuronal cultures a transient NO-dependent increase in cGMP, but not cAMP, was seen when the CO2level was raised from 5 to 14%. No changes were seen in astrocytes. The 7-NI and indomethacin-inhibitable increases in pial arteriolar diameter and cyclic nucleotide production during hypercapnia suggest a link between these two responses. One possible, although not exclusive, interpretation of these findings is that the cyclic nucleotides have an obligatory function in the CO2response. The large overlap in the abilities of nNOS and COX inhibitors to elicit those effects further implies interactions (“cross talk”) between the cGMP and cAMP vasodilating pathways. The in vitro data suggest that hypercapnia stimulates NO production in neurons.
Adenosine-induced activation of ATP-sensitive K+channels in excised membrane patches is mediated by PKC
Authors: Hu Keli , Li Gui-Rong , Nattel Stanley
Published: December 2017

Both protein kinase C (PKC) and adenosine receptor activation have been shown to enhance ATP-sensitive K+(KATP) channels. The present studies were designed to determine whether PKC mediates adenosine effects on the KATPchannel. The dependence of KATPchannel activity ( nPo) on intracellular ATP concentration ([ATP]i) was determined in excised rabbit ventricular membrane patches. External adenosine (100 μM in the pipette solution) significantly increased KATPnPoat all [ATP]ibetween 5 and 50 μM by decreasing channel sensitivity to [ATP]i(dissociation constant increased from 7.4 ± 0.8 to 22.2 ± 3.1 μM, P < 0.001), an effect blocked by the adenosine receptor antagonist 8-phenyltheophylline (10 μM). When the highly selective PKC blocker bisindolylmaleimide (BIM) was included in the internal (bath) solution, the KATP-stimulating action of adenosine was prevented. The addition of BIM to the superfusate rapidly inhibited KATPchannels activated by adenosine. Endogenous PKC activation by phorbol 12,13-didecanoate (PDD), but not administration of the inactive congener 4α-PDD, enhanced KATPactivity. Internal guanosine 5′- O-(2-thiodiphosphate) prevented KATPactivation by adenosine, an effect which could be overridden by exposure to PDD. We conclude that PKC mediates adenosine activation of KATPchannels in excised membrane patches in a membrane-delimited fashion.