bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypoxia-induced alterations in Ca2+mobilization in brain microvascular endothelial cells
Authors: Kimura Chiwaka , Oike Masahiro , Ito Yushi
Published: December 2017

To investigate the possible cellular mechanisms of the ischemia-induced impairments of cerebral microcirculation, we investigated the effects of hypoxia/reoxygenation on the intracellular Ca2+ concentration ([Ca2+]i) in bovine brain microvascular endothelial cells (BBEC). In the cells kept in normal air, ATP elicited Ca2+ oscillations in a concentration-dependent manner. When the cells were exposed to hypoxia for 6 h and subsequent reoxygenation for 45 min, the basal level of [Ca2+]i was increased from 32.4 to 63.3 nM, and ATP did not induce Ca2+ oscillations. Hypoxia/reoxygenation also inhibited capacitative Ca2+entry (CCE), which was evoked by thapsigargin (Δ[Ca2+]i-CCE: control, 62.3 ± 3.1 nM; hypoxia/reoxygenation, 17.0 ± 1.8 nM). The impairments of Ca2+ oscillations and CCE, but not basal [Ca2+]i, were restored by superoxide dismutase and the inhibitors of mitochondrial electron transport, rotenone and thenoyltrifluoroacetone (TTFA). By using a superoxide anion (O2 −)-sensitive luciferin derivative MCLA, we confirmed that the production of O2 − was induced by hypoxia/reoxygenation and was prevented by rotenone and TTFA. These results indicate that hypoxia/reoxygenation generates O2 − at mitochondria and impairs some Ca2+mobilizing properties in BBEC.
Effects of whole body heating on dynamic baroreflex regulation of heart rate in humans
Authors: Crandall C. G. , Zhang R. , Levine B. D.
Published: December 2017

The purpose of this project was to identify whether dynamic baroreflex regulation of heart rate (HR) is altered during whole body heating. In 14 subjects, dynamic baroreflex regulation of HR was assessed using transfer function analysis. In normothermic and heat-stressed conditions, each subject breathed at a fixed rate (0.25 Hz) while beat-by-beat HR and systolic blood pressure (SBP) were obtained. Whole body heating significantly increased sublingual temperature, HR, and forearm skin blood flow. Spectral analysis of HR and SBP revealed that the heat stress significantly reduced HR and SBP variability within the high-frequency range (0.2–0.3 Hz), reduced SBP variability within the low-frequency range (0.03–0.15 Hz), and increased the ratio of low- to high-frequency HR variability (all P < 0.01). Transfer function gain analysis showed that the heat stress reduced dynamic baroreflex regulation of HR within the high-frequency range (from 1.04 ± 0.06 to 0.54 ± 0.6 beats · min−1 · mmHg−1; P < 0.001) without significantly affecting the gain in the low-frequency range ( P = 0.63). These data suggest that whole body heating reduced high-frequency dynamic baroreflex regulation of HR associated with spontaneous changes in blood pressure. Reduced vagal baroreflex regulation of HR may contribute to reduced orthostatic tolerance known to occur in humans during heat stress.
Diurnal variation of flow-mediated vasodilation in healthy premenopausal women
Authors: Ringqvist Åsa , Caidahl Kenneth , Petersson Ann-Sofi , Wennmalm Åke
Published: December 2017

The present study was designed to test the hypothesis of a diurnal variation of endothelial function. Sixteen healthy, nonsmoking women were studied, each on four occasions during one 24-h period (2:00 PM, 8:00 PM, 2:00 AM, and 8:00 AM). Endothelial function was assessed by ultrasound determinations of flow-mediated vasodilation (FMD%) in the brachial artery. FMD% was contrasted with endothelium-independent vasodilation, i.e., nitroglycerine-induced vasodilation (NTG%). Additionally, plasma concentrations and urinary excretion of nitrate and cGMP were analyzed. FMD% and NTG% displayed diurnal, albeit not parallel, patterns of variation. Whereas FMD% gradually increased from 2:00 PM and peaked at 2:00 AM (means ± SE: 3.1 ± 0.4, 4.4 ± 0.4, 5.1 ± 0.9, and 3.9 ± 0.8%), the NTG% demonstrated a nadir at 2:00 AM. Plasma levels and urinary excretion of nitrate and cGMP did not display diurnal variation and no clear association with the variations seen in FMD% and NTG%. This study demonstrates a diurnal variation in both endothelium-dependent and -independent vasodilation in the brachial artery of healthy women. The background and possible implication of such a variation require further studies.
Angiotensin II enhances β-adrenergic receptor-mediated vasorelaxation in aortas from young but not old rats
Authors: Schutzer William E. , Xue Hong , Reed John F. , Roullet Jean-Baptiste , Anderson Sharon , Mader Scott L.
Published: December 2017

β-Adrenergic receptor (β-AR)-mediated (cAMP-dependent) vasorelaxation declines with advancing age. It has been shown that angiotensin II (ANG II), a potent vasoconstrictor, enhances cAMP-mediated vasorelaxation. Therefore, we questioned whether ANG II could reverse age-related, impaired β-AR-mediated vasorelaxation and cAMP production. Pretreatment of aortic rings from 6-wk-old or 6-mo-old male Fischer 344 rats with ANG II significantly enhanced vasorelaxation induced by isoproterenol (Iso), a β-AR agonist, and forskolin, a direct activator of adenylyl cyclase, but not dibutyryl-cAMP or isobutylmethylxanthine. The ANG II effect was blocked by losartan but not PD-123319 and was not observed in the aortas from 12- and 24-mo-old animals. Iso-stimulated cAMP production in the aorta was enhanced in the presence of ANG II in the 6-wk-old and 6-mo-old age groups only. Results suggest ANG II cannot reverse the age-related impairment in β-AR-dependent vasorelaxation. We conclude aging may affect a factor common to both ANG II-receptors and β-AR signaling pathways or aging may impair cross-talk between these two receptor pathways.
TNF-α increases entry of macromolecules into luminal endothelial cell glycocalyx
Authors: Henry Charmaine B. S. , Duling Brian R.
Published: December 2017

The endothelial luminal glycocalyx has been largely ignored as a target in vascular pathophysiology even though it occupies a key location. As a model of the inflammatory response, we tested the hypothesis that tumor necrosis factor-α (TNF-α) can alter the properties of the endothelial apical glycocalyx. In the intact hamster cremaster microcirculation, fluorescein isothiocyanate (FITC)-labeled Dextrans 70, 580, and 2,000 kDa are excluded from a region extending from the endothelial surface almost 0.5 μm into the lumen. This exclusion zone defines the boundaries of the glycocalyx. Red blood cells (RBC) under normal flow conditions are excluded from a region extending even farther into the lumen. The cremaster microcirculation was pretreated with topical or intrascrotal applications of TNF-α. After infusion of FITC-dextran, FITC-albumin, or FITC-immunoglubulin G (IgG) via a femoral cannula, microvessels were observed with bright-field and fluorescence microscopy to obtain estimates of the anatomic diameters and the widths of fluorescent tracer columns and of the RBC columns (means ± SE). After 2 h of intrascrotal TNF-α exposure, there was a significant increase in access of FITC-Dextrans 70 and 580 to the space bounded by the apical glycocalyx in arterioles, capillaries, and venules, but no significant change in access of FITC-Dextran 2,000. The effects of TNF-α could be observed as early as 20 min after the onset of topical application. TNF-α treatment also significantly increased the penetration rate of FITC-Dextran 40, FITC-albumin, and FITC-IgG into the glycocalyx and caused a significant increase in the intraluminal volume occupied by flowing RBC. White blood cell adhesion increased during TNF-α application, and we used the selectin antagonist fucoidan to attenuate leukocyte adhesion during TNF-α stimulation. This did not inhibit the TNF-α-mediated increase in permeation of the glycocalyx. These results show that proinflammatory cytokines can cause disruption of the endothelial apical glycocalyx, leading to an increased macromolecular permeation in the absence of an increase in leukocyte recruitment.
Regulation of endothelial heme oxygenase activity during hypoxia is dependent on chelatable iron
Authors: Ryter Stefan W. , Si Minliang , Lai Chen-Ching , Su Ching-Yuan
Published: December 2017

The regulation of heme oxygenase (HO) activity and its dependence on iron was studied in bovine aortic endothelial cells (BAEC) subjected to hypoxia-reoxygenation (H/R). HO activity was induced by hypoxia (10 h) and continued to increase during the reoxygenation phase. HO-1 protein levels were strongly induced by hypoxia from undetectable levels and remained elevated at least 8 h postreoxygenation. Addition of the Fe3+chelator desferrioxamine mesylate (DFO) or the Fe2+chelator o-phenanthroline during hypoxia alone or during the entire H/R period inhibited the induction of HO activity and HO-1 protein levels. However, DFO had no effect and o-phenanthroline had a partial inhibitory effect on HO activity and protein levels when added only during reoxygenation. Loading of BAEC with Fe3+enhanced the activation of the HO-1 gene by H/R, whereas loading withl-aminolevulinic acid, which stimulates heme synthesis, had little effect. These results suggest that chelatable iron participates in regulating HO expression during hypoxia.
Renal vasodilatory influence of endogenous carbon monoxide in chronically hypoxic rats
Authors: O'Donaughy Theresa L. , Walker Benjimen R.
Published: December 2017

Chronic hypoxia (CH) attenuates systemic vasoconstriction to a variety of agonists in conscious rats. Recent evidence suggests that similarly diminished responses to vasoconstrictors in aortic rings from CH rats may be due to increased endothelial heme oxygenase (HO) activity and enhanced production of the vasodilator carbon monoxide (CO). Thus we hypothesized that a hypoxia-induced increase in HO activity is responsible for decreased vasoconstrictor responsiveness observed in conscious CH rats. CH (4 wk at 0.5 atm) and control rats were renal denervated and instrumented for the measurement of renal blood flow (RBF) and blood pressure. First, renal vasoconstrictor responses to graded intravenous infusion of phenylephrine (PE) were assessed in conscious rats. CH rats demonstrated significantly diminished renal vasoconstrictor responses to PE compared with control responses that persisted even with acute restoration of normoxia. In additional experiments, CH rats exhibited increased renal vascular resistance and decreased RBF in response to the HO inhibitor zinc protoporphyrin IX (11 μmol/kg iv), whereas renal hemodynamics were unaffected by the inhibitor in control animals. Furthermore, we demonstrated greater HO enzyme activity in renal tissue from CH rats compared with controls. These data suggest that enhanced HO activity contributes a tonic vasodilatory influence in the renal vasculature of CH rats that may be responsible for the diminished sensitivity to vasoconstrictor agonists observed under these conditions.
Pharmacological profile of depressor response elicited by sarthran in rat ventrolateral medulla
Authors: Ito Satoru , Sved Alan F.
Published: December 2017

Injection of sarthran, an angiotensin receptor antagonist, bilaterally into the rostral ventrolateral medulla (RVLM) of α-chloralose-anesthetized rats decreases arterial pressure (AP) to the same extent as total autonomic blockade. This response is not reproduced by selective AT1antagonists. To examine the pharmacological profile of the response elicited by [Sar1, Thr8]ANG II (sarthran), the ability of angiotensin analogs to inhibit the effect of sarthran injected into the RVLM was tested. Coinjection of angiotensin II (ANG II) prevented the sarthran-evoked decrease in AP, but this action of ANG II was markedly attenuated by pretreatment of the RVLM with the aminopeptidase inhibitor amastatin. Coinjection of ANG(3–8) or a selective agonist of AT4receptors prevented the effect of sarthran injected into the RVLM. ANG(1–7) was also able to prevent the effect of sarthran. None of the angiotensin fragments tested substantially altered blood pressure when injected alone into the RVLM. These results suggest that the depressor action of sarthran injected into the RVLM is not dependent on ANG II receptors, though the nature of the site or sites of action of sarthran within the RVLM remains uncertain.
Effects of exercise training on cardiac function, gene expression, and apoptosis in rats
Authors: Jin Hongkui , Yang Renhui , Li Wei , Lu Hsienwie , Ryan Anne M. , Ogasawara Annie K. , Van Peborgh John , Paoni Nicholas F.
Published: December 2017

This study determined the effects of exercise training on cardiac function, gene expression, and apoptosis. Rats exposed to a regimen of treadmill exercise for 13 wk had a significant increase in cardiac index and stroke volume index and a concomitant decrease in systemic vascular resistance compared with both age-matched and body weight-matched sedentary controls in the conscious state at rest. In exercise-trained animals, there was no change in the expression of several marker genes known to be associated with pathological cardiac adaptation, including atrial natriuretic factor, β-myosin heavy chain, α-skeletal and smooth muscle actins, and collagens I and III. Exercise training, however, produced a significant induction of α-myosin heavy chain, which was not observed in rats with myocardial infarction. No histological features of cardiac apoptosis were observed in the treadmill-trained rats. In contrast, apoptotic myocytes were detected in animals with myocardial infarction. In summary, exercise training improves cardiac function without evidence of cardiac apoptosis and produces a pattern of cardiac gene expression distinct from pathological cardiac adaptation.
Comparing cardiac action potentials recorded with metal and glass microelectrodes
Authors: Omichi Chikaya , Lee Moon-Hyoung , Ohara Toshihiko , Naik Ajay M. , Wang Nina C. , Karagueuzian Hrayr S. , Chen Peng-Sheng
Published: December 2017

Machine-pulled high-impedance glass capillary microelectrode is standard for transmembrane potential (TMP) recordings. However, it is fragile and difficult to impale, especially in beating myocardial tissues. We hypothesize that a high-impedance pure iridium metal electrode can be used as an alternative to the glass microelectrode for TMP recording. The TMPs were simultaneously recorded from isolated perfused swine right ventricles with a metal microelectrode and a standard glass microelectrode during pacing and during ventricular fibrillation. The basic morphology of TMP recorded with these electrodes was comparable. The action potential duration (APD) at 90% repolarization was 241 ± 29 ms for the metal microelectrode and 236 ± 31 ms for the glass microelectrode with a good correlation ( r = 0.99, P < 0.0001). The maximum slope value of the APD restitution curves during pacing was also significantly correlated. One metal microelectrode and >20 glass microelectrodes were needed per study. We conclude that, in isolated perfused swine right ventricles, the TMP recorded by the metal microelectrode is comparable with that recorded by the glass microelectrode. Because the metal microelectrode is more durable than the glass microelectrode, it can serve as an alternative for APD recording and for restitution analyses.
Decreased fractal component of human heart rate variability during non-REM sleep
Authors: Togo Fumiharu , Yamamoto Yoshiharu
Published: December 2017

The physiological significance of the fractal component of short-term, spontaneous heart rate variability (HRV) in humans remains unclear. The aim of the present study was to gain further information about the respective fractal components by extracting them from HRV, blood pressure variability (BPV), and instantaneous lung volume (ILV) time series via coarse graining spectral analysis in nine healthy subjects during waking and sleep states. The results show that the contribution made by the fractal component to the total variance in the beat-to-beat R-R interval declined significantly as the depth of non-rapid eye movement (non-REM) sleep increased, that the ILV time series was largely periodic (i.e., nonfractal), and that BPV was unaffected by sleep stage. Finally, the fractal component of HRV during REM sleep was found to be quite similar to that seen during waking. These results suggest that mechanisms involving electroencephalographic desynchronization and/or conscious states of the brain are reflected in the fractal component of HRV.
Induction of endothelial cell cytoplasmic lipid bodies during hypoxia
Authors: Scarfo Lisa M. , Weller Peter F. , Farber Harrison W.
Published: December 2017

Lipid bodies (LBs), lipid-rich cytoplasmic inclusions found in many cell types, seem to act as nonmembrane sites of eicosanoid formation. Because alterations in eicosanoid products have been demonstrated in endothelial cells (ECs) during hypoxia, we investigated induction of LBs in systemic and pulmonary ECs exposed to acute and/or chronic hypoxia. LBs in ECs were O2-concentration dependent, increasing approximately fivefold during acute exposure to 0% O2in both cell types. During chronic exposure to 3% O2, LBs were induced only in systemic ECs. LBs were not induced by other cellular stresses (heat shock or glucose deprivation). Subsequent studies suggested that protein kinase C-dependent and tyrosine kinase-dependent pathways are important in LB induction during hypoxia. PGH synthase was demonstrated in LBs in every case in which they were induced. These are the initial studies to demonstrate induction of LBs in ECs and to demonstrate LB induction during exposure to hypoxia in any cell type. These results imply that in ECs, LBs are structurally distinct inducible sites for synthesis of eicosanoid mediators.
Role of EP2and EP3PGE2receptors in control of murine renal hemodynamics
Authors: Audoly Laurent P. , Ruan Xiaoping , Wagner Victoria A. , Goulet Jennifer L. , Tilley Stephen L. , Koller Beverly H. , Coffman Thomas M. , Arendshorst William J.
Published: December 2017

The kidney plays a central role in long-term regulation of arterial blood pressure and salt and water homeostasis. This is achieved in part by the local actions of paracrine and autacoid mediators such as the arachidonic acid-prostanoid system. The present study tested the role of specific PGE2E-prostanoid (EP) receptors in the regulation of renal hemodynamics and vascular reactivity to PGE2. Specifically, we determined the extent to which the EP2and EP3receptor subtypes mediate the actions of PGE2on renal vascular tone. Renal blood flow (RBF) was measured by ultrasonic flowmetry, whereas vasoactive agents were injected directly into the renal artery of male mice. Studies were performed on two independent mouse lines lacking either EP2or EP3(−/−) receptors and the results were compared with wild-type controls (+/+). Our results do not support a unique role of the EP2receptor in regulating overall renal hemodynamics. Baseline renal hemodynamics in EP2−/− mice [RBF EP2−/−: 5.3 ± 0.8 ml · min−1· 100 g kidney wt−1; renal vascular resistance (RVR) 19.7 ± 3.6 mmHg · ml−1· min · g kidney wt] did not differ statistically from control mice (RBF +/+: 4.0 ± 0.5 ml · min−1· 100 g kidney wt−1; RVR +/+: 25.4 ± 4.9 mmHg · ml−1· min · 100 g kidney wt−1). This was also the case for the peak RBF increase after local PGE2(500 ng) injection into the renal artery (EP2−/−: 116 ± 4 vs. +/+: 112 ± 2% baseline RBF). In contrast, we found that the absence of EP3receptors in EP3−/− mice caused a significant increase (43%) in basal RBF (7.9 ± 0.8 ml · min−1· g kidney wt−1, P < 0.05 vs. +/+) and a significant decrease (41%) in resting RVR (11.6 ± 1.4 mmHg · ml−1· min · g kidney wt−1, P < 0.05 vs. +/+). Local administration of 500 ng of PGE2into the renal artery caused more pronounced renal vasodilation in EP3−/− mice (128 ± 2% of basal RBF, P < 0.05 vs. +/+). We conclude that EP3receptors mediate vasoconstriction in the kidney of male mice and its actions are tonically active in the basal state. Furthermore, EP3receptors are capable of buffering PGE2-mediated renal vasodilation.
Postischemic anti-inflammatory effects of bradykinin preconditioning
Authors: Shigematsu Sakuji , Ishida Shuji , Gute Dean C. , Korthuis Ronald J.
Published: December 2017

We sought to determine the mechanisms whereby brief administration of bradykinin (bradykinin preconditioning, BK-PC) before prolonged ischemia followed by reperfusion (I/R) prevents postischemic microvascular dysfunction. Intravital videomicroscopic approaches were used to quantify I/R-induced leukocyte/endothelial cell adhesive interactions and microvascular barrier disruption in single postcapillary venules of the rat mesentery. I/R increased the number of rolling, adherent, and emigrated leukocytes and enhanced venular albumin leakage, effects that were prevented by BK-PC. The anti-inflammatory effects of BK-PC were largely prevented by concomitant administration of a B2-receptor antagonist but not by coincident B1receptor blockade, nitric oxide (NO) synthase inhibition, or cyclooxygenase blockade. However, NO synthase blockade during reperfusion after prolonged ischemia was effective in attenuating the anti-inflammatory effects of BK-PC. Pan protein kinase C (PKC) inhibition antagonized the beneficial effects of BK-PC but only when administered during prolonged ischemia. In contrast, specific inhibition of the conventional PKC isotypes failed to alter the effectiveness of BK-PC. These results indicate that bradykinin can be used to pharmacologically precondition single mesenteric postcapillary venules to resist I/R-induced leukocyte recruitment and microvascular barrier dysfunction by a mechanism that involves B2receptor-dependent activation of nonconventional PKC isotypes and subsequent formation of NO.
Validation and utility of novel volume reduction technique for determination of parallel conductance
Authors: White Paul A. , Brookes Carl I. O. , Ravn Hanne , Hjortdal Vibeke , Chaturvedi Rajiv R. , Redington Andrew N.
Published: December 2017

The parallel conductance volume, created by the conductivity of structures surrounding the ventricular blood pool, can be estimated by using a saline dilution technique. This paper examines the use of a novel volume reduction method, during a standard vena caval preload reduction maneuver, as an alternative to the routinely used saline dilution method to calibrate conductance catheter measurements in the left (LV) and right ventricle (RV) of animals and humans. The serial reproducibility of both methods was examined by measurement of percent difference, and by assessing the coefficient of repeatability 1) between two measurements within the same subject, 2) between the two techniques, and 3) interobserver variability. The effect of ventricular size and contractile state on the volume reduction technique was also observed. It was essential to ensure the technique was not affected by inotropic state. The volume reduction technique and saline dilution method were repeated at three different loading states (baseline, 5, and 10 μg · kg−1 · min−1 of dobutamine). The coefficient of repeatability between serial measurements was similar for both the volume reduction and saline dilution methods, and good interobserver variability was demonstrated. The volume reduction technique was compared with the saline dilution technique over a large range of ventricular sizes. No significant difference was observed in the RV or LV of adult humans or in the LV of neonatal pigs and children. There was no significant effect on either the saline dilution or the volume reduction technique as the inotropic state increased. In conclusion, the volume reduction technique is neither affected by ventricular size nor contractile state, is repeatable between different observers, and can be used to substitute the saline dilution method when preload reduction of the ventricle is being employed.
Noninvasive measurements of transmural myocardial metabolites using 3-D 31P NMR spectroscopy
Authors: Cho Yong K. , Merkle Hellmut , Zhang Jianyi , Tsekos Nikolaos V. , Bache Robert J. , Uǧurbil Kâmil
Published: December 2017

A completely noninvasive three-dimensional (3-D) static magnetic field magnitude spatially localized 31P spectroscopy technique has been developed and applied to study the in vivo canine myocardium at 9.4 T. The technique incorporates both Fourier series windows and selective Fourier transform methods utilizing all three orthogonal gradients for 3-D phase encoding. The number of data acquisitions for each phase-encoding step was weighted according to the Fourier coefficients to define cylindrical voxels. Spatially localized 31P spectra can be generated for voxels of desired location within the field of view as a postprocessing step. The quality of localization was first demonstrated by using a three-compartment phantom. The technique was then applied to in vivo canine models and yielded 31P cardiac spectra with an excellent signal-to-noise ratio. The in vivo validation experiments, using an implanted 2-phosphoenolpyruvate-containing marker, demonstrated that the technique is capable of measuring at least two transmural layers of left ventricular myocardium representing the subepicardium and subendocardium.
12-Lipoxygenase in porcine coronary microcirculation: implications for coronary vasoregulation
Authors: Zink Martin H. , Oltman Christine L. , Lu Tong , Katakam Prasad V. G. , Kaduce Terry L. , Lee Hon-Chi , Dellsperger Kevin C. , Spector Arthur A. , Myers Paul R. , Weintraub Neal L.
Published: December 2017

Noncyclooxygenase metabolites of arachidonic acid (AA) have been proposed to mediate endothelium-dependent vasodilation in the coronary microcirculation. Therefore, we examined the formation and bioactivity of AA metabolites in porcine coronary (PC) microvascular endothelial cells and microvessels, respectively. The major noncyclooxygenase metabolite produced by microvascular endothelial cells was 12( S)-hydroxyeicosatetraenoic acid (HETE), a lipoxygenase product. 12( S)-HETE release was markedly increased by pretreatment with 13( S)-hydroperoxyoctadecadienoic acid but not by the reduced congener 13( S)-hydroxyoctadecadienoic acid, suggesting oxidative upregulation of 12( S)-HETE output. 12( S)-HETE produced potent relaxation and hyperpolarization of PC microvessels (EC50, expressed as −log[M] = 13.5 ± 0.5). Moreover, 12( S)-HETE potently activated large-conductance Ca2+-activated K+currents in PC microvascular smooth muscle cells. In contrast, 12( S)-HETE was not a major product of conduit PC endothelial AA metabolism and did not exhibit potent bioactivity in conduit PC arteries. We suggest that, in the coronary microcirculation, 12( S)-HETE can function as a potent hyperpolarizing vasodilator that may contribute to endothelium-dependent relaxation, particularly in the setting of oxidative stress.
KATP + channels, nitric oxide, and adenosine are not required for local metabolic coronary vasodilation
Authors: Tune Johnathan D. , Richmond Keith Neu , Gorman Mark W. , Feigl Eric O.
Published: December 2017

The role of ATP-sensitive K+ (KATP +) channels, nitric oxide, and adenosine in coronary exercise hyperemia was investigated. Dogs ( n = 10) were chronically instrumented with catheters in the aorta and coronary sinus and instrumented with a flow transducer on the circumflex coronary artery. Cardiac interstitial adenosine concentration was estimated from arterial and coronary venous plasma concentrations using a previously tested mathematical model. Experiments were conducted at rest and during graded treadmill exercise with and without combined inhibition of KATP + channels (glibenclamide, 1 mg/kg iv), nitric oxide synthesis ( N ω-nitro-l-arginine, 35 mg/kg iv), and adenosine receptors (8-phenyltheophylline, 3 mg/kg iv). During control exercise, myocardial oxygen consumption increased ∼2.9-fold, coronary blood flow increased ∼2.6-fold, and coronary venous oxygen tension decreased from 19.9 ± 0.4 to 13.7 ± 0.6 mmHg. Triple blockade did not significantly change the myocardial oxygen consumption or coronary blood flow response during exercise but lowered the resting coronary venous oxygen tension to 10.0 ± 0.4 mmHg and during exercise to 6.2 ± 0.5 mmHg. Cardiac adenosine levels did not increase sufficiently to overcome the adenosine receptor blockade. These results indicate that combined inhibition of KATP + channels, nitric oxide synthesis, and adenosine receptors lowers the balance between total oxygen supply and consumption at rest but that these factors are not required for local metabolic coronary vasodilation during exercise.
Transgenic incorporation of skeletal TnT into cardiac myofilaments blunts PKC-mediated depression of force
Authors: Montgomery David E. , Chandra Murali , Huang Qi-Quan , Jin Jian-Ping , Solaro R. John
Published: December 2017

Protein kinase C (PKC)-mediated phosphorylation of cardiac troponin I (cTnI) and troponin T (cTnT) has been shown to diminish maximum activation of myofilaments. The functional role of cTnI phosphorylation has been investigated. However, the impact of cTnT phosphorylation on myofilament force is not well studied. We tested the effect of endogenous PKC activation on steady-state tension development and Ca2+sensitivity in skinned fiber bundles from transgenic (TG) mouse hearts expressing fast skeletal TnT (fsTnT), which naturally lacks the PKC sites present in cTnT. The 12- O-tetradecanoylphorbol 13-acetate (TPA) treatment induced a 29% (46.1 ± 2.5 vs. 33.4 ± 2.6 mN/mm2) reduction in maximum tension in the nontransgenic (NTG) preparations ( n = 7) and was inhibited with chelerythrine. However, TPA did not induce a change in the maximum tension in the TG preparations ( n = 11). TPA induced a small but significant ( P < 0.02) increase in Ca2+sensitivity (untreated pCa50= 5.63 ± 0.01 vs. treated pCa50= 5.72 ± 0.01) only in TG preparations. In TG preparations,32P incorporation was not evident in TnT and was also significantly diminished in cTnI, compared with NTG. Our data indicate that incorporation of fsTnT into the cardiac myofilament lattice blunts PKC-mediated depression of maximum tension. These data also suggest that cTnT may play an important role in amplifying the myofilament depression induced by PKC-mediated phosphorylation of cTnI.
Maturation depresses cGMP-mediated decreases in [Ca2+]i and Ca2+ sensitivity in ovine cranial arteries
Authors: Nauli Surya M. , Zhang Lubo , Pearce William J.
Published: December 2017

Because cerebrovascular cGMP levels vary significantly during maturation, we examined the hypothesis that the ability of cGMP to relax cerebral arteries also changes during maturation. In concentration-response experiments, potassium-induced tone in basilar arteries was significantly more sensitive to a nonmetabolizable cell-permeant cGMP analogue 8-( p-chlorophenylthio)-cGMP (8-pCPT-cGMP) in term fetal [−log one-half maximal concentration (EC50) = 4.4 ± 0.1 M] than in adult (−log EC50 = 4.0 ± 0.1 M) ovine basilar arteries. Serotonin-induced tone also revealed significantly greater sensitivity to the cGMP analogue in fetal (−log EC50 = 4.9 ± 0.1 M) than in adult (−log EC50 = 4.7 ± 0.1 M) basilars. In fura 2-loaded preparations, 8-pCPT-cGMP had no significant effect on cytosolic calcium concentrations in potassium-contracted arteries but at 6 μM significantly reduced calcium only in fetal basilars (Δ = 33 ± 8%). Higher 8-pCPT-cGMP concentrations reduced cytosolic calcium in both fetal and adult basilars. Similarly, in both potassium- and 5-hydroxytryptamine (5-HT)-contracted preparations, low concentrations of 8-pCPT-cGMP reduced myofilament calcium sensitivity only in fetal basilars (Δ = 29 ± 6 and Δ = 42 ± 10%, respectively), whereas higher concentrations reduced calcium sensitivity in both fetal and adult arteries. In β-escin-permeabilized arteries, equivalent reductions in basal and agonist-enhanced myofilament calcium sensitivity were produced by much lower 8-pCPT-cGMP concentrations in fetal (172 and 61 μM, respectively) than in adult (410 and 231 μM, respectively) basilars. The mechanisms mediating cGMP-induced vasorelaxation appear similar in fetal and adult arteries, with the exception that they are much more sensitive to cGMP in fetal than adult arteries. These age-related differences in the sensitivity of cytosolic calcium concentration, basal, and agonist-enhanced myofilament calcium sensitivity to cGMP can easily explain why both potassium- and 5-HT-induced tone are more sensitive to cGMP in fetal than adult cerebral arteries.
Pituitary adenylate cyclase-activating polypeptide activates KATPcurrent in rat atrial myocytes
Authors: Baron Anne , Monnier Dominique , Roatti Angela , Baertschi Alex J.
Published: December 2017

Because the electrophysiological effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on the heart are little known, we studied the regulation of the atrial ATP-sensitive K+(KATP) current by PACAP on primary cultured neonatal rat atrial myocytes. PACAP-38 stimulates cAMP production with EC50= 0.28 nmol/l ( r = 0.92, P < 0.02). PACAP-38 and PACAP-27 (10 nmol/l) have similar maximal effects, whereas 100 nmol/l vasoactive intestinal polypeptide (VIP) is 2.7 times less effective ( P < 0.05). RT-PCR shows the presence of cloned PACAP receptors PAC1(≥2 isoforms), VPAC1, and VPAC2. PACAP-38 dose dependently activates the whole cell atrial KATPcurrent with EC50= 1–3 nmol/l ( n = 44). Maximal effects occur at 10 nmol/l (91 ± 15 pA/pF, n = 18). Diazoxide further increases the PACAP-activated current by 78% ( P < 0.05; n = 6). H89(500 nmol/l), a protein kinase A (PKA) inhibitor, reduces the PACAP-activated KATPcurrent to 17.8 ± 9.6% ( n = 5) of the maximal diazoxide-induced current and totally inhibits the cAMP-induced KATPcurrent. A protein kinase C (PKC) inhibitor peptide (50 μmol/l) in the pipette reduces the PACAP-38-induced KATPcurrent to 33 ± 17 pA/pF ( P < 0.05, n = 6) without significantly affecting the currents induced by cAMP or VIP. The results suggest that: 1) PAC1, VPAC1, and VPAC2are present in atrial myocytes; and 2) PACAP-38 activates the atrial KATPchannels through both PKA and PKC pathways.
20-HETE modulates myogenic response of skeletal muscle resistance arteries from hypertensive Dahl-SS rats
Authors: Frisbee Jefferson C. , Roman Richard J. , Krishna U. Murali , Falck John R. , Lombard Julian H.
Published: December 2017

The present study determined the role of 20-hydroxyeicosatetraenoic acid [20-HETE; produced by ω-hydroxylation of arachidonic acid via cytochrome P-450 (CP450) 4A enzymes] in regulating myogenic activation of skeletal muscle resistance arteries from normotensive (NT) and hypertensive (HT) Dahl salt-sensitive (SS) rats. Gracilis arteries (GA) were isolated from each rat and viewed via television microscopy, and changes in vessel diameter with altered transmural pressure were measured with a video micrometer. Under control conditions, GA from both groups exhibited strong, endothelium-independent myogenic activation. Treatment of GA with 17-octadecynoic acid (17-ODYA; inhibitor of CP450 4A enzymes) did not alter myogenic activation in NT rats, but impaired this response in HT animals. Treatment of GA from HT rats with dibromo-dodecynyl-methylsulfimide (DDMS; inhibitor of 20-HETE production) impaired myogenic activation, as did application of 20-hydroxyeicosa-6( Z),15( Z)-dienoic acid, an antagonist for 20-HETE receptors. Application of iberiotoxin, a Ca2+-activated potassium (KCa) channel inhibitor, restored myogenic activation from HT rats treated with DDMS. These results suggest that myogenic activation of skeletal muscle resistance arteries from NT Dahl-SS rats does not depend on CP450, whereas myogenic activation of these vessels in HT Dahl-SS rats is partly a function of 20-HETE production, inhibiting KCachannels through a receptor-mediated process.
Comparison of spontaneous vs. metronome-guided breathing on assessment of vagal modulation using RR variability
Authors: Bloomfield Daniel M. , Magnano Anthony , Bigger J. Thomas , Rivadeneira Harold , Parides Michael , Steinman Richard C.
Published: December 2017

R-R interval variability (RR variability) is increasingly being used as an index of autonomic activity. High-frequency (HF) power reflects vagal modulation of the sinus node. Since vagal modulation occurs at the respiratory frequency, some investigators have suggested that HF power cannot be interpreted unless the breathing rate is controlled. We hypothesized that HF power during spontaneous breathing would not differ significantly from HF power during metronome-guided breathing. We measured HF power during spontaneous breathing in 20 healthy subjects and 19 patients with heart disease. Each subject's spontaneous breathing rate was determined, and the calculation of HF power was repeated with a metronome set to his or her average spontaneous breathing rate. There was no significant difference between the logarithm of HF power measured during spontaneous and metronome-guided breathing [4.88 ± 0.29 vs. 5.29 ± 0.30 ln(ms2), P = 0.32] in the group as a whole and when patients and healthy subjects were examined separately. We did observe a small (9.9%) decrease in HF power with increasing metronome-guided breathing rates (from 9 to 20 breaths/min). These data indicate that HF power during spontaneous and metronome-guided breathing differs at most by very small amounts. This variability is several logarithmic units less than the wide discrepancies observed between healthy subjects and cardiac patients with a heterogeneous group of cardiovascular disorders. In addition, HF power is relatively constant across the range of typical breathing rates. These data indicate that there is no need to control breathing rate to interpret HF power when RR variability (and specifically HF power) is used to identify high-risk cardiac patients.
Effect of anemia on cardiac function, microvascular structure, and capillary hematocrit in rat hearts
Authors: Rakusan Karel , Cicutti N. , Kolar F.
Published: December 2017

The effect of anemia on the coronary microcirculation was studied in young male rats. Chronic anemia resulted in increased left ventricular end-diastolic pressure and decreased functional reserve. Cardiac mass in anemic animals increased by 25%. Capillary and arteriolar densities in these hearts remained unchanged, indicating angiogenesis in this experimental situation (estimated aggregate capillary length in the left ventricle of anemic hearts was 3.06 km compared with 2.35 km in control hearts). Capillary hematocrit was decreased in chronic anemia less than systemic hematocrit: from 25 to 18% in anemia versus 45 to 28% in controls. Capillary hematocrit and red blood cell spacing were also studied after acute blood withdrawal. Here, capillary hematocrit was preserved even more: 22 versus 24% in systemic hematocrit. Finally, the same was studied in isolated hearts perfused with solutions of various hematocrits. After perfusion with low-hematocrit solution (14%), the capillary hematocrit (24%) was even higher than the perfusate hematocrit! In conclusion, we found evidence of angiogenesis in cardiomegaly induced by chronic anemia. Microvascular growth was accompanied by advantageous regulation of red blood cell spacing within these vessels. This was even more pronounced during acute hemodilution and in isolated perfused hearts.
Contributions of prostacyclin and nitric oxide to carbon monoxide-induced cerebrovascular dilation in piglets
Authors: Leffler Charles W. , Nasjletti Alberto , Johnson Robert A. , Fedinec Alexander L.
Published: December 2017

Carbon monoxide (CO) is an endogenous dilator in the newborn cerebral microcirculation. Other dilators include prostanoids and nitric oxide (NO), and interactions among the systems are likely. Experiments on anesthetized piglets with cranial windows address the hypothesis that CO-induced dilation of pial arterioles involves interaction with the prostanoid and NO systems. Topical application of CO or the heme oxygenase substrate heme-l-lysinate (HLL) produced dilation. Indomethacin, N ω-nitro-l-arginine (l-NNA), and either iberiotoxin or tetraethylammonium chloride (TEA) were used to inhibit prostanoids, NO, and Ca2+-activated K+ (KCa) channels, respectively. Indomethacin, l-NNA, iberiotoxin, or TEA blocked cerebral vasodilation to CO and HLL. Vasodilations to both CO and HLL were returned to indomethacin-treated piglets by topical application of iloprost. Vasodilations to both CO and HLL were returned to l-NNA-treated piglets by sodium nitroprusside but not iloprost. In iberiotoxin- or TEA-treated piglets, dilations to CO and HLL could not be restored by either iloprost or sodium nitroprusside. The dilator actions of CO involve prostacyclin and NO as permissive enablers. The permissive actions of prostacyclin and NO may alter the KCa channel response to CO because neither iloprost nor sodium nitroprusside could restore dilation to CO when these channels were blocked.
Constructive and destructive addition of forward and reflected arterial pulse waves
Authors: Quick Christopher M. , Berger David S. , Noordergraaf Abraham
Published: December 2017

Although the physics of arterial pulse wave propagation and reflection is well understood, there is considerable debate as to the effect of reflection on vascular input impedance ( Z in), pulsatile pressure, and stroke work (SW). This may be related to how reflection is studied. Conventionally, reflection is experimentally abolished (thus radically changing unrelated parameters), or a specific model is assumed from which reflection can be removed (yielding model-dependent results). The present work proposes a simple, model-independent method to evaluate the effect of reflection directly from measured pulsatile pressure (P) and flow (Q). Because characteristic impedance ( Z 0) is Z in in the absence of reflection, the P with reflection theoretically removed can be calculated from Q · Z 0. Applying this insight to an illustrative case indicates that reflection has the least effect on P and SW at normal pressure but a greater effect with vasodilation and vasoconstriction. Z in, P, and SW are increased or decreased depending on the relative amount of constructive and destructive addition of forward and reflected arterial pulse waves.
Differential dynamic baroreflex regulation of cardiac and renal sympathetic nerve activities
Authors: Kawada Toru , Shishido Toshiaki , Inagaki Masashi , Tatewaki Teiji , Zheng Can , Yanagiya Yusuke , Sugimachi Masaru , Sunagawa Kenji
Published: December 2017

Although regional difference in sympathetic efferent nerve activity has been well investigated, whether this regional difference exists in the dynamic baroreflex regulation of sympathetic nerve activity remains uncertain. In anesthetized, vagotomized, and aortic-denervated rabbits, we isolated carotid sinuses and randomly perturbed intracarotid sinus pressure (CSP) while simultaneously recording cardiac (CSNA) and renal sympathetic nerve activities (RSNA). The neural arc transfer function from CSP to CSNA and that from CSP to RSNA revealed high-pass characteristics. The increasing slope of the transfer gain in the frequencies between 0.03 and 0.3 Hz was significantly greater for CSNA than for RSNA (2.96 ± 0.72 vs. 1.64 ± 0.73 dB/octave, P < 0.01, n = 9). The difference was hardly explained by the difference in static nonlinear characteristics of CSP-CSNA and CSP-RSNA relationships or by the difference in conduction velocities in the multifiber recording. These results indicate that the central processing in the brain stem differs between CSNA and RSNA. The neural arc of the baroreflex may exert differential effects on the heart and kidney in response to dynamic baroreflex activation.
Hypertonic saline-dextran suppresses burn-related cytokine secretion by cardiomyocytes
Authors: Horton Jureta W. , Maass David L. , White Jean , Sanders Billy
Published: December 2017

Whereas hypertonic saline-dextran (HSD, 7.5% NaCl in 6% D70) improves cardiac contractile function after burn trauma, the mechanisms of HSD-related cardioprotection remain unclear. We recently showed that cardiomyocytes secrete tumor necrosis factor-α (TNF-α), a response that was enhanced by burn trauma. This study addressed the question: does HSD modulate cardiac contraction/relaxation by altering cardiomyocyte TNF-α secretion? Wistar-Furth rats (325 g) were given a burn injury over 40% of the total body surface area and were then randomized to receive a bolus of either isotonic saline or HSD (4 ml/kg, n = 14 rats/group). Sham burn rats were given either isotonic saline or HSD ( n = 14 rats/group) to provide appropriate controls for the two burn groups. Hearts were isolated 24 h postburn for either Langendorff perfusion ( n = 8 hearts/group) or to prepare cardiomyocytes ( n = 6 hearts/group). Myocytes were stimulated with lipopolysaccharide (LPS) (0, 10, 25, or 50 μg for 18 h) to measure cytokine secretion. Burn trauma increased myocyte TNF-α and interleukin-1β and -6 secretion, exacerbated cytokine response to LPS stimulus, and impaired cardiac contraction. HSD treatment of burns decreased cardiomyocyte cytokine secretion, decreased responsiveness to LPS challenge with regard to cytokine secretion, and improved ventricular function. These data suggest that HSD mediates cardioprotection after burn trauma, in part, by downregulating cardiomyocyte secretion of inflammatory cytokines.
Differential effects of caspase inhibitors on endotoxin-induced myocardial dysfunction and heart apoptosis
Authors: Fauvel Harold , Marchetti Philippe , Chopin Claude , Formstecher Pierre , Nevière Rémi
Published: December 2017

Endotoxin is one of the major factors causing myocardial depression and death during sepsis in humans. Recently, it was reported that endotoxin may induce cardiomyocyte apoptosis. Also, multiple caspase activation has been implicated in endotoxin-induced apoptosis in several organ systems. In this study, we investigated whether endotoxin would increase myocardial caspase activities and evaluated the effects of in vivo administration (3 mg/kg) of the broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone(z-VAD.fmk), the caspase-3-like inhibitor benzyloxycarbonyl-Asp-Glu-Val-Asp-chloromethylketone (z-DEVD.cmk), and the caspase-1-like inhibitor acetyl-Tyr-Val-Ala-Asp-chloromethylketone (Ac-YVAD. fmk), on endotoxin-induced myocardial dysfunction and apoptosis. Endotoxin administration (10 mg/kg iv) induced myocardial contractile dysfunction that was associated with caspase activity increases and nuclear apoptosis. Broad-spectrum z-VAD.fmk and z-DEVD.cmk improved endotoxin-induced myocardial dysfunction and reduced caspase activation and nuclear apoptosis when given immediately and 2 h after endotoxin. In contrast, no effects of Ac-YVAD.fmk were observed on myocardial function and caspase-induced apoptosis. Administration of caspase inhibitors 4 h after endotoxin treatment was not able to protect the rat heart from myocardial dysfunction and nuclear apoptosis. These observations provide evidence that in our model, caspase activation plays a role in endotoxin-induced myocardial apoptosis. Caspase inhibition strategy may represent a therapeutic approach to endotoxin-induced myocardial dysfunction.
Effects of simulated ischemia on spiral wave stability
Authors: Xie Fagen , Qu Zhilin , Garfinkel Alan , Weiss James N.
Published: December 2017

Regional hyperkalemia during acute myocardial ischemia is a major factor promoting electrophysiological abnormalities leading to ventricular fibrillation (VF). However, steep action potential duration restitution, recently proposed to be a major determinant of VF, is typically decreased rather than increased by hyperkalemia and acute ischemia. To investigate this apparent contradiction, we simulated the effects of regional hyperkalemia and other ischemic components (anoxia and acidosis) on the stability of spiral wave reentry in simulated two-dimensional cardiac tissue by use of the Luo-Rudy ventricular action potential model. We found that the hyperkalemic “ischemic” area promotes wavebreak in the surrounding normal tissue by accelerating the rate of spiral wave reentry, even after the depolarized ischemic area itself has become unexcitable. Furthermore, wavebreak and fibrillation can be prevented if the dynamical instability of the normal tissue is reduced significantly by targeting electrical restitution properties, suggesting a novel therapeutic approach.