bluuebunny/crossref_metadata_2025 huggingface dataset:
Entropies of short binary sequences in heart period dynamics
Authors: Cysarz D. , Bettermann H. , van Leeuwen P.
Published: December 2017

Dynamic aspects of R-R intervals have often been analyzed by means of linear and nonlinear measures. The goal of this study was to analyze binary sequences, in which only the dynamic information is retained, by means of two different aspects of regularity. R-R interval sequences derived from 24-h electrocardiogram (ECG) recordings of 118 healthy subjects were converted to symbolic binary sequences that coded the beat-to-beat increase or decrease in the R-R interval. Shannon entropy was used to quantify the occurrence of short binary patterns (length N = 5) in binary sequences derived from 10-min intervals. The regularity of the short binary patterns was analyzed on the basis of approximate entropy (ApEn). ApEn had a linear dependence on mean R-R interval length, with increasing irregularity occurring at longer R-R interval length. Shannon entropy of the same sequences showed that the increase in irregularity is accompanied by a decrease in occurrence of some patterns. Taken together, these data indicate that irregular binary patterns are more probable when the mean R-R interval increases. The use of surrogate data confirmed a nonlinear component in the binary sequence. Analysis of two consecutive 24-h ECG recordings for each subject demonstrated good intraindividual reproducibility of the results. In conclusion, quantification of binary sequences derived from ECG recordings reveals properties that cannot be found using the full information of R-R interval sequences.
Electrotonic suppression of early afterdepolarizations in isolated rabbit Purkinje myocytes
Authors: Huelsing Delilah J. , Spitzer Kenneth W. , Pollard Andrew E.
Published: December 2017

Many studies suggest that early afterdepolarizations (EADs) arising from Purkinje fibers initiate triggered arrhythmias under pathological conditions. However, electrotonic interactions between Purkinje and ventricular myocytes may either facilitate or suppress EAD formation at the Purkinje-ventricular interface. To determine conditions that facilitated or suppressed EADs during Purkinje-ventricular interactions, we coupled single Purkinje myocytes and aggregates isolated from rabbit hearts to a passive model cell via an electronic circuit with junctional resistance ( R j). The model cell had input resistance ( R m,v) of 50 MΩ, capacitance of 39 pF, and a variable rest potential ( V rest,v). EADs were induced in Purkinje myocytes during superfusion with 1 μM isoproterenol. Coupling at high R j to normally polarized V rest,v established a repolarizing coupling current during all phases of the Purkinje action potential. This coupling current preferentially suppressed EADs in single cells with mean membrane resistance ( R m,p) of 297 MΩ, whereas EAD suppression in larger aggregates with mean R m,p of 80 MΩ required larger coupling currents. In contrast, coupling to elevated V rest,v established a depolarizing coupling current during late phase 2, phase 3, and phase 4 that facilitated EAD formation and induced spontaneous activity in single Purkinje myocytes and aggregates. These results have important implications for arrhythmogenesis in the infarcted heart when reduction of the ventricular mass due to scarring alters the R m,p-to- R m,v ratio and in the ischemic heart when injury currents are established during coupling between polarized Purkinje myocytes and depolarized ventricular myocytes.
Diacylglycerol and fatty acids synergistically increase cardiomyocyte contraction via activation of PKC
Authors: Pi Yeqing , Walker Jeffery W.
Published: December 2017

Lipid signaling pathways are thought to play a prominent role in transducing extracellular signals into contractile responses in cardiac muscle. Two putative lipid messengers, diacyglycerol and arachidonic acid, can be generated via distinct phospholipases in separate signaling pathways, but certain stimuli cause them to be elevated in parallel. We tested the hypothesis that these lipids function as comessengers in ventricular myocytes by activating protein kinase C (PKC). In previous work, we demonstrated that the diacylglycerol analog dioctanoylglycerol (diC8) can be stimulatory or inhibitory toward myocyte twitches depending on how it is applied. Here we report that arachidonic acid and other cis-unsaturated fatty acids (UFA), at concentrations too low for direct effects, synergistically enhance the stimulatory effects of diC8and convert inhibitory effects of diC8into stimulation of myocyte twitches. Intracellular Ca2+transients changed in parallel with twitch amplitude, suggesting regulation of Ca2+homeostasis by these lipids. cis-UFA also interacted synergistically with the PKC activator phorbol 12-myristate 13-acetate to promote positive inotropic responses. Responses were blocked by the PKC antagonists chelerythrine chloride, bisindolylmaleimide, and Gö-6976. DiC8and arachidonic acid also synergistically translocated PKC-ε and PKC-α in intact myocytes. We propose that PKC integrates diacylglycerol and cis-UFA signals in the heart, resulting in preferential activation of positive inotropic mechanisms.
Mechanism of decreased adenosine protection in reperfusion injury of aging rats
Authors: Gao Feng , Christopher Theodore A. , Lopez Bernard L. , Friedman Eitan , Cai Guoping , Ma Xin L.
Published: December 2017

The purpose of this study was to determine whether the protective effects of adenosine on myocardial ischemia-reperfusion injury are altered with age, and if so, to clarify the mechanisms that underlie this change related to nitric oxide (NO) derived from the vascular endothelium. Isolated perfused rat hearts were exposed to 30 min of ischemia and 60 min of reperfusion. In the adult hearts, administration of adenosine (5 μmol/l) stimulated NO release (1.06 ± 0.19 nmol · min−1· g−1, P < 0.01 vs. vehicle), increased coronary flow, improved cardiac functional recovery (left ventricular developed pressure 79 ± 3.8 vs. 57 ± 3.1 mmHg in vehicle, P < 0.001; maximal rate of left ventricular pressure development 2,385 ± 103 vs. 1,780 ± 96 in vehicle, P < 0.001), and reduced myocardial creatine kinase loss (95 ± 3.9 vs. 159 ± 4.6 U/100 mg protein, P < 0.01). In aged hearts, adenosine-stimulated NO release was markedly reduced (+0.42 ± 0.12 nmol · min−1· g−1vs. vehicle), and the cardioprotective effects of adenosine were also attenuated. Inhibition of NO production in the adult hearts significantly decreased the cardioprotective effects of adenosine, whereas supplementation of NO in the aged hearts significantly enhanced the cardioprotective effects of adenosine. The results show that the protective effects of adenosine on myocardial ischemia-reperfusion injury are markedly diminished in aged animals, and that the loss in NO release in response to adenosine may be at least partially responsible for this age-related alteration.
Substrate-dependent proton load and recovery of stunned hearts during pyruvate dehydrogenase stimulation
Authors: Griffin Julian L. , White Lawrence T. , Lewandowski E. Douglas
Published: December 2017

Stimulation of pyruvate dehydrogenase (PDH) improves functional recovery of postischemic hearts. This study examined the potential for a mechanism mediated by substrate-dependent proton production and intracellular pH. After 20 min of ischemia, isolated rabbit hearts were reperfused with or without 5 mM dichloroacetate (DCA) in the presence of either 5 mM glucose, 5 mM glucose + 2.5 mM lactate, or 5 mM glucose + 2.5 mM pyruvate. DCA inhibits PDH kinase, increasing the proportion of dephosphorylated, active PDH. Unlike pyruvate or glucose alone, lactate + glucose did not support the effects of DCA on the recovery of rate-pressure product (RPP) (without DCA, RPP = 14,000 ± 1,200, n = 6; with DCA, RPP = 13,700 ± 1,800, n = 9). Intracellular pH, from31P nuclear magnetic resonance spectra, returned to normal within 2.1 min of reperfusion with all substrates except for lactate + glucose + DCA or lactate + DCA, which delayed pH recovery for up to 12 min (at 2.1 min pH = 6.00 ± 0.08, lactate + glucose + DCA; pH = 6.27 ± 0.34, for lactate + DCA). Hearts were also reperfused after 10 min of ischemia with 0.5 mM palmitate + 5 mM DCA and either 2.5 mM pyruvate or 2.5 mM lactate. Again, intracellular pH recovery was delayed in the presence of lactate. PDH activation in the presence of lactate also decreased coupling of oxidative metabolism to mechanical work. These findings have implications for therapeutic use of stimulated carbohydrate oxidation in stunned hearts.
Progressive left ventricular remodeling and apoptosis late after myocardial infarction in mouse heart
Authors: Sam Flora , Sawyer Douglas B. , Chang Donny L.-F. , Eberli Franz R. , Ngoy Soeun , Jain Mohit , Amin Jay , Apstein Carl S. , Colucci Wilson S.
Published: December 2017

We tested the hypothesis that left ventricular (LV) remodeling late after myocardial infarction (MI) is associated with myocyte apoptosis in myocardium remote from the infarcted area and is related temporally to LV dilation and contractile dysfunction. One, four, and six months after MI caused by coronary artery ligation, LV volume and contractile function were determined using an isovolumic balloon-in-LV Langendorff technique. Apoptosis and nuclear morphology were determined by terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) and Hoechst 33258 staining. Progressive LV dilation 1–6 mo post-MI was associated with reduced peak LV developed pressure (LVDP). In myocardium remote from the infarct, there was increased wall thickness and expression of atrial natriuretic peptide mRNA consistent with reactive hypertrophy. There was a progressive increase in the number of TUNEL-positive myocytes from 1 to 6 mo post-MI (2.9-fold increase at 6 mo; P < 0.001 vs. sham). Thus LV remodeling late post-MI is associated with increased apoptosis in myocardium remote from the area of ischemic injury. The frequency of apoptosis is related to the severity of LV dysfunction.
PKC-dependent delayed metabolic preconditioning is independent of transient MAPK activation
Authors: Mockridge James W. , Punn Anu , Latchman David S. , Marber Michael S. , Heads Richard J.
Published: December 2017

In this study we used an in vitro model of delayed preconditioning to investigate activation of mitogen-activated protein kinases (MAPKs) and their potential role in protection. Neonatal rat cardiomyocytes were preconditioned using a buffer containing glycolytic inhibitors and low pH (minimal metabolic preconditioning; MMPC) consisting of modified Krebs buffer, 10 mM 2-deoxyglucose, and 20 mM lactate, pH 6.8, for 2 h followed by 24 h of simulated reperfusion before lethal simulated ischemia (LSI). MAPK activation during the MMPC protocol was determined using phospho-specific antisera and the effect on protection determined following LSI. Rapid, transient phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 MAPK was observed during each of the MMPC, reperfusion, and LSI phases; an effect blocked by MAPK inhibitors PD-98059 and SB-203580, respectively, but not by the protein kinase C (PKC) inhibitor Ro31-8220. However, although MMPC was blocked by Ro31-8220, treatment with the MAPK inhibitors during the preconditioning protocol did not block delayed protection conferred by MMPC. Thus the data suggest that, in this model of delayed preconditioning, protection appears to be PKC dependent but independent of ERK1/2 or p38 MAPK activation.
Acute hypoxia modulates 5-HT receptor density and agonist affinity in fetal and adult ovine carotid arteries
Authors: Angeles Danilyn M. , Williams James , Zhang Lubo , Pearce William J.
Published: December 2017

In light of recent observations that receptor-ligand binding and coupling are physiologically regulated, the present study examined the hypothesis that the direct effects of hypoxia on vascular contractility involve modulation of pharmacomechanical coupling via changes in agonist affinity and/or receptor density. Because the direct effects of hypoxia on vascular smooth muscle contractility can vary with age, we carried out these experiments using both fetal and adult arteries. In common carotid arteries from near-term fetal and adult sheep, hypoxia (Po 2 = 9–12 Torr for 30 min) reduced the maximum responses to potassium by 17.8 ± 3.5% (fetus) and 20.5 ± 2.2% (adult), significantly reduced the pD2for 5-HT in the fetus (7.01 ± 0.1 to 6.3 ± 0.2) but not the adult (6.1 ± 0.1 to 6.0 ± 0.1), and significantly reduced 5-HT-induced maximum contractions (as % maximum response to 120 mM K+) not in the fetus (from 114 ± 7 to 70 ± 10%, not significant) but only in the adult (from 83 ± 15 to 25 ± 7%, P < 0.05) arteries. Hypoxia significantly attenuated 5-HT binding affinity (pKA, determined by partial irreversible blockade with phenoxybenzamine) in both fetal (from 6.5 ± 0.2 to 6.0 ± 0.2) and adult arteries (from 6.2 ± 0.2 to 5.7 ± 0.1) and also decreased receptor density (fmol/mg protein, determined by competitive binding with ketanserin and mesulergine) in adult (from 18.3 ± 1.1 to 10.9 ± 1.0) but not in fetal (21.0 ± 1.0 to 23.2 ± 1.4) arteries. These results suggest that acute hypoxia modulates receptor-ligand binding via age-dependent modulation of agonist affinity and receptor density. These effects may contribute to hypoxic vasodilatation and help explain why the effects of hypoxia on vascular contractility differ between fetuses and adults.
Antihypertensive properties of a nitric oxide-releasing naproxen derivative in two-kidney, one-clip rats
Authors: Muscará Marcelo N. , McKnight Webb , Lovren Fina , Triggle Christopher R. , Cirino Giuseppe , Wallace John L.
Published: December 2017

Nonsteroidal anti-inflammatory drugs have been reported to exacerbate hypertension. In this study, we tested the hypothesis that a nitric oxide-releasing derivative of naproxen would ameliorate hypertension in the rat. Hypertension was induced by partially occluding one renal artery (the “2K,1C” model), and 2 wk later the rats started receiving naproxen, the nitric oxide-releasing derivative HCT-3012, or vehicle each day for 2 wk. Naproxen significantly exacerbated the hypertension. HCT-3012 significantly reduced blood pressure relative to both the naproxen- and vehicle-treated groups. Both naproxen and HCT-3012 markedly suppressed whole blood thromboxane B2 synthesis. In studies of anesthetized rats, naproxen significantly enhanced the late hypertensive response to endothelin-1 and significantly blunted the early hypotensive response. In contrast, HCT-3102 did not affect either response to endothelin-1. In vitro, HCT-3012 significantly reduced the responsiveness of aortic rings to the contractile effects of phenylephrine. These studies suggest that HCT-3012 reduces blood pressure in hypertensive rats, not simply through the vasodilatory actions of the nitric oxide it releases, but through alterations in the responsiveness of the vasculature to endogenous pressor agents.
Effects of forearm bier block with bretylium on the hemodynamic and metabolic responses to handgrip
Authors: Lee Frank , Shoemaker J. Kevin , McQuillan Patrick M. , Kunselman Allen R. , Smith Michael B. , Yang Qing X. , Smith Harvey , Gray Kristen , Sinoway Lawrence I.
Published: December 2017

We tested the hypothesis that a reduction in sympathetic tone to exercising forearm muscle would increase blood flow, reduce muscle acidosis, and attenuate reflex responses. Subjects performed a progressive, four-stage rhythmic handgrip protocol before and after forearm bier block with bretylium as forearm blood flow (Doppler) and metabolic (venous effluent metabolite concentration and31P-NMR indexes) and autonomic reflex responses (heart rate, blood pressure, and sympathetic nerve traffic) were measured. Bretylium inhibits the release of norepinephrine at the neurovascular junction. Bier block increased blood flow as well as oxygen consumption in the exercising forearm ( P < 0.03 and P < 0.02, respectively). However, despite this increase in flow, venous K+release and H+release were both increased during exercise ( P < 0.002 for both indexes). Additionally, minimal muscle pH measured during the first minute of recovery with NMR was lower after bier block (6.41 ± 0.08 vs. 6.20 ± 0.06; P < 0.036, simple effects). Meanwhile, reflex effects were unaffected by the bretylium bier block. The results support the conclusion that sympathetic stimulation to muscle during exercise not only limits muscle blood flow but also appears to limit anaerobiosis and H+release, presumably through a preferential recruitment of oxidative fibers.
Differences in mechanisms of SR dysfunction in ischemic vs. idiopathic dilated cardiomyopathy
Authors: Sen Luyi , Cui Guanggen , Fonarow Gregg C. , Laks Hillel
Published: December 2017

We examined 1) contractile properties and the intracellular Ca2+concentration ([Ca2+]i) transient in cardiac myocytes and 2) sarcoplasmic reticulum (SR) Ca2+uptake and release function in myocardium from patients with end-stage heart failure caused by ischemic (ICM) vs. idiopathic dilated cardiomyopathy (DCM). The amplitude of cell motion was decreased 43 ± 6% in ICM and 68 ± 7% in DCM compared with that in normal organ donors (DN). Time to peak of shortening was increased 43 ± 15% in DCM, but not in ICM. Prolongation of the relaxation time was more predominant in ICM. In DCM the systolic [Ca2+]iwas decreased 27 ± 9% and diastolic [Ca2+]iwas increased 36 ± 11%. In ICM the diastolic [Ca2+]iwas increased 59 ± 12% but the systolic [Ca2+]iwas unchanged. A significant decrease of the ATP-dependent SR Ca2+uptake rate associated with the reduction of the SR Ca2+-ATPase protein level was found in ICM. In contrast, the significant decrease in SR Ca2+release rate was distinct in DCM. The large amount of Ca2+retained in the SR associated with a significant decrease in the maximum reaction velocity and increase in the Michaelis-Menten constant in the caffeine concentration-response curve suggests a fundamental abnormality in the SR Ca2+release channel gating property in DCM. We conclude that potentially important differences exist in the intracellular Ca2+homeostasis and excitation-contraction coupling in ICM vs. DCM. The SR Ca2+release dysfunction may play an important pathogenetic role in the abnormal Ca2+homeostasis in DCM, and the SR Ca2+uptake dysfunction may be responsible for the contractile dysfunction in ICM.
Exercise adaptation attenuates VEGF gene expression in human skeletal muscle
Authors: Richardson R. S. , Wagner H. , Mudaliar S. R. D. , Saucedo E. , Henry R. , Wagner P. D.
Published: December 2017

Angiogenesis is a component of the multifactoral adaptation to exercise training, and vascular endothelial growth factor (VEGF) is involved in extracellular matrix changes and endothelial cell proliferation. However, there is limited evidence supporting the role of VEGF in the exercise training response. Thus we studied mRNA levels of VEGF, using quantitative Northern analysis, in untrained and trained human skeletal muscle at rest and after a single bout of exercise. Single leg knee-extension provided the acute exercise stimulus and the training modality. Four biopsies were collected from the vastus lateralis muscle at rest in the untrained and trained conditions before and after exercise. Training resulted in a 35% increase in muscle oxygen consumption and an 18% increase in number of capillaries per muscle fiber. At rest, VEGF/18S mRNA levels were similar before (0.38 ± 0.04) and after (1.2 ± 0.4) training. When muscle was untrained, acute exercise greatly elevated VEGF/18S mRNA levels (16.9 ± 6.7). The VEGF/18S mRNA response to acute exercise in the trained state was markedly attenuated (5.4 ± 1.3). These data support the concept that VEGF is involved in exercise-induced skeletal muscle angiogenesis and appears to be subject to a negative feedback mechanism as exercise adaptations occur.
Role of ETA receptors in the regulation of vascular reactivity in rats with congestive heart failure
Authors: Thorin Eric , Lucas Martin , Cernacek Peter , Dupuis Jocelyn
Published: December 2017

Endothelium-derived nitric oxide (NO) and endothelin (ET)-1 interact to regulate vascular tone. In congestive heart failure (CHF), the release and/or the activity of both factors is affected. We hypothesized that the increased ET-1 production associated with CHF may result in a reduced smooth muscle sensitivity to NO. The aim of this study was to evaluate the effects of a chronic treatment with the ETA-receptor (ET receptor A) antagonist LU-135252 (LU) on cerebrovascular reactivity to sodium nitroprusside (SNP) in the rat infarct model of CHF. Rats were subjected to coronary artery ligation and were treated for 4 wk with placebo ( n = 24) or LU (50 mg · kg−1 · day−1, n = 29). CHF was associated with a decreased ( P < 0.05) efficacy of SNP to induce relaxation of isolated middle cerebral arteries. Furthermore, neither NO synthase inhibition with N ω-nitro-l-arginine (l-NNA) nor endothelial denudation affected the efficacy of SNP. Thus the endothelium no longer influences smooth muscle sensitivity to SNP. LU treatment, however, normalized ( P < 0.05) smooth muscle sensitivity to SNP. Sensitivity of ET-1-induced contraction was increased in CHF only in the presence of l-NNA, whereas contraction induced by ETB receptor (receptor B) stimulation was increased ( P < 0.05) in endothelium-denuded vessels. LU treatment restored these changes in reactivity and revealed a significant endothelium-dependent ETB-mediated relaxation after NO synthase inhibition. In conclusion, CHF decreases and uncouples cerebrovascular smooth muscle sensitivity to SNP from endothelial regulation. The observation that chronic ETAblockade restored most of the changes associated with CHF suggests that activation of the ET-1 system importantly contributes to the alteration in vascular reactivity observed in experimental CHF.
Altered cardiac Na+/H+exchange in phospholipase D-treated sarcolemmal vesicles
Authors: Goel Danny P. , Vecchini Alba , Panagia Vincenzo , Pierce Grant N.
Published: December 2017

Cardiac sarcolemmal Na+/H+exchange is critical for the regulation of intracellular pH, and its activity contributes to ischemia-reperfusion injury. It has been suggested that the membrane phospholipid environment does not modulate Na+/H+exchange. The present study was carried out to determine the effects on Na+/H+exchange of modifying the endogenous membrane phospholipids through the addition of exogenous phospholipase D. Incubation of 0.825 U of phospholipase D with 1 mg of porcine cardiac sarcolemmal vesicles hydrolyzed 34 ± 2% of the sarcolemmal phosphatidylcholine and increased phosphatidic acid 10.2 ± 0.5-fold. Treatment of vesicles with phospholipase D resulted in a 46 ± 2% inhibition of Na+/H+exchange. Na+/H+exchange was measured as a function of reaction time, extravesicular pH, and extravesicular Na+. All of these parameters of Na+/H+exchange were inhibited following phospholipase D treatment compared with untreated controls. Passive efflux of Na+was unaffected. Treatment of sarcolemmal vesicles with phospholipase C had no effect on Na+/H+exchange. We conclude that phospholipase D-induced changes in the cardiac sarcolemmal membrane phospholipid environment alter Na+/H+exchange.
Effects of estrogen on cerebral blood flow and pial microvasculature in rabbits
Authors: Littleton-Kearney M. T. , Agnew D. M. , Traystman R. J. , Hurn P. D.
Published: December 2017

We tested the hypothesis that intracarotid estrogen infusion increases cerebral blood flow (CBF) in a concentration-dependent manner and direct application of estrogen on pial arterioles yields estrogen receptor-mediated vasodilation. Rabbits of both genders were infused with estrogen via a branch of the carotid artery. Estrogen doses of 20 or 0.05 μg · ml−1 · min−1 were used to achieve supraphysiological or physiological plasma estrogen levels, respectively. CBF and cerebral vascular resistance were determined at baseline, during the infusion, and 60-min postinfusion, and effects on pial diameter were assessed via a cranial window. Pial arteriolar response to estrogen alone and to estrogen after administration of tamoxifen (10−7), an antiestrogen drug that binds to both known estrogen receptor subtypes, was tested. No gender differences were observed; therefore, data were combined for both males and females. Systemic estrogen infusion did not increase regional CBF. Estradiol dilated pial arteries only at concentrations ranging from 10−4–10−7 M ( P ≤ 0.05). Pretreatment with tamoxifen alone had no effect on arteriolar diameter but inhibited estrogen-induced vasodilation ( P < 0.001). Our data suggest that estrogen does not increase CBF under steady-state conditions in rabbits. In the pial circulation, topically applied estradiol at micromolar concentrations dilates vessels. The onset is rapid and dependent on estrogen receptor activation.
Influence of heart rate and sympathetic stimulation on arrhythmogenic T wave alternans
Authors: Kaufman Elizabeth S. , Mackall Judith A. , Julka Birendra , Drabek Carole , Rosenbaum David S.
Published: December 2017

We determined the temporal stability of T wave alternans (TWA) during constant rate stimulation and the dependence of alternans on heart rate (HR) and β-adrenergic stimulation. Although it is established that exercise can provoke microvolt-level TWA in patients at risk for reentrant ventricular arrhythmias, the mechanisms underlying TWA in humans are not well understood. Specifically, the temporal stability of alternans at any given HR and the influence of HR vs. sympathetic activation on alternans remain unclear. TWA was measured during prolonged fixed-rate atrial pacing at multiple cycle lengths (CLs) in 10 subjects referred for electrophysiological testing and in 14 additional subjects in whom atrial pacing was performed at identical pacing CLs with and without isoproterenol. During constant CL stimulation, TWA amplitude oscillated significantly over time (typically by 10 μV) in a quasiperiodic fashion with periodicity of ∼2–3 min. Alternans amplitude was strongly dependent on HR but not on adrenergic stimulation. There was a patient-specific threshold HR over which alternans appeared. At higher HR, alternans amplitude increased and oscillations were less prominent. Adrenergic stimulation was required to produce TWA that was not already elicited by moderate elevation of HR in only 2 of 14 (14%) patients. In conclusion, TWA 1) fluctuates spontaneously over 2–3 min and 2) increases monotonically with increased HR (without a major adrenergic contribution in most patients). These data suggest that increased HR rather than sympathetic activation is responsible for arrhythmogenic microvolt-level TWA measured during exercise.
Polyamines decrease Ca2+ sensitivity of tension and increase rates of activation in skinned cardiac myocytes
Authors: Harris Samantha P. , Patel Jitandrakumar R. , Marton Laurence J. , Moss Richard L.
Published: December 2017

Owing in part to their interactions with membrane proteins, polyamines (e.g., spermine, spermidine, and putrescine) have been identified as potential modulators of membrane excitability and Ca2+ homeostasis in cardiac myocytes. To investigate whether polyamines also affect cardiac myofilament proteins, we assessed the effects of polyamines on contractility using rat myocytes and trabeculae that had been permeabilized with Triton X-100. Spermine, spermidine, and putrescine reversibly increased the [Ca2+] required for half-maximal tension (i.e., right-shifted tension pCa curves), with the following order of efficacy: spermine (+4) > spermidine (+3) > putrescine (+2). However, synthetic analogs that differed from spermine in charge distribution were not as effective as spermine in altering isometric tension. None of the polyamines had a significant effect on maximal tension, except at high concentrations. After flash photolysis of DM-Nitrophen (a caged Ca2+ chelator), spermine accelerated the rate of tension development at low and intermediate but not high [Ca2+]. These results indicate that polyamines, especially spermine, interact with myofilament proteins to reduce apparent Ca2+ binding affinity and speed cross-bridge cycling kinetics at submaximal [Ca2+].
Development of a multifrequency conductance catheter-based system to determine LV function in mice
Authors: Feldman Marc D. , Mao Yi , Valvano Jonathan W. , Pearce John A. , Freeman Gregory L.
Published: December 2017

Transgenic mice offer a valuable way to relate gene products to phenotype, but the ability to assess the cardiovascular phenotype with pressure-volume analysis has lagged. Conductance measurement offers a method to generate an instantaneous left ventricular (LV) volume signal in the mouse but has been limited by the volume signal being a combination of blood and LV muscle. We hypothesized that by developing a mouse conductance system that operates at several simultaneous frequencies, we could identify and correct for the myocardial contribution to the instantaneous volume signal. This hypothesis is based on the assumption that mouse myocardial conductivity will vary with frequency, whereas mouse blood conductivity will not. Consistent with this hypothesis, we demonstrated that at higher excitation frequency, greater end-diastolic and end-systolic conductance are detected, as well as a smaller difference between the two. We then empirically solved for LV blood volume using two frequencies. We combined measured resistivity of mouse myocardium with an analytic approach and extracted an estimate of LV blood volume from the raw conductance signal. Development of a multifrequency catheter-based system to determine LV function could be a tool to assess cardiovascular phenotype in transgenic mice.
Evidence for involvement of the PKC-α isoform in myogenic contractions of the coronary microcirculation
Authors: Dessy Chantal , Matsuda Naruto , Hulvershorn Justin , Sougnez Carrie L. , Sellke Frank W. , Morgan Kathleen G.
Published: December 2017

The role of protein kinase C (PKC) isoforms in myogenic tone of the ferret coronary microcirculation was investigated by measuring fura 2 Ca2+signals, PKC immunoblots, contractile responses, and confocal microscopy of PKC translocation. Phorbol ester-evoked contractions were completely abolished in the absence of extracellular Ca2+but involved a Ca2+sensitization relative to KCl contractions. Immunoblotting using isoform-specific antibodies showed the presence of PKC-α and -ι and traces of PKC-ɛ and -μ in the ferret coronary microcirculation. PKC-β was not detectable. When intraluminal pressure (40 to 60 and 80 mmHg) was increased, ferret coronary arterioles showed a transient increase in fura 2 Ca2+signals, whereas the myogenic tone remained sustained. The increase in Ca2+and tone was sustained at 100 mmHg. Isolated ferret coronary arterioles were fixed and immunostained for PKC-α at 40 and 100 mmHg intraluminal pressure. PKC translocation was determined by confocal microscopy. Increased PKC translocation was observed when vessels were exposed to 100 mmHg relative to that at resting pressure (40 mmHg). These results suggest a link between the Ca2+sensitization that occurs during the myogenic contraction and activation of the α-isoform of PKC.
Early sequence of cardiac adaptations and growth factor formation in pressure- and volume-overload hypertrophy
Authors: Modesti Pietro Amedeo , Vanni Simone , Bertolozzi Iacopo , Cecioni Ilaria , Polidori Gianluca , Paniccia Rita , Bandinelli Brunella , Perna Avio , Liguori Piero , Boddi Maria , Galanti Giorgio , Serneri Gian Gastone Neri
Published: December 2017

To investigate the time sequence of cardiac growth factor formation, echocardiographic and hemodynamic measurements were performed at scheduled times, and mRNAs for angiotensinogen, prepro-endothelin-1 (ppET-1), and insulin-like growth factor I (IGF-I) were quantified with RT-PCR and localized with in situ hybridization in pigs (fluothane anesthesia) by use of pressure or volume overload (aortic banding and aorta-cava fistula, respectively). Relative peptide formation was also measured by radioimmunoassay. In pressure overload, angiotensinogen and ppET-1 mRNA overexpression on myocytes (13 times vs. sham at 3 h and 112 times at 6 h, respectively) was followed by recovery (12 h) of initially decreased (0.5–6 h) myocardial contractility. In volume overload, contractility was not decreased, the angiotensinogen gene was slightly upregulated at 6 h (6.7 times), and ppET-1 was not overexpressed. IGF-I mRNA was overexpressed on myocytes (at 24 h) in both volume and pressure overload (14 times and 37 times, respectively). In the latter setting, a second ppET-1 overexpression was detectable on myocytes at 7 days. In conclusion, acute cardiac adaptation responses involve different growth factor activation over time in pressure versus volume overload; growth factors initially support myocardial contractility and thereafter induce myocardial hypertrophy.
Transarterial wall oxygen gradients at the deployment site of an intra-arterial stent in the rabbit
Authors: Santilli Steven Michael , Tretinyak Alexander Spencer , Lee Eugene Sangkeu
Published: December 2017

Intimal hyperplasia, common at the deployment site of an intra-arterial stent, may be caused by artery wall hypoxia. The purpose of this study was to determine the effect of an intra-arterial stent on artery wall oxygen concentrations. Transarterial wall oxygen gradients were measured by microelectrode at stent deployment sites in New Zealand White rabbits. Thinned artery walls and decreased oxygen tensions were noted throughout the artery wall immediately following stent deployment with a return toward control values at 28 days. Angioplasty alone had no acute effect on artery wall oxygen concentrations. Larger stent deployment diameters yielded acutely lower artery wall oxygen tensions. Using a linear one-dimensional model for the oxygen profile, we noted that stent deployment resulted in acute changes in oxygen consumption in the inner artery wall that rapidly returned to control values. Changes were noted without differences in blood pressure or arterial blood oxygen concentrations. Oxygen delivery to and consumption within the artery wall are altered by intra-arterial stent deployment. A role for artery wall hypoxia in artery wall pathology at the deployment site of an intra-arterial stent is supported by these findings.
KATP channel activation reduces the severity of postresuscitation myocardial dysfunction
Authors: Tang Wanchun , Weil Max Harry , Sun Shijie , Pernat Andrej , Mason Earl
Published: December 2017

Postresuscitation myocardial dysfunction has been recognized as a leading cause of the high postresuscitation mortality rate. We investigated the effects of ischemic preconditioning and activation of ATP-sensitive K+(KATP) channels on postresuscitation myocardial function. Ventricular fibrillation (VF) was induced in 25 Sprague-Dawley rats. Cardiopulmonary resuscitation (CPR), including mechanical ventilation and precordial compression, was initiated after 4 min of untreated VF. Defibrillation was attempted after 6 min of CPR. The animals were randomized to five groups treated with 1) ischemic preconditioning, 2) KATP channel opener, 3) ischemic preconditioning with KATP channel blocker administered 1 min after VF, 4) KATPchannel blocker administered 45 min before induction of ischemic preconditioning, and 5) placebo. Postresuscitation myocardial function, as measured by the rate of left ventricular pressure increase at 40 mmHg, the rate of left ventricular decline, cardiac index, and duration of survival, was significantly improved in both preconditioned and KATP channel opener-treated animals. KATP channel blocker administered 45 min before induction of ischemic preconditioning completely abolished the myocardial protective effects of preconditioning. We conclude that ischemic preconditioning significantly improved post-CPR myocardial function and survival. These results also provide evidence that the myocardial protective effects of ischemic preconditioning are mediated by KATP channel activation.
Time course of vasodilatory responses in skeletal muscle arterioles: role in hyperemia at onset of exercise
Authors: Wunsch Stacy A. , Muller-Delp Judy , Delp Michael D.
Published: December 2017

At the onset of dynamic exercise, muscle blood flow increases within 1–2 s. It has been postulated that local vasodilatory agents produced by the vascular endothelium or the muscle itself contribute to this response. We hypothesized that only vasodilators that act directly on the vascular smooth muscle could produce vasodilation of skeletal muscle arterioles in <2 s. To test this hypothesis, we determined the time course of the vasodilatory response of isolated skeletal muscle arterioles to direct application of potassium chloride, adenosine, acetylcholine, and sodium nitroprusside. Soleus and gastrocnemius muscles were dissected from the hindlimbs of male Sprague-Dawley rats. First-order arterioles (100–200 μm) were isolated, cannulated on micropipettes, and pressurized to 60 cmH2O in an organ bath. Vasodilatory agents were added directly to the bath, and diameter responses of the arterioles were recorded in real time on a videotape recorder. Frame-by-frame analysis of the diameter responses indicated that none of the vasodilator agents tested produced significant diameter increases in <4 s in either soleus or gastrocnemius muscle arterioles. These results indicate that, although these local vasodilators produce significant vasodilation of skeletal muscle resistance arterioles, these responses are not rapid enough (within 1–2 s) to contribute to the initiation of the exercise hyperemic response at the onset of dynamic exercise.
Alterations of endothelium and smooth muscle function in monocrotaline-induced pulmonary hypertensive arteries
Authors: Ito Kaoru M. , Sato Miharu , Ushijima Keiko , Nakai Masaaki , Ito Katsuaki
Published: December 2017

We examined how monocrotaline (MCT), which impairs the endothelium and causes pulmonary hypertension, altered the endothelial regulation of pulmonary artery functions. Rats were given a single injection of MCT (60 mg/kg sc). Pulmonary arteries were depolarized to −48.3 ± 2.6 and −39.8 ± 2.2 mV at 2 and 3 wk after treatment with MCT, respectively (control arteries −59.9 ± 1.9 mV). The basal tone in the resting state was only slightly elevated at 3 wk in endothelium-intact arteries. Removal of the endothelium caused further depolarization in MCT-affected arteries at 2 wk, but not at 3 wk, and greatly elevated the basal tone at 2 and 3 wk. Nω-nitro-l-arginine (200 μM), a nitric oxide synthase inhibitor, also caused depolarization in endothelium-intact arteries in both groups and elevated the basal tone of MCT-affected arteries. The relaxant responses of pulmonary arteries to ACh and A-23187 were depressed at 2 and 3 wk after MCT treatment. Thus chronic impairment of the endothelium altered the property of the pulmonary artery leading to depolarization. During the early stage of depolarization, a rise in the basal tone was offset by nitric oxide released from the injured endothelium.
Effects of mammary engorgement and feed withdrawal on microvascular function in lactating goat mammary glands
Authors: Farr Vicki C. , Prosser Colin G. , Davis Stephen R.
Published: December 2017

The responses of the mammary microvasculature in lactating goats ( n = 8) during feed withdrawal (18–20 h) and mammary engorgement (26–28 h of milk accumulation) were compared using an indicator-dilution technique with FITC-albumin and [14C]sucrose as the intravascular and diffusible indicators, respectively. Feed withdrawal and mammary engorgement caused a 50–60% decrease in mammary arterial flow and in the permeability-surface area product ( PS) values for sucrose. Only feed withdrawal increased the mean transit time [from 17.3 to 30.0 s, SE of the difference (SED) = 2.16, P< 0.01] of FITC-albumin, whereas only mammary engorgement reduced sucrose extraction (0.63 to 0.51, SED = 0.04, P < 0.05). Mammary engorgement also caused a substantial reduction in the sucrose-accessible extravascular space from 92 to 44 ml (SED = 15.2, P < 0.01). In a separate experiment using five goats, milking after mammary engorgement did not immediately restore arterial flow or sucrose extraction, indicating that the effect of milk accumulation was not mediated simply via increased intramammary pressure. In conclusion, feed withdrawal resulted in slower flow in the capillary bed but apparently no change in capillary recruitment, whereas mammary engorgement caused capillary derecruitment.
Biphasic effects of hyposmotic challenge on excitation-contraction coupling in rat ventricular myocytes
Authors: Brette F. , Calaghan S. C. , Lappin S. , White E. , Colyer J. , Le Guennec J.-Y.
Published: December 2017

The effects of short (1 min) and long (7–10 min) exposure to hyposmotic solution on excitation-contraction coupling in rat ventricular myocytes were studied. After short exposure, the action potential duration at 90% repolarization (APD90), the intracellular Ca2+concentration ([Ca2+]i) transient amplitude, and contraction increased, whereas the L-type Ca2+current ( ICa,L) amplitude decreased. Fractional sarcoplasmic reticulum (SR) Ca2+release increased but SR Ca2+load did not. After a long exposure, ICa,L, APD90, [Ca2+]itransient amplitude, and contraction decreased. The abbreviation of APD90was partially reversed by 50 μM DIDS, which is consistent with the participation of Cl−current activated by swelling. After 10-min exposure to hyposmotic solution in cells labeled with di-8-aminonaphthylethenylpyridinium, t-tubule patterning remained intact, suggesting the loss of de-t-tubulation was not responsible for the fall in ICa,L. After long exposure, Ca2+load of the SR was not increased, and swelling had no effect on the site-specific phosphorylation of phospholamban, but fractional SR Ca2+release was depressed. The initial positive inotropic response to hyposmotic challenge may be accounted for by enhanced coupling between Ca2+entry and release. The negative inotropic effect of prolonged exposure can be accounted for by shortening of the action potential duration and a fall in the ICa,Lamplitude.
Cardiac synthesis, processing, and coronary release of enkephalin-related peptides
Authors: Younès Antoine , Pepe Salvatore , Barron Barbara A. , Spurgeon Harold A. , Lakatta Edward G. , Caffrey James L.
Published: December 2017

Although preproenkephalin mRNA is abundant in the heart, the myocardial synthesis and processing of proenkephalin is largely undefined. Isolated working rat hearts were perfused to determine the rate of myocardial proenkephalin synthesis, its processing into enkephalin-containing peptides, their subsequent release into the coronary arteries, and the influence of prior sympathectomy. Enkephalin-containing peptides were separated by gel filtration and quantified with antisera for specific COOH-terminal sequences. Proenkephalin, peptide B, and [Met5]enkephalin-Arg6-Phe7(MEAP) comprised 95% of the extracted myocardial enkephalins (35 pmol/g). Newly synthesized enkephalins, estimated during a 1-h perfusion with [14C]phenylalanine (4 pmol · h−1· g wet wt−1), were rapidly cleared from the heart during a second isotope-free hour. Despite a steady release of enkephalins into the coronary effluent (4 pmol · h−1· g wet wt−1), enkephalin replacement apparently exceeded its release, and tissue enkephalins actually accumulated during hour 2. In contrast to the tissue, methionine-enkephalin accounted for more than half of the released enkephalin. Chemical sympathectomy produced an increase in total enkephalin content similar to that observed after 2-h control perfusion. This observation suggested that the normal turnover of myocardial enkephalin may depend in part on continued sympathetic influences.
High spatial resolution measurements of organ blood flow in small laboratory animals
Authors: Bernard Susan L. , Ewen Jon R. , Barlow Clyde H. , Kelly Jeff J. , McKinney Steven , Frazer David A. , Glenny Robb W.
Published: December 2017

With the use of a newly developed Imaging Cryomicrotome to determine the spatial location of fluorescent microspheres in organs, we validate and report our processing algorithms for measuring regional blood flow in small laboratory animals. Microspheres (15-μm diameter) of four different fluorescent colors and one radioactive label were simultaneously injected into the left ventricle of a pig. The heart and kidneys were dissected, and the numbers of fluorescent and radioactive microspheres were determined in 10 randomly selected pieces. All microsphere counts fell well within the 95% expected confidence limits as determined from the radioactive counts. Fluorescent microspheres (15-μm diameter) of four different colors were also injected into the tail vein of a rat and the left ventricle of a rabbit. After correction for Poisson noise, correlation coefficients between the colors were 0.99 ± 0.02 (means ± SD) for the rabbit heart and 0.99 ± 0.02 for the rat lung. Mathematical dissection algorithms, statistics to analyze the spatial data, and methods to visualize blood flow distributions in small animal organs are presented.
A metabolic role for mitochondria in palmitate-induced cardiac myocyte apoptosis
Authors: Sparagna Genevieve C. , Hickson-Bick Diane L. , Buja L. Maximilian , McMillin Jeanie B.
Published: December 2017

After cardiac ischemia, long-chain fatty acids, such as palmitate, increase in plasma and heart. Palmitate has previously been shown to cause apoptosis in cardiac myocytes. Cultured neonatal rat cardiac myocytes were studied to assess mitochondrial alterations during apoptosis. Phosphatidylserine translocation and caspase 3-like activity confirmed the apoptotic action of palmitate. Cytosolic cytochrome cwas detected at 8 h and plateaued at 12 h. The mitochondrial membrane potential (ΔΨ) in tetramethylrhodamine ethyl ester-loaded cardiac myocytes decreased significantly in individual mitochondria by 8 h. This loss was heterogeneous, with a few energized mitochondria per myocyte remaining at 24 h. Total ATP levels remained high at 16 h. The ΔΨ loss was delayed by cyclosporin A, a mitochondrial permeability transition inhibitor. Mitochondrial swelling accompanied changes in ΔΨ. Carnitine palmitoyltransferase I activity fell at 16 h; this decline was accompanied by ceramide increases that paralleled decreased complex III activity. We conclude that carnitine palmitoyltransferase I inhibition, ceramide accumulation, and complex III inhibition are downstream events in cardiac apoptosis mediated by palmitate and occur independent of events leading to caspase 3-like activation.
Characterization of nifedipine-resistant calcium current in neonatal rat ventricular cardiomyocytes
Authors: Pignier Christophe , Potreau Daniel
Published: December 2017

Calcium current was recorded from ventricular cardiomyocytes of rats at various stages of postnatal development using the whole cell patch-clamp technique. In cultured 3-day-old neonatal cells, the current carried by Ca2+ or Ba2+ (5 mM) was not completely inhibited by 2 μM nifedipine. A residual current was activated in the same voltage range as the L-type, nifedipine-sensitive Ca2+ current, but its steady-state inactivation was negatively shifted by 16 mV. This nifedipine-resistant calcium current was not further inhibited by other organic calcium current antagonists such as PN200-110, verapamil, and diltiazem nor by nickel, ω-conotoxin, or tetrodotoxin. It was completely blocked by cadmium and increased by isoproterenol and forskolin. This current was >20% of total calcium current in ventricular myocytes freshly isolated from neonatal rats, and it decreased during postnatal maturation, disappearing at the adult stage. This suggests that this current could be caused by an isoform of the L-type calcium channel expressed in a way that reflects the developmental stage of the rat heart.