bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of endothelial intermediate conductance KCachannels in cerebral EDHF-mediated dilations
Authors: Marrelli Sean P. , Eckmann Maxim S. , Hunte Michael S.
Published: March 2015

The present study evaluated the role of endothelial intermediate conductance calcium-sensitive potassium channels (IKCa) in the mechanism of endothelium-derived hyperpolarizing factor (EDHF)-mediated dilations in pressurized cerebral arteries. Male rat middle cerebral arteries (MCA) were mounted in an isolated vessel chamber, pressurized (85 mmHg), and luminally perfused (100 μl/min). Artery diameter was measured simultaneously with either endothelial intracellular Ca2+concentration ([Ca2+]i; fura-2) or changes in endothelial membrane potential [4-{2-[6-(dioctylamino)-2-naphthalenyl]ethenyl}1-(3-sulfopropyl)-pyridinium (di-8-ANEPPS)]. Nitric oxide synthase and cyclooxygenase inhibitors were present throughout. Luminal application of UTP produced EDHF-mediated dilations that correlated with significant endothelial hyperpolarization. The dilation and endothelial hyperpolarization were virtually abolished by inhibitors of IKCachannels but not by selective inhibitors of small or large conductance KCachannels (apamin and iberiotoxin, respectively). Additionally, direct stimulation of endothelial IKCachannels with 1-ethyl-2-benzimidazolinone (1-EBIO) produced endothelial hyperpolarization and vasodilatation that were blocked by inhibitors of IKCachannels. 1-EBIO hyperpolarized the endothelium but did not affect endothelial [Ca2+]i. We conclude that the mechanism of EDHF-mediated dilations in cerebral arteries requires stimulation of endothelial IKCachannels to promote endothelial hyperpolarization and subsequent vasodilatation.
Pressure overload alters stress-strain properties of the developing chick heart
Authors: Miller Christine E. , Wong Chandra L. , Sedmera David
Published: March 2015

As a first step in investigating a control mechanism regulating stress and/or strain in the embryonic heart, this study tests the hypothesis that passive mechanical properties of left ventricular (LV) embryonic myocardium change with chronically increased pressure during the chamber septation period. Conotruncal banding (CTB) created ventricular pressure overload in chicks from Hamburger-Hamilton (HH) stage 21 (HH21) to HH27, HH29, or HH31. LV sections were cyclically stretched while biaxial strains and force were measured. Wall architecture was assessed with scanning electron microscopy. In controls, porosity-adjusted stress-strain relations decreased significantly from HH27 to HH31. CTB at HH21 resulted in significantly stiffer stress-strain relations by HH27, with larger increases at HH29 and HH31, and nearly constant wall thickness. Strain patterns, hysteresis, and loading-curve convergence showed few differences after CTB. Trabecular extent decreased with age, but neither extent nor porosity changed significantly after CTB. The stiffened stress-strain relations and constant wall thickness suggest that mechanical load may play a regulatory role in this response.
Developmental changes in left and right ventricular diastolic filling patterns in mice
Authors: Zhou Yu-Qing , Foster F. Stuart , Parkes Robert , Adamson S. Lee
Published: March 2015

Developmental changes in left and right ventricular diastolic filling patterns were determined noninvasively in isoflurane-anesthetized outbred ICR mice. Blood velocities in the mitral and tricuspid orifices were recorded in 16 embryos at days 14.5 (E14.5) and 17.5 of gestation (E17.5) using an ultrasound biomicroscope and also serially in three groups of postnatal mice aged 1–7 days ( n = 23), 1–4 wk ( n = 18), and 4–12 wk ( n = 27) using 20-MHz pulsed Doppler. Postnatal body weight increased rapidly to 8 wk. Heart rate increased rapidly from ∼180 beats/min at E14.5 to ∼380 beats/min at 1 wk after birth and then more gradually to plateau at ∼450 beats/min after 4 wk. Ventricular filling was quantified using the ratio of peak velocity of early ventricular filling due to active relaxation (E wave) to that of the late ventricular filling caused by atrial contraction (A wave) (peak E/A ratio) and the ratio of the peak E velocity to total time-velocity integral of E and A waves (peak E/total TVI ratio). Both ventricles had similar diastolic filling patterns in embryos (peak E/A ratio of 0.28 ± 0.02 for mitral flow and 0.27 ± 0.02 for tricuspid flow at E14.5). After birth, mitral peak E/A increased to >1 between the third and fifth day, continued to increase to 2.25 ± 0.25 at ∼3 wk, and then remained stable. The tricuspid peak E/A ratio increased much less but stabilized at the same age (increased to 0.79 ± 0.03 at 3 wk). The peak E/total TVI ratio showed similar left-right differences and changes with development. Age-related changes were largely due to increases in peak E velocity. The results suggest that diastolic function matures ∼3 wk postnatally, presumably in association with maturation of ventricular recoil and relaxation mechanisms.
Properties of potassium currents in Purkinje cells of failing human hearts
Authors: Han Wei , Zhang Liming , Schram Gernot , Nattel Stanley
Published: March 2015

Cardiac Purkinje fibers play an important role in cardiac arrhythmias, but no information is available about ionic currents in human cardiac Purkinje cells (PCs). PCs and midmyocardial ventricular myocytes (VMs) were isolated from explanted human hearts. K+ currents were evaluated at 37°C with whole cell patch clamp. PCs had clear inward rectifier K+current ( I K1), with a density not significantly different from VMs between −110 and −20 mV. A Cs+-sensitive, time-dependent hyperpolarization-activated current was measurable negative to −60 mV. Transient outward current ( I to) density was smaller, but end pulse sustained current ( I sus) was larger, in PCs vs. VMs. I to recovery was substantially slower in PCs, leading to strong frequency dependence. Unlike VM I to, which was unaffected by 10 mM tetraethylammonium, Purkinje I to was strongly inhibited by tetraethylammonium, and Purkinje I to was 10-fold more sensitive to 4-aminopyridine than VM. PC I sus was also reduced strongly by 10 mM tetraethylammonium. In conclusion, human PCs demonstrate a prominent I K1, a time-dependent hyperpolarization-activated current, and an I towith pharmacological sensitivity and recovery kinetics different from those in the atrium or ventricle and compatible with a different molecular basis.
Plasmalemmal KATPchannels shape triggered calcium transients in metabolically impaired rat atrial myocytes
Authors: Baumann Philippe , Poitry Serge , Roatti Angela , Baertschi Alex J.
Published: March 2015

The relative role of plasmalemmal and mitochondrial ATP-sensitive K+(KATP) channels in calcium homeostasis of the atrium is little understood. Electrically triggered (1 Hz) cytoplasmic calcium transients were measured by 340-to-380-nm wavelength fura 2 emission ratios in cultured rat atrial myocytes. CCCP, a mitochondrial protonophore (100–400 nmol/l), dose dependently reduced the transient amplitude by up to 85%, caused a slow rise in baseline calcium, and reduced the recovery time constant of the transient from 143 to 91 ms ( P < 0.05). However, neither 5-hydroxydecanoate, a mitochondrial KATPchannel blocker, nor diazoxide (500 μmol/l) affected the amplitude, baseline, or time constant in CCCP-treated cells. HMR-1098 (30 μmol/l), a plasmalemmal KATPchannel blocker, and glibenclamide (1 μmol/l) increased the amplitude in CCCP-treated myocytes by 69–82%, sharply elevated the calcium baseline, and prolonged the recovery time constant to 181–193 ms ( P < 0.01). Thus opening of plasmalemmal but not mitochondrial KATPchannels reduces the calcium overload in metabolically compromised but otherwise intact atrial myocytes. Mitochondrial KATPchannels probably operate through a different mechanism to afford ischemic protection.
Alterations in rat coronary vasoreactivity and vascular protein kinase C isoforms in Type 1 diabetes
Authors: Tickerhoof M. M. , Farrell P A. , Korzick D. H.
Published: March 2015

Vascular complications associated with diabetes mellitus (DM) have been linked to activation of PKC-dependent signaling pathways in both human and animal models of DM. To determine whether aberrant PKC signaling mechanisms specifically impact the coronary circulation, we assessed isolated coronary artery (CA) responses after the induction of Type 1 DM. Male Sprague-Dawley rats were subjected to partial pancreatectomy (DM; n = 23) and compared with age-matched controls (CTL; n = 19). Vasoreactivity was assessed in single CAs (∼250 μm internal diameter) after abluminal administration of the Gq-dependent vasoconstrictors endothelin (ET)-1 (10–10–10–9M) and U-44619 (10–9–10–5M) or the voltage-gated Ca2+channel agonist BAY K 8644 (10–9–10–5M) with and without the PKC inhibitor bisindolylmaleimide (Bis; 10–6M). Dilator responses to ACh (10–9–10–5M) were also assessed. ET-1 resulted in significantly greater constriction in the DM versus CTL group (50 ± 4% vs. 33 ± 5%, P < 0.0001), whereas responses to U-44619 and BAY K 8644 were similar between groups. Importantly, inhibition of ET-1 and U-44619 constriction by Bis occurred in the DM but not CTL group ( P < 0.05). Western blotting on isolated CAs revealed greater levels of PKC-α, PKC-βI, and PKC-βIIby 22%, 15.3%, and 17.6%, respectively, in the DM versus CTL group ( P < 0.05), whereas PKC-δ and PKC-ϵ protein levels were unchanged. DM was also associated with attenuated CA dilation after ACh treatment ( P < 0.0566) and reductions in endothelial nitric oxide synthase protein levels versus CTL ( P < 0.03). These data suggest that Ca2+-dependent PKC signaling pathways, particularly for ET-1, play a greater role in modulating CA vasoconstrictor responses in DM versus CTL. These data further suggest that aberrant CA constrictor and dilator responses are likely to contribute to the coronary vascular pathology associated with DM.
Estrogen therapy induces collateral and microvascular remodeling
Authors: Lamping Kathryn G. , Christensen Lance P. , Tomanek Robert J.
Published: March 2015

Estrogen increases proliferation and migration of cultured endothelial cells and perfusion of ischemic hindlimbs of rabbits. We tested the hypothesis that estrogen is angiogenic and arteriogenic in the heart during progressive coronary occlusion. Ovariectomized (OVX) and 17β-estradiol (1 mg · kg–1 · wk–1 im)-treated OVX (OVX-ES) female New Zealand White rabbits were instrumented with an ameroid occluder on a proximal coronary artery. Four weeks after implantation of an ameroid occluder, we measured myocardial perfusion with microspheres at rest and during adenosine-induced maximal vasodilation. The heart was fixed by perfusion at physiological pressure, and capillary angiogenesis and remodeling were assessed by image analysis of tissue sections in collateral-dependent myocardium. Coronary conductance was higher at rest and during maximal vasodilation in collateral-dependent myocardium of OVX-ES than OVX rabbits. Estrogen treatment increased the wall-to-lumen ratio of collateral vessels while it decreased the wall-to-lumen ratio of noncollateral arteries in normal regions. In normal and collateral-dependent myocardium, mean capillary diameter and capillary volume density were greater in OVX-ES rabbits. However, estrogen had no effect on capillary length density in either region of the myocardium. These data suggest that estrogen induces remodeling of the collateral vasculature and may stimulate growth of the resistance vessels, thereby providing protection during development of a gradual coronary occlusion.
Acute adenosinergic cardioprotection in ischemic-reperfused hearts
Authors: Headrick John P. , Hack Ben , Ashton Kevin J.
Published: March 2015

Cells of the cardiovascular system generate and release purine nucleoside adenosine in increasing quantities when constituent cells are “stressed” or subjected to injurious stimuli. This increased adenosine can interact with surface receptors in myocardial, vascular, fibroblast, and inflammatory cells to modulate cellular function and phenotype. Additionally, adenosine is rapidly reincorporated back into 5′-AMP to maintain the adenine nucleotide pool. Via these receptor-dependent and independent (metabolic) paths, adenosine can substantially modify the acute response to ischemic insult, in addition to generating a more sustained ischemia-tolerant phenotype (preconditioning). However, the molecular basis for acute adenosinergic cardioprotection remains incompletely understood and may well differ from more widely studied preconditioning. Here we review current knowledge and some controversies regarding acute cardioprotection via adenosine and adenosine receptor activation.
Modulatory role of a constitutively active population of α1D-adrenoceptors in conductance arteries
Authors: Ziani Khalid , Gisbert Regina , Noguera Maria Antonia , Ivorra Maria Dolores , D'Ocon Pilar
Published: March 2015

A constitutively active population of α1D-adrenoceptors in iliac and proximal, distal, and small mesenteric rat arteries was studied. The increase in resting tone (IRT) that evidences it was observed only in iliac and proximal mesenteric and was inhibited by prazosin (pIC50 = 9.57), 5-methylurapidil (pIC50 = 7.61), and BMY 7378 (pIC50 = 8.77). Chloroethylchlonidine (100 μmol/l) did not affect IRT, but when added before the other antagonists it blocked their effect. The potency shown by BMY 7378 confirms the α1D-subtype as responsible for IRT. BMY 7378 displayed greater inhibition of adrenergic responses in iliac (pIC50 = 7.57 ± 0.11) and proximal mesenteric arteries (pIC50 = 8.05 ± 0.2) than in distal (pIC50 = 6.94 ± 0.13) or small mesenteric arteries (pIC50 = 6.30 ± 0.14), which confirms the functional role of the α1D-adrenoceptor in iliac and proximal mesenteric arteries. This subtype prevents abrupt changes in iliac and proximal mesenteric artery caliber when the agonist disappears, and this modulatory role is evidenced by the slower decay in the response to norepinephrine after removal.
Differential expression of TNF-α, IL-6, and IGF-1 by graded mechanical stress in normal rat myocardium
Authors: Palmieri Emiliano A. , Benincasa Giulio , Di Rella Francesca , Casaburi Cosma , Monti Maria G. , De Simone Giuseppe , Chiariotti Lorenzo , Palombini Lucio , Bruni Carmelo B. , Saccà Luigi , Cittadini Antonio
Published: March 2015

An isovolumic normal rat heart Langendorff model was used to examine the effects of moderate (15 mmHg) and severe (35 mmHg) mechanical stretch on the time course (from 0 to 60 min) of myocardial expression of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and insulin-like growth factor (IGF)-1 and their cognate receptors. After 10 min of moderate stretch, TNF-α was de novo expressed, whereas constitutive IL-6 and IGF-1 levels were slightly upregulated; no further changes occurred up to 60 min. In comparison, severe stretch resulted in a higher and progressive increase in TNF-α, IL-6, and IGF-1 expression up to 20 min. After 20 min, whereas TNF-α expression further increased, IL-6 and IGF-1 levels progressively reduced to values lower than those observed under moderate stretch and in unstretched (5 mmHg) control myocardium (IL-6). Mechanical stretch did not significantly alter the expression of the cognate receptors. Indeed, the TNF-α receptor (p55) tended to be progressively upregulated under severe stretch over time. The current data provide the first demonstration that TNF-α, IL-6, and IGF-1 ligand-receptor systems are differentially expressed within the normal rat myocardium in response to graded mechanical stretch. Such findings may have potential implications with regard to compensatory hypertrophy and failure.
In vivo measurement of coronary circulation angiotensin-converting enzyme activity in humans
Authors: Staniloae Cezar , Schwab Andreas J. , Simard André , Gallo Richard , Dyrda Ihor , Gosselin Gilbert , Lespérance Jacques , Ryan James W. , Dupuis Jocelyn
Published: March 2015

Angiotensin-converting enzyme (ACE) is present on the luminal surface of the coronary vessels, mostly on capillary endothelium. ACE is also expressed on coronary smooth muscle cells and on plaque lipid-laden macrophages. Excessive coronary circulation (CC)-ACE activity might be linked to plaque progression. Here we used the biologically inactive ACE substrate3H-labeled benzoyl-Phe-Ala-Pro ([3H]BPAP) to quantify CC-ACE activity in 10 patients by means of the indicator-dilution technique. The results were compared with atherosclerotic burden determined by coronary angiography. There was a wide range of CC-ACE activity as revealed by percent [3H]BPAP hydrolysis (30–74%). The atherosclerotic extent scores ranged from 0.0 to 66.97, and the plaque area scores ranged from 0 to 80 mm2. CC-ACE activity per unit extracellular space ( V max/ K m V i), an index of metabolically active vascular surface area, was correlated with myocardial blood flow ( r = 0.738; P = 0.03) but not with measures of the atherosclerotic burden. These results show that CC-ACE activity can be safely measured in humans and that it is a good marker of the vascular area of the perfused myocardium. It does not, however, reflect epicardial atherosclerotic burden, suggesting that local tissue ACE may be more important in plaque development.
Mechanism of enhanced calcium sensitivity and α2-AR vasoreactivity in chronic NOS inhibition hypertension
Authors: Carter Rebecca W. , Kanagy Nancy L.
Published: March 2015

PKC augments calcium sensitivity in spontaneously hypertensive rats and contributes to α2-adrenergic receptor (AR) contraction in rabbit saphenous vein. We showed previously that denuded aortic rings from Nω-nitro-l-arginine-treated hypertensive rats (LHR) contract more to CaCl2and to the α2-AR agonist UK-14304 than do rings from normotensive rats (NR). We hypothesized that enhanced PKC activity or a change in PKC isoform contributes to augmented calcium sensitivity and enhanced α2-AR contraction in LHR aorta. Current studies demonstrate that non-isoform-specific PKC inhibitors reduced UK-14304 contraction in both NR and LHR aorta. However, the calcium-dependent PKC inhibitor Gö-6976 only attenuated contraction in LHR aorta. Additionally, UK-14304 translocated PKC-δ to the membrane in NR aorta, whereas PKC-α was translocated to the membrane in LHR aorta. Finally, in ionomycin-permeabilized aorta Gö-6976 eliminated enhanced basal and augmented α2-AR-stimulated calcium sensitivity in LHR aorta but did not affect NR contraction. Together, these data suggest that PKC-α contributes to augmented calcium sensitivity and α2-AR reactivity after chronic nitric oxide synthase inhibition hypertension.
Ouabain-induced hypertension is accompanied by increases in endothelial vasodilator factors
Authors: Rossoni Luciana V. , Salaices Mercedes , Miguel Marta , Briones Ana M. , Barker Louis A. , Vassallo Dalton V. , Alonso María J.
Published: March 2015

The involvement of nitric oxide (NO), prostaglandins, and calcium-dependent potassium channel (KCa) activators on the negative modulation of phenylephrine-induced contractions was evaluated on the isolated aorta and caudal (CAU) artery obtained from rats treated with ouabain for 5 wk to induce hypertension. In ouabain-treated rats, the reactivity to phenylephrine was reduced in the endothelium-intact aorta but not the CAU segments. Endothelial modulation of phenylephrine contraction, as demonstrated by endothelium removal, NO synthase (NOS) inhibition with N ω-nitro-l-arginine methyl ester and aminoguanidine, as well as KCa inhibition with tetraethylammonium, was more pronounced in segments from ouabain-treated animals, and here greater effects were seen in the aorta than in CAU. An increased expression of endothelial NOS and neuronal NOS was seen in the aorta after ouabain treatment. In CAU, only endothelial NOS was detected and ouabain treatment did not alter its expression. These results suggest that ouabain-induced hypertension is accompanied by increased NO release derived from endothelial NOS and neuronal NOS and increased release of an endothelial hyperpolarizing factor that presumably opens KCa, all of which contribute to the increased negative modulation of the phenylephrine contraction.
Right ventricular diastolic function in canine models of pressure overload, volume overload, and ischemia
Authors: Pasipoularides Ares , Shu Ming , Shah Ashish , Silvestry Scott , Glower Donald D.
Published: March 2015

By limiting filling, abnormalities of right ventricular (RV) diastolic function may impair systolic function and affect adaptation to disease. To quantify diastolic RV pressure-volume relations and myocardial compliance (MC), a new sigmoidal model was developed. RV micromanometric and sonomicrometric data in alert dogs at control ( n = 16) and under surgically induced subacute (2–5 wk) RV pressure overload ( n = 6), volume overload ( n = 7), and ischemia ( n = 6) were analyzed. The conventional exponential model detected no changes from control in the passive filling pressure-volume (Ppf-V) relations. The new sigmoidal model revealed significant quantifiable changes in Ppf-V relations. Maximum RV MC (MCmax), attained during early filling, is reduced from control in pressure overload ( P = 0.0016), whereas filling pressure at maximum MC (PMCmax) is increased ( P = 0.0001). End-diastolic RV MC increases significantly in volume overload ( P = 0.0131), whereas end-diastolic pressure is unchanged. In ischemia, MCmax is decreased ( P = 0.0102), with no change in PMCmax. We conclude that the sigmoidal model quantifies important changes in RV diastolic function in alert dog models of pressure overload, volume overload, and ischemia.
Phase I and phase II of short-term mechanical restitution in perfused rat left ventricles
Authors: Dumitrescu Cristian , Narayan Prakash , Cheng Yuanna , Efimov Igor R. , Altschuld Ruth A.
Published: March 2015

We examined the contributions of the Ca2+channels of the sarcolemma and of the sarcoplasmic reticulum to electromechanical restitution. Extrasystoles (F1) were interpolated 40–600 ms following a steady-state beat (F0) in perfused rat ventricles paced at 2 or 3 Hz. Plots of F1/F0versus the extrasystolic interval consisted of phase I, which occurred before relaxation of the steady-state beat, and phase II, which occurred later. Phase I exhibited a period of enhanced left ventricular pressure development that coincided with action potential prolongation. Phase I was eliminated by −BAY K 8644 (100 nM) and FPL 64176 (150 nM), augmented by 3 μM thapsigargin plus 200 nM ryanodine and unaffected by KN-93 and KB-R7943. Phase II was accelerated by the Ca2+channel agonists and by isoproterenol but was eliminated by thapsigargin plus ryanodine. The results suggest that phase I of electromechanical restitution is caused by a transient L-type Ca2+current facilitation, whereas phase II represents the recovery of the ability of the sarcoplasmic reticulum to release Ca2+.
Regulation of murine myocardial energy metabolism during adrenergic stress studied by in vivo31P NMR spectroscopy
Authors: Naumova A. V. , Weiss R. G. , Chacko V. P.
Published: March 2015

Image-guided, spatially localized31P magnetic resonance spectroscopy (MRS) was used to study in vivo murine cardiac metabolism under resting and dobutamine-induced stress conditions. Intravenous dobutamine infusion (24 μg · min–1· kg body wt–1) increased the mean heart rate by ∼39% from 482 ± 46 per min at baseline to 669 ± 77 per min in adult mice. The myocardial phosphocreatine (PCr)-to-ATP (PCr/ATP) ratio remained unchanged at 2.1 ± 0.5 during dobutamine stress, compared with baseline conditions. Therefore, we conclude that a significant increase in heart rate does not result in a decline in the in vivo murine cardiac PCr/ATP ratio. These observations in very small mammals, viz., mice, at extremely high heart rates are consistent with studies in large animals demonstrating that global levels of high-energy phosphate metabolites do not regulate in vivo myocardial metabolism during physiologically relevant increases in cardiac work.
Acetylcholine but not adenosine triggers preconditioning through PI3-kinase and a tyrosine kinase
Authors: Qin Qining , Downey James M. , Cohen Michael V.
Published: March 2015

Adenosine and acetylcholine (ACh) trigger preconditioning by different signaling pathways. The involvement of phosphatidylinositol 3-kinase (PI3-kinase), a protein tyrosine kinase, and Src family tyrosine kinase in preconditioning was evaluated in isolated rabbit hearts. Either wortmannin (PI3-kinase blocker), genistein (tyrosine kinase blocker), lavendustin A (tyrosine kinase blocker), or 4-amino-5-(4-chlorophenyl)-7-( t-butyl)pyrazolol[3,4-d]pyrimidine (PP2; Src family tyrosine kinase blocker) was given for 15 min to bracket a 5-min infusion of either adenosine or ACh (trigger phase). The hearts then underwent 30 min of regional ischemia. Infarct size for ACh alone was 9.3 ± 3.5% of the risk zone versus 34.3 ± 4.1% in controls. All four inhibitors blocked ACh-induced protection. When wortmannin or PP2 was infused only during the 30-min ischemic period (mediator phase), ACh-induced protection was not affected (7.4 ± 2.1% and 9.7 ± 1.7% infarction, respectively). Adenosine-triggered protection was not blocked by any of the inhibitors. Therefore, PI3-kinase and at least one protein tyrosine kinase, probably Src kinase, are involved in the trigger phase of ACh-induced, but not adenosine-induced, preconditioning. Neither PI3-kinase nor Src kinase is a mediator of the protection of ACh.
Low arterial compliance in young African-American males
Authors: Zion Adrienne S. , Bond Vernon , Adams Richard G. , Williams Deborah , Fullilove Robert E. , Sloan Richard P. , Bartels Matthew N. , Downey John A. , De Meersman Ronald E.
Published: March 2015

Hypertension remains a common public health challenge because of its prevalence and increase in co-morbid cardiovascular diseases. Black males have disproportionate pathophysiological consequences of hypertension compared with any other group in the United States. Alterations in arterial wall compliance and autonomic function often precede the onset of disease. Accordingly, our purpose was to investigate whether differences exist in arterial compliance and autonomic function between young, healthy African-American males without evidence of hypertension and age- and gender-matched non-African-American males. All procedures were carried out noninvasively following rest. Arterial compliance was calculated as the integrated area starting at the well-defined nadir of the incisura of the dicrotic notch to the end of diastole of the radial artery pulse wave. Power spectral analysis of heart rate and blood pressure variability provided distributions representative of parasympathetic and sympathetic modulations and sympathovagal balance. Baroreflex sensitivity (BRS) was calculated using the sequence method. Thirty-two African-American and twenty-nine non-African-American males were comparable in anthropometrics and negative family history of hypertension. t-Tests revealed lower arterial compliance (5.8 ± 2.4 vs. 8.6 ± 4.0 mmHg · s; P = 0.0017), parasympathetic modulation (8.9 ± 1.1 vs. 9.7 ± 1.1 ln ms2; P = 0.0063), and BRS (13.7 ± 7.3 vs. 21.1 ± 8.5 ms/mmHg; P = 0.0007) and higher sympathovagal balance (2.9 ± 3.2 vs. 1.5 ± 1.1; P = 0.03) in the African-American group. In summary, differences exist in arterial compliance and autonomic balance in African-American males. These alterations may be antecedent markers of disease and valuable in the detection of degenerative cardiovascular processes in individuals at risk.
Inhibition of NO production increases myocardial blood flow and oxygen consumption in congestive heart failure
Authors: Traverse Jay H. , Chen Yingjie , Hou Mingxiao , Bache Robert J.
Published: March 2015

Coronary blood flow (CBF) and myocardial oxygen consumption (MV˙o 2) are reduced in dogs with pacing-induced congestive heart failure (CHF), which suggests that energy metabolism is downregulated. Because nitric oxide (NO) can inhibit mitochondrial respiration, we examined the effects of NO inhibition on CBF and MV˙o 2 in dogs with CHF. CBF and MV˙o 2 were measured at rest and during treadmill exercise in 10 dogs with CHF produced by rapid ventricular pacing before and after inhibition of NO production with N G-nitro-l-arginine (l-NNA, 10 mg/kg iv). The development of CHF was accompanied by decreases in aortic and left ventricular (LV) systolic pressure and an increase in LV end-diastolic pressure (25 ± 2 mmHg). l-NNA increased MV˙o 2 at rest (from 3.07 ± 0.61 to 4.15 ± 0.80 ml/min) and during exercise; this was accompanied by an increase in CBF at rest (from 31 ± 2 to 40 ± 4 ml/min) and during exercise (both P < 0.05). Althoughl-NNA significantly increased LV systolic pressure, similar increases in pressure produced by phenylephrine did not increase MV˙o 2. The findings suggest that NO exerts tonic inhibition on respiration in the failing heart.
Branching tree model with fractal vascular resistance explains fractal perfusion heterogeneity
Authors: Marxen M. , Henkelman R. M.
Published: March 2015

Perfusion heterogeneities in organs such as the heart obey a power law as a function of scale, a behavior termed “fractal.” An explanation of why vascular systems produce such a specific perfusion pattern is still lacking. An intuitive branching tree model is presented that reveals how this behavior can be generated as a consequence of scale-independent branching asymmetry and fractal vessel resistance. Comparison of computer simulations to experimental data from the sheep heart shows that the values of the two free model parameters are realistic. Branching asymmetry within the model is defined by the relative tissue volume being fed by each branch. Vessel ordering for fractal analysis of morphology based on fed or drained tissue volumes is preferable to the commonly used Strahler system, which is shown to depend on branching asymmetry. Recently, noninvasive imaging techniques such as PET and MRI have been used to measure perfusion heterogeneity. The model allows a physiological interpretation of the measured fractal parameters, which could in turn be used to characterize vascular morphology and function.
Role of receptor kinase in long-term desensitization of the cardiac muscarinic receptor-K+channel system
Authors: Shui Z. , Khan I. A. , Tsuga H. , Dobrzynski H. , Haga T. , Henderson Z. , Boyett M. R.
Published: March 2015

Desensitization of the cardiac muscarinic K+channel was studied in cultured neonatal rat atrial cells and in Chinese hamster ovary (CHO) cells transfected with muscarinic receptor (HM2), G protein-coupled inward rectifying K+channels 1 and 4, and G protein-coupled receptor kinase 2. In atrial cells incubated in 10 μM carbachol for 24 h, channel activity in cell-attached patches was substantially reduced as a result of long-term desensitization. The long-term desensitization was also observed in CHO cells transfected with the wild-type receptor and receptor kinase (as well as the channel). However, long-term desensitization was greatly reduced or abolished if the cells were 1) not transfected with the receptor kinase, 2) transfected with a mutant receptor lacking phosphorylation sites (rather than the wild-type receptor), or 3) transfected with a mutant receptor kinase lacking kinase activity (rather than the wild-type receptor kinase). We suggest that long-term desensitization of the cardiac muscarinic receptor-K+channel system to muscarinic agonist may involve phosphorylation of the receptor by receptor kinase.
Exercise-induced improvement in endothelial dysfunction is not mediated by changes in CV risk factors: pooled analysis of diverse patient populations
Authors: Green Daniel J. , Walsh Jennifer H. , Maiorana Andrew , Best Matthew J. , Taylor Roger R. , O'Driscoll J. Gerard
Published: March 2015

We have pooled data from a series of our exercise training studies undertaken in groups with a broad range of vascular (dys) function to the examine the hypothesis that exercise-induced improvements in the conduit and/or resistance vessel function are related to improvements in risk factors for cardiovascular (CV) disease. Endothelium-dependent and -independent conduit vessel function were assessed by using wall tracking of high-resolution ultrasound images of the brachial artery response to flow-mediated dilation (FMD) and glyceryl trinitrate. Resistance vessel function was assessed using intrabrachial administration of acetylcholine (ACh), sodium nitroprusside, and NG-monomethyl-l-arginine. Randomized cross-over studies of 8-wk exercise training were undertaken in untreated hypercholesterolemic ( n = 11), treated hypercholesterolemic ( n = 11), coronary artery disease ( n = 10), chronic heart failure ( n = 12), Type 2 diabetic ( n = 15), and healthy control subjects ( n = 16). Exercise training did not significantly alter plasma lipids, blood pressure, blood glucose, waist-to-hip ratio, or body mass index values, despite significant improvement in both FMD and ACh responses. There were no correlations between changes in any risk factor variables and indexes of either resistance or conduit vessel function. We conclude that, in these subjects with antecedent vascular dysfunction, the beneficial effects of relatively short-term exercise training on vascular function are not solely mediated by the effects of exercise on CV risk factors.
Effect of PDE5 inhibition on coronary hemodynamics in pacing-induced heart failure
Authors: Chen YingJie , Traverse Jay H. , Hou Mingxiao , Li Yunfang , Du Ruisheng , Bache Robert J.
Published: March 2015

Inhibition of phosphodiesterase type 5 (PDE5) can relax systemic and coronary vessels by causing accumulation of cGMP. Both the endothelial dysfunction with decreased nitric oxide production and increased natriuretic peptide levels in congestive heart failure (CHF) have the potential to alter cGMP production, thereby influencing the response to PDE5 inhibition. Consequently, this study examined the effects of PDE5 inhibition with sildenafil in dogs with CHF produced by rapid ventricular pacing. CHF resulted in decreases of left ventricular (LV) systolic pressure, coronary blood flow, and the maximal first time derivative of LV pressure (LV dP/d t max) at rest and during treadmill exercise compared with normal, whereas resting LV end-diastolic pressure increased from 10 ± 1.4 to 23 ± 1.4 mmHg. Sildenafil (2 and 10 mg/kg per os) caused a 5- to 6-mmHg decrease of aortic pressure ( P < 0.05), with no change of heart rate, LV systolic pressure, or LV dP/d t max. Sildenafil caused no change in coronary flow or myocardial oxygen consumption in animals with CHF at rest or during exercise. In contrast to findings in normal animals, sildenafil did not augment endothelium-dependent coronary vasodilation in response to acetylcholine in animals with CHF. Furthermore, Western blotting showed decreased PDE5 protein expression in myocardium from failing hearts. These findings demonstrate that PDE5 contributes little to regulation of coronary hemodynamics in CHF.
Role of T-type calcium channels in myogenic tone of skeletal muscle resistance arteries
Authors: VanBavel Ed , Sorop Oana , Andreasen Ditte , Pfaffendorf Martin , Jensen Boye L.
Published: March 2015

T-type calcium channels may be involved in the maintenance of myogenic tone. We tested their role in isolated rat cremaster arterioles obtained after CO2anesthesia and decapitation. Total RNA was analyzed by RT-PCR and Southern blotting for calcium channel expression. We observed expression of voltage-operated calcium (CaV) channels CaV3.1 (T-type), CaV3.2 (T-type), and CaV1.2 (L-type) in cremaster arterioles ( n= 3 rats). Amplification products were observed only in the presence of reverse transcriptase and cDNA. Concentration-response curves of the relatively specific L-type blocker verapamil and the relatively specific T-type blockers mibefradil and nickel were made on cannulated vessels with either myogenic tone (75 mmHg) or a similar level of constriction induced by 30 mM K+ at 35 mmHg. Mibefradil and nickel were, respectively, 162-fold and 300-fold more potent in inhibiting myogenic tone compared with K+-induced constriction [log(IC50, M): mibefradil, basal −7.3 ± 0.2 ( n = 9) and K+ −5.1 ± 0.1 ( n = 5); nickel, basal −4.1 ± 0.2 ( n = 5) and K+ −1.6 ± 0.5 ( n = 5); means ± SE]. Verapamil had a 17-fold more potent effect [log(IC50, M): basal −6.6 ± 0.1 ( n = 5); K+ −5.4 ± 0.3 ( n = 4); all log(IC50) P < 0.05, basal vs. K+]. These data suggest that T-type calcium channels are expressed and involved in maintenance of myogenic tone in rat cremaster muscle arterioles.
Time course of right ventricular remodeling in rats with experimental myocardial infarction
Authors: Nahrendorf Matthias , Hu Kai , Fraccarollo Daniela , Hiller Karl-Heinz , Haase Axel , Bauer Wolfgang R. , Ertl Georg
Published: March 2015

Right ventricular (RV) weight increases dependent on time after myocardial infarction (MI) and on MI size. The sequential changes in RV volume and hemodynamics and their relations to left ventricular (LV) remodeling after MI are unknown. We therefore examined the time course of RV remodeling in rats with LV MI. MI was produced by left coronary artery ligation. Four, eight, and sixteen weeks later, LV and RV hemodynamic measurements were performed and pressure-volume curves were obtained. For serial measurement of RV volumes and performance, cine-MRI was performed 2 and 8 wk after MI. The ratios of β-myosin heavy chain (MHC) to α-MHC and skeletal to cardiac α-actin were determined for the RV and LV after large MI or sham operation. RV weight increased in rats with MI, as did RV volume. RV pressure-volume curves were shifted toward larger volumes 16 wk after large MI. RV systolic pressure increased gradually over time; however, the gain in RV weight was always in excess of RV systolic pressure. The ratios of skeletal to cardiac α-actin and β-MHC to α-MHC were increased after MI in both ventricles in a similar fashion. Because RV wall stress was not increased after infarction, mechanical factors may not conclusively explain hypertrophy, which maintained balanced loading conditions for the RV even after large LV infarction.
O2release from Hb vesicles evaluated using an artificial, narrow O2-permeable tube: comparison with RBCs and acellular Hbs
Authors: Sakai Hiromi , Suzuki Yoji , Kinoshita Megumi , Takeoka Shinji , Maeda Nobuji , Tsuchida Eishun
Published: March 2015

A phospholipid vesicle that encapsulates a concentrated hemoglobin (Hb) solution and pyridoxal 5′-phosphate as an allosteric effector [Hb vesicle (HbV) diameter, 250 nm] has been developed to provide an O2carrying ability to plasma expanders. The O2release from flowing HbVs was examined using an O2-permeable, fluorinated ethylenepropylene copolymer tube (inner diameter, 28 μm) exposed to a deoxygenated environment. Measurement of O2release was performed using an apparatus that consisted of an inverted microscope and a scanning-grating spectrophotometer with a photon-count detector, and the rate of O2release was determined based on the visible absorption spectrum in the Q band of Hb. HbVs and fresh human red blood cells (RBCs) were mixed in various volume ratios at a Hb concentration of 10 g/dl in isotonic saline that contained 5 g/dl albumin, and the suspension was perfused at the centerline flow velocity of 1 mm/s through the narrow tube. The mixtures of acellular Hb solution and RBCs were also tested. Because HbVs were homogeneously dispersed in the albumin solution, increasing the volume of the HbV suspension resulted in a thicker marginal RBC-free layer. Irrespective of the mixing ratio, the rate of O2release from the HbV/RBC mixtures was similar to that of RBCs alone. On the other hand, the addition of 50 vol% of acellular Hb solution to RBCs significantly enhanced the rate of deoxygenation. This outstanding difference in the rate of O2release between the HbV suspension and the acellular Hb solution should mainly be due to the difference in the particle size (250 vs. 7 nm) that affects their diffusion for the facilitated O2transport.
Differences in E2F subunit expression in quiescent and proliferating vascular smooth muscle cells
Authors: Fujita Nobuya , Furukawa Yusuke , Itabashi Naoki , Okada Koji , Saito Toshikazu , Ishibashi Shun
Published: March 2015

E2F is a family of transcriptional factors that control G1/S transition. We investigated how the E2F family participates in the biological responses of vascular smooth muscle cells (VSMC) to vasoconstrictive hormones compared with fetal bovine serum (FBS). FBS induced upregulation of E2F-1 and E2F-5 at both mRNA and protein levels and slightly reduced E2F-3 protein. Angiotensin II (ANG II) and arginine vasopressin increased E2F-3 protein, but not E2F-1 and E2F-5, without upregulating its mRNA level. FBS transactivated the E2F-1 gene through the induction of free E2F-1 binding onto its promoter, whereas ANG II-induced binding of E2F-3 did not result in activation of the E2F-1 promoter. These changes are responsible for hypertrophic or hyperplastic response of VSMC to different growth factors or stimulants. In contrast, both FBS and vasoconstrictive hormones drove transcription of the cdc6 gene by downregulating p130 and recruiting free E2F-3 in the latter, which underlies the progression of VSMC into S phase.
Estimation of capillary density in human skeletal muscle based on maximal oxygen consumption rates
Authors: McGuire B. J. , Secomb T. W.
Published: March 2015

A previously developed Krogh-type theoretical model was used to estimate capillary density in human skeletal muscle based on published measurements of oxygen consumption, arterial partial pressure of oxygen, and blood flow during maximal exercise. The model assumes that oxygen consumption in maximal exercise is limited by the ability of capillaries to deliver oxygen to tissue and is therefore strongly dependent on capillary density, defined as the number of capillaries per unit cross-sectional area of muscle. Based on an analysis of oxygen transport processes occurring at the microvascular level, the model allows estimation of the minimum number of straight, evenly spaced capillaries required to achieve a given oxygen consumption rate. Estimated capillary density values were determined from measurements of maximal oxygen consumption during knee extensor exercise and during whole body cycling, and they range from 459 to 1,468 capillaries/mm2. Measured capillary densities, obtained with either histochemical staining techniques or electron microscopy on quadriceps muscle biopsies from healthy subjects, are generally lower, ranging from 123 to 515 capillaries/mm2. This discrepancy is partly accounted for by the fact that capillary density decreases with muscle contraction and muscle biopsy samples typically are strongly contracted. The results imply that estimates of maximal oxygen transport rates based on capillary density values obtained from biopsy samples do not fully reflect the oxygen transport capacity of the capillaries in skeletal muscle.
Mechanisms of shock-induced arrhythmogenesis during acute global ischemia
Authors: Cheng Yuanna , Mowrey Kent A. , Nikolski Vladimir , Tchou Patrick J. , Efimov Igor R.
Published: March 2015

Little is known about the mechanisms of vulnerability and defibrillation under ischemic conditions. We investigated these mechanisms in 18 Langendorff-perfused rabbit hearts during 75% reduced-flow ischemia. Electrical activity was optically mapped from the anterior epicardium during right ventricular shocks applied at various phases of the cardiac cycle while the excitation-contraction decoupler 2,3-butanedione monoxime (BDM; 15 mM) was used to suppress motion artifacts caused by contraction of the heart. During ischemia, vulnerable window width increased [from 30–90% of the action potential duration (APD) in the control to −10 to 100% of the APD in ischemia]. Moreover, arrhythmia severity increased along with the reduction of APD (176 ± 9 ms in control and 129 ± 26 ms in ischemia, P < 0.01) and increased dispersion of repolarization (45 ± 17 ms in control and 73 ± 28 ms in ischemia, P < 0.01). Shock-induced virtual electrode polarization was preserved. Depolarizing (contrary to hyperpolarizing) response time constants increased. Virtual electrode-induced wavefronts of excitation had much more tortuous pathways leading to wavefront fractionation. Defibrillation failure at all shock strengths was observed in four hearts. Optical mapping revealed that the shock extinguished the arrhythmia; however, the arrhythmia self-originated after an isoelectric window of 339 ± 189 ms. In conclusion, in most cases, virtual electrode-induced phase singularity (VEIPS) was responsible for shock-induced arrhythmogenesis during acute global ischemia. Enhancement of arrhythmogenesis was associated with an increased dispersion of repolarization and altered deexcitation. In four hearts, arrhythmogenesis could not be explained by VEIPS.
Sodium selenite reduces hemoglobin-induced venular leakage in the rat mesentery
Authors: Baldwin Ann L. , Wiley Elizabeth B. , Summers Amber G. , Alayash Abdu I.
Published: March 2015

Modified Hbs are being developed as “blood substitutes,” but intravascular injection of diaspirin cross-linked Hb (DBBF-Hb) can produce venular leakage. Hb toxicity may arise from reactive oxygen species, so the antioxidant sodium selenite (Na2SeO3) was used in an attempt to reduce leak formation. In anesthetized Sprague-Dawley rats, one-half of which received 2 × 10−6 g/ml Na2SeO3 in their drinking water for 3 wk, the mesenteric microvasculature was perfused with 2 mg/ml DBBF-Hb ( N = 8) for 10 min. Controls ( N= 7) received saline. This was followed by perfusion with FITC-albumin for 3 min, fixation, and microscopic examination. In rats given DBBF-Hb, Na2SeO3 significantly reduced leak number, leak area, and mast cell degranulation. Venular leakage was also reduced in rats that only received Na2SeO3locally during DBBF-Hb perfusion. However, Na2SeO3 did not affect animals receiving cyanomet-DBBF-Hb instead of DBBF-Hb and significantly increased leak number and mast cell degranulation in animals receiving saline. In vitro, Na2SeO3 reduced the oxidation rate of DBBF-Hb while in the presence of oxidants. These results suggest that Na2SeO3 reduces DBBF-Hb-induced microvascular leakage partly by retarding the oxidation of its heme iron.
Regional upregulation of Kv2.1-encoded current,I K,slow2, in Kv1DN mice is abolished by crossbreeding with Kv2DN mice
Authors: Zhou Jun , Kodirov Sodikdjon , Murata Mitsunobu , Buckett Peter D. , Nerbonne Jeanne M. , Koren Gideon
Published: March 2015

Overexpression of a truncated Kv1.1 channel transgene in the heart (Kv1DN) resulted in mice with a prolonged action potential duration due to marked attenuation of a rapidly activating, slowly inactivating potassium current ( I K,slow1) in ventricular myocytes. Optical mapping and programmed electrical stimulation revealed inducible ventricular tachycardia due to spatial dispersion of repolarization and refractoriness. Here we show that a delayed rectifier with slower inactivation kinetics ( I K,slow2) was selectively upregulated in Kv1DN cardiocytes. This electrical remodeling was spatially restricted to myocytes derived from the apex of the left ventricle. Biophysical and pharmacological studies of I K,slow2 indicate that it resembles Kv2-encoded currents. Northern blot analyses and real-time PCR revealed upregulation of Kv2.1 transcript in Kv1DN mice. Crossbreeding of Kv1DN mice with mice expressing a truncated Kv2.1 polypeptide (Kv2DN) eliminated I K,slow2. In summary, our data indicate that the spatially restrictive upregulation of Kv2.1-encoded currents underlies the increased dispersion of the repolarization observed in Kv1DN mice.