bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of simulated ischemia on apoptosis induction by oxidative stress in adult cardiomyocytes of rats
Authors: Inserte J. , Taimor G. , Hofstaetter B. , Garcia-Dorado D. , Piper H. M.
Published: December 2017

Oxidative stress may cause apoptosis of cardiomyocytes in ischemic-reperfused myocardium. We investigated whether ischemia-reperfusion modifies the susceptibility of cardiomyocyte induction of apoptosis by oxidative stress. Ischemia was simulated by incubating isolated cardiomyocytes from adult rats in an anoxic, glucose-free medium, pH 6.4, for 3 h. Annexin V-fluorescein isothiocyanate/propidium iodide staining and the detection of DNA laddering were used as apoptotic markers. H2O2(7.5 μmol/l) induced apoptosis in 20.1 ± 1.8% of cells under normoxic conditions but only 14.4 ± 1.6% ( n = 6, P < 0.05) after ischemia-reoxygenation. This partial protection of ischemic-reoxygenated cells was observed despite a reduction in their cellular glutathione content, from 11.4 ± 1.9 in normoxic controls to 2.9 ± 0.8 nmol/mg protein ( n = 3, P < 0.05). Elevation of end-ischemic glutathione contents by pretreatment with 1 mmol/l N-acetylcysteine entirely protected ischemic-reoxygenated cells against induction of apoptosis by H2O2. In conclusion, ischemia-reperfusion can protect cardiomyocytes against induction of apoptosis by exogenous oxidative stress. This endogenous protective effect is most clearly demonstrated when control and postischemic cardiomyocytes are compared at similar glutathione levels.
Effects of recombinant eNOS gene expression on reactivity of small cerebral arteries
Authors: Tsutsui Masato , Onoue Hisashi , Iida Yasuhiko , Smith Leslie , O'Brien Timothy , Katusic Zvonimir S.
Published: December 2017

Resistance arteries are an important target for vascular gene therapy because they play a key role in the regulation of tissue blood flow. The present study was designed to determine the effects of recombinant endothelial (e) nitric oxide synthase (NOS) gene expression on vasomotor reactivity of small brain stem arteries (internal diameter, 253 ± 2.5 μm). Arterial rings were exposed ex vivo to an adenoviral vector (109and 1010plaque-forming units/ml) encoding eNOS gene or β-galactosidase gene. Twenty-four hours after transduction, vascular function was examined by isometric force studies. Transgene expression was evident mainly in adventitia. In arteries with endothelium transduced with eNOS gene but not with control β-galactosidase gene, relaxations to bradykinin and substance P were significantly augmented. Removal of endothelium abolished relaxations to bradykinin and substance P in control and β-galactosidase arteries. However, in endothelium-denuded arteries transduced with recombinant eNOS, bradykinin and substance P caused relaxations that were abolished in the presence of the NOS inhibitor NG-nitro-l-arginine methyl ester. In control arteries, endothelium removal augmented relaxations to the nitric oxide donors sodium nitroprusside and diethylamine NONOate. This augmentation was absent in eNOS gene-transduced arteries without endothelium. Our results suggest that, in small brain stem arteries, expression of recombinant eNOS increases biosynthesis of nitric oxide. Adventitia of small arteries is a good target for expression of recombinant eNOS. Genetically engineered adventitial cells may serve as a substitute source of nitric oxide in cerebral arteries with dysfunctional endothelium.
Spatial variations in endothelial barrier function in disturbed flows in vitro
Authors: Phelps Jeffrey E. , DePaola Natacha
Published: December 2017

Hindered barrier function has been implicated in the initiation and progression of atherosclerosis, a disease of focal nature associated with altered hemodynamics. In this study, endothelial permeability to macromolecules and endothelial electrical resistance were investigated in vitro in monolayers exposed to disturbed flow fields that model spatial variations in fluid shear stress found at arterial bifurcations. After 5 h of flow, areas of high shear stress gradients showed a 5.5-fold increase in transendothelial transport of dextran (molecular weight 70,000) compared with no-flow controls. Areas of undisturbed fully developed flow, within the same monolayer, showed a 2.9-fold increase. Monolayer electrical resistance decreased with exposure to flow. The resistance measured during flow and the rate of change in monolayer resistance after removal of flow were lowest in the vicinity of flow reattachment (highest shear stress gradients). These results demonstrate that endothelial barrier function and permeability to macromolecules are regulated by spatial variations in shear stress forces in vitro.
Elevated salt intake impairs dilation of rat skeletal muscle resistance arteries via ANG II suppression
Authors: Weber David S. , Lombard Julian H.
Published: December 2017

Vasodilator responses were assessed in resistance arteries (100–200 μm) isolated from the gracilis muscle of normotensive rats after changes in dietary salt intake. Sprague-Dawley rats were maintained on either a high-salt (HS) diet (4.0% NaCl) or a low-salt (LS) diet (0.4% NaCl) for 4–8 wk (chronic) or 3 days (short-term) with water ad libitum. One group of short-term HS rats received a continuous intravenous infusion of a low dose (5 ng ⋅ kg− 1 ⋅ min− 1) of ANG II to prevent the ANG II suppression that occurs with HS diet. Short-term and chronic HS diet eliminated arterial dilation in response to ACh and reduced[Formula: see text] (30–40 mmHg) and the stable prostacyclin analog iloprost. ANG II infusion preserved the response to these vasodilator stimuli in short-term HS animals. Dilator responses to sodium nitroprusside and forskolin were unaffected by HS diet. These findings suggest that ANG II suppression during HS diet impairs vascular relaxation mechanisms upstream from the cAMP and cGMP second messenger systems.
Heme oxygenase-1-derived bilirubin ameliorates postischemic myocardial dysfunction
Authors: Clark James E. , Foresti Roberta , Sarathchandra Padmini , Kaur Harparkash , Green Colin J. , Motterlini Roberto
Published: December 2017

Bilirubin is a potent antioxidant generated intracellularly during the degradation of heme by the enzyme heme oxygenase. The purpose of this study was to determine the role of increased cardiac bilirubin in protection against postischemic myocardial dysfunction. Rat hearts were isolated and perfused according to the Langendorff technique to evaluate the recovery of myocardial function after 30 min of global ischemia and 60 min of reperfusion. We found that upregulation of the inducible isoform of heme oxygenase (HO-1) by treatment of animals with hemin 24 h before ischemia ameliorated myocardial function and reduced infarct size (tetrazolium staining) on reperfusion of isolated hearts. Tin protoporphyrin IX, an inhibitor of heme oxygenase activity, completely abolished the improved postischemic myocardial performance observed after hemin-mediated HO-1 induction. Likewise, cardiac tissue injury was exacerbated by treatment with tin protoporphyrin IX. Increased cardiac HO-1 expression and heme oxygenase activity were associated with enhanced tissue bilirubin content and an increased rate of bilirubin release into the perfusion buffer. Furthermore, exogenously administered bilirubin at concentrations as low as 100 nanomolar significantly restored myocardial function and minimized both infarct size and mitochondrial damage on reperfusion. Our data provide strong evidence for a primary role of HO-1-derived bilirubin in cardioprotection against reperfusion injury.
Caffeine-induced Ca2+ sparks in mouse ventricular myocytes
Authors: Ritter Michael , Su Zhi , Spitzer Kenneth W. , Ishida Hideyuki , Barry William H.
Published: December 2017

Ca2+ sparks are spatially localized intracellular Ca2+ release events that were first described in 1993. Sparks have been ascribed to sarcoplasmic reticulum Ca2+ release channel (ryanodine receptor, RyR) opening induced by Ca2+ influx via L-type Ca2+ channels or by spontaneous RyR openings and have been thought to reflect Ca2+ release from a cluster of RyR. Here we describe a pharmacological approach to study sparks by exposing ventricular myocytes to caffeine with a rapid solution-switcher device. Sparks under these conditions have properties similar to naturally occurring sparks in terms of size and intracellular Ca2+ concentration ([Ca2+]i) amplitude. However, after the diffusion of caffeine, sparks first appear close to the cell surface membrane before coalescing to produce a whole cell transient. Our results support the idea that a whole cell [Ca2+]i transient consists of the summation of sparks and that Ca2+ sparks consist of the opening of a cluster of RyR and confirm that characteristics of the cluster rather than the L-type Ca2+ channel-RyR relation determine spark properties.
Characterization and functional consequences of delayed rectifier current transient in ventricular repolarization
Authors: Gintant Gary A.
Published: December 2017

Although inactivation of the rapidly activating delayed rectifier current ( I Kr) limits outward current on depolarization, the role of I Kr (and recovery from inactivation) during repolarization is uncertain. To characterize I Krduring ventricular repolarization (and compare with the inward rectifier current, I K1), voltage-clamp waveforms simulating the action potential were applied to canine ventricular, atrial, and Purkinje myocytes. In ventricular myocytes, I Kr was minimal at plateau potentials but transiently increased during repolarizing ramps. The I Kr transient was unaffected by repolarization rate and maximal after 150-ms depolarizations (+25 mV). Action potential clamps revealed the I Kr transient terminating the plateau. Although peak I Kr transient density was relatively uniform among myocytes, potentials characterizing the peak transients were widely dispersed. In contrast, peak inward rectifier current ( I K1) density during repolarization was dispersed, whereas potentials characterizing I K1 defined a narrower (more negative) voltage range. In summary, rapidly activating I Kr provides a delayed voltage-dependent (and functionally time-independent) outward transient during ventricular repolarization, consistent with rapid recovery from inactivation. The heterogeneous voltage dependence of I Kr provides a novel means for modulating the contribution of this current during repolarization.
Meta-analysis of the age-associated decline in maximal aerobic capacity in men: relation to training status
Authors: Wilson Teresa M. , Tanaka Hirofumi
Published: December 2017

Based on cross-sectional data, we recently reported that, in contrast to the prevailing view, the rate of decline in maximal oxygen consumption (V˙o 2 max) with age is greater in physically active compared with sedentary healthy women. We tested this hypothesis in men using a meta-analytic study ofV˙o 2 max values in the published literature. A total of 242 studies (538 subject groups and 13,828 subjects) met the inclusion criteria and were arbitrarily separated into sedentary (214 groups, 6,231 subjects), active (159 groups, 5,621 subjects), and endurance-trained (165 groups, 1,976 subjects) populations. Body fat percent increased with age in sedentary and active men ( P < 0.001), whereas no change was observed in endurance-trained men.V˙o 2 max was inversely and strongly related to age within each population ( r = −0.80 to −0.88, all P < 0.001) and was highest in endurance-trained and lowest in sedentary populations at any age. Absolute rates of decline inV˙o 2 max with age were not different ( P > 0.05) in sedentary (−4.0 ml ⋅ kg−1 ⋅ min−1 ⋅ decade−1), active (−4.0), and endurance-trained (−4.6) populations. Similarly, there were no group differences ( P > 0.05) in the relative (%) rates of decline inV˙o 2 max with advancing age (−8.7, −7.3, and −6.8%/decade, respectively). Maximal heart rate was inversely related to age within each population ( r = −0.88 to −0.93, all P < 0.001), but the rate of age-related reduction was not different among the populations. There was a significant decline in running mileage and speed with advancing age in the endurance-trained men. The present cross-sectional meta-analytic findings do not support the hypothesis that the rate of decline inV˙o 2 max with age is related to habitual aerobic exercise status in men.
Role of cAMP in activation of ischemically sensitive abdominal visceral afferents
Authors: Guo Zhi-Ling , Longhurst John C.
Published: December 2017

A number of metabolites produced during abdominal ischemia can stimulate and/or sensitize visceral afferents. The precise mechanisms whereby these metabolites act are uncertain. Other studies have shown that the adenylate cyclase-cAMP system may be involved in the activation of sensory neurons. Therefore, we hypothesized that cAMP contributes to the activation of ischemically sensitive abdominal visceral afferents. Single-unit activity of abdominal visceral C fibers was recorded from the right thoracic sympathetic chain in anesthetized cats before and during 7 min of abdominal ischemia. Forty-six percent of ischemically sensitive C fibers responded to intra-arterial injection of 8-bromo-cAMP (0.35–1.0 mg/kg), an analog of cAMP, with responses during ischemia increasing from 0.50 ± 0.06 to 0.84 ± 0.08 impulses/s ( P < 0.05, n = 11 C fibers). Conversely, an inhibitor of adenylate cyclase, 2′,5′-dideoxyadenosine (DDA; 0.1 mg/kg iv), attenuated ischemia-induced increase in activity of afferents from 0.66 ± 0.10 to 0.34 ± 0.09 impulses/s ( P < 0.05; n = 8). Furthermore, whereas exogenous PGE2 (3–4 μg/kg ia) augmented the ischemia-induced increase in activity of afferents ( P < 0.05, n = 10), treatment with DDA (0.1 mg/kg iv) substantially reduced the increase in discharge activity of afferents during ischemia, which was augmented by PGE2 (1.45 ± 0.24 vs. 0.70 ± 0.09 impulses/s, −DDA vs. +DDA; P < 0.05) in six fibers. A time control group ( n = 4), however, demonstrated similar increases in the activity of afferents with repeated administration of PGE2. These data suggest that cAMP contributes to the activation of abdominal visceral afferents during ischemia, particularly to the action of PGs on activation and/or sensitization of these endings.
K+currents responsible for repolarization in mouse ventricle and their modulation by FK-506 and rapamycin
Authors: DuBell W. H. , Lederer W. J. , Rogers T. B.
Published: December 2017

Modulation of mouse ventricular action potentials and K+currents was examined using the whole cell patch-clamp technique. The composite mouse ventricular K+current (consisted of an outward transient followed by a slowly decaying sustained component. Use of the K+channel blockers tetraethylammonium and 4-aminopyridine and a transgenic mouse model revealed three pharmacologically and kinetically distinct currents: Ito, which contributed to the transient component; IK, which contributed to the sustained component; and a slowly activating current ( Islow), which contributed to both components. The immunosuppressant FK-506 increased action potential duration at 90% repolarization by 66.7% by decreasing the sustained component (−48% at +60 mV) and prolonging recovery from inactivation (by 26% at 200 ms) of the transient component. These effects were isolated to IKand Ito, respectively. Rapamycin had strikingly similar effects on these currents. Both FK-506 and rapamycin are known to target the immunophilin FKBP12. Thus we conclude that FKBP12 modulates specific mouse K+channels, and thus the mouse ventricular action potential, by interacting directly with K+channel proteins or with other associated regulatory proteins.
Role of TNF-α in myocardial dysfunction after hemorrhagic shock and lower-torso ischemia
Authors: Shahani Rohan , Marshall John G. , Rubin Barry B. , Li Ren-Ke , Walker Paul M. , Lindsay Thomas F.
Published: December 2017

Ruptured abdominal aortic aneurysm (RAAA) repair, a combination of hemorrhagic shock and lower-torso ischemia, is associated with a 50–70% mortality. Myocardial dysfunction may contribute to the high rate of mortality after aneurysm repair. We attempted to determine whether RAAA repair results in cardiac dysfunction mediated by tumor necrosis factor-α (TNF-α). We modeled aortic rupture and repair in the rat by inducing hemorrhagic shock to a mean blood pressure of 50 mmHg for 1 h, followed by supramesenteric clamping of the aorta for 45 min. After 90 min of reperfusion, cardiac contractile function was assessed with a Langendorff preparation. Myocardial TNF-α, ATP and creatine phosphate (CP) levels, and markers of oxidant stress (F2-isoprostanes) were measured. Cardiac function in the combined shock and clamp rats was significantly depressed compared with sham-operated control rats but was similar to that noted in animals subjected to shock alone. Myocardial TNF-α concentrations increased 10-fold in the combined shock and clamp rats compared with sham rats, although there was no difference in myocardial ATP, CP, or F2-isoprostanes. TNF-α neutralization improved cardiac function by 50% in the combined shock and clamp rats. Hemorrhagic shock is the primary insult inducing cardiac dysfunction in this model of RAAA repair. An improvement in cardiac contractile function after immunoneutralization of TNF-α indicates that TNF-α mediates a significant portion of the myocardial dysfunction in this model.
Influence of sarcoplasmic reticulum calcium loading on mechanical and relaxation restitution
Authors: Hoit Brian D. , Kadambi Vivek J. , Tramuta Daniel A. , Ball Nancy , Kranias Evangelia G. , Walsh Richard A.
Published: December 2017

Mechanical and relaxation restitution represent the restoration of contractile force and relaxation, respectively, in premature beats having progressively longer extrasystolic intervals (ESI); these phenomena are related to intracellular activator Ca2+ by poorly defined mechanisms. We tested the hypothesis that the level of phospholamban [which modulates the affinity of the sarcoplasmic reticulum (SR) Ca2+-ATPase for Ca2+, and thus the SR Ca2+ load] may be an important determinant of both mechanical and relaxation restitution. Five mice with ablation of the phospholamban (PLB) gene (PLBKO), eight isogenic wild-type controls (129SvJ), eleven mice with PLB overexpression (PLBOE), and nine isogenic wild-type (FVB/N) controls were anesthetized and instrumented with a 1.4-Fr Millar catheter in the left ventricle and a 1-Fr pacemaker in the right atrium. At a cycle length of 200 ms, extrastimuli with increasing ESI were introduced, and the peak rates of left ventricular isovolumic contraction (±dP/d t max) were normalized and fit to monoexponential equations. In a subset, the protocols were repeated after ryanodine (4 ng/g) was administered to deplete SR Ca2+ stores. The time constant of mechanical restitution in PLBKO was significantly shorter [6.3 ± 1.2 (SE) vs. 47.7 ± 7.6 ms] and began earlier (50 ± 10 vs. 70 ± 19 ms) than in 129SvJ. In contrast, the time constant of mechnical restitution was significantly longer (80.3 ± 7.6 vs. 54.1 ± 9.2 ms) in PLBOE than in FVB/N. The time constant of relaxation restitution was less in PLBKO than in 129SvJ (26.2 ± 9.9 vs. 44.6 ± 3.3, P < 0.05) but was similar in PLBOE and FVB/N (21.1 ± 6.3 vs. 20.5 ± 5.7 ms). Intravenous ryanodine decreased significantly the time constants of mechanical restitution in PLBOE, 129SvJ, and FVB/N but was lethal in PLBKO. In contrast, ryanodine increased the time constant of relaxation restitution. Thus 1) the phospholamban level is a critical determinant of mechanical restitution and (to a lesser extent) relaxation restitution in these transgenic models, and 2) ryanodine differentially affects mechanical and relaxation restitution. Furthermore, our data suggest a dissociation of processes within the SR that govern contraction and relaxation.
Inhibition of calcium signaling in descending vasa recta endothelia by ANG II
Authors: Pallone Thomas L. , Silldorff Erik P. , Zhang Zhong
Published: December 2017

The intracellular calcium ([Ca2+]i) response of outer medullary descending vasa recta (OMDVR) endothelia to ANG II was examined in fura 2-loaded vessels. Abluminal ANG II (10−8M) caused [Ca2+]ito fall in proportion to the resting [Ca2+]i( r =0.82) of the endothelium. ANG II (10−8M) also inhibited both phases of the [Ca2+]iresponse generated by bradykinin (BK, 10−7M), 835 ± 201 versus 159 ± 30 nM (peak phase) and 169 ± 26 versus 103 ± 14 nM (plateau phase) (means ± SE). Luminal ANG II reduced BK (10−7M)-stimulated plateau [Ca2+]ifrom 180 ± 40 to 134 ± 22 nM without causing vasoconstriction. Abluminal ANG II added to the bath after luminal application further reduced [Ca2+]ito 113 ± 9 nM and constricted the vessels. After thapsigargin (TG) pretreatment, ANG II (10−8M) caused [Ca2+]ito fall from 352 ± 149 to 105 ± 37 nM. This effect occurred at a threshold ANG II concentration of 10−10M and was maximal at 10−8M. ANG II inhibited both the rate of Ca2+entry into [Ca2+]i-depleted endothelia and the rate of Mn2+entry into [Ca2+]i-replete endothelia. In contrast, ANG II raised [Ca2+]iin the medullary thick ascending limb and outer medullary collecting duct, increasing [Ca2+]ifrom baselines of 99 ± 33 and 53 ± 11 to peaks of 200 ± 47 and 65 ± 11 nM, respectively. We conclude that OMDVR endothelia are unlikely to be the source of ANG II-stimulated NO production in the medulla but that interbundle nephrons might release Ca2+-dependent vasodilators to modulate vasomotor tone in vascular bundles.
Generation of intracellular pH gradients in single cardiac myocytes with a microperfusion system
Authors: Spitzer Kenneth W. , Ershler Philip R. , Skolnick Rita L. , Vaughan-Jones Richard D.
Published: December 2017

This study describes the use of a microperfusion system to create rapid, large regional changes in intracellular pH (pHi) within single ventricular myocytes. The spatial distribution of pHi in single myocytes was measured with seminaphthorhodafluor-1 fluorescence using confocal imaging. Changes in pHi were induced by local external application of NH4Cl, CO2, or sodium propionate. Local application was achieved by simultaneously directing two parallel square microstreams, each 275 μm wide, over a single myocyte oriented perpendicular to the direction of flow. One stream contained the control solution, and the other contained a weak acid or base. End-to-end, stable pHi gradients as large as 1 pH unit were readily created with this technique. This result indicates that pH within a single cardiac cell may not always be spatially uniform, particularly when weak acid or base gradients are present, which can occur, for example, in regional myocardial ischemia. The microperfusion method should be useful for studying the effects of localized acidosis on myocyte function, estimating intracellular ion diffusion rates, and, possibly, inducing regional changes in other important intracellular ions.
Importance of bicarbonate transport for protection of cardiomyocytes against reoxygenation injury
Authors: Schäfer C. , Ladilov Y. V. , Siegmund B. , Piper H. M.
Published: December 2017

Isolated cardiomyocytes from adult rats were incubated in anoxic bicarbonate-buffered media at extracellular pH (pHo) 6.4 until a cytosolic Ca2+overload and intracellular pH (pHi) of 6.4 were reached. On reoxygenation, the pH of the medium was changed to 7.4 to activate the Na+/H+exchanger (NHE) and the Na+-[Formula: see text] symporter (NBS). The reoxygenation was performed in the absence or presence of the NHE inhibitor HOE-642 (3 μmol/l) and/or the NBS inhibitor DIDS (0.5 mmol/l ), as in bicarbonate-free media. In reoxygenated control cells pHirapidly recovered to the preanoxic level, and a burst of spontaneous oscillations of cytosolic Ca2+occurred, accompanied by the development of hypercontracture. When NBS and NHE were simultaneously inhibited during reoxygenation, pHirecovery was prevented, Ca2+oscillations were attenuated, and hypercontracture was abolished. Sole inhibition of NBS or NHE showed no protection against hypercontracture. In the absence of cytosolic acidosis, HOE-642 or DIDS did not prevent hypercontracture induced by Ca2+overload. The results demonstrate that simultaneous inhibition of NHE and NBS is needed to protect myocardial cells against reoxygenation-induced hypercontracture.
Amelioration with vessel dilator of acute tubular necrosis and renal failure established for 2 days
Authors: Clark Linda C. , Farghaly Hanan , Saba Sabiha R. , Vesely David L.
Published: December 2017

Seventeen Sprague-Dawley rats had ischemic nonoliguric acute renal failure (ARF) induced by vascular clamping resulting in their preischemic blood urea nitrogen (BUN) and creatinine levels of 16 ± 1 and 0.56 ± 0.05 mg/dl to increase to 162 ± 4 and 8.17 ± 0.5 mg/dl, P < 0.001, respectively, at day 4 of postischemia. Vessel dilator, a 37-amino-acid cardiac peptide hormone (0.3 μg ⋅ kg−1⋅ min−1ip), decreased the BUN and creatinine levels to 53 ± 17 mg/dl and 0.98 ± 0.12 mg/dl ( P < 0.001) in another seven animals where ARF had been established for 2 days. Water excretion doubled with ARF and was further augmented by vessel dilator. Transthoracic echocardiography revealed left ventricular dilation as a probable cause of the increase in vessel dilator in the circulation with ARF, and vessel dilator infusion reversed this dilation. At day 6 of ARF, mortality decreased to 14% with vessel dilator from 88% without vessel dilator. Acute tubular necrosis was <5% in the vessel dilator-treated rats compared with 25% to >75% in the placebo-treated ARF animals. We conclude that vessel dilator improves acute tubular necrosis and renal function in established ARF.
Interstitial flow through the internal elastic lamina affects shear stress on arterial smooth muscle cells
Authors: Tada Shigeru , Tarbell John M.
Published: December 2017

Interstitial flow through the tunica media of an artery wall in the presence of the internal elastic lamina (IEL), which separates it from the subendothelial intima, has been studied numerically. A two-dimensional analysis applying the Brinkman model as the governing equation for the porous media flow field was performed. In the numerical simulation, the IEL was modeled as an impermeable barrier to water flux, except for the fenestral pores, which were uniformly distributed over the IEL. The tunica media was modeled as a heterogeneous medium composed of a periodic array of cylindrical smooth muscle cells (SMCs) embedded in a fiber matrix simulating the interstitial proteoglycan and collagen fibers. A series of calculations was conducted by varying the physical parameters describing the problem: the area fraction of the fenestral pore (0.001–0.036), the diameter of the fenestral pore (0.4–4.0 μm), and the distance between the IEL and the nearest SMC (0.2–0.8 μm). The results indicate that the value of the average shear stress around the circumference of the SMC in the immediate vicinity of the fenestral pore could be as much as 100 times greater than that around an SMC in the fully developed interstitial flow region away from the IEL. These high shear stresses can affect SMC physiological function.
Interstitial fluid pressure, composition of interstitium, and interstitial exclusion of albumin in hypothyroid rats
Authors: Wiig Helge , Reed Rolf K. , Tenstad Olav
Published: December 2017

Lack of thyroid hormones may affect the composition and structure of the interstitium. Hypothyrosis was induced in rats by thyroidectomy 4–12 wk before the experiments. In hypothyroid rats ( n = 16), interstitial fluid pressure measured with micropipettes in hindlimb skin and muscle averaged +0.1 ± 0.2 and +0.5 ± 0.2 mmHg, respectively, with corresponding pressures in control rats ( n = 16) of −1.5 ± 0.1 ( P < 0.001) and −0.8 ± 0.1 mmHg ( P < 0.001). Interstitial fluid volume, measured as the difference between the distribution volumes of 51Cr-EDTA and125I-labeled BSA, was similar or lower in skin and higher in hypothyroid muscle. Total protein and albumin concentration in plasma and interstitial fluid (isolated from implanted wicks) was lower in hypothyroid compared with control rats. Hyaluronan content ( n = 9) in rat hindlimb skin was 2.05 ± 0.15 and 1.92 ± 0.09 mg/g dry wt ( P > 0.05) in hypothyroid and control rats, respectively, with corresponding content in hindlimb skeletal muscle of 0.35 ± 0.07 and 0.23 ± 0.01 mg/g dry wt ( P < 0.01). Interstitial exclusion of albumin in skin and muscle was measured after 125I-labeled rat serum albumin infusion for 120–168 h with an implanted osmotic pump. Relative excluded volume for albumin (Ve/Vi) was calculated as 1 − Va/Vi, and averaged 28 and 28% in hindlimb muscle ( P > 0.05), 44 and 45% in hindlimb skin ( P > 0.05), and 19 and 32% in back skin ( P < 0.05) in hypothyroid and control rats, respectively. Albumin mass was higher in back skin in spite of a lower interstitial fluid albumin concentration, a finding explained by a reduced Ve/Vi in back skin in hypothyroid rats. These experiments suggest that lack of thyroid hormones in rats changes the interstitial matrix again leading to reduced interstitial compliance and changes in the transcapillary fluid balance.
Beating rate of isolated neonatal cardiomyocytes is regulated by the stable microtubule subset
Authors: Webster Daniel R. , Patrick Darby L.
Published: December 2017

We investigated the roles of microtubule (MT) dynamics (growth and shrinkage), the stable, nongrowing MT subset, the posttranslationally detyrosinated MT subset, and artificially elevated tubulin levels in the negative regulation of heart cell beating rate. We manipulated the MT populations in isolated, neonatal cardiomyocytes obtained from normal animals in several ways and then measured heart cell beating rate directly. We found that the stabilized population of MTs was sufficient to maintain a normal beating rate, whereas MT dynamics and detyrosination made no observable contribution. Furthermore, by directly and acutely increasing the level of tubulin within otherwise normally beating cells, we found that the increased tubulin (and MT) levels further depressed the beating rate. In conclusion, the stabilized MT subset is sufficient to maintain the normal beating rate in these cells, whereas increasing the MT density depresses it.
Leukocyte adhesion and microvessel permeability
Authors: He P. , Wang J. , Zeng M.
Published: December 2017

To investigate the direct effect of leukocyte adherence to microvessel walls on microvessel permeability, we developed a method to measure changes in hydraulic conductivity ( Lp) before and after leukocyte adhesion in individually perfused venular microvessels in frog mesentery. In 19 microvessels that were initially free of leukocyte sticking or rolling along the vessel wall, control Lpwas measured first with Ringer-albumin perfusate. Blood flow was then restored in each vessel with a reduced flow rate in the range of 30–116 μm/s to facilitate leukocyte adhesion. Each vessel was recannulated in 45 min. The mean number of leukocytes adhering to the vessel wall was 237 ± 22 leukocytes/mm2. At the same time, Lpincreased to 4.7 ± 0.5 times the control value. Superfusion of isoproterenol (10 μM) after leukocyte adhesion brought the increased Lpback to 1.1 ± 0.2 times the control in 5–10 min ( n = 9). Superfusing isoproterenol before leukocyte adhesion prevented the increase in Lp( n = 6). However, the number of leukocytes adhering to the vessel wall was not significantly affected. These results demonstrated that leukocyte adhesion caused an increase in microvessel permeability that could be prevented or restored by increasing cAMP levels in endothelial cells using isoproterenol. Thus cAMP-dependent mechanisms that regulate inflammatory agent-induced increases in permeability also modulate leukocyte adhesion-induced increases in permeability but act independently of mechanisms that regulate leukocyte adhesion to the microvessel wall. Application of ketotifen, a mast cell stabilizer, and desferrioxamine mesylate, an iron-chelating reagent, attenuated the increase in Lpinduced by leukocyte adhesion, suggesting the involvement of oxidants and the activation of mast cells in leukocyte adhesion-induced permeability increase. Furthermore, with the use of an in vivo silver stain technique, the locations of the adherent leukocytes on the microvessel wall were identified quantitatively in intact microvessels.
Inhibition of Rho protein stimulates iNOS expression in rat vascular smooth muscle cells
Authors: Muniyappa Ranganath , Xu Rui , Ram Jeffrey L. , Sowers James R.
Published: December 2017

Inducible nitric oxide synthase (iNOS) in vascular smooth muscle cells (VSMCs) is upregulated in arterial injury and plays a role in regulating VSMC proliferation and restenosis. Inflammatory cytokines [e.g., interleukin-1β (IL-1β)] released during vascular injury induce iNOS. Small GTP-binding proteins of the Ras superfamily play a major role in IL-1β-dependent signaling pathways. In this study, we examined the role of Rho GTPases in regulating iNOS expression in VSMCs. Treatment of VSMCs with mevastatin, which inhibits isoprenylation of Rho and other small GTP-binding proteins, produced significantly higher amounts of IL-1β-evoked NO and iNOS protein compared with control. Similarly, bacterial toxins [Toxin B from Clostridium difficile and C3 ADP-ribosyl transferase (C3) toxin from Clostridium botulinium] that specifically inactivate Rho proteins increased NOS products (NO and citrulline) and iNOS expression. Toxin B increased the activity of iNOS promoter-reporter construct in VSMCs. Both toxins enhanced IL-1β-stimulated iNOS expression and NO production. These data demonstrate for the first time that inhibition of Rho induces iNOS and suggest a role for Rho protein in IL-1β-stimulated NO production in VSMCs.
NTS A2a purinoceptor activation elicits hindlimb vasodilation primarily via a β-adrenergic mechanism
Authors: Kitchen Amy M. , Scislo Tadeusz J. , O'Leary Donal S.
Published: December 2017

Previously, we have shown that activation of adenosine A2a receptors in the subpostremal nucleus tractus solitarii (NTS) via microinjection of the selective A2a receptor agonist CGS-21680 elicits potent, dose-dependent decreases in mean arterial pressure and preferential, marked hindlimb vasodilation. Although A2a receptor activation does not change lumbar sympathetic nerve activity, it does markedly enhance the preganglionic adrenal sympathetic nerve activity, which will increase epinephrine release and could subsequently elicit hindlimb vasodilation via activation of β2-adrenergic receptors. Therefore we investigated whether this hindlimb vasodilation was due to neural or humoral mechanisms. In chloralose-urethan-anesthetized male Sprague-Dawley rats, we monitored cardiovascular responses to stimulation of NTS adenosine A2a receptors (CGS-21680, 20 pmol/50 nl) in the intact control animals; after pretreatment with propranolol (2 mg/kg iv), a β-adrenergic antagonist; after bilateral lumbar sympathectomy; after bilateral adrenalectomy; and after combined bilateral lumbar sympathectomy and adrenalectomy. After β-adrenergic blockade, stimulation of NTS adenosine A2a receptors produced a pressor response and a hindlimb vasoconstriction. Lumbar sympathectomy reduced the vasodilation seen in the intact animals by ∼40%, and adrenalectomy reduced it by ∼80%. The combined sympathectomy and adrenalectomy virtually abolished the hindlimb vasodilation evoked by NTS A2a receptor activation. We conclude that the preferential, marked hindlimb vasodilation produced by stimulation of NTS adenosine A2a receptors is mediated by both the efferent sympathetic nerves directed to the hindlimb and the adrenal glands via primarily a β-adrenergic mechanism.
Ischemic preconditioning prevents I/R-induced alterations in SR calcium-calmodulin protein kinase II
Authors: Osada Mitsuru , Netticadan Thomas , Kawabata Kenichi , Tamura Kohji , Dhalla Naranjan S.
Published: December 2017

Although Ca2+/calmodulin-dependent protein kinase II (CaMK II) is known to modulate the function of cardiac sarcoplasmic reticulum (SR) under physiological conditions, the status of SR CaMK II in ischemic preconditioning (IP) of the heart is not known. IP was induced by subjecting the isolated perfused rat hearts to three cycles of brief ischemia-reperfusion (I/R; 5 min ischemia and 5 min reperfusion), whereas the control hearts were perfused for 30 min with oxygenated medium. Sustained I/R in control and IP groups was induced by 30 min of global ischemia followed by 30 min of reperfusion. The left ventricular developed pressure, rate of the left ventricular pressure, as well as SR Ca2+-uptake activity and SR Ca2+-pump ATPase activity were depressed in the control I/R hearts; these changes were prevented upon subjecting the hearts to IP. The beneficial effects of IP on the I/R-induced changes in contractile activity and SR Ca2+pump were lost upon treating the hearts with KN-93, a specific CaMK II inhibitor. IP also prevented the I/R-induced depression in Ca2+/calmodulin-dependent SR Ca2+-uptake activity and the I/R-induced decrease in the SR CaMK II activity; these effects of IP were blocked by KN-93. The results indicate that IP may prevent the I/R-induced alterations in SR Ca2+handling abilities by preserving the SR CaMK II activity, and it is suggested that CaMK II may play a role in mediating the beneficial effects of IP on heart function.
Decreased passive stiffness of cardiac myocytes and cardiac tissue from copper-deficient rat hearts
Authors: Heller Lois Jane , Mohrman David E. , Prohaska Joseph R.
Published: December 2017

Passive stiffness characteristics of isolated cardiac myocytes, papillary muscles, and aortic strips from male Holtzman rats fed a copper-deficient diet for ∼5 wk were compared with those of rats fed a copper-adequate diet to determine whether alterations in these characteristics might accompany the well-documented cardiac hypertrophy and high incidence of ventricular rupture characteristic of copper deficiency. Stiffness of isolated cardiac myocytes was assessed from measurements of cellular dimensional changes to varied osmotic conditions. Stiffness of papillary muscles and aortic strips was determined from resting length-tension analyses and included steady-state characteristics, dynamic viscoelastic stiffness properties, and maximum tensile strength. The primary findings were that copper deficiency resulted in cardiac hypertrophy with increased cardiac myocyte size and fragility, decreased cardiac myocyte stiffness, and decreased papillary muscle passive stiffness, dynamic stiffness, and tensile strength and no alteration in aortic connective tissue passive stiffness or tensile strength. These findings suggest that a reduction of cardiac myocyte stiffness and increased cellular fragility could contribute to the reduced overall cardiac tissue stiffness and the high incidence of ventricular aneurysm observed in copper-deficient rats.
Differential expression of KvLQT1 isoforms across the human ventricular wall
Authors: Péréon Yann , Demolombe Sophie , Baró Isabelle , Drouin Emmanuel , Charpentier Flavien , Escande Denis
Published: December 2017

Long Q-T mutant (KvLQT1) K+ channels associate with their regulatory subunit IsK to produce the slow component of the delayed rectifier potassium ( I Ks) cardiac current. The amplitude of KvLQT1 current depends on the expression of a KvLQT1 splice variant (isoform 2) that exerts strong dominant negative effects on the full-length KvLQT1 protein (isoform 1). We used RNase protection assays to determine the relative expression of KvLQT1 isoforms 1 and 2 and IsK mRNAs in human ventricular layers. Overall expression of KvLQT1 and IsK genes was similar in the three layers. However, there was a significant difference in the ratio between KvLQT1 isoforms 1 and 2. Isoform 2 represented 25.2 ± 2.3%, 31.7 ± 1.2%, and 24.9 ± 1.7% of total KvLQT1 expression in left ventricular endocardial, midmyocardial, and epicardial tissues, respectively. Similar data were obtained from right ventricular samples. COS-7 cells were intranuclearly injected with KvLQT1 isoforms 1 or 2 plus IsK cDNAs, using two different isoform 2-to-isoform 1 ratios. Cells injected with an isoform 2-to-isoform 1 ratio mimicking that in the midmyocardium showed a K+current with ∼75% reduced amplitude compared with those injected with a ratio mimicking that in the epicardium. Our results suggest that differential expression of KvLQT1 isoform 2 in endocardial, midmyocardial, and epicardial tissues is responsible for differential I Ks amplitude and contributes to the regional action potential heterogeneity observed across the ventricular wall.
Exercise training restores adenosine-induced relaxation in coronary arteries distal to chronic occlusion
Authors: Heaps Cristine L. , Sturek Michael , Rapps Julie A. , Laughlin M. Harold , Parker Janet L.
Published: December 2017

We previously reported that canine collateral-dependent coronary arteries exhibit impaired relaxation to adenosine but not sodium nitroprusside. In contrast, exercise training enhances adenosine sensitivity of normal porcine coronary arteries. These results stimulated the hypothesis that chronic coronary occlusion and exercise training produce differential effects on cAMP- versus cGMP-mediated relaxation. To test this hypothesis, Ameroid occluders were surgically placed around the proximal left circumflex coronary artery (LCx) of female Yucatan miniature swine 8 wk before initiating sedentary or exercise training (treadmill run, 16 wk) protocols. Relaxation to the cAMP-dependent vasodilators adenosine (10− 7 to 10− 3 M) and isoproterenol (3 × 10− 8 to 3 × 10− 5 M) were impaired in collateral-dependent LCx versus nonoccluded left anterior descending (LAD) arterial rings isolated from sedentary but not exercise-trained pigs. Furthermore, adenosine-mediated reductions in simultaneous tension and myoplasmic free Ca2+ were impaired in LCx versus LAD arteries isolated from sedentary but not exercise-trained pigs. In contrast, relaxation in response to the cAMP-dependent vasodilator forskolin (10− 9 to 10− 5 M) and the cGMP-dependent vasodilator sodium nitroprusside (10− 9 to 10− 4 M) was not different in LCx versus LAD arteries of sedentary or exercise-trained animals. These data suggest that chronic occlusion impairs receptor-dependent, cAMP-mediated relaxation; receptor-independent cAMP- and cGMP-mediated relaxation were unimpaired. Importantly, exercise training restores cAMP-mediated relaxation of collateral-dependent coronary arteries.
Existence of a transient outward K+ current in guinea pig cardiac myocytes
Authors: Li Gui-Rong , Yang Baofeng , Sun Haiying , Baumgarten Clive M.
Published: December 2017

A novel transient outward K+current that exhibits inward-going rectification ( I to.ir) was identified in guinea pig atrial and ventricular myocytes. I to.ir was insensitive to 4-aminopyridine (4-AP) but was blocked by 200 μmol/l Ba2+or removal of external K+. The zero current potential shifted 51–53 mV/decade change in external K+. I to.ir density was twofold greater in ventricular than in atrial myocytes, and biexponential inactivation occurs in both types of myocytes. At −20 mV, the fast inactivation time constants were 7.7 ± 1.8 and 6.1 ± 1.2 ms and the slow inactivation time constants were 85.1 ± 14.8 and 77.3 ± 10.4 ms in ventricular and atrial cells, respectively. The midpoints for steady-state inactivation were −36.4 ± 0.3 and −51.6 ± 0.4 mV, and recovery from inactivation was rapid near the resting potential (time constants = 7.9 ± 1.9 and 8.8 ± 2.1 ms, respectively). I to.ir was detected in Na+-containing and Na+-free solutions and was not blocked by 20 nmol/l saxitoxin. Action potential clamp revealed that I to.ir contributed an outward current that activated rapidly on depolarization and inactivated by early phase 2 in both tissues. Although it is well known that 4-AP-sensitive transient outward current is absent in guinea pig, this Ba2+-sensitive and 4-AP-insensitive K+ current has been overlooked.
Acute cardiovascular response to isocapnic hypoxia. I. A mathematical model
Authors: Ursino Mauro , Magosso Elisa
Published: December 2017

A mathematical model of the acute cardiovascular response to isocapnic hypoxia is presented. It includes a pulsating heart, the systemic and pulmonary circulation, a separate description of the vascular bed in organs with the higher metabolic need, and the local effect of O2 on these organs. Moreover, the model also includes the action of several reflex regulatory mechanisms: the peripheral chemoreceptors, the lung stretch receptors, the arterial baroreceptors, and the hypoxic response of the central nervous system. All parameters in the model are given in accordance with the physiological literature. The simulated overall response to a deep hypoxia (28 mmHg) agrees with the experimental data quite well, showing a biphasic pattern. The early phase (8–10 s), caused by activation of peripheral chemoreceptors, exhibits a moderate increase in mean systemic arterial pressure, a decrease in heart rate, a quite constant cardiac output, and a redistribution of blood flow to the organs with higher metabolic need at the expense of other organs. The later phase (20 s) is characterized by the activation of lung stretch receptors and by the central nervous system hypoxic response. During this phase, cardiac output and heart rate increase together, and blood flow is restored to normal levels also in organs with lower metabolic need. The model may be used to gain a deeper understanding of the role of each mechanism in the overall cardiovascular response to hypoxia.
Postextrasystolic contractile decay always contains exponential and alternans components in canine heart
Authors: Shimizu Juichiro , Araki Junichi , Iribe Gentaro , Imaoka Takeshi , Mohri Satoshi , Kohno Kunihisa , Matsubara Hiromi , Ohe Tohru , Takaki Miyako , Suga Hiroyuki
Published: December 2017

In isolated, blood-perfused canine hearts, postextrasystolic potentiation (PESP) decays monotonically after a noncompensatory pause following a spontaneous extrasystole (ES). The monotonic PESP decay yields myocardial internal Ca2+ recirculation fraction (RF). We have found that after a compensatory pause (CP), PESP decays in alternans, consisting of an exponential and a sinusoidal decay component. We have proposed that this exponential component also yields RF. In the present study, we examined the reliability of this alternative method by widely changing the ES coupling interval (ESI), CP, and heart rate in the canine excised, cross-circulated left ventricle. We found that all PESP decays consisted of the sum of an exponential and a sinusoidal decay component of variable magnitudes whether a CP existed or not. Their decay constants as well as the calculated RF were independent of the ESI and CP. This confirmed the utility of our alternative RF determination method regardless of the ESI, CP, and heart rate. Direct experimental evidence of Ca2+ dynamics supportive of this alternative method, however, remains to be obtained.
Basic FGF reduces stunning via a NOS2-dependent pathway in coronary-perfused mouse hearts
Authors: Hampton Thomas G. , Amende Ivo , Fong Jason , Laubach Victor E. , Li Jian , Metais Carolyn , Simons Michael
Published: December 2017

Basic fibroblast growth factor (FGF-2) may protect the heart from ischemia-reperfusion injury (stunning) by stimulating nitric oxide (NO) production. To test this hypothesis, we pretreated coronary-perfused mouse hearts with 1 μg/ml FGF-2 or vehicle control before the onset of ischemia. Intracellular calcium (Cai2+) was estimated by aequorin, and NO release was measured with an NO-selective electrode. Hearts perfused with FGF-2 maintained significantly better left ventricular (LV) function during ischemia than hearts perfused with vehicle. FGF-2 significantly delayed the onset of ischemic contracture and improved LV recovery during reperfusion. Cai2+was similar in both groups at baseline during ischemia and reperfusion.l- N6-(1-iminoethyl)lysine, a selective inhibitor of inducible NO synthase (NOS2), obliterated the protective effects of FGF-2. In transgenic hearts deficient in the expression of NOS2 (NOS2−/−), FGF-2 did not attenuate ischemia-induced LV dysfunction. Measurements of NO release demonstrated that FGF-2 perfusion significantly increased NO in wild-type but not in NOS2−/− hearts. We conclude that basic FGF attenuates myocardial stunning independent of alterations in Cai2+by stimulating NO production via an NOS2-dependent pathway.