bluuebunny/crossref_metadata_2025 huggingface dataset:
H2O2opens BKCachannels via the PLA2-arachidonic acid signaling cascade in coronary artery smooth muscle
Authors: Barlow Robert S. , El-Mowafy Abdalla M. , White Richard E.
Published: December 2017

H2O2is a reactive oxygen species that contracts or relaxes vascular smooth muscle, but the molecular basis of these effects remains obscure. We previously demonstrated that H2O2opens the large-conductance, calcium- and voltage-activated (BKCa) potassium channel of coronary myocytes (2) and now report physiological and biochemical evidence that the effect of H2O2on coronary smooth muscle involves the phospholipase A2(PLA2)/arachidonic acid (AA) signaling cascades. H2O2stimulation of BKCachannel activity was inhibited by arachidonyl trifluoromethyl ketone, an inhibitor of cytosolic PLA2. Furthermore, H2O2stimulated release of [3H]AA from coronary myocytes, and exogenous AA mimicked the effect of H2O2on BKCachannels. Inhibitors of protein kinase C activity attenuated the effect of H2O2on BKCachannels, [3H]AA release, or intact coronary arteries. In addition, the effect of H2O2or AA on BKCachannels was inhibited by blockers of lipoxygenase metabolism. In contrast, inhibitors of cyclooxygenase or cytochrome P-450 had no effect. We propose that H2O2relaxes coronary arteries by stimulating BKCachannels via the PLA2/AA signaling cascade and that lipoxygenase metabolites mediate this response.
Piinhibits the SR Ca2+pump and stimulates pump-mediated Ca2+leak in rabbit cardiac myocytes
Authors: Smith G. L. , Duncan A. M. , Neary P. , Bruce L. , Burton F. L.
Published: December 2017

Measurements of sarcoplasmic reticulum (SR) Ca2+uptake were made from aliquots of dissociated permeabilized ventricular myocytes using fura 2. Equilibration with 10 mM oxalate ensured a reproducible exponential decline of [Ca2+] from 600 nM to a steady state of 100–200 nM after addition of Ca2+. In the presence of 5 μM ruthenium red, which blocks the ryanodine receptor, the time course of the decline of [Ca2+] can be modeled by a Ca2+-dependent uptake process and a fixed Ca2+leak. Partial inhibition of the Ca2+pump with 1 μM cyclopiazonic acid or 50 nM thapsigargin reduced the time constant for Ca2+uptake but did not affect the SR Ca2+leak. Addition of 10 mM inorganic phosphate (Pi) decreased the rate of Ca2+accumulation by the SR and increased the Ca2+leak rate. This effect was reversed on addition of 10 mM phosphocreatine. 10 mM Pihad no effect on Ca2+leak from the SR after complete inhibition of the Ca2+pump. In conclusion, Pidecreases the Ca2+uptake capacity of cardiac SR via a decrease in pump rate and an increase in Ca2+pump-dependent Ca2+leak.
CD14-independent activation of cardiomyocyte signal transduction by bacterial endotoxin
Authors: Cowan Douglas B. , Poutias Dimitrios N. , Del Nido Pedro J. , McGowan Francis X.
Published: December 2017

In the heart, lipopolysaccharide (LPS) induces the production of proinflammatory cytokines that cause myocardial dysfunction; however, the signaling pathways involved in cardiomyocyte responses are poorly understood. We studied LPS-induced signaling by treating cardiomyocyte cultures with 0.01–10 μg/ml LPS for 0–24 h in the presence or absence of 2.5% serum. Cytosolic and nuclear proteins were analyzed for expression and activation of protein kinases. Members of the extracellular signal-regulated kinase (ERK) and signal transducer and activators of transcription (STAT) protein families were uniformly expressed and specifically phosphorylated in response to LPS. Activation was biphasic; peaking at 5–10 min and 24 h after treatment. Inhibitor experiments provided evidence that ERK proteins may regulate STAT activity. Serum did not augment endotoxin-induced phosphorylation. Although cardiomyocytes expressed low levels of CD14 and LPS-binding protein, specific enzymatic removal of glycosyl phosphatidylinositol-linked receptors or incubation with an anti-CD14 antibody had no effect on kinase activation. Treatment of cells with an excess of detoxified LPS attenuated endotoxin-induced signaling. In addition, endotoxin stimulated specific binding of nuclear factors to AP-1, nuclear factor-κB (NF-κB), STAT1 (SIE, sis-inducible element), and STAT3 consensus-binding sequences. Finally, inhibition of ERK phosphorylation reduced, and NF-κB nuclear translocation prevented, tumor necrosis factor-α production. Our results indicate that LPS-induced activation of signal transduction in cardiomyocytes occurs by a CD14-independent mechanism.
Adenosine A2Aand A2Breceptors in cultured human and porcine coronary artery endothelial cells
Authors: Olanrewaju Hammed A. , Qin W. , Feoktistov I. , Scemama Jean-Luc , Mustafa S. Jamal
Published: December 2017

We investigated the role of the cAMP link to the signal transduction mechanism coupled with adenosine A2Aand A2Breceptors in cultured human coronary artery endothelial cells (HCAEC) and porcine coronary artery endothelial cells (PCAEC). 2-[4-[2-{2-[(4-aminophenyl)methylcarbonylamino]ethylaminocarbonyl}ethyl]phenyl]ethylamino-5′- ethylcarboxamidoadenosine (125I-PAPA-APEC) (PAPA-APEC) was used to demonstrate the specific binding in PCAEC membranes. The specific binding was saturable and reversible with a maximal number of binding sites (Bmax) of 240 fmol/mg protein, and scatchard analysis revealed a single class of binding site with an equilibrium dissociation constant ( Kd) of 1.17 ± 0.035 nM. In competition experiments, adenosine receptor agonists showed the following order of potency (based on IC50): 5′-( N-ethylcarboxamido)adenosine (NECA) ≥ CGS-21680 > 2-chloroadenosine. This order appears to be consistent with the A2adenosine receptor classification. We also studied the effects of adenosine agonists on the accumulation of cAMP as an indirect approach to show the presence of functional A2receptors. Similarly, the same adenosine agonists (10−7-10−4M) elicited the production of cAMP in intact endothelial cells in a dose-dependent manner, exhibiting consistently with the A2adenosine receptor classification. A selective A2Aadenosine receptor antagonist (ZM-241385, 10−8M) significantly inhibited the effect of CGS-21680 on cAMP but only partly inhibited the effect of NECA, suggesting the presence of both A2Aand A2Breceptors. Western blot analysis further showed the immunoreactivity of A2Aand A2Breceptor at 45 and 36 kDa, respectively, in both HCAEC and PCAEC. Direct evidence for the presence of A2Aand A2Breceptors in cultured HCAEC and PCAEC by reverse transcription-polymerase chain reaction (RT-PCR), revealed expected PCR product sizes (205 and 173 bp) for A2Aand A2Breceptors in HCAEC and PCAEC, respectively. The data show that adenylate cyclase-coupled adenosine A2Aand A2Breceptors are present in coronary endothelial cells.
Pyruvate potentiates inotropic effects of isoproterenol and Ca2+in rabbit cardiac muscle preparations
Authors: Hermann Hans-Peter , Zeitz Oliver , Keweloh Boris , Hasenfuss Gerd , Janssen Paul M. L.
Published: December 2017

Catecholamines and elevated extracellular Ca2+concentration ([Ca2+]o) augment contractile force by increased Ca2+influx and subsequent increased sarcoplasmic reticulum (SR) Ca2+release. We tested the hypothesis that pyruvate potentiates Ca2+release and inotropic response to isoproterenol and elevated [Ca2+]o, since this might be of potential importance in a clinical setting to circumvent deleterious effects on energy demand during application of catecholamines. Therefore, we investigated isometrically contracting myocardial preparations from rabbit hearts at 37°C, pH 7.4, and a stimulation frequency of 1 Hz. At a [Ca2+]oof 1.25 mM, pyruvate (10 mM) alone increased developed force (Fdev) from 1.89 ± 0.42 to 3.62 ± 0.62 (SE) mN/mm2( n = 8, P < 0.05) and isoproterenol (10−6M) alone increased Fdevfrom 2.06 ± 0.55 to 25.11 ± 2.1 mN/mm2( P < 0.05), whereas the combination of isoproterenol and pyruvate increased Fdevoverproportionally from 1.89 ± 0.42 to 33.31 ± 3.18 mN/mm2( P < 0.05). In a separate series of experiments, we assessed SR Ca2+content by means of rapid cooling contractures and observed that, despite no further increase in Fdevby increasing [Ca2+]ofrom 8 to 16 mM, 10 mM pyruvate could still increase Fdevfrom 26.4 ± 6.8 to 29.7 ± 7.1 mN/mm2( P < 0.05, n = 9) as well as the Ca2+load of the SR. The results show that the positive inotropic effects of pyruvate potentiate the inotropic effects of isoproterenol or Ca2+, because in the presence of pyruvate, Ca2+and isoproterenol induced larger increases in inotropy than can be calculated by mere addition of the individual effects.
NO metabolites accumulate in erythrocytes in proportion to carbon dioxide and bicarbonate concentration
Authors: Recchia Fabio A. , Vogel Traci R. , Hintze Thomas H.
Published: December 2017

It is not known whether the ratio between the concentrations of NO metabolites (NOx) in plasma (pNOx) and in erythrocytes (eNOx) is constant or correlates with chemical parameters of the blood. We measured pH, Po 2, and Pco 2 and calculated bicarbonate concentration in 19 blood samples from the aorta, coronary sinus, and leg veins of 7 dogs. Erythrocytes were then separated by centrifugation and lysed with distilled water, and the lysate was ultrafiltered with a molecular cutoff of 50 kDa to remove the hemoglobin. NOx were measured in plasma and in the ultrafiltrate. NOx concentration was higher in erythrocytes, with eNOx/pNOx ranging from 4.38 to 14.60. Linear and significant correlations were found between the natural logarithm of eNOx/pNOx and Pco 2 ( r = 0.70, P < 0.001) or bicarbonate concentration ( r = 0.72, P< 0.001). These results demonstrate, for the first time, that plasma NOx cannot be considered as a constant fraction of the total NOx in blood but varies dramatically in proportion to the CO2/bicarbonate concentration. To prevent an underestimation of venous-arterial difference of NOx across organs, NOx should be measured in whole blood.
Heterogeneity of local myocardial flow and oxidative metabolism
Authors: Schwanke Uwe , Deussen Andreas , Heusch Gerd , Schipke Jochen D.
Published: December 2017

In mammalian hearts, local myocardial flow (LMF) varies between 20 and 200% of the mean. It is not clear whether oxidative metabolism has a similar degree of heterogeneity. Therefore, we investigated the relation between LMF and local oxidative metabolism in isolated rabbit hearts. Buffer oxygenation with18O2resulted in labeled myocardial oxidation water (H218O). In four hearts, myocardial oxygen consumption (MV˙o2) was calculated from the H218O production and compared with that calculated according to Fick. In eight additional hearts, LMF was measured using microspheres. Coronary venous H218O kinetics and local H218O residues were determined and analyzed by mathematical modeling. MV˙o2recovery from H218O was >93% compared with that according to Fick. LMF ranged from 1.91 to 11.24 ml · min−1· g−1, and local H218O residue ranged from 0.41 to 1.04 μmol/g. Both variables correlated ( r = 0.62, n = 64, P < 0.001). Measurements in nine hearts were fitted by modeling using capillary permeability-surface area products ( PSc) from 2 to 10 ml · min−1· g−1. With flow-proportional PSc, a 3.33-fold difference in LMF was associated with a 6.45-fold difference in local MV˙o2. Both LMF and local oxidative metabolism are spatially heterogeneous, and they correlate to one another.
Active and passive liver microvascular responses from angiotensin, endothelin, norepinephrine, and vasopressin
Authors: Rothe Carl F. , Maass-Moreno Roberto
Published: December 2017

Vasoconstrictor agents may induce a decrease in hepatic vascular volume passively, by decreasing distending pressure, or actively, by stimulating contractile elements of capacitance vessels. Hepatic venular resistance was estimated in anesthetized rabbits from hepatic venular pressure (Pμhv; by servo-null micropipette), inferior vena cava pressure, and total hepatic blood flow (Fhv; by ultrasound flow probe). Changes in liver volume were estimated from measures of liver lobe thickness. Angiotensin (ANG) II, endothelin (ET)-1, norepinephrine (NE), and vasopressin (VP) were infused into the portal vein at a constant rate for 5 min. We conclude that ANG II and NE induced active constriction of hepatic capacitance vessels, because the liver lobe thickness decreased significantly even though Pμhv and portal venous distending pressure (Ppv) increased. All four agents increased splanchnic and hepatic venous resistances in similar proportions. With VP, Pμhv and Ppv decreased, but with ET-1, Pμhv and Ppv increased. However, lobe thickness was not significantly changed by either drug during the infusion compared with the 2-min control period. Thus VP and ET-1 have only minor effects on hepatic capacitance vessels. ET-1, at 0.04 μg · min−1 · kg body wt−1, caused an increase in systemic arterial blood pressure, but erythrocyte movement through the sinusoids in some animals stopped.
Effects of hypoxia on pulmonary microvascular volume
Authors: Clough Anne V. , Haworth Steven T. , Ma Wei , Dawson Christopher A.
Published: December 2017

To determine the effects of alveolar hypoxia on pulmonary microvascular volume, X-ray microfocal angiographic images of isolated perfused dog lung lobes were obtained during passage of a bolus of radiopaque contrast medium during both normoxic (alveolar gas, 15% O2, 6% CO2, and 79% N2) and hypoxic (3% O2, 6% CO2, and 91% N2) conditions. Regions of interest (ROIs) over the lobar artery and vein at low magnification and a feeding artery (∼500 μm diameter) and the nearby microvasculature (vessels smaller than ∼50 μm) at high magnification were identified, and X-ray absorbance vs. time curves were acquired under both conditions from the same ROIs. The total pulmonary vascular volume was calculated from the flow and the mean transit time for the contrast medium passage from the lobar artery to lobar vein. The fractional changes in microvascular volume were determined from the areas under the high-magnification X-ray absorbance curves. Hypoxia decreased lobar volume by 13 ± 3% (SE) and regional microvascular volume by 26 ± 4% (SE). Given the morphometry of the lung vasculature, these results suggest that capillary volume was decreased by hypoxia.
Conditioning of β1-adrenoceptor effect via β2-subtype on L-type Ca2+current in canine ventricular myocytes
Authors: Nagykaldi Zsolt , Kem David , Lazzara Ralph , Szabo Bela
Published: December 2017

We investigated the roles of β1- and β2-receptors (β-AR) in adrenergic enhancement of L-type Ca2+current ( ICaL) in canine ventricular myocytes. Isoproterenol and l-norepinephrine produced a monophasic and a biphasic concentration- ICaLrelationship (CR), respectively. α1-AR inhibition with prazosin and β2-AR stimulation with zinterol or l-epinephrine shifted the CR of l-norepinephrine leftward. Zinterol (50 nM) and l-epinephrine (10 nM), but not prazosin, altered the biphasic CR of l-norepinephrine to a monophasic CR. Zinterol and l-epinephrine applied after l-norepinephrine had no effect on ICaL. β2-AR inhibition with ICI-118551 reduced the Emaxof isoproterenol and l-norepinephrine by 60% and abolished the augmentation of l-norepinephrine by zinterol and l-epinephrine. Carbachol (100 nM) modestly reduced the ICaLresponse to β1-AR stimulation but abolished the enhancement via β2-AR. Zinterol augmented the enhancement of ICaLby forskolin, IBMX, and theophylline, but not in the presence of CGP-20712A. We conclude that selective β2-AR stimulation does not increase ICaLbut enhances adenylyl cyclase activity when stimulated via β1-AR and with forskolin. β2-AR activity preconditions adenylyl cyclase for β1-AR stimulation.
Thrombin and leukocyte recruitment in endotoxemia
Authors: Woodman Richard C. , Teoh Diane , Payne Derrice , Kubes Paul
Published: December 2017

Because thrombin has been implicated in sepsis, it has been proposed that antithrombin III (AT III) is beneficial due to its anticoagulatory and antiadhesive effects. Using intravital microscopy, we visualized leukocyte-endothelium interactions in postcapillary venules of the feline mesentery exposed to lipopolysaccharide (LPS). At a concentration of AT III that blocks leukocyte adhesion in postischemic mesentery, we found no role for thrombin in LPS-induced rolling, adhesion and emigration, or microvascular dysfunction. Furthermore, AT III did not attenuate leukocyte-endothelial interactions after tumor necrosis factor-α superfusion of the mesentery. In contrast, fucoidan, a selectin inhibitor, prevented almost all LPS-induced rolling and reduced adhesion, emigration, and microvascular dysfunction. In a model of endotoxemia, leukocyte recruitment into mesentery or lungs was unaffected by AT III. Finally, in a human cell system that mimics the flow conditions in vivo, human neutrophils rolled, adhered, and emigrated similar to the feline postcapillary microvessels, and AT III had no effect on leukocyte recruitment induced by LPS. If AT III has beneficial effects in endotoxemia, it is not due to a direct effect upon leukocyte rolling, adhesion, or emigration in postcapillary venules in vivo.
Selective transport of adenosine into porcine coronary smooth muscle
Authors: Rubin L. J. , Johnson L. R. , Dodam J. R. , Dhalla A. K. , Magliola L. , Laughlin M. H. , Jones A. W.
Published: December 2017

Adenosine (ADO), an endogenous regulator of coronary vascular tone, enhances vasorelaxation in the presence of nucleoside transport inhibitors such as dipyridamole. We tested the hypothesis that coronary smooth muscle (CSM) contains a high-affinity transporter for ADO. ADO-mediated relaxation of isolated large and small porcine coronary artery rings was enhanced 12-fold and 3.4-fold, respectively, by the transport inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI). Enhanced relaxation was independent of endothelium and was selective for ADO over synthetic analogs. Uptake of [3H]ADO into freshly dissociated CSM cells or endothelium-denuded rings was linear and concentration dependent. Kinetic analysis yielded a maximum uptake ( V max) of 67 ± 7.0 pmol · mg protein−1 · min−1 and a Michaelis constant ( K m) of 10.5 ± 5.8 μM in isolated cells and a V max of 5.1 ± 0.5 pmol · min−1 · mg wet wt−1and a K m of 17.6 ± 2.6 μM in intact rings. NBTI inhibited transport into small arteries (IC50 = 42 nM) and cells. Analyses of extracellular space and diffusion kinetics using [3H]sucrose indicate the V max and K m for ADO transport are sufficient to clear a significant amount of extracellular adenosine. These data indicate CSM possess a high-affinity nucleoside transporter and that the activity of this transporter is sufficient to modulate ADO sensitivity of large and small coronary arteries.
Effect of milrinone on left ventricular relaxation and Ca2+uptake function of cardiac sarcoplasmic reticulum
Authors: Yano Masafumi , Kohno Michihiro , Ohkusa Tomoko , Mochizuki Mamoru , Yamada Jutaro , Kohno Masateru , Hisaoka Takayuki , Ono Kaoru , Tanigawa Taketo , Kobayashi Shigeki , Matsuzaki Masunori
Published: December 2017

Milrinone, a phosphodiesterase 3 (PDE3) inhibitor, is known to enhance left ventricular (LV) contractility by an inhibition of the breakdown of cAMP through the mechanism inhibiting PDE3. However, it is unclear whether milrinone also exerts positive lusitropy, like dobutamine. Here, we assessed the effects of milrinone on in vivo LV relaxation, as well as the Ca2+-ATPase activity and the Ca2+uptake function of the cardiac sarcoplasmic reticulum (SR), compared with the effect of dobutamine on those functions. After dobutamine (3 μg · kg−1· min−1) was administered, the peak value of the first derivative of LV pressure (+dP/d t) increased by 46%, whereas the time constant (τ) of LV pressure decay decreased by 6.9%, respectively. After milrinone (10 μg/kg) was administered, the peak +dP/d tincreased to a similar extent as dobutamine (46%), whereas τ decreased much more than dobutamine (19.9%; P < 0.05). In LV crude homogenate, the thapsigargin-sensitive, Ca2+-ATPase activity-cAMP relationships was significantly less increased by milrinone compared with dobutamine ( P< 0.05), indicating the higher sensitivity of the SR Ca2+-ATPase activity on cAMP by milrinone than by dobutamine. In the SR vesicles purified from LV muscles, the addition of cAMP increased the SR Ca2+uptake in a dose-dependent fashion, and the PDE3 inhibitors (milrinone and cGMP) significantly augmented this response ( P < 0.05). Hence, milrinone substantially improved LV relaxation in association with an acceleration of the SR Ca2+-ATPase activity and the SR Ca2+uptake. This acceleration might be due to an inhibition of the membrane-bound PDE3 in the SR, leading to a local elevation of cAMP.
Oxygen dependency and precision of cytochrome oxidase signal from full spectral NIRS of the piglet brain
Authors: Springett R. , Newman J. , Cope M. , Delpy D. T.
Published: December 2017

Oxidation changes of the copper A (CuA) center of cytochrome oxidase in the brain were measured during brief anoxic swings at both normocapnia and hypercapnia (arterial Pco2≈55 mmHg). Hypercapnia increased total hemoglobin from 37.5 ± 9.1 to 50.8 ± 12.9 μmol/l (means ± SD; n = 7), increased mean cerebral saturation (SmcO2) from 65 ± 4 to 77 ± 3%, and oxidized CuAby 0.43 ± 0.23 μmol/l. During the onset of anoxia, there were no significant changes in the CuAoxidation state until SmcO2had fallen to 43 ± 5 and 21 ± 6% at normocapnia and hypercapnia, respectively, and the maximum reduction during anoxia was not significantly different at hypercapnia (1.49 ± 0.40 μmol/l) compared with normocapnia (1.53 ± 0.44 μmol/l). Residuals of the least squares fitting algorithm used to convert near-infrared spectra to concentrations are presented and shown to be small compared with the component of attenuation attributed to the CuAsignal. From these observations, we conclude that there is minimal interference between the hemoglobin and CuAsignals in this model, the CuAoxidation state is independent of cerebral oxygenation at normoxia, and the oxidation after hypercapnia is not the result of increased cerebral oxygenation.
Tyrosine kinase signaling in action potential shortening and expression of HSP72 in late preconditioning
Authors: Okubo Shinji , Bernardo Nelson L. , Elliott Gary T. , Hess Michael L. , Kukreja Rakesh C.
Published: December 2017

We investigated the role of tyrosine kinase (TK) signaling in the opening of the ATP-sensitive K+(KATP) channel and 72-kDa heat shock protein (HSP72) expression during late preconditioning. Rabbits were subjected to surgical operation (sham) or were preconditioned (PC) with four cycles of 5 min of ischemia and 10 min of reperfusion. Twenty-four hours later, animals were subjected to 30 min of ischemia and 180 min of reperfusion. Genistein (1 mg/kg ip) was used to block the receptor TK. Six groups were studied: control, sham, genistein-sham, PC, genistein-PC, and vehicle-PC group (1% dimethyl sulfoxide). Genistein or vehicle was given 30 min before the surgical procedure. Genistein pretreatment decreased the expression of HSP72 in PC hearts and suppressed action potential duration shortening during ischemia in sham and PC groups. Infarct size (%risk area) was reduced in the PC (11.6 ± 1.0%) and vehicle-PC (19.3 ± 2.0%) compared with the control (40.0 ± 3.8%) or sham (46.0 ± 2.0%) groups ( P < 0.05). Genistein pretreatment increased infarct size to 46.4 ± 4.1% in the PC hearts. We conclude that TK signaling is involved in KATPchannel opening and HSP72 expression during late PC.
Local and remote arteriolar dilations initiated by skeletal muscle contraction
Authors: Murrant Coral L. , Sarelius Ingrid H.
Published: December 2017

To investigate the relationship between skeletal muscle metabolism and arteriolar dilations in the region local to contracting muscle fibers as well as dilations at remote arteriolar regions upstream, we used a microelectrode on cremaster muscle of anesthetized hamsters to stimulate four to five muscle fibers lying approximately perpendicular to and overlapping a transverse arteriole. Before, during, and after muscle contraction, we measured the diameter of the arteriole at the site of muscle fiber overlap (local) and at a remote site ∼1,000 μm upstream. Two minutes of 2-, 4-, or 8-Hz stimulation (5–10 V, 0.4-ms duration) produced a significant dilation locally (8.2 ± 2.0-, 22.5 ± 2.4-, and 30.9 ± 2.1-μm increase, respectively) and at the remote site (4.2 ± 0.8, 11.0 ± 1.1, and 18.9 ± 2.7 μm, respectively). Muscle contraction at 4 Hz initiated a remote dilation that was unaffected by 15-min micropipette application of either 2 μM tetrodotoxin, 0.07% halothane, or 40 μM 18-β-glycyrrhetinic acid between the local and upstream site. Therefore, at the arteriolar level, muscle contraction initiates a robust remote dilation that does not appear to be transmitted via perivascular nerves or gap junctions.
Na+ current contribution to the diastolic depolarization in newborn rabbit SA node cells
Authors: Baruscotti Mirko , DiFrancesco Dario , Robinson Richard B.
Published: December 2017

Isolated newborn, but not adult, rabbit sinoatrial node (SAN) cells exhibit spontaneous activity that (unlike adult) are highly sensitive to the Na+ current ( I Na) blocker TTX. To investigate this TTX action on automaticity, cells were voltage clamped with ramp depolarizations mimicking the pacemaker phase of spontaneous cells (−60 to −20 mV, 35 mV/s). Ramps elicited a TTX-sensitive current in newborn (peak density 0.89 ± 0.14 pA/pF, n = 24) but not adult ( n = 5) cells. When depolarizing ramps were preceded by steplike depolarizations to mimic action potentials, ramp current decreased 54.6 ± 8.0% ( n = 3) but was not abolished. Additional experiments demonstrated that ramp current amplitude depended on the slope of the ramp and that TTX did not alter steady-state holding current at pacemaker potentials. This excluded a steady-state Na+ window component and suggested a kinetic basis, which was investigated by measuring TTX-sensitive I Na during long step depolarizations. I Na exhibited a slow but complete inactivation time course at pacemaker voltages (τ = 33.9 ± 3.9 ms at −50 mV), consistent with the rate-dependent ramp data. The data indicate that owing to slow inactivation of I Naat diastolic potentials, a small TTX-sensitive current flows during the diastolic depolarization in neonatal pacemaker myocytes.
Impact of acute hypoxia on heart rate and blood pressure variability in conscious dogs
Authors: Yasuma Fumihiko , Hayano Jun-Ichiro
Published: December 2017

To examine whether the impacts of hypoxia on autonomic regulations involve the phasic modulations as well as tonic controls of cardiovascular variables, heart rate, blood pressure, and their variability during isocapnic progressive hypoxia were analyzed in trained conscious dogs prepared with a permanent tracheostomy and an implanted blood pressure telemetry unit. Data were obtained at baseline and when minute ventilation (V˙i) first reached 10 (V˙i10), 15 (V˙i15), and 20 (V˙i20) l/min during hypoxia. Time-dependent changes in the amplitudes of the high-frequency component of the R-R interval (RRIHF) and the low-frequency component of mean arterial pressure (MAPLF) were analyzed by complex demodulation. In a total of 47 progressive hypoxic runs in three dogs, RRIHF decreased atV˙i15 and V˙i20 and MAPLF increased at V˙i10 and V˙i15 but not atV˙i20, whereas heart rate and arterial pressure increased progressively with advancing hypoxia. We conclude that the autonomic responses to isocapnic progressive hypoxia involve tonic controls and phasic modulations of cardiovascular variables; the latter may be characterized by a progressive reduction in respiratory vagal modulation of heart rate and a transient augmentation in low-frequency sympathetic modulation of blood pressure.
Interaction of the vestibular system and baroreflexes on sympathetic nerve activity in humans
Authors: Ray Chester A.
Published: December 2017

Muscle sympathetic nerve activity (MSNA) is altered by vestibular otolith stimulation. This study examined interactive effects of the vestibular system and baroreflexes on MSNA in humans. In study 1, MSNA was measured during 4 min of lower body negative pressure (LBNP) at either −10 or −30 mmHg with subjects in prone posture. During the 3rd min of LBNP, subjects lowered their head over the end of a table (head-down rotation, HDR) to engage the otolith organs. The head was returned to baseline upright position during the 4th min. LBNP increased MSNA above baseline during both trials with greater increases during the −30-mmHg trial. HDR increased MSNA further during the 3rd min of LBNP at −10 and −30 mmHg (Δ32% and Δ34%, respectively; P < 0.01). MSNA returned to pre-HDR levels during the 4th min of LBNP when the head was returned upright. In study 2, MSNA was measured during HDR, LBNP, and simultaneously performed HDR and LBNP. The sum of MSNA responses during individual HDR and LBNP trials was not significantly different from that observed during HDR and LBNP performed together (Δ131 ± 28 vs. Δ118 ± 47 units and Δ340 ± 77 vs. Δ380 ± 90 units for the −10 and −30 trials, respectively). These results demonstrate that vestibular otolith stimulation can increase MSNA during unloading of the cardiopulmonary and arterial baroreflexes. Also, the interaction between the vestibulosympathetic reflex and baroreflexes is additive in humans. These studies indicate that the vestibulosympathetic reflex may help defend against orthostatic challenges in humans by increasing sympathetic outflow.
Normal values of regional left ventricular endocardial motion: multicenter color kinesis study
Authors: Mor-Avi Victor , Spencer Kirk , Gorcsan John , Demaria Anthony , Kimball Thomas , Monaghan Mark , Perez Julio , Sun Jing Ping , Weinert Lynn , Bednarz James , Collins Keith , Edelman Kathy , Kwan Oi Ling , Glascock Betty , Hancock Jane , Baumann Chris , Thomas James , Lang Roberto
Published: December 2017

Our goal was to establish normal values for quantitative color kinesis indexes of left ventricular (LV) wall motion over a wide range of ages, which are required for objective diagnosis of regional systolic and diastolic dysfunction. Color-encoded images were obtained in 194 normal subjects (95 males, 99 females, age 2 mo to 79 yr) in four standard views. Quantitative indexes of magnitude and timing of systolic and diastolic function were studied for age- and gender-related differences. Normal limits of all ejection and filling indexes were in a narrow range (≤25% of the mean), with no major gender-related differences. Despite invariable ejection fractions, both peak filling and ejection rates decreased with age (30 and 20%, correspondingly) with a concomitant increase in mean filling and ejection times, resulting in five- and twofold increases in the late to early filling and ejection ratios, correspondingly. Diastolic asynchrony increased with age (from 4.7 ± 2.0 to 6.4 ± 3.2 from the 2nd to 7th decade). The normal values of color kinesis indexes should allow objective detection of regional LV systolic and diastolic dysfunction.
Cyclic strain modulates resistance to oxidant stress by increasing G6PDH expression in smooth muscle cells
Authors: Leopold Jane A. , Loscalzo Joseph
Published: December 2017

Vascular smooth muscle cells (VSMC) may be subjected to mechanical forces, such as cyclic strain, that promote the formation of reactive oxygen species (ROS). We hypothesized that VSMC modulate this adverse milieu by increasing the expression of glucose-6-phosphate dehydrogenase (G6PDH) to maintain or restore intracellular glutathione (GSH) levels. Cyclic strain increased superoxide formation, which resulted in diminished GSH because of an increase in oxidized glutathione formation; there was also an increase in glutathione peroxidase and glutathione reductase activities. G6PDH activity and protein expression were enhanced concomitant with decreases in GSH levels and remained elevated until intracellular GSH levels were restored. To confirm the role of G6PDH in repleting GSH stores, we inhibited G6PDH activity with DHEA or inhibited enzyme expression with an antisense oligodeoxynucleotide. Diminished G6PDH activity or expression was associated with persistently depleted GSH levels and inhibition of the cyclic strain-mediated increase in glutathione reductase activity. These observations demonstrate that cyclic strain promotes oxidant stress in VSMC, which, in turn, induces G6PDH expression. When G6PDH is inhibited, GSH levels are not restored because of impaired glutathione reductase activity. These data suggest that G6PDH is a critical determinant of the response to oxidant stress in VSMC.
Mediators of the mitogenic action of human V1vascular vasopressin receptors
Authors: Thibonnier Marc , Conarty Doreen M. , Plesnicher Christine L.
Published: December 2017

Arginine vasopressin (AVP) activation of V1vascular receptors (V1Rs) stimulates cell growth and proliferation in different tissues via cellular signaling pathways that remain to be identified. To explore the intracellular mediators of the mitogenic action of V1R, Chinese hamster ovary (CHO) cells were stably transfected with the human V1R cDNA clone we isolated previously. We assessed AVP effects on kinase activation (immunoblotting with phosphospecific antibodies), DNA synthesis (tritiated thymidine uptake), cell cycle progression (flow cytometry analysis after nuclear labeling with propidium iodide), and cell proliferation (conversion of the colorimetric reagent MTS) in the presence or absence of various pathway inhibitors. AVP stimulation of V1Rs leads to the phosphorylation of several kinases, an increase in DNA synthesis, a progression through the S and G2–M phases of the cell cycle, and an increase in cell proliferation. The mediators of the mitogenic action of V1R activation included calcium mobilization, coupling to a Gqprotein, and the simultaneous and parallel activation of several kinases, mainly calcium/calmodulin-dependent kinase II, phosphatidylinositol 3 kinase, protein kinase C, and p42/p44 mitogen-activated protein kinase.
T-type calcium currents in rat cardiomyocytes during postnatal development: contribution to hormone secretion
Authors: Leuranguer Valérie , Monteil Arnaud , Bourinet Emmanuel , Dayanithi Govindan , Nargeot Joël
Published: December 2017

T-type Ca2+ channels have been suggested to play a role in cardiac automaticity, cell growth, and cardiovascular remodeling. Although three genes encoding for a T-type Ca2+ channel have been identified, the nature of the isoform(s) supporting the cardiac T-type Ca2+ current ( I Ca,T) has not yet been determined. We describe the postnatal evolution of I Ca,T density in freshly dissociated rat atrial and ventricular myocytes and its functional properties at peak current density in young atrial myocytes. I Ca,T displays a classical low activation threshold, rapid inactivation kinetics, negative steady-state inactivation, slow deactivation, and the presence of a window current. Interestingly, I Ca,T is poorly sensitive to Ni2+ and insensitive to R-type current toxin SNX-482. RT-PCR experiments and comparison of functional properties with recombinant Ca2+ channel subtypes suggest that neonatal I Ca,T is related to the α1G-subunit. Atrial natriuretic factor (ANF) secretion was measured using peptide radioimmunoassays in atrial tissue. Pharmacological dissection of ANF secretion indicates an important contribution of I Ca,T to Ca2+signaling during the neonatal period.
Effect of estrogen on global myocardial ischemia-reperfusion injury in female rats
Authors: Zhai Peiyong , Eurell Thomas E. , Cotthaus Robert , Jeffery Elizabeth H. , Bahr Janice M. , Gross David R.
Published: December 2017

We investigated the effects of estrogen on global myocardial ischemia-reperfusion injury in rats that were ovariectomized (Ovx), sham-operated, or ovariectomized and then given 17β-estradiol (E2β) supplementation (Ovx+E2β). Hearts were excised, cannulated, perfused with and then immersed in chilled (4°C) cardioplegia solution for 30 min, and then retrogradely perfused with warm (37°C), oxygenated Krebs-Henseleit bicarbonate buffer for 120 min. The coronary flow rate, first derivative of left ventricular pressure, and nitrite production were all significantly lower in Ovx than in sham-operated or Ovx+E2β hearts. However, coronary flow rates or nitrate production were not consistently different throughout the entire reperfusion period. Ca2+accumulated more in Ovx rat hearts than in sham-operated or Ovx+E2β hearts, and mitochondrial respiratory function was lower in Ovx hearts than in hearts from the other two groups. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of Ovx rat hearts but not in hearts from either of the other groups. Hematoxylin-basic fuchsin-picric acid-stained sections revealed fewer viable myocytes in hearts from the Ovx group than from the sham or Ovx+E2β group. Transmission electron microscopy demonstrated more severely damaged mitochondria and ultrastructural damage to myocytes in Ovx rat hearts. Our results indicate that estrogen plays a cardioprotective role in global myocardial ischemia-reperfusion injury in female rats.
Enhanced gene expression of Na+/Ca2+exchanger attenuates ischemic and hypoxic contractile dysfunction
Authors: Hampton Thomas G. , Wang Ju-Feng , DeAngelis Joseph , Amende Ivo , Philipson Kenneth D. , Morgan James P.
Published: December 2017

Enhanced gene expression of the Na+/Ca2+exchanger in failing hearts may be a compensatory mechanism to promote influx and efflux of Ca2+, despite impairment of the sarcoplasmic reticulum (SR). To explore this, we monitored intracellular calcium (Cai 2+) and cardiac function in mouse hearts engineered to overexpress the Na+/Ca2+ exchanger and subjected to ischemia and hypoxia, conditions known to impair SR Cai 2+transport and contractility. Although baseline Cai 2+and function were similar between transgenic and wild-type hearts, significant differences were observed during ischemia and hypoxia. During early ischemia, Cai 2+ was preserved in transgenic hearts but significantly altered in wild-type hearts. Transgenic hearts maintained 40% of pressure-generating capacity during early ischemia, whereas wild-type hearts maintained only 25% ( P < 0.01). During hypoxia, neither peak nor diastolic Cai 2+ decreased in transgenic hearts. In contrast, both peak and diastolic Cai 2+ decreased significantly in wild-type hearts. The decline of Cai 2+ was abbreviated in hypoxic transgenic hearts but prolonged in wild-type hearts. Peak systolic pressure decreased by nearly 10% in hypoxic transgenic hearts and >25% in wild-type hearts ( P < 0.001). These data demonstrate that enhanced gene expression of the Na+/Ca2+ exchanger preserves Cai 2+ homeostasis during ischemia and hypoxia, thereby preserving cardiac function in the acutely failing heart.
Hepatocyte growth factor is upregulated by low-density lipoproteins and inhibits endothelin-1 release
Authors: Haug Cornelia , Schmid-Kotsas Alexandra , Zorn Ulrike , Bachem Max G. , Schuett Sabine , Gruenert Adolf , Rozdzinski Eva
Published: December 2017

Low-density lipoproteins (LDL) are known to cause endothelial injury and to promote the development of atherosclerotic lesions. This study demonstrates a significant concentration-dependent stimulatory effect of LDL on hepatocyte growth factor (HGF) synthesis (maximum release: 423 ± 16% of control) and HGF receptor mRNA expression in cultured human coronary artery endothelial cells (HCAEC). HGF is a potent mitogen for endothelial cells but does not affect smooth muscle cell proliferation. In contrast, endothelin-1 (ET-1) acts as a mitogen on vascular smooth muscle cells and seems to be upregulated in coronary atherosclerosis. In this study, the basal ET-1 synthesis in HCAEC was concentration-dependently reduced by HGF (minimum: 54 ± 3% of control). This inhibitory effect seems to be mediated via the tyrosine kinase activity of the HGF receptor c- met, since it was antagonized by the tyrosine kinase inhibitor lavendustin A. In addition, HGF also significantly reduced the LDL-stimulated ET-1 release. The LDL-induced upregulation of HGF synthesis in HCAEC and the inhibitory effect of HGF on ET-1 synthesis suggest a protective role of HGF in coronary atherosclerosis.
The lung HETEs (and EETs) up
Authors: Jacobs Elizabeth R. , Zeldin Darryl C.
Published: December 2017

Arachidonic acid metabolites of the cyclooxygenase and lipoxygenase pathways have a variety of important lung functions. Recent observations indicate that cytochrome P-450 ( P-450) monooxygenases are also expressed in the lung, localized to specific pulmonary cell types (e.g., epithelium, endothelium, and smooth muscle), and may modulate critical lung functions. This review summarizes recent data on the presence and biological activity of P-450-derived eicosanoids in the pulmonary vasculature and airways, including effects on pulmonary vascular and bronchial smooth muscle tone and airway epithelial ion transport. We hypothesize a number of potential functions of P-450-derived arachidonate metabolites in the lungs such as contribution to hypoxic pulmonary vasoconstriction, regulation of bronchomotor tone, control of the composition of airway lining fluid, and limitation of pulmonary inflammation. Finally, we describe a number of emerging technologies, including congenic and transgenic strains of experimental animals, P-450 isoform-specific inhibitors and inhibitory antibodies, eicosanoid analogs, and vectors for delivery of P-450 cDNAs and antisense oligonucleotides. These tools will facilitate further studies on the contribution of endogenously formed P-450 eicosanoid metabolites to lung function, under both normal and pathological conditions.
Myocardial remodeling and arrhythmogenesis in moderate cardiac hypertrophy in rats
Authors: Stilli Donatella , Sgoifo Andrea , Macchi Emilio , Zaniboni Massimiliano , De Iasio Sergio , Cerbai Elisabetta , Mugelli Alessandro , Lagrasta Costanza , Olivetti Giorgio , Musso Ezio
Published: December 2017

In 47 male adult Wistar rats with 4-wk aortic coarctation (AC) and 39 age-matched sham-operated rats (SO) chronically instrumented for telemetry electrocardiogram recording, we investigated the mechanisms of arrhythmogenesis in moderate cardiac hypertrophy, with an approach from “in vivo” toward the cellular level, analyzing 1) stress-induced cardiac arrhythmias in all rats and 2) myocardial fibrosis in 35 animals and action potential duration and density of hyperpolarization-activated current in 19 others at the ventricular level. Aortic banding increased arterial blood pressure, cardiac weight, and ventricular myocyte volume by 11, 25, and 14%, respectively ( P < 0.001–0.05). Ventricular arrhythmias occurred at similar rates in AC and SO rats throughout the stress procedure. Action potential duration and hyperpolarization-activated current were about twice as great and myocardial fibrosis about four times greater in AC animals ( P < 0.005–0.05). Electrocardiogram data also revealed more supraventricular arrhythmias in AC rats during the baseline period and after stress and fewer atrioventricular block episodes after stress ( P < 0.05). Thus stress-induced supraventricular and atrioventricular nodal, but not ventricular, arrhythmias were affected in moderate cardiac hypertrophy when ventricular morphofunctional alterations were evident.
Myocardial stunning in exercise-induced ischemia in dogs: lack of late preconditioning
Authors: Parent De Curzon Olivier , Ghaleh Bijan , Tissier Renaud , Giudicelli Jean-François , Hittinger Luc , Berdeaux Alain
Published: December 2017

Late preconditioning (PC) against myocardial stunning develops after coronary artery occlusion (CAO) at rest and subsequent reperfusion. We investigated whether late PC occurs after exercise-induced ischemia (high-flow ischemia) in dogs. A circumflex coronary artery stenosis (by using occluders) was set up before the onset of treadmill exercise in nine chronically instrumented dogs to suppress exercise-induced increase in mean coronary blood flow velocity (CBFV, Doppler) without simultaneously affecting left ventricular (LV) wall thickening (Wth) at rest. Two similar exercises were performed 24 h apart. On day 1, LV Wth was reduced by 84 ± 5% ( P < 0.01), and exercise-induced increases in transmural myocardial blood flow (MBF, fluorescent microspheres) in the ischemic zone were blunted. LV Wth was depressed throughout the first 10 h and returned to its baseline value after 24 h. On day 2, changes in LV Wth and MBF were similar as was the time course for LV Wth recovery, indicating lack of late PC. Also, CBFV responses to acetylcholine, nitroglycerin, and reactive hyperemia (20-s CAO) were not significantly different on days 1 and 2. Similar results were obtained in a subgroup of four additional dogs with more severe stenosis during exercise. Late PC against myocardial stunning was confirmed to occur in a model of 10-min CAO followed by coronary artery reperfusion (CAR) in another four dogs. Thus in contrast with CAO at rest followed by CAR, severe myocardial ischemia in coronary flow-limited exercising dogs does not induce late PC against myocardial stunning.
Protection of cardiac myocytes via δ1-opioid receptors, protein kinase C, and mitochondrial KATP channels
Authors: Huh Joon , Gross Garrett J. , Nagase Hiroshi , Liang Bruce T.
Published: December 2017

The objective of the present study was to investigate the role of δ1-opioid receptors in mediating cardioprotection in isolated chick cardiac myocytes and to investigate whether protein kinase C and mitochondrial ATP-sensitive K+(KATP) channels act downstream of the δ1-opioid receptor in mediating this beneficial effect. A 5-min preexposure to the selective δ1-opioid receptor agonist (−)-TAN-67 (1 μM) resulted in less myocyte injury during the subsequent prolonged ischemia compared with untreated myocytes. 7-Benzylidenenaltrexone, a selective δ1-opioid receptor antagonist, completely blocked the cardioprotective effect of (−)-TAN-67. Naltriben methanesulfonate, a selective δ2-opioid receptor antagonist, had only a slight inhibitory effect on (−)-TAN-67-mediated cardioprotection. Nor-binaltorphimine dihydrochloride, a κ-opioid receptor antagonist, did not affect (−)-TAN-67-mediated cardioprotection. The protein kinase C inhibitor chelerythrine and the KATP channel inhibitors glibenclamide, a nonselective KATP antagonist, and 5-hydroxydecanoic acid, a mitochondrial selective KATPantagonist, reversed the cardioprotective effect of (−)-TAN-67. These results suggest that the δ1-opioid receptor is present on cardiac myocytes and mediates a potent cardioprotective effect via protein kinase C and the mitochondrial KATP channel.
Brief rapid pacing depresses contractile function via Ca2+/PKC-dependent signaling in cat ventricular myocytes
Authors: Wang Yong Gao , Benedict William J. , Hüser Jörg , Samarel Allen M. , Blatter Lothar A. , Lipsius Stephen L.
Published: December 2017

The purpose of this study is to determine the effects of brief rapid pacing (RP; ∼200–240 beats/min for ∼5 min) on contractile function in ventricular myocytes. RP was followed by a sustained inhibition of peak systolic cell shortening (−44 ± 4%) that was not due to changes in diastolic cell length, membrane voltage, or L-type Ca2+current ( ICa,L). During RP, baseline and peak intracellular Ca2+concentration ([Ca2+]i) increased markedly. After RP, Ca2+transients were similar to control. The effects of RP on cell shortening were not prevented by 1 μM calpain inhibitor I, 25 μMl- N5-(1-iminoethyl)-orthinthine, or 100 μM NG-monomethyl-l-arginine. However, RP-induced inhibition of cell shortening was prevented by lowering extracellular [Ca2+] (0.5 mM) during RP or exposure to chelerythrine (2–4 μM), a protein kinase C (PKC) inhibitor, or LY379196 (30 nM), a selective inhibitor of PKC-β. Exposure to phorbol ester (200 nM phorbol 12-myristate 13-acetate) inhibited cell shortening (−46 ± 7%). Western blots indicated that cat myocytes express PKC-α, -δ, and -ε as well as PKC-β. These findings suggest that brief RP of ventricular myocytes depresses contractility at the myofilament level via Ca2+/PKC-dependent signaling. These findings may provide insight into the mechanisms of contractile dysfunction that follow paroxysmal tachyarrhythmias.