bluuebunny/crossref_metadata_2025 huggingface dataset:
Delayed preconditioning with adenosine is mediated by opening of ATP-sensitive K+ channels in rabbit heart
Authors: Bernardo Nelson L. , Okubo Shinji , Maaieh Mohammed M. , Wood Mark A. , Kukreja Rakesh C.
Published: December 2017

The adenosine agonist 2-chloro- N 6-cyclopentyladenosine (CCPA) induces delayed ischemic protection in vivo. We hypothesized that this protection is mediated by opening of ATP-sensitive K+(KATP) channels and increased synthesis of 72-kDa heat shock protein (HSP 72). Six groups ( n = 9–13 animals/group) of animals were studied: group I, control rabbits that received no treatment; group II, animals given glibenclamide (0.3 mg/kg iv) 30 min before ischemia; group III, animals given 5-hydroxydecanoate (5-HD; 5 mg/kg iv) 15 min before ischemia; group IV, rabbits treated with CCPA (0.1 mg/kg iv) 24 h before ischemia; and groups V and VI, CCPA-treated animals that received the KATP-channel blockers glibenclamide or 5-HD, respectively, 30 or 15 min before ischemia. All animals were subjected to ischemia by 30 min of coronary artery occlusion followed by 3 h of reperfusion. Risk area was delineated by injection of 10% Evans blue dye, and infarct size was determined by triphenyltetrazolium staining. Action potential duration (APD) was measured with an epicardial electrode. HSP 72 was measured by Western blotting. CCPA caused a significant reduction in infarct size [12.02 ± 1.0 vs. 40.0 ± 3.8% (%area at risk) in controls, P < 0.01] that was blocked by glibenclamide (36.2 ± 3.1%, P < 0.01) and 5-HD (35.0 ± 2.9%, P < 0.01). Glibenclamide and 5-HD did not change infarct size in control rabbits. These blockers significantly suppressed ischemia-induced APD shortening in control and CCPA-treated animals. CCPA treatment did not induce HSP 72 in hearts. These data suggest that adenosine-initiated delayed protection is mediated via opening of KATP channels but does not involve the synthesis of HSP 72.
Electrophysiological mechanisms by which hypothyroidism delays repolarization in guinea pig hearts
Authors: Bosch Ralph F. , Wang Zhiguo , Li Gui-Rong , Nattel Stanley
Published: December 2017

Thyroid hormone is known to exert important effects on cardiac repolarization, but the underlying mechanisms are poorly understood. We investigated the electrophysiological mechanisms of differences in repolarization between control guinea pigs and hypothyroid animals (thyroidectomy plus 5-propyl-2-thiouracil). Hypothyroidism significantly prolonged the rate-corrected Q-T interval in vivo and action potential duration (APD) of isolated ventricular myocytes. Whole cell voltage-clamp studies showed no change in current density or kinetics of L-type Ca2+current, inward rectifier K+current, or Na+ current in hypothyroid hearts. Dofetilide-resistant current ( I Ks) step current densities were smaller by ∼65%, and tail current densities were reduced by 80% in myocytes from hypothyroid animals compared with controls. The ratio of delayed rectifier step current at +50 mV to tail current at −40 mV was significantly larger in hypothyroid cells for test pulses from 60- to 4,200-ms duration, reflecting a smaller I Ks. Dofetilide-sensitive current ( I Kr) densities were not significantly changed. I Kshalf-activation voltage shifted to more positive voltages in hypothyroidism (29.5 ± 2.2 vs. 21.3 ± 2.7 mV in control, P < 0.01), whereas I Kr voltage dependence was unchanged. We conclude that hypothyroidism delays repolarization in the guinea pig ventricle by decreasing I Ks, a novel and potentially important mechanism for thyroid regulation of cardiac electrophysiology.
Even slight movements disturb analysis of cardiovascular dynamics
Authors: Fortrat Jacques-Olivier , Formet Cédric , Frutoso Jean , Gharib Claude
Published: December 2017

We hypothesized that spontaneous movements (postural adjustments and ideomotion) disturb analysis of heart rate and blood pressure variability and could explain the discrepancy between studies. We measured R-R intervals and systolic blood pressure in nine healthy sitting subjects during three protocols: 1) no movement allowed, 2) movements allowed but not standing, 3) movements and standing allowed. Heart rate and blood pressure were not altered by movements. Movements with or without standing produced a twofold or greater increase of the overall variability of R-R intervals and of the low-frequency components of spectral analysis of heart rate variability. The spectral exponent β of heart rate variability (1.123 at rest) was changed by movements (1.364), and the percentage of fractal noise (79% at rest) was increased by standing (91%, coarse-graining spectral analysis). Spontaneous movements could induce a plateau in the correlation dimensions of heart rate variability, but they changed its nonlinear predictability. We suggest that future studies on short-term cardiovascular variability should control spontaneous movements.
Effects of F I O 2 on hemodynamic responses and O2 transport during RSR13-induced reduction in P50
Authors: Eichelbrönner Otto , Sielenkämper Andreas , Ellis Mark D’Almeida, Christopher G. , Sibbald William J. , Chin-Yee Ian H.
Published: December 2017

Reduced Hb-O2 affinity facilitates O2 release to tissue but may impair pulmonary O2 uptake, affecting cardiac output and systemic vascular resistance (SVR). We studied the effects of shifting the O2-dissociation curve (ODC) to the right with a continuous infusion of RSR13, an allosteric modifier of Hb, and of different inspired O2fractions ([Formula: see text]) on arterial O2 saturations ([Formula: see text]) in Hb and on hemodynamics in nonanesthetized rats. At an[Formula: see text] of 0.21,[Formula: see text] fell during RSR13 from 95 to 81%. Elevation of [Formula: see text] to 0.30 returned [Formula: see text] to baseline in the RSR13 group. The decrease in mean arterial pressure (MAP) was significantly greater in the control than in the RSR13 group at 30% O2. Cardiac index (CI) increased only during RSR13 at 21% O2 and returned to baseline at 30% O2. In contrast, SVR decreased after RSR13 was infused at 21% O2 but returned to baseline at 30%O2, whereas controls showed the opposite, a sustained SVR. In the follow-up period, when 21 O2% was reestablished and mild anemia was present, MAP and SVR fell significantly more in controls, whereas CI only increased in controls. Lactate was significantly lower in the RSR13 than in the control group during RSR13 and the follow-up period. These results demonstrate that 1) continuous infusion of RSR13 produces a constant shift in the O2 tension at which Hb is 50% saturated (P50), 2)[Formula: see text] of 0.30 compensates for the effects of increased P50 on pulmonary O2 loading, and 3) right-shifted ODC combined with supplemental O2 may improve tissue O2 availability.
Cardiac expression of the Na+/Ca2+exchanger NCX1 is GATA factor dependent
Authors: Nicholas Susanne B. , Philipson Kenneth D.
Published: December 2017

The cardiac sarcolemmal Na+/Ca2+exchanger plays a primary role in Ca2+efflux and is important in regulating intracellular Ca2+and beat-to-beat contractility. Of the three Na+/Ca2+exchanger genes cloned (NCX1, NCX2, and NCX3), only NCX1 is expressed in cardiac myocytes. NCX1 has alternative promoters for heart, kidney, and brain tissue-specific transcripts. Analysis of the cardiac NCX1 promoter (at −336 bp) identified a cardiac-specific minimum promoter (at −137) and two GATA sites (at −75 and −145). In this study, gel shift and supershift analyses identified GATA-4 in primary neonatal cardiac myocytes. Site-directed mutagenesis of the GATA-4 site at −75 abolishes binding and reduces activity of the minimum and full-length promoters by >90 and ∼60%, respectively. Mutation of the GATA site at −145 reduces activity of the full-length promoter by ∼30%. Mutation of an E-box at −175 does not alter promoter activity.
A novel heart failure model induced by sequential coronary artery occlusions and tachycardiac stress in awake pigs
Authors: Shen You-Tang , Lynch Joseph J. , Shannon Richard P. , Wiedmann Richard T.
Published: December 2017

A heart failure model was developed using conscious pigs subjected to serial myocardial infarctions followed by intermittent rapid ventricular pacing. Aortic and atrial catheters, left ventricular (LV) pressure gauge, LV dimension crystals, ascending aortic flow probe, pacing leads, and two coronary artery occluders were implanted in 15 pigs. The initial distal left circumflex coronary artery (LCX) occlusion produced a modest infarct, i.e., 18 ± 3% of LV, and the second proximal LCX occlusion, performed 48 h later, enlarged the infarct to 33 ± 2% of the LV with only modest changes in LV function. Thereafter, the pigs were subjected to ventricular pacing at 220 beats/min, which was maintained for 7 days and terminated for 3 days. This pacing cycle was repeated two more times and resulted in significantly impaired LV function and systemic hemodynamics. For example, after the second cycle of pacing, LV rate of pressure change (dP/d t, −41 ± 4% from 2,778 ± 112 mmHg/s), velocity of circumferential fiber shortening ( Vcf: −53 ± 6% from 1.1 ± 0.1 s−1), and cardiac index (CI: −42 ± 5% from 122 ± 4 ml ⋅ min−1⋅ kg−1) were reduced significantly, whereas LV end-diastolic diameter (EDD: +34 ± 6% from 39 ± 2 mm), total peripheral resistance (TPR: +75 ± 16% from 0.79 ± 0.05 U), and mean left atrial pressure (LAP) (+21 ± 1 mmHg from 5 ± 1 mmHg) were increased significantly. Importantly, 3 wk after cessation of the final pacing cycle, LV dP/d t (−40 ± 5%), Vcf(−48 ± 9%), and CI (−30 ± 4%) remained depressed, whereas LV EDD (+39 ± 5%), TPR (+43 ± 9%), and LAP (+13 ± 4 mmHg) were still increased. In contrast, hemodynamic impairment in six conscious pigs subjected to pacing only did not persist when pacing was terminated. Thus this model could provide a unique opportunity to study both the effects of preclinical therapeutic interventions and the mechanisms involved in the development of heart failure.
Human heart failure: cAMP stimulation of SR Ca2+-ATPase activity and phosphorylation level of phospholamban
Authors: Schmidt Ulrich , Hajjar Roger J. , Kim Catherine S. , Lebeche Djamel , Doye Angelia A. , Gwathmey Judith K.
Published: December 2017

Failing human myocardium has been associated with decreased sarcoplasmic reticulum (SR) Ca2+-ATPase activity. There remains controversy as to whether the regulation of SR Ca2+-ATPase activity is altered in heart failure or whether decreased SR Ca2+-ATPase activity is due to changes in SR Ca2+-ATPase or phospholamban expression. We therefore investigated whether alterations in cAMP-dependent phosphorylation of phospholamban may be responsible for the reduced SR Ca2+-ATPase activity in human heart failure. Protein levels of phospholamban and SR Ca2+-ATPase, detected by Western blot, were unchanged in failing compared with nonfailing human myocardium. There was decreased responsiveness to the direct activation of the SR Ca2+-ATPase activity by either cAMP (0.01–100 μmol/l) or protein kinase A (1–30 μg) in failing myocardium. Using the backphosphorylation technique, we observed a decrease of the cAMP-dependent phosphorylation level of phospholamban by 20 ± 2%. It is concluded that the impaired SR function in human end-stage heart failure may be due, in part, to a reduced cAMP-dependent phosphorylation of phospholamban.
Translocation of myocardial GLUT-4 and increased glucose uptake through activation of AMPK by AICAR
Authors: Russell Raymond R. , Bergeron Raynald , Shulman Gerald I. , Young Lawrence H.
Published: December 2017

Insulin increases glucose uptake through the translocation of GLUT-4 via a pathway mediated by phosphatidylinositol 3-kinase (PI3K). In contrast, myocardial glucose uptake during ischemia and hypoxia is stimulated by the translocation of GLUT-4 to the surface of cardiac myocytes through a PI3K-independent pathway that has not been characterized. AMP-activated protein kinase (AMPK) activity is also increased by myocardial ischemia, and we examined whether AMPK stimulates glucose uptake and GLUT-4 translocation. In isolated rat ventricular papillary muscles, 5-aminoimidazole-4-carboxyamide-1-β-d-ribofuranoside (AICAR), an activator of AMPK, as well as cyanide-induced chemical hypoxia and insulin, increased 2-[3H]deoxyglucose uptake two- to threefold. Wortmannin, a PI3K inhibitor, did not affect either the AICAR- or the cyanide-stimulated increase in deoxyglucose uptake but eliminated the insulin-stimulated increase in deoxyglucose uptake. Immunofluorescence studies demonstrated translocation of GLUT-4 to the myocyte sarcolemma in response to stimulation with AICAR, cyanide, or insulin. Preincubation of papillary muscles with the kinase inhibitor iodotubercidin or adenine 9-β-d-arabinofuranoside (araA), a precursor of araATP (a competitive inhibitor of AMPK), decreased AICAR- and cyanide-stimulated glucose uptake but did not affect basal or insulin-stimulated glucose uptake. In vivo infusion of AICAR caused myocardial AMPK activation and GLUT-4 translocation in the rat. We conclude that AMPK activation increases cardiac muscle glucose uptake through translocation of GLUT-4 via a pathway that is independent of PI3K. These findings suggest that AMPK activation may be important in ischemia-induced translocation of GLUT-4 in the heart.
Salt-induced hypertension in Dahl salt-resistant and salt-sensitive rats with NOS II inhibition
Authors: Rudd M. Audrey , Trolliet Maria , Hope Susan , Scribner Anne Ward , Daumerie Geraldine , Toolan George , Cloutier Timothy , Loscalzo Joseph
Published: December 2017

Although recent evidence suggests that reduced nitric oxide (NO) production may be involved in salt-induced hypertension, the specific NO synthase (NOS) responsible for the conveyance of salt sensitivity remains unknown. To determine the role of inducible NOS (NOS II) in salt-induced hypertension, we treated Dahl salt-resistant (DR) rats with the selective NOS II inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT) for 12 days. Tail-cuff systolic blood pressures rose 29 ± 6 and 42 ± 8 mmHg in DR rats given 150 and 300 nmol AMT/h, respectively ( P < 0.01, 2-way ANOVA) after 7 days of 8% NaCl diet. We observed similar results with two other potent selective NOS II inhibitors, S-ethylisourea (EIT) and N-[3-(aminomethyl)benzyl]acetamidine hydrochloride (1400W). Additionally, AMT effects were independent of alterations in endothelial function as assessed by diameter change of mesenteric arterioles in response to methacholine using videomicroscopy. We, therefore, conclude from these data that NOS II is important in salt-induced hypertension.
Sarcoplasmic reticulum and endothelium independently regulate venous smooth muscle [Ca2+]iand contraction
Authors: Laporte Régent , Laher Ismail
Published: December 2017

In rings of rabbit facial vein (RFV), depletion of sarcoplasmic reticulum (SR) Ca2+by caffeine abolished the subsequent isometric contraction to 25 mM K+physiological salt solution (25K-PSS). However, the associated steady-state increase of smooth muscle intracellular free Ca2+concentration ([Ca2+]i), measured using fura PE3 and cuvette photometry, was not altered. Treatment with the specific SR Ca2+pump inhibitor cyclopiazonic acid (30 μM) after caffeine-induced SR Ca2+depletion restored and greatly augmented the 25K-PSS-induced contraction. This suggests that SR Ca2+depletion leads to a dissociation of K+-induced [Ca2+]iincrease from contraction that was dependent on Ca2+pump-mediated SR Ca2+uptake. Endothelium removal augmented the 25K-PSS-induced [Ca2+]iincrease after caffeine-induced SR Ca2+depletion. However, this was associated with only a small and transient contraction. Exposure of endothelium-denuded RFV to cyclopiazonic acid after caffeine-induced SR Ca2+depletion further amplified the 25K-PSS-induced [Ca2+]iincrease, which was associated with a large and sustained contraction. However, the latter [Ca2+]iincrease was still higher than in endothelium-intact RFV. This suggests that the endothelium dampens the [Ca2+]irise associated with K+-induced Ca2+influx, but independently of Ca2+pump-mediated SR Ca2+uptake.
PR-39, a proline/arginine-rich antimicrobial peptide, prevents postischemic microvascular dysfunction
Authors: Korthuis Ronald J. , Gute Dean C. , Blecha Frank , Ross Chris R.
Published: December 2017

We and others have previously demonstrated that intestinal ischemia-reperfusion (I/R) is associated with a large increase in oxidant production that contributes to microvascular barrier disruption in the small bowel. It has been suggested that the bulk of tissue damage during reperfusion can be attributed to adherent, activated neutrophils. From these observations, we hypothesized that pretreatment with PR-39, an endogenous neutrophil antibacterial peptide that is also a potent inhibitor of the neutrophil NADPH oxidase, would prevent postischemic oxidant production and the development of oxidant-dependent sequelae to I/R such as increased venular protein leakage. To test this postulate, oxidant production, venular protein leakage, leukocyte adhesion, and leukocyte emigration were monitored during reperfusion in control (no ischemia) rat mesenteric venules and in mesenteric venules subjected to I/R alone or PR-39 + I/R. Treatment with a single intravenous bolus injection of PR-39 (administered at a dose to achieve an initial blood concentration of 5 μM) abolished I/R-induced leukocyte adhesion and emigration in vivo. In vitro studies indicated that PR-39 prevents platelet-activating factor-induced neutrophil chemotaxis as well as phorbol myristate acetate (PMA)-stimulated intercellular adhesion molecule-1 expression by cultured endothelial cells. PR-39 pretreatment of rat neutrophils also blocked PMA-stimulated neutrophil adhesion to activated endothelial monolayers. In vivo, I/R was associated with a marked and progressive increase in oxidant production and venular protein leakage during reperfusion, effects that were abolished by PR-39 treatment. The results of this study indicate that PR-39 completely abolishes postischemic leukocyte adhesion and emigration. The time course for inhibition of oxidant production by PR-39 suggests that its antiadhesive properties account for this effect of the peptide. PR-39 may thus be therapeutically useful for prevention of neutrophil adhesion and activation during the postischemic inflammatory response.
cAMP-dependent protein kinase is in an active state in rat small arteries possessing a myogenic tone
Authors: Schubert Rudolf , Lehmann Gernot , Serebryakov Vladimir N. , Mewes Hartmut , Hopp Hans-Heinrich
Published: December 2017

The hypothesis that cAMP-dependent protein kinase (protein kinase A; PKA) is in an active state in small arteries possessing a myogenic tone was investigated in pressurized rat tail small arteries. At a pressure of 80 mmHg, these vessels constricted to 71.6 ± 1.0% ( n = 32) of the diameter of the fully relaxed state. The PKA inhibitors Rp-8-(4-chlorophenylthio)-adenosine 3′,5′-cyclic monophosphothioate (Rp-CPT-cAMPS) and N-(2-{[3-(4-bromophenyl)-2-propenyl]amino}-ethyl)-5-isoquinolinesulfonamide HCl (H-89) constricted these vessels dose dependently. For example, 300 μM Rp-CPT-cAMPS and 9 μM H-89 reduced vessel diameter by 11.0 ± 1.2% ( n = 8) and 14.3 ± 3.6% ( n = 5), respectively. The cGMP-dependent protein kinase (protein kinase G; PKG) inhibitor Rp-8-bromo-β-phenyl-1, N2-etheno-guanosine 3′,5′-cyclic monophosphothioate (Rp-8-Br-PET-cGMPS) did not alter vessel diameter up to a concentration of 10 μM. Neither endothelium removal nor inhibition of neural transmission affected the action of Rp-CPT-cAMPS. The effect of 300 μM Rp-CPT-cAMPS was reduced by 82% after pretreatment of the vessel with 100 nM iberiotoxin, a blocker of calcium-activated potassium (KCa) channels. However, the effect of 300 μM Rp-CPT-cAMPS was not altered after pretreatment with 1 mM 4-aminopyridine, a blocker of delayed rectifier potassium channels, or 10 μM ryanodine, a blocker of ryanodine receptor-generated calcium sparks. In inside-out patch-clamp experiments on cells isolated from rat tail small arteries, 10 U/ml of the catalytic subunit of PKA together with 100 μM MgATP increased KCachannel activity 30.1 ± 9.8-fold ( n = 9). Additionally, neither inhibition of PKA or PKG nor moderate activation of PKA or PKG altered the vessel response to a pressure step from 80 to 120 mmHg. These results suggest that in rat tail small arteries possessing a myogenic tone 1) PKA is in an active state modulating the level of the myogenic tone, and 2) KCachannels mediate, at least partly, this effect of PKA.
Increased protein synthesis is necessary for the development of late preconditioning against myocardial stunning
Authors: Rizvi Ali , Tang Xian-Liang , Qiu Yumin , Xuan Yu-Ting , Takano Hitoshi , Jadoon Asad K. , Bolli Roberto
Published: December 2017

In phase I of this study, the rate of protein synthesis was measured by the incorporation of [3H]leucine into the protein pool in the heart of conscious rabbits. At 2 h after ischemic preconditioning (PC) with six 4-min occlusion/4-min reperfusion (O/R) cycles ( group II), the [3H]leucine content in the ischemic-reperfused region was increased by 82% compared with that in controls ( group I), indicating increased protein synthesis. This increase was completely abrogated by pretreatment with cycloheximide (CH; group III). In phase II, rabbits underwent six O/R cycles for three consecutive days ( days 1–3). Controls ( group IV) exhibited late PC against myocardial stunning on days 2 and 3. In group V, which received CH 30 min before the 1st O/R cycle on day 1 (same dose as group III), late PC against stunning on day 2 was completely abrogated. In group VI, pretreatment with CH 24 h before the 1st sequence of O/R cycles had no effect on myocardial stunning on day 1, indicating that the absence of late PC on day 2 in group V cannot be ascribed to delayed toxicity of CH. Taken together, these results demonstrate that, in the conscious rabbit, ischemic PC causes a rapid increase in myocardial protein synthesis and that this increased protein synthesis (or at least a fraction of it) is necessary for the development of the protection against myocardial stunning 24 h later. The late phase of ischemic PC is therefore dependent on the formation of new proteins in intact animals.
LPS pretreatment ameliorates peritonitis-induced myocardial inflammation and dysfunction: role of myocytes
Authors: Neviere Remi R. , Cepinskas Gediminas , Madorin W. Sean , Hoque Nina , Karmazyn Morris , Sibbald William J. , Kvietys Peter R.
Published: December 2017

Peritonitis induced by cecal ligation and puncture (CLP) produces a systemic inflammatory response that can be largely mitigated by pretreatment of the animals with lipopolysaccharide (LPS tolerance). Although cells of myeloid origin and endothelial cells have been shown to contribute to the development of LPS tolerance, little is known regarding the potential role of parenchymal cells in this phenomenon. The major aim of the present study was to assess whether cardiac parenchymal cells (myocytes) contribute to the development of LPS tolerance. Six hours after induction of CLP rats were neutropenic and acidotic, the myocardium contained a leukocyte infiltrate [myeloperoxidase (MPO) activity was increased], and myocardial contractile function was impaired (left ventricular developed pressure was decreased). In animals that were pretreated with LPS these manifestations of sepsis were largely reversed. Further studies focused on the responses of cardiac myocytes to CLP and whether myocytes contributed to the development of LPS tolerance. Myocytes were isolated from rat hearts 6 h after induction of CLP. These myocytes 1) exhibited an impaired ability to shorten in response to pacing, 2) contained the nuclear transcription factor NF-κB in their nuclei, 3) increased their surface levels of intercellular adhesion molecule-1 (ICAM-1), and 4) were hyperadhesive for neutrophils. All of these events did not occur in myocytes obtained from animals that were pretreated with LPS before induction of CLP. These findings indicate that LPS tolerance can be induced in myocytes with respect to polymorphonuclear leukocyte adhesion, presumably by an inability of CLP to mobilize NF-κB to the myocyte nuclei and, thereby, preventing an increase in surface levels of ICAM-1.
Dietary salt increases endothelial nitric oxide synthase and TGF-β1 in rat aortic endothelium
Authors: Ying Wei-Zhong , Sanders Paul W.
Published: December 2017

The amount of NaCl in the diet plays an important role in modulating nitric oxide (NO) synthesis in vivo. In the glomerulus, dietary NaCl also regulates transforming growth factor-β1 (TGF-β1) production. We hypothesized that dietary NaCl intake regulated expression of the endothelial isoform of nitric oxide synthase (NOS3) and TGF-β1 in the aorta. Administration of 8.0% NaCl diet to rats for 7 days did not affect blood pressure but increased steady-state mRNA and protein levels of NOS3 in the arterial wall compared with animals on 0.3% NaCl diet. Northern analysis demonstrated increased steady-state amounts of mRNA of TGF-β1 in aortas of rats on 8.0% NaCl diet. By ELISA, both total and active TGF-β1 were increased in these vessel segments. Endothelial denudation of aortic rings reduced active TGF-β1 secretion to undetectable levels. Addition of a neutralizing antibody to TGF-β to aortic ring segments attenuated NO production but not to that observed in animals on the 0.3% NaCl diet. The data showed that dietary NaCl intake modulated NOS3 and TGF-β1 expression in the arterial wall; NOS3 expression was at least partially regulated by endothelial cell production of TGF-β1.
Potassium channel-mediated vasorelaxation is impaired in experimental renal failure
Authors: Kalliovalkama Jarkko , Jolma Pasi , Tolvanen Jari-Petteri , Kähönen Mika , Hutri-Kähönen Nina , Saha Heikki , Tuorila Seija , Moilanen Eeva , Pörsti Ilkka
Published: December 2017

Chronic renal failure is associated with increased cardiovascular morbidity and abnormal arterial tone, but the underlying pathophysiological mechanisms are poorly understood. Therefore, we studied the responses of isolated mesenteric arterial rings from Wistar-Kyoto rats in standard organ chambers 6 wk after subtotal (5/6) nephrectomy or sham operation. Subtotal nephrectomy resulted in a 1.7-fold elevation of plasma urea nitrogen, whereas blood pressure was not significantly affected. Endothelium-mediated relaxations of norepinephrine-precontracted rings to ACh were impaired in renal failure rats. The nitric oxide (NO) synthase inhibitor NG-nitro-l-arginine methyl ester inhibited relaxations to ACh more effectively in the renal failure group, whereas the cyclooxygenase inhibitor diclofenac did not significantly affect the response in either group. Inhibition of Ca2+-activated K+channels by charybdotoxin and apamin attenuated NO synthase- and cyclooxygenase-resistant relaxations to ACh in control but not renal failure rats and abolished the difference between these groups. Endothelium-independent relaxations to isoproterenol and cromakalim, vasodilators acting via β-adrenoceptors and ATP-sensitive K+channels, respectively, were impaired in the renal failure group, whereas relaxations to the NO donor nitroprusside were similar in both groups. In conclusion, endothelium-mediated relaxation in renal failure rats was impaired in the absence and presence of NO synthase and cyclooxygenase inhibition but not with prevented smooth muscle hyperpolarization. Endothelium-independent relaxations to isoproterenol and cromakalim were also attenuated after 5/6 nephrectomy. These results suggest that impaired vasodilatation in experimental renal failure could be attributed to reduced relaxation via arterial K+channels.
TBAK-1 and TASK-1, two-pore K+ channel subunits: kinetic properties and expression in rat heart
Authors: Kim Yangmi , Bang Hyoweon , Kim Donghee
Published: December 2017

A mammalian K+ channel subunit (TBAK-1/TASK-1) containing two pore domains and four transmembrane segments and whose mRNA is highly expressed in the heart has been cloned recently. TBAK-1 and TASK-1 are identical except for the additional nine amino acids in the NH2 terminus of TBAK-1. We examined their kinetic properties, pH sensitivity, and regional cardiac mRNA expression and determined whether a native cardiac K+ channel with similar kinetic properties was present. When TBAK-1 or TASK-1 was transiently expressed in COS-7 cells, time- and voltage-independent whole cell currents were observed. Single-channel conductances of TBAK-1 and TASK-1 were 14.6 ± 1.0 and 13.8 ± 2.8 pS, respectively, at −80 mV in 140 mM extracellular K+, and the mean open times were 0.8 ± 0.1 and 0.6 ± 0.1 ms, respectively. Both TBAK-1 and TASK-1 were highly sensitive to extracellular pH such that a decrease from 7.2 to 6.4 reduced their open probability ( P o) by 81 ± 14% and 80 ± 16%, whereas a decrease in intracellular pH from 7.2 to 6.4 reduced the P o by 42 ± 10% and 47 ± 12%, respectively. TBAK-1/TASK-1 mRNA was expressed in all regions of the rat heart, with the highest level of expression in the right atrium. A 14-pS K+channel with kinetic properties similar to those of TBAK-1/TASK-1 was identified in rat atrial and ventricular cells. These results indicate that TBAK-1/TASK-1 represents a functional native K+ channel in the rat heart.
Epoxide hydrolases regulate epoxyeicosatrienoic acid incorporation into coronary endothelial phospholipids
Authors: Weintraub Neal L. , Fang Xiang , Kaduce Terry L. , VanRollins Mike , Chatterjee Papri , Spector Arthur A.
Published: December 2017

Cytochrome P-450-derived epoxyeicosatrienoic acids (EETs) are avidly incorporated into and released from endothelial phospholipids, a process that results in potentiation of endothelium-dependent relaxation. EETs are also rapidly converted by epoxide hydrolases to dihydroxyeicosatrienoic acid (DHETs), which are incorporated into phospholipids to a lesser extent than EETs. We hypothesized that epoxide hydrolases functionally regulate EET incorporation into endothelial phospholipids. Porcine coronary artery endothelial cells were treated with an epoxide hydrolase inhibitor, 4-phenylchalcone oxide (4-PCO, 20 μmol/l), before being incubated with3H-labeled 14,15-EET (14,15-[3H]EET). 4-PCO blocked conversion of 14,15-[3H]EET to 14,15-[3H]DHET and doubled the amount of radiolabeled products incorporated into cell lipids, with >80% contained in phospholipids. Moreover, pretreatment with 4-PCO before incubation with 14,15-[3H]EET enhanced A-23187-induced release of radiolabeled products into the medium. In contrast, 4-PCO did not alter uptake, distribution, or release of [3H]arachidonic acid. In porcine coronary arteries, 4-PCO augmented 14,15-EET-induced potentiation of endothelium-dependent relaxation to bradykinin. These data suggest that epoxide hydrolases may play a role in regulating EET incorporation into phospholipids, thereby modulating endothelial function in the coronary vasculature.
Role of K ATP + channels in local metabolic coronary vasodilation
Authors: Richmond Keith Neu , Tune Johnathan D. , Gorman Mark W. , Feigl Eric O.
Published: December 2017

ATP-sensitive potassium ([Formula: see text]) channels have been shown to play a role in the maintenance of basal coronary vascular tone in vivo. [Formula: see text] channels are also involved in the coronary vasodilator response to adenosine. The aim of this study was to determine the role of[Formula: see text] channels in local metabolically mediated increases in coronary blood flow during cardiac electrical paired pacing without catecholamine effects. In 10 anesthetized closed-chest dogs, coronary blood flow was measured in the left circumflex coronary artery, and myocardial O2 consumption was calculated using the arteriovenous O2difference. Cardiac interstitial adenosine concentration was estimated from coronary venous and arterial plasma adenosine measurements using a previously described, multicompartmental, axially distributed, mathematical model. Paired stimulation increased heart rate from 57 to 120 beats/min, myocardial O2consumption 88%, and coronary blood flow 76%. During[Formula: see text] channel blockade with glibenclamide, baseline coronary blood flow decreased in relation to myocardial O2 consumption and thus coronary sinus O2 tension fell. Paired-pulse pacing with glibenclamide resulted in increases in myocardial O2 consumption and coronary blood flow similar to those during control pacing. Coronary venous and estimated interstitial adenosine concentration did not increase sufficiently to overcome the glibenclamide blockade. In conclusion, [Formula: see text] channels are not required for locally mediated metabolic increases in coronary blood flow that accompany myocardial O2consumption during pacing tachycardia without catecholamines, and adenosine levels do not increase sufficiently to overcome the glibenclamide blockade.
Chronic run training suppresses α-adrenergic response of rat cardiomyocytes and isovolumic left ventricle
Authors: Palmer Bradley M. , Olsson M. Charlotte , Lynch Joshua M. , Mace Lisa C. , Snyder Steven M. , Valent Scott , Moore Russell L.
Published: December 2017

The effects of endurance run training on α-adrenergic responsiveness of rat left ventricle (LV) were examined in cardiomyocytes and isovolumic LV. Female Sprague-Dawley rats were sedentary (Sed) or trained (Tr) for >20 wk by treadmill running. Cardiomyocyte shortening and fura 2 fluorescence ratio were recorded before and during 5-min exposure to 5 μM phenylephrine (PE) while paced at 0.5 Hz in 2 mM extracellular Ca2+concentration at 29°C. Cardiomyocyte shortening and shortening velocity increased with PE, and these effects were more pronounced in the Sed group. The rate of cytosolic Ca2+concentration removal was reduced by PE in the Sed cardiomyocytes, but was unaffected in the Tr. Isovolumic LV pressure was recorded immediately before and during 5-min perfusion with 5 μM PE during pacing at 280 beats/min and 37°C, and positive inotropy due to PE was more pronounced in the Sed than in the Tr. These data demonstrated that the effects of α-adrenergic stimulation on myocardial positive inotropy and calcium regulation were reduced in this rat model of run training at both the cellular and whole organ levels.
Intravenous pyruvate prolongs survival during hemorrhagic shock in swine
Authors: Mongan Paul D. , Fontana John L. , Chen Rouyan , Bünger Rolf
Published: December 2017

Pyruvate improves cellular and organ function during hypoxia and ischemia and stabilizes the NADH redox state and cytosolic ATP phosphorylation potential. In this in vivo study, we evaluated the effects of intravenous pyruvate on cardiovascular and neocortical function, indexes of the cytosolic redox state (lactate/pyruvate ratio, L/P) and cellular energy state (adenosine and degradative products hypoxanthine and inosine, ADO + HX + Ino) during controlled arterial hemorrhage (40 mmHg) in sedated swine (45 kg). Na+ pyruvate was infused 1 h before (1 g ⋅ kg−1 ⋅ h−1) and 2 h during (0.5 g ⋅ kg−1 ⋅ h−1) hemorrhage to attain arterial pyruvate levels of 6 mM. Volume (0.9% NaCl) and osmotic (10% NaCl) effects were matched in controls. Time to peak hemorrhage (57 min) and peak hemorrhage volume (43 ml/kg) were similar in all groups. The volume and osmotic groups experienced spontaneous cardiovascular decompensation between 60 and 90 min, with an average time until death of 82.7 ± 5.5 and 74.8 ± 8.2 min. In contrast, survival in the pyruvate group was 151.2 ± 10.0 min ( P < 0.001). During hemorrhage, the pyruvate group had better cardiovascular and cerebrovascular function with significantly higher systemic and cerebral oxygen consumption and less attenuation of the amplitude and frequency of the electrocorticogram. In addition, pyruvate prevented metabolic acidosis and stabilized the L/P. Pyruvate slowed the rise in neocortical microdialysis levels of ADO + HX + Ino, and prevented the net efflux of ADO + HX + Ino into the sagittal sinus. The findings reveal considerable metabolic and functional enhancement by pyruvate during severe hemorrhagic shock with a 75-min delay in spontaneous cardiovascular decompensation and death.
Preconditioning reduces tissue complement gene expression in the rabbit isolated heart
Authors: Tanhehco Elaine J. , Yasojima Koji , McGeer Patrick L. , Washington Ruth A. , Kilgore Kenneth S. , Homeister Jonathon W. , Lucchesi Benedict R.
Published: December 2017

Both preconditioning and inhibition of complement activation have been shown to ameliorate myocardial ischemia-reperfusion injury. The recent demonstration that myocardial tissue expresses complement components led us to investigate whether preconditioning affects complement expression in the isolated heart. Hearts from New Zealand White rabbits were exposed to either two rounds of 5 min global ischemia followed by 10 min reperfusion (ischemic preconditioning) or 10 μM of the ATP-dependent K+(KATP) channel opener pinacidil for 30 min (chemical preconditioning) before induction of 30 min global ischemia followed by 60 min of reperfusion. Both ischemic and chemical preconditioning significantly ( P < 0.05) reduced myocardial C1q, C1r, C3, C8, and C9 mRNA levels. Western blot and immunohistochemistry demonstrated a similar reduction in C3 and membrane attack complex protein expression. The KATPchannel blocker glyburide (10 μM) reversed the depression of C1q, C1r, C3, C8, and C9 mRNA expression observed in the pinacidil-treated hearts. The results suggest that reduction of local tissue complement production may be one means by which preconditioning protects the ischemic myocardium.
Opening of mitochondrial KATPchannel induces early and delayed cardioprotective effect: role of nitric oxide
Authors: Ockaili Ramzi , Emani Venkata R. , Okubo Shinji , Brown Michael , Krottapalli Kavitha , Kukreja Rakesh C.
Published: December 2017

Opening of mitochondrial ATP-sensitive (mitoKATP) channel with diazoxide induces an early phase (EP) of cardioprotection. It is unknown whether diazoxide also induces a delayed phase (DP) of cardioprotection. Because nitric oxide (NO) modulates ATP sensitivity of the KATPchannel, we hypothesized that NO may play a role in diazoxide-induced cardioprotection. Diazoxide (1 mg/kg) was administered either 30 min (for EP) or 24 h (DP) before 30 min of lethal ischemia. Blockers of mitoKATPchannel [5-hydroxydecanoate (5-HD)] or NO synthase [ NG-nitro-l-arginine methyl ester (l-NAME)] were given 10 min before ischemia-reperfusion performed by 30 min of left anterior descending coronary artery occlusion and 3 h of reperfusion. A risk area (RA) was demarcated by Evans blue dye, and infarct size (IS) was measured by tetrazolium staining. Diazoxide caused a decrease in IS (%RA) from 27.8 ± 4.2% in the vehicle group to 12.9 ± 1.2% during EP and from 30.4 ± 4.2% in vehicle-treated rabbits to 19.6 ± 2.4% during DP ( P < 0.05). IS increased to 31.3 ± 1.1% and 27.9 ± 1.0% (EP) and 29.9 ± 2.3% and 35.1 ± 1.8% (DP) with 5-HD andl-NAME, respectively ( P < 0.05). 5-HD andl-NAME caused no proischemic effect in controls. Diazoxide induced both early and delayed anti-ischemic effects via opening of mitoKATPchannels, which was NO dependent.
Pharmacological manipulation of Ins(1,4,5)P3signaling mimics preconditioning in rabbit heart
Authors: Gysembergh Anne , Lemaire Stéphanie , Piot Christophe , Sportouch Catherine , Richard Sylvain , Kloner Robert A. , Przyklenk Karin
Published: December 2017

Recent evidence revealed biphasic alterations in myocardial concentrations of the second messenger inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3] with ischemic preconditioning (PC), i.e., increase during brief PC ischemia and decrease early during sustained test occlusion. Our aim was to determine whether an agonist and an antagonist of Ins(1,4,5)P3signaling {d- myo-inositol-1,4,5-trisphosphate hexasodium salt [d- myo-Ins(1,4,5)P3] and 2-aminoethoxydiphenyl borate (2-APB), respectively}, given such that they mimic this biphasic profile, would mimic infarct size reduction with PC. To test this concept, isolated, buffer-perfused rabbit hearts received no intervention (control), ischemic PC,d- myo-Ins(1,4,5)P3,d- myo-Ins(1,4,5)P3+ PC, 2-APB, or 2-APB + PC. All hearts then underwent 30-min coronary occlusion and 2 h reflow, and infarct size was delineated by tetrazolium staining. In addition, the effects ofd- myo-Ins(1,4,5)P3and 2-APB on Ins(1,4,5)P3signaling were evaluated in isolated fura 2-loaded rat cardiomyocytes. Mean infarct size was reduced with PC and in alld- myo-Ins(1,4,5)P3- and 2-APB-treated groups versus control (59 and 42–55%, respectively, vs. 80% of myocardium at risk, P < 0.05). Thus pharmacological manipulation of Ins(1,4,5)P3signaling mimics the cardioprotection achieved with ischemic PC in rabbit heart.
Improved contractile performance of right ventricle in response to increased RV afterload in newborn lamb
Authors: de Vroomen Maartje , Cardozo Robbert H. Lopes , Steendijk Paul , van Bel Frank , Baan Jan
Published: December 2017

Pulmonary hypertension results in an increased afterload for the right ventricle (RV). To determine the effects of this increased afterload on RV contractile performance, we examined RV performance before and during 4 h of partial balloon occlusion of the pulmonary artery and again after releasing the occlusion in nine newborn lambs. RV contractile performance was quantified by indexes derived from systolic RV pressure-volume relations obtained by a combined pressure-conductance catheter during inflow reduction. An almost twofold increase of end-systolic RV pressure (from 22 to 38 mmHg) was maintained during 4 h. Cardiac output (CO) (0.74 ± 0.08 l/min) and stroke volume (4.3 ± 0.4 ml) were maintained, whereas end-diastolic volume (7.9 ± 1.3 ml) did not change significantly during this period. RV systolic function improved substantially; the end-systolic pressure-volume relation shifted leftward indicated by a significantly decreased volume intercept (up to 70%), together with a slightly increased slope. In this newborn lamb model, maintenance of CO during increased RV afterload is not obtained by an increased end-diastolic volume (Frank-Starling mechanism). Instead, the RV maintains its output by improving contractile performance through homeometric autoregulation.
Role of cell contractions in cAMP-induced cardiomyocyte atrial natriuretic peptide release
Authors: Church D. J. , Rebsamen M. C. , Morabito D. , van der Bent V. , Vallotton M. B. , Lang U.
Published: December 2017

Incubation of spontaneously beating ventricular cardiomyocytes from neonatal rats with prostaglandin E2(0.1 μM) or forskolin (0.1 μM) simultaneously increased the rate of cellular contraction and atrial natriuretic peptide (ANP) secretion. Both responses were maximal within 10–20 min of application and were accompanied by three- to fourfold increases in cAMP formation. By contrast, a higher regimen of forskolin (10 μM) promoted a 20- to 30-fold increase in basal cAMP production, which was accompanied by the abolition of contractile activity and ANP release. Low regimens of forskolin (0.1 μM) doubled the occurrence of cytosolic Ca2+transients associated with monolayer contraction, whereas higher regimens of forskolin (10 μM) completely suppressed Ca2+transients. Moreover, in quiescent cultures that were pretreated with ryanodine, tetrodotoxin, nifedipine, or butanedione monoxime, prostaglandin E2(0.1 μM) and forskolin (0.1 μM) failed to elicit significant ANP secretion, suggesting that cAMP-elevating agents promote ANP secretion to a great extent via an increase in cellular contraction frequency in ventricular cardiomyocytes.
Human femoral artery diameter in relation to knee extensor muscle mass, peak blood flow, and oxygen uptake
Authors: Rådegran G. , Saltin B.
Published: December 2017

It is not known whether the diameter of peripheral conduit arteries may impose a limitation on muscle blood flow and oxygen uptake at peak effort in humans, and it is not clear whether these arteries are dimensioned in relation to the tissue volume they supply or, rather, to the type and intensity of muscular activity. In this study, eight humans, with a peak pulmonary oxygen uptake of 3.90 ± 0.31 (range 2.29–5.03) l/min during ergometer cycle exercise, performed one-legged dynamic knee extensor exercise up to peak effort at 68 ± 7 W (range 55–100 W). Peak values for knee extensor blood flow (thermodilution) and oxygen uptake of 6.06 ± 0.74 (range 4.75–9.52) l/min and 874 ± 124 (range 590–1,521) ml/min, respectively, were achieved. Pulmonary oxygen uptake reached a peak of 1.72 ± 0.19 (range 1.54–2.33) l/min. Diameters of common and profunda femoral arteries determined by ultrasound Doppler were 10.6 ± 0.4 (range 8.2–12.7) and 6.0 ± 0.4 (range 4.5–8.0) mm, respectively. Thigh and quadriceps muscle volume measured by computer tomography were 10.06 ± 0.66 (range 6.18–10.95) and 2.36 ± 0.19 (range 1.31–3.27) liters, respectively. The common femoral artery diameter, but not that of the profunda branch, correlated with the thigh volume and quadriceps muscle mass. There were no relationships between either of the diameters and the absolute or muscle mass-related resting and peak values of blood flow and oxygen uptake, peak pulmonary oxygen uptake, or peak power output during knee extensor exercise. However, common femoral artery diameter correlated to peak pulmonary oxygen uptake during ergometer cycle exercise. In conclusion, common and profunda femoral artery diameters are sufficient to ensure delivery to the quadriceps muscle. However, the common branch may impose a limitation during ergometer cycle exercise.
Cardiovascular response to acute hypovolemia in relation to age. Implications for orthostasis and hemorrhage
Authors: Olsen Henrik , Vernersson Einar , Länne Toste
Published: December 2017

Venous compliance in the legs of aging man has been found to be reduced with decreased blood pooling (capacitance response) in dependent regions, and this might lead to misinterpretations of age-related changes in baroreceptor function during orthostasis. The hemodynamic response to hypovolemic circulatory stress was studied with the aid of lower-body negative pressure (LBNP) of 60 cmH2O in 33 healthy men [18 young (mean age 22 yr) and 15 old (mean age 65 yr)]. Volumetric technique was used in the study of capacitance responses in the calf and arm as well as transcapillary fluid absorption in the arm. LBNP led to smaller increase in heart rate ( P < 0.001) and peripheral resistance ( P < 0.01) and reduced transcapillary fluid absorption in the arm ( P < 0.05) in old subjects. However, blood pooling in the calf was reduced in old subjects (1.66 ± 0.10 vs. 2.17 ± 0.13 ml/100 ml tissue; P < 0.01). Accordingly, during similar blood pooling in the calf (LBNP 80 cmH2O in old subjects), no changes in cardiovascular reflex responses with age were found. The capacitance response in the arm (mobilization of peripheral blood to the central circulation) was still reduced, however (0.67 ± 0.10 vs. 1.37 ± 0.11 ml/100 ml tissue; P < 0.01). Thus the reduced cardiovascular reflex response found in the elderly during orthostatic stress seems to be caused by a reduced capacitance response in the legs with age and a concomitant smaller central hypovolemic stimulus rather than a reduced efficiency of the reflex response. With similar hypovolemic circulatory stress, no changes in cardiovascular reflex responses are seen with age. The capacitance response in the arm (mobilization of peripheral blood toward the central circulation) is reduced, however, by ∼50% in the elderly. This might seriously impede the possibility of survival of an acute blood loss.