bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical workload-myocardial water content relationship in isolated rat hearts
Authors: Schertel E. R. , Daye R. M. , McClure D. E. , Lai T. , Miyamoto M. , Myerowitz P. D.
Published: December 2017

We tested the hypothesis that the mechanical workload of the heart inversely determines the rate of myocardial edema formation in an isolated, perfused rat heart preparation. Heart rate (HR) was varied in three groups by pacing at 125 (HR125), 250 (HR250), or 350 beats/min (HR350). Left ventricular pressure (LVP) was varied in two additional groups by pacing at 250 beats/min and with the addition of either epinephrine (Epi) or propranolol (Pro) to the perfusate. In five otherwise identical groups, variation of coronary vascular resistance was minimized by adenosine. Myocardial water content (MWC) varied significantly and inversely with HR in the HR125, HR250, and HR350 groups. MWC of the HR250 group was significantly less than that of the Pro group but did not differ from the Epi group. However, when adenosine was used, MWC had significant inverse relationships with HR and LVP. We concluded that the mechanical workload of the heart inversely determines the rate and degree of myocardial edema formation in this isolated heart preparation, and both HR and LVP are determinants of this relationship.
Effects of sevoflurane on inward rectifier K+ current in guinea pig ventricular cardiomyocytes
Authors: Stadnicka A. , Bosnjak Z. J. , Kampine J. P. , Kwok W. M.
Published: December 2017

The effects of sevoflurane on the inward rectifier potassium current (IKIR) were examined in guinea pig ventricular cardiomyocytes using the whole cell patch-clamp methodology. Sevoflurane had a unique dual effect on the steady-state current amplitude, producing a reversible, concentration- and voltage-dependent block of the inward current at potentials negative to the potassium equilibrium potential (EK) but enhancing the outward current positive to EK. Accordingly, the steady-state conductance negative to EK was reduced by sevoflurane, but conductance positive to EK was increased. The chord conductance-voltage relationship showed depolarizing shifts at 0.7, 1.3, and 1.6 mM sevoflurane. When the myocytes were dialyzed with 10 mM Mg2+, but not with 1.0 mM Mg2+, sevoflurane further slowed current activation kinetics. With 10 mM intracellular Mg2+, the outward current enhancement by sevoflurane and the associated shifts in half-activation potential were abolished. Polyamines abolished all effects of sevoflurane on IKIR. With the use of the Woodhull model for voltage-dependent block, we determined the sevoflurane interaction site with the inward rectifier potassium channel to be at an electrical distance of 0.2 from the extracellular side.
Role of nitric oxide in skeletal muscle blood flow at rest and during dynamic exercise in humans
Authors: Hickner R. C. , Fisher J. S. , Ehsani A. A. , Kohrt W. M.
Published: December 2017

The role of nitric oxide at rest and in the active hyperemic response within skeletal muscle was investigated in eight physically active men. Three microdialysis probes were inserted into the vastus lateralis of the quadriceps femoris muscle group in each subject. Microdialysis probes were perfused with a Ringer solution containing 5.0 mM ethanol, 2.5 mM glucose, and either 10 mg/ml of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) monoacetate salt, 30 mg/ml of the nitric oxide precursor L-arginine, or no additional substance (control probe). Subjects performed one-legged cycling exercise at work rates ranging from 25 to 100 W. Dialysate and perfusate ethanol concentrations were presented as the ratio of [ethanol]dialysate to [ethanol]perfusate (ethanol outflow-to-inflow ratio), an indicator that is inversely related to blood flow. The ethanol outflow-to-inflow ratios at rest were 0.614 +/- 0.032, 0.523 +/- 0.023, and 0.578 +/- 0.039 in the L-NMMA, L-arginine, and control probes, respectively. Calculated resting blood flows were therefore 8.7 +/- 4.1, 20.5 +/- 4.6, and 14.0 +/- 4.7 ml.min-1.100 g-1 around the L-NMMA, L-arginine, and control probes, respectively. The ethanol outflow-to-inflow ratios were significantly higher at all exercise intensities in the L-NMMA probe than in the control and L-arginine probes, resulting in calculated blood flows of 195 +/- 55, 407 +/- 47, and 352 +/- 60 ml.min-1.100 g-1 at 25 W and 268 +/- 65, 602 +/- 129, and 519 +/- 113 ml.min-1.100 g-1 at 100 W around the L-NMMA, L-arginine, and control probes, respectively. Skeletal muscle blood flow was therefore reduced both at rest and during continuous, dynamic exercise by the action of L-NMMA, whereas blood flow was increased only at rest by L-arginine.
Relationship between cardiac function and substrate oxidation in hearts of diabetic rats
Authors: Chatham J. C. , Forder J. R.
Published: December 2017

The effects of streptozotocin-induced diabetes on myocardial substrate oxidation and contractile function were investigated using 13C nuclear magnetic resonance (NMR) spectroscopy. To determine the consequences of diabetes on glucose oxidation, hearts were perfused with [1–13C]glucose (11 mM) alone as well as in the presence of insulin (to stimulate glucose transport) and dichloroacetate (to stimulate pyruvate dehydrogenase). The contribution of glucose to the tricarboxylic acid (TCA) cycle was significantly decreased in hearts from diabetic animals compared with controls, with glucose alone and with insulin; however, the addition of dichloroacetate significantly increased the contribution of glucose to the TCA cycle. Contractile function in hearts from diabetic animals was significantly depressed with glucose as the sole substrate, regardless of the presence of insulin or dichloroacetate (P < 0.0005). To determine whether diabetes had any direct effects on beta-oxidation and the TCA cycle, hearts were perfused with glucose (11 mM) plus [6-13C]hexanoate (0.5 mM) as substrates. In control hearts, with glucose plus hexanoate as substrates, hexanoate contributed 98.9 +/- 2% of the substrate entering the TCA cycle; this was significantly decreased to 90.7 +/- 0.6% in the diabetic group (P < 0.02). The addition of hexanoate to the perfusate resulted in a significant increase in peak systolic pressure in the diabetic group (P < 0.001) such that contractile function was indistinguishable from controls.
Pelvic nerve stimulation-induced pressor responses in corpus cavernosum of anesthetized dogs
Authors: Ayajiki Kazuhide , Hayashida Hideshi , Okamura Tomio , Toda Noboru
Published: December 2017

To analyze the mechanism of penile erection and pathogenesis of impotence, pressures in the corpus cavernosum in anesthetized dogs were measured. Pelvic nerve stimulation produced pressor responses in a frequency-dependent manner. Intravenous injections of N G-nitro-l-arginine, a nitric oxide (NO) synthase inhibitor, dose dependently attenuated the response, and the inhibition was reversed by intravenous injection ofl-arginine but not ofd-arginine. The response was also inhibited by N G-nitro-l-arginine injected into the corpus cavernosum, the potency being ∼10 times of that applied intravenously. The intracavernous injection ofl-arginine restored the response. N G, N G-dimethylarginine, an endogenous NO synthase inhibitor, dose dependently attenuated the stimulation-induced response, which was restored by an intracavernous injection of l-arginine. An intravenous injection of hexamethonium abolished the pressor response to nerve stimulation, whereas phentolamine and atropine did not significantly alter the response. These findings suggest that an increase in intracavernous pressure caused by pelvic nerve stimulation in anesthetized dogs is mediated by NO liberated from postganglionic neurons that originate in the ganglion located in the vicinity of corpus cavernosum.
Calcium transient alternans in blood-perfused ischemic hearts: observations with fluorescent indicator Fura Red
Authors: Wu Yiming , Clusin William T.
Published: December 2017

Ischemia produces striking electrophysiological abnormalities in blood-perfused hearts that may be caused, in part, by effects of ischemia on intracellular calcium. To test this hypothesis, intracellular Ca2+ concentration ([Ca2+]i) transients were recorded from the epicardial surface of blood- and saline-perfused rabbit hearts using the long-wavelength indicator Fura Red. Calcium transients were much larger than the movement artifact, representing up to 29% of the total signal. Switching the perfusate from saline to blood did not affect the time course of the transients or the apparent level of [Ca2+]i. Compartmentation of Fura Red fluorescence was estimated by exposure to Mn2+. The results were cytosol 60 ± 3%, organelles 12 ± 2%, and autofluorescence plus partly deesterified Fura Red 29 ± 4%. [Ca2+]itransients were calibrated in situ by perfusion of the extracellular space with high-Ca2+ and Ca2+-free EGTA solutions. Peak systolic [Ca2+]iwas 663 ± 74 nM, and end-diastolic [Ca2+]iwas 279 ± 59 nm. Ischemia was produced by interruption of aortic perfusion for 2.5 min during pacing (150 beats/min). Ischemia produced broadening of the [Ca2+]itransient, along with beat-to-beat alternations in the peak systolic and end-diastolic level of [Ca2+]i(calcium transient alternans). [Ca2+]itransient alternans occurred in 82% of blood-perfused hearts vs. 43% of saline-perfused hearts. The discrepancy between large and small transients (mean alternans ratio) was larger in the blood-perfused hearts (0.23 ± 0.04 vs. 0.07 ± 0.03, P = 0.005). These observations are important because of the apparent relationship of [Ca2+]itransient alternans to electrical alternans and arrhythmias during ischemia.
Microvascular blood flow resistance: role of endothelial surface layer
Authors: Pries Axel R. , Secomb Timothy W. , Jacobs Helfried , Sperandio Markus , Osterloh Kurt , Gaehtgens Peter
Published: December 2017

Observations of blood flow in microvascular networks have shown that the resistance to blood flow is about twice that expected from studies using narrow glass tubes. The goal of the present study was to test the hypothesis that a macromolecular layer (glycocalyx) lining the endothelial surface contributes to blood flow resistance. Changes in flow resistance in microvascular networks of the rat mesentery were observed with microinfusion of enzymes targeted at oligosaccharide side chains in the glycocalyx. Infusion of heparinase resulted in a sustained decrease in estimated flow resistance of 14–21%, hydrodynamically equivalent to a uniform increase of vessel diameter by ∼1 μm. Infusion of neuraminidase led to accumulation of platelets on the endothelium and doubled flow resistance. Additional experiments in untreated vascular networks in which microvascular blood flow was reduced by partial microocclusion of the feeding arteriole showed a substantial increase of flow resistance at low flow rates (average capillary flow velocities < 100 diameters/s). These observations indicate that the glycocalyx has significant hemodynamic relevance that may increase at low flow rates, possibly because of a shear-dependent variation in glycocalyx thickness.
Energetics of heart muscle contraction under high K perfusion: verapamil and Ca effects
Authors: Consolini Alicia E. , Márquez María T. , Ponce-Hornos Jorge E.
Published: December 2017

Tension-dependent (TDH) and tension-independent heat (TIH) release were measured during single isovolumetric contractions in the arterially perfused rat ventricle. Under perfusion with 7 mM K-0.5 mM Ca, TDH showed only one component (H3), whereas TIH could be divided into two components (H1and H2) of short evolution (similar to the classically identified activation heat) and one component (H4) of long duration (dependent on mitochondrial respiration). Under 25 mM K, TIH components (i.e., H1, H2, and H4) increased with the increase in extracellular Ca concentration ([Ca]o) from 0.5 to 4 mM, and H3correlated with pressure at all [Ca]o, with regression parameters similar to those observed under 7 mM K. Under 25 mM K-2 mM Ca, peak pressure development (P), H1, H2, and H3, plotted against the number of beats under 0.4 μM verapamil, exponentially decreased, but H4decreased to 5.5 ± 2.9% in the first contraction and remained constant thereafter. Under hypoxia, P, H1, H2, and H3progressively decreased for about six contractions, but H4was not detectable from the second contraction. The results suggest that increasing extracellular K concentration decreases contractile economy mainly by increasing energy expenditure related to a Ca-dependent (verapamil-sensitive) mitochondrial activity that is not related to force generation.
Effect of endogenous natriuretic peptide system on ventricular and coronary function in failing heart
Authors: Yamamoto Kazuhiro , Burnett John C. , Redfield Margaret M.
Published: December 2017

Ventricular concentrations of atrial, brain (BNP) and C-type natriuretic peptide are enhanced in congestive heart failure (CHF). Natriuretic peptide receptors are present on ventricular myocytes and stimulate guanosine 3′,5′-cyclic monophosphate (cGMP) production. cGMP has been demonstrated to affect myocyte function in vitro. Thus we hypothesized that the intracardiac natriuretic peptide system may modulate myocardial and coronary function in CHF. To test this hypothesis, the effects of an intracoronary infusion of the natriuretic peptide receptor antagonist HS-142–1 on ventricular and coronary function were examined in anesthetized dogs with chronic CHF. To determine whether receptor stimulation had contrasting effects to those of receptor blockade, intracoronary BNP was infused in anesthetized normal and CHF dogs. Low-dose HS-142–1 delayed and slowed left ventricular (LV) relaxation and decreased coronary blood flow without changes in LV pressures. Higher doses further impaired LV relaxation without further decreases in coronary blood flow. In normal and CHF dogs, exogenous BNP produced the opposite effect with a quicker onset and faster rate of LV relaxation without effects on LV pressures or coronary blood flow. The endogenous natriuretic peptide system has an autocrine-paracrine role to modulate LV and coronary vascular function in CHF.
Sarcoplasmic reticulum function in determining atrioventricular contractile differences in rat heart
Authors: Minajeva Ave , Kaasik Allen , Paju Kalju , Seppet Enn , Lompré Anne-Marie , Veksler Vladimir , Ventura-Clapier Renée
Published: December 2017

The relationships between the contractile characteristics and the sarcoplasmic reticulum (SR) function of rat atrial and ventricular trabeculae were compared. The isometric developed tension (DT) and the rates of contraction (+dT/d t) and relaxation (−dT/d t) normalized to cross-sectional area were 3.7, 2.2, and 1.8 times lower, respectively, in intact atrial strips compared with ventricular strips, whereas +dT/d t and −dT/d t(normalized to DT) were 2.3 and 2.8 times higher, respectively, in atria. Atria exhibited a maximal potentiation of DT after shorter rest periods than ventricles and a lower reversal for prolonged rest periods. Caffeine-induced tension transients in saponin-permeabilized fibers suggested that the Ca2+concentration released in atrial myofibrils reached a lower maximum and decayed more slowly than in ventricular preparations. However, the tension-time integrals indicated an equivalent capacity of sequestrable Ca2+in SR from both tissues. In atrial, as in ventricular myocardium, the SR Ca2+uptake was more efficiently supported by ATP produced by the SR-bound MM form of creatine kinase (CK; MM-CK) than by externally added ATP, suggesting a tight functional coupling between the SR Ca2+adenosinetriphosphatase (ATPase) and MM-CK. The maximal rate of oxalate-supported Ca2+uptake was two times higher in atrial than in ventricular tissue homogenates. The SR Ca2+-ATPase 2a mRNA content normalized to 18S RNA was 38% higher in atria than in ventricles, whereas the amount of mRNA encoding the α-myosin heavy chain, calsequestrin, and the ryanodine receptor was similar in both tissues. Thus a lower amount of readily releasable Ca2+together with a faster uptake rate may partly account for the shorter time course and lower tension development in intact atrial myocardium compared with ventricular myocardium.
Left atrial distension and antiorthostatic decrease in arterial pressure and heart rate in humans
Authors: Pump Bettina , Christensen Niels Juel , Videbæk Regitze , Warberg Jørgen , Hendriksen Ole , Norsk Peter
Published: December 2017

It was investigated to what degree left atrial distension augments the hypotensive effects of a 15-min moderate antiorthostatic maneuver in humans. Ten healthy males underwent a posture change from upright seated (Seat, legs horizontal) to supine (Sup) or to supine with simultaneous lower body negative pressure (Sup + LBNP) to keep left atrial diameter (LAD) unchanged. After 2.5 min of Sup, mean arterial pressure (MAP) decreased from 94 ± 3 to 86 ± 3 mmHg ( P < 0.05), whereas a similar decrease was delayed 7.5 min into Sup + LBNP. Heart rate (HR) decreased within 2.5 min of Sup from 68 ± 2 to 60 ± 3 beats/min ( P < 0.05) and remained significantly decreased for at least 2.5 min longer than during Sup + LBNP. Aortic systolic distension (ASD) increased by 59 ± 17% during Sup ( P < 0.05) but was unchanged during Sup + LBNP. The 29 ± 4% decrease in plasma norepinephrine (NE) during Sup ( P < 0.05) was abolished during Sup + LBNP. In conclusion, the increases in LAD and ASD seem important stimuli for the prompt decrease in MAP, the 2.5-min longer-lasting decrease in HR, and the sustained decrease in NE during a 15-min moderate antiorthostatic posture change in humans.
Adenosine-induced hyperpolarization in guinea pig coronary artery involves A2breceptors and KATPchannels
Authors: Mutafova-Yambolieva Violeta N. , Keef Kathleen D.
Published: December 2017

The role of P1purinoceptor subtypes, the adenylyl cyclase (AC) pathway, and ATP-sensitive K+(KATP) channels in adenosine (Ado)-induced membrane hyperpolarization was investigated in isolated segments of the guinea pig coronary artery using conventional microelectrode techniques. Ado (1–100 μM) elicited concentration-dependent hyperpolarization (half-maximal effective concentration 7.5 ± 0.5 μM) that averaged 28.6 ± 2.9 mV at 100 μM Ado. The A1selective agonist N6-cyclopentyladenosine (CPA), the A1/A2agonist 2-chloroadenosine, and the A2a/A2bagonist 5-( N-ethylcarboxamido)adenosine (NECA) each induced glibenclamide (3 μM)-sensitive hyperpolarization at 10 μM. However, the selective A2a-receptor agonists CGS-21680 and N6-[2-(3,5-dimethoxyphenyl)-2-(2-methoxyphenyl]ethyladenosine (10 μM each) were without effect. Responses to CPA and NECA were significantly reduced by the AC inhibitor SQ-22,536 (100 μM). Activation of the AC-adenosine 3′,5′-cyclic monophosphate (cAMP)-protein kinase A (PKA) pathway by four additional methods, i.e., 1) forskolin (0.3–1 μM), 2) isoproterenol (0.1–1 μM), 3) combined milrinone (0.4 μM) and rolipram (30 μM), and 4) combined N6-phenyladenosine 3′,5′-monophosphate, 8-(6-aminohexyl)aminoadenosine 3′,5′-cyclic monophosphate, and the Sp-isomer of 5,6-dichloro-1-d-ribofuranosylbenzimidazole-3′,5′-cyclic monophosphothioate (100 μM each), also gave rise to glibenclamide-sensitive hyperpolarization. These results suggest that stimulation of A2breceptors coupled to AC represents the predominant mechanism by which Ado elicits hyperpolarization in this vessel. The ensuing increase in cAMP activates PKA, which then increases the activity of KATPchannels. Our results further suggest that KATPchannels are an important target for numerous pathways that raise cAMP levels in the coronary artery.
Modulatory role of endothelial calcium level in vascular tension of canine depolarized coronary arteries
Authors: Sato Kazuo , Yamazaki Jun , Nagao Taku
Published: December 2017

The vascular tension in the coronary artery is modulated by factors released by endothelial cells. We investigated the relationship between the Ca2+level in endothelium and endothelium-mediated changes in smooth muscle tone in high K+-depolarized canine coronary arteries by measuring intracellular Ca2+concentration fluorimetrically with the Ca2+indicator fura 2. Addition of Ca2+(1 mM) caused an increase in endothelial Ca2+and relaxed the 30 mM K+-depolarized arteries following inhibition of Ca2+influx in the smooth muscle with diltiazem. This relaxation was inhibited by NG-monomethyl-l-arginine. As extracellular K+concentration was decreased, increases of endothelial Ca2+were augmented, whereas the relaxation was decreased. Basal muscle tone was found to be decreased in low K+by measuring relaxation by sodium nitroprusside. These results suggest the importance of Ca2+level in the endothelium in playing a modulatory role in coronary tension through the production of nitric oxide. The correlation of extracellular K+to Ca2+level in the endothelium indicates a typical characteristic of the passive Ca2+entry pathway in the endothelium, whereas the resultant relaxation appears to be restricted by the basal muscle tone.
Protein tyrosine phosphorylation mediates TNF-induced endothelial-neutrophil adhesion in vitro
Authors: Kelly Susan A. , Goldschmidt-Clermont Pascal J. , Milliken Emily E. , Arai Toshiyuki , Smith Elise H. , Bulkley Gregory B.
Published: December 2017

Proinflammatory cytokines initiate the vascular inflammatory response via the upregulation of adhesion molecules on the luminal endothelial surface. We investigated directly the role of protein tyrosine phosphorylation in the upregulation of the endothelial adhesion molecules, intercellular adhesion molecule 1 (ICAM-1) and E-selectin, and the consequent adhesion of neutrophils, after tumor necrosis factor (TNF)-α-stimulation of human aortic endothelial cells in vitro. Time- and dose-dependent TNF-α-stimulated ICAM-1 and E-selectin upregulation and neutrophil adhesion each were suppressed by tyrosine kinase inhibitors, including genistein (200 μM), but not genistin, its isoflavone analog without tyrosine kinase inhibitory activity. Tyrphostin AG 126, a synthetic selective tyrosine kinase inhibitor, also suppressed ICAM-1 and E-selectin upregulation and neutrophil adhesion, each in a dose-dependent manner, whereas tyrphostin AG 1288 had no effect. Tyrosine phosphorylation of two proteins (85 and 145 kDa in the cytoskeleton fraction) found minutes after TNF-α-stimulation was also inhibited by genistein. These findings suggest that, in endothelial cells, TNF-α upregulates ICAM-1 and E-selectin expression and consequent neutrophil adhesion via protein tyrosine phosphorylation.
Downregulation of 5′-nucleotidase in rabbit heart during coronary underperfusion
Authors: Gustafson Lori A. , Kroll Keith
Published: December 2017

The hydrolysis of AMP to adenosine during acute coronary underperfusion is temporarily beneficial to myocardial survival yet may cause tissue injury during sustained underperfusion because of depletion of adenine nucleotides. We hypothesized that the enzyme mediating AMP hydrolysis, 5′-nucleotidase (5′-NT), is downregulated during sustained coronary underperfusion to prevent excessive loss of nucleotides. Langendorff-perfused rabbit hearts were subjected to two successive, identical 45-min periods of underperfusion (4–5% of baseline flow) separated by 20 min of reperfusion. Although coronary venous lactate efflux was comparable in the two periods, total coronary purine efflux during the second period of underperfusion was attenuated by 75%. Phosphorus nuclear magnetic resonance data showed that ATP fell 46% in the first period but fell only another 10% in the second period. Phosphocreatine levels fell comparably (75–78%) during both periods of underperfusion. Analysis using a mathematical model describing the kinetics of myocardial energetics revealed that the combined data set was best described by a lower activity of 5′-NT (52% decrease in maximal reaction velocity) during the second period of underperfusion. Additional time course experiments showed that the decrease in 5′-NT activity was slow in onset, requiring ∼20 min of underperfusion. The decrease in 5′-NT activity during sustained underperfusion may benefit tissue survival by limiting the depletion of myocardial adenine nucleotides. In conclusion, at the onset of coronary underperfusion, there is a high activity of 5′-NT, but later during sustained underperfusion, 5′-NT is downregulated, resulting in decreased AMP hydrolysis to adenosine.
Load-sensitive diastolic relaxation in hypertrophied left ventricles
Authors: Hayashida Wataru , Donckier Julian , Van Mechelen Henri , Charlier André A. , Pouleur Hubert
Published: December 2017

We studied effects of enalaprilat and L-158,809, an angiotensin II type-1 receptor antagonist, on left ventricular (LV) diastolic relaxation in 11 normal control dogs and 16 LV hypertrophied (LVH) dogs with perinephritic hypertension. At baseline, LV systolic and end-diastolic pressures and end-systolic elastance were increased in the LVH group (all P < 0.01 vs. the control group). LV relaxation time constant was also prolonged ( P < 0.01), suggesting impaired LV diastolic relaxation in this model of LVH. Before and after the administration of enalaprilat (0.25 mg/kg) and L-158,809 (0.30 mg/kg), LV relaxation was assessed over a wide range of LV loading conditions during vena caval occlusion. LV relaxation time constant was insensitive to load reduction in the control group, which was not affected by enalaprilat or L-158,809. In contrast, LV unloading caused a significant prolongation of the relaxation time constant in the LVH group. This load-sensitive LV relaxation abnormality was significantly improved by enalaprilat or L-158,809. These results support the concept that angiotensin II is involved in the pathogenesis of diastolic dysfunction in pressure-overloaded LVH and also suggest that angiotensin-converting enzyme inhibitors and angiotensin II type-1 receptor antagonists are potentially beneficial in the treatment of the hypertrophied heart.
Protein kinase G is not essential to NO-cGMP modulation of basal tone in rat pulmonary circulation
Authors: Fouty Brian , Komalavilas Padmini , Muramatsu Masashi , Cohen Alan , McMurtry Ivan F. , Lincoln Thomas M. , Rodman David M.
Published: December 2017

Nitric oxide (NO) is important in modulating increased pulmonary vascular tone. Whereas in other systems it is believed that the action of NO is mediated through guanosine 3′,5′-cyclic monophosphate (cGMP) and protein kinase G (PKG), the validity of this pathway in the pulmonary circulation has not been established. Using isolated salt-perfused normotensive and hypertensive rat lungs, we studied the effects of the soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), and the PKG inhibitors, KT5823, Rp-8-pCPT-cGMPS, and { N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide} (H-8), on pulmonary vascular resistance. In isolated normotensive lungs, ODQ-mediated inhibition of soluble guanylyl cyclase augmented hypoxic pulmonary vasoconstriction, whereas the PKG inhibitors had no effect. Despite the marked differences in the physiological effect, ODQ and Rp-8-pCPT-cGMPS inhibited PKG activity to a similar degree as determined by a back-phosphorylation assay showing decreased PKG-mediated phosphorylation of serine 1755 on thed- myo-inositol 1,4,5-trisphosphate receptor. In hypertensive lungs, inhibition of soluble guanylyl cyclase by ODQ increased perfusion pressure by 101 ± 20% ( P < 0.05), an increase similar to that seen with inhibition of NO synthase (NOS), confirming an essential role for cGMP. In contrast, KT5823, Rp-8-pCPT-cGMPS, and H-8 (used in doses 5- to 100-fold in excess of their reported inhibitory concentrations for PKG) caused only a small increase in baseline perfusion pressure (14 ± 2%, P = not significant from vehicle control). Effectiveness of PKG inhibition in the hypertensive lungs was also confirmed with the back-phosphorylation assay. These studies suggest that whereas NO-mediated modulation of vascular tone in the normotensive and hypertensive pulmonary circulation is dependent on cGMP formation, activation of PKG may not be essential.
Magnetic resonance imaging accurately estimates LV mass in a transgenic mouse model of cardiac hypertrophy
Authors: Franco Fatima , Dubois Susan K. , Peshock Ronald M. , Shohet Ralph V.
Published: December 2017

Transgenic mice with a dysfunctional guanylyl cyclase A gene (GCA −/−) are unable to transduce the signals from atrial naturetic peptide and develop hypertension and cardiac hypertrophy. Magnetic resonance imaging (MRI) was performed to assess cardiac hypertrophy in these animals, using wild-type siblings as controls. Anesthetized mice were studied by gated multislice, multiphase cine MRI at 1.5 T. Simpson’s rule was used to estimate left ventricle (LV) mass and volumes from short-axis images. Correlation between LV mass evaluated by MRI and at necropsy was excellent, with LVnecropsy = 1.04 × LVMRI + 4.69 mg ( r 2 = 0.95). By MRI, GCA −/− LV mass was significantly different when compared with isogenic controls [GCA −/−, 226 ± 43 mg ( n = 14) vs. controls, 156 ± 14 mg ( n = 10); P < 0.0001]. LV volumes and ejection fraction in the two groups were not significantly different. MRI provides an accurate means for the noninvasive assessment of murine cardiac phenotype and may be useful in following the effects of genetic modification.
Mechanisms of cell injury in rat mesentery and cremaster muscle
Authors: Harris A. G. , Costa J. J. , Delano F. A. , Zweifach B. W. , Schmid-Schönbein G. W.
Published: December 2017

The events responsible for cell injury after a tissue stimulation are only incompletely understood. The purpose of this study was to examine mechanisms of cell injury in two tissues, rat mesentery and cremaster muscle, after tissue stimulation with N-formylmethionyl-leucyl-phenylalanine (FMLP) and platelet-activating factor (PAF). The response was studied in the same animal in random order using normal and leukopenic rats. The tissues were exteriorized after pentobarbital anesthesia. Five to six vascularized areas were chosen in each tissue, and cell injury and hydroperoxide production were assessed visually by continuous superfusion with 1 μM propidium iodide and 5 μM dichlorofluorescin diacetate (DCFH), respectively. FMLP (1 × 10−8M) and then PAF (1 × 10−8M) were added to the superfusate, and measurements were made at several time points. The second tissue was then examined using the same protocol. In the cremaster, there was little hydroperoxide production, and the tissue injury was eliminated after leukopenia. Leukopenia had no effect on tissue injury in the mesentery. Although hydroperoxide production was observed, there was no correlation between it and the tissue injury. The level of preactivation showed no correlation with either tissue injury or hydroperoxide production. In light of these results, mast cell degranulation may be an important mechanism of tissue injury in the mesentery.
Mechanisms of length history-dependent tension in an ionic model of the cardiac myocyte
Authors: Bluhm Wolfgang F. , Lew Wilbur Y. W. , Garfinkel Alan , McCulloch Andrew D.
Published: December 2017

The ionic model of the ventricular myocyte developed by Luo and Rudy ( Circ. Res. 74: 1071–1096, 1994) was used to investigate potential mechanisms of the slow changes in stress (SCS) that follow step changes in muscle length. A step change in myofilament sensitivity alone caused an immediate increase in active tension, but no SCS. The effects of additional step changes in the parameters of sarcolemmal ion fluxes were examined for each ion flux in the model. Changes in the coefficients of Ca2+ or K+ channels did not produce SCS. SCS was produced by step changes in parameters of the Na+-K+pump or the Na+ leak current. This simulated mechanism was mediated through a slow increase in intracellular Na+ concentration and a resulting increase in systolic Ca2+ entry through the Na+/Ca2+exchanger. The model reproduced the effects of several experimental interventions such as sarcoplasmic reticulum Ca2+ depletion, “diastolic” length changes, and changes in extracellular Ca2+. Thus SCS in cardiac muscle may be caused by length-induced changes in sarcolemmal Na+ fluxes.
Heart rate dynamics during accentuated sympathovagal interaction
Authors: Tulppo Mikko P. , Mäkikallio Timo H. , Seppänen Tapio , Airaksinen Juhani K. E. , Huikuri Heikki V.
Published: December 2017

Concomitant sympathetic and vagal activation can occur in various physiological conditions, but there is limited information on heart rate (HR) behavior during the accentuated sympathovagal antagonism. Beat-to-beat HR and blood pressure were recorded during intravenous infusion of incremental doses of norepinephrine in 18 healthy male volunteers (mean age 23 ± 5 yr). HR and blood pressure spectra and two-dimensional Poincaré plots were generated from the baseline recordings and from the recordings at different doses of norepinephrine. The mean blood pressure increased (from 90 ± 7 to 120 ± 9 mmHg, P < 0.001), HR decreased (from 60 ± 9 to 48 ± 7 beats/min, P < 0.001), and the high-frequency spectral component of HR variability increased ( P < 0.001) during the norepinephrine infusion as evidence of accentuated sympathovagal interaction. Abrupt aperiodic changes in sinus intervals that were not related to respiratory cycles or changes in blood pressure occurred in 14 of 18 subjects during the norepinephrine infusions. These fluctuations in sinus intervals resulted in a complex or parabola-shaped structure of the Poincaré plots of successive R-R intervals and a widening of the high-frequency spectral peak. In four subjects, the abrupt fluctuations in sinus intervals were followed by a sudden onset of fixed R-R interval dynamics with a loss of respiratory modulation of HR, resulting in a torpedo-shaped structure of the Poincaré plots. These data show that HR behavior becomes remarkably unstable during accentuated sympathovagal interaction, resembling stochastic dynamics or deterministic chaotic behavior. These features of HR dynamics can be better identified by dynamic analysis of beat-to-beat behavior of R-R intervals than by traditional analysis techniques of HR variability.
Heterogeneous fatty acid uptake early after reperfusion in rat hearts
Authors: Yamane Yuriko , Ishide Nobumasa , Kagaya Yutaka , Takeyama Daiya , Shiba Nobuyuki , Chida Masanobu , Nozaki Tetsuji , Takahashi Toshihiro , Ido Tatsuo , Shirato Kunio
Published: December 2017

We determined whether spatial distributions of substrate uptake are heterogeneous within the area at risk during reperfusion. Quantitative autoradiography with imaging plates and two long-lived radioisotopes was applied to 15 open-chest, anesthetized rats subjected to 30 min of coronary artery ligation and 30 min of reperfusion. Regions showing increased β-methyl-[1-14C]heptadecanoic acid ([14C]BMHDA) uptake (166 ± 17% of that in the nonischemic area) appeared at the lateral borders and subepicardial layer within the area at risk, and 2-deoxy-d-[1-3H]glucose ([3H]DG) uptake was 103 ± 24% in these regions. Regions with decreased [14C]BMHDA uptake (28 ± 11%) occupied the midmyocardial layer except at the lateral borders within the area at risk, and [3H]DG uptake was 62 ± 18% in these regions. The percentage interregional coefficientsof variation (index of heterogeneity) in [14C]BMHDA uptake, [3H]DG uptake, and blood flow were higher in the area at risk than in the nonischemic area (76 ± 23 vs. 21 ± 7%, 39 ± 10 vs. 21 ± 7%, and 49 ± 19 vs. 14 ± 4%, respectively). Heterogeneous distributions of substrate uptake may explain the conflicting results concerning substrate metabolism during reperfusion.
Incomplete global cerebral ischemia alters platelet biology in neonatal and adult sheep
Authors: Littleton-Kearney Marguerite T. , Hurn Patricia D. , Kickler Thomas S. , Traystman Richard J.
Published: December 2017

Platelets are implicated as etiologic agents in cerebral ischemia and as modulators of neural injury following an ischemic insult. We examined the effects of severe, transient global ischemia on platelet aggregation during 45-min ischemia and 30-, 60-, and 120-min reperfusion in adult and neonatal lambs. We also examined postischemic platelet deposition in brain and other tissues (120-min reperfusion) using indium-111-labeled platelets. Ischemic cerebral blood flow fell to 5 ± 1 and 5 ± 2 ml ⋅ min−1⋅ 100 g−1in lambs and sheep, respectively. During ischemia, platelet counts fell to 47.5 ± 5.1% of control ( P < 0.05) in lambs and 59 ± 4.9% of control in sheep ( P < 0.05). Ischemia depressed platelet aggregation response ( P < 0.01) to 4 μg collagen in lambs and sheep (20.4 ± 29.2 and 26 ± 44.7% of control, respectively). Marked platelet deposition occurred in brain and spleen in sheep, whereas significant platelet entrapment occurred only in brain in lambs. Our findings suggest that ischemia causes platelet activation and deposition in brain and noncerebral tissues.
Ischemia-induced phosphorylation and translocation of stress protein αB-crystallin to Z lines of myocardium
Authors: Golenhofen Nikola , Ness Winfried , Koob Rainer , Htun Patrik , Schaper Wolfgang , Drenckhahn Detlev
Published: December 2017

It is becoming clear that stress proteins play a role in various aspects of postischemic myocardial recovery and that the cytoskeleton of cardiac myocytes is an important determinant for cellular survival during ischemia and energy depletion. In the present study, we addressed the question of whether the cytoskeleton-binding stress protein αB-crystallin may be involved in early cellular responses of rat and porcine myocardium to ischemia. Immunostaining and subcellular fractionation revealed a rapid ischemia-induced redistribution of αB-crystallin from a cytosolic pool to intercalated disks and Z lines of the myofibrils. This striking translocation of αB-crystallin from the cytosol to sites of the myofibrillar system that are known to be sensitive to ischemiareperfusion injury was accompanied by a rapid shift of a fraction of αB-crystallin to a more acidic isoelectric point. This shift is caused by αB-crystallin phosphorylation, as identified by its augmentation in the presence of phosphatase inhibitors (vanadate, fluoride) and comigration of the acidic αB-crystallin form with the phosphorylated B1form of lenticular αB-crystallin. In view of the chaperone-like function of αB-crystallin in conjunction with its high level of constitutive expression in the myocardium (1–2% of soluble protein content), we consider αB-crystallin an excellent candidate to play a role in early aspects of the protection of the myocardial contractile apparatus against ischemia-reperfusion injury.
Cholinergic nerve function in monkey ciliary arteries innervated by nitroxidergic nerve
Authors: Toda Noboru , Toda Megumi , Ayajiki Kazuhide , Okamura Tomio
Published: December 2017

We sought to determine the control of ciliary arterial tone by neurogenic acetylcholine (ACh) acting directly on smooth muscle and in conjunction with vasodilator nerves. Isolated posterior ciliary arteries from monkeys responded to ACh (10−8–10−5M) with dose-related contractions, which were endothelium independent. The response was not affected by cyclooxygenase inhibitors but was abolished by atropine. Relaxations induced at 10−4 M ACh in the atropine-treated arterial strips were abolished by hexamethonium and N G-nitro-l-arginine (l-NNA), andl-arginine (l-Arg) reversed the response suppressed by l-NNA. Similar results were also obtained on the nicotine (10−4 M)-induced relaxation. Contractions due to transmural electrical stimulation in the endothelium-denuded strips treated withl-NNA were potentiated by physostigmine and depressed by atropine; the remaining contraction in the presence of atropine was abolished by prazosin. Relaxations associated with electrical stimulation, sensitive to tetrodotoxin, were abolished or reversed to contractions byl-NNA and restored byl-Arg. Stimulation-induced relaxation was attenuated by exogenous ACh and physostigmine and was potentiated by atropine. ACh did not affect the relaxation caused by nitric oxide (NO). Nerve fibers and bundles containing NADPH diaphorase and acetylcholinesterase were histologically demonstrated in the adventitia of ciliary arteries. We conclude that 1) endogenous and exogenous ACh contracts monkey ciliary arteries by acting on muscarinic receptors in smooth muscle cell membranes, 2) vasodilatation elicited by nerve stimulation with electrical pulses or nicotine is mediated by NO synthesized froml-Arg, 3) neurogenic ACh seems to interfere with the nitroxidergic nerve function by acting on prejunctional muscarinic receptors, and 4) high concentrations of ACh stimulate nicotinic receptors in vasodilator nerve terminals and promote the synthesis and/or release of NO.
Modeling cerebral autoregulation and CO2 reactivity in patients with severe head injury
Authors: Lodi Carlo Alberto , Ter Minassian Aram , Beydon Laurent , Ursino Mauro
Published: December 2017

The mathematical model presented in a previous work is used to simulate the time pattern of intracranial pressure (ICP) and of blood velocity in the middle cerebral artery ( V MCA) in response to maneuvers simultaneously affecting mean systemic arterial pressure (SAP) and end-tidal CO2pressure. In the first stage of this study, a sensitivity analysis was performed to clarify the role of some important model parameters [cerebrospinal fluid (CSF) outflow resistance, intracranial elastance coefficient, autoregulation gain, and the position of the regulation curve] during CO2 alteration maneuvers performed at different SAP levels. The results suggest that the dynamic “ICP- V MCA” relationship obtained during changes in CO2 pressure may contain important information on the main factors affecting intracranial dynamics. In the second stage, the model was applied to the reproduction of real ICP and velocity tracings in neurosurgical patients. Ten distinct tracings, taken from six patients during CO2changes at different mean SAP levels, were reproduced. Best fitting between model and clinical curves was achieved by minimizing a least-squares criterion function and adjusting certain parameters that characterize CSF circulation, intracranial compliance, and the strength of the regulation mechanisms. A satisfactory reproduction was achieved in all cases, with parameter numerical values in the ranges reported in clinical literature. It is concluded that the model may be used to give reliable estimations of the main factors affecting intracranial dynamics in individual patients, starting from routine measurements performed in neurosurgical intensive care units.
Blunted hypoxic pulmonary vasoconstrictive response in the rodentOchotona curzoniae(pika) at high altitude
Authors: Ge Ri-Li , Kubo K. , Kobayashi T. , Sekiguchi M. , Honda T.
Published: December 2017

To investigate the possible mechanisms of adaptation to chronic hypoxia in the pulmonary circulation, we made direct measurements of pulmonary arterial pressure (Ppa) in 10 awake pika rodents that were transported to Xining, People’s Republic of China (altitude 2,260 m) after being captured at 4,300 m and in 10 Wistar rats in a decompression chamber (simulated altitudes of 4,300 and 5,000 m) in Xining. Ppawas obtained at 1 h of exposure to each simulated altitude. The histology and immunohistochemistry of the lung tissues were also studied. Ppain the pikas after the 4,300- and 5,000-m altitude exposures did not significantly increase, whereas in the rats Pparose significantly. Mean changes in Ppafrom 2,260 to 4,300 and 5,000 m were 1.48 ± 0.49 and 4.80 ± 0.67 mmHg in the pikas and 10.38 ± 3.36 and 19.10 ± 2.28 mmHg in the rats. The ratio of right ventricular to left ventricular plus septal weight in the pikas and rats was 0.22 and 0.45, respectively. The pikas maintained levels of Hb, hematocrit, and 2,3-diphosphoglycerate lower than those of the rats. The percent wall thickness of the small pulmonary arteries in the pikas and rats was 9.22 and 27.21%, respectively, and it was well correlated with the degree of Ppain both groups. Mast cells were observed in the lungs of the rats (7.1 ± 0.33 cells/mm2) but not in the pikas. There was highly positive staining for mast cell tryptase and transforming growth factor-β around pulmonary vessels in the rats, whereas no demonstrable reaction was observed in the pikas. We conclude that the pika has adapted to high altitude by losing hypoxic pulmonary vasoconstriction and thin-walled pulmonary arterioles.
Carbon monoxide inhibition of regulatory pathways in myocardium
Authors: Glabe Alan , Chung Youngran , Xu Dejun , Jue Thomas
Published: December 2017

The1H nuclear magnetic resonance (NMR) myoglobin (Mb) Val E11 signal provides a unique opportunity to assess the functional role of Mb in the cell. On CO infusion in perfused myocardium, the MbO2signal at −2.76 parts per million (ppm) gradually disappears, whereas the corresponding MbCO signal emerges at −2.26 ppm, reflecting the state of Mb inhibition. Up to 76.8% MbCO saturation, myocardial O2consumption (MV˙o2) remains constant, whereas the rate-pressure product (RPP) has already dropped to 92% of the control level. At 87.6% MbCO saturation, the lactate formation rate has increased by a factor of two, and MV˙o2begins to decline. However, the ratio CO/O2is still 1/10, well below the inhibition threshold for cytochrome oxidase activity. The MV˙o2decline in the face of an adequate O2supply and an unperturbed high-energy phosphate level implies that Mb may play a role in directly regulating respiration, mediated potentially by a shift in NADH/NAD. Although nitrite inhibits Mb, nitrite also directly affects the myocardial function.
Estimation of nitric oxide production and reactionrates in tissue by use of a mathematical model
Authors: Vaughn Mark W. , Kuo Lih , Liao James C.
Published: December 2017

Nitric oxide (NO) produced by the vascular endothelium is an important biologic messenger that regulates vessel tone and permeability and inhibits platelet adhesion and aggregation. NO exerts its control of vessel tone by interacting with guanylyl cyclase in the vascular smooth muscle to initiate a series of reactions that lead to vessel dilation. Previous efforts to investigate this interaction by mathematical modeling of NO diffusion and reaction have been hampered by the lack of information on the production and degradation rate of NO. We use a mathematical model and previously published experimental data to estimate the rate of NO production, 6.8 × 10−14μmol ⋅ μm−2 ⋅ s−1; the NO diffusion coefficient, 3,300 μm2s−1; and the NO consumption rate coefficient in the vascular smooth muscle, 0.01 s−1 (1st-order rate expression) or 0.05 μM−1 ⋅ s−1 (2nd-order rate expression). The modeling approach is discussed in detail. It provides a general framework for modeling the NO produced from the endothelium and for estimating relevant physical parameters.
“Physiological genomics”: mutant screens in zebrafish
Authors: Warren Kerri S. , Fishman Mark C.
Published: December 2017

Large-scale mutagenesis screens have proved essential in the search for genes that are important to development in the fly, worm, and yeast. Here we present the power of large-scale screening in a vertebrate, the zebrafish Danio rerio, and propose the use of this genetic system to address fundamental questions of vertebrate developmental physiology. As an example, we focus on zebrafish mutations that reveal single genes essential for normal development of the cardiovascular system. These single gene mutations disrupt specific aspects of rate, rhythm, conduction, or contractility of the developing heart.