bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural arc of baroreflex optimizes dynamic pressure regulation in achieving both stability and quickness
Authors: Ikeda Y. , Kawada T. , Sugimachi M. , Kawaguchi O. , Shishido T. , Sato T. , Miyano H. , Matsuura W. , Alexander J. , Sunagawa K.
Published: December 2017

The baroreflex loop consists of a fast neural arc and a slow mechanical arc. We hypothesized that the neural baroreflex arc compensates the slow mechanical response and thus improves the quality of blood pressure regulation. We estimated the open-loop transfer characteristics of the neural baroreflex arc (HP), i.e., from carotid sinus pressure to sympathetic nerve activity (SNA), and that of the effective peripheral baroreflex arc (Hp), i.e., from SNA to arterial pressure, in anesthetized rabbits. The gain of Hn was constant below 0.12 +/- 0.057 Hz and increased with a slope of 6.1 +/- 0.06 dB/octave above its frequency up to 1 Hz. In contrast, the gain of Hp was constant below 0.071 +/- 0.03 Hz and decreased with a slope of -11.0 +/- 1.48 dB/octave above the frequency. These data indicate that Hn accelerates slow peripheral responses in the frequency range of 0.1-1 Hz. Although too much acceleration in the high-frequency range could result in instability of the system, numerical analysis of the closed-loop baroreflex response indicated that the neural arc optimized arterial pressure regulation in achieving both stability and quickness.
Phenylephrine suppresses outward K+ currents in rat atrial myocytes
Authors: Van Wagoner D. R. , Kirian M. , Lamorgese M.
Published: December 2017

The modulation of whole cell K+ currents by the alpha 1-adrenergic agonist, phenylephrine, was studied in isolated rat atrial myocytes by use of perforated-patch whole cell recording techniques. The out ward K+ current in these myocytes consists of two inactivating components (iK,f and iK,s), which differ in the kinetics of inactivation and recovery from inactivation, and a noninactivating component, (iK,ss). Superfusion of these myocytes with 10 microM phenylephrine caused a rapid suppression of iK,ss, with little effect on the other current components. This effect of phenylephrine could be mimicked by exogenous application of 1,2-dioctanoyl-sn-glycerol (20 microM), a membrane-permeant diacylglycerol analogue; however, it was clearly distinct from the effect of 5 nM alpha-dendrotoxin, which selectively suppressed the slowly inactivating current component, iK,s, while having no effect on iK,ss. At a dose of 50 microM, phenylephrine also suppressed iK,s. There was no significant effect of phenylephrine (10 or 50 microM) or alpha-dendrotoxin (5 nM) on the rapidly inactivating current component, iK,f. The kinetic and pharmacological differences between these current components suggest that they represent the activity of distinct K+ channels.
Viscoelastic behavior of the isolated guinea pig left ventricle in diastole
Authors: Starc V. , Yellin E. L. , Nikolic S. D.
Published: December 2017

To determine left ventricular (LV) viscoelastic properties during acute volume changes, the relaxation of LV pressure (2-Fr, Millar) at steady LV volume after a known volume change was measured in 14 isolated guinea pig left ventricles arrested in diastole. The left ventricle was loaded and unloaded by manual injection and withdrawal of saline in 10 x 0.1-ml steps, controlling the steadiness of LV volume by measuring LV major and minor diameters (ultrasonic crystals). Cyclic stepwise volume loading and unloading resulted in a hysteresis loop, the complexity of which was caused by stress relaxation at each steady volume. With the use of linear regression analysis, the gross elastic effect of the pressure signal was separated from the viscoelastic part, decomposed into the fast and the slow component with time constants of relaxation equal to 1 and 20 s, respectively. The amplitudes of the fast and the slow component showed that 1) stress relaxation is more expressed at higher LV volume and 2) it is asymmetric, i.e., it is well expressed during volume loading and almost absent during volume unloading. Both suggest that viscoelasticity of passive myocardium is not quasilinear, when the left ventricle is subjected to aperiodic volume loading to a high LV volume. The asymmetric viscoelastic behavior is consistent with the hypothesis of extracellular fluid filtration.
Expression of phagocyte NADPH oxidase components in human endothelial cells
Authors: Jones S. A. , O'Donnell V. B. , Wood J. D. , Broughton J. P. , Hughes E. J. , Jones O. T.
Published: December 2017

Low-level generation of reactive oxygen species (ROS) by endothelial cells in response to a variety of stimuli has been observed; however, the enzyme system responsible is unknown. Using a variety of techniques, we examined for components of the phagocyte superoxide-generating NADPH oxidase to elucidate whether this enzyme could be a source of endothelial-derived ROS. Superoxide generation on addition of 100 microM NAD(P)H to human umbilical vein endothelial cell (HUVEC) sonicates (using lucigenin-enhanced chemiluminescence) was partially inhibited on addition of the flavoenzyme inhibitor diphenyliodonium (IDP). Reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated expression of gp91phox, p22phox, p67phox, and p47phox in four independent HUVEC isolates. Expression of p22phox was also confirmed by Northern blotting. RT-PCR for tumor necrosis factor-alpha was negative, indicating an absence of mononuclear cell contamination (a potential source of NADPH oxidase). Immunoperoxidase staining, using anti-p47phox (JW-1)- and anti-p67phox (JW-2)-specific antibodies, showed protein expression of these cytosolic components. However, heme spectroscopy failed to indicate the presence of the low-potential cytochrome b558. These data indicate that cultured human endothelial cells express both mRNA and protein for cytosolic components of the phagocyte superoxide-generating NADPH oxidase. However, because the cytochrome b558 heme could not be conclusively demonstrated, a contribution of the phagocyte NADPH oxidase to endothelial oxidant generation may be unlikely.
Skeletal muscle beta-adrenoreceptors and phosphate metabolism abnormalities in heart failure in rats
Authors: Chati Z. , Michel C. , Escanye J. M. , Mertes P. M. , Ribuot C. , Canet D. , Zannad F.
Published: December 2017

To investigate the mechanisms leading to skeletal muscle metabolic abnormalities in chronic heart failure (CHF), we studied phosphate metabolism and skeletal muscle beta-adrenoreceptors (beta-AR) in rats 12-14 wk after coronary ligation (CL). We performed 31P magnetic resonance spectroscopy in the gastrocnemius muscle during motor activity produced by electrical stimulation (5 Hz). The initial slope of phosphocreatine (PCr) depletion was higher in the CL rats compared with sham-operated rats (Pi/PCr/time: 0.211 +/- 0.045 vs. 0.113 +/- 0.029; P < 0.05). During recovery, both PCr resynthesis rate and maximal rate of oxidative ATP synthesis were reduced threefold in the CL rats compared with controls (11 +/- 2 vs. 37 +/- 7 mmol.l-1.min-1, P < 0.04; and 20 +/- 3 vs. 79 +/- 18 mmol.l-1.min-1, P < 0.03, respectively). There were no significant differences either for the skeletal muscle density (13 +/- 6 vs. 15 +/- 3 fM/mg) or for the affinity (0.244 +/- 0.149 vs. 0.246 +/- 0.146 nM) of beta-AR between the two groups. This study showed that, although in moderate CHF skeletal muscle metabolic abnormalities can be demonstrated, these changes could not be explained by skeletal muscle beta-adrenergic receptor alterations in this experimental model.
Short- and long-term effects of neonatal hypo- and hyperthyroidism on coronary arterioles in rat
Authors: Heron M. I. , Rakusan K.
Published: December 2017

Neonatal hypo- and hyperthyroid effects on coronary arteriolar geometry were examined in newborn male Sprague-Dawley rats treated for 12 or 28 days with either triiodothyronine or propylthiouracil. Long-term effects were assessed in weaned rats 52 days after stopping treatment. Influence of both neonatal conditions was more pronounced after 28 days. Neonatal hyperthyroidism induced cardiac hypertrophy; neonatal hypothyroidism attenuated cardiac growth. Hyperthyroid rats had similar arteriolar and capillary numerical densities and arteriolar length density but significantly greater (P < 0.05) total arteriolar length than control. Hypothyroid rats had similar arteriolar numerical and length densities, greater capillary numerical density (P < 0.05), but markedly lower total arteriolar length (P < 0.01) than control. Results suggest that neonatal hyperthyroidism stimulates arteriolar and capillary growth, whereas neonatal hypothyroidism attenuates arteriolar but not capillary growth. After cessation of treatment, total arteriolar length in previously hyperthyroid rats did not change despite increased cardiac mass, whereas previously hypothyroid rats demonstrated marked increases in both cardiac mass and total arteriolar length (P < 0.01). These results indicate a lasting inhibitory effect of early hyperthyroidism on subsequent arteriolar growth.
Direct preconditioning of cardiac ventricular myocytes via adenosine A1 receptor and KATP channel
Authors: Liang B. T.
Published: December 2017

Both adenosine receptor and ATP-sensitive K (KATP) channel mediate the protective effect of ischemic preconditioning in the intact heart. The objective of the present study was to determine the role of adenosine receptor and KATP channel as well as their interaction in simulating and mediating preconditioning of the cardiac myocyte. Cardiac ventricular myocytes cultured from chick embryos 14 days in ovo were developed as a myocyte model of preconditioning. Myocytes were preconditioned by exposing them to 5-min hypoxia, termed preconditioning hypoxia, before a second 90-min hypoxia. Preconditioning resulted in a 64 +/- 3% decrease in the amount of creatine kinase released and a 66 +/- 2% reduction in the percentage of myocytes (+/-SE, n = 11) killed. Glibenclamide or 5-hydroxydecanoic acid (5-HD), when present during the preconditioning hypoxia, blocked the preconditioning effect. Prior exposure of the myocytes to pinacidil also led to a decrease in the injury sustained during the 90-min hypoxia. The protective effect of pinacidil was blocked by glibenclamide or 5-HD, suggesting that KATP channel activation can mimic as well as mediate preconditioning. Adenosine receptor antagonist 8-sulfophenyltheophylline (8-SPT) blocked the protective effect of preconditioning hypoxia. Adenosine or the A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) can replace preconditioning hypoxia and mimic preconditioning; this effect was fully antagonized by 8-SPT, glibenclamide, or 5-HD. Adenosine A1-receptor activation caused a glibenclamide-sensitive inhibition of the basal 45Ca influx and basal myocyte contractile amplitude, consistent with coupling of A1 receptor to stimulation of KATP channel in the myocytes. The data provide direct evidence that myocyte KATP channel is the effector downstream from adenosine A1 receptor in mediating the direct preconditioning of cardiac myocytes.
Effects of hemodilution on gastric regional perfusion and intramucosal pH
Authors: Kleen M. , Habler O. , Hutter J. , Podtschaske A. , Tiede M. , Kemming G. , Welte M. , Corso C. , Messmer K.
Published: December 2017

Acute normovolemic hemodilution (ANH) has been shown to be a cost-effective method of reducing allogenic blood transfusion during elective surgery. ANH has been implicated with impaired oxygenation in isolated canine gastric flaps. The present study was designed to investigate the effects of ANH on gastric mucosal oxygenation using a model closely imitating the clinical situation. Sixteen splenectomized anesthetized beagles were isovolemically hemodiluted to a hematocrit of 20 +/- 1% (6% hydroxyethyl starch; mol wt 200,000; substitution ratio 0.45-0.55). Blood volume (indocyanine green), cardiorespiratory parameters, gastric intramucosal pH (pHi), and gastric regional blood flow (radioactive microspheres; 15 microns) were measured before and after ANH. Results: blood volume was unchanged (87 +/- 8 ml/kg before and 88 +/- 7 ml/kg after ANH). Median total gastric mucosal blood flow at baseline was 0.51 +/- 0.35 ml.min-1.g-1 and did not change significantly upon ANH. The mean pHi was 7.29 +/- 0.05 before and 7.28 +/- 0.05 after hemodilution. There was a homogenization of blood flow distribution in gastric mucosa. Severe hemodilution to a hematocrit of 20% does not impair gastric mucosal oxygenation and poses no risk to gastric mucosal integrity.
A time-dependent balance between endothelins and nitric oxide regulating portal resistance after endotoxin
Authors: Pannen B. H. , Bauer M. , Zhang J. X. , Robotham J. L. , Clemens M. G.
Published: December 2017

To test whether endothelins are involved in the regulation of portal resistance after endotoxin pretreatment and whether their effects are modulated by nitric oxide (NO), rats received intraperitoneal injections of Escherichia coli lipopolysaccharide (LPS, 1 mg/kg body wt) or saline. Six and twenty-four hours later, livers were isolated and perfused. Analyses of portal pressure-flow (P-Q) relationships and epifluorescence microscopy were performed before and after administration of 1) the NO synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 10(-3) M), followed by L-arginine (2 x 10(-3) M), or 2) the endothelin ETA/ETB-receptor antagonist bosentan (2 x 10(-4) M), followed by L-NAME (10(-3) M). LPS pretreatment increased all measures of resistance, which included total portal resistance, zero flow, incremental resistance (slopes of P-Q relationship), and sinusoid resistance. L-NAME had no effect in sham controls but increased all measures of resistance at 6 h after LPS and increased total and incremental resistance 24 h after LPS. L-Arginine reversed these changes. Bosentan reduced total and sinusoid resistance slightly in control livers and caused substantial reductions in all measures of resistance at 6 and 24 h after LPS; these were partially reversed after L-NAME at 6 but not at 24 h. Our data support the hypothesis that a critical balance between endothelin-mediated vasoconstrictor influences and NO-mediated vasodilator influences controls portal resistance after endotoxin pretreatment.
NOS activity in brain and endothelium: relation to hypercapnic rise of cerebral blood flow in rats
Authors: Fabricius M. , Rubin I. , Bundgaard M. , Lauritzen M.
Published: December 2017

We examined whether attenuation of the hypercapnic increase of cerebral blood flow (CBF) associated with nitric oxide synthase (NOS) inhibition is related to local neuronal or aortic endothelial NOS activity or local endothelial/neuronal NOS-dependent vasodilation. Halothane-anesthetized rats were ventilated, and CBF was measured by laser-Doppler flowmetry over the parietal and cerebellar cortex. Intravenous N omega-nitro-L-arginine (L-NNA; 30 mg/kg) inhibited brain and aortic NOS activity by 67-70%. Topical L-NNA (1 mM) inhibited brain NOS activity by 91-94%, whereas aortic NOS activity remained constant. In contrast, intravenous L-NNA attenuated the hypercapnic CBF rise much more efficiently than topical L-NNA. 7-Nitroindazole, another NOS inhibitor, attenuated endothelial and neuronal NOS activity equally well and inhibited the hypercapnic CBF increase as effectively as L-NNA. Topical L-NNA and 7-nitroindazole abolished local endothelial NOS-dependent vasodilation after 15 min, whereas hypercapnic CBF was only slightly reduced. L-NNA injected into the tissue abolished neuronal NOS-dependent vasodilation, whereas hypercapnic CBF was unchanged. The findings suggest that local NOS activity, whether neuronal or endothelial, is unimportant for the hypercapnic rise of CBF.
A sialyl Lewis(x)-containing carbohydrate reduces infarct size: role of selectins in myocardial reperfusion injury
Authors: Flynn D. M. , Buda A. J. , Jeffords P. R. , Lefer D. J.
Published: December 2017

Previous studies have implicated the selectins (P- and L-selectin) in the acute phase of myocardial reperfusion injury. However, it is unclear whether these adhesion molecules are involved in the pathogenesis of myocardial reperfusion associated with longer periods of reperfusion. Dogs (n = 8/group) were subjected to 90 min of coronary ischemia and 48 h of reperfusion. Animals were initially treated with a 35 mg/kg intravenous bolus of a sialyl Lewis(x) oligosaccharide (SLe(x)-OS) 10 min before reperfusion, followed by a 1.75 mg.kg-1.h-1 infusion for the first 24 h of reperfusion. A control group of dogs received a normal saline bolus followed by saline infusion for the first 24 h of reperfusion. In a subsequent group of dogs treatment consisted of only the 35 mg/kg bolus of SLe(x)-OS to help elucidate the time course of selectin involvement. The saline control group exhibited marked decreases in blood flow in the ischemic-reperfused myocardium, sustained depression of left ventricular function, an average infarct size of 29 +/- 5% of the myocardial area at risk, and excessive polymorphonuclear leukocyte accumulation in the infarcted myocardium after 48 h of reperfusion. Dogs that received a bolus followed by an infusion of SLe(x)-OS exhibited significant preservation of myocardial blood flow and left ventricular function at 4.5 and 48 h of reperfusion, dramatic attenuation (56%) of infarct size (P < 0.05), and a 55% reduction (P < 0.05) in polymorphonuclear leukocyte accumulation compared with the saline group. Interestingly, SLe(x)-OS bolus treatment alone exerted early (i.e., at 4.5 h) cardioprotective effects that waned by 48 h of reperfusion. These results demonstrate that the selectin family of adhesion molecules plays an extended role in myocardial reperfusion injury and is not only involved in the acute phase of this disease process.
Activation of human platelets by protein kinase C antibody: role for surface phosphorylation in homeostasis
Authors: Babinska A. , Ehrlich Y. H. , Kornecki E.
Published: December 2017

A monoclonal antibody that inhibits protein kinase C (PKC) activity, as well as PKC pseudosubstrate inhibitory peptides, was found to cause aggregation of human platelets followed by granular secretion. Binding of this antibody to the platelet surface was demonstrated directly by flow cytometry and immunofluorescence microscopy. Assays of ecto-protein kinase activity revealed that this antibody inhibits the phosphorylation of five proteins on the platelet surface. The platelet aggregation induced by extracellular PKC inhibitors could be blocked by the addition of the membrane-impermeable phosphatase inhibitor, microcystin. Thus the inhibition of surface protein phosphorylation together with continuous dephosphorylation, namely, a decrease in the phosphorylation state of surface proteins, causes the activation of platelets. The aggregation caused by decreased surface phosphorylation appears to be initiated by the exposure of active fibrinogen-binding sites on the platelet surface, as demonstrated by the formation of fibrinogen-dependent microaggregates, as the first step in this process. We conclude that the phosphorylation of surface proteins by a platelet ecto-protein kinase C protects platelets from spontaneous aggregation and thus can play an important role in homeostatic mechanisms that maintain circulating platelets in a resting state.
Contribution of cytosolic and membrane-bound 5'-nucleotidases to cardiac adenosine production
Authors: Darvish A. , Pomerantz R. W. , Zografides P. G. , Metting P. J.
Published: December 2017

The purpose of this study was to evaluate the relative contributions of AMP-specific cytosolic 5'-nucleotidase and ecto-5'-nucleotidase to cardiac adenosine production and its regulation by ADP and Mg2+. 5'-Nucleotidase activity was measured spectrophotometrically in the total homogenate, the 150,000-g supernatant fraction (cytosolic 5'-nucleotidase), and the membrane pellet fraction (ecto-5'-nucleotidase) of dog left ventricles. Increasing [MgCl2] over a range from 0 to 6 mmol/l increased 5'-nucleotidase activity in both the supernatant and pellet; only cytosolic 5'-nucleotidase exhibited an absolute requirement for Mg2+. ADP, (20-480 mumol/l) activated supernatant and inhibited membrane-bound 5'-nucleotidase activity. At 80 mumol/l ADP, 5 mmol/l MgCl2, 100 mumol/l AMP, and pH 7.3, the average 5'-nucleotidase activities of the supernatant vs. pellet were 74% of total and 26% of total, respectively. Total adenosine production in unfractionated samples of ventricular homogenates decreased an average of 73% by specific inhibition of cytosolic 5'-nucleotidase, using antibodies against the cytosolic enzyme, and 46% by specific inhibition of ecto-5'-nucleotidase with alpha, beta-methylene adenosine 5'-diphosphate (AOPCP). These findings support the hypotheses that 1) both cytosolic and ecto-5'-nucleotidase contribute to cardiac adenosine production in dog heart homogenates; 2) AMP-specific cytosolic 5'-nucleotidase activity exceeds ecto-5'-nucleotidase activity at physiological concentrations of ADP, AMP, and Mg2+; and 3) Mg2+ is an important regulator of cardiac adenosine production via activation of both ecto- and AMP-specific cytosolic 5'-nucleotidases.
Regulation by acetylcholine of Ca2+ current in rabbit atrioventricular node cells
Authors: Habuchi Y. , Nishio M. , Tanaka H. , Yamamoto T. , Lu L. L. , Yoshimura M.
Published: December 2017

Effects of acetylcholine (ACh) on L-type Ca2+ current (ICa) were examined in isolated atrioventricular (AV) node cells exhibiting spontaneous contractions and pacemaker current (If). ACh at a saturating concentration of 10 microM reduced basal ICa by 48 +/- 6%. The ACh effect was abolished by dialysis with 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), an adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase inhibitor, or guanosine-5'-O-(2-thiodiphosphate). Dialysis with guanosine 3',5'-cyclic monophosphate (cGMP) or NG-monomethyl-L-arginine (L-NMMA) and application of the cGMP-dependent protein kinase inhibitor KT-5823 (1 microM) did not affect ACh inhibition of ICa. Nitric oxide donor 3-morpholinosydnonimine (100 microM) and type III phosphodiesterase (PDE) inhibitor trequinsin (10 nM) enhanced basal ICa by 10-20%, whereas type IV PDE inhibitor Ro-20-1724 (30 microM) together with trequinsin caused a large ICa stimulation comparable to that by 3-isobutyl-1-methylxanthine (IBMX). These findings indicate that ACh inhibits basal ICa primarily by suppressing cAMP synthesis and that these cells have a potent type III and IV PDE activity to determine the basal cAMP concentration. When ICa was stimulated by IBMX (100 microM), the inhibitory effect of ACh was slightly reduced by L-NMMA, cGMP, and methylene blue but not by KT-5823 or Ro-20-1724. ACh hardly inhibited, or even enhanced, IBMX-stimulated Ica when forskolin (3 microM) was coapplied or the IBMX concentration was increased to 500 microM. These findings suggest that cAMP is degraded in the presence of 100 microM IBMX to some extent. Type II PDE, for which IBMX has a relatively high inhibitor constant, seems to contribute partially to the cAMP degradation.
Blood flow response to treadmill running in the rat spinotrapezius muscle
Authors: Musch T. I. , Poole D. C.
Published: December 2017

The rat spinotrapezius muscle has been utilized to investigate the microcirculatory consequences of exercise training. It was the purpose of this investigation to determine whether, and to what extent, this muscle is recruited during treadmill exercise. Radioactive 15-micron microspheres were used to measure blood flow to the spinotrapezius and hind limb musculature as well as to the abdominal organs of female Wistar rats. Blood flows were measured at rest and during two levels of treadmill-running exercise (i.e., 0% grade, 15 m/min and 10% grade, 24 m/min). As expected, exercise increased blood flow to the soleus, plantaris, red gastrocnemius, mixed gastrocnemius, and white gastrocnemius muscles, whereas blood flow to the stomach, intestines, pancreas, spleen, and kidneys was decreased (P < 0.05). However, contrary to our expectation, blood flow to the spinotrapezius muscle decreased from 61 +/- 6 ml.100 g-1.min-1 at rest to 39 +/- 2 ml.100 g-1.min-1 at 0% grade, 15 m/min and 46 +/- 4 ml.100 g-1.min-1 at 10% grade, 24 m/min (P < 0.05). These findings support the premise that treadmill running does not recruit the spinotrapezius muscle and suggest that previous training-induced arteriolar adaptations produced in this muscle may result from mechanisms unrelated to augmented exercise blood flow or muscle metabolism.
Properties of human atrial ICa at physiological temperatures and relevance to action potential
Authors: Li G. R. , Nattel S.
Published: December 2017

There are no published characterizations of Ca2+ current (ICa) at physiological temperatures in human atrium. Depolarization of human atrial myocytes at 36 degrees C elicited ICa that peaked at +10 mV, with a mean maximum current density of 10.8 +/- 1.1 pA/pF and no evidence for T-type current. Overlap between activation and inactivation curves and incomplete inactivation during pulses comparable to normal action potential duration (APD) were compatible with the observed role of ICa in maintaining the plateau. ICa was frequency dependent between 0.1 and 2 Hz and ICa blockade with 0.2 mM Cd2+ reduced rate-dependent changes in APD: under control, APD at 90% repolarization was 230 +/- 15 ms at 0.1 Hz and 178 +/- 14 ms at 2 Hz (decrease of 52 +/- 5 ms); with Cd2+, values were 121 +/- 7 ms at 0.1 H2 and 115 +/- 6 ms at 2 Hz (decrease of 6 +/- 3 ms, P < 0.01) Isoproterenol (1 microM) increased ICa and prolonged APD from 138 +/- 13 to 199 +/- 15 ms (P < 0.01). These results indicate that, in human atrial cells at 36 degrees C, the properties of L-type ICa contribute importantly to the rate-dependent and autonomic control of APD.
Endothelium-dependent pulmonary vasodilation is selectively attenuated during isoflurane anesthesia
Authors: Gambone L. M. , Fujiwara Y. , Murray P. A.
Published: December 2017

We have recently reported that halothane (Hal) anesthesia attenuates the pulmonary vasodilator responses to both bradykinin (BK) and sodium nitroprusside (SNP) compared with responses measured in the conscious state. These agonists have been classically used to activate endothelium-dependent and -independent vasodilator pathways, respectively. Our present goal was to assess the effect of isoflurane (Iso) anesthesia on pulmonary vasodilation activated via these pathways. Left pulmonary vascular pressure-flow (P-Q) plots were used to measure the pulmonary vascular responses to cumulative intravenous doses of BK, SNP, and 3-morpholinosydonimine-N-ethylcarbamide (SIN-1), a nitric oxide donor, in chronically instrumented dogs in the conscious state and during Iso anesthesia after matched preconstriction with the thromboxane analogue U-46619. Iso attenuated the vasodilator response to BK (P < 0.05). However, Iso had a differential effect on the responses to SIN-1 and SNP. Iso potentiated the vasodilator response to SIN-1 (P < 0.05), whereas Iso attenuated the response to SNP (P < 0.05). The vasodilator response to SIN-1 was unchanged during Hal anesthesia. The ATP-sensitive potassium (KATP)-channel inhibitor glibenclamide attenuated the vasodilator response to SNP (P < 0.05) but not to SIN-1. Thus Iso and Hal selectively attenuate the endothelium-dependent pulmonary vasodilator response to BK. Both anesthetics attenuate vasodilation induced by SNP but not by SIN-1. Moreover, a component of SNP-induced vasodilation involves KATP-channel activation.
KATP channels and memory of ischemic preconditioning in dogs: synergism between adenosine and KATP channels
Authors: Yao Z. , Mizumura T. , Mei D. A. , Gross G. J.
Published: December 2017

Results from numerous studies have shown that there is an important link between adenosine A1 receptors and ATP-sensitive potassium (KATP) channels in mediating the cardioprotective effects of ischemic preconditioning (PC). The major aim of the present study was to determine whether occupation of A1 receptors and/or the opening of KATP channels is involved in the time delay between the PC stimulus and the prolonged ischemic insult or the “memory” of PC to reduce infarct size. Barbital sodium-anesthetized dogs were subjected to 1 h of left anterior descending coronary artery (LAD) occlusion followed by 4 h of reperfusion. Ischemic PC was elicited by 10 min of LAD occlusion followed by 1 h of reperfusion (1-h memory) before the 1-h occlusion period. Either adenosine (800 g/min), bimakalim (3 g/min), a combination of two lower doses of each agent (400 g/min of adenosine and 0.3 g/min of bimakalim), or an equivalent volume of saline was infused into the LAD for 10 min followed by a 1-h drug-free period before the 1-h ischemic insult. In another series, glibenclamide, 8-cyclopentyl-1,3-dipropylxanthine (a selective A1-receptor blocker), or PD-115199 (a nonselective adenosine-receptor antagonist) was administered 50 min after ischemic PC (10 min before the 1-h occlusion period). Infarct size (IS) was expressed as a percentage of the area at risk. PC with 1 h of reperfusion resulted in a marked reduction in IS (8.1 +/- 6.5 vs. 29.8 +/- 5.8% in control dogs). Administration of adenosine or bimakalim followed by a 1-h drug-free period had no effect on IS; however, the simultaneous administration of adenosine and bimakalim resulted in a marked decrease in IS (11.5 +/- 2.7%). One hour after ischemic PC, administration of glibenclamide blocked the protective effect of ischemic PC, whereas 8-cyclopentyl-1,3-dipropylxanthine or PD-115199 did not affect it. These results provide evidence that the opening of myocardial KATP channels may play an important role in the memory of ischemic PC in the canine heart and also suggest that adenosine and the KATP channel may have a synergistic interaction that is important for the memory phase of PC.
Selective activation of vasomotor component of SAP spectrum by nucleus reticularis ventrolateralis in rats
Authors: Kuo T. B. , Yang C. C. , Chan S. H.
Published: December 2017

We evaluated the contribution of the rostral nucleus reticularis ventrolateralis (NRVL) to the vasomotor component in the spectrum of systemic arterial pressure (SAP) signals by quantifying the transfer function between electrical stimulation of this medullary nucleus and the SAP response. Sprague-Dawley rats anesthetized with pentobarbital sodium, paralyzed with pancuronium, and mechanically ventilated were used. Broad-band stimulation of the NRVL with computer-generated rectangular current pulses (10-50 microA, 1 ms), at a mean spike rate of 50 pulses/s and randomized modulation frequency of 0-3 Hz, elicited a site-specific and intensity-related pressor response. Intriguingly, the corresponding autospectrum of SAP signals exhibited prevailing power density only in the lower frequency range (0-0.8 Hz). This low-pass response characteristic was confirmed by the observation that 90% of the total magnitude of transfer function between NRVL stimulation and SAP response concentrated between 0 and 0.6 Hz. The magnitude of NRVL-SAP transfer function was significantly reduced by phentolamine or prazosin but appreciably enhanced by yohimbine. We conclude that the NRVL may contribute to the very-low (0-0.25 Hz)- and low (0.25-0.8 Hz)-frequency components of the SAP spectrum, which are belived to reflect sympathetic modulation on vasomotor activity via alpha-adrenergic neurotransmission.
Changes in myocardial blood volume with graded coronary stenosis
Authors: Lindner J. R. , Skyba D. M. , Goodman N. C. , Jayaweera A. R. , Kaul S.
Published: December 2017

Vasodilation of microvessels distal to a stenosis results in an increase in myocardial blood volume (MBV). The purpose of this study was to examine the changes in MBV induced by graded coronary artery stenoses by using myocardial contrast echocardiography (MCE). Accordingly, 21 dogs underwent progressive stenosis of a coronary artery in a random order, the severity of which was judged by the pressure distal to it. Total myocardial blood flow (MBF) to the bed distal to the artery (both anterograde and collateral) was measured by injection of radiolabeled microspheres into the left atrium. In seven dogs, anterograde and total MBF were measured at each stenosis stage by injection of different microspheres into the left atrium and directly into the coronary artery, respectively. MBV was calculated by dividing MBF by the mean transit rate of microbubbles injected directly into the coronary artery during MCE. The perfusion bed size of the artery was also measured by MCE. Our major findings are as follows: 1) there is a nonlinear increase in MBV with increasing degrees of coronary stenosis until the coronary stenosis becomes critical; 2) at moderate levels of coronary stenosis, MBV remains constant despite ongoing autoregulation because of reduction in the size of the perfusion bed supplied by the stenotic vessel; and 3) after exhaustion of autoregulation, a decrease in MBV is noted with increasing levels of stenosis. We conclude that assessment of MBV provides insights into myocardial perfusion distal to a coronary stenosis above and beyond that provided by the measurement of MBF alone.
Dual role of cGMP in modulation of macromolecule permeability of aortic endothelial cells
Authors: Holschermann H. , Noll T. , Hempel A. , Piper H. M.
Published: December 2017

The effect of guanosine 3',5'-cyclic monophosphate (cGMP) on cytosolic Ca2+ dynamics and associated alterations in macromolecule permeability was investigated in cultured monolayers of aortic endothelial cells. Addition of the membrane-permeable cGMP analogue 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP, 5 x 10(-4)M) or activators of the soluble (3-morpholinosydnonimine, 10(-5) M) or the particulate guanylyl cyclase (atrial natriuretic peptide, 10(-7) M) to unstimulated monolayers led to a decrease in permeability (8-BreGMP: 62 +/- 8% of control) without affecting low basal cytosolic Ca2+ concentration ([Ca2+]i, 87 +/- 8 nM). In contrast, under conditions of elevated [Ca2+]i (503 +/- 95 nM) and increased permeability (155 +/- 7% of control) induced by 10(-6) M ionomycin, 8-BrcGMP, 3-morpholinosydnonimine, or atrial natriuretic peptide provoked a further increase in permeability (8-BrcGMP: 255 +/- 27%). These agents failed to increase permeability when added before or after the ionomycin-triggered transitory rise in [Ca2+]i. The increase in permeability in response to 8-BrcGMP was due to a secondary further rise in [Ca2+]i (758 +/- 87 nM), which was abolished in the absence of extracellular Ca2+, indicating influx of exogenous Ca2+ as the cause. Changes in [Ca2+]i and permeability were inhibited, in the presence of the Rp diastereomer of 8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphothioate (2 x 10(-5) M), an inhibitor of the cGMP-dependent protein kinase. These findings show that, depending on [Ca2+]i, cGMP can play opposite roles in endothelial permeability in one and the same cell preparation.
Endogenous nitric oxide buffers blood pressure variability between 0.2 and 0.6 Hz in the conscious rat
Authors: Nafz B. , Wagner C. D. , Persson P. B.
Published: December 2017

Shear stress is a potent stimulus for the formation and release of nitric oxide (NO). It seems, therefore, possible that a short-term increase in arterial blood pressure (ABP), which leads to a concomitant rise in endothelial shear stress, enhances NO release. The latter elicits a relaxation of vascular smooth muscle cells that, in turn, counteracts the initial rise in blood pressure (BP). Thus this chain of events may constitute a negative feedback loop reducing BP variability (BPV). To test this hypothesis, BP-time series were determined via telemetry in freely moving conscious Sprague-Dawley rats. Because it was reported recently that NO effects on ABP are more pronounced in females, the experiments were performed on 2 groups consisting of 10 female and 11 male animals. This was done under control conditions and after fixing NO plasma levels via an intravenous bolus of 15 mg/kg body wt N(G)-nitro-L-arginine methyl ester together with a continuous infusion of nitroprusside (15 +/- 0.8 microg/min). This combined infusion maintained mean ABP and heart rate at physiological levels, thus avoiding as much as possible interferences with other reflexes, e.g., the baroreflex. To quantitate BPV, fast Fourier transforms of the BP-time series were determined. The absolute power in the frequency range below 1 Hz increased during fixed NO to approximately 350% vs. control animals (female control, 2.1 x 10(9) +/- 1.5 x 10(8) mmHg2 vs. fixed NO, 8.0 x 10(9) +/- 1.3 x 10(9) mmHg2, P < 0.005; male control, 3.4 x 10(9) +/- 4.6 x 10(8) mmHg2 vs. fixed NO, 8.3 x 10(9) +/- 2.0 x 10(9) mmHg2, P < 0.05). This was mainly caused by a substantial rise in the power ranging from 0.2 to 0.6 Hz, which increased roughly fourfold in both females and males. It is concluded that the NO system is a potent buffer of spontaneous BP oscillations in the freely moving rat. This system is most efficient in buffering frequencies within the range of 0.2-0.6 Hz and shows no gender-specific differences with respect to its BP buffering capacity.
Sodium-independent inward chloride pumping in rat cardiac ventricular cells
Authors: Chipperfield A. R. , Davis J. P. , Harper A. A.
Published: December 2017

The intracellular Cl concentration ([Cl]i) in rat cardiac ventricular muscle, measured with double-barreled microelectrodes in vitro, was 21.3 +/- 1.5 (SD) mM [number of observations (n) = 46]. With the Na-K-Cl cotransport inhibitor bumetanide (10 microM), it fell to 13.4 +/- 1.4 mM (n = 27), and with 1 mM acetazolamide, it fell further, to 7.2 +/- 1.5 mM (n = 5), close to equilibrium with the membrane potential. In the absence of Na, [Cl]i was 15.9 +/- 1.4 mM (n = 8), and with 1 mM acetazolamide, it fell to 6.5 +/- 0.6 mM (n = 4), again close to equilibrium. The bumetanide- and Na-insensitive components of inward Cl pumping were inhibited by chlorothiazide and ethacrynic acid but were unaffected by the Na-Cl cotransport inhibitor metolazone. There was inhibition of Na-K-Cl cotransport by chlorothiazide = acetazolamide > metolazone. The anion exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and HCO3 had no effect on [Cl]i in any condition. Thus Cl accumulation in the rat ventricle is fully accounted for by two systems, namely, Na-K-Cl cotransport and an Na-independent, possibly primary active, process.
beta-Adrenergic regulation of cAMP and protein phosphorylation in phospholamban-knockout mouse hearts
Authors: Kiss E. , Edes I. , Sato Y. , Luo W. , Liggett S. B. , Kranias E. G.
Published: December 2017

The stimulatory effects of beta-adrenergic agonists reflect increases in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels and phosphorylation of key regulatory proteins in the heart. One of these phosphoproteins is phospholamban (PLB) in sarcoplasmic reticulum, and ablation of PLB is associated with attenuation of the contractile responses to beta-adrenergic stimulation in the mouse heart. To determine whether this attenuation of beta-stimulation is due to altered phosphorylation characteristics of the other key cardiac phosphoproteins and/or to compensatory responses occurring in the absence of PLB, PLB-knockout and wild-type hearts were perfused and their protein phosphorylation patterns examined. The beta-adrenergic receptor density, adenylyl cyclase activity, tissue cAMP levels, and the basal phosphoprotein pattern were similar between PLB-knockout and wild-type hearts. Isoproterenol perfusion resulted in similar increases in the tissue cAMP levels and the degree of phosphorylation of troponin I, C protein, and the 21-kDa microsomal protein in wild-type and PLB-knockout hearts. These findings indicate that the attenuation of isoproterenol-mediated increases in contractility of the PLB-knockout hearts is not due to alterations in the beta-adrenergic signal transduction pathway or the degree of phosphorylation of the key cardiac regulatory phosphoproteins in myofibrils and sarcolemma.
Baroreflex control of sinus node during dynamic exercise in humans: effects of central command and muscle reflexes
Authors: Iellamo F. , Legramante J. M. , Raimondi G. , Peruzzi G.
Published: December 2017

This study evaluated the influence of central command and muscle afferent stimulation (mechanical and chemical) on the integrated arterial baroreflex control of the sinus node during dynamic exercise. Twenty-two healthy men performed voluntary knee extension and electrically induced dynamic knee extension under free-flow and arrested-flow (n = 18) conditions. Systolic arterial pressure (SAP) and pulse interval (PI) were measured continuously and noninvasively. The arterial baroreflex was evaluated by analyzing the slopes of sequences of three or more consecutive beats characterized by the SAP and PI of the following beat; both increased or decreased in a linear fashion. Compared with rest, both voluntary exercise and electrically induced exercise under arrested-flow conditions resulted in a maintained baroreflex sensitivity (BRS; 11.7 +/- 1.2 vs. 9.6 +/- 0.7 and 11.3 +/- 1.4 vs. 9.8 +/- 1.5 ms/mmHg, respectively; not significant), with an apparent rightward shift in the regression line relating SAP to PI. Electrically induced exercise under free-flow conditions resulted in a significant decrease in BRS (12.1 +/- 1.4 vs. 8.8 +/- 0.8 ms/mmHg; P < 0.05). These data suggest that the central command and muscle chemoreflex act to preserve the BRS, possibly "resetting" the baroreceptor-cardiac response relationship, whereas stimulation of mechanosensitive receptors appears capable of modifying the integrated baroreflex control of sinus node function in humans. The first two mechanisms seem, however, to overwhelm the latter to maintain BRS, thus permitting a concomitant increase in arterial pressure and heart rate.
Preconditioning cultured human pediatric myocytes requires adenosine and protein kinase C
Authors: Ikonomidis J. S. , Shirai T. , Weisel R. D. , Derylo B. , Rao V. , Whiteside C. I. , Mickle D. A. , Li R. K.
Published: December 2017

We showed previously that 20 min of low-volume anoxia ("ischemia") and 20 min of "reperfusion" preconditions quiescent pediatric myocyte cultures against damage resulting from 90 min of subsequent prolonged ischemia and 30 min of reperfusion. The purpose of this study was to assess the roles of adenosine and protein kinase C (PKC) in this preconditioning model. Our results suggest that 1) preconditioned myocytes secrete a protective mediator(s) into the "ischemic" supernatant that is transferable to other cells, and adenosine is released into the supernatant in quantities sufficient for adenosine-receptor activation (2) preconditioning is inhibited by adenosine-receptor antagonism, and myocyte protection similar to preconditioning can be achieved with exogenously administered adenosine or adenosine-receptor stimulation; (3) brief ischemic and adenosine-induced myocyte preconditioning is mimicked by the phorbol ester 4beta-phorbol 12-myristate 13-acetate (PKC agonist) and inhibited by PKC antagonists; and (4) brief ischemic and adenosine-induced myocyte preconditioning both induce PKC translocation to myocyte membranes and increase the PKC phosphorylation rate. These data suggest that adenosine released from ischemic human pediatric myocytes mediates preconditioning through activation of PKC.
Traumatic brain injury does not alter cerebral artery contractility
Authors: Bukoski R. D. , Wang S. N. , Bian K. , DeWitt D. S.
Published: December 2017

Previous studies have shown that traumatic brain injury (TBI) significantly reduces cerebral blood flow determined in vivo and reduces vascular reactivity in the pial circulation measured with cranial window preparations. We have now tested the hypothesis that TBI induces these changes by impairing intrinsic contractile activity of cerebral arteries. Anesthetized rats underwent moderate (2.2 atm) and severe (3.0 atm) midline fluid percussion TBI or sham injury following which posterior cerebral or middle cerebral arteries were isolated and isometric force generation was measured. Moderate (n = 5) and severe (n = 3) trauma had no effect on the magnitude of serotonin- or K+-induced force generation or sensitivity to serotonin in arteries isolated within 10 min of TBI. Functional disruption of the endothelium of posterior cerebral arteries isolated 10 min after moderate trauma or sham injury caused a reduction in the active tension response to serotonin that was similar in both groups. Blockade of cyclooxygenase with 5 microM indomethacin had no effect on serotonin-induced force generated by vessels with moderate trauma or in sham-treated rats. Acetylcholine induced an endothelium-dependent relaxation of posterior and middle cerebral arteries; the magnitude of the response was unaffected by moderate TBI. To determine whether prolonged in situ exposure of vessels to the traumatized cerebral milieu could reveal an alteration in intrinsic contractility, posterior cerebral arteries were isolated 30 min after TBI; again, no differences in the tension or relaxation responses were observed. It is concluded that midline fluid percussion TBI did not affect contraction or relaxation of proximal middle or posterior cerebral arteries in rats.
Adenosine stimulation of DNA synthesis in human endothelial cells
Authors: Ethier M. F. , Dobson J. G.
Published: December 2017

We investigated adenosine stimulation of DNA synthesis in human endothelial cells by measuring [3H]thymidine incorporation in cultures derived from human umbilical veins. After 18 h of exposure to adenosine in serum-free medium, endothelial cell [3H]thymidine incorporation was increased by 30-64%. Adenosine-induced DNA synthesis was not mimicked by adenosine receptor agonists and was not inhibited by adenosine receptor antagonists. Adenosine-induced DNA synthesis was inhibited 81% by 100 microM 5'-(N,N-dimethyl)amiloride, an inhibitor of Na+/H+ exchange, and was totally inhibited by 10 microM 2',4'-dibromoacetophenone, an inhibitor of phospholipase A2 (PLA2). Adenosine increased adenosine 3',5'-cyclic monophosphate levels in endothelial cells, but adenosine-induced DNA synthesis was not inhibited by the protein kinase A (PKA) inhibitor Rp-cAMPS. Both ATP and the phorbol ester 4beta-phorbol 12-myristate 13-acetate (PMA) increased DNA synthesis in human endothelial cells. Stimulation by ATP was inhibited by the P2-receptor antagonist suramin, and PMA stimulation was inhibited by the protein kinase C (PKC) inhibitor H-7. Neither suramin nor H-7 inhibited adenosine-stimulated DNA synthesis. The results suggest that Na+/H+ exchange and PLA2 are involved in adenosine-induced DNA synthesis in cultures of human endothelial cells independently of adenosine receptor, PKA, or PKC activation.
Relationship of the fourth heart sound to atrial systolic transmitral flow deceleration
Authors: McGuire A. M. , Hagley M. T. , Hall A. F. , Kovacs S. J.
Published: December 2017

The fourth heart sound (S4) is thought to be due to cardiohemic vibrations, powered by deceleration of transmitral blood flow, that occur when atrial systole leads to a disproportionately high rise in ventricular end-diastolic pressure (relative to diastasis), associated with an enhanced atrial systolic blood filling volume or a stiff ventricular wall. To characterize S4 production, we modeled the cardiohemic system as a forced, damped nonlinear harmonic oscillator. The forcing term used a closed-form expression for the Doppler A-wave contour. We simultaneously recorded transthoracic phonocardiograms and Doppler A waves in subjects with and without audible S4 and compared model predictions for S4 amplitude, frequency, and power spectrum with those of the recorded S4. Excellent agreement was observed between the model-predicted amplitude, duration, timing, and power spectrum and those of the phonocardiographic S4. We conclude that, with a normal mitral valve, there should always be an oscillation of the cardiohemic system during A-wave deceleration. However, oscillations may not have high enough amplitude, frequency, or coupling to the chest wall to be clinically audible as an S4.