bluuebunny/crossref_metadata_2025 huggingface dataset:
Cardiovascular reflex responses to ischemia during occlusion of celiac and/or superior mesenteric arteries
Authors: Rendig S. V. , Chahal P. S. , Longhurst J. C.
Published: December 2017

Global abdominal visceral ischemia leads to profound cardiovascular reflex adjustments. However, the separate contributions of the celiac artery and superior mesenteric artery (SMA) vascular beds to this reflex are unknown. Accordingly, we compared the effects of single and combined occlusions of these vessels on blood pressure (BP) in anesthetized cats. Tissue mass and pH of selected organs, regional blood gases, pH, and lactate also were measured as potential contributing factors. Occlusion of the SMA or celiac artery produced significantly (P < 0.05) different increments in BP (30 +/- 4 vs. 18 +/- 4 mmHg, respectively). Combined occlusion of the two vessels augmented BP by 53 +/- 12 mmHg, a significantly greater increase than during celiac ligation. Venous lactate levels increased significantly during SMA, but not celiac, occlusion, and the decline in venous pH was significantly greater in the SMA than in the celiac vascular bed (-0.20 +/- 0.03 vs. -0.08 +/- 0.02 pH units, P < 0.05, respectively). The decline in tissue pH of SMA-perfused organs during SMA occlusion was significantly greater than in celiac-perfused organs during celiac occlusion. Conversely, tissue mass subserved by the celiac artery was significantly greater than that subserved by the SMA (182 +/- 27 vs. 131 +/- 17 g, respectively). These data suggest that the larger cardiovascular reflex produced by SMA occlusion compared with celiac occlusion may be related to a greater increase of lactic acid concentration in tissue supplied by the SMA. In addition, the large reflex increase in BP produced by combined occlusion of these vessels is an additive effect, presumably related to larger organ mass and recruitment of more sensory nerve fibers.
Regulation of Ca2+ channel currents by intracellular ATP in smooth muscle cells of rat mesenteric artery
Authors: Yokoshiki H. , Katsube Y. , Sperelakis N.
Published: December 2017

Regulation of L-type Ca2+ channels of vascular smooth muscle (VSM) cells by adenosine 3',5'-cyclic monophosphate (cAMP)-dependent and guanosine 3',5'-cyclic monophosphate (cGMP)-dependent phosphorylation, which requires Mg2+ATP as a phosphate donor, has been reported (T. Ishikawa, J. R. Hume, and K. D. Keef. Circ. Res. 73: 1128-1137, 1993; Z. Xiong, N. Sperelakis, and C. Fenoglio-Preiser. J. Vasc. Res. 31: 271-279, 1994), and regulation by ATP has been demonstrated (Y. Ohya and N. Sperelakis. Circ. Res. 64: 145-154, 1989). However, it has not been elucidated whether the regulation by ATP is mediated by a mechanism that is distinct from phosphorylation. In the present study, we examined the effects of intracellularly perfused ATP on Ca2+ channel currents of VSM cells isolated from rat mesenteric arteries using a whole cell voltage clamp combined with an intracellular perfusion technique. Ba2+ currents (I(Ba)) through Ca2+ channels were evoked by depolarizing pulses from a holding potential of -80 mV with 130 mM Cs+ in the pipette and 100 mM Ba2+ in the bath. The decrease in the ATP concentration (from 5 to 0.1 mM) in the pipette caused a 45 +/- 5% (n = 8) reduction of maximal I(Ba) obtained at +40 mV within 10 min. The dose-response relation between I(Ba) and ATP showed a dissociation constant of 0.53 mM ATP. This concentration is much higher than that usually required for phosphorylation (e.g., few micromolar). Increase in the ATP (from 0.1 to 5 mM) caused an enhancement of maximal I(Ba) by 57 +/- 10% (n = 6), and this enhancement was not prevented in the presence of 30 microM H-7, a nonspecific inhibitor of protein kinases, or 1 microM protein kinase inhibitor, an inhibitor protein of cAMP-dependent protein kinase. These results indicate that slow Ca2+ channels in VSM cells are regulated by intracellular ATP, independently of phosphorylation, implying a direct regulatory action, such as a requirement for ATP binding to the inner surface of the channel, to exhibit activity.
S-nitrosothiols inhibit neuronal norepinephrine transport
Authors: Kaye D. M. , Wiviott S. D. , Kobzik L. , Kelly R. A. , Smith T. W.
Published: December 2017

Although it has been recently shown that nitric oxide (NO) and its congeners (NO(x)), including nitrosothiols, may modify catecholamine turnover in the brain, it is not known whether NO(x) affect norepinephrine (NE) uptake by sympathetic neurons. The nitrosothiol NO donor S-nitroso-acetylpenicillamine (SNAP, 100 microM for 1 h) elicited a concentration-dependent reduction in desipramine-sensitive [3H]NE uptake into PC-12 cells (66 +/- 3%; P < 0.01) or cultured rat superior cervical ganglia (74 +/- 5%; P < 0.001), whereas desipramine-insensitive [3H]NE uptake was unaffected, indicating a selective effect on uptake-1-mediated transport. Short-term coculture of PC-12 cells with microvascular endothelial cells expressing the cytokine-inducible NO synthase (NOS2) also exhibited a reduction in [3H]NE uptake (33 +/- 3%, P < 0.001) that could be prevented by the addition of the NOS inhibitor N-monomethyl-L-arginine (L-NMMA, 1 mM). Endogenous production of NO(x) by nerve growth factor-pretreated PC-12 cells also exhibited an L-NMMA-inhibitable reduction in [3H]NE uptake. Whereas SNAP resulted in a 10-fold elevation of PC-12 guanosine 3',5'-cyclic monophosphate (cGMP) content (P < 0.01), its effect on [3H]NE uptake was not mimicked by exposure to 8-bromo-cGMP. However, the inhibitory effect of SNAP on uptake-1-mediated [3H]NE transport could be attenuated by 1 mM cysteine, a sulfhydryl compound that could act as a sink for NO(x)-mediated nitrosation reactions, although cysteine did not affect the increase in intracellular cGMP with SNAP. These data suggest that an endogenous NO(x) source(s) modifies the activity of the uptake-1 catecholamine transporter in postganglionic sympathetic neurons, which, as we demonstrate, express both NOS1 and NOS3 isoforms, possibly by S-nitrosothiol-mediated nitrosation of regulatory sites on the transporter.
Regulation of bFGF expression and ANG II secretion in cardiac myocytes and microvascular endothelial cells
Authors: Fischer T. A. , Ungureanu-Longrois D. , Singh K. , de Zengotita J. , DeUgarte D. , Alali A. , Gadbut A. P. , Lee M. A. , Balligand J. L. , Kifor I. , Smith T. W. , Kelly R. A.
Published: December 2017

Basic fibroblast growth factor (bFGF; fibroblast growth factor-2) and angiotensin II (ANG II), among other peptide signaling autacoids (cytokines), are known to regulate the phenotypic adaptation of cardiac muscle to physiological stress. The cell type(s) in cardiac muscle responsible for ANG II synthesis and secretion and the role of endogenous cytokines in the regulation of bFGF induction remain unclear. With the use of confluent, serum-starved, low-passage cultures of cardiac microvascular endothelial cells (CMEC), ANG II could be detected in cellular lysates and in medium conditioned by these cells with the use of high-performance liquid chromatography followed by radioimmunoassay. The secretion of angiotensins by individual CMEC could be detected with a cell-blot assay technique. ANG II secretion was decreased by brefeldin A, an agent that interrupts constitutive and regulated secretory pathways for peptide autacoid/ hormone synthesis, suggesting de novo synthesis, activation, and secretion of angiotensins by CMEC. In primary isolates of adult rat ventricular myocytes (ARVM) and CMEC, ANG II, acting at ANG II type 1 receptors in both cell types, was found to increase bFGF mRNA levels measured by ribonuclease protection assay. Endothelin-1 (ET-1), which is known to be synthesized by CMEC, and bFGF itself, which has been detected in both ARVM and CMEC, increased bFGF transcript levels in both cell types. Interleukin-1beta (IL-1beta), which like ANG II and ET-1 is known to activate mitogen-activated protein kinases in both ARVM and CMEC, increased bFGF mRNA levels only in cardiac myocytes. Thus cytokines such as ANG II, ET-1, bFGF, and IL-1beta locally generated by cellular constituents of cardiac muscle, including CMEC, regulate bFGF mRNA levels in a cell type-specific manner.
Enhancement by vasopressin of adrenergic responses in human mesenteric arteries
Authors: Medina P. , Noguera I. , Aldasoro M. , Vila J. M. , Flor B. , Lluch S.
Published: December 2017

Vasopressin not only acts directly on blood vessels through V1-receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments in vitro and in vivo. The aim of the present study was to investigate whether subpressor concentrations of vasopressin could modify the constrictor responses to norepinephrine and electrical stimulation of the perivascular nerves in human mesenteric arteries. Human mesenteric artery rings (3-3.5 mm long, 0.8-1.2 mm OD) were obtained from 38 patients undergoing abdominal operations. The arterial rings were suspended in organ bath chambers for isometric recording of tension. Vasopressin (3 x 10(-11) M) enhanced the contractions elicited by electrical stimulation at 2, 4, and 8 Hz (by 100, 100, and 72%, respectively) and produced a leftward shift of the concentration-response curves to norepinephrine (half-maximal effective concentration decreased from 2.2 x 10(-6) to 5.0 x 10(-7) M; P < 0.05) without any alteration in maximal contractions. Vasopressin also potentiated KCl- and calcium-induced contractions. The V1-receptor antagonist 1-[beta-mercapto-beta,beta-cyclopentamethylenepropionic acid-2-O-methyl-tyrosine, 8-arginine]vasopressin (10(-6) M) prevented the potentiation evoked by vasopressin in all cases. The calcium antagonist nifedipine (10(-6) M) did not affect the potentiation of electrical stimulation and norepinephrine induced by vasopressin but abolished KCl-induced contractions. The results suggest that vasopressin, in addition to its direct vasoconstrictor effect, strongly potentiates the responses to adrenergic stimulation and KCl depolarization. Both the direct and indirect effects of vasopressin appear to be mediated by V1-receptor stimulation. The amplifying effect of vasopressin on constrictor responses may be relevant in those clinical situations characterized by increased plasma vasopressin levels.
Dissociation between positive inotropic and alkalinizing effects of angiotensin II in feline myocardium
Authors: Mattiazzi A. , Perez N. G. , Vila-Petroff M. G. , Alvarez B. , Camilion de Hurtado M. C. , Cingolani H. E.
Published: December 2017

The present study examines the intracellular pH (pHi) dependence of angiotensin (ANG) II-induced positive inotropic effect in cat papillary muscles contracting isometrically (0.2 Hz, 30 degrees C). Muscles were loaded with the fluorescent dye 2'-7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester for simultaneous measurement of pHi and contractility. In N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffer (n = 4), there was a temporal dissociation between the positive inotropic and the alkalinizing effects of ANG II (0.5 microM). The positive inotropic effect of ANG II peaked at 9.7 +/- 0.8 min (240 +/- 57% above control) without significant changes in pHi. The increase in pHi became significant (0.05 +/- 0.01 pH units) only after 16 min of exposure to the drug, when the positive inotropic effect of ANG II was already fading. In HCO3- buffer (n = 7), the ANG II-induced positive inotropic effect occurred without significant pHi changes. In the presence of 5 microM ethyl isopropyl amiloride (EIPA, to specifically inhibit the Na+/H+ exchanger), the alkalinizing effect of ANG II was changed to a significant decrease in pHi, despite which ANG II still increased contractility by 87 +/- 16% (n = 6). The results indicate that in HEPES buffer only a fraction of the ANG II-induced positive inotropic effect can be attributed to a pHi change, whereas in a physiological CO2-HCO3- medium the positive inotropic effect of ANG II is independent of pHi changes. Furthermore, an ANG II-induced increase in myocardial contractility was observed even when ANG II administration elicited a decrease in pHi, as occurred after Na+/H+ exchanger blockade. The results show that in feline myocardium, the increase in contractility evoked by ANG II in a physiological CO2-HCO3- medium is not due to an increase in Ca2+ myofilament sensitivity secondary to an increase in myocardial pHi.
Measurement of intraventricular pressure and cardiac performance in the intact closed-chest anesthetized mouse
Authors: Lorenz J. N. , Robbins J.
Published: December 2017

To fully utilize the potential of newly developed mouse models with specific genetic mutations, it is necessary to study the functional consequences of genetic manipulation in the fully intact animal. To this end, the purpose of the present study was to develop and validate a methodology for the study of myocardial performance in the fully intact, closed-chest mouse. Left ventricular function was evaluated in euthyroid, hypothyroid, and hyperthyroid mice, animals with well-documented alterations in myocardial function. The mice were anesthetized and instrumented with polyethylene catheters in the right femoral artery and vein and with a Millar MIKRO-TIP transducer in the left ventricle via the right carotid artery. Structural and functional evidence suggested that the instrumentation procedure did not cause myocardial damage, valvular insufficiency, or aortic obstruction. Isovolumic indexes of myocardial contractility derived from the left ventricular pressure pulse and its first derivative demonstrated a 40% increase in contractility in the hyperthyroid animals and a 40% decrease in contractility in the hypothyroid animals. Similar differences in the indexes of relaxation were observed. Furthermore, isoproterenol dose-response relationships of these contractile parameters were blunted in the hypothyroid animals and augmented in the hyperthyroid animals compared with euthyroid control animals. Given the small size of the mouse and the high frequency of the cardiac cycle, these data demonstrate the feasibilty of combining a high-fidelity, microtip manometer with a high-speed data-acquisition system to obtain faithful recordings of cardiac performance in the fully intact mouse.
Activator calcium and myocardial contractility in fetal sheep exposed to long-term high-altitude hypoxia
Authors: Browne V. A. , Stiffel V. M. , Pearce W. J. , Longo L. D. , Gilbert R. D.
Published: December 2017

We studied myocardial contractility in fetal sheep from ewes exposed to approximately 112 days of hypoxia at high altitude (3,820 m). We measured the inotropic response to extracellular Ca2+ concentration ([Ca2+]o, 0.2-10 mM) and ryanodine (10(-10) to 10(-4) M) in isometrically contracting papillary muscles and quantified dihydropyridine (DHPR) and ryanodine (RyR) receptors. In hypoxic fetuses, curves describing the force-[Ca2+]o relationship were shifted left, and the top plateaus were decreased by approximately 35% in both left and right ventricles. In normoxic and hypoxic fetuses, ryanodine (10(-4) M) reduced maximum active tension (Tmax) to approximately 25-40% of baseline values, indicating that the sarcoplasmic reticulum was the chief source of activator Ca2+ and that Ca2+ influx alone was not sufficient to activate a contraction of normal amplitude. Hypoxia resulted in a lower Tmax in the right ventricle and a lower maximum rate of rise in the left ventricle after treatment with ryanodine. DHPR number did not change, but RyR number and the RyR/DHPR in both ventricles were higher in hypoxic fetuses. We conclude that hypoxia decreases contractility, possibly by reducing the availability of activator Ca2+. Further studies are needed to directly measure the Ca2+ current and intracellular Ca2+ transient and to examine myofilament protein and adenosinetriphosphatase activity.
Magnesium shifts voltage dependence of activation of delayed rectifier I(K) in guinea pig ventricular myocytes
Authors: Williams B. A. , Beatch G. N.
Published: December 2017

The sensitivity of the delayed rectifier K+ current (I(K)) to intracellular Mg2+ was investigated in guinea pig ventricular myocytes using the whole cell patch-clamp technique. An increase in free intracellular Mg2+ concentration ([Mg2+]i) led to a dose-dependent decrease in I(K) with a half-maximal effect of approximately 20 nM. Activation of I(K) was shifted toward more positive voltages on increasing [Mg2+]i, but little effect was observed on activation and deactivation kinetics. Isoproterenol increased I(K) and was partially reversible in both control and 100 nM [Mg2+]i. The antiarrhythmic drug dofetilide was used to separate I(K) into its two components, rapidly activating (I(Kr)) and slowly activating (I(Ks)). The magnitude of both components decreased to a similar extent with an increase in [Mg2+]i. As [Mg2+]i was reduced, however, the number of experiments in which the dofetilide-sensitive current I(Kr) displayed inward rectification was reduced. In contrast to results previously reported for frog myocytes, it is unlikely that Mg2+ effects on guinea pig I(K) are mediated by a protein phosphatase.
Interaction of central venous pressure, intramuscular pressure, and carotid baroreflex function
Authors: Shi X. , Foresman B. H. , Raven P. B.
Published: December 2017

Seven healthy volunteer men participated in an experiment involving lower body positive pressure (LBPP) of 30 Torr and acute volume expansions of 5-6% (VE-I) and 9-10% (VE-II) of their total blood volume (TBV) to differentiate the effect of increased intramuscular pressure and central venous pressure (CVP) on the maximal gain (Gmax) of the carotid baroreflex. During each experimental condition, the heart rate (HR), mean arterial pressure (MAP; intraradial artery or Finapres), and CVP (at the 3rd-4th intercostal space) were monitored continuously. Gmax was derived from the logistic modeling of the HR and MAP responses to ramped changes in carotid sinus transmural pressure using a protocol of pulsatile changes in neck chamber pressure from +40 to -65 Torr. The increase in CVP during +30-Torr LBPP was 1.5 mmHg (P < 0.05) and was similar to that observed during VE-I (1.7 mmHg, P > 0.05). The Gmax of the carotid baroreflex of HR and MAP was significantly decreased during LBPP by -0.145 +/- 0.039 beats x min(-1) x mmHg(-1) (38%) and -0.071 +/- 0.013 mmHg/mmHg (25%), respectively; however, VE-I did not affect Gmax. During VE-II, CVP was significantly greater than that elicited by LBPP, and the Gmax of the carotid baroreflex of the HR and MAP responses was significantly reduced. We conclude that carotid baroreflex responsiveness was selectively inhibited by increasing intramuscular pressure, possibly resulting in an activation of the intramuscular mechanoreceptors during LBPP. Furthermore, it would appear that the inhibition of the carotid baroreflex, via cardiopulmonary baroreceptor loading (increased CVP), occurred when a threshold pressure (CVP) was achieved.
Resistance to mineralocorticoids in Wistar-Furth rats
Authors: Ullian M. E. , Islam M. M. , Robinson C. J. , Fitzgibbon W. R. , Tobin E. T. , Paul R. V.
Published: December 2017

Wistar-Furth rats (WF) do not develop hypertension when treated with salt and mineralocorticoids and therefore may be useful for investigating the mechanisms of mineralocorticoid action and hypertension. In the present studies, we determined vascular and renal responses of WF to mineralocorticoids. Control Wistar rats (W) developed deoxycorticosterone acetate (DOCA)-NaCl and dexamethasone hypertension, whereas WF rats developed dexamethasone hypertension only. Aldosterone treatment of vascular smooth muscle cells cultured from WF resulted in 82% less upregulation of angiotensin II radioligand binding, 50% less induction of angiotensin II AT1a receptor mRNA, and 76% less potentiation of angiotensin II-stimulated inositol phosphates than did aldosterone treatment of cells from W. Similarly, DOCA-NaCl potentiated angiotensin II- and phenylephrine-stimulated contractions in aortic rings from W but not from WF. Although DOCA-NaCl treatment affected hypokalemia to an equal degree in WF and W, increases in renal citrate synthase activity (a specific renal mineralocorticoid response) were greater in W than in WF. WF manifest a partial defect in mineralocorticoid responsiveness in vascular smooth muscle and, possibly, in the kidney.
Hypoxia-induced hyperpolarization is not associated with vasodilation of bovine coronary resistance arteries
Authors: Gauthier-Rein K. M. , Bizub D. M. , Lombard J. H. , Rusch N. J.
Published: December 2017

The effect of reduced PO2 on the transmembrane potential and diameter of small cannulated coronary resistance arteries was evaluated by microelectrode and videomicroscopic methods. Bovine coronary resistance arteries (158 +/- 8 microm ID) were cannulated with glass micropipettes and perfused and superfused with physiological salt solution. Lowering the PO2 of the physiological salt solution from 140 +/- 4 to 36 +/- 2 mmHg increased the smooth muscle cell transmembrane potential from -51 +/- 2 to -62 +/- 2 mV in both endothelium-intact and -denuded coronary resistance arteries. This hyperpolarization was blocked by superfusion with the K+-channel blocker glibenclamide (1 microM). However, low PO2 did not significantly dilate either endothelium-intact or -denuded coronary resistance arteries, although superfusion with 1 microM cromakalim, a K+-channel activator, induced a 6-mV hyperpolarization and increased the diameter by 33 +/- 10 microm. These results suggest that reduced PO2 directly hyperpolarizes the vascular smooth muscle of coronary resistance arteries by activation of glibenclamide-sensitive K+ channels, but other nonvascular mechanisms may mediate the vasodilation response to low PO2.
Contribution of ATP to oxidative stress-induced changes in action potential of isolated cardiac myocytes
Authors: Bhatnagar A.
Published: December 2017

The role of ATP in oxidative stress-mediated changes in the cardiac action potential was investigated in isolated adult rat cardiac myocytes. Superfusion with H2O2 led to a decrease in the energy charge and depletion of nonprotein thiols and elicited hypercontracture of the myocytes. Treatment with 3-aminobenzamide (3-AB), an inhibitor of protein ribosylation, increased the lifetime of H2O2-exposed myocytes and attenuated depletion of ATP and nonprotein thiols. H2O2-mediated DNA strand breaks were increased in the presence of 3-AB. On exposure to H2O2, myocytes patch clamped with 1 mM ATP in the pipette initially displayed prolonged action potential durations (APD), which were later markedly abbreviated and accompanied by the activation of ATP-sensitive K+ currents (I(K,ATP)). The late decrease in APD was inhibited by glibenclamide (which inhibits I(K,ATP)), but the initial prolongation of the action potential was exacerbated. Treatment with 3-AB or recordings with 10 mM ATP in the patch pipette caused an initial delay in the expression of H2O2-induced changes, but later caused a more pronounced and sustained increase in APD. These interventions delayed the activation of I(K,ATP). Thus enhanced ribosylation (presumably due to activation of DNA repair) appears to be a significant source of ATP depletion under oxidative stress that, via activation of I(K,ATP), mediates oxidative modifications in the action potential.
Ca2+ sequestration as a determinant of chaos and mixed-mode dynamics in agonist-induced vasomotion
Authors: Griffith T. M. , Edwards D. H.
Published: December 2017

We have investigated the contribution of smooth muscle Ca2+ stores to chaotic vasomotion in isolated rabbit ear resistance arteries. In preparations constricted by histamine, exposure to cyclopiazonic acid (CPA) and thapsigargin (TSG), which inhibit the Ca2+-adenosinetriphosphatase (ATPase) pump of the sarcoplasmic reticulum, first induced then abolished highly characteristic mixed-mode oscillatory behavior. The fractal dimension of the vasomotion, which reflects the minimum number of contributing dynamic variables, remained between 2 and 4 until the point at which oscillations disappeared completely. By contrast, ryanodine, which attenuates Ca2+-induced Ca2+ release, decreased the fractal dimension of the responses to <2 in a graded concentration-dependent fashion by selectively suppressing a slow subcomponent of the overall rhythmic activity. CPA-associated oscillations were insensitive to ryanodine but could be abolished by verapamil and modulated in an inhibitory or stimulatory fashion by charybdotoxin, which blocks Ca2+-activated K+ channels, and by ouabain, which blocks the Na+-K+-ATPase. We conclude that there is nonlinear cross talk between CPA/TSG-sensitive Ca2+ stores and a membrane oscillator that regulates Ca2+ influx and that the kinetics of Ca2+ uptake by the CPA/TSG-sensitive pool can be distinguished dynamically from the kinetics of Ca2+ release from its ryanodine-sensitive subcomponent.
Cytokine-induced leukocyte rolling in mouse cremaster muscle arterioles in P-selectin dependent
Authors: Thorlacius H. , Lindbom L. , Raud J.
Published: December 2017

Leukocyte rolling and adhesion are generally observed in venules but rarely observed in arterioles. With the use of intravital microscopy, we found that a 4-h treatment with interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) dose dependently induced leukocyte rolling and adhesion in arterioles of the mouse cremaster muscle. The rolling response lasted more than 24 h and was completely inhibited by treatment with the sulfated polysaccharide fucoidin. Moreover, we found that costimulation with IL-1beta and TNF-alpha for 4 h synergistically increased arteriolar leukocyte rolling, i.e., threshold doses of IL-1beta and TNF-alpha together caused a more than 10-fold increase of rolling in arterioles compared with the sum of the individual responses. This rolling interaction was abolished by treatment with a monoclonal antibody directed against P-selectin (RB40.34), but it apparently was unaffected by a monoclonal antibody against L-selectin (MEL-14). Taken together, our functional data show that IL-1beta and TNF-alpha separately induce and synergistically increase P-selectin-dependent leukocyte rolling and firm adhesion in mouse cremaster arterioles.
Development of inwardly rectifying K+ channel family in rat ventricular myocytes
Authors: Xie L. H. , Takano M. , Noma A.
Published: December 2017

The ATP-sensitive K+ current (I(K,ATP)), the inward rectifier K+ current (I(K1)), and the acetylcholine-activated K+ current (I(K,ACh)) were recorded in fetal, neonatal, and adult rat ventricular myocytes using the patch-clamp technique. The density (pA/pF) of I(K1) increased from gestation day 10 through neonatal day 1 and then decreased after neonatal day 30. The density of I(K,ATP) activated maximally by metabolic inhibition changed in parallel with the I(K1) density, and the density of I(K,ATP) channel distribution was 1.3 times higher than that of I(K1) throughout the development. We failed to observe developmental changes in the single-channel conductance and the mean open time of I(K1) and I(K,ATP) channels. However, the open probability of the I(K,ATP) channel was lower in fetuses, and the sensitivity to ATP was highest in 1-day neonates. I(K,ACh) were present in the ventricle at all stages of development but at a much lower density than in atrium. The relationship between the resting membrane potential and the development of the inwardly rectifying K-channel family is discussed.
K+ and Cl- contribute to resting membrane conductance of cultured porcine endocardial endothelial cells
Authors: Fransen P. , Sys S. U.
Published: December 2017

The conventional whole cell patch-clamp technique was used to measure the resting membrane conductance and membrane currents of single, nonstimulated, cultured endocardial endothelial cells of the porcine right ventricle in different ionic conditions. All cells displayed the barium-sensitive, inwardly rectifying potassium (K+) current (I(Ki)). In 65% of the cells, I(Ki) was the predominant membrane current. The mean zero-current potential (V0) was -61.0 +/- 12.5 mV (+/- SD, n = 45). In 35% of the cells, I(Ki) was superposed on an outwardly rectifying (OR) current. V0 of these cells was more depolarized (-33.5 +/- 22.0 mV, n = 26). High intracellular Cl- (122 instead of 52 mmol/l) activated or increased the OR current and shifted V0 in the direction of the equilibrium potential for Cl-. In cells displaying the OR current, V0 was dependent on extracellular Cl-, indicating the contribution of an OR Cl- current in setting V0. At low intracellular Cl- (6 instead of 52 mmol/l), the OR current was decreased and V0 shifted in the direction of the equilibrium potential for K+. In cells not displaying the OR current, V0 was dependent on extracellular K+ but not on Cl-, indicating major permeability to K+ in these conditions. Block of the OR current by the Cl(-)-channel blockers anthracene-9-carboxylic acid (1 mmol/l), flufenamic acid (100-500 micromol/l), and Zn2+ (100-200 micromol/l) provided further evidence for the anionic nature of the OR current. After inhibition of I(Ki) and the OR Cl- current, a third current component was observed in 50% of the cells. The pharmacology and voltage dependence of this current suggested the presence of Ca2+-activated K+ channels in endocardial endothelial cells. We concluded that the resting membrane conductance of nonstimulated endocardial endothelial cells is mainly determined by the combined activity of inwardly rectifying K+, OR Cl-, and Ca2+-activated K+ channels.
Sympathetic and vascular responses to head-down neck flexion in humans
Authors: Shortt T. L. , Ray C. A.
Published: December 2017

Animal studies have demonstrated increases in sympathetic nerve outflow with vestibular stimulation. The purpose of the present study was to determine whether vestibulosympathetic reflexes are engaged in humans. Muscle sympathetic nerve activity (MSNA), heart rate, arterial pressure, calf blood flow (CBF), and calculated calf vascular resistance (CVR; mean arterial pressure/CBF) were determined during 10 min of baseline (laying prone with chin supported) and 10 min of head-down neck flexion (HDNF). MSNA responses were measured in nine subjects, and calf vascular responses were determined in seven of these subjects. Heart rate increased during the first minute of HDNF (71 +/- 2 to 76 +/- 3 beats/min; P < 0.05) and remained slightly elevated (71 +/- 2 to 74 +/- 3 beats/min; P < 0.05) for the duration of HDNF. Diastolic and mean arterial pressures also increased slightly with HDNF (80 +/- 3 to 82 +/- 3 and 96 +/- 3 to 98 +/- 3 mmHg, respectively; P < 0.05). Systolic arterial pressure did not change significantly during HDNF. CBF decreased 14% (4.63 +/- 0.78 to 3.97 +/- 0.60 ml x min(-1) x 100 ml(-1); P < 0.05), and CVR increased 12% (24.0 +/- 4.3 to 27.4 +/- 4.7 units; P < 0.05) during HDNF. These changes corresponded with significant increases in MSNA during HDNF. MSNA, expressed as burst frequency, increased from 14 +/- 2 to 20 +/- 2 bursts/min (P < 0.05) and increased 63 +/- 23% (P < 0.05) when expressed as the percent change in total activity. All variables returned to baseline during recovery. Thoracic impedance measured in five subjects did not change during HDNF (19.6 +/- 1.2 to 19.7 +/- 1.5 omega), suggesting no major change in central blood volume. The results indicate that HDNF elicits increases in CVR that are mediated by the augmentation of MSNA. Arterial pressure responses and thoracic impedance data suggest that high and low pressure baroreflexes were not the mechanism for sympathetic activation. The immediate increase in MSNA with HDNF suggests a role for vestibulosympathetic reflexes.
Role of activation of calcium-sensitive K+ channels in NO- and hypoxia-induced pial artery vasodilation
Authors: Armstead W. M.
Published: December 2017

It has been previously observed that nitric oxide (NO) contributes to hypoxic pial artery dilation and that both sodium nitroprusside (SNP), a releaser of NO, and hypoxia elicit dilation via activation of ATP-sensitive K+ channels in the newborn pig. Other studies, however, have shown that NO activates calcium-sensitive K+ (K(Ca)) channels. The present study, therefore, was designed to investigate the role of K(Ca)-channel activation in NO and hypoxic dilation and to relate this mechanism to the previously observed role of NO in hypoxic dilation in newborn pigs equipped with closed cranial windows. SNP (10(-8) and 10(-6) M) elicited pial artery dilation that was unchanged in the presence of the K(Ca)-channel antagonist iberiotoxin (10(-7) M; 10 +/- 1 and 20 +/- 1 vs. 9 +/- 1 and 20 +/- 2% for 10(-8) and 10(-6) M SNP in the absence and presence of iberiotoxin, respectively). Responses to S-nitroso-N-acetylpenicillamine and 8-bromoguanosine 3',5'-cyclic monophosphate were similarly unchanged by iberiotoxin. In contrast, iberiotoxin attenuated the dilation resulting from moderate and severe hypoxia (arterial PO2 approximately 35 and 25 mmHg, respectively; 27 +/- 1 vs. 21 +/- 2 and 34 +/- 1 vs. 16 +/- 2% for moderate and severe hypoxia in the absence and presence of iberiotoxin, respectively). Iberiotoxin blocked responses to the K(Ca)-channel agonist NS-1619, whereas responses to the ATP-sensitive K+ agonist cromakalim were unchanged (8 +/- 1 and 15 +/- 1 vs. 1 +/- 1 and 1 +/- 1% for 10(-8) and 10(-6) M NS-1619 in the absence and presence of iberiotoxin, respectively). These data show that NO and guanosine 3',5'-cyclic monophosphate do not elicit dilation via K(Ca)-channel activation. However, activation of K(Ca) channels does contribute to hypoxic pial dilation. Finally, these data suggest that substances other than NO are involved in the contribution of K(Ca)-channel activation to hypoxic pial artery dilation.
Cardiac swelling-induced chloride current depolarizes canine atrial myocytes
Authors: Du X. Y. , Sorota S.
Published: December 2017

The effect of the cardiac swelling-induced chloride current (I(Cl,swell)) on the transmembrane potential was examined. Osmotic swelling affected the resting potassium current through an apparent dilution of intracellular potassium. Inflating cells by applying positive pressure to the patch electrode prevented the effect on the resting potassium current. Inflation depolarized dog atrial myocytes when the recording electrodes contained either 17 or 42 mM Cl-. The depolarization coincided with activation of I(Cl,swell) and was antagonized by the chloride-channel blocker niflumic acid. Substituting extracellular chloride with the more permeant ion SCN- shifted the reversal potential for I(Cl,swell) to more negative values and antagonized inflation-induced depolarization. The depolarization was accentuated by replacing extracellular chloride with a less permeant ion, aspartate. We conclude that activation of I(Cl,swell) in atrial cells causes significant depolarization of the resting membrane. The outward rectification of I(Cl,swell) and the high cell membrane resistance during the action potential plateau suggest that I(Cl,swell) will also have significant effects on atrial action potential configuration.
Cardiac inotropic actions of urocortin in conscious sheep
Authors: Parkes D. G. , Vaughan J. , Rivier J. , Vale W. , May C. N.
Published: December 2017

Urocortin (Ucn) is a recently isolated peptide related to the corticotropin-releasing factor (CRF) family, which can produce hemodynamic and hormonal actions in conscious rats. This study examined in detail the cardiovascular actions of Ucn and CRF after intravenous injection in chronically instrumented, conscious sheep. Injection of Ucn produced dose-dependent changes in cardiac contractility [rate of increase of aortic flow (dF/dt)], maximum aortic flow (Fmax), mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), and coronary blood flow (CF). Ucn injected at 100 micrograms produced a potent increase in dF/dt, from 909 +/- 44 to a maximum of 1,849 +/- 901.min-1.s-1, and in Fmax, from 25.5 +/- 0.8 to 36.6 +/- 1.4 l/min. Cardiac contractility increased within 30 min of injection and remained significantly elevated for up to 24 h. MAP increased from 78 +/- 2 to 90 +/- 3 mmHg, and HR increased from 73 +/- 4 to 103 +/- 9 beats/min. CO rose from 5.0 +/- 0.1 to 5.8 +/- 0.2 l/min, whereas central venous pressure, total peripheral conductance, and stroke volume were unchanged. All Ucn-induced cardiovascular effects were inhibited by prior treatment with the CRF antagonist alpha-helical CRF-(9-41). Equimolar doses of CRF produced little change in any hemodynamic parameter. Both peptides increased plasma levels of adrenocorticotropin and cortisol, with Ucn having a more potent effect than CRF. We have shown for the first time that Ucn can produce potent and long-lasting actions to elevate cardiac contractility in conscious animals.
Expression of a recombinant preproendothelin-1 gene in arteries stimulates vascular contractility
Authors: Schott E. , Tostes R. C. , San H. , Paul M. , Webb R. C. , Nabel E. G.
Published: December 2017

Endothelin (ET)-1 is a potent vasoconstrictor peptide that is elevated in cardiovascular diseases. However, the biological function of ET-1 gene expression within arteries in vivo has not been determined. The effects of ET-1 gene expression were investigated using gene-transfer methods on porcine vascular cells in vitro and porcine arteries in vivo. Transfection of vascular cells with a vector encoding for human preproendothelin-1 cDNA (pVR-ppET) resulted in significant increase in active ET-1 levels in culture supernatant compared with nontransfected cells (P < 0.05). This supernatant contracted rat aortic strips at concentrations 10-fold lower than synthetic ET-1 protein, which was inhibited by the ET-A receptor antagonist BQ-123. Transfection of pVR-ppET into pig iliofemoral arteries resulted in an increase in contractile responses to angiotensin I compared with control vessels (P < 0.05), in contrast to serotonin, phenylephrine, synthetic ET-1, and angiotensin II. A mitogenic effect of recombinant ET-1 on intimal cell growth was not observed. These findings demonstrate that expression of a recombinant ET-1 gene in vivo augments vascular contractility due to an increased sensitivity to angiotensin I, suggesting a role for ET-1 in the pathogenesis of cardiovascular diseases.
Laminar structure of the heart: a mathematical model
Authors: Legrice I. J. , Hunter P. J. , Smaill B. H.
Published: December 2017

A mathematical description of cardiac anatomy is presented for use with finite element models of the electrical activation and mechanical function of the heart. The geometry of the heart is given in terms of prolate spheroidal coordinates defined at the nodes of a finite element mesh and interpolated within elements by a combination of linear Lagrange and cubic Hermite basis functions. Cardiac microstructure is assumed to have three axes of symmetry: one aligned with the muscle fiber orientation (the fiber axis); a second set orthogonal to the fiber direction and lying in the newly identified myocardial sheet plane (the sheet axis); and a third set orthogonal to the first two, in the sheet-normal direction. The geometry, fiber-axis direction, and sheet-axis direction of a dog heart are fitted with parameters defined at the nodes of the finite element mesh. The fiber and sheet orientation parameters are defined with respect to the ventricular geometry such that 1) they can be applied to any heart of known dimensions, and 2) they can be used for the same heart at various states of deformation, as is needed, for example, in continuum models of ventricular contraction.
Autonomic interactions for control of atrial rate are maintained after SA nodal parasympathectomy
Authors: McGuirt A. S. , Schmacht D. C. , Ardell J. L.
Published: December 2017

Autonomic control of atrial rate was evaluated in anesthetized dogs by electrical stimulation of stellate ganglia and/or cervical vagi before and after the intrinsic cardiac right atrial ganglionated plexus (RAGP) was injected with the nicotinic blocker hexamethonium or the membrane stabilizing chemical lidocaine, or the RAGP was surgically removed. Injections of lidocaine or hexamethonium into or surgical removal of the RAGP eliminated the bradycardia elicited by vagal stimulation without reducing the tachycardia induced by stellate stimulation. Yet, after surgical ablation of the RAGP, the tachycardia induced by sympathetic stimulation was still reduced by 94% by parasympathetic stimulation. After injections of hexamethonium or lidocaine into the RAGP were administered, the sympathetically induced tachycardia was reduced by 39 and 85%, respectively, by parasympathetic stimulation. After RAGP ablation, when atrial rate was increased by infusion of beta-adrenergic agonists, parasympathetic stimulation reduced atrial rate by 13%. Sinoatrial (SA) nodal parasympathectomy, produced by disrupting the RAGP, eliminates direct vagal control of the SA node while leaving prejunctional parasympathetic projections to sympathetic afferents innervating the SA node intact.
Hypoxic pHi and function modulation by Na+/H+ exchange and alpha-adrenoreceptor inhibition in heart in vivo
Authors: Portman M. A. , Xiao Y. , Broers B. G. , Ning X. H.
Published: December 2017

Regulation of intracellular pH (pHi) may contribute to maintenance of cardiac contractile function during graded hypoxia in vivo. To test this hypothesis, we disturbed pHi regulation in vivo using two approaches: alpha-adrenoreceptor antagonism with phentolamine (1 mg/kg) (Phen; n = 9); and Na+/H+ exchange inhibition with HOE-642 (2 mg/kg; n = 6) before graded hypoxia in open-chest sheep. Hemodynamic parameters including left ventricular maximal pressure development (dP/dtmax) cardiac index (CI), and left ventricular power were monitored continuously and simultaneously with high-energy phosphate levels and pHi, measured with 31P nuclear magnetic resonance spectroscopy in Phen, HOE-642, and control (Con; n = 9). In subgroups (n = 6) in Con and Phen, coronary flow, myocardial oxygen consumption (MVO2), and lactate uptake were also measured. During hypoxia, the functional parameters left ventricular dP/dtmax, CI, and left ventricular power decreased significantly compared with baseline and Con values. These decreases were preceded by a significant drop (P < 0.05) in pHi from 7.10 +/- 0.04 to 6.69 +/- 0.05 in Phen and corresponded temporally to a pHi drop from 7.10 +/- 0.02 to 6.77 +/- 0.03 in HOE-642. Decreases in pHi in Phen were not preceded by decreases in cardiac function or MVO2. In contrast, cardiac function parameters increased significantly in Con, whereas no significant pHi decrease occurred (7.07 +/- 0.03 to 6.98 +/- 0.04). We conclude that these data indicate that pHi regulation can be disrupted through alpha-adrenergic antagonism or Na+/H(+)-exchange inhibition in vivo. These studies demonstrate that pHi regulation performs a role in the modulation of cardiac function during hypoxia in vivo.
Mechanism of atrioventricular nodal facilitation in the rabbit heart: role of the distal AV node
Authors: Fahy G. J. , Efimov I. , Cheng Y. , Kidwell G. A. , Van Wagoner D. , Tchou P. J. , Mazgalev T.
Published: December 2017

We investigated whether atrioventricular (AV) nodal facilitation is the result of distal AV nodal action potential shortening. Atrial and bundle of His (H) electrograms and microelectrode recordings from proximal and distal AV nodal cells were analyzed in eight superfused rabbit AV node preparations in response to two pacing protocols. In the facilitation protocol, an atrial extrastimulus (A3) was preceded by an atrial impulse (A2) introduced 300, 200, 150, or 125 ms after 30 basic beats (A1). The preexcitation protocol differed from the facilitation protocol by the addition of a premature His depolarization (h2) such that the H1-h2 interval was shorter than the H1-H2 interval. Conduction curves (A3-H3 vs. H2-A3, h2-A3, and A2-A3 intervals) were constructed. Facilitation was demonstrated in all preparations when H2-A3 was used (P = 0.02) but not in the A2-A3 format. Compared with facilitation at the same A1-A2 intervals, preexcitation, despite shortening the distal cellular action potential duration, resulted in longer A3-H3 delays (P = 0.002), shorter A2-A3 intervals, and depression of the proximal nodal cellular response. Thus facilitation does not result from altered distal AV nodal characteristics and instead is a manifestation of an uncontrolled pacing protocol-dependent modulation of proximal AV nodal function.
Effect of ventricular contraction, pressure, and wall stretch on vessels at different locations in the wall
Authors: Vis M. A. , Bovendeerd P. H. , Sipkema P. , Westerhof N.
Published: December 2017

A cylindrical model of the heart was used to calculate the influence of ventricular filling and (isovolumic and isobaric) contraction on the cross-sectional area and resistance of a subendocardial and subepicardial maximally dilated arteriole and venule. Contraction is defined as the difference between static diastole and static systole. Furthermore, a small piece of rectangular myocardium containing the vessel was modeled to distinguish between the individual contributions of contractility (i.e., myocardial elastic properties), ventricular pressure, and local circumferential stretch to the changes in vascular area and resistance during contraction. Calculations were performed assuming the muscle fibers ran in either an apex-to-base or a circumferential direction. The results were similar for the two directions. Assuming constant, physiological arteriolar and venular pressures of 45 and 10 mmHg, respectively, coronary blood vessels were predicted not to collapse during ventricular contraction. Moreover, vascular area reduction was found to be larger for the arteriole (approximately 50%) than for the venule (approximately 30%) during both isovolumic and isobaric contractions. Consequently, arteriolar resistance was found to increase more than venular resistance (approximately 340 and 120%, respectively). Subendocardial area reductions were found to be somewhat smaller than subepicardial area reductions for the venule (by approximately 10%) but not for the arteriole. Contractility was found to be the main contributor to the changes in vascular area and resistance in the subepicardium but to contribute by < 50% to the changes in the subendocardium. Because pressure does, but stretch does not, contribute to the area change during isovolumic contraction and the reverse is true during isobaric contraction, it was concluded that although changes in vascular area and resistance may be similar for different contractions, the causes for these changes are very different.