bluuebunny/crossref_metadata_2025 huggingface dataset:
Cs+inhibits spontaneous Ca2+release from sarcoplasmic reticulum of skinned cardiac myocytes
Authors: Kawai Makoto , Hussain Munir , Orchard Clive H.
Published: December 2017

The effect of Cs+on the function of the cardiac sarcoplasmic reticulum (SR) has been investigated in skinned cardiac myocytes. Isolated rat ventricular myocytes were permeabilized using saponin and then perfused with a solution containing 150 nmol/l Ca2+and 10 μmol/l fura 2. Fura 2 fluorescence from the skinned cell was monitored to assess SR Ca2+release. The frequency of spontaneous Ca2+release from the SR decreased when K+in the bathing solution was completely replaced with Cs+. Cs+had little effect on the amplitude of spontaneous release but prolonged both the rise time and decay time. The SR Ca2+content, assessed by application of caffeine, was reduced in the Cs+solution. Cyclopiazonic acid produced effects similar to those of Cs+. Extracellular Cs+(20 mmol/l) increased the amplitude of the Ca2+transient and the SR Ca2+content in intact field-stimulated cells but had little effect on the Ca2+transient when the amplitude and duration of depolarization were kept constant using voltage clamp. These data suggest that Cs+slows Ca2+movement across the SR membrane, possibly by blocking the SR K+channel, but has additional effects in intact cells that overcome its inhibitory effects on the SR.
β-Adrenoceptor activation and PKA regulate delayed rectifier K+channels of vascular smooth muscle cells
Authors: Aiello E. Alejandro , Malcolm A. Todd , Walsh Michael P. , Cole William C.
Published: December 2017

Macroscopic 4-aminopyridine (4-AP)-sensitive, delayed rectifier K+current of vascular smooth muscle cells is increased during β-adrenoceptor activation with isoproterenol via a signal transduction pathway involving adenylyl cyclase and cAMP-dependent protein kinase (PKA) (Aiello, E. A., M. P. Walsh, and W. C. Cole. Am. J. Physiol. 268 ( Heart Circ. Physiol. 37): H926–H934, 1995.). In this study, we identified the single delayed rectifier K+(KDR) channel(s) of rabbit portal vein myocytes affected by treatment with isoproterenol or the catalytic subunit of PKA. 4-AP-sensitive KDRchannels of 15.3 ± 0.6 pS ( n = 5) and 14.8 ± 0.6 pS ( n = 5) conductance, respectively, were observed in inside-out (I-O) and cell-attached (C-A) membrane patches in symmetrical KCl recording conditions. The kinetics of activation (time constant of 10.7 ± 3.02 ms) and inactivation (fast and slow time constants of 0.3 and 2.5 s, respectively) of ensemble currents produced by these channels mimicked those reported for inactivating, 4-AP-sensitive whole cell KDRcurrent of vascular myocytes. Under control conditions, the open probability ( NPo) of KDRchannels of C-A membrane patches at −40 mV was 0.014 ± 0.005 ( n = 8). Treatment with 1 μM isoproterenol caused a significant, approximately threefold increase in NPoto 0.041 ± 0.02 ( P < 0.05). KDRchannels of I-O patches exhibited rundown after ∼5 min, which was not affected by ATP (5 mM) in the bath solution. Treatment with the purified catalytic subunit of PKA (50 nM; 5 mM ATP) restored KDRchannel activity and caused NPoto increase from 0.011 ± 0.003 to 0.138 ± 0.03 ( P < 0.05; n = 11). These data indicate that small-conductance, 15-pS KDRchannels are responsible for inactivating the macroscopic delayed rectifier K+current of rabbit portal vein myocytes and that the activity of these channels is enhanced by a signal transduction mechanism involving β-adrenoceptors and phosphorylation by PKA at a membrane potential consistent with that observed in the myocytes in situ.
Mechanisms of cardioprotection by peroxynitrite in myocardial ischemia and reperfusion injury
Authors: Nossuli Tareck O. , Hayward Reid , Jensen David , Scalia Rosario , Lefer Allan M.
Published: December 2017

Peroxynitrite (ONOO−), an intermediate formed from the equimolar interaction of nitric oxide (NO) and superoxide, is thought to be an important mediator of tissue injury in myocardial ischemia-reperfusion. However, physiologically relevant (i.e., maximally achievable) concentrations of ONOO−significantly decreased neutrophil-endothelium interactions in the rat mesentery. We therefore examined the dose-response relationship of infusion of different concentrations of ONOO−in a feline model of myocardial ischemia-reperfusion and provide data on the cellular mechanisms responsible for these observed effects. Cats subjected to 90 min of ischemia followed by 270 min of reperfusion were infused with different concentrations of ONOO−10 min before reperfusion and continuing throughout reperfusion. We observed that infusion of 2 μM ONOO−provided significant cardioprotection, whereas either 0.2 or 20 μM ONOO−did not protect. ONOO−at 2 μM also preserved coronary endothelial function, decreased P-selectin expression, and attenuated polymorphonuclear leukocyte (PMN) adherence to the vascular endothelium. ONOO−did not exert its cardioprotective effects by acting as a direct NO donor in solution. However, in vitro, ONOO−can react with glutathione to form S-nitrosoglutathione, which can act as an NO carrier and exert beneficial effects. Thus only maximally achievable concentrations of ONOO−exert significant cardioprotective effects, in part by decreasing surface expression of P-selectin and decreasing PMN-endothelium interactions.
α1-Adrenergic activation of myocardial Na-K-2Cl cotransport involving mitogen-activated protein kinase
Authors: Andersen Geir Øystein , Enger Mette , Thoresen G. Hege , Skomedal Tor , Osnes Jan-Bjørn
Published: December 2017

The translocation mechanisms involved in the α1-adrenoceptor-stimulated efflux of the potassium analog86Rb+were studied in isolated rat hearts. Phenylephrine (in the presence of a β-blocker) increased the efflux of86Rb+and42K+, and the Na-K-2Cl (or K-Cl) cotransport inhibitor bumetanide reduced the response by 42 ± 11%. Furosemide inhibited the response with a lower potency than that of bumetanide. The bumetanide-insensitive efflux was largely sensitive to the K+channel inhibitor 4-aminopyridine. Inhibitors of the Na+/H+exchanger or the Na+-K+pump had no effect on the increased86Rb+efflux. The activation of the Na-K-2Cl cotransporter was dependent on the extracellular signal-regulated kinase (ERK) subgroup of the mitogen-activated protein (MAP) kinase family. Phenylephrine stimulation increased ERK activity 3.4-fold. PD-98059, an inhibitor of the ERK cascade, reduced both the increased86Rb+efflux and ERK activity. Specific inhibitors of protein kinase C and Ca2+/calmodulin-dependent kinase II had no effect. In conclusion, α1-adrenoceptor stimulation increases86Rb+efflux from the rat heart via K+channels and a Na-K-2Cl cotransporter. Activation of the Na-K-2Cl cotransporter is apparently dependent on the MAP kinase pathway.
Simultaneous LV and RV volumes by conductance catheter: effects of lung insufflation on parallel conductance
Authors: Szwarc Richard S. , Ball Howard A.
Published: December 2017

One aspect in the measurement of ventricular volume using the conductance catheter technique is the assessment of parallel electrical conductivity of structures extrinsic to the ventricular blood pool. Because it is sometimes necessary to make volume measurements during ventilation or spontaneous respiration, the extent to which parallel conductance may vary with lung insufflation was investigated. Anesthetized pigs (11–15 kg) were ventilated and instrumented with both left (LV) and right ventricular (RV) conductance and pressure-tip catheters and end-hole catheters for injection of hypertonic saline into the inferior vena cava and pulmonary artery. Data were recorded during ventilation with tidal volumes of 10 and 20 ml/kg, and the associated fluctuations to LV and RV end-diastolic (EDV) and stroke (SV) volumes were measured. With the use of a saline dilution technique, parallel conductance (Vc) was determined for each ventricle with the ventilator off and lungs insufflated to 0, 10, and 20 ml/kg. Whereas ventilation caused marked oscillations in LV and RV EDV and SV, these variations could not be attributed to Vc, which remained statistically unchanged from their baseline values of 34.1 ± 3.1 in the LV and 31.1 ± 4.4 in the RV. These results indicate that the fluctuations that occur in conductance catheter-derived LV and RV volume signals with ventilation are not caused by any significant changes to parallel conductance.
Hypothalamic angiotensin receptor subtypes in normotensive and hypertensive rats
Authors: Han N. L. , Sim M. K.
Published: December 2017

The binding of125I-labeled [Sar1,Ile8]angiotensin II to the hypothalamic membranes of the normotensive Wistar-Kyoto rat (WKY) and the spontaneously hypertensive rat (SHR) was studied. Displacement experiments with four centrally active angiotensins, losartan, and PD-123319 confirm the known existence of angiotensin AT1and AT2receptors in the rat hypothalamus. The values of the inhibitory constants for angiotensin II and PD-123319 in the SHR were significantly lower than the corresponding values in the WKY, indicating the possible existence of high-affinity hypothalamic AT1and AT2receptors for the two ligands in the SHR. The angiotensin AT1receptor was further separated into a 5′-guanylyl imidodiphosphate-sensitive and -nonsensitive subtype, indicating that one of the subtypes is G protein coupled. The SHR has significantly higher numbers of measurable AT1-receptor subtypes as well as AT2receptor subtypes. The former data support the findings of other investigators showing that the hypothalamus of the SHR expressed more AT1Aand AT1BmRNAs than that of the normotensive rat. Des-Asp1-angiotensin I, which is known to attenuate the central pressor action of angiotensin II and angiotensin III, acts on both the AT1and AT2receptors, although it has a higher affinity for the AT1receptors. The overall increase in the number of AT1and AT2receptors in the SHR is in line with the contention that the brain of the hypertensive rat, compared with that of the WKY, has a hyperactive renin-angiotensin system.
Enhanced in vivo α1- and α2-adrenoceptor-mediated venoconstriction with indomethacin in humans
Authors: Callow Ian D. , Campisi Paolo , Lambert Michelle L. , Feng Qingping , Arnold J. Malcolm O.
Published: December 2017

Vasodilator prostaglandins are released in vitro from endothelium during adrenergic stimulation. We hypothesized that indomethacin would block this production in vivo and increase venoconstriction to α1- and α2-stimulation but not to the nonadrenergic agonist PGF2α. Hand vein distension was measured in 24 normal subjects (23.0 ± 0.5 yr) during local infusions of phenylephrine (8–12,000 ng/min), clonidine (3–7,000 ng/min), or PGF2α(1–2,048 ng/min) plus indomethacin (3 μg/min) versus saline on two separate days. Dose-dependent venoconstriction to phenylephrine occurred in all subjects, with a parallel shift to the left with indomethacin ( P = 0.003) and a decrease in the phenylephrine 50% effective dose (1,009 vs. 241 ng/min, geometric means, P = 0.012). Venoconstriction to clonidine was more variable, with most subjects eliciting a biphasic response (initial venoconstriction followed by attenuation). With indomethacin, the dose-response curve was displaced up and to the left ( P = 0.005), and peak venoconstriction was increased (51.1 ± 6.8 vs. 27.2 ± 5.3% of control, P = 0.018) without a biphasic response. In all subjects, PGF2αelicited dose-dependent venoconstriction that was not altered by indomethacin. Thus venous α1- and α2-stimulation results in release of vasodilator prostaglandins that antagonize the venoconstrictor response. This modulates the sympathetic response of venous smooth muscle and may be important in diseases with endothelial dysfunction.
Functional and metabolic effects of extracellular magnesium in normoxic and ischemic myocardium
Authors: Headrick John P. , McKirdy James C. , Willis Roger J.
Published: December 2017

Metabolic and functional responses to extracellular Mg2+concentration ([Mg2+]o) were studied in perfused rat heart. Elevations of [Mg2+]ofrom 1.2 to 2.4, 5.0, and 8.0 mM dose dependently reduced contractile function and myocardial oxygen consumption (MV˙o2) up to 80%. Intracellular Mg2+concentration ([Mg2+]i) remained stable (0.45–0.50 mM) during perfusion with 1.2–5.0 mM [Mg2+]obut increased to 0.81 ± 0.14 mM with 8.0 mM [Mg2+]o. Myocardial ATP was unaffected by [Mg2+]o,phosphocreatine (PCr) increased up to 25%, and Pideclined by up to 50%. Free energy of ATP hydrolysis (Δ GATP) increased from −60 to −64 kJ/mol. Adenosine efflux declined in parallel with changes in MV˙o2and [AMP]. At comparable workload and MV˙o2, the effects of [Mg2+]oon cytosolic free energy were mimicked by reduced extracellular Ca2+concentration ([Ca2+]o) or Ca2+antagonism with verapamil. Moreover, functional and energetic effects of [Mg2+]owere reversed by elevated [Ca2+]o. Despite similar reductions in preischemic function and MV˙o2, metabolic and functional recovery from 30 min of global ischemia was enhanced in hearts treated with 8.0 mM [Mg2+]ovs. 2.0 μM verapamil. It is concluded that 1) 1.2–8.0 mM [Mg2+]oimproves myocardial cytosolic free energy indirectly by reducing metabolic rate and Ca2+entry; 2) [Mg2+]idoes not respond rapidly to elevations in [Mg2+]ofrom 1.2 to 5.0 mM and is uninvolved in acute functional and metabolic responses to [Mg2+]o; 3) adenosine formation in rat heart is indirectly reduced during elevated [Mg2+]o; and 4) 8.0 mM [Mg2+]oprovides superior protection during ischemia-reperfusion compared with functionally equipotent Ca2+channel blockade.
Dynamics of heart rate response to sympathetic nerve stimulation
Authors: Mokrane Abdelkader , Nadeau Réginald
Published: December 2017

Electrical stimulation of the right cardiac sympathetic nerve was used to achieve a step increase of norepinephrine concentration at the sinus node. The heart rate (HR) response to sympathetic stimulation was characterized by a first-order process with a time delay. For moderate to high intensities of stimulation the mean delay and time constant were 0.7 and 2.1 s, respectively, and for low intensities of stimulation they were 0.4 and 1.1 s, respectively. From the analysis of the HR response to different patterns of nerve stimulation, in vivo neurotransmitter kinetics were estimated. The time constant of norepinephrine dissipation averaged ∼9 s. These results combined with computer simulations revealed two facets of sympathetic neural control of HR: 1) negligible role of the sympathetic system in beat-to-beat regulation of HR under stationary conditions and 2) ability of HR to react relatively quickly (within a few seconds) to sharp increases in sympathetic nerve traffic.
Regional differences in effects of 4-aminopyridine within the sinoatrial node
Authors: Boyett M. R. , Honjo H. , Yamamoto M. , Nikmaram M. R. , Niwa R. , Kodama I.
Published: December 2017

4-Aminopyridine (4-AP)-sensitive transient outward current ( I to) has been observed in the sinoatrial node, but its role is unknown. The effect of block of I to by 5 mM 4-AP on small ball-like tissue preparations (diameter ∼0.3–0.4 mm) from different regions of the rabbit sinoatrial node has been investigated. 4-AP elevated the plateau, prolonged the action potential, and decreased the maximum diastolic potential. Effects were greater in tissue from the periphery of the node than from the center. In peripheral tissue, 4-AP abolished the action potential notch, if present. 4-AP slowed pacemaker activity of peripheral tissue but accelerated that of central tissue. Differences in the response to 4-AP were also observed between tissue from more superior and inferior regions of the node. In the intact sinoatrial node, 4-AP resulted in a shift of the leading pacemaker site consistent with the regional differences in the response to 4-AP. It is concluded that 4-AP-sensitive outward current plays a major role in action potential repolarization and pacemaker activity in the sinoatrial node and that its role varies regionally.
Effects of red and white wine on endothelium-dependent vasorelaxation of rat aorta and human coronary arteries
Authors: Flesch Markus , Schwarz Andreas , Böhm Michael
Published: December 2017

Beneficial effects of wine on myocardial infarction mortality may be because of its vasodilatory properties. This study investigated whether the vasodilatory activity involves the endothelium and is specific for certain wines. Effects of different red and white wines and phenolic grape ingredients on vascular tension and cGMP content were studied in human coronary arteries and rat aortic rings in vitro. Only French and Italian red wines produced “en barrique” (Bordeaux, Châteauneuf du Pape, Barolo) (1:1,000, vol/vol), quercetin (1–100 μM), and tannic acid (1–100 μg/ml) decreased tension of precontracted vascular rings and increased vascular cGMP content (both P < 0.001). The effects were abolished after endothelial denudation and reversible by nitric oxide synthase inhibition. Red wines not produced en barrique (Valpolicella, Ahr Spätburgunder), white wines (en barrique-produced Rioja, Chardonnay, Mosel-Riesling), and ethanol did not affect vascular tension or cGMP content. Thus endothelium-dependent vasodilatory effects appear to be specific for red barrique wines, possibly because of their high content of phenolic substances. Divergent effects of wines indicate that a general view on the effects of wine and alcoholic beverages is not warranted.
Demonstration of an early and a late phase of ischemic preconditioning in mice
Authors: Guo Yiru , Wu Wen-Jian , Qiu Yumin , Tang Xian-Liang , Yang Zequan , Bolli Roberto
Published: December 2017

It is unknown whether ischemic preconditioning (PC; either early or late) occurs in the mouse. The goal of this study was to answer this question and to develop a reliable and physiologically relevant murine model of both early and late ischemic PC. A total of 201 mice were used. In nonpreconditioned open-chest animals subjected to 30 min of coronary occlusion followed by 24 h of reperfusion, infarct size (tetrazolium staining) averaged 52% of the region at risk. When the 30-min occlusion was performed 10 min after a PC protocol consisting of six cycles of 4-min occlusion and 4-min reperfusion, infarct size was reduced by 75%, indicating an early PC effect. When the 30-min occlusion was performed 24 h after the same PC protocol, infarct size was reduced by 48%, indicating a late PC effect. In mice in which the 30-min occlusion was followed by 4 h of reperfusion, infarct size was similar to that observed after 24 h of reperfusion, indicating that a 4-h reperfusion interval is sufficient to detect the final extent of cell death in this model. Fundamental physiological variables (body temperature, arterial oxygenation, acid-base balance, heart rate, and arterial pressure) were measured and found to be within normal limits. Taken together, these results demonstrate that, in the mouse, a robust infarct-sparing effect occurs during both the early and the late phases of ischemic PC, although the early phase is more powerful. This murine model is physiologically relevant, provides reliable measurements, and should be useful for elucidating the cellular mechanisms of ischemic PC in genetically engineered animals.
Nifedipine increases microvascular permeability via a direct local effect on postcapillary venules
Authors: Taherzadeh Morteza , Das Asit K. , Warren John B.
Published: December 2017

Calcium-channel antagonist drugs are prescribed widely for angina and hypertension. A limiting side effect is edema, which can make heart failure worse. We show that nifedipine, a dihydropyridine-type calcium-channel antagonist, can increase vascular permeability in rat skeletal muscle and skin when injected locally. In nifedipine-injected cremaster muscle, the copper content, used to quantify Monastral blue dye accumulation, was 15.0 ± 2.4 μg/g compared with 5.3 ± 0.7 μg/g in control preparations ( P < 0.05). The injection of nifedipine in rat skin in vivo increased local plasma leakage in injected sites from 5.5 ± 1.1 μl in control sites to 9.9 ± 2.5, 17.0 ± 2.4, 24.3 ± 5.9, and 23.3 ± 5.4 μl in sites injected with 10−10, 10−9, 10−8, or 10−7.2 mol/site, respectively ( P < 0.05 in each case compared with control). Vascular labeling techniques using light microscopy, electron microscopy, and microanalysis show that the microvascular site of leakage is not from capillaries but from postcapillary venules of 12–36 μm in diameter, the same site that controls the edema response in inflammation. Nifedipine can act within the microcirculation to increase the permeability of the postcapillary venule.
Potassium channels mediate dilatation of cerebral arterioles in response to arachidonate
Authors: Sobey Christopher G. , Heistad Donald D. , Faraci Frank M. ,   (With the Technical Assistance of Dale Kinzenbaw)
Published: December 2017

We tested the hypothesis that cerebral vasodilatation in response to arachidonate is dependent on activation of cyclooxygenase and cytochrome P-450 pathways and formation of endogenous reactive oxygen species and is mediated by activation of potassium channels. The diameter of cerebral arterioles was measured using cranial windows in anesthetized rats. Under control conditions [baseline diameter = 45 ± 1 μm (mean ± SE)], arachidonate (1–100 μM) and papaverine (10–50 μM) produced concentration-dependent vasodilatation. Cerebral vasodilator responses to arachidonate, but not papaverine, were abolished during topical application of indomethacin (10 μM, an inhibitor of cyclooxygenase) or catalase (100 U/ml, which inactivates hydrogen peroxide). In contrast, clotrimazole (10 μM) and 17-ODYA (20 μM), inhibitors of cytochrome P-450 activity, had no effect on dilator responses of cerebral arterioles to arachidonate. Superoxide dismutase (SOD, 100 U/ml) had no effect on vasodilator responses to papaverine or lower concentrations of arachidonate, whereas dilator responses to 100 μM arachidonate were inhibited modestly (by 22%) by SOD. Similarly, deferoxamine (1 mM) partly inhibited dilator responses to 10 and 100 μM arachidonate (by ∼30% at each concentration). Tetraethylammonium ion (1 mM) or iberiotoxin (50 nM), inhibitors of calcium-activated potassium channels, markedly inhibited vasodilatation in response to arachidonate (by 70–90%) but not papaverine. These findings suggest that dilatation of cerebral arterioles in response to arachidonate is mediated largely by endogenously formed reactive oxygen species, which are generated from cyclooxygenase activity, and activation of calcium-activated potassium channels. Thus activation of potassium channels appears to be a major mechanism of cerebral vasodilatation in response to reactive oxygen species produced endogenously.
Intracellular chloride activity increases in guinea pig ventricular muscle during simulated ischemia
Authors: Lai Zhong-Fang , Nishi Katsuhide
Published: December 2017

We investigated the effects of simulated ischemia on intracellular Cl− activity ([Cl−]i) in isolated guinea pig ventricular papillary muscles using ion-selective microelectrode techniques. Simulated ischemia in ventricular muscles was produced by stopping the flow of superfusion and immersing preparations in mineral oil as previously described [B. Vanheel, L. Leybaert, A. De Hemptinne, and I. Leusen. Am. J. Physiol. 257 ( Cell Physiol. 26): C365–C379, 1989; Z. F. Lai, J. Liu, and K. Nishi. Jpn. J. Pharmacol. 72: 161–174, 1996]. When preparations were exposed to paraffin oil for 15 min, [Cl−]imarkedly increased and the peak magnitude of [Cl−]ireached 55.3 ± 2.5 mM from 18.7 ± 3.5 mM, whereas membrane potentials ( V m) depolarized from −82.5 ± 1.1 to −54.7 ± 2.4 mV ( n = 6 muscles from 6 animals). SITS (0.5 mM), a known blocker of the Cl−/[Formula: see text]exchanger, suppressed the ischemia-induced depolarization of V m and delayed the onset of the ischemia-induced increase in [Cl−]ibut did not suppress the magnitude of the increase of [Cl−]i. Under Cl−-free conditions created by replacing Cl−with equimolar gluconate, the increase in [Cl−]iduring ischemia was transient and suppressed by >60% compared with that in normal-Cl− conditions (peak value was 20.3 ± 1.7 mM, n = 6 muscles from 6 animals). The present results provide direct evidence that [Cl−]iin ventricular muscle increases in ischemic conditions in quiescent guinea pig ventricular muscle, suggesting that activation of the Cl−/[Formula: see text]exchanger by ischemia would partially contribute to the elevation of [Cl−]iduring the initial stage of ischemia.
Dynamic restitution of action potential duration during electrical alternans and ventricular fibrillation
Authors: Koller Marcus L. , Riccio Mark L. , Jr. Robert F. Gilmour
Published: December 2017

The restitution kinetics of action potential duration (APD) were investigated in paced canine Purkinje fibers (P; n = 9) and endocardial muscle (M; n = 9), in isolated, perfused canine left ventricles during ventricular fibrillation (VF; n = 4), and in endocardial muscle paced at VF cycle lengths (simulated VF; n = 4). Restitution was assessed with the use of two protocols: delivery of a single extrastimulus after a train of stimuli at cycle length = 300 ms (standard protocol), and fixed pacing at short cycle lengths (100–300 ms) that induced APD alternans (dynamic protocol). The dynamic protocol yielded a monotone increasing restitution function with a maximal slope of 1.13 ± 0.13 in M and 1.14 ± 0.17 in P. Iteration of this function reproduced the APD dynamics found experimentally, including persistent APD alternans. In contrast, the standard protocol yielded a restitution relation with a maximal slope of 0.57 ± 0.18 in M and 0.84 ± 0.20 in P, and iteration of this function did not reproduce the APD dynamics. During VF, the restitution kinetics at short diastolic interval were similar to those determined with the dynamic protocol (maximal slope: 1.72 ± 0.47 in VF and 1.44 ± 0.49 in simulated VF). Thus APD dynamics at short coupling intervals during fixed pacing and during VF were accounted for by the dynamic, but not the standard, restitution relation. These results provide further evidence for a strong relationship among the kinetics of electrical restitution, the occurrence of APD alternans, and complex APD dynamics during VF.
Influence of age on arterial baroreflex inhibition of sympathetic nerve activity in healthy adult humans
Authors: Davy Kevin P. , Tanaka Hirofumi , Andros Elizabeth A. , Gerber John G. , Seals Douglas R.
Published: December 2017

Resting levels of muscle sympathetic nerve activity (MSNA) increase markedly with age in healthy adult humans. An age-related reduction in arterial baroreflex inhibition of MSNA could contribute to these elevations. To test this hypothesis, we measured MSNA using peroneal microneurography in young (age, 25 ± 1 yr; n = 8) and older (69 ± 1 yr; n = 7) healthy normotensive men before (baseline control) and during graded constant infusion of phenylephrine hydrochloride (0.5–2.0 μg ⋅ kg−1 ⋅ min−1) that produced a sustained ∼10-mmHg increase in arterial blood pressure. Central venous pressure was controlled at baseline levels (±1 mmHg) using lower body negative pressure. Resting MSNA was ∼95% higher in the older compared with the young subjects (43 ± 5 vs. 22 ± 3 bursts/min; P < 0.05). However, arterial baroreflex MSNA inhibitory responsiveness was similar in the older compared with the young subjects (254 ± 112 vs. 259 ± 40 arbitrary integration units/mmHg, respectively), although the percent reduction in MSNA was smaller in the older men (8.9 ± 0.7 vs. 5.2 ± 1.1%/mmHg), due to their elevated baseline levels. The reflex increase in the R-R interval was not different in the two groups (13 ± 10 vs. 16 ± 7 ms/mmHg). In summary, our findings suggest that arterial baroreflex inhibition of MSNA is preserved with age in healthy normotensive adult humans. As such, this mechanism does not appear to contribute to the age-related rise in tonic MSNA.
Mechanisms responsible for enhanced inflammatory response to ischemia-reperfusion in diabetes
Authors: Salas Azucena , Panés Julián , Elizalde J. Ignasi , Casadevall Maria , Anderson Donald C. , Granger D. Neil , Piqué Josep M.
Published: December 2017

The objective of the present study was to assess the role of lipid mediators and adhesion molecule expression in exacerbation of ischemia-reperfusion-induced inflammatory response in diabetes. Leukocyte-endothelial cell interactions were studied in mesenteric venules by intravital microscopy. Endothelial expression of intercellular adhesion molecule (ICAM)-1 was measured by the double-radiolabeled monoclonal antibody technique, and β2-integrin expression was measured by flow cytometry. Ischemia-reperfusion elicited significantly larger increases in leukocyte adhesion and emigration in diabetic rats that were prevented by a platelet-activating factor (PAF)-receptor antagonist or a leukotriene synthesis inhibitor. Leukotriene B4(LTB4) superfusion induced similar leukocyte recruitment in diabetic and control rats, whereas PAF elicited larger increases in diabetic rats. CD11a, but not CD11b, expression was higher in leukocytes from diabetic animals. Endothelial ICAM-1 in mesentery and in intestine did not differ between diabetic and control rats. These results indicate that diabetes is associated with an enhanced response to ischemia-reperfusion that depends on both PAF and leukotrienes. An increased sensitivity to PAF, along with an increased CD11a expression, may account for the exaggerated inflammatory response to ischemia-reperfusion in diabetes.
Ischemic preconditioning triggers tyrosine kinase signaling: a potential role for MAPKAP kinase 2
Authors: Maulik Nilanjana , Yoshida Tetsuya , Zu You-Li , Sato Motoaki , Banerjee Anirban , Das Dipak K.
Published: December 2017

Myocardial adaptation to ischemia has been shown to activate protein tyrosine kinase, potentiating activation of phospholipase D, which leads to the stimulation of mitogen-activated protein (MAP) kinases and MAP kinase-activated protein (MAPKAP) kinase 2. The present study sought to further examine the signal transduction pathway for the MAPKAP kinase 2 activation during ischemic adaptation. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase, whereas SB-203580 was used to inhibit p38 MAP kinases. Western blot analysis demonstrated that p38 MAP kinase is phosphorylated during ischemic stress adaptation. Phosphorylation of p38 MAP kinase was blocked by genistein, suggesting that activation of p38 MAP kinase during ischemic adaptation is mediated by a tyrosine kinase signaling pathway. MAPKAP kinase 2 was estimated by following in vitro phosphorylation with recombinant human heat shock protein 27 as specific substrate for MAPKAP kinase 2. Again, both genistein and SB-203580 blocked the activation of MAPKAP kinase 2 during myocardial adaptation to ischemia. Immunofluorescence microscopy with anti-p38-antibody revealed that p38 MAP kinase is primarily localized in perinuclear regions. p38 MAP kinase moves to the nucleus after ischemic stress adaptation. After ischemia and reperfusion, cytoplasmic striations in the myocytes become obvious, indicating translocation of p38 MAP kinase from nucleus to cytoplasm. Corroborating these results, myocardial adaptation to ischemia improved the left ventricular functions and reduced myocardial infarction that were reversed by blocking either tyrosine kinase or p38 MAP kinase. These results demonstrate that myocardial adaptation to ischemia triggers a tyrosine kinase-regulated signaling pathway, leading to the translocation and activation of p38 MAP kinase and implicating a role for MAPKAP kinase 2.
Reflex pressor response to arterial phenylbiguanide: role of abdominal sympathetic visceral afferents
Authors: Fu Liang-Wu , Longhurst John C.
Published: December 2017

Phenylbiguanide (PBG), a 5-HT3 (serotonin) receptor agonist, has been used in many studies as a “selective” agonist to elicit reflex bradycardia and hypotension through activation of cardiac and pulmonary vagal afferents. Because we have shown that endogenous 5-HT stimulates ischemically sensitive abdominal sympathetic afferents through 5-HT3 receptors, we investigated the possibility that left ventricular (LV) and intra-arterial administration of PBG may evoke a competing reflex response by increasing the activity of sympathetic visceral afferents in anesthetized cats. Mean arterial pressure (MAP) and heart rate (HR) were monitored. When both vagal and sympathetic afferents were intact, PBG (40 μg/kg, injected into the LV) significantly decreased MAP and HR in 8 of 10 cats but increased MAP in the remaining 2 cats. After bilateral cervical vagotomy, LV PBG significantly increased MAP. PBG (40 μg/kg ia) significantly increased MAP and HR, whereas intravenous PBG significantly decreased MAP and HR ( n = 10 cats). Furthermore, the pressor response to PBG (40 μg /kg ia) was reduced by 68% ( P < 0.05; n = 4 cats) by celiac and mesenteric ganglionectomies. In studies of single-unit abdominal sympathetic afferents, intra-arterial but not intravenous PBG (40 μg/kg) significantly increased activity of 10 ischemically sensitive afferents but not ischemically insensitive afferents. Blockade of 5-HT3 receptors with tropisetron (200 μg/kg iv) eliminated the response of the afferents and the pressor response to PBG. These data indicate that PBG administered into the LV usually, but not always, evokes a depressor response that is converted to a pressor response following cervical vagotomy. Also, intra-arterial PBG induces a pressor response by stimulating 5-HT3receptors largely associated with ischemically sensitive abdominal sympathetic afferents.
Stimulation of cerebellar fastigial nucleus inhibits interleukin-1β-induced cerebrovascular inflammation
Authors: Galea Elena , Glickstein Sara B. , Feinstein Douglas L. , Golanov Eugene V. , Reis Donald J.
Published: December 2017

Electrical stimulation of the cerebellar fastigial nucleus (FN) in rat protects the brain against ischemia. We studied whether FN could reduce the cerebrovascular inflammation as a mechanism of protection. FN or dentate nucleus (sham controls) was electrically stimulated for 1 h, and 72 h later rats were either injected with interleukin (IL)-1β into the striata or processed to analyze inflammatory responses in isolated brain microvessels. In striata, IL-1β induced a recruitment of leukocytes that was reduced by 50% by FN stimulation. In isolated microvessels, IL-1β induced the transient and dose-dependent upregulation of the mRNAs encoding for the inducible nitric oxide synthase (NOS-2), intercellular adhesion molecule 1 (ICAM-1), and inhibitory κB-α (IκB-α), an inhibitor of nuclear factor-κB. FN stimulation decreased the upregulation of NOS-2 and ICAM-1 mRNAs, whereas it increased IκB-α mRNA expression. Dentate nucleus stimulation did not mimic the FN actions. These findings suggest that FN stimulation may render brain microvessels refractory to IL-1β by overproduction of IκB-α and support the hypothesis that alteration of microvascular inflammation may contribute to the central neurogenic neuroprotection elicited from the FN.
14,15-Epoxyeicosatrienoic acid inhibits prostaglandin E2production in vascular smooth muscle cells
Authors: Fang Xiang , Moore Steven A. , Stoll Lynn L. , Rich Gretchen , Kaduce Terry L. , Weintraub Neal L. , Spector Arthur A.
Published: December 2017

14,15-Epoxyeicosatrienoic acid (EET), a cytochrome P-450 epoxygenase product of arachidonic acid (AA), reduced PGE2formation by 40–75% in porcine aortic and murine brain microvascular smooth muscle cells. The inhibition was reversed 6–10 h after removal of 14,15-EET from the medium and was regioisomeric specific; 8,9-EET produced a smaller effect, whereas 11,12- and 5,6-EET were ineffective. Although the cells converted 14,15-EET to 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), 14,15-DHET did not inhibit PGE2formation, and the 14,15-EET-induced inhibition was potentiated by 4-phenylchalcone oxide, an epoxide hydrolase inhibitor. The inhibition occurred when substrate amounts of AA were used and was not accompanied by enhanced production of other PGs, suggesting an effect on PGH synthase; however, in murine cells, 14,15-EET did not reduce PGH synthase mRNA or protein. Moreover, the 14,15-EET-induced decrease in PGE2production was overcome by increasing the concentration of AA, but not oleic acid (which is not a substrate for PGH synthase). These findings suggest that 14,15-EET competitively inhibits PGH synthase activity in vascular smooth muscle cells. The 14,15-EET-induced inhibition of PGE2production resulted in potentiation of platelet-derived growth factor-induced smooth muscle cell proliferation, suggesting that the competitive inhibition of PGH synthase by 14,15-EET can affect growth responses in smooth muscle cells.
Differential control of renal vs. adrenal sympathetic nerve activity by NTS A2a and P2x purinoceptors
Authors: Scislo Tadeusz J. , O’Leary Donal S.
Published: December 2017

Activation of adenosine A2a and ATP P2x purinoceptors in the subpostremal nucleus tractus solitarii (NTS) via microinjection of the selective agonists CGS-21680 and α,β-methylene ATP (α,β-MeATP), respectively, elicits large dose-dependent decreases in arterial pressure and heart rate, differential regional vasodilation, and differential inhibition of regional sympathetic outputs. With marked hypotensive hemorrhage, preganglionic adrenal sympathetic nerve activity (pre-ASNA) increases, whereas renal (RSNA) and postganglionic adrenal sympathetic nerve activity (post-ASNA) decrease. In this setting, adenosine levels in the brain stem increase. Therefore, we investigated whether stimulation of specific purinoceptors in the NTS may evoke differential sympathetic responses. RSNA was recorded simultaneously with pre-ASNA or post-ASNA in chloralose-urethan-anesthetized male Sprague-Dawley rats. CGS-21680 (2 and 20 pmol in 50 nl) inhibited RSNA and post-ASNA, whereas pre-ASNA increased markedly. α,β-MeATP (25 and 100 pmol in 50 nl) inhibited all sympathetic outputs. Sinoaortic denervation plus vagotomy markedly prolonged the responses to P2x-purinoceptor stimulation. Glutamate (100 pmol in 50 nl) caused differential inhibition of all sympathetic outputs similar to that evoked by α,β-MeATP. We conclude that NTS A2a-purinoceptor activation evokes differential sympathetic responses similar to those observed during hemorrhage, whereas P2x-purinoceptor and glutamate-receptor activation evokes differential inhibition of sympathetic outputs similar to arterial baroreflex responses.
Exercise training increases L-type calcium current density in coronary smooth muscle
Authors: Bowles D. K. , Hu Q. , Laughlin M. H. , Sturek M.
Published: December 2017

Exercise training produces numerous adaptations in the coronary circulation, including an increase in coronary tone, both in conduit and resistance arteries. On the basis of the importance of voltage-gated Ca2+channels (VGCC) in regulation of vascular tone, we hypothesized that exercise training would increase VGCC current density in coronary smooth muscle. To test this hypothesis, VGCC current was compared in smooth muscle from conduit arteries (>1.0 mm), small arteries (200–250 μm), and large arterioles (75–150 μm) from endurance-trained (Ex) or sedentary miniature swine (Sed). After 16–20 wk of treadmill training, VGCC current was determined using whole cell voltage-clamp techniques. In both Ex and Sed, VGCC current density was inversely related to arterial diameter, i.e., large arterioles > small arteries > conduit arteries. Exercise training increased peak inward currents approximately twofold in smooth muscle from all arterial sizes compared with those from Sed (large arteriole, −12.52 ± 2.05 vs. −5.74 ± 0.99 pA/pF; small artery, −6.20 ± 0.97 vs. −3.18 ± 0.44 pA/pF; and conduit arteries, −4.22 ± 0.30 vs. −2.41 ± 0.55 pA/pF; 10 mM Ba2+external). Dihydropyridine sensitivity, voltage dependence, and inactivation kinetics identified this Ca2+current to be L-type current in all arterial sizes from both Sed and Ex. Furthermore, peak VGCC current density was correlated with treadmill endurance in all arterial sizes. We conclude that smooth muscle L-type Ca2+current density is increased within the coronary arterial bed by endurance exercise training. This increased VGCC density may provide an important mechanistic link between functional and cellular adaptations in the coronary circulation to exercise training.
Plasma viscosity regulates capillary perfusion during extreme hemodilution in hamster skinfold model
Authors: Tsai Amy G. , Friesenecker Barbara , McCarthy Michael , Sakai Hiromi , Intaglietta Marcos
Published: December 2017

Effect of increasing blood viscosity during extreme hemodilution on capillary perfusion and tissue oxygenation was investigated in the awake hamster skinfold model. Two isovolemic hemodilution steps were performed with 6% Dextran 70 [molecular weight (MW) = 70,000] until systemic hematocrit (Hct) was reduced by 65%. A third step reduced Hct by 75% and was performed with the same solution [low viscosity (LV)] or a high-molecular-weight 6% Dextran 500 solution [MW = 500,000, high viscosity (HV)]. Final plasma viscosities were 1.4 and 2.2 cP (baseline of 1.2 cP). Hct was reduced to 11.2 ± 1.1% from 46.2 ± 1.5% for LV and to 11.9 ± 0.7% from 47.3 ± 2.1% for HV. HV produced a greater mean arterial blood pressure than LV. Functional capillary density (FCD) was substantially higher after HV (85 ± 12%) vs. LV (38 ± 30%) vs. baseline (100%).[Formula: see text] levels measured with Pd-porphyrin phosphorescence microscopy were not statistically changed from baseline until after the third hemodilution step. Wall shear rate (WSR) decreased in arterioles and venules after LV and only in arterioles after HV. Wall shear stress (WSR × plasma viscosity) was substantially higher after HV vs. LV. Increased mean arterial pressure and shear stress-dependent release of endothelium-derived relaxing factor are possible mechanisms that improved arteriolar and venular blood flow and FCD after HV vs. LV exchange protocols.
Autonomic control of heart rate in dogs treated chronically with morphine
Authors: Napier Leslie D. , Stanfill Amber , Yoshishige Darice A. , Jackson Keith E. , Barron Barbara A. , Caffrey James L.
Published: December 2017

The vagotonic effect of chronic morphine on the parasympathetic control of the heart was examined in dogs treated with morphine for 2 wk. Because normal vagal function is critical to myocardial stability, the study was conducted to evaluate for potential impairments following chronic vagal stimulation. The hypothesis that persistent vagal outflow would result in a loss of vagal reserve and reduced vagal control of heart rate was tested. Heart rate and the high-frequency variation in heart rate (power spectral analysis) declined shortly after initiation of subcutaneous morphine infusion. A progressive bradycardia correlated well with the rising plasma morphine. The resting bradycardia (57 beats/min) was maintained through day 2 and was accompanied by a significant parallel increase in vagal effect and a decline in the intrinsic heart rate (160 vs. 182 beats/min). A compensatory increase in the ambient sympathetic control of heart rate was evident on day 2 and was supported by an increase in circulating catecholamines. The lowered intrinsic heart rate and elevated sympathetic activity were maintained through day 10 despite a return of the resting heart rate and plasma catecholamines to pretreatment values. These observations suggested that chronic morphine alters either the intrinsic function of the sinoatrial node or reduces the postvagal tachycardia normally attributed to nonadrenergic, noncholinergic agents. Both acute and chronic morphine depressed the rate of development of bradycardia during direct vagal nerve stimulation without altering the rate of recovery afterward. This last observation suggests that acute morphine reduces the rate of acetylcholine release. Results provide insight into the mechanisms that maintain vagal responsiveness. The results are also relevant clinically because opiates are increasingly prescribed for chronic pain and opiate abuse is currently in resurgence.
Protective roles of nitric oxide and testosterone in endotoxemia: evidence from NOS-2-deficient mice
Authors: Laubach Victor E. , Foley Patricia L. , Shockey Kim S. , Tribble Curtis G. , Kron Irving L.
Published: December 2017

Lipopolysaccharide (LPS)-induced septic shock, which triggers nitric oxide (NO) overproduction, multiple organ dysfunction, and death, can be affected by gender and sex hormones. We hypothesized that NO is beneficial during endotoxemia and that this beneficial effect is influenced by sex hormones. C57BL/6 wild-type (WT) mice and congenic inducible NO synthase knockout (KO) mice were injected with LPS, and mortality was recorded for 4 days. After 5 mg/kg LPS, female KO mice had significantly higher mortality than WT. After 12.5 mg/kg LPS, both male and female KO mice had significantly higher mortality than WT. Ovariectomy did not alter mortality, but orchiectomy dramatically increased mortality in KO mice. After 5 mg/kg LPS, exogenous testosterone completely prevented the increased mortality in KO female and orchiectomized KO male mice. WT survival was not affected by exogenous testosterone. After 12.5 mg/kg LPS, exogenous testosterone significantly improved survival of female KO mice. Serum enzymes and organ edema, which may not correlate with mortality, were significantly and similarly increased in both WT and KO endotoxemic mice; however, edema was not observed in KO hearts. Thus, NO plays a protective role in endotoxemia while having differential effects on different organs. Importantly, testosterone is beneficial in endotoxemia when NO production is deficient, and may be therapeutic in certain septic patients.
Specific heat shock proteins protect microtubules during simulated ischemia in cardiac myocytes
Authors: Bluhm Wolfgang F. , Martin Jody L. , Mestril Ruben , Dillmann Wolfgang H.
Published: December 2017

The protective effects of heat shock proteins (HSPs) during myocardial ischemia are now well documented, but little is known about the mechanisms of protection and the specificity of different HSPs. Because cytoskeletal injury plays a crucial role in the pathogenesis of irreversible ischemic damage, we tested whether overexpression of specific HSPs protects the integrity of microtubules during simulated ischemia in rat neonatal cardiac myocytes. Overexpression of specific HSPs was achieved by adenovirus-mediated transgene expression. Damage was assessed by comparing control cells to cells that were subjected to a simulated ischemia protocol. Microtubular integrity was measured by indirect immunofluorescence, confocal microscopy, and image analysis. Within 14 h of simulated ischemia, microtubular integrity decreased significantly in uninfected myocytes (from 24.6 ± 1.2 to 13.2 ± 0.4) and in myocytes infected with a control virus that expressed no transgene (from 25.9 ± 1.8 to 13.1 ± 1.4). Microtubular integrity after ischemia was significantly better preserved in cells overexpressing constitutive Hsp70 (21.7 ± 1.6) or αB-crystallin (18.0 ± 2.7) but not in cells overexpressing inducible Hsp70 (11.5 ± 0.8) or Hsp27 (14.0 ± 2.2). We conclude that specific HSPs protect the microtubules during simulated cardiac ischemia.