bluuebunny/crossref_metadata_2025 huggingface dataset:
Protamine inhibits coronary collateral development in a canine model of repetitive coronary occlusion
Authors: Kersten J. R. , Pagel P. S. , Warltier D. C.
Published: December 2017

Protamine has been demonstrated to inhibit angiogenesis in vitro and in vivo; however, its effect on coronary collateral development has not been examined. The present investigation tested the hypothesis that subcutaneously administered protamine inhibits canine coronary collateral development in response to chronic myocardial ischemia. Dogs underwent daily, repetitive, 2-min, left anterior descending coronary artery (LAD) occlusions for 22 consecutive days. Regional myocardial blood flow (radioactive microspheres), LAD segment shortening, and coronary flow debt repayment were measured in saline-treated (n = 7) and protamine-treated (n = 6) dogs on days 1, 8, 15, and 22. Coronary collateral development in saline-treated dogs was demonstrated by time-dependent significant (P < 0.05) increases in collateral blood flow to ischemic myocardium [day 1 0.10 +/- 0.01 vs. day 22 0.88 +/- 0.05 (SE) ml.min-1.g-1], progressive normalization of myocardial contractile function during LAD occlusion, and successive reduction in flow debt repayment. In contrast, protamine treatment significantly attenuated, increases in collateral perfusion (day 1 0.13 +/- 0.02 vs. day 22 0.36 +/- 0.03 ml.min-1.g-1). Regional contractile dysfunction and postocclusive reactive hyperemic responses were sustained over time in protamine-treated compared with saline-treated dogs. The results demonstrate that protamine inhibits coronary collateral development in response to chronic myocardial ischemia.
Protection from pulmonary hypertension with an orally active endothelin receptor antagonist in hypoxic rats
Authors: Eddahibi S. , Raffestin B. , Clozel M. , Levame M. , Adnot S.
Published: December 2017

The aim of this study was to investigate the potential role of endothelin (ET) in the development of chronic hypoxic pulmonary hypertension. Pulmonary vascular reactivity to ET-1 was first examined in isolated perfused lungs from normoxic and chronically hypoxic rats in the presence of bosentan, a new nonpeptide mixed antagonist of ETA and ETB receptors. The effect of chronic treatment with bosentan was then examined in rats that were exposed to chronic hypoxia and developed pulmonary hypertension. In lungs from normoxic rats, bosentan (10(-5) M) abolished the vasodilator responses to ET-1 (10(-10) M) or to the ETB-selective agonist IRL-1620 (10(-10) M) and attenuated the vasoconstrictor responses to 10(-9) M ET-1 (from 8.7 +/- 0.7 to 1.8 +/- 0.3 mmHg, P < 0.01) or 10(-9) M IRL-1620 (from 1.5 +/- 0.4 to 0.4 +/- 0.1 mmHg, P < 0.05). In lungs from chronically hypoxic rats, the pressor response to 3 x 10(-10) M ET-1 was abolished by bosentan and partially reduced by the selective ETA antagonist BQ-123. In conscious rats previously exposed to hypoxia for 15 days, pretreatment with bosentan (100 mg.kg-1.day-1 by gavage) for 3 days attenuated the increase in systemic arterial pressures and the concomitant decrease of cardiac output in response to an intravenous bolus of ET-1 (3 x 10(-10) M). In rats exposed to hypoxia for 15 days and simultaneously treated with bosentan, pulmonary arterial pressure was lower (P < 0.05) and right ventricular hypertrophy was less severe (P < 0.01) than in control hypoxic rats treated with vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)
Hypoglycemia selectively abolishes hypoxic reactivity of pial arterioles in piglets: role of adenosine
Authors: Park T. S. , Gonzales E. R. , Shah A. R. , Gidday J. M.
Published: December 2017

Episodes of hypoxia often occur in hypoglycemic newborns, but it is not known whether dysfunctions in cerebrovascular regulation contribute to brain injury incurred by these affected neonates. We tested the hypotheses that 1) perinatal hypoglycemia impairs cerebrovascular responses to hypoxia and 2) a reduced vascular smooth muscle sensitivity to adenosine accounts for this impairment. Responses of 25- to 50-mu m-diam pial arterioles were determined using the cranial window technique in isoflurane-anesthetized newborn piglets < 5 days of age. Hypoxia (arterial PO2 = 28 +/- 1 mmHg) caused a 47 +/- 5% increase (P = 0.0008) in arteriolar diameter, 89% of which could be blocked by prior superfusion of the window space with the preferential A2-adenosine receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX; 50 microM). Insulin-induced hypoglycemia (blood glucose = 18 +/- 1 mg/dl without isoelectric electroencephalogram) caused a 31 +/- 5% increase (P = 0.002) in arteriolar diameter; however, no additional dilatative response to hypoxia (arterial PO2 = 28 +/- 1 mmHg) could be elicited in these animals. Arteriolar dilation of 41 +/- 6% (P = 0.002) induced by superfusion of 20 microM adenosine under normoglycemic conditions was also completely abolished after the animals were rendered hypoglycemic. Unlike the response to hypoxia and adenosine, hypoglycemia only attenuated prostanoid-dependent dilations to hypercapnia (arterial PCO2 = 68 +/- 3 mmHg) by 55 +/- 9%. These results indicate that, in the newborn, hypoglycemia selectively abolishes hypoxic reactivity through an impairment in adenosine-mediated cerebrovascular dilation.
A model of combined feedforward and feedback control of coronary blood flow
Authors: Miyashiro J. K. , Feigl E. O.
Published: December 2017

Recent evidence shows that norepinephrine affects coronary blood flow not only by alpha-receptor-mediated vasoconstriction and by feedback metabolic vasodilation that occurs as a result of myocardial beta-receptor activation, but also by the direct activation of coronary vascular beta-receptors that increase flow in a feedforward manner. The implications of combined feedforward and feedback control in maintaining the balance between metabolism and flow were investigated in the present mass balance model. Feedback was represented by a closed loop and was based on the hypothesis that the regulated variables are myocardial PO2 and PCO2 and that divergence of these variables from their operating point values functions as the metabolic error signals that manipulate coronary vascular smooth muscle and flow to match metabolism. alpha-Receptor-mediated vasoconstriction and beta-receptor-mediated vasodilation are represented by feedforward open loops that are activated simultaneously with increases in metabolism. The postulated control schemes of 1) metabolic feedback control alone, 2) feedback plus alpha- and beta-adrenergic feedforward control, and 3) feedback plus beta-adrenergic feedforward control were able to simulate the steady-state increase in coronary flow and the decrease in coronary venous PO2 that occurs during comparable experimental conditions. The simulations demonstrate that 1) the speed and accuracy of the flow response improve as beta-adrenergic feedforward control is added and alpha-adrenergic feedforward control is removed from the control scheme, 2) high feedback gain also improves the accuracy of the flow response, but the penalty is instability, and 3) a lag in alpha-adrenergic feedforward control improves the stability of the coronary response.
Monocyte chemoattractant protein 1 inhibits growth of rat vascular smooth muscle cells
Authors: Ikeda U. , Okada K. , Ishikawa S. , Saito T. , Kasahara T. , Shimada K.
Published: December 2017

The early atherosclerotic lesion is characterized by the migration of inflammatory cells, including monocytes, which may serve as a source of cytokines such as monocyte chemoattractant protein 1 (MCP-1), a homologue of mouse JE. We investigated the effect of MCP-1 on the growth of vascular smooth muscle cells (VSMC) isolated from rat aortae. In Northern blot analysis, MCP-1/JE transcripts were not observed in unstimulated VSMC, but its expression was clearly observed by exposure to lipopolysaccharide (1 micrograms/ml) for 6 h. Human recombinant MCP-1 inhibited the uptake of [3H]thymidine by VSMC cultured in 0.5% fetal bovine serum (FBS) containing Dulbecco's modified Eagle's medium (DMEM) in a dose-dependent manner. The inhibitory effect of MCP-1 on the growth of VSMC was also confirmed by a change in cell counts. The antiproliferative effect of MCP-1 was significantly blocked in the presence of an anti-MCP-1 antibody. MCP-1-induced inhibition of [3H]thymidine uptake was not affected in the presence of indomethacin (1 micrograms/ml) or NG-monomethyl-L-arginine (0.1 mM), and MCP-1 showed no effect on 6-ketoprostaglandin F1 alpha, guanosine 3',5'-cyclic monophosphate, and adenosine 3',5'-cyclic monophosphate syntheses in VSMC. These results indicate that MCP-1 inhibits the proliferation of VSMC in vitro and that its effect is independent of prostaglandin or nitric oxide generation.
Sympathetic responses to stimulation of area postrema in decerebrate and anesthetized rats
Authors: Hegarty A. A. , Hayward L. F. , Felder R. B.
Published: December 2017

The effects of electrical and chemical stimulation of the area postrema (AP) on mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) were examined in urethan- and pentobarbital sodium-anesthetized rats and in unanesthetized decerebrate rats. The AP was electrically stimulated over a range of frequencies (10–100 Hz) and intensities (10–80 microA) with a pulse duration of 0.2 or 1.0 ms. The excitatory amino acid L-glutamate (100 or 200 mM) was microinjected into the AP to preferentially stimulate neuronal cell bodies. In urethan-anesthetized rats, electrical stimulation of the AP decreased MAP and RSNA. In pentobarbital sodium-anesthetized rats, MAP and RSNA were markedly increased by AP stimulation. In unanesthetized decerebrate rats, increases in MAP and RSNA were also observed during electrical AP stimulation. Microinjection of L-glutamate had no effect on MAP and RSNA in anesthetized or in unanesthetized rats. These results indicate that electrical AP stimulation increases sympathetic output in the unanesthetized decerebrate rat and that anesthesia modifies this sympathetic response. The findings also suggest that peripheral responses to L-glutamate and electrical stimulation of the AP are mediated over different central pathways.
Differential regulation of L-arginine transport and inducible NOS in cultured vascular smooth muscle cells
Authors: Durante W. , Liao L. , Schafer A. I.
Published: December 2017

Experiments were performed to characterize the uptake of L-arginine in rat aortic smooth muscle cells (SMC) and to examine whether inducers of nitric oxide synthase (NOS) could regulate the transport of L-arginine into these cells. L-Arginine transport by SMC was saturable, Na+ independent, strongly inhibited in the presence of other cationic amino acids, and could be stimulated by preloading the cells with cationic amino acids. Kinetic studies revealed the presence of both a high [Michaelis constant (Km) approximately 125 microM] and low (Km approximately 1.4 mM) affinity L-arginine transporter. Treatment of vascular SMC with interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) resulted in parallel increases in L-arginine transport and nitric oxide (NO) synthesis, as measured by nitrite production. Increasing the concentration of IL-1 beta and TNF-alpha caused a progressive elevation in nitrite production but did not further stimulate L-arginine uptake. Treatment of SMC with the combination of TNF-alpha and interferon-gamma (IFN-gamma) synergistically enhanced nitrite release without having any additional effect on L-arginine transport. Both induction of L-arginine transport and NOS activity by these cytokines were blocked by cycloheximide. Finally, treatment of SMC with interferon-gamma and N6,2'-O-dibutyryl adenosine 3',5'-cyclic monophosphate selectively stimulated the formation of nitrite by SMC but had no effect on L-arginine transport. These results demonstrate that L-arginine transport by cultured vascular SMC is mediated by the system y+ carrier and that inducers of NOS differentially regulate the activity of this transporter.(ABSTRACT TRUNCATED AT 250 WORDS)
A model study of changes in excitability of ventricular muscle cells: inhibition, facilitation, and hysteresis
Authors: Beaumont J. , Michaels D. C. , Delmar M. , Davidenko J. , Jalife J.
Published: December 2017

A model study was carried out to investigate the mechanism of changes in excitability at long cycle lengths (i.e., > 1,000 ms), which are responsible for various phenomena, including electrotonic inhibition, active facilitation, and hysteresis of excitability in ventricular muscle at slow frequencies of stimulation. Experimental studies suggested that with repetitive activity the inward rectifier potassium current (IK1) is not a passive component of membrane response and that the dynamics of IK1 are responsible for the changes in excitability at long cycle lengths. In the present study, we have used new experimental data as the basis to modify the equations for IK1 in the ionic model for ventricular muscle of the Luo and Rudy (LR) model. The modified equations for IK1 incorporate an additional slow gate (s-gate), which governs the transition from a high steady-state conductance at rest to a lower conductance with repetitive stimulation. In simulation studies, electronic inhibition was seen in the original and the modified LR model and was shown to depend on changes in the delayed rectifier current (IK). However, addition of the s-gate to IK1 of the LR model extended the frequency dependence of excitability to longer cycle lengths and allowed for the demonstration of active facilitation and hysteresis. These results support the hypothesis that the inward rectifier is involved in the dynamic control of membrane excitability. The overall results provide mechanistic explanations for heart rate-dependent excitation abnormalities that may be involved in the genesis of cardiac arrhythmias.
Evidence for presence of Ca2+ channel-gated Ca2+ stores in neonatal human atrial myocytes
Authors: Hatem S. N. , Sweeten T. , Vetter V. , Morad M.
Published: December 2017

The characteristics of Ca2+ signaling in fura 2-loaded whole cell-clamped myocytes obtained from samples of human atrial appendages of 3-day to 4-yr-old patients were examined. In isolated myocytes, activation of Ca2+ current (ICa) (2.47 +/- 0.23 pA/pF) at 0 mV elicited sizable intracellular Ca2+ (Cai) transients (240 +/- 45 nM), which were caused by the release of Ca2+ from intracellular stores as they were suppressed in the presence of ryanodine or caffeine. The voltage dependence of both Cai transients and ICa were similar and bell shaped. The rate of release of Ca2+, normalized for the maximal Ca2+ release, increased with age, indicating increased efficiency of Ca2+ signaling in more mature myocytes. The results suggest that ICa-gated release of Ca2+ from the sarcoplasmic reticulum is the primary mechanism regulating the signaling of contraction in early postnatal as well as older human atrial myocytes.
Effect of dynamic exercise on human carotid-cardiac baroreflex latency
Authors: Potts J. T. , Raven P. B.
Published: December 2017

We compared the beat-to-beat responses of heart rate (HR) after brief activation of carotid baroreceptors in resting humans with the responses obtained during mild-to-moderate levels of dynamic exercise [25 and 50% of peak O2 uptake (VO2peak)] to investigate the effect of exercise on baroreflex latency. Carotid baroreceptors were activated by a pressure pulse (5 s) of neck suction (NS, -80 Torr) and neck pressure (NP, +40 Torr) during held expiration. At rest the peak change in HR to NS/NP occurred during the first several heartbeats (1st-3rd beat), whereas during mild and moderate exercise peak HR responses occurred near the end of the NS/NP pulse (6th-8th beat). In contrast, time (s) to the peak change in HR was not different between rest and exercise (P > 0.05). Reflex tachycadia to NP progressively decreased during exercise (17 +/- 3, 10 +/- 1, and 4 +/- 1% of control, rest vs. 25% VO2peak, vs. 50% VO2peak, respectively, P < 0.05), and a strong positive correlation was found between the magnitude of the reflex tachycardia and a measure of HR variability (cardiac vagal tone index, r = 0.74, P < 0.0001). Reflex bradycardia to NS gradually increased during exercise (13 +/- 2, 17 +/- 2, and 18 +/- 2% of control, rest vs. 25% VO2peak, vs. 50% VO2peak, respectively, P = 0.10) and was negatively correlated with cardiac vagal tone (r = 0.42, P < 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)
Structural and metabolic correlates of the reversibility of chronic left ventricular ischemic dysfunction in humans
Authors: Depre C. , Vanoverschelde J. L. , Melin J. A. , Borgers M. , Bol A. , Ausma J. , Dion R. , Wijns W.
Published: December 2017

Assessment of regional myocardial perfusion and glucose uptake with positron emission tomography (PET) identifies dysfunctional myocardium that shows improvement in function after revascularization. Yet little is known about the ultrastructural patterns of ischemic injury in myocardium with and without postoperative functional improvement in relation to residual perfusion and metabolism. Therefore dynamic PET with [13N]ammonia and 18F-labeled deoxyglucose was performed in 24 patients with coronary artery disease and anterior wall dysfunction undergoing bypass surgery. Transmural biopsies were obtained from the dysfunctional area during surgery and analyzed by optical and electron microscopy to quantify the presence of fibrosis and cardiomyocytes. As judged from the postoperative changes in contraction, left ventricular function improved in 16 patients. In myocardium that showed improved function after revascularization, preoperative flow and glucose uptake were higher by PET than in persistently dysfunctional myocardium. In tissue samples from myocardium that improved postoperatively, there were more cardiomyocytes, including a larger proportion of cells with excess glycogen stores (35 vs. 21%), and there was less fibrosis (24 vs. 49%) than in tissue samples from myocardium that did not improve functionally. Preoperative perfusion and postoperative wall motion were inversely correlated with the amount of tissue fibrosis, whereas preoperative 18F-labeled deoxyglucose uptake correlated positively with the amount of cardiomyocytes showing excess glycogen stores.
Acetylcholine potentiates acetylcholine-induced increases in K+ current in cat atrial myocytes
Authors: Wang Y. G. , Lipsius S. L.
Published: December 2017

A nystatin-perforated patch whole cell recording method was used to study the effects of acetylcholine (ACh) on ACh-induced K+ currents in atrial myocytes isolated from cat hearts. The general protocol involved an initial 4-min exposure to ACh (ACh1), followed by a 4-min washout in ACh-free Tyrode solution and then a second 4-min ACh exposure (ACh2). Voltage ramps (40 mV/s) between -130 and +30 mV were used to assess changes in total membrane conductance. ACh2 (10 microM) induced an increase in K+ conductance that was significantly larger than that induced by ACh1 (10 microM) at voltages both negative and positive to the reversal potential. The potentiated current induced by ACh2 reversed at about -80 mV and inwardly rectified at voltages positive to the reversal potential. External Ba2+ (5 mM) or tetraethylammonium (10 mM) abolished all ACh2-induced increases in membrane conductance. The sensitivity to K+ channel blockers, reversal potential, and the rectifying properties indicate that the current potentiated by ACh2 is a K+ current. Atropine (1 microM) blocked all effects of ACh on K+ currents. Potentiation of K+ current by ACh2 required 1) ACh1 concentrations > or = 1 microM, 2) ACh1 duration > or = 2 min, and 3) recovery interval > or = 2 min. We conclude that an initial exposure to ACh potentiates subsequent ACh-induced increases in K+ current. ACh-induced potentiation depends on the concentration and duration of the initial ACh exposure and the recovery interval between consecutive ACh exposures.(ABSTRACT TRUNCATED AT 250 WORDS)
Comparison of Ito in young and adult human atrial myocytes: evidence for developmental changes
Authors: Crumb W. J. , Pigott J. D. , Clarkson C. W.
Published: December 2017

In an effort to understand the ionic basis for the developmental changes that have been reported to occur in the configuration of the human atrial action potential, we characterized the transient outward current (Ito) and the inward rectifier current in atrial myocytes isolated from 20 young (ages 1 day-2.5 yr) and 8 adult (11–68 yr) human hearts using the whole cell patch-clamp technique. We found evidence for statistically significant (P < 0.05) age-related changes in the Ito, including 1) the presence of an Ito in only 67% of the cells isolated from young hearts vs. 100% of the cells isolated from adult hearts, 2) an almost twofold increase in the current density of Ito in adult cells vs. young cells, and 3) recovery kinetics that are approximately twofold slower in young myocytes relative to adult myocytes. In contrast, there were no age-related changes found in the current density of the inward rectifier current or the sustained current measured after the decay of Ito. These results suggest important current-dependent changes that occur with age in human atria.
Enhanced sympathetic reactivity to glutamate stimulation in medulla oblongata of spontaneously hypertensive rats
Authors: Yang T. L. , Chai C. Y. , Yen C. T.
Published: December 2017

The distribution and reactivity of vasomotor sites in the ventrolateral (VLM) and dorsomedial medulla (DMM) of stroke-prone spontaneously hypertensive rats (SHRSP), spontaneously hypertensive rats (SHR), and Wistar-Kyoto rats (WKY) were compared. Rats were anesthetized with alpha-chloralose and urethan. Baroreceptor denervation and vagotomy were performed. L-Glutamate (Glu, 10 mM, 30 nl) was microinjected into the DMM or VLM to identify vasoactive sites. The extent and the patterns of distribution of these sites in the three strains of rats were similar. The dose-response curve of the vasoactive site was studied with 1–500 pmol of Glu. The maximum responses of blood pressure and renal sympathetic activity were larger and threshold doses of Glu were lower in hypertensive rats. The significance of the differences among the strains was analyzed before and after adjustment for baseline pressure or activity. Most of the differences were statistically significant before baseline adjustment. After baseline adjustment, many differences between the SHRSP and the WKY remained significant. However, the only significant difference detected between the SHR and the WKY was the threshold dose for eliciting renal sympathetic change in the caudal VLM. These results suggest that there may be a general increase in excitability of the vasomotor neurons in the medulla of the hypertensive rats.
Endothelin regulation of cardiac contractility in absence of added endothelin
Authors: McClellan G. , Weisberg A. , Winegrad S.
Published: December 2017

Endothelin has a positive inotropic effect on cardiac muscle, but its role in the regulation of contraction in cardiac tissue is not clear, inasmuch as there has been no demonstration of endothelin regulation of contractility in the absence of added endothelin. To address this question, the changes in contractility of isolated rat ventricular trabeculae produced by endothelin and by BQ-123, an endothelin receptor A antagonist, were measured in tissues with different levels of contractility resulting from bathing the tissues for different lengths of time. The effect of endothelin depended on the extent to which tension had declined from its peak level: the greater the decline, the larger the increase in developed force produced by endothelin. The effect of BQ-123 also depended on the extent to which force had declined. The effects of the addition of endothelin or BQ-123 indicate the presence of substantial regulation of contractility due to basal secretion of endothelin: the degree of endothelin activity is greater in cardiac tissue generating more tension. Damage to the endocardial endothelium from a brief exposure to Triton X-100 reduced the response to BQ-123. The response to BQ-123 depends on the number of functioning endothelial cells. From the extent of the effect of endothelin or BQ-123, it appears that as much as 50% of total force-generating capacity of the tissue is sensitive to endothelin produced by the endothelial cells in the isolated heart. This stimulation of contractility is gradually lost in the isolated cardiac tissue, contributing to the progressive decline in developed force with time.
Modulation of oxidized low-density lipoprotein-induced microvascular dysfunction by nitric oxide
Authors: Liao L. , Granger D. N.
Published: December 2017

The objectives of this study were to determine 1) whether the leukocyte-endothelial cell adhesion in postcapillary venules elicited by copper-oxidized low-density lipoproteins (Cu-LDL) is accompanied by enhanced vascular albumin leakage and mast cell degranulation and 2) whether nitric oxide (NO) donors attenuate the Cu-LDL-induced microvascular dysfunction. Infusion of Cu-LDL, but not normal LDL, caused significant increases in leukocyte rolling, adherence, emigration, mast cell degranulation, and an enhanced albumin leakage in rat mesenteric venules. Treatment with the NO donors sodium nitroprusside and spermine-NO or pretreatment with superoxide dismutase or L-arginine significantly reduced the Cu-LDL-induced leukocyte adherence, emigration, mast cell degranulation, and albumin leakage, whereas spermine and D-arginine had no effect. These results indicate that NO protects the microvasculature against the deleterious effects of oxidized LDL, an effect that may be related to NO's ability to reduce leukocyte-endothelial cell adhesion and/or prevent mast cell degranulation.
Myocyte performance during evolution of myocardial infarction in rats: effects of propionyl-L-carnitine
Authors: Li P. , Park C. , Micheletti R. , Li B. , Cheng W. , Sonnenblick E. H. , Anversa P. , Bianchi G.
Published: December 2017

To determine whether alterations in the mechanical properties and calcium transients of myocytes are important factors in the evolution of the postinfarcted heart, these physiological parameters were measured in the viable muscle cells of the left ventricle 6 h, 2–3 days, 1 wk, and 1 mo after coronary artery occlusion and the documentation of left ventricular failure. In addition, the effects of propionyl-L-carnitine (PLC) on shortening properties and calcium dynamics of single myocytes were established to demonstrate whether the potential increase in ATP generation by this intervention improved myocyte cell function. Myocardial infarction was associated with a progressive increase in length of the spared myocytes, whereas the changes in myocyte diameter were apparent only at the 1-mo interval. Mechanically, myocyte shortening was decreased 43% at 6 h, 34% at 2–3 days, 26% at 1 wk, and 41% at 1 mo after infarction. Similar abnormalities were noted in the velocity of myocyte shortening. Peak systolic calcium was decreased at all intervals after infarction. In contrast, diastolic calcium remained within control values. PLC was capable of ameliorating the mechanical behavior and calcium transients of myocytes, particularly 1 mo after infarction. Thus alterations in muscle cell performance may be important determinants in the development and progression of ischemic cardiomyopathy, and interventions improving myocyte contractility may interfere with the unfavorable outcome of the disease.
Effect of intracellular and extracellular acidosis on sodium current in ventricular myocytes
Authors: Watson C. L. , Gold M. R.
Published: December 2017

Conduction slowing is an essential element in the generation of ischemic ventricular arrhythmias and is determined in part by the inward Na+ current (INa). Because intracellular acidosis is an early consequence of ischemia, we hypothesized that lowering intracellular pH (pHi) would reduce or kinetically modulate INa and thus affect cardiac conduction. To test this hypothesis, the whole cell patch-clamp method was used to measure INa in neonatal rat ventricular myocytes exposed to varying extracellular pH (pHo 6.4–7.4), while perfusing the cells with acidic solutions (pHi 6.2–7.2). With simultaneous acidification of pHo and pHi there was a progressive increase in time to peak current, a 31% decrease in peak INa (298 +/- 18 to 206 +/- 16 pA/pF), and a complex slowing of inactivation kinetics. At the most extreme levels of acidification, there was a 5-mV hyperpolarizing shift in steady-state inactivation and a 6-mV depolarizing shift in activation. Independent changes of pHo and pHi indicate that the reduction of peak INa is a function of pHo. However, steady-state inactivation is modulated by pHi. The time course of activation and inactivation appears to depend on both pHo and pHi. We conclude that both intracellular and extracellular acidosis are significant but distinct modulators of INa amplitude and kinetics in cardiac myocytes.
ANP secretion from small cell lung cancer cell lines: a potential model of ANP release
Authors: Wigle D. A. , Campling B. G. , Sarda I. R. , Shin S. H. , Watson J. D. , Frater Y. , Flynn T. G. , Pang S. C.
Published: December 2017

Although atrial distension is widely accepted as the primary stimulus for atrial natriuretic peptide (ANP) release, a number of agonists are also known to induce its secretion. The mechanisms underlying these processes are not well understood. Studies of this nature are hampered by the inherent difficulty in culturing homogeneous populations of cardiac myocytes in sufficient quantities to perform molecular investigations. For this reason, we have examined the possibility of using other cell types as a model of ANP release. It has been reported that a number of tumor samples from small cell lung cancer (SCLC) patients express the ANP gene. Characterization of a large number of cell lines derived from SCLC tumor samples indicated that two of these cell lines, OS-A and SHP-77, secrete ANP at rates of approximately 10(-20) g.cell-1.min-1. This is a sufficient quantity to facilitate secretion studies using a perifusion system. We have demonstrated that ANP is released through regulated secretory pathways, as the Ca2+ ionophore A-23187, arginine vasopressin (AVP), and the sodium ionophore, monensin, were capable of modifying secretion rates. High-pressure liquid chromatography (HPLC) analysis indicated that the primary secretory product is ANP-(99-126), the circulating form of this hormone. Intracellularly, both ANP-(99-126) and ANP-(1-126) were present, suggesting the synthesis and appropriate cleavage of pro-ANP-(1-126). Because both of these cell lines have doubling times in the range of 3-5 days, they could serve as a rapidly proliferating and easily maintainable supply of homogeneous tissue for release studies.(ABSTRACT TRUNCATED AT 250 WORDS)
Transmural bioenergetic responses of normal myocardium to high workstates
Authors: Zhang J. , Duncker D. J. , Xu Y. , Zhang Y. , Path G. , Merkle H. , Hendrich K. , From A. H. , Bache R. J. , Ugurbil K.
Published: December 2017

The response of myocardial high-energy and inorganic phosphates (HEP and Pi, respectively) and associated changes in myocardial blood flow, lactate uptake, and O2 consumption (MVo2) rates were examined in an open-chest canine model during progressively increasing workloads achieved by catecholamine infusion. HEP and Pi levels (measured with transmurally localized 31P-nuclear magnetic resonance spectroscopy) were unaffected by moderate increases in the level of energy expenditure but were significantly altered by high workloads, especially in the subepicardium. The MVo2 and HEP data from three different protocols that utilized pharmacological augmentation of blood flow demonstrated that the maximal rate of myocardial energy production during inotropic stimulation was dictated by perfusion limitation. This limitation was more severe in the subepicardial layer at the high workloads despite equivalent or even higher increases in blood flow to this layer, reflecting a preferential enhancement of demand in the outer layer by catecholamines. In contrast, under basal conditions, existence of a marginal perfusion limitation was evident in the inner but not in the outer layer.
A noninvasive comparative study of myocardial strains in ischemic canine hearts using tagged MRI in 3-D
Authors: Azhari H. , Weiss J. L. , Rogers W. J. , Siu C. O. , Shapiro E. P.
Published: December 2017

Regional reduction in myocardial function has long been utilized for noninvasive detection and localization of ischemic regions in the left ventricle. In this study, we compared the ability of 13 different myocardial strain indexes to discriminate between ischemic and nonischemic tissue. Using magnetic resonance imaging with tagging and three-dimensional reconstruction, we noninvasively tracked the deformation of 24 myocardial cuboids in each of nine canine hearts with acute ischemia induced by coronary artery ligation. Monastral blue staining was used for postmortem assessment of ischemia. The ability of each index to discriminate between normal and ischemic zones was evaluated using the "t" statistic. The best discrimination was obtained by the endocardial area strain [t = 7.5 +/- 3.0 (SD)], a local measure of systolic shrinkage on the endocardial surface, and by the magnitude of the endocardial principal strain (t = 7.0 +/- 1.9). Transmural wall thickening (t = 6.1 +/- 2.3) was the third best functional index. The same three indexes correlated most closely with perfusion, as assessed by monastral blue staining. These findings imply that these are the preferable functional indexes for mapping of ischemic myocardial regions.
Sarcoplasmic reticulum Ca2+ pumps in heart and diaphragm of cardiomyopathic hamster: effects of perindopril
Authors: Anger M. , Lambert F. , Chemla D. , Desche P. , Scalbert E. , Lompre A. M. , Lecarpentier Y.
Published: December 2017

The polymyopathy of the Syrian hamster is associated with alterations of cellular calcium regulation and contractile performance of cardiac and skeletal muscles and, in particular, the diaphragm. Angiotensin-converting enzyme (ACE) inhibitors have been shown to preserve contractile performance. Therefore we analyzed the expression of the genes coding for the sarco(endo)plasmic reticulum Ca(2+)-adenosinetriphosphatase (SERCA) in heart and diaphragm of the cardiomyopathic Syrian hamster (CSH) from the dilated strain Bio 53-58, and we tested the influence of ACE inhibition on accumulation of the different SERCA mRNAs. In the diaphragm of healthy hamsters, two SERCA mRNA isoforms were present: SERCA 1 and SERCA 2. At 6 mo of age, the myopathic process resulted in decreased levels of SERCA 1, whereas the level of SERCA 2 was unchanged. The ACE inhibitor perindopril (1 mg.kg-1.day-1), administered by force feeding from 1 to 6 mo of age, had no effect on the SERCA 1 mRNA level. In heart, the myopathy was associated with a depressed level of SERCA 2 mRNA in 9- but not in 6-mo-old animals. Perindopril treatment from 6 to 9 mo reversed cardiac hypertrophy and the relative decrease in SERCA 2 mRNA level. Preventive treatment with perindopril from 1 to 9 mo tended to prevent (not significantly) the development of cardiac hypertrophy and reduction in SERCA gene expression. In conclusion, the myopathic process affects SERCA gene expression in the diaphragm and subsequently in the heart. Perindopril treatment can prevent SERCA mRNA loss in heart but not in diaphragm.
Endothelin-1 and its binding sites are upregulated in pressure overload cardiac hypertrophy
Authors: Arai M. , Yoguchi A. , Iso T. , Takahashi T. , Imai S. , Murata K. , Suzuki T.
Published: December 2017

The purpose of this study was to determine whether endothelin and endothelin receptors play an important role in the development of cardiac hypertrophy due to pressure overload in vivo. Cardiac hypertrophy was produced by placing a constricting clip around the suprarenal abdominal aorta of rats. Hemodynamic parameters and plasma and ventricular concentrations of endothelin-1 (ET-1) were measured in control unoperated rats, and 30 min, 2 and 6 h, and 1 and 8 days after operation in pressure overload rats and sham-operated rats. The density and dissociation constant of ET-1 binding sites were also measured in control rats and 1 and 8 days after pressure overload and sham operation. Additionally, in situ mRNA hybridization for preproendothelin-1 (preproET-1) mRNA was performed to determine which cells were responsible for increased ET-1 levels. Ventricular ET-1 levels increased markedly on day 8 of pressure overload, whereas plasma ET-1 levels increased transiently only 30 min after operation, quickly returning to control level. In addition, ventricular ET-1 levels on day 8 showed a significant positive correlation with the degree of cardiac hypertrophy. In situ mRNA hybridization revealed that cardiac myocytes expressed preproET-1 mRNA in hypertrophied hearts in vivo. In accord with the elevation of ventricular ET-1 levels, the density of ET-1 binding sites was increased significantly, without affecting their binding affinity, on day 8 of pressure overload. These data are compatible with the hypothesis that increases in locally produced ET-1 and the density of ET-1 binding sites have an important relationship with the development of cardiac hypertrophy in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanisms of oxidized chylomicron-induced leukocyte-endothelial cell adhesion
Authors: Kurtel H. , Liao L. , Grisham M. B. , Tso P. , Aw T. Y. , Anderson D. C. , Miyasaka M. , Granger D. N.
Published: December 2017

The objectives of this study were to determine whether oxidatively modified chylomicrons (oxCM) can elicit leukocyte-endothelial cell adhesion in the mesenteric microcirculation and to define the mechanisms underlying the oxCM-induced adhesive interactions. Oxidation of chylomicrons (CM) with the peroxyl radical generator 2,2'-azobis(2-amidinopropane)hydrochloride was associated with the formation of thiobarbituric acid-reactive substances and lipid hydroperoxides. Leukocyte rolling, adherence, and emigration as well as erythrocyte velocity were monitored in rat mesenteric venules infused with either native CM or oxCM. oxCM, but not native CM, increased the numbers of rolling, adherent, and emigrated leukocytes. The oxCM-induced leukocyte adherence was significantly blunted by pretreating the animals with either superoxide dismutase, a platelet-activating factor (PAF) receptor antagonist, or monoclonal antibodies (MAb) directed against either CD11/CD18 or intracellular adhesion molecule 1. A MAb against P-selectin reduced oxCM-induced leukocyte rolling but not adherence. These findings suggest that the increased plasma oxCM levels associated with ingestion of oxidized lipids may promote leukocyte adhesion through a mechanism that involves the superoxide anion, PAF, and adhesion receptors on leukocytes and endothelial cells.
Effects of an endogenous inhibitor of nitric oxide synthesis on postcapillary venules
Authors: Kurose I. , Wolf R. , Grisham M. B. , Granger D. N.
Published: December 2017

The objective of this study was to determine whether an inhibitor of nitric oxide (NO) synthase (NG,NG'-dimethyl-L-arginine; L-DMA) that is produced by vascular endothelium elicits the inflammatory responses induced by synthetic analogues of L-arginine such as NG-nitro-L-arginine methyl ester (L-NAME). Leukocyte adherence and emigration, leukocyte-platelet aggregation, and albumin leakage were monitored in rat mesenteric venules exposed to different concentrations of either L-DMA or L-NAME. Increases in leukocyte adherence (7- to 9-fold) and emigration (3- to 5-fold), platelet-leukocyte aggregation, mast cell degranulation, and an enhanced albumin leakage (30-50%) were observed within 30 min after exposing the microvascular bed to either inhibitor; however, leukocyte emigration and albumin leakage responded more intensely to L-NAME than to L-DMA. The microvascular alterations and mast cell degranulation were attenuated by addition of L-arginine to the superfusate. These results suggest that the L-DMA is capable of eliciting an inflammatory response at concentrations detected in plasma under certain pathological conditions.
Effect of provocative maneuvers on heart rate variability in subjects with quadriplegia
Authors: Grimm D. R. , DeMeersman R. E. , Garofano R. P. , Spungen A. M. , Bauman W. A.
Published: December 2017

This study investigated heart rate variability (HRV) in individuals with quadriplegia who have disruption of autonomic control of the heart. Seven male subjects with neurological complete quadriplegia and seven with incomplete quadriplegia were studied at rest and during provocation. HRV was measured by power spectral analysis using a fast Fourier transform. Two spectral components were generated: 1) the high-frequency (HF) peak, a reflection of parasympathetic activity, and 2) the low-frequency (LF) peak, primarily sympathetic activity with some parasympathetic input. Results of the provocative maneuvers were grouped into one composite variable. Significant differences in the LF spectral component were found between the groups with complete and incomplete lesions in the supine position and after provocation (LF supine: P = 0.01; LF provocation: P = 0.002). After provocation, significant differences were demonstrated in the HF spectral component between these groups (P = 0.005). In contrast to previous findings, a LF component in subjects with complete quadriplegia was observed; this LF component decreased after provocation, suggesting the parasympathetic component withdrew during stressful maneuvers. There also appeared to be general downregulation of parasympathetic activity to the heart in subjects with complete quadriplegia. The presence of an increased LF spectral component during provocation in those with incomplete lesions implies sympathetic stimulation of the heart and may be used as a marker of sympathetic activity in individuals with quadriplegia.
Predicting the potential gradient field in ventricular fibrillation from shocks delivered in paced rhythm
Authors: Idriss S. F. , Melnick S. B. , Wolf P. D. , Smith W. M. , Ideker R. E.
Published: December 2017

A method of defibrillation threshold determination that utilizes low-strength shocks delivered in a benign rhythm would be desirable. Because the two-dimensional epicardial potential gradient (PG) is a shock parameter that is linked to defibrillation, we examined whether the epicardial PG measured for shocks delivered in paced rhythm could be used to predict the PG for defibrillation-strength shocks delivered in ventricular fibrillation (VF). In six open-chest pentobarbital-anesthetized pigs with left ventricular apex and right atrial internal defibrillation patches, we measured the epicardial PG field for shocks delivered in paced rhythm and during VF. We determined that there was a linear relationship between epicardial PG and shock strength for shocks delivered in paced rhythm. However, prediction of the PG measured for shocks in VF from those measured in paced rhythm resulted in a statistically significant overestimation of the PG in VF. We conclude that, for equivalent strength shocks, the epicardial PG field is weaker for shocks delivered in VF. This change in the potential gradient field can have an effect on defibrillation threshold estimates that are based on shocks delivered in paced rhythm.
A fast transient outward current in cultured cells from human pulmonary artery smooth muscle
Authors: James A. F. , Okada T. , Horie M.
Published: December 2017

A voltage-dependent transient outward current (I(to)) was observed in cells cultured from human pulmonary artery smooth muscle when K+, but not Cs+, was the dominant cation in the pipette solution. In 30% of cells investigated using the Cs+ pipette solution, a tetrodotoxin-sensitive inward current (I(in)) dependent on extracellular Na+ was evoked from depolarizations positive to -30 mV.Iin showed voltage-dependent inactivation with a membrane potential at 50% of the evoked current (V50%) of -75.53 +/- 0.81 mV and slope factor potential (Vs) of -10.73 +/- 0.01 mV. In the presence of 1 microM tetrodotoxin, I(to) was rapidly evoked by depolarizations positive to -40 mV and decayed with a single exponential time course (tau = 9.9 +/- 1.1 ms, pulse potential = +50 mV). I(to) also showed voltage-dependent inactivation with a V50% of -70.9 +/- 2.63 mV and Vs of -7.7 +/- 0.03 mV. I(to) was inhibited concentration dependently by the K+ channel blocker, 4-aminopyridine (4-AP), with a concentration of 4-AP at which I(to) was reduced to 50% of control of 36.5 +/- 2.8 microM. These cells possess voltage-dependent currents characteristic of the K(+)-selective fast transient outward and Na(+)-selective inward currents of smooth muscle cells.
Computer model of current-induced early afterdepolarizations in guinea pig ventricular myocytes
Authors: Nordin C. , Ming Z.
Published: December 2017

We tested the ability of a computer model of transmembrane current and intracellular Ca2+ flux in the isolated guinea pig myocyte (Nordin, C., Am. J. Physiol. 265 (Heart Circ. Physiol. 34): H2117-H2136, 1993) to reproduce data from prior experimental studies and new data presented in this study regarding the behavior of early afterdepolarizations induced by constant inward current, a response closely related to the effect of localized injury currents in damaged myocardial syncytia. The goals of the study were to confirm the model's capacity to reproduce relevant experimental responses for which it was not originally designed and to analyze the mechanisms underlying the experimental phenomena. Under normal conditions, current-induced early afterdepolarizations in the model developed only from membrane potentials associated with L-type Ca2+ channel window current, and the magnitude of upstrokes was unaffected by blockade of either delayed rectifier K+ current or sarcoplasmic reticulum Ca2+ release. After Ca2+ loading secondary to either reduced extracellular [K+] or inhibition of Na(+)-K(+)-adenosinetriphosphatase activity, the threshold potential for current-induced early afterdepolarizations in the model, as with experimental myocytes, shifted to membrane potentials negative to the threshold potential for Ca2+ channel activation. Upstrokes were initiated by inward currents generated by electrogenic Na/Ca exchange following oscillatory Ca2+ release from the sarcoplasmic reticulum. New experiments presented in this study demonstrate that bursts of rapid depolarizing stimulations terminate current-induced early afterdepolarizations. Termination is caused by transient hyperpolarizations, which increase as a function of number or duration of stimulations, and if strong enough, cross the all-or-none threshold and lead to full repolarization. This experimental response was accurately simulated by the model through interactions that led to activation of delayed rectifier current, inactivation of Ca2+ channel current, and a reduction in inward Na/Ca exchange current secondary to altered intracellular Ca2+ cycling. We confirm that the model accurately simulates a wide range of responses beyond its original experimental constraints and suggest that current-induced early afterdepolarizations are initiated and terminated by complex processes that vary with specific experimental conditions and involve multiple currents.