bluuebunny/crossref_metadata_2025 huggingface dataset:
Heparin inhibits collagenase gene expression mediated by phorbol ester-responsive element in primate arterial smooth muscle cells.
Authors: Au Y P , Montgomery K F , Clowes A W
Published: June 2012

Heparin is a potent inhibitor of arterial smooth muscle cell (SMC) migration and proliferation in vivo and in vitro. We propose that heparin affects these SMC functions by interfering with either the expression or the activity of secreted proteases required for cell movement. We have reported that heparin selectively inhibits the expression of tissue-type plasminogen activator in SMCs during mitogenesis. In this study we show that the gene expression of another kind of protease, interstitial collagenase, is induced by fetal bovine serum and is also suppressed by heparin. The inhibitory effect on the induced collagenase mRNA is specific to heparin-like molecules and does not depend on the anticoagulant activity of heparin. The induction of the collagenase gene depends on the protein kinase C pathway, since it can be induced by phorbol esters such as phorbol 12-myristate 13-acetate and blocked by inhibitors such as H-7 and staurosporine. In transient transfection assays with chloramphenicol acetyltransferase constructs containing the phorbol ester-responsive element introduced into baboon SMCs, heparin inhibits transcription induced by serum or phorbol 12-myristate 13-acetate. These results support the conclusion that, in primate SMCs, interstitial collagenase gene transcription mediated by the phorbol ester-responsive element is blocked by heparin.
Regulated tissue- and cell-specific expression of the human renin gene in transgenic mice.
Authors: Sigmund C D , Jones C A , Kane C M , Wu C , Lang J A , Gross K W
Published: June 2012

Transgenic mice containing the human renin gene were constructed with the aim of examining the tissue- and cell-specific expression of human renin. The human renin transgene used consisted of a genomic sequence extending approximately 900 bp upstream and 400 bp downstream of the coding region and included all exon and intron sequences. Two assays were developed to differentiate human renin transcripts from endogenous mouse renin transcripts at the whole-tissue level. High level human renin expression was evident in the kidney, adrenal gland, ovary, testis, lung, and adipose tissue of all four transgenic lines examined. Human renin mRNA could also be detected at lower levels in the submandibular gland and heart of two different individual lines. No expression was evident in the liver or brain of any line tested. In situ hybridization revealed the human renin mRNA to be localized and exquisitely restricted to renal juxtaglomerular cells. Treatment of transgenic mice with captopril resulted in an increase in the accumulation of renal renin mRNAs derived from both the mouse and human renin genes. Plasma renin activity assays using synthetic human renin substrate clearly demonstrated the elaboration of active human renin into the systemic circulation of transgenic mice. These data strongly suggest that the human renin transgene exhibits both tissue- and cell-specific expression in transgenic mice. Its expression is entrained to the same regulatory signals as the endogenous renin gene in kidney, and active human renin is released into the plasma of the transgenic mice.(ABSTRACT TRUNCATED AT 250 WORDS)
Energy metabolism and contractile function after 15 beats of moderate myocardial ischemia.
Authors: Arai A E , Pantely G A , Thoma W J , Anselone C G , Bristow J D
Published: June 2012

Difficulties in studying myocardial metabolism with adequate time resolution have led to contradictory conclusions regarding the mechanisms causing contractile abnormalities during the early stages of ischemia. In acutely instrumented swine, we investigated whether abnormalities in subendocardial ATP, phosphocreatine, or lactate content develop rapidly enough during the first few heart beats after onset of partial myocardial ischemia to contribute to contractile failure. Within the first 15 beats of a 40-50% reduction in left anterior descending coronary artery blood flow, regional myocardial function was significantly reduced but continuing to deteriorate. Rapidly frozen transmural left ventricular biopsies obtained on the 15th heart beat (+/- 1.5 beats) after the onset of ischemia revealed significant decrements in subendocardial phosphocreatine and ATP levels to 77% (p less than 0.05) and 84% (p less than 0.005) of control values, respectively, but minimal change in lactate content. Metabolic effects as assessed by transmural averages took longer to become detectable; thus, there was a tendency to underestimate the importance of subendocardial metabolic effects on myocardial function. When left ventricular preload was assessed during this early time period, left ventricular end-diastolic wall thickness only decreased by 3%, and left ventricular end-diastolic pressure did not change significantly despite a large fall in coronary perfusion pressure. Thus, in an in vivo pig model with techniques optimized to detect subendocardial metabolic changes within the period of very early moderate myocardial ischemia, abnormalities in high energy phosphate compounds occurred rapidly enough to contribute to developing myocardial dysfunction, whereas preload-mediated mechanisms related to vascular distending pressure could not explain the functional deterioration under these conditions.
Relation between glycolysis and calcium homeostasis in postischemic myocardium.
Authors: Jeremy R W , Koretsune Y , Marban E , Becker L C
Published: June 2012

This study examined the hypothesis that glycolysis is required for functional recovery of the myocardium during reperfusion by facilitating restoration of calcium homeostasis. [Ca2+]i was measured in isolated perfused rabbit hearts by using the Ca2+ indicator 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5F-BAPTA) and 19F nuclear magnetic resonance spectroscopy. In nonischemic control hearts, inhibition of glycolysis with iodoacetate did not alter [Ca2+]i. In hearts subjected to 20 minutes of global zero-flow ischemia, [Ca2+]i increased from 260 +/- 80 nM before ischemia to 556 +/- 44 nM after 15 minutes of ischemia (p less than 0.05). After reperfusion with 5 mM pyruvate as a carbon substrate, [Ca2+]i increased further in hearts with intact glycolysis to 851 +/- 134 nM (p less than 0.05 versus ischemia) during the first 10 minutes of reperfusion, before returning to preischemic levels. In contrast, inhibition of glycolysis during the reperfusion period resulted in persistent severe calcium overload ([Ca2+]i, 1,380 +/- 260 nM after 15 minutes of reperfusion, p less than 0.02 versus intact glycolysis group). Furthermore, despite the presence of pyruvate and oxygen, inhibition of glycolysis during early reperfusion resulted in greater impairment of functional recovery (rate/pressure product, 3,722 +/- 738 mm Hg/min) than did reperfusion with pyruvate and intact glycolysis (rate/pressure product, 9,851 +/- 590 mm Hg/min, p less than 0.01). Inhibition of glycolysis during early reperfusion was also associated with a marked increase in left ventricular end-diastolic pressure during reperfusion (41 +/- 5 mm Hg) compared with hearts with intact glycolysis (16 +/- 2 mm Hg, p less than 0.01). The detrimental effects of glycolytic inhibition during early reperfusion were, however, prevented by initial reperfusion with a low calcium solution ([Ca]o, 0.63 mM for 30 minutes, then 2.50 mM for 30 minutes). In these hearts, the rate/pressure product after 60 minutes of reperfusion was 12,492 +/- 1,561 mm Hg/min (p less than 0.01 versus initial reflow with [Ca]o of 2.50 mM). These findings indicate that the functional impairment observed in postischemic myocardium is related to cellular Ca2+ overload. Glycolysis appears to play an important role in restoration of Ca2+ homeostasis and recovery of function of postischemic myocardium.
Bovine angiotensin converting enzyme cDNA cloning and regulation. Increased expression during endothelial cell growth arrest.
Authors: Shai S Y , Fishel R S , Martin B M , Berk B C , Bernstein K E
Published: June 2012

Angiotensin converting enzyme (ACE) is a zinc-containing dipeptidase that converts angiotensin I to angiotensin II, a powerful vasoconstrictor and smooth muscle growth factor. ACE activity has been shown to be dynamically regulated by hormones, ACE inhibitors, and endothelial cell growth state. To study how ACE expression is regulated, we isolated and sequenced the bovine ACE gene using both ACE-specific cDNA and genomic clones. Bovine ACE cDNA encodes a single polypeptide of 1,306 residues with a molecular mass of 150 kd. Bovine ACE is approximately 80% homologous to that of other species. It contains two homologous domains of equal size. Alignment of ACE sequences from bovine, human, mouse, and rabbit reveals that during evolution both domains have been highly conserved. We used the bovine ACE cDNA to study regulation of ACE gene expression during density-dependent growth arrest. As endothelial cells became growth-arrested (6 days after confluence), there was a 12-fold increase in ACE activity and a 90% decrease in DNA synthesis. Immunocytochemically detectable ACE markedly increased in growth-arrested cells. The increase in ACE was due to increased ACE gene expression, as assayed by RNase protection, which showed a 20-fold increase in ACE-specific mRNA. The present study shows that bovine ACE is highly regulated by endothelial cell growth state at the level of protein and mRNA expression. Such dynamic regulation may have important consequences for angiotensin II production during endothelial cell proliferation after arterial injury.
Subcellular electrolyte alterations during progressive hypoxia and following reoxygenation in isolated neonatal rat ventricular myocytes.
Authors: Thandroyen F T , Bellotto D , Katayama A , Hagler H K , Willerson J T , Buja L M
Published: June 2012

This study characterizes the sequential alterations of, and relations between, multiple electrolytes in cytoplasm, mitochondria, and whole cells during hypoxia and on reoxygenation in isolated neonatal rat ventricular myocytes. Subcellular electrolyte content and distribution were measured by electron probe x-ray microanalysis, membrane phospholipid degradation by tritiated arachidonic acid release, and cell morphology by electron microscopy. At 1-2 hours of hypoxia, the myocyte population showed a loss of cytoplasmic potassium, magnesium, and chlorine without alteration of cytoplasmic sodium or calcium. Mitochondria showed increased potassium with unchanged magnesium content. There was no morphological evidence of cell injury or tritiated arachidonic acid release. At 3-5 hours of hypoxia, the myocyte population showed a further loss of cytoplasmic potassium and magnesium and an increase in cytoplasmic sodium, chlorine, and calcium. At a single-cell level, the increase in cytoplasmic sodium preceded the increase in cytoplasmic calcium. Mitochondria showed increased sodium and chlorine and decreased magnesium before increased calcium content; potassium loss was manifest only at 5 hours of hypoxia. At 3-5 hours of hypoxia, there was also tritiated arachidonic acid release and morphological evidence of cell injury. Reoxygenation for 1 hour after 5 hours of hypoxia partially reversed the mean alterations of all electrolytes, except calcium, in the cytoplasm of the myocyte population, whereas analysis was required at a single-cell level to show a partial reversal in calcium levels in cytoplasm of reoxygenated cells. Reoxygenation for 1 hour after 5 hours of hypoxia partially reversed the mean alterations of all electrolytes, including calcium, in the mitochondria of the myocyte population. Recovery of potassium in the cytoplasm correlated with reduction of mitochondrial calcium content on reoxygenation and best predicted recovery of cellular homeostasis of sodium, chlorine, magnesium, and calcium. This study demonstrates that in this experimental model of hypoxia 1) initial losses of cytoplasmic potassium and magnesium occur in the absence of cell injury; 2) increases of sodium, chlorine, and calcium occur in association with cell injury, with sodium increasing before calcium; 3) membrane phospholipid degradation and electrolyte derangement, including increased calcium, may contribute to reversible and irreversible phases of cell injury; 4) analysis of calcium at a subcompartmental level and at a single-cell level is required to correlate reduction of calcium on reoxygenation with recovery of cell homeostasis; 5) reduction of calcium content in mitochondria may predict recovery of cell homeostasis; and 6) recovery of potassium on reoxygenation best predicts recovery of cell membrane function and cell homeostasis.
Gap junctional conductance in ventricular myocyte pairs isolated from postischemic rabbit myocardium.
Authors: Kieval R S , Spear J F , Moore E N
Published: June 2012

Abnormalities of myocardial gap junction-mediated cell coupling have been implicated in cardiac arrhythmogenesis. The potential role of gap junctional dysfunction in the generation of reperfusion-induced arrhythmias is uncertain. The purpose of this study was to measure the effects of myocardial ischemia and reperfusion on gap junctional conductance (gj) between isolated ventricular myocytes. By using a new experimental model, myocyte pairs were isolated from Langendorff-perfused rabbit hearts 1) after 30 minutes of global normothermic ischemia followed by 30 minutes of reperfusion, 2) after 75 minutes of control perfusion, or 3) immediately after removal of the heart. Myocytes and myocyte pairs were studied using whole-cell recording techniques. Action potential characteristics of cells in all three groups were normal. Despite similar mean gj in all three groups (0.88 +/- 0.27, 1.15 +/- 0.18, and 1.24 +/- 0.25 microS, respectively; p greater than 0.05), the postischemic group was more widely distributed and had a significantly greater proportion of poorly communicating cell pairs than either control group (gj less than 25% of mean in eight of 15 myocyte pairs versus zero of 15 and one of 13, respectively; p less than 0.02). Thus, postischemic myocyte pairs represent a heterogeneous population of electrically coupled cells in which individual deficits in coupling are masked by a normal mean value. In the reperfused intact heart, local disturbances of cell coupling, similarly undetected by gross measures of conduction, could disrupt myocardial conduction and activation on a microscopic scale and thus enhance arrhythmogenicity.
Arterial mechanics in spontaneously hypertensive rats. Mechanical properties, hydraulic conductivity, and two-phase (solid/fluid) finite element models.
Authors: Gaballa M A , Raya T E , Simon B R , Goldman S
Published: June 2012

To characterize the interaction between mechanical and fluid transport properties in hypertension, we measured in vivo elastic material constants and hydraulic conductivity in intact segments of carotid arteries in normal and spontaneously hypertensive rats (SHR). With the use of a finite element model, the arterial wall was modeled as a large-deformation, two-phase (solid/fluid) medium, which accounts for the existence and motion of the tissue fluid. Measurements of internal diameter and transmural pressures were obtained during continuous increases in pressure from 0 to 200 mm Hg. Strain and stress components were calculated based on a pseudostrain exponential energy density function. To measure the hydraulic conductivity, segments of the carotid artery were isolated, filled with a 4% oxygenated albumin-Tyrode's solution, and connected to a capillary tube. The movement of the meniscus of the capillary tube represented the fluid filtration across the artery. To study the influence of transmural pressure on hydraulic conductivity, measurement of fluid filtration across the arterial wall was obtained at transmural pressures of 50 and 100 mm Hg. The material constants in the SHR (n = 9) were higher (p less than 0.05 for all variables) than in normal rats (n = 10): c = 1,343 +/- 96 versus 1,158 +/- 65 mm Hg, b1 = 1.84 +/- 0.24 versus 1.22 +/- 0.22, b2 = 0.769 +/- 0.114 versus 0.616 +/- 0.11, b3 = 0.017 +/- 0.005 versus 0.0065 +/- 0.002, b4 = 0.206 +/- 0.04 versus 0.083 +/- 0.03, b5 = 0.0594 +/- 0.007 versus 0.0217 +/- 0.006, and b6 = 0.22 +/- 0.09 versus 0.123 +/- 0.02, respectively. The hydraulic conductivity of the total wall, calculated from the filtration data, was lower (p less than 0.05) at both 50 and 100 mm Hg in the SHR (n = 6) compared with normal rats (n = 7): 1.12 +/- 0.31 x 10(-8) and 0.72 +/- 0.23 x 10(-8) versus 1.95 +/- 0.53 x 10(-8) and 1.35 +/- 0.47 x 10(-8) cm/(sec.mm Hg), respectively. The intergroup comparisons between 50 and 100 mm Hg in both SHR and normal rats were also different (p less than 0.05). The finite element model was used to predict tissue fluid pressure distribution, tissue fluid velocity distribution, and total Cauchy stress gradients developed in the arterial wall during fluid pressurization in both species.(ABSTRACT TRUNCATED AT 400 WORDS)
ATP dependence of calcium uptake by the Na-Ca exchanger of adult heart cells.
Authors: Haworth R A , Goknur A B
Published: June 2012

The ATP dependence of the Na-Ca exchanger was investigated in isolated adult rat heart cells to evaluate the extent to which ATP depletion after a period of ischemia plus reperfusion in whole hearts could limit calcium uptake by Na-Ca exchange. A standard state for measurement of Na-Ca exchange activity that could be used with cells depleted of ATP to different degrees was defined. This was a state of zero sarcolemmal gradient for sodium, potassium, and pH and was achieved by incubation of the cells for 5 minutes with EDTA, EGTA, ouabain, and nigericin. Heterogeneity of cell ATP levels was minimized by using a protocol of total ATP depletion by incubation under conditions similar to ischemia, followed by reoxygenation to give partial restoration of ATP levels. No ATP was regenerated when cells were reoxygenated in the presence of rotenone, and such cells showed a very low rate of calcium uptake. Without rotenone, cells showed an almost complete restoration of Na-Ca exchange activity, in spite of a restoration of ATP levels to only one third of control values. Thus, the dependence of calcium uptake on ATP was highly nonlinear under these conditions. The calculated Km for ATP was no more than 10% of normal ATP levels. We conclude that ATP depletion after ischemia plus reperfusion is unlikely to limit the rate of calcium uptake through Na-Ca exchange in the whole heart if at least one quarter of the ATP is restored. In addition, we measured the apparent ATP dependence of calcium uptake by Na-Ca exchange in cells under conditions in which we previously had concluded that cell ATP distributions were very heterogeneous: when cells undergo contracture during incubation with oligomycin and without glucose. A linear relation between calcium uptake rate and ATP was observed at all ATP levels. This can be understood if cells in contracture that are incubated with oligomycin cannot take up calcium because of low ATP, whereas rod-shaped cells are able to retain a full uptake capability. This result further supports our conclusion that the ATP level declines catastrophically to near zero in these oligomycin-incubated cells just before contracture.
Balloon injury and interleukin-1 beta induce nitric oxide synthase activity in rat carotid arteries.
Authors: Joly G A , Schini V B , Vanhoutte P M
Published: June 2012

Experiments were performed to investigate whether balloon injury induces nitric oxide synthase activity in the blood vessel wall. Contractions to phenylephrine were compared in left carotid arteries of the rat, previously injured by balloon catheterization and excised either immediately (t = 0), 6, or 24 hours after the procedure, with those in control right carotid arteries (with and without endothelium). Phenylephrine evoked comparable concentration-dependent contractions in balloon-injured (t = 0) and control carotid arteries without endothelium, whereas those in control arteries with endothelium were depressed. In the balloon-injured carotid arteries (6 and 24 hours), the concentration-contraction curves to phenylephrine were shifted to the right compared with those observed in balloon-injured arteries (t = 0). In balloon-injured carotid arteries (6 hours), the hyporeactivity to phenylephrine was enhanced by superoxide dismutase. In balloon-injured carotid arteries (24 hours), nitro-L-arginine and methylene blue restored full contractions, whereas superoxide dismutase potentiated the hyporesponsiveness to phenylephrine. The depressed contractions were associated with a concomitant increase in the basal level of cGMP; this production was abolished by nitro-L-arginine. The depression of the concentration-contraction curves to phenylephrine and the increase of the tissue level of cGMP induced by interleukin-1 beta (4 hours) were more pronounced in balloon-injured arteries (24 hours) than in control arteries without endothelium. The effects of interleukin-1 beta were inhibited by nitro-L-arginine. These observations indicate that in vivo endothelial injury of the rat carotid arteries induces the production of nitric oxide from L-arginine in the blood vessel wall, an effect which is potentiated by interleukin-1 beta.
Indirect relation between rises in oxygen consumption and left ventricular output at birth in lambs.
Authors: Smolich J J , Soust M , Berger P J , Walker A M
Published: June 2012

To examine the relation between increased newborn oxygen requirements and the postnatal rise in cardiac output, we measured left ventricular (LV) output, organ blood flows, and whole-body oxygen consumption using radioactive microspheres in late-gestation sheep fetuses and in the same animals 1 and 4 hours after cesarean section delivery. LV output rose from 264 +/- 23 ml.min-1.kg body wt-1 in fetuses to 444 +/- 33 ml.min-1.kg body wt-1 in lambs at 1 hour after delivery (p less than 0.005) and was unchanged at 4 hours after delivery. This rise in LV output was associated with a more than fourfold increase in the LV flow contribution to tissues situated distal to the ductus arteriosus (fetus, 51 +/- 9 ml.min-1.kg body wt-1; lamb, 226 +/- 22 ml.min-1.kg body wt-1; p less than 0.005), which were mainly perfused by the right ventricle in utero. However, average blood flow to body tissues was similar in fetuses (37 +/- 4 ml.min-1.100 g tissue-1), 1-hour lambs (39 +/- 4 ml.min-1.100 g tissue-1), and 4-hour lambs (40 +/- 5 ml.min-1.100 g tissue-1). Oxygen consumption increased by 58%, from 7.84 +/- 0.43 ml.min-1.kg body wt-1 in fetuses to 12.38 +/- 2.4 ml.min-1.kg body wt-1 in 1-hour lambs (p less than 0.01), and was unchanged in 4-hour lambs.(ABSTRACT TRUNCATED AT 250 WORDS)
Dissociation between contractile function and oxidative metabolism in postischemic myocardium. Attenuation by ruthenium red administered during reperfusion.
Authors: Benzi R H , Lerch R
Published: June 2012

The oxidative metabolic rate may be disproportionately high compared with contractile function in postischemic reperfused myocardium. To study the potential involvement of intracellular calcium transport in high energy expenditure after reperfusion, we determined in isolated rat hearts the effect of ruthenium red, an inhibitor of mitochondrial calcium transport, on recovery of contractile function and oxidative metabolic rate. Hearts subjected to 60 minutes of no-flow ischemia exhibited, at 15 minutes after the onset of reperfusion, poor recovery of left ventricular pressure development to only 7% of the corresponding value measured in control hearts (p less than 0.01). However, myocardial oxygen consumption was recovered to 84% of control (p = NS). The ratio of isovolumic contractile performance (expressed as the product of heart rate and left ventricular pressure development) to myocardial oxygen consumption was severely depressed to 6% of control (p less than 0.01). Supplementation of the perfusate with 6 microM ruthenium red during the initial 40 minutes of reperfusion resulted in a reduction of myocardial oxygen consumption to 65% of the value measured after 15 minutes of reperfusion in hearts reperfused without ruthenium red (p less than 0.01), despite a threefold increase of left ventricular pressure development (p less than 0.05). Oxidation of both palmitate and glucose was reduced to a comparable extent by ruthenium red. The ratio of contractile performance to myocardial oxygen consumption increased progressively during infusion of ruthenium red and did not differ further from control hearts after 30 minutes of reperfusion. Cumulative myocardial release of creatine kinase was reduced by 47% (p less than 0.05) in hearts reperfused with ruthenium red-containing medium. The results provide circumstantial evidence for the hypothesis suggesting that enhanced energy expenditure by intracellular calcium transport may be involved in the mechanisms underlying the dissociation between left ventricular performance and myocardial oxidative metabolic rate early after postischemic reperfusion.
Comprehensive model of transport and metabolism of adenosine and S-adenosylhomocysteine in the guinea pig heart.
Authors: Kroll K , Deussen A , Sweet I R
Published: June 2012

Regulation of blood flow and mitochondrial respiration in the heart would be clarified by improved knowledge of interstitial concentrations and cellular production rates of adenosine; however, these variables cannot be measured directly. To interpret indexes that are available, a comprehensive mathematical model was developed, based on a large body of experimental data. The model describes most of the important pathways of capillary-tissue transport and cellular metabolism of adenosine in the guinea pig heart. It includes capillary flow, solute transport between tissue regions, nonlinear enzyme kinetics for adenosine kinase and adenosine deaminase, and reversible biunireactant kinetics for S-adenosylhomocysteine hydrolase in cardiomyocytes and endothelial cells, intracellular production of adenosine via AMP hydrolysis and transmethylation, and extracellular production of adenosine. A single set of parameter values for the model was obtained in the first stage of the analysis by taking certain values directly from published sources, other values were subject to specific constraints, and other values were determined by parameter optimization. The effects of flow and endothelial metabolism on the relation between interstitial and venous adenosine concentrations were determined. The relation between myocardial adenosine production rate and S-adenosylhomocysteine accumulation in the presence of excess homocysteine was estimated. In the second stage of the analysis, the model was used to investigate the mechanism of myocardial adenosine production, without changing the parameter values. Cellular adenosine production rates were estimated by fitting measurements of venous adenosine release obtained during altered energetic conditions in experiments by different investigators. The original results showed a dissociation between measurements of cytosolic AMP concentrations and venous adenosine release. It is concluded that 1) it is essential to account for the effect of flow on interstitial and venous adenosine concentrations, since decreased flow may produce effects outwardly resembling inhibition of the enzyme 5'-nucleotidase, 2) adenosine concentrations in epicardial transudate are not in equilibrium with interstitial fluid, and 3) the rate of cellular adenosine production increases monotonically with free cytosolic concentrations of AMP during a variety of alterations in energy balance of the guinea pig heart.
Epicardial excitation during ventricular pacing. Relative independence of breakthrough sites from excitation sequence in canine right ventricle.
Authors: Arisi G , Macchi E , Corradi C , Lux R L , Taccardi B
Published: June 2012

In a previous investigation, epicardial recordings with 1,124 closely spaced electrodes revealed 20-35 breakthrough (BKT) sites and an equal number of separate wave fronts on the ventricular surface of exposed dog hearts during normal sinus rhythm. In the present study we tried 1) to determine whether ventricular pacing also produced multiple BKTs and wave fronts and 2) to determine whether the number and location of BKTs were, to some degree, independent of pacing site. The study mainly focused on right ventricular BKTs observed during right ventricular pacing. To test hypotheses 1 and 2 we identified many breakthrough sites during sinus rhythm in seven exposed dog hearts and then paced the heart from several BKT and non-BKT sites on the right ventricle. Epicardial potential maps and excitation time maps were obtained by using 1,124 epicardial electrodes covering the anterior right ventricle and part of the anterior left ventricle. A primary wave front spread radially for several centimeters from the pacing site, and no BKTs appeared in the areas covered by the primary wave front. In the remaining areas (secondary areas), multiple BKTs appeared; their number was close to that observed during sinus rhythm in the same areas (113 versus 115, respectively, in 12 paced beats). The majority of paced BKTs (83 out of 115, or 72%) occurred exactly at the same locations where they appeared during sinus rhythm. However, 30 right ventricular BKTs observed during sinus rhythm disappeared in the secondary areas and were replaced by approximately the same number of new BKTs. Many areas without BKTs in normal beats remained so in paced beats.(ABSTRACT TRUNCATED AT 250 WORDS)
Sequence of excitation as a factor in sympathetic-parasympathetic interactions in the heart.
Authors: Yang T , Levy M N
Published: June 2012

We determined the influence of differences in the time of initiation of sympathetic and vagal stimulation (both at 10 Hz) on the cardiac autonomic interactions in 16 open-chest anesthetized dogs. We always ended the concurrent sympathetic and vagal stimulations simultaneously. Sympathetic stimulation alone for 1 minute increased heart rate by 90 +/- 7 (mean +/- SEM) beats per minute, and vagal stimulation alone for 1 minute decreased heart rate by 67 +/- 5 beats per minute; i.e., the algebraic sum of these responses was an increase of 23 beats per minute. However, combined sympathetic and vagal stimulation for 1 minute actually decreased heart rate by 35 beats per minute; i.e., the vagal effects predominated. When vagal stimulation was initiated first, the chronotropic responses to combined stimulation were not significantly affected by the duration of antecedent vagal stimulation. However, when sympathetic stimulation was initiated first, the vagal predominance (disparity between the summated individual responses and the combined response) progressively diminished as we increased the duration of antecedent sympathetic stimulation. The vagal predominance diminished from a value of 67 +/- 21 beats per minute when the stimulations were initiated simultaneously to a value of 37 +/- 21 beats per minute when the duration of antecedent sympathetic stimulation was 10 minutes. Sympathetic stimulation releases not only norepinephrine but also neuropeptide Y, and this neuropeptide inhibits vagal neurotransmission. Our data suggest, therefore, that the longer the antecedent sympathetic stimulation, the greater the inhibition of vagal neurotransmission (presumably by the neuropeptide Y) and, therefore, the less pronounced the vagal predominance.
Albumin transport characteristics of rat aorta in early phase of hypertension.
Authors: Tedgui A , Merval R , Esposito B
Published: June 2012

The effects of early-stage hypertension on the macromolecular transport characteristics of the aorta have been investigated in rats 1 week after the ligature of the abdominal aorta between the two renal arteries. The animals were left untreated or treated for 1 week with an angiotensin converting enzyme inhibitor (enalapril, 6 mg/kg per day). Blood pressure of a subgroup of hypertensive rats was acutely lowered to a normal level by injection of enalaprilat (1.5 mg/kg) at the time of the experiment. 131I-Albumin and 125I-albumin were injected 90 minutes and 5 minutes, respectively, before the rats were killed. The transmural distribution of the relative tissue concentrations across the wall was obtained using a serial frozen-section technique. Short-term albumin uptake permitted calculation of apparent endothelial permeability coefficients, and 90-minute uptake was used to estimate the steady-state albumin distribution within the media. The effect of early-stage hypertension on the characteristics of the arterial macromolecular transport depended on the aortic site; the ascending aortic arch appeared not to be affected. In the thoracic and abdominal aorta, the endothelial permeability coefficients increased significantly in hypertensive rats. This increase was not a direct effect of the arterial pressure, since the values were not significantly different when the pressure was acutely normalized. The 90-minute albumin concentration in the media was enhanced in hypertensive rats and returned to the normal value by acutely lowering the blood pressure, indicating that the increase observed in hypertensive rats resulted from a direct effect of pressure, possibly increased pressure-driven convection and/or pressure-induced stretching of the wall. Treatment by angiotensin converting enzyme inhibitor prevented hypertension and protected against its effects in hypertensive animals.
Depression of cardiac sarcolemmal phospholipase D activity by oxidant-induced thiol modification.
Authors: Dai J , Meij J T , Padua R , Panagia V
Published: June 2012

Myocardial phospholipase D (PLD) is primarily localized at the sarcolemmal level and selectively hydrolyzes phosphatidylcholine to form phosphatidic acid as part of the signal transduction mechanisms for regulating Ca2+ movements in the heart. Since the myocardial cell damage induced by oxidative stress is associated with abnormalities in Ca2+ homeostasis and thiol status, we examined the thiol group dependence and the effects of oxidant species on this enzyme. Sarcolemmal membranes isolated from rat heart were exposed to several types of thiol group modifiers. Alkylation with N-ethylmaleimide or methyl methanethiosulfonate, mercaptide formation with p-chloromercuriphenylsulfonic acid, and thiol-disulfide exchange with 5,5'-dithio-bis(2-nitrobenzoate) depressed sarcolemmal PLD activity; in all cases the depression was prevented by dithiothreitol. At different concentrations of N-ethylmaleimide the PLD depression correlated well (r = 0.98) with the decrease in total thiol group content of the membrane. The enzyme activity was not affected by xanthine-xanthine oxidase, a superoxide anion-generating system, but was depressed by hydrogen peroxide (H2O2) in a concentration-dependent manner. This inhibitory effect was prevented by catalase as well as by dithiothreitol, but not by D-mannitol. The effect of a hydroxyl radical-generating system (Fenton reaction) could not be assessed because of an interfering direct inhibition by Fe2+. Dithiothreitol was also able to restore PLD activity in H2O2-pretreated membranes and to prevent a severe deactivation of the enzyme by hypochlorous acid (HOCI). Protection by glutathione and inhibition by its oxidized form were also observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of cycling and rigor crossbridges on the conformation of cardiac troponin C.
Authors: Hannon J D , Martyn D A , Gordon A M
Published: June 2012

The results of work by several investigators indicate that crossbridge attachment serves as a positive feedback mechanism that transiently increases the Ca2+ affinity of troponin C (TnC) during each normal heartbeat. To monitor structural changes in the cardiac isoform of TnC (cTnC) associated with Ca2+ binding and crossbridge attachment in muscle, we labeled cTnC with the sulfhydryl-specific fluorescent probe 2-(4'-iodoacetamidoanilino)naphthalene-6-sulfonic acid (IAANS). When IAANS-labeled cTnC (cTnCIAANS) was substituted for endogenous TnC, the fluorescence intensity of cardiac and skeletal muscle preparations increased substantially during rigor crossbridge attachment in the absence of Ca2+ (pCa 9.2). In cardiac muscle, the fluorescence signal increased the same amount in rigor and maximal activation, whereas in skeletal muscle, it was higher in rigor (rigor: cardiac and skeletal = 1; pCa 4.0: cardiac = 0.98 +/- 0.13, skeletal = 0.59 +/- 0.05). This indicates that crossbridge attachment alone is capable of influencing the structure of cTnCIAANS. Because the relative fluorescence intensity of cTnCIAANS was more sensitive to Ca2+ than was force in both preparations (cardiac: pCa50 fluorescence = 6.05 +/- 0.05, pCa50 force = 5.51 +/- 0.11; skeletal: pCa50 fluorescence = 5.94 +/- 0.13, pCa50 force = 5.65 +/- 0.14), we measured the Ca2+ sensitivity of the strong crossbridge attachment (sinusoidal stiffness was measured by imposing 1 kHz at 0.1-0.2% muscle length) in rat trabeculae.(ABSTRACT TRUNCATED AT 250 WORDS)
Culture of renal arteriolar smooth muscle cells. Mitogenic responses to angiotensin II.
Authors: Dubey R K , Roy A , Overbeck H W
Published: June 2012

We cultured smooth muscle cells from rat renal preglomerular arterioles by injecting a suspension of iron oxide into the left ventricle, separating the arterioles magnetically, and growing cells from explants. In passaged cultures we ascertained vascular smooth muscle purity of > 98% by morphology; contraction to norepinephrine and angiotensin; positive immunofluorescence staining through the sixth passage with monoclonal antibodies to smooth muscle-specific alpha- and gamma-isoactins, myosin, and desmin; and the absence of von Willebrand factor. Angiotensin II (10(-12)-10(-5) M) induced dose-dependent DNA synthesis and proliferation of subcultured (three times) arteriolar smooth muscle cells from a growth-arrested state (p < 0.01). Angiotensin II (10(-5) M) also induced the cells to express c-fos mRNA. We find no previous report of culture of smooth muscle cells from renal preglomerular arterioles. Our findings also provide evidence that angiotensin II is mitogenic to arteriolar muscle cells and thus may be involved in their hyperplasia accompanying hypertension.
Mechanism of hind limb vasoconstriction due to cyclosporin A in the dog.
Authors: Tronc F , Carrier M , Pelletier C L
Published: June 2012

Cyclosporin A (CSA) causes an acute vasoconstriction of hind limb arterial vessels. To determine the mechanism of action of CSA on the peripheral arterial bed, studies were performed on the isolated femoral artery perfused at constant flow in 61 dogs. Changes in femoral perfusion pressure reflected variations in vascular resistance. Pure powder CSA was dissolved in autologous blood and injected at doses of 1, 5, 10, and 20 mg. Infusions of 1 and 5 mg CSA caused nonsignificant mean increases of 4 +/- 2 mm Hg (95% confidence interval [CI], 0-8; p > 0.05) and 10 +/- 4 mm Hg (95% CI, 0-21; p > 0.05) in femoral perfusion pressure, with CSA blood levels in the femoral vein averaging 40 +/- 16 and 126 +/- 50 nmol/l, respectively, at the end of the injections. Infusions of 10 and 20 mg CSA caused significant increases in femoral perfusion pressure averaging of 8 +/- 3 mm Hg (95% CI, 1-14; p < 0.05) and 20 +/- 4 mm Hg (95% CI, 11-29; p < 0.05) in femoral perfusion pressure. CSA blood levels at the end of injections averaged 271 +/- 99 and 431 +/- 146 nmol/l, respectively, in the femoral vein. Blockade of alpha-adrenergic receptors with phentolamine and surgical lumbar sympathectomy decreased significantly the CSA vasoconstrictive effect in peripheral arterial vessels, with increases in perfusion pressure averaging 29 +/- 5 mm Hg before and 14 +/- 3 mm Hg after phentolamine (p < 0.05) and 30 +/- 2 mm Hg before and 8 +/- 2 mm Hg after sympathectomy (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanisms of alpha 1-adrenergic vascular desensitization in conscious dogs.
Authors: Kiuchi K , Vatner D E , Uemura N , Bigaud M , Hasebe N , Hempel D M , Graham R M , Vatner S F
Published: June 2012

To investigate the mechanisms of alpha 1-adrenergic vascular desensitization, osmotic minipumps containing either saline (n = 9) or amidephrine mesylate (AMD) (n = 9), a selective alpha 1-adrenergic receptor agonist, were implanted subcutaneously in dogs with chronically implanted arterial and right atrial pressure catheters and aortic flow probes. After chronic alpha 1-adrenergic receptor stimulation, significant physiological desensitization to acute AMD challenges was observed, i.e., pressor and vasoconstrictor responses to the alpha 1-adrenergic agonist were significantly depressed (p < 0.01) compared with responses in the same dogs studied in the conscious state before pump implantation. However, physiological desensitization to acute challenges of the neurotransmitter norepinephrine (NE) (0.1 micrograms/kg per minute) in the presence of beta-adrenergic receptor blockade was not observed for either mean arterial pressure (MAP) (30 +/- 7 versus 28 +/- 5 mm Hg) or total peripheral resistance (TPR) (29.8 +/- 4.9 versus 28.9 +/- 7.3 mm Hg/l per minute). In the presence of beta-adrenergic receptor plus ganglionic blockade after AMD pump implantation, physiological desensitization to NE was unmasked since the control responses to NE (0.1 micrograms/kg per minute) before the AMD pumps were now greater (p < 0.01) than after chronic AMD administration for both MAP (66 +/- 5 versus 32 +/- 2 mm Hg) and TPR (42.6 +/- 10.3 versus 23.9 +/- 4.4 mm Hg/l per minute). In the presence of beta-adrenergic receptor, ganglionic, plus NE-uptake blockade after AMD pump implantation, desensitization was even more apparent, since NE (0.1 micrograms/kg per minute) induced even greater differences in MAP (33 +/- 5 versus 109 +/- 6 mm Hg) and TPR (28.1 +/- 1.8 versus 111.8 +/- 14.7 mm Hg/l per minute). The maximal force of contraction induced by NE in the presence or absence of endothelium was significantly decreased (p < 0.05) in vitro in mesenteric artery rings from AMD pump dogs compared with saline control dogs. Furthermore, alpha 1-adrenergic receptor density, as determined by [3H]prazosin binding in membrane preparations from vessels in the mesentery, was decreased (8.2 +/- 1.0 versus 18.4 +/- 1.4 fmol/mg protein, p < 0.001) without any change in Kd in the AMD pump dogs compared with the saline pump dogs.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of serotonin on intracellular pH and contraction in vascular smooth muscle.
Authors: Kahn A M , Bishara M , Cragoe E J , Allen J C , Seidel C L , Navran S S , O'Neil R G , McCarty N A , Shelat H
Published: June 2012

Serotonin (5-HT) and other contractile agonists stimulate Na(+)-H+ exchange in vascular smooth muscle. Since intracellular alkalinization, per se, stimulates contraction, we tested whether 5-HT-induced contraction was associated with an increased pHi. In HCO3(-)-free buffer (pHo 7.4), 5-HT (10(-5) M) increased pHi, as measured by 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence, from 7.10 +/- 0.03 to 7.34 +/- 0.03 (p < 0.01) in primary cultures of canine femoral artery vascular smooth muscle cells grown to confluence in the presence of 10% fetal calf serum. In HCO3- buffer (24 mM, pHo 7.4), resting pHi was 7.26 +/- 0.04 (p < 0.01 versus HCO3(-)-free buffer) but was not altered by 5-HT. In both types of buffer, 5-HT stimulated 5-(N-ethyl-N-isopropyl)amiloride-sensitive 22Na+ uptake (Na(+)-H+ exchange). In HCO3- buffer and in Na(+)- and HCO3(-)-free buffer, 5-HT increased 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive 36Cl- uptake, suggesting that 5-HT stimulated Na(+)-independent Cl(-)-HCO3- and Cl(-)-Cl- exchange activities, respectively. Individual vascular smooth muscle cells were then cultured on rat tail tendon collagen gels in the presence of 0.5% fetal calf serum, and cell length and pHi were measured by video and epifluorescence microscopy. 5-HT contracted cells in a dose-dependent, reversible, and ketanserin-inhibitable manner. These cells, like cells grown in 10% fetal calf serum, exhibited Na(+)-H+ and Na(+)-independent Cl(-)-HCO3- exchange. In HCO3- buffer, 5-HT contracted cells without an associated change in pHi. We concluded the following: 1) 5-HT stimulated both Na(+)-H+ and Na(+)-independent Cl(-)-HCO3- exchange activities in cultured vascular smooth muscle cells in parallel. 2) As a result of enhanced H+ and HCO3- efflux, pHi was not altered. 3) In the presence of HCO3-, 5-HT-induced contraction was not associated with a change in pHi.
Decreased myofilament responsiveness in myocardial stunning follows transient calcium overload during ischemia and reperfusion.
Authors: Carrozza J P , Bentivegna L A , Williams C P , Kuntz R E , Grossman W , Morgan J P
Published: June 2012

The purpose of this study was to test the hypothesis that abnormal intracellular calcium handling characterizes myocardial stunning. Isolated, isovolumic, buffer-perfused ferret hearts were loaded with the bioluminescent calcium indicator aequorin for simultaneous measurement of individual calcium transients and left ventricular pressure. After 15 minutes of global ischemia and 20 minutes of reperfusion, left ventricular developed pressure was significantly reduced (75 +/- 7 versus 93 +/- 6 mm Hg, p < 0.05). During ischemia, [Ca2+]i levels were significantly elevated compared with preischemic levels, both during systole (1.38 +/- 0.31 versus 0.88 +/- 0.2 microM, p < 0.05) and end diastole (0.85 +/- 0.16 versus 0.38 +/- 0.13 microM, p < 0.05). Early during reperfusion, [Ca2+]i was also significantly elevated during systole (1.63 +/- 0.44 versus 0.88 +/- 0.20 microM, p < 0.05) and end diastole (0.75 +/- 0.15 versus 0.38 +/- 0.13 microM, p < 0.05). After 20 minutes of reperfusion, myocardial stunning occurred, but [Ca2+]i was not significantly different from preischemic levels. Thus, myocardial stunning does not result from decreased levels of activator calcium. The force-pCa relation generated by the stunned hearts was shifted downward compared with that generated by the control hearts, consistent with a decrease in maximum calcium-activated force (Fmax). At steady state during tetanus, the decrease in Fmax was confirmed, but there was no significant difference in the slope of the force-pCa relation of the stunned hearts versus controls. Thus, we conclude that stunned myocardium is characterized by decreased Fmax without desensitization of the myofilaments to [Ca2+]i.(ABSTRACT TRUNCATED AT 250 WORDS)