bluuebunny/crossref_metadata_2025 huggingface dataset:
Is fibrillation chaos?
Authors: Kaplan D T , Cohen R J
Published: June 2012

Ventricular fibrillation is examined to determine whether it is an instance of deterministic chaos. Surface ECGs from dogs in fibrillation were used to generate a state space representation of fibrillation. Our analysis failed to identify a low-dimensional attractor that could be associated with fibrillation. The results suggest that fibrillation is similar to a nonchaotic random signal. We note, however, that such random-looking but nonchaotic behavior can also be generated by a nonlinear deterministic system.
Alpha 1-adrenergic receptors in pulmonary and systemic vascular smooth muscle. Alterations with development and pregnancy.
Authors: Shaul P W , Magness R R , Muntz K H , DeBeltz D , Buja L M
Published: June 2012

alpha 1-Adrenergic receptors mediate vasoconstriction in the pulmonary and systemic vasculature. In sheep the in vivo vasoconstrictor response to alpha 1-adrenergic stimulation is less in the pulmonary circulation compared with the systemic circulation of the fetus, the response increases in both vascular beds with fetal and postnatal development, and it decreases in the systemic vasculature with pregnancy. In an effort to determine the mechanisms underlying these differences, alpha 1-adrenergic receptor binding characteristics were determined by using [3H]prazosin in intrapulmonary and systemic (thoracic aorta) vascular smooth muscle (VSM) from late-gestation fetal lambs and from pregnant and nonpregnant ewes. alpha 1-Adrenergic receptor density was less in fetal intrapulmonary VSM that in fetal aortic VSM (12.4 +/- 1.5 versus 29.4 +/- 3.2 fmol/mg protein, p less than 0.05), and it was less (p less than 0.05) in the fetus compared with the pregnant ewe in both intrapulmonary and aortic VSM (51.0 +/- 5.2 and 76.5 +/- 5.9 fmol/mg protein, respectively). alpha 1-Adrenergic receptor density in intrapulmonary VSM was similar in the pregnant and nonpregnant ewe (61.9 +/- 7.2 fmol/mg protein), whereas in aortic VSM it was less (p less than 0.05) in pregnant ewes compared with nonpregnant ewes (101.0 +/- 5.5 fmol/mg protein). alpha 1-Adrenergic receptor affinity was similar in all the VSM sources tested.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of temperature on the rise in intracellular sodium caused by calcium depletion in ferret ventricular muscle and the mechanism of the alleviation of the calcium paradox by hypothermia.
Authors: Suleiman M S , Chapman R A
Published: June 2012

The effects of temperature over the range 37-10 degrees C on the responses of isolated ferret ventricular trabeculae to the depletion and repletion of bathing calcium has been investigated. Cooling is found to reduce the rate of rise of intracellular sodium activity (measured with an ion-sensitive microelectrode) induced by depletion of bathing divalent cations, without affecting the prolonged depolarization. The rate of rise of [Na]i (with the sodium pump inhibited) shows a dependence on temperature (energy of activation, 67 kJ.mol-1; Q10, 2.3-2.8) that increases with increasing temperature. This contrasts with previously published data for the sodium pump for which the temperature dependence falls with increasing temperature. These results offer an explanation for the alleviation of the calcium paradox caused by cooling during the period of calcium depletion, which is similar to other procedures that offer protection by limiting the rise in [Na]i by having effects on the L-type calcium channel.
Stimulation of serotonin2 receptors in the ventrolateral medulla of the cat results in nonuniform increases in sympathetic outflow.
Authors: Mandal A K , Kellar K J , Norman W P , Gillis R A
Published: June 2012

Topical application of the serotonin2 agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane or DOI, in a dose of 30 micrograms/side to the intermediate area of the ventrolateral surface of the medulla produced a significant increase in mean arterial pressure with no significant change in heart rate both in intact animals (n = 8) and in cervically vagotomized animals (n = 3). The pressor response of DOI was blocked by pretreatment of the intermediate area with ketanserin, a serotonin2 antagonist (n = 7). Pretreatment with intravenous phentolamine did not block the pressor response of DOI (n = 3). However, this pressor response could be counteracted by intravenous propranolol (n = 5) or by bilateral stellate ganglionectomy (n = 3). These data suggest that sympathoexcitation by centrally applied DOI selectively increased cardiac inotropy but not chronotropy. Further studies indicate that DOI increased contractile force without increasing heart rate and that the positive inotropic effect of DOI could be counteracted by bilateral stellate ganglionectomy. Bilateral microinjections of DOI into the subretrofacial nucleus in a dose of 100 ng (n = 3) and a dose of 300 ng (n = 3) increased mean arterial blood pressure by 23 +/- 2 and 44 +/- 6 mm Hg, respectively, without producing any changes in heart rate. These data suggest that DOI has a central site of action in the ventrolateral medulla, presumably at the subretrofacial nucleus, which leads to selective sympathoexcitation of the cardiac ventricles.
Effect of chemodenervation on the cerebral vascular and microvascular response to hypoxia.
Authors: Anwar M , Kissen I , Weiss H R
Published: June 2012

This study evaluated the effect of bilateral carotid chemodenervation on the cerebrovascular response to hypoxia in conscious rats. Cerebral blood flow was measured using 4-iodo[N-methyl-14C]antipyrine, and the total and perfused microvasculature was studied by injection of fluorescein isothiocyanate dextran and alkaline phosphatase staining. To maintain constant PCO2, hypoxia was achieved in chemoreceptor-intact rats by the use of 4% CO2-8% O2-88% N2 and in chemodenervated rats by the administration of 8% O2-92% N2. Blood gas and hemodynamic parameters were similar in the two groups of rats. Chemodenervation had no significant effect on either resting blood flow or the perfused microvasculature during normoxia. A significant increase in cerebral blood flow (from 71 +/- 3 to 138 +/- 9 ml/min/100 g in control and from 91 +/- 5 to 127 +/- 7 ml/min/100 g in chemodenervated rats) and in the percent of cerebral arterioles and capillaries perfused occurred in both hypoxic control and chemodenervated rats. In chemoreceptor-intact rats, the greatest increase in blood flow and in perfused microvasculature occurred in caudal structures (medulla and pons) in comparison with rostral structures (cortex, thalamus, and hypothalamus). In chemodenervated rats, a similar increase in blood flow and perfused microvasculature occurred in all brain regions, with no regional differences. Thus, chemodenervation did not affect the overall cerebral blood flow or the microvascular response to hypoxia; however, rostral-to-caudal regional differences in the hypoxic response were lost after chemodenervation.
Ellipsoidal shell subtraction model of right ventricular volume. Comparison with regional free wall dimensions as indexes of right ventricular function.
Authors: Feneley M P , Elbeery J R , Gaynor J W , Gall S A , Davis J W , Rankin J S
Published: June 2012

Pulse-transit sonomicrometry was used to measure the base-apex (a), anteroposterior (b), and septal-free wall (c) diameters of the left ventricle and the septal-free wall diameter of the right ventricle (d) in eight excised and three isolated, pump-perfused canine heart preparations, as well as in nine conscious dogs. In the three perfused hearts and in four of the excised hearts, right ventricular free wall regional segment lengths and segment area also were assessed. Biventricular volumes were measured directly with intracavitary balloons in all isolated hearts. When left ventricular balloon volume was held constant, relations between right ventricular free wall dimensions and right ventricular balloon volume were highly linear. With increments in left ventricular volume, however, these relations remained linear but shifted progressively upward, indicating an independent relation between right ventricular free wall dimensions and left ventricular cavitary volume. An ellipsoidal shell subtraction model (pi/6.abd minus right ventricular free wall volume) was developed to estimate right ventricular cavitary volume from cardiac dimensions. With this method, a highly linear relation was observed between calculated right ventricular volume and right ventricular balloon volume (mean r = 0.99 +/- 0.01). Moreover, this relation appeared to be independent of changes in left ventricular balloon volume. With the shell subtraction model, dynamic right ventricular volume was computed in nine conscious dogs, and in four, stroke volume derived from dimensions was compared with right ventricular stroke volume measured with ultrasonic flow probes. A highly linear relation was observed, suggesting the accuracy of the shell subtraction method in vivo. Right ventricular end-systolic pressure-volume and stroke work/end-diastolic volume relations then were evaluated, and both proved to be highly linear in the right ventricle (both mean r = 0.99 +/- 0.01). Thus, the shell subtraction model allows a simple estimate of dynamic right ventricular volume in the intact heart and facilitates assessment of right ventricular performance in vivo.
Myocardial capillary permeability after regional ischemia and reperfusion in the in vivo canine heart. Effect of superoxide dismutase.
Authors: Svendsen J H , Bjerrum P J , Haunsø S
Published: June 2012

This study assesses the effect of the superoxide anion scavenger superoxide dismutase on myocardial capillary permeability-surface area (PS) products for small hydrophilic molecules after ischemia and reperfusion. Open-chest dogs underwent a 20-minute occlusion of the left anterior descending coronary artery followed by 1 hour of reperfusion. Myocardial plasma flow rate and capillary extraction of chromium 51-labeled EDTA or technetium 99m-labeled diethylenetriaminepentaacetic acid were measured by the single-injection, residue-detection method before ischemia and 5 and 60 minutes after the start of reperfusion. In 13 dogs, no scavenger treatment was given (nonprotected control group), whereas eight dogs were treated systemically with 15,000 units/kg superoxide dismutase during 1 hour, starting 20 minutes before ischemia. In the control group, three dogs developed reperfusion ventricular fibrillation in contrast to none in the superoxide dismutase group. Before ischemia, plasma flow rate, myocardial capillary extraction fraction, and PS values were similar in the two groups. Five minutes after the start of reperfusion, plasma flow rate increased significantly (p less than 0.01) in both groups. In the control group, capillary extraction fraction increased by 12% (p = NS) in spite of the higher plasma flow; these increases in capillary extraction fraction and plasma flow induced a 69% increase in PS (p less than 0.01). In the superoxide dismutase-treated group, capillary extraction fraction decreased by 32% (p less than 0.05) in accordance with the increased plasma flow rate, resulting in an unchanged PS (p = NS). Sixty minutes after reperfusion, plasma flow rate, capillary extraction fraction, and PS returned to preocclusion values in both groups (p = NS). The increased capillary extraction fraction and PS values seen in the control group suggest an increased capillary permeability after ischemia and reperfusion. Superoxide anions seem to participate, directly or indirectly, in this response.
Oxidation of membrane cholesterol alters active and passive transsarcolemmal calcium movement.
Authors: Kutryk M J , Maddaford T G , Ramjiawan B , Pierce G N
Published: June 2012

Oxygen free radicals have the ability to oxidize cholesterol. However, nothing is known about the effects of cholesterol oxidation on ion transport in isolated myocardial membranes. The purpose of the present study was to investigate the effects of in situ oxidative modification of sarcolemmal cholesterol on Ca2+ flux. Cholesterol oxidase was used to oxidatively modify membrane cholesterol. After incubation of cardiac sarcolemmal vesicles with cholesterol oxidase, cholest-4-en-3-one (cholestenone) was the predominant species of oxidated cholesterol produced. Cholesterol oxidase inhibited sarcolemmal Na(+)-Ca2+ exchange in a concentration-dependent manner. Both the Vmax and Km of the reaction were altered after cholesterol oxidase treatment. Extensive treatment of the sarcolemmal membranes with cholesterol oxidase increased the passive permeability characteristics of the membrane. Passive Ca2+ efflux from the sarcolemmal vesicles was stimulated by increasing the concentration of cholesterol oxidase. ATP-dependent Ca2+ uptake was also inhibited after cholesterol oxidase treatment, but it was not as sensitive as the Na(+)-Ca2+ exchange. Conversely, passive Ca2+ binding to sarcolemmal vesicles was strikingly stimulated by cholesterol oxidase treatment. The results demonstrate that oxidative modification of sarcolemmal membrane cholesterol can directly affect ionic interactions with the sarcolemmal vesicle and provide potentially important mechanistic information for the molecular basis of the effects of free radicals on ion flux and function in the heart.
Mathematical models of myosin heterodimer formation in the rat heart during thyroid hormone alterations.
Authors: Rupp H , Dietz K
Published: June 2012

To characterize the mechanisms involved in the formation of the myosin heavy chain (MHC) heterodimer V2 (alpha beta-MHC) and the homodimers V3 (beta beta-MHC) and V1 (alpha alpha-MHC), 82 5-week-old normotensive rats with homogeneous V1 were made hypothyroid with propylthiouracil (0.8%, drinking water), and the proportion of V2, V3, and V1 was determined by pyrophosphate gel electrophoresis in multicellular specimens of the left and right ventricles. After the switch from alpha-MHC to beta-MHC, the beta-MHC occurred initially in the form of the heterodimer. After 4 and 6 days, V2 was greater (p less than 0.05) than V3. At day 8, V2 was smaller than V3, and at day 10, V2 was not statistically different from V3. From day 12 onward, V2 was smaller than V3. After 21 days, the propylthiouracil treatment was stopped, and the remaining 34 hypothyroid rats were injected with a daily dose of thyroxine (average, 0.1 mg/kg body wt), resulting in a switch from beta-MHC to alpha-MHC. After 1 day, V2 still was greater than V1; however, already from day 3 onward, V2 was smaller than V1. This characteristic but unexplained heterodimeric and homodimeric organization of the thick filament was analyzed by mathematical models involving probability calculations. Two principally different models were established that assume either the exchange of MHC dimers or of single MHC in the thick filament. The parameters of the models were estimated by minimization routines using the squared discrepancies between the experimental and predicted isoenzyme populations. Based on goodness of fit and crucial model parameters, we concluded that the characteristic organization of the thick filament can be accounted for by an exchange involving predominantly MHC dimers and not single MHC. The fact that V2 was lower than expected if formation of heterodimers and homodimers were random was attributed to the preferred homodimerization of 35% of the newly synthesized MHC.
ATP-sensitive potassium channel modulation of the guinea pig ventricular action potential and contraction.
Authors: Nichols C G , Ripoll C , Lederer W J
Published: June 2012

The role of ATP-sensitive potassium (KATP) channels in modulating the action potential and contraction of guinea pig ventricular myocytes was investigated. Under voltage clamp, the maximum whole-cell KATP channel conductance was estimated (195 +/- 10 nS, n = 6) by exposing the cells to complete metabolic blockade (2 mM cyanide in the presence of 10 mM 2-deoxy-glucose). In isolated inside-out membrane patches, the ATP dependence of KATP channel activity under relevant conditions was measured (half-maximal inhibition at 114 microM). Under current clamp (with intracellular ATP concentration = 5 mM), the effect of graded KATP channel activation on the action potential and the twitch was estimated by injection of a current (proportional to voltage) that simulated the KATP conductance. As this "conductance" was increased, the action potential was shortened, and contractile amplitude declined, as expected. From the results of these experiments, the quantitative dependence of the action potential duration on intracellular ATP concentration was estimated, without relying on a mathematical model of the cell membrane. The results imply that KATP-dependent action potential shortening is likely to occur if ATP concentration falls below normal levels (approximately 5 mM), as may happen regionally, or globally, during myocardial ischemia.
Neuropeptide Y upregulates the adhesiveness of human endothelial cells for leukocytes.
Authors: Sung C P , Arleth A J , Feuerstein G Z
Published: June 2012

The nervous system and the autonomic system in particular have been associated with stress-induced changes in host resistance to infections and inflammatory reactions. Since a key step in initiation of inflammation is adhesion of leukocytes to the endothelium, we hypothesized that neuron-derived factors might be involved in this process. Neuropeptide Y (NPY), a 36-amino acid neuropeptide that is colocalized and released with norepinephrine from sympathetic nerves, has already been implicated in inflammatory reactions via modulation of histamine release from mast cells. This study was undertaken to examine the potential role of NPY in proinflammatory processes via modulation of endothelium-leukocyte interaction. NPY (0.01-10 microM) increased the adhesion of 51Cr-labeled human neutrophils or the human monocytic U937 cell line to human umbilical vein endothelial cells in a dose- and time-dependent manner. The stimulation of human umbilical vein endothelial cell adhesiveness occurred as early as 30 minutes and lasted over 48 hours. The increase of leukocyte adhesion to human umbilical vein endothelial cells by NPY was not inhibited by protein synthesis inhibitor cycloheximide, nor was it associated with expression of intercellular adhesion molecule-1 on human umbilical vein endothelial cells; in contrast, strong expression of intercellular adhesion molecule-1 was induced by tumor necrosis factor alpha and lipopolysaccharide endotoxin. These data suggest that neuron-derived factors such as NPY may serve as modulators of not only the neuromuscular unit but also the interaction of endothelial cells with leukocytes. In this capacity, the sympathetic nervous system might play an important role in the regulation of proaggregatory and hemostatic activity of microvessels.
Membrane potential fluctuations and transient inward currents induced by reactive oxygen intermediates in isolated rabbit ventricular cells.
Authors: Matsuura H , Shattock M J
Published: June 2012

The cellular basis of reactive oxygen intermediate-induced arrhythmias was investigated in isolated rabbit ventricular cells using the whole-cell voltage- and current-clamp techniques. Singlet oxygen and superoxide were generated by the photoactivation of rose bengal. Single ventricular cells exposed to rose bengal (10-100 nM) exhibited spontaneous membrane potential fluctuations at plateau potentials and at the level of the resting membrane potential. The voltage fluctuations induced in the resting potential occasionally triggered repetitive action potential discharges. At the resting membrane potential, the magnitude and dominant frequency of the voltage fluctuations were 1-3 mV and 1.5 Hz, respectively. At plateau potentials, the amplitude of the voltage fluctuations was about 2-5 mV, and the dominant oscillatory frequency was 2.6 Hz. In voltage-clamp experiments, transient inward currents were induced on repolarization after a depolarizing clamp step. Oscillatory currents also occurred occasionally during clamp steps to positive potentials. The peak frequencies of transient inward currents recorded at -20 and -70 mV were approximately 3.7 and 2.3 Hz, respectively, indicating that these currents may underlie the arrhythmogenic membrane potential fluctuations observed in current-clamp experiments. The rose bengal-induced transient inward currents were shown to be dependent on the magnitude and duration of the preceding voltage step. Studies of the voltage dependence of transient inward currents showed that these currents remained inward even at positive potentials (+30 mV), and replacement of extracellular sodium with lithium decreased transient inward current to approximately 10% of its initial value. Thus, the major component of oxidant stress-induced inward current appears to be electrogenic Na-Ca exchange. This oscillatory transient inward current may be responsible for the arrhythmias induced in isolated hearts exposed to reactive oxygen intermediates, and since oxidant stress has been implicated in reperfusion injury, it is possible that similar oscillatory currents may underlie reperfusion-induced arrhythmias.
Angiotensin II induces smooth muscle cell proliferation in the normal and injured rat arterial wall.
Authors: Daemen M J , Lombardi D M , Bosman F T , Schwartz S M
Published: June 2012

The present study was undertaken to explore the possibility that neointimal smooth muscle cells, the characteristic cells of restenosis and atherosclerosis, are selectively stimulated to replicate by a hypertensive stimulus. Angiotensin II (AII) was infused by osmotic minipumps for 2 weeks in 4.5-month-old rats. Group A received AII (200 ng/min) 2 weeks after a balloon catheter-induced injury of the thoracic aorta and left common carotid artery. Group B received only AII, group C only balloon denudation, and group D neither balloon injury nor AII. During the AII or Ringer's solution infusion, all animals received [3H]thymidine via a second minipump to measure DNA synthesis. AII increased the systolic pressure by more than 40 mm Hg. AII significantly increased DNA synthesis in the media of the carotid artery from 0.2 +/- 0.2% in group C to 2.5 +/- 1.5% in group A (mean +/- SD, n = 5 or 6). DNA synthesis in the neointima of the carotid artery significantly increased with AII from 4.8 +/- 4.2% in group C to 19.8 +/- 13.9% in group A. Cross-sectional area of the neointima almost doubled during AII infusion, and it increased approximately 25% in the media. Comparable results were obtained in the aorta. In a second experiment, AII was infused (125 ng/min) for 2 weeks in 11-week-old rats. Concomitantly, [3H]thymidine was given. Control rats received Ringer's solution and [3H]thymidine in their pumps. Blood pressures were elevated to the same extent as in the older animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Synergistic action of myocardial oxygen and carbon dioxide in controlling coronary blood flow.
Authors: Broten T P , Romson J L , Fullerton D A , Van Winkle D M , Feigl E O
Published: June 2012

A two-part experiment was designed to test the hypothesis that myocardial oxygen and carbon dioxide tensions, as measured by coronary venous oxygen and carbon dioxide tensions, determine coronary blood flow during increases in myocardial oxygen consumption. The left main coronary artery was pump-perfused at constant pressure in closed-chest, anesthetized dogs. Oxygenators in the perfusion circuit permitted control of coronary arterial gas tensions. The steady-state relation between coronary venous oxygen and carbon dioxide tensions and coronary flow at a constant myocardial oxygen consumption was determined by locally altering coronary arterial oxygen and carbon dioxide tensions. Values of coronary venous oxygen and carbon dioxide tensions and coronary flow were also obtained at normal coronary arterial gas tensions during pacing-induced increases in myocardial oxygen consumption. The data yielded a hyperbolic relation among coronary venous oxygen and carbon dioxide tension and coronary flow during constant myocardial metabolism, suggesting a synergistic interaction between myocardial oxygen and carbon dioxide tensions in determining coronary flow. This relation was then used to predict the coronary flow change during pacing-induced increases in myocardial metabolism. Approximately 40% of the flow response during pacing-induced increases in myocardial oxygen consumption was predicted. In conclusion, coronary venous oxygen and carbon dioxide tensions synergistically interact to produce steady-state changes in coronary flow at a constant myocardial oxygen consumption. Changes in myocardial oxygen and carbon dioxide tensions can account for about 40% of the change in coronary flow during moderate changes in myocardial oxygen consumption.
Inotropic response to norepinephrine is augmented early and maintained late in conscious dogs with perinephritic hypertension.
Authors: Shannon R P , Gelpi R J , Hittinger L , Vatner D E , Homcy C J , Graham R M , Vatner S F
Published: June 2012

We studied the inotropic responses to intravenous infusions of norepinephrine in nine conscious chronically instrumented dogs before and early (2-4 weeks) in the development of perinephritic hypertension; seven conscious dogs were studied later (approximately 14 weeks), during a more stable phase of hypertension. perinephritic hypertension was associated with a 24% increase in left ventricular (LV) mass during developing hypertension; no further increase was seen during the stable hypertension phase. LV end-systolic stress was increased early (p less than 0.01) but was normalized later. The LV end-systolic stress-volume relation demonstrated an enhanced contractile response to norepinephrine during developing hypertension, which returned toward control later in the course of stable hypertension. The LV dP/dt responses to norepinephrine (0.4 microgram/kg/min) were significantly greater during developing hypertension (7,509 +/- 337 mm Hg/sec, p less than 0.05) compared with the control period (4,737 +/- 286 mm Hg/sec) and returned toward the control value during stable hypertension (5,168 +/- 465 mm Hg/sec). The enhanced inotropic responses to norepinephrine in developing hypertension were preserved in the presence of ganglionic blockade, suggesting that the augmentation was not mediated via reflex mechanisms. These physiological responses were associated with an increase in beta-adrenergic receptor density, but no significant change in basal or maximal adenylate cyclase stimulation occurred during developing hypertension. Thus, in contrast to prior studies in anesthetized animals, the inotropic response to beta-adrenergic stimulation is not depressed in conscious dogs but is enhanced selectively during the development of hypertension and maintained during stable hypertension.
Effects of inosine on glycolysis and contracture during myocardial ischemia.
Authors: Lewandowski E D , Johnston D L , Roberts R
Published: June 2012

The effects of inosine (INO) on substrate metabolism and rigor formation in ischemic myocardium were examined in isolated rabbit hearts. Metabolite content was assessed in tissue extracts by chemical analysis and in the whole heart by 13C and 31P nuclear magnetic resonance spectroscopy. In ischemic hearts metabolizing either [3-13C]pyruvate or [1-13C]glucose, 1 mM INO increased both total and 13C-labeled alanine content; lactate content was unaffected. At 3 minutes of ischemia, tissue alanine was 1.81 +/- 0.11 microM/g wet wt (mean +/- SEM) in hearts perfused with pyruvate+INO versus 1.23 +/- 0.15 microM/g wet wt in hearts perfused with pyruvate alone (p less than 0.05). INO reduced tissue glycogen during ischemia in pyruvate-perfused hearts. Tissue alanine content in ischemic hearts that were supplied glucose+INO (1.29 +/- 0.13 microM/g wet wt) was greater than in ischemic hearts supplied glucose alone (0.65 +/- 0.14 microM/g wet wt). Alanine was found to originate from pyruvate and was a glycolytic end product in glucose-perfused hearts. INO raised the [3-13C]alanine/[3-13C]lactate ratio in ischemic, intact hearts (glucose = 0.24 +/- 0.07 versus glucose+INO = 0.60 +/- 0.09; pyruvate = 0.49 +/- 0.08 versus pyruvate+INO = 0.89 +/- 0.08). At 7 minutes of ischemia, ATP content fell to 70 +/- 3% with glucose+INO versus 58 +/- 5% with glucose alone. Rigor (stone heart) was delayed from 14.7 +/- 1.3 to 23.2 +/- 1.6 minutes with INO. INO did not change ATP content in ischemic hearts that were supplied pyruvate but delayed rigor (pyruvate = 9.9 +/- 1.2 minutes; pyruvate+INO = 15.6 +/- 1.0 minutes), possibly at the expense of glycogen. Supplemental glucose improved the effectiveness of INO with pyruvate to preserve ATP (pyruvate+glucose = 42 +/- 6%; pyruvate+glucose+INO = 72 +/- 6%) and further delayed rigor (pyruvate+glucose = 13.3 +/- 1.5 minutes; pyruvate+glucose+INO = 20.3 +/- 1.8 minutes). Glucose metabolism supported improved energetic and contractile states in ischemic hearts treated with INO. Thus, cardioprotection of the ischemic heart by INO was associated with preservation of functional integrity and improved energy production due to increased glycolytic activity. Activation of glycolysis in the presence of INO was accommodated by augmented alanine production without the additional accumulation of lactate.
Myocardial sulfhydryl pool alterations occur during reperfusion after brief and prolonged myocardial ischemia in vivo.
Authors: Lesnefsky E J , Dauber I M , Horwitz L D
Published: June 2012

Myocardial sulfhydryl (SH)-containing compounds, including reduced glutathione (GSH), are both defenses against and potential markers of reactive oxygen metabolite injury during ischemia and reperfusion. We examined the alterations in GSH and other myocardial SH pools during reperfusion in anesthetized dogs exposed to brief (15 minutes, n = 7) or prolonged (90 minutes, n = 6) regional ischemia caused by occlusion of the left anterior descending artery. Ninety minutes of ischemia followed by 5 hours of reperfusion, which resulted in myocardial necrosis of 43.9 +/- 4.0% of the area at risk, caused a 22% reduction in total myocardial SH groups (p less than 0.01), a 57% decrease in nonprotein myocardial SH groups (p less than 0.01), a 56% decrease in GSH (p less than 0.01), and a 62% decrease in non-GSH, nonprotein SH groups (p less than 0.02). However, protein SH groups were not significantly reduced (12% decrease, p = NS). Also, myocardial release of GSH and oxidized glutathione (GSSG) into the coronary venous effluent occurred during early reperfusion. In contrast, 15 minutes of ischemia, followed by 30 minutes of reperfusion, did not alter myocardial total SH groups, protein SH groups, or GSH (9% decrease, p = NS); nor was there reperfusion release of GSH or GSSG. However, even with brief ischemia, nonprotein SH groups decreased 23% (p less than 0.05), due mainly to a 59% decrease in the non-GSH, nonprotein SH pool (p less than 0.05). These changes after brief ischemia occurred without alterations in myocardial GSSG or the GSH/GSSG ratio.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of dibutyryl cyclic AMP, ouabain, and xanthine derivatives on crossbridge kinetics in rat cardiac muscle.
Authors: Hoh J F , Rossmanith G H , Hamilton A M
Published: June 2012

In a previous communication, we showed that beta-adrenergic stimulation of cardiac muscles was associated with an increase in the rate of cycling of crossbridges as measured by perturbation analysis in the frequency domain. In this analysis, the frequency at which dynamic stiffness is a minimum (fmin) is taken as a measure of the rate of crossbridge cycling. In this paper, we test the hypothesis that the beta-adrenergic receptor-induced increase in crossbridge cycling rate is mediated by elevation of the intracellular level of cyclic AMP. The approach taken is to compare the effects on fmin in rat papillary muscles during Ba(2+)-activated contractures of 1) an agonist of cyclic AMP that can easily penetrate the cell, namely, dibutyryl cyclic AMP, 2) agents that block cyclic AMP phosphodiesterase, namely, the xanthine derivatives isobutylmethylxanthine and caffeine, and 3) an inotropic agent that does not affect the intracellular level of cyclic AMP, namely, ouabain. Our results showed that dibutyryl cyclic AMP at a dose of 5 mM has the same actions as beta-adrenergic stimulation: it potentiated the isometric twitch force, reduced the time to peak tension and time to half relaxation, and shifted fmin by a factor of 1.8 +/- 0.1 (n = 5). Isobutylmethylxanthine at up to 1.1 mM also acted in the same manner, increasing fmin by a factor of 1.8 +/- 0.2 (n = 6), but ouabain, at a dose (0.03 mM) sufficient to potentiate twitch force by 40 +/- 2% (n = 4), was without effect on the time course of the twitch nor was fmin changed (n = 4). Our findings support the hypothesis that a beta-adrenergic receptor-mediated increase in crossbridge cycling rate is due to an increase in intracellular cyclic AMP level and illustrate the usefulness of the frequency domain analysis approach in the analysis of the mechanism of action of inotropic agents.
Expression of connexin43 in the developing rat heart.
Authors: Fishman G I , Hertzberg E L , Spray D C , Leinwand L A
Published: June 2012

Connexin43 is the predominant gap junction protein expressed in the heart. To determine the relation between cardiac maturation and gap junction gene expression, the developmental profiles of connexin43 mRNA and protein were examined in the rat heart. Connexin43 mRNA levels accumulate progressively (eightfold) during embryonic and early neonatal stages, accompanied by a parallel, but temporally delayed, accumulation of connexin43 protein (15-fold). As the heart matures further, both mRNA and protein levels subsequently decline, to about 50% and 30% of their maximum levels, respectively. These observations suggest that increases in intercellular coupling that characterize cardiac development do not depend solely on modulation of connexin43 gene expression, but rather are likely to involve organization of gap junction channels into the intercalated disc.
Ryanodine does not affect calcium current in guinea pig ventricular myocytes in which Ca2+ is buffered.
Authors: Balke C W , Wier W G
Published: June 2012

Calcium current in mammalian ventricular muscle is altered in the presence of ryanodine. Previous studies performed on rat ventricular cells have shown a slowing of Ca2+ current inactivation and suggest the hypothesis that ryanodine, by reducing the release of Ca2+ from the sarcoplasmic reticulum, reduces the availability of Ca2+ for inactivation of Ca2+ current (Ca(2+)-dependent inactivation). Another hypothesis is that the effects of ryanodine on Ca2+ current are due to a mechanical connection of the ryanodine receptor with the L-type Ca2+ channel. To further test these hypotheses we examined the effect of ryanodine on Ca2+ current in single voltage-clamped guinea pig ventricular myocytes that contained Ca2+ indicator and Ca2+ buffer. We used fura 2 (pentapotassium salt) to confirm that the ryanodine we used was capable of abolishing Ca2+ release from the sarcoplasmic reticulum during the period in which it was present. We perfused the cells with 10 mM EGTA to block changes in intracellular Ca2+ concentration. In the absence of internal EGTA, Ca2+ currents displayed biexponential inactivation and Ca(2+)-dependent inactivation (steady-state inactivation curves turned up at positive potentials). Inactivation was slowed by ryanodine at 10 microM. In cells perfused internally with EGTA, however, ryanodine had no effects, and steady-state inactivation curves were not shifted to the right. We conclude that, in guinea pig ventricular myocytes, the effects of ryanodine on Ca2+ current are mediated by Ca2+ and thus the effects of ryanodine do not provide a basis on which to postulate a physical connection between the L-type Ca2+ channel and the ryanodine receptor (sarcoplasmic reticulum Ca2+ release channel).
Thromboxane mediates diapedesis after ischemia by activation of neutrophil adhesion receptors interacting with basally expressed intercellular adhesion molecule-1.
Authors: Goldman G , Welbourn R , Klausner J M , Valeri C R , Shepro D , Hechtman H B
Published: June 2012

Ischemic injury is characterized by neutrophil (PMN)--endothelial cell adhesion and diapedesis associated with thromboxane (TX) generation. Neutrophil-endothelial cell interaction is regulated in part by the leukocyte adhesion receptor CD 18 glycoprotein complex and the endothelial intercellular adhesion molecule-1 (ICAM-1). This study tests the role of TX in ischemia-induced diapedesis and evaluates whether the diapedesis is regulated by neutrophil or endothelial adhesion receptors. Plasma derived from rabbit hind limbs made ischemic for 3 hours (n = 6) and reperfused for 10 minutes had increased levels of TXB2 3,450 pg/ml, which was higher than sham rabbit (n = 6) values of 653 pg/ml (p less than 0.05). When introduced into abraded skin chambers placed on the dorsum of other normal rabbits (n = 6), this ischemic plasma induced 1,000 pg/ml of new TX synthesis and diapedesis of 1,235 PMN/mm3. The total TX concentration and PMN accumulations in blister fluid were correlated (r = 0.88, p less than 0.05). In contrast, sham rabbit plasma induced no TX synthesis and diapedesis of only 77 PMN/mm3 (p less than 0.05). Administration of 50 ng/ml of authentic TXB2 into blisters induced an accumulation of 453 PMN/mm3, which was higher than that in saline controls (18 PMN/mm3) (p less than 0.05). Pretreatment of normal rabbits used for the diapedesis assay (n = 4) with the TX synthetase inhibitor OKY 046 (2 mg/kg/hr) limited ischemic plasma and authentic TXB2 induced diapedesis to 142 and 76 PMN/mm3, respectively (both p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Electrophysiological and receptor binding studies to assess activation of the cardiac adenosine receptor by adenine nucleotides.
Authors: Ragazzi E , Wu S N , Shryock J , Belardinelli L
Published: June 2012

Adenosine and adenine nucleotides shorten the action potential duration of atrial myocytes and activate a specific acetylcholine and adenosine receptor-operated potassium outward current referred to as IKACh,Ado. The objective of this study was to determine whether adenine nucleotides shorten the action potential duration and increase IKACh,Ado in guinea pig atrial myocytes by directly activating adenosine receptors. The potency and efficacy of AMP and adenosine in increasing IKACh,Ado and shortening atrial action potential duration were similar; the EC50 values for AMP and adenosine were 3.4 +/- 0.8 and 3.1 +/- 0.4 microM, respectively. Likewise, the maximum increases in IKACh,Ado caused by AMP and adenosine were similar (122 +/- 11% versus 123 +/- 9%). In comparison, ATP and the stable analogue of AMP, adenosine monophosphorothioate (AMPS), were significantly less potent and efficacious than adenosine and AMP, and adenosine receptor antagonist 8-(p-sulfophenyl)theophylline and abolished in the presence of adenosine deaminase and alpha, beta-methylene-ADP (APCP, an inhibitor of AMP degradation). Binding of the A1-adenosine antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine (DPCPX) to guinea pig atrial membranes treated with adenosine deaminase and APCP was reduced up to 60% by 100 microM concentrations of AMP, AMPS, and adenosine. Inosine inhibited binding by 43 +/- 3% at 100 microM, whereas hypoxanthine and xanthine had little (5-10% inhibition) and uric acid had no effect. Only 3% of AMP and 35% of AMPS were recovered intact after a 90-minute incubation at 21 degrees C with preparations of guinea pig atrial membranes. Percent displacement of [3H]DPCPX binding to atrial membranes by 100 microM AMP was significantly less in the presence of nucleoside phosphorylase and xanthine oxidase (to degrade inosine, hypoxanthine, and xanthine to uric acid) than in their absence (12.4 +/- 3.1% versus 49.7 +/- 1.5%). The results suggest that the observed electrophysiological actions of adenine nucleotides in cardiomyocytes are mediated by adenosine and are consistent with activation of A1-adenosine receptors.
Increased Ca2+ signaling after alpha-adrenoceptor activation in vascular hypertrophy.
Authors: Papageorgiou P , Morgan K G
Published: June 2012

In an effort to explain the increased sensitivity to agonists of hypertrophic vascular muscle, intracellular Ca2+ concentration ([Ca2+]i)-signaling mechanisms were studied in normal and hypertrophic rat aortas from normotensive and coarctation-hypertensive rats. Based on both fura 2 fluorescence and aequorin luminescence measurements, qualitatively different patterns of Ca2+ mobilization occur in normal and hypertrophic rat aortic muscle. Normal rat aortic muscle contracts to phenylephrine with little or no increase in [Ca2+]i, whereas the angiotensin II-induced contraction is accompanied by a marked [Ca2+]i transient. In contrast, hypertrophic rat aortic muscle shows a dramatic increase in Ca2+ signaling after phenylephrine stimulation. Moreover, both the amplitude of the angiotensin-induced [Ca2+]i transient and the contractile sensitivity to this agonist are decreased in the hypertrophic muscle. Our results strongly suggest that the amplitude of the [Ca2+]i transient after agonist stimulation determines the contractile sensitivity and that there is an altered coupling of the alpha-adrenoceptor in the hypertrophic vascular muscle.
Heterotopic cardiac transplantation decreases the capacity for rat myocardial protein synthesis.
Authors: Klein I , Samarel A M , Welikson R , Hong C
Published: June 2012

Heterotopic cardiac isografts are vascularly perfused hearts that maintain structural and functional integrity for prolonged periods of time. When placed in an infrarenal location, the heart is hemodynamically unloaded and undergoes negative growth, leading to cardiac atrophy. At 7 and 14 days after transplantation, the transplanted heart was decreased in size compared with the in situ heart (p less than 0.001). To assess the possible mechanism(s) to account for this reduction in size we studied in vivo rates of total left ventricular (LV) protein synthesis, total LV RNA content, and 18S ribosomal RNA content by nucleic acid hybridization. The LV protein synthetic rate was 4.7 and 5.3 mg/day in the in situ heart and was significantly decreased to 2.9 and 2.7 mg/day in the transplanted hearts at 7 and 14 days, respectively. LV RNA content of the transplant declined to 53% and 48% of the in situ value at 7 and 14 days, respectively. Hybridization studies revealed that LV 18S ribosomal subunit content was reduced proportionately to total RNA in the heterotopic hearts. As a result of these changes, there was no significant difference in the efficiency of total LV protein synthesis between the in situ and transplanted hearts. The present studies demonstrate that the hemodynamic unloading and cardiac atrophy that is characteristic of heterotopic cardiac transplantation is accompanied by a decrease in LV total RNA content and 18S RNA, resulting in a decreased capacity for myocardial protein synthesis.
Direct effect of increased hemodynamic load on cardiac mass.
Authors: Korecky B , Masika M
Published: June 2012

The hearts of rats were transplanted into the abdomens of recipients of the same inbred strain by attaching the stumps of aorta and pulmonary artery end to side to the abdominal aorta and inferior vena cava, respectively, of the recipient. The transplant functions as a denervated "nonworking" Langendorff heart; the recipient in situ heart serves as a normal control. One week after surgery, an onset of atrophy is observed in the transplanted heart, which stabilizes after 2 weeks; the in situ heart grows normally. Using this model, we increased the load of the left ventricle (LV) in the transplant by inserting a permanent polyethylene cannula into its aortic orifice during surgery to induce valvular incompetence and/or stenosis (TPE group). This resulted in significantly increased LV systolic pressure (115 +/- 5 versus 95 +/- 3 mm Hg) and a significantly increased rate-pressure product (34.7 +/- 1.7 versus 24.4 +/- 1.4 mm Hg.min-1 x 10(3) as compared with rats with control transplants (TC group). The LV mass in the TPE group decreased to only 85 +/- 4.8% of the mass of the corresponding in situ recipient heart as compared with 59 +/- 2.6% in the TC group (p less than 0.001). In three cases in the TPE group with highest overload, we observed about 20% larger LV mass in transplanted hearts as compared with the corresponding recipient in situ hearts. These results indicate that the increased load significantly attenuated the atrophy observed in LV of the isotransplants. This attenuation could be correlated with the increment of load as indicated by higher peak LV pressures and higher rate-pressure products.
Thrombin-mediated release of lipids from pulmonary artery endothelial cells promotes neutrophil adherence.
Authors: Fisher M A , Del Vecchio P J , Palace G P , Denholm E M , Lai L , Malik A B
Published: June 2012

We previously have described the ability of alpha-thrombin (the native procoagulant enzyme) to stimulate adherence of neutrophils to pulmonary artery endothelial cells. In the present study, we observed that conditioned medium factors released by alpha-thrombin (10(-8) M) treatment of cultured ovine pulmonary artery endothelial cells increased neutrophil adherence to naive pulmonary artery endothelial monolayers. This effect was independent of any residual alpha-thrombin present in the medium. In contrast to thrombin-induced neutrophil adherence, adherence of neutrophils mediated by the conditioned medium was not inhibited by the anti-CD18 monoclonal antibody 60.3, indicating a CD18-independent mechanism. The factors generated by the action of alpha-thrombin on endothelial cells also resulted in concentration-dependent neutrophil migration. The neutrophil adherence- and migration-promoting activities were isolated in the ether portion after extraction of the conditioned medium. Chromatographic analysis showed that the active components (which resolved into two peaks by reversed-phase high-performance liquid chromatography) were relatively hydrophilic low molecular weight lipids without phosphorus or amino acids. Reconstitution of these peaks indicated that they mediated neutrophil adhesion and migration responses. The results indicate that lipid factors promoting neutrophil adhesion and migration are generated by the action of thrombin on pulmonary artery endothelial cells. The generation of these factors may contribute to the amplification of the lung inflammatory response after pulmonary intravascular coagulation induced by thrombin.
Distinction between metabolic and myogenic mechanisms of coronary hyperemic response to brief diastolic occlusion.
Authors: Dubé G P , Bemis K G , Greenfield J C
Published: June 2012

We monitored an index of coronary vascular resistance (mean aortic pressure/mean coronary flow) in 19 heart-blocked conscious dogs paced at 60 beats/min and instrumented with an aortic pressure catheter, left circumflex artery electromagnetic flow probe, and a coronary occluder. Cessation of pacing for a single beat resulted in a long diastole control (LDC) intervention beat of 2-second duration characterized by a progressive rise in diastolic coronary vascular resistance index. A 400-msec coronary artery occlusion early in a long diastole (LD4) dramatically inhibited the rate of rise in resistance index during the first 600 msec (phase 1) after occlusion. Partial recovery of the resistance index rise rate was evident during the remaining 400 msec (phase 2) of the long diastole. In nine dogs, LDC and LD4 intervention beats were instituted during two conditions of myocardial metabolic activity in which the myogenic stimuli associated with coronary occlusion would be similar: 1) paired pacing and 2) normal pacing plus intravenous adenosine and phenylephrine infusions (AP) to maintain mean aortic pressure and coronary flow at paired pacing levels. During paired pacing, the LD4-LDC differences in phase 1 and 2 resistance index rise rates (-69 +/- 18 and -48 +/- 31 mmHg/ml/sec2, respectively) were greater than during normal pacing plus AP (-32 +/- 14 and -1 +/- 32 mm Hg/ml/sec2, phase 1 and 2, respectively) (p less than 0.05). These differences are consistent with operation of a metabolic mechanism in response to occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)