bluuebunny/crossref_metadata_2025 huggingface dataset:
Species differences in myocardial beta-adrenergic receptor regulation in response to hyperthyroidism.
Authors: Crozatier B , Su J B , Corsin A , Bouanani N el-H
Published: June 2012

The coupling between myocardial beta-adrenergic receptors, adenylate cyclase activity, and the in vivo cardiac response to catecholamines is controversial in hyperthyroidism. The possibility of species differences in beta-adrenoceptor regulation after thyroxine treatment was studied in dogs and in rats. In dogs instrumented with a left ventricular (LV) pressure micromanometer, hyperthyroidism was induced by L-thyroxine (0.5 mg/kg/day i.v. for 10 days). After hyperthyroidism, heart rate was increased to 167 +/- 10 beats/min (control, 107 +/- 8 beats/min; p less than 0.005) with an increase of peak LV dP/dt from 4,243 +/- 471 to 6,105 +/- 862 mm Hg/sec (p less than 0.01). LV response to injection of increasing doses of isoproterenol and dobutamine was not significantly different before and after induction of the hyperthyroid state, as shown by the unchanged slopes of the LV peak dP/dt versus the log of the dose of isoproterenol and dobutamine. Bmax of beta-receptors measured in crude membranes using 3H-CGP 12177 and in homogenates using 125I-cyanopindolol was not increased in hyperthyroid animals as compared with a control group. Basal adenylate cyclase activity was not different in control and hyperthyroid dogs (32 +/- 3 versus 29 +/- 3 pmol/mg/min), and maximal adenylate cyclase activity response to isoproterenol was similar in control and hyperthyroid dogs. In contrast, in rats subjected to hyperthyroidism (0.5 mg/kg/day i.p. L-thyroxine for 10 days), Bmax of adrenoceptors measured using the same methods was significantly increased as compared with control (+72.5% using 3H-CGP 12177 and +41% using 125I-cyanopindolol, but adenylate cyclase activity was not increased in hyperthyroid rats. We conclude that both adenylate cyclase activity and LV response to catecholamines are not increased by thyroxine-induced hyperthyroidism in dogs and that, in contrast with rats, beta-adrenergic density is not increased in hyperthyroid dogs. This indicates a species difference in myocardial beta-adrenoceptor regulation in response to hyperthyroidism.
Chronic treatment with polyethylene-glycolated superoxide dismutase partially restores endothelium-dependent vascular relaxations in cholesterol-fed rabbits.
Authors: Mügge A , Elwell J H , Peterson T E , Hofmeyer T G , Heistad D D , Harrison D G
Published: June 2012

The endothelium-derived relaxing factor is rapidly inactivated by superoxide radicals, and atherosclerotic vessels generate excess radical species. We tested the hypothesis that an imbalance between intrinsic superoxide dismutase (SOD) activity and the generation of superoxide radicals in atherosclerotic arteries may result in augmented inactivation of endothelium-derived relaxing factor. Vascular SOD was increased in normal and cholesterol-fed (1% cholesterol for 4 months) rabbits approximately twofold by treatment with polyethylene-glycolated SOD (PEG-SOD; 41,000 units/kg/day i.m.) for 1 week. Aortic rings from these animals and nontreated control and atherosclerotic rabbits subsequently were studied in organ chambers. Endothelium-dependent relaxations to acetylcholine and the calcium ionophore A23187 were improved by PEG-SOD in atherosclerotic but not in normal rabbits. PEG-SOD pretreatment did not alter endothelium-independent relaxations to nitroprusside. Thus, treatment with PEG-SOD can partially restore impaired endothelium-dependent relaxation of atherosclerotic arteries. We conclude that generation of oxygen-derived radicals likely contributes to endothelial dysfunction of atherosclerotic arteries.
Single cardiac vagal fiber activity, acute myocardial ischemia, and risk for sudden death.
Authors: Cerati D , Schwartz P J
Published: June 2012

Experimental and clinical evidence indicates that high risk for sudden death is significantly correlated with post-myocardial infarction depression in two "markers" of vagal activity, heart rate variability and baroreflex sensitivity. The present experiments were designed to answer some of the questions generated by those findings. In 33 anesthetized cats, the neural activity of single cardiac vagal efferent fibers was recorded in control conditions and after injection of phenylephrine (n = 33), before and during a 1-hour coronary artery occlusion (CAO) (n = 17), and before and after removal of the left stellate ganglion (n = 16). In the first minute after CAO, vagal activity increased by 35% from 1.66 +/- 0.37 to 2.57 +/- 0.62 impulses/sec (p less than 0.01); despite a slight decline, it remained for the entire CAO above the control values, to which it returned after CAO release. Of 17 cats, ventricular fibrillation occurred in nine (susceptible) and eight survived (resistant). Resistant and susceptible cats had different reflex vagal responses to CAO. Whereas the resistant cats had a 48% (p less than 0.01) increase by the second minute of CAO, susceptible cats had no change (-18%, p = NS) in vagal activity. These differences were independent of blood pressure changes. The increase in vagal efferent activity in response to the blood pressure rise induced by phenylephrine (baroreceptive reflex) was more marked in the resistant cats compared with the susceptible cats (+246 +/- 66% versus +80 +/- 14%, p less than 0.025). Just before the injection of phenylephrine, vagal activity was not different between resistant and susceptible cats (1.58 +/- 0.35 versus 1.48 +/- 0.30 impulses/sec, p = NS). In 16 cats, left stellectomy increased cardiac vagal efferent activity by 75% (p less than 0.01), and the reflex vagal activation secondary to phenylephrine was further enhanced (from 2.2 +/- 0.4 to 4.7 +/- 0.7 impulses/sec, p less than 0.001). These data demonstrate that 1) cardiac vagal efferent activity increases in response to acute myocardial ischemia--much more so among the animals destined to survive, 2) before CAO, susceptible and resistant animals can be identified by the vagal response to blood pressure increase (assessed clinically by baroreflex sensitivity) and not by tonic vagal activity (assessed clinically by heart rate variability), and 3) the findings with left stellectomy support the hypothesis that vagal activity decreases after myocardial infarction because of an increase, secondary to abnormal stretch of the cardiac mechanoreceptors, in cardiac sympathetic afferent traffic, which exerts a tonic restraint on vagal outflow.
Morphological, biochemical, and electrophysiological characterization of a clonal cell (H9c2) line from rat heart.
Authors: Hescheler J , Meyer R , Plant S , Krautwurst D , Rosenthal W , Schultz G
Published: June 2012

Morphological, electrophysiological, and biochemical properties of H9c2 cells, a permanent cell line derived from rat cardiac tissue, were studied. Although the lectin binding pattern revealed similar sugar residues in the surface coat of H9c2 cells and isolated rat cardiocytes, heart-specific morphological structures could not be detected in H9c2 cells. Under physiological ionic conditions, H9c2 cells exhibited an outwardly rectifying, transient K+ current. When this current component was blocked by Ba2+ and Cs+, we observed an inward current through Ca2+ channels (15.8 +/- 2.2 pA/pF, n = 18, measured as Ba2+ current) that showed all characteristics of cardiac L-type currents. The activation kinetics were fast, and the current was stimulated by isoproterenol. The effect of isoproterenol was mimicked by forskolin or intracellularly applied cAMP. In radioligand binding experiments, we identified a specific, saturable, stereoselective and reversible high-affinity [3H]-(+)PN 200-110 binding with a dissociation constant Kd = 0.53 +/- 0.28 nM and a maximal specific binding of Bmax = 129.3 +/- 16.1 fmol/mg protein. There was an additional low-affinity/high-capacity binding site, which is unlikely to be related to a Ca2+ channel protein. Signal-transducing G proteins in membranes were characterized by [32P]ADP-ribosylation catalyzed by bacterial toxins and by the use of various antibodies. Cholera toxin substrates of 42 and 45 kd were identified that apparently correlated to Gs alpha-subunits. Pertussis toxin substrates of 40-41 kd were tentatively identified as Gi alpha-subunits. The G protein Go was absent or at least extremely low in concentration.
Transfusion Reactions due to Plasma Incompatibility in Dogs
Authors: BLISS J. Q. , JOHNS D. G. , BURGEN A. S. V.
Published: June 2012

Plasma incompatibility was investigated as a possible factor in transfusion reactions in dogs. Urticaria, failure to retain within the circulation the equivalent of transfused plasma volume and protein, and increased gastric acid secretion almost invariably followed transfusion of plasma from another dog but not transfusion of the dog's own plasma. The cutaneous reactions were abolished and the retention of plasma was improved by administration of an antihistamine. Erythrocyte isoagglutinins did not appear to be involved in these reactions.
The Interpretation of "Spurious" Correlations in Coronary Flow Literature
Authors: SCOTT J. C. , BALOURDAS T. A.
Published: June 2012

Coefficients of correlation between coronary sinus blood flow and several cardiac variables have been analyzed from data obtained by the nitrous oxide desaturation method in dogs. The
r
value for flow and left ventricular oxygen consumption is an example of the correlation of two variables having a common element. The high values reported in the literature for this relationship may also be obtained with numbers drawn at random. Accordingly such values should not be accepted as valid evidence of a functional relationship between coronary blood flow and myocardial oxygen consumption.

A high positive correlation, between flow and heart rate in the normal dogs and a significant inverse correlation between flow and arteriovenous oxygen difference in the chronic sympathectomized dogs, was observed.
Synthesis of Precordial Potentials from the SVEC III Vectorcardiographic System
Authors: OKADA ROBERT H. , LANGNER PAUL H. , BRILLER STANLEY A.
Published: June 2012

Precordial potentials were synthesized from the components of the SVEC III vectorcardiographic system as an application of the Becking-Burger technic for testing the validity of the single dipole concept. The data was further utilized to construct Burger image loops from living subjects. Discrepancies from pure dipole theory and from the applicability of the SVEC III system are quantified. Limitations of even a perfect vectorcardiographic lead system are defined and discussed.
Epinephrine Levels in the Peripheral Blood During Irreversible Hemorrhagic Shock in Dogs
Authors: GREEVER CARL J. , WATTS DANIEL T.
Published: June 2012

Dogs were bled to a mean arterial pressure of 40 mm. Hg until 10 per cent of the shed blood had automatically reinfused from an elevated reservoir. The remaining blood was then rapidly infused intravenously. The procedure was fatal to all 13 dogs. Arterial blood epinephrine levels were followed during the time of hemorrhage and the post-hemorrhagic survival period in 9 of these animals. Arterial blood epinephrine levels in the 9 dogs increased from control values of less than one µg./L. to a maximum of 29 µg./L. during early hemorrhage, and then decreased during the period of spontaneous reinfusion to 7.5 µg./L. After complete reinfusion the blood pressure returned to normal, and epinephrine disappeared from the circulation. The blood pressure then gradually failed under normovolemic conditions, and the animals died in shock after an average of 220 minutes. Blood samples obtained immediately before death when the mean arterial pressure was 45 mm. Hg contained only 3.5 µg./L. epinephrine.
Directional Difference of Conduction Velocity in the Cardiac Ventricular Syncytium Studied by Microelectrodes
Authors: SANO TOYOMI , TAKAYAMA NORIYUKI , SHIMAMOTO TAKIO
Published: June 2012

In the theory of electrocardiography the direction of myocardial fibers has been almost ignored. In order to evaluate whether this is proper or not, directional difference of conduction velocity in the ventricular syncytium was examined by capillary microelectrodes. Conduction velocity in the direction of myocardial fibers was found to be usually several times larger than that vertical to them. This difference is significantly large and cannot be ignored even though rapidity of conduction through Purkinje fibers is considered. This statement became more applicable in various abnormal conditions. Thus it is concluded that the direction of myocardial fibers should be given more attention in discussion of propagation of excitation waves in the cardiac ventricle.
Frequencies in Pulsatile Flow and Response of Magnetic Meter
Authors: FERGUSON DONALD J. , WELLS HERBERT S.
Published: June 2012

An electromagnetic meter has been calibrated for pulsatile flow with use of a sinusoidal driver operating up to 45 c.p.s. Accurate recording of alternating flow at this frequency was possible under specified conditions. Pulsatile flow measurements from animals were directly calibrated by fractional collection of blood after it passed through the meter. Harmonic analyses of flow curves indicated that full response to 20 c.p.s. permitted adequate recording of femoral artery flow in an anesthetized dog.
Effect of Vitamin D, Sucrose, Corn Oil and Endocrines on Tissue Cholesterol in Rats
Authors: LEE CHENG-CHUN , HERRMANN ROY G.
Published: June 2012

A diet containing 65 per cent sucrose with added cholesterol resulted in hypercholesteremia and increased tissue cholesterol deposition in rats. Ten per cent corn oil with added cholesterol in Purina laboratory chow had no apparent effect on the serum total cholesterol but increased cholesterol deposition in tissues. Ovariectomy was without significant effect. Thyroidectomy or hypophysectomy aggravated the hypercholesteremia and the increased tissue cholesterol deposition induced by the sucrose diet. The effect of hypophysectomy was not due to the loss of thyrotrophic hormone alone. Addition of vitamin D aggravated hypercholesteremia and increased liver cholesterol deposition in normal, thyroidectomized or hypophysectomized rats fed the sucrose diet. In ovariectomized rats, the tissue cholesterol deposition was also augmented. When corn oil diet was fed, the supplementary vitamin D increased the serum total cholesterol level of the thyroidectomized rat.
Effect of Histamine on the Pulmonary Circulation in Dogs
Authors: STORSTEIN OLE , CUDKOWICZ LÉON , ATTWOOD H. D.
Published: June 2012

Histamine was administered to dogs by the intravenous route near the right atrium in doses of 9.6 to 19 γ/Kg. body weight. It produced a severe drop in systemic blood pressure, negligible changes in heart rate and respiration, usually a fall in cardiac output and no change in left atrial or pulmonary artery wedge pressure. The pulmonary artery pressure showed an initial rise and then a fall following the drop in systemic blood pressure. Pulmonary arteriolar resistance followed the changes in cardiac output. There appeared to be no consistent evidence of pulmonary vascular constriction following the injection of histamine in the doses used in this study.
Atheromatous Changes in Cholesterol-Fed Rabbits Treated with Eggplant Extract
Authors: GRAHAM W. DONALD , BEARE JOYCE L. , GRICE HAROLD C.
Published: June 2012

Cholesterol-induced changes in rabbits were studied with and without administration of an extract of eggplant. An anemia, accompanied by atrophic gastritis, developed in the cholesterol-fed animals. Their atheromatous plaques, and elevated serum cholesterol, lipoalbumin, α-lipoprotein, and neutral fat were not affected by the eggplant extract.
Effects of Renal Hypertension on Coronary Blood Flow, Cardiac Oxygen Consumption and Related Circulatory Dynamics of the Dog
Authors: WEST JAMES W. , MERCKER HERMANN , WENDEL HERBERT , FOLTZ ELWOOD L.
Published: June 2012

A comparative study is presented on the circulatory dynamics of the renal hypertensive state, the stability (repeatability) of the findings in a given subject, the effect of anemia as a complicating factor and the amount of cardiac hypertrophy present in each animal at the end of the series of observations. The results indicate that in nonanemic renal hypertensive dogs with cardiac hypertrophy the coronary blood flow and cardiac oxygen consumption are the same per unit weight of myocardial tissue as in normal dogs. However, when a mild chronic anemia is a complicating factor, the coronary blood flow and the myocardial oxygen uptake are both increased. The coronary sinus venous oxygen saturation is essentially unchanged in the nonanemic hypertensives, whereas in the anemic hypertensives it is significantly lowered.
Effect of Bilateral Internal Mammary Artery Ligation on Coronary Circulation in Dogs
Authors: HURLEY RICHARD E. , ECKSTEIN RICHARD W.
Published: June 2012

The internal mammary arteries of dogs were ligated bilaterally subsequent to surgical narrowing of the circumflex arteries. Six weeks later measurements of retrograde circumflex flows were made to assess the extent of collateral development. The results when compared with control dogs indicated that internal mammary ligation did not significantly improve the blood supply to the myocardium.
Some Determinants of Coronary Collateral Blood Flow in the Open-Chest Dog
Authors: KATTUS A. A. , GREGG D. E.
Published: June 2012

Dynamics of the coronary collateral circulation have been investigated by means of the retrograde flow technic. A principal determinant of retrograde flow appears to be the perfusion pressure irrespective of the rate of coronary inflow. Nitroglycerine, histamine and norepinephrine failed to augment retrograde flow. Reactive hyperemia and temporary myocardial ischemia resulted in a reduction of retrograde flow which could be due to active vasoconstriction or to myocardial stretching. Changes in heart rate and the onset of ventricular fibrillation did not alter retrograde flow, but low blood viscosity increased it.
Passage of Labeled Cholesterol into the Aortic Wall of the Normal Dog
Authors: DUNCAN LEROY E. , BUCK KATHERIN , LYNCH ALMORRIS
Published: June 2012

In the normal dog the rate of movement of cholesterol from the serum into the inner layer of the aortic wall is greatest at the proximal end of the aorta and decreases progressively along the length of the aorta until in the terminal aorta the rate is only about one sixth that in the proximal aorta. A similar gradient of rates was previously demonstrated for albumin which enters the aortic wall about three times as fast as cholesterol. The similarity of the gradients and the relative magnitude of the rates for cholesterol and albumin support the concept that cholesterol is carried into the aortic wall of the normal dog by the passage of the lipoproteins of which it is a part.
Staphylococcal Endocarditis and Glomerulonephritis in Dogs
Authors: HIGHMAN BENJAMIN , ALTLAND PAUL D. , ROSHE JOSEPH
Published: June 2012

Endocarditis was induced in dogs with aortic insufficiency by intravenous injection of 1 ml. of a culture of
Staphylococcus aurens
. Endocarditis could be prevented by a single intravenous injection of penicillin given within 8 hours after injecting the bacteria. The infection was aborted or modified when treatment was delayed 16 hours. When treatment was delayed 24 hours or longer, symptoms often recurred after cessation of therapy. The endocarditis was arrested by treatment of relapses, but some animals died from acute heart failure due to valvular deformity or insufficiency. A proliferative glomerulonephritis, which developed in nearly all dogs given delayed treatment, persisted despite therapy. There was evidence that a chronic glomerulonephritis may be a sequel to this proliferative glomerulonephritis.
Mechanical deformation of vessel wall and shear stress determine the basal release of endothelium-derived relaxing factor in the intact rabbit coronary vascular bed.
Authors: Lamontagne D , Pohl U , Busse R
Published: June 2012

We investigated the mechanisms that are responsible for the basal release of endothelium-derived relaxing factor (EDRF), which is likely to be identical with nitric oxide, in the intact coronary circulation. The increase in cGMP content of platelets passing through the coronary bed of the isolated rabbit heart was used as an index of EDRF release. Platelet cGMP content after passage through the heart under control conditions (flow rate of 20 ml/min) amounted to 0.50 +/- 0.10 pmol/mg protein. Inhibition of endothelial nitric oxide synthesis by 30 microM NG-nitro-L-arginine (L-NNA) reduced this amount by more than 60%. Increasing flow rate from 20 ml/min to 40 and 60 ml/min led to flow-dependent dilation as reflected by the subsequent drop in perfusion pressure after an initial rise. The flow-dependent dilation was associated with a significant increase in the normalized platelet cGMP content. L-NNA abolished completely both the flow-dependent dilation and the increase in platelet cGMP content. Increasing shear stress by a strong vasoconstriction (1 nM endothelin-1) at constant flow was also accompanied by a 2.5-fold increase in platelet cGMP content. To investigate whether mechanical forces applied to the vascular wall by the myocardial contraction cycle were also a stimulus for EDRF release, cardiac arrest was induced by a continuous infusion of mepivacaine (final concentration, 0.02%). Under these conditions, a decrease in platelet cGMP content comparable to that after nitric oxide synthesis inhibition was observed in the arrested heart.(ABSTRACT TRUNCATED AT 250 WORDS)
Cellular and ventricular contractile dysfunction in experimental canine mitral regurgitation.
Authors: Urabe Y , Mann D L , Kent R L , Nakano K , Tomanek R J , Carabello B A , Cooper G
Published: June 2012

This study was designed to answer two questions. First, does the left ventricular contractile dysfunction resulting from mitral regurgitation (MR) reflect a primary defect in the cardiac muscle cell? Second, what is the basis for any change in cellular contractile function that might be observed? Left ventricular volume overload was produced in 10 dogs by catheter transection of mitral chordae tendineae. Three months later in these and in seven control dogs, left ventricular contractile function was characterized by the end-ejection stress-volume relation (EESVR). Investigators who were blinded to these results then characterized the contractile performance of cardiac muscle cells, or cardiocytes, from these same left ventricles in terms of the viscosity (graded external load)-velocity relation. Finally, the tissue and cellular components of these same left ventricles were analyzed morphometrically. Both the left ventricles from the MR group and their constituent cardiocytes showed marked contractile abnormalities. By matching ventricles with cells from the same MR dogs, ventricular EESVR was correlated with cardiocyte peak sarcomere shortening velocity (SSV). The correlation coefficient between EESVR and SSV was 0.63, but between a size-independent measure of active ventricular stiffness and SSV, it was 0.88. No change in left ventricular interstitial volume fraction was found in MR dogs, but both ventricular and cellular contractile dysfunction strongly correlated with a decreased volume fraction of cardiocyte myofibrils. Last, in an attempt to relate the degree of contractile dysfunction to the hypertrophic response, left ventricular mass in the MR dogs was correlated with both cellular and ventricular contractile indexes; no significant correlation was found. Three conclusions are warranted by these studies. First, chronic left ventricular volume overload from mitral regurgitation leads to contractile defects at both the ventricular and cellular levels, the extent of which correlates well in individual animals. Second, no quantitative interstitial change resulted from MR. Taken together, these two findings strongly suggest that the contractile defect is intrinsic to the cardiocyte. Third, while the contractile abnormality in MR remains undefined, the most basic defects appear to be a combination of myofibrillar loss with the failure of compensatory hypertrophy to occur in response to progressive decrements in cellular and ventricular function.
Pulmonary vasodilatory action of endogenous atrial natriuretic factor in rats with hypoxic pulmonary hypertension. Effects of monoclonal atrial natriuretic factor antibody.
Authors: Raffestin B , Levame M , Eddahibi S , Viossat I , Braquet P , Chabrier P E , Cantin M , Adnot S
Published: June 2012

We administered ascitic fluid containing atrial natriuretic factor (ANF) monoclonal antibody to rats after 3 weeks of exposure to hypoxia while the rats were still hypoxic. In additional chronically hypoxic rats, we infused synthetic rat ANF. In conscious chronically instrumented rats, after a bolus dose of 5 micrograms i.v. ANF, pulmonary arterial pressure fell significantly from 26.5 +/- 2 to 21 +/- 2 mm Hg (p less than 0.01), reaching its nadir at 5 minutes without change of systemic arterial pressure, cardiac output, or heart rate. Pulmonary arterial pressure increased gradually from 26 +/- 4 to 34 +/- 4 mm Hg within 30 minutes (p less than 0.05) after acute administration of ANF monoclonal antibody and decreased transiently to return to baseline within 15 minutes after infusion of control ascitic fluid containing monoclonal antibody against an apolipoprotein. Cardiac output and heart rate remained unchanged after both ANF monoclonal antibody and control ascitic fluid. In normoxic rats, acute administration of ANF monoclonal antibody did not cause significant changes in pulmonary arterial pressure, cardiac output, or heart rate. Rats receiving weekly intravenous injections of ANF monoclonal antibody that were started before initiation of exposure to hypoxia experienced significantly aggravated pulmonary hypertension and right ventricular hypertrophy compared with rats receiving repeated infusions of control ascitic fluid. However, there was no significant difference in small pulmonary arterial wall thickness or percentage of muscularized arteries at the alveolar duct level. These results suggest that endogenous ANF attenuates hypoxic pulmonary hypertension by decreasing pulmonary vascular tone.
Characterization of acetylcholine-induced membrane hyperpolarization in endothelial cells.
Authors: Chen G F , Cheung D W
Published: June 2012

The characteristics of the hyperpolarization response to acetylcholine (ACh) in endothelial cells from the guinea pig coronary artery were studied by microelectrode recording technique. ACh (30 nM to 3 microM) induced membrane hyperpolarization in a dose-dependent manner. The sustenance of the response required the presence of external calcium. The hyperpolarization was not affected by nifedipine (1 microM) but was inhibited by the potassium channel blockers charybdotoxin (10 nM), tetraethylammonium (1 mM), and 4-aminopyridine (0.5 mM). Glibenclamide (10 microM) and apamin (1 microM) were not effective. The inhibitors of endothelium-derived relaxing factor/nitric oxide synthesis N omega-nitro L-arginine (50 microM) and NG-monomethyl L-arginine (30 microM) had no effect on the resting membrane potential or the ACh-induced responses. No hyperpolarization was observed with application of sodium nitroprusside (10 microM) or 8-bromo-cGMP (0.1 microM). Ouabain (10 microM) depolarized the membrane significantly by 5 mV, but the ACh hyperpolarization was not affected. Indomethacin (10 microM) was without effect on the resting membrane potential or the hyperpolarization to ACh. These results show that ACh-induced hyperpolarization is dependent on external calcium and can be inhibited by certain potassium channel blockers. The hyperpolarization response is not mediated by endothelium-derived relaxing factor/nitric oxide, cGMP, a cyclooxygenase product, or stimulation of the Na-K pump.
Dose-dependent modulation of the cardiac sodium channel by sea anemone toxin ATXII.
Authors: el-Sherif N , Fozzard H A , Hanck D A
Published: June 2012

The effects of sea anemone toxin ATXII on single sodium channels were studied in cell-attached patches on rabbit ventricular myocytes at 20-22 degrees C. Exposure of patches to 1,000 nM ATXII induced long-lasting bursts of openings, which were more dramatically different from control at -20 mV than at -50 mV. Mean open duration, which had a biphasic dependence on voltage in control patches, was monotonically dependent on voltage in toxin-exposed patches, being 3.5 times longer than control at -20 mV and 4.5 times longer at -10 mV. Multiple mean open durations were detected at depolarized potentials. To test whether the multiple mean open durations resulted from a mixture of modified and unmodified openings, histograms of late openings (when unmodified channels would be inactivated) were constructed. Because in most cases these fit a single exponential with a mean open duration like that of modified channels, we conclude that voltage-dependent toxin unbinding produced a mixed population of unmodified and modified openings. Consistent with this hypothesis, lower concentrations of toxin most often produced open-duration histograms best fit with two exponentials. Ensembles revealed complex decay kinetics, which could be interpreted within the context of the toxin-induced increase in mean open duration and burst duration and the summation of modified and unmodified events. Analysis of the numbers of early versus late events at -20 mV for patches exposed to 20 nM, 100 nM, and 1,000 nM ATXII predicted the ED50 for ATXII block to be 285 nM at this potential. Using a five-state Markovian model, the action of ATXII could be explained as a reduction of the open-to-inactivated rate constant without effect on inactivation from closed states or other rate transitions.
Genetically engineered endothelial cells remain adherent and viable after stent deployment and exposure to flow in vitro.
Authors: Flugelman M Y , Virmani R , Leon M B , Bowman R L , Dichek D A
Published: June 2012

Intravascular stents, currently in experimental human use for recurrent arterial stenosis, are plagued by subacute thrombosis. As a therapeutic approach to stent-related thrombosis, we and others have suggested coating stents with endothelial cells before implantation. In a previous study we demonstrated the feasibility of coating stents with endothelial cells that were genetically modified to secrete large amounts of human tissue plasminogen activator. In the present study we attempted both to develop a clinically applicable protocol for stent seeding and to test whether seeded cells would remain adherent to stents after exposure to pulsatile flow. Endothelial cells were harvested from the saphenous veins of sheep with survival of the donor animals. Harvested cells were transduced with a retroviral vector containing a marker gene and seeded onto catheter-mounted stents under sterile conditions. Scanning electron microscopy revealed complete coverage of the stent surfaces by seeded cells. Stents were expanded and exposed to pulsatile flow in vitro. Substantial cell retention was observed on the lateral stent surfaces by light microscopy and scanning electron microscopy; fewer cells were seen on the luminal and abluminal surfaces. Removal of seeded cells from flow-exposed stents by trypsin digestion resulted in the recovery of approximately 70% of the seeded cells. These cells were viable and healthy as judged by their ability to proliferate to confluence with the same kinetics as control (non-flow-exposed) cells. Autologous genetically modified endothelial cells can be seeded onto catheter-mounted stents in a sterile manner, and stent deployment under flow conditions results in substantial retention of viable cells.
Pulmonary vasodilator response to vagal stimulation is blocked by N omega-nitro-L-arginine methyl ester in the cat.
Authors: McMahon T J , Hood J S , Kadowitz P J
Published: June 2012

The effect of N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of endothelium-derived relaxing factor production, on the vasodilator response to efferent vagal stimulation was investigated in the pulmonary vascular bed of the intact-chest cat under conditions of controlled blood flow and constant left atrial pressure. When pulmonary vascular tone was increased with U46619, efferent vagal stimulation decreased lobar arterial pressure in a stimulus-frequency-dependent manner. The decreases in lobar arterial pressure were enhanced by pretreatment with reserpine, were blocked by atropine, and were not altered by propranolol, indicating that the neurogenic vasodilator response was cholinergic in nature. The decreases in lobar arterial pressure in response to vagal stimulation and to exogenously administered acetylcholine were reduced after administration of L-NAME (100 mg/kg i.v.). Although L-NAME decreased pulmonary vasodilator responses to vagal stimulation and to acetylcholine, responses to adenosine, nicorandil, lemakalim, isoproterenol, prostaglandin E1, sodium nitroprusside, and 8-bromo-cGMP, agents that act by a variety of mechanisms, were not decreased. These results are consistent with the hypothesis that efferent vagal stimulation releases acetylcholine, which dilates the pulmonary vascular bed by stimulating the production of nitric oxide or a labile nitroso compound from L-arginine.
Early changes in extracellular potassium in ischemic rabbit myocardium. The role of extracellular carbon dioxide accumulation and diffusion.
Authors: Cascio W E , Yan G X , Kléber A G
Published: June 2012

The role of local accumulation and diffusion of CO2 to modify cellular loss and extracellular accumulation of K+ during the initial, reversible phase of myocardial ischemia was investigated in isolated, cylindrical papillary muscles of the rabbit. The muscles were blood-perfused through their vascular tree and placed in a (permanently flowing) humidified gas mixture with predetermined partial pressures of N2, O2, and CO2. Ischemia was produced by total arrest of perfusion and O2 withdrawal from the gas mixture. With surface PCO2 kept constant during ischemia, [K+]o varied markedly with muscle geometry. After 10 minutes of ischemia, K+ accumulation was approximately 2.5 mM in muscles with a radius of 0.35 mm and approximately 14 mM in muscles with a radius of 0.9 mm, indicating that a large fraction of K+ accumulation was dependent on diffusion of a volatile metabolite. Computer simulation of CO2 accumulation and diffusion within a tissue cylinder suggested a close phenomenological relation between PCO2 and [K+]o in ischemia. This was confirmed by the finding that an increase of tissue PCO2 in small cylinders before or during ischemia by externally applied CO2 produced an increase in K+ accumulation. The importance of CO2 diffusion for local inhomogeneities in K+ within the same preparation was demonstrated by showing [K+]o gradients with simultaneous or consecutive measurements between the papillary muscle cylinders and the adjacent septum and within 300 microns from the surface of the papillary muscle cylinders. These gradients predict an inhomogeneity of impulse conduction that might contribute to the genesis of ventricular arrhythmias. Besides the demonstration that accumulation and diffusion introduce inhomogeneities of [K+]o in ischemia, our results suggest that a significant component of cellular ischemic K+ loss is associated with production and extrusion of metabolic acid. On the basis of previous measurements of pHo and pHi in identical conditions, possible mechanisms of ischemic cellular K+ loss are discussed.
Direct measurement of L-type Ca2+ window current in heart cells.
Authors: Hirano Y , Moscucci A , January C T
Published: June 2012

The activation and inactivation relations of several ion channel currents overlap, suggesting the existence of a steady-state or "window" current. We studied L-type Ca2+ channel window current in single cardiac Purkinje cells using a voltage-clamp protocol by which channels were first inactivated nearly completely during a long-duration depolarizing step, and then the recovery of Ca2+ current was observed during repolarizing steps into the L-type Ca2+ window voltage range. With these conditions, a small-amplitude inward Ca2+ current gradually developed after repolarization to voltages within the window but not after steps to voltages positive or negative to it. Window current was suppressed by Cd2+ (50 microM), nifedipine (1 microM), and nicardipine (1 microM), and it was augmented by isoproterenol (5 microM) and Bay K 8644 (1 microM). At voltages at which window current developed, L-type Ca2+ channels also recovered to a closed state from which they could be reopened by an additional depolarizing step. At voltages positive to the window range, channel recovery to a closed state(s) was absent, whereas at voltages negative to the window range, channel recovery to a closed state(s) increased, as expected from the "steady-state" inactivation relation. Our results provide direct measurement of L-type Ca2+ window current and distinguish it from other processes, such as slow inactivation. Our findings support the postulate that within a window there occur channel transitions from inactivated to closed states, and these channels (re)open, and this process may occur repetitively. Some physiological and pathophysiological roles for L-type Ca2+ window current are discussed.
NG-methyl-L-arginine, an inhibitor of L-arginine-derived nitric oxide synthesis, stimulates renal sympathetic nerve activity in vivo. A role for nitric oxide in the central regulation of sympathetic tone?
Authors: Sakuma I , Togashi H , Yoshioka M , Saito H , Yanagida M , Tamura M , Kobayashi T , Yasuda H , Gross S S , Levi R
Published: June 2012

Continuous production of endothelium-derived nitric oxide (NO) in peripheral vessels has been shown to modulate vascular resistance and blood pressure. NO is also formed in the brain upon activation of glutamate receptors, which are thought to mediate central autonomic reflexes. In the present study we assessed whether NO plays a role in central autonomic regulation. For this, we have investigated the effects of NG-methyl-L-arginine (NMA), a selective inhibitor of NO synthesis from L-arginine, on sympathetic renal nerve activity (RNA), blood pressure, and heart rate in the anesthetized rat. NMA elicited a dose-dependent sustained increase in blood pressure (approximately 20 and 30 mm Hg, 5 minutes after 10 and 50 mumol/kg i.v., respectively). Heart rate and RNA decreased transiently (15 beats per minute and 40%, respectively); RNA subsequently increased (100%) while blood pressure remained elevated. Baroreceptor deafferentation markedly altered these responses to NMA; the transient decreases in heart rate and RNA were abolished, whereas the increases in RNA and blood pressure were significantly potentiated. After spinal C-1-C-2 transection, there was no increase in RNA, and blood pressure increased to a smaller extent. L-Arginine blocked the NMA-induced increases in blood pressure and RNA. Thus, in addition to modulating vascular resistance by a peripheral action, NO may also play a role in the central regulation of sympathetic tone.
Endothelin blocks ATP-sensitive K+ channels and depolarizes smooth muscle cells of porcine coronary artery.
Authors: Miyoshi Y , Nakaya Y , Wakatsuki T , Nakaya S , Fujino K , Saito K , Inoue I
Published: June 2012

ATP-sensitive K+ channels with a conductance of 30 pS in smooth muscle cells of porcine coronary artery were found to be highly active in the intact cell-attached patch configuration when the pipette contained a physiological concentration of Ca2+ (greater than 10(-4) M). In the inside-out configuration, these channels were activated by extracellular Ca2+ and blocked by cytosolic ATP and glibenclamide. Endothelin applied to the pipette specifically blocked these channels in a concentration-dependent manner in the cell-attached configuration (half-maximal inhibition, 1.3 x 10(-9) M). A K+ channel opener, nicorandil, activated these channels even in the presence of 10(-8) M endothelin. In the whole-cell current-clamp method, the cell membrane was depolarized by endothelin and then repolarized by nicorandil. The membrane depolarization is closely related to contraction of smooth muscle cells. These results suggest that the ATP-sensitive K+ channels are important in controlling the vascular tone of the coronary artery and that endothelin can increase vascular tone by blocking these channels.
Endocardial endothelium modulates myofilament Ca2+ responsiveness in aequorin-loaded ferret myocardium.
Authors: Wang J , Morgan J P
Published: June 2012

The influence of selective removal of the endocardial endothelium (by a 1-second exposure to the detergent Triton X-100, 0.5%) on myofilament Ca2+ responsiveness and intracellular Ca2+ transients was studied in ferret papillary muscles loaded with the Ca(2+)-regulated bioluminescent indicator aequorin. The removal of endocardial endothelium produced three major effects: 1) a decrease in peak developed tension and an early onset in isometric relaxation without corresponding changes in the intracellular Ca2+ transient; 2) a rightward shift in the peak [Ca2+]i-peak tension relation with no change in maximum Ca(2+)-activated twitch tension; and 3) a decrease in steady-state tetanic force with a slight increase in the steady-state [Ca2+]i (at 4 mM [Ca2+]o) and an unchanged steady-state tetanic force with a clear increase in the steady-state [Ca2+]i (at 10 mM [Ca2+]o). These results suggest that intact endocardium may enhance performance of the heart by increasing the myofilament Ca2+ responsiveness through endothelium-derived compounds such as endothelin. This hypothesis is supported by our observations that endothelin 1) induced a leftward shift in peak [Ca2+]i-peak tension curve and 2) could reverse the characteristic changes produced by the removal of endocardium.
Dimethylthiourea, an oxygen radical scavenger, protects isolated cardiac myocytes from hypoxic injury by inhibition of Na(+)-Ca2+ exchange and not by its antioxidant effects.
Authors: Ziegelstein R C , Zweier J L , Mellits E D , Younes A , Lakatta E G , Stern M D , Silverman H S
Published: June 2012

Myocardial reoxygenation injury may be attenuated by oxygen free radical scavengers, arguing for a role of oxygen radicals in this process. To determine whether free radical scavengers affect reoxygenation injury in isolated cardiac myocytes, resting rat ventricular myocytes were exposed to hypoxic (PO2 less than 0.02 mm Hg) glucose-free buffer alone (n = 50) or with the addition of the oxygen radical scavengers 1,3-dimethyl-2-thiourea (DMTU, 25 mM, n = 46), human recombinant superoxide dismutase (SOD, 1,000 units/ml, n = 40), or the combination of these agents (n = 41). All cells responded by undergoing contracture to a rigor form. Hypoxia was then continued for a second period (T2), the duration of which correlates inversely with survival. After reoxygenation, cells either retained their rectangular shape (survival) or hypercontracted to a rounded form (death). For the group of cells with a T2 period greater than 30 minutes, no cell exposed to buffer alone (n = 20) or to SOD (n = 16) survived, in contrast to 15 of 24 (63%) cells exposed to DMTU. The addition of SOD to DMTU offered no advantage to DMTU alone. The protective effect of DMTU was not observed when it was added at reoxygenation, suggesting that this agent has an important effect during the hypoxic period when intracellular Ca2+ is known to rise, most likely because of the reversal of Na(+)-Ca2+ exchange. Therefore, the effects of DMTU on Ca2+ regulation (indexed by indo-1 fluorescence) during hypoxia were studied. DMTU significantly blunted the [Ca2+] rise during the hypoxic period.(ABSTRACT TRUNCATED AT 250 WORDS)
Antisense nonmuscle myosin heavy chain and c-myb oligonucleotides suppress smooth muscle cell proliferation in vitro.
Authors: Simons M , Rosenberg R D
Published: June 2012

Smooth muscle cell (SMC) proliferation is a poorly understood process that plays a critical role in several pathological states, including atherosclerosis and hypertension. Recent work suggests that the oncogene c-myb and myosin, a ubiquitous cytoskeletal protein, may be directly involved in this process. We have used antisense nonmuscle myosin heavy chain (NMMHC) or c-myb phosphorothiolate oligonucleotides to inhibit proliferation of SMCs in vitro. The suppression of growth is accompanied by reductions in the concentrations of NMMHC and c-myb mRNAs as well as decreases in the levels of the corresponding proteins. The specificity of the antiproliferative effect is underscored by the absence of any detectable growth inhibition with sense NMMHC or c-myb phosphorothiolate oligonucleotides, an antisense c-myb mismatch phosphorothiolate oligonucleotide, or an antisense thrombomodulin phosphorothiolate oligonucleotide. Furthermore, the treatment of SMCs with antisense phosphorothiolate oligonucleotides for as little as 2 hours causes maximal inhibition of cell growth over the next 72 hours. Under these conditions, SMCs attain normal rates of growth over the following 48 hours, which shows that proliferation is suppressed in a reversible fashion by antisense phosphorothiolate oligonucleotides. These experiments indicate that both c-myb and nonmuscle myosin play critical roles in SMC proliferation and that reductions of either mRNA by antisense phosphorothiolate oligonucleotides arrest the process.
Reoxygenation of endothelial cells increases permeability by oxidant-dependent mechanisms.
Authors: Lum H , Barr D A , Shaffer J R , Gordon R J , Ezrin A M , Malik A B
Published: June 2012

We investigated the effects of hypoxia/reoxygenation exposure on the barrier function of endothelial cell monolayers. Bovine pulmonary microvessel endothelial cells were grown to confluence on microporous filters (0.8-microns pore diameter) and exposed to hypoxia (0.1% O2 or PO2 approximately 1 mm Hg) for 2, 4, 12, or 24 hours, followed by reoxygenation with room air for a period ranging from 16 seconds to 2 hours. The transendothelial clearance rate of 125I-albumin was measured to determine the permeability of endothelial monolayers. Permeability increased twofold or fivefold over control values after 1 hour of reoxygenation in monolayers that had been exposed to either 12 or 24 hours of hypoxia. The response occurred within 5 minutes of reoxygenation, increased maximally by 40 minutes, and remained elevated with continuous reoxygenation for up to 2 hours. The increase in permeability was associated with F-actin reorganization, a change to spindlelike cells, and injured mitochondria. Immunoblot analysis indicated that neither hypoxia alone nor reoxygenation changed CuZn superoxide dismutase (SOD), MnSOD, and catalase levels. However, release of superoxide anions (O2-) into the extracellular medium increased by twofold within 40-60 minutes of reoxygenation. Treatment of endothelial cells with CuZnSOD (100 units/ml) for the 24-hour hypoxia period prevented O2- generation and approximately 50% of the increase in permeability. Higher CuZnSOD concentrations (greater than or equal to 200 units/ml) were not protective. Treatment with catalase (100-1,000 units/ml) inhibited the reoxygenation-induced increase in permeability at the highest catalase concentration (1,000 units/ml), suggesting a critical role of hydrogen peroxide in mediating the response.(ABSTRACT TRUNCATED AT 250 WORDS)