bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypoxia-induced activation of KATP channels limits energy depletion in the guinea pig heart
Authors: Decking U. K. , Reffelmann T. , Schrader J. , Kammermeier H.
Published: December 2017

The functional role of ATP-dependent potassium (KATP) in hypoxic cardiac failure was investigated in isolated guinea pig hearts with glibenclamide and rimalkalim as inhibitor and activator, respectively. Monophasic action potential duration at 90% of repolarization (MAP50), left ventricular function, and cardiac energy status (31P nuclear magnetic resonance spectroscopy) were measured during normotoxic (95% O2) and hypoxic (20% O2) perfusion. In normoxic hearts, 1 microM glibenclamide did not affect MAP50, left ventricular function, and coronary flow (n = 4). In contrast, rimalkalim rapidly shortened MAP50 and left ventricular pressure (LVP) in a dose-dependent fashion (e.g., by 60.2 +/- 3.5 and 80.8 +/- 8.2%, respectively, with 0.6 microM rimalkalim). This latter effect was reversed by 1 microM (glibenclamide (n = 4). With hypoxic perfusion, a reduction in LVP was observed, along with a shortening of the action potential (MAP90; 202 +/- 13 vs. 164 +/- 9 ms) and an increase in coronary flow. Glibenclamide (1 microM) reversed the MAP90 shortening and the increase in coronary flow. In addition, glibenclamide increased LVP transiently (n = 4). When coronary flow of hypoxic hearts was kept constant, however, glibenclamide elicited a sustained positive inotropic effect (n = 7). After glibenclamide, an increase in LVP from 54 +/- 4 to 64 +/- 3 mmHg was observed, along with a reduction in the free energy change of ATP hydrolysis from -54.5 +/- 1.9 to -52.9 +/- 0.2 nJ/mol and a further increase in the coronary venous adenosine from 269 +/- 48 to 1,680 +/- 670 nmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of central infusion of benzamil on Dahl S rat hypertension
Authors: Gomez-Sanchez E. P. , Gomez-Sanchez C. E.
Published: December 2017

The effect of continuous central infusion of benzamil, a Na+ channel-selective amiloride analogue, on the salt-induced hypertension in inbred Dahl salt-sensitive (SS/jr) rats was assessed. The continuous intracerebroventricular or subcutaneous infusion of benzamil at doses which have no effect when infused systemically was started at the same time or 2 wk after saline was substituted for drinking water, when the rats' blood pressures had become significantly elevated. Within 13 days, drinking saline caused a similar and significant increase in the blood pressures of rats receiving the vehicle intracerebroventricularly and 1 microgram/h of benzamil subcutaneously, which persisted throughout the 4-wk experiment. The intracerebroventricular infusion of 1 or 0.3 microgram/h benzamil, started at the same time the salt challenge was instituted, significantly deterred the increase in blood pressure over 4 wk. The intracerebroventricular, but not the subcutaneous, infusion of benzamil at 0.5 microgram/h arrested the increase in blood pressure in rats that were already hypertensive after 12 days on saline. Within 3 days the pressures in the intracerebroventricular and subcutaneous benzamil groups became significantly different, due to the further increase of the blood pressure in those animals receiving the intracerebroventricular vehicle with subcutaneous benzamil. There was no significant difference in weight gain throughout the experiment or in 24-h urine volumes and urinary Na(+)-to-K+ ratio at days 5 and 12 of benzamil infusion between groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Biaxial mechanical behavior of excised porcine mitral valve leaflets
Authors: May-Newman K. , Yin F. C.
Published: December 2017

Anterior and posterior leaflets from excised porcine mitral valves were mechanically tested under cyclic equibiaxial and strip biaxial stretch protocols at a strain rate of 4-12%/s after preconditioning. Cauchy stress and Lagrangian strain were calculated for both membrane and three-dimensional cases. The leaflets exhibited nonlinearly elastic, anisotropic behavior. Both anterior and posterior leaflets were less extensible in the circumferential than in the radial direction under equibiaxial stretch, with stress ratios of 5.7 and 4.3, respectively. The posterior leaflets exhibited greater extensibility in both directions and lower circumferential posttransitional moduli (ranges 690-820 vs. 2,500-3,200 N/m for anterior). This larger posterior extensibility may be due to the greater number of chordal attachments, which provide additional mechanical stability to this structure. Coupling of radial and circumferential mechanical behavior was evidenced by the response to different stretch protocols, indicating a complex microstructural coupling between individual collagen fibers or bundles. These are the first biaxial data for mitral valves and are a foundation for the development of a more detailed quantitative material description.
Relationship of simultaneous atrial and ventricular pressures in stage 16-27 chick embryos
Authors: Hu N. , Keller B. B.
Published: December 2017

Ventricular filling is determined by a dynamic balance between atrial and ventricular load and function. The embryonic cardiovascular system undergoes simultaneous growth and morphogenesis at the cellular, tissue, and organ levels to match the embryo's geometrically increasing metabolic demands. As part of our long-term investigation of atrial/ventricular coupling during primary cardiac morphogenesis, we defined the relationship between simultaneous atrial and ventricular pressures in the stage 16-27 white Leghorn chick embryo. We measured atrial and ventricular blood pressures with servo-null micropressure systems and sampled analog waveforms digitally at 500 Hz. Peak atrial pressure increased geometrically from 0.38 +/- 0.03 to 1.21 +/- 0.17 mmHg, while ventricular end-diastolic pressure increased linearly from 0.18 +/- 0.03 to 0.55 +/- 0.04 mmHg. The passive and active mean pressure gradients increased from 0.23 +/- 0.04 and 0.20 +/- 0.03 mmHg at stage 16 to 0.52 +/- 0.10 and 0.62 +/- 0.11 mmHg at stage 27, respectively. The atrioventricular pressure gradients were similar for stages 16, 18, and 21, then increased to stage 27. This diastolic pressure gradient identifies the atrioventricular orifice and developing endocardial cushions as a site of flow resistance that may influence both ventricular filling and chamber morphogenesis.
Mechanoenergetics of negative inotropism of ventricular wall vibration in dog heart
Authors: Nishioka T. , Goto Y. , Hata K. , Takasago T. , Saeki A. , Taylor T. W. , Suga H.
Published: December 2017

Mechanical vibration depresses cardiac contractility. We studied the mechanoenergetic effects of this negative inotropism in the left ventricle (LV) of an isolated, cross-circulated dog heart preparation. We took full advantage of the mechanoenergetic relationship among the LV end-systolic elastance (Emax, contractility index), systolic pressure-volume area (PVA), and myocardial oxygen consumption (VO2). PVA is a measure of the total mechanical energy that cardiac contraction generates. PVA correlates closely with VO2. The VO2 intercept of the VO2-PVA relation reflects the VO2 component for excitation-contraction (E-C) coupling plus basal metabolism (PVA-independent VO2). VO2 above the PVA-independent VO2 reflects the VO2 component for mechanical contraction (PVA-dependent VO2). When we applied 70-Hz vibration of 2-mm amplitude to a LV wall region, it instantly decreased Emax and PVA by 20%, followed by a 10% decrease in VO2 at a fixed volume. However, the vibration neither lowered the VO2-PVA relation obtained at different LV volumes, unlike ordinary negative inotropism, nor changed its slope (1.88 +/- 0.23 vs. 1.86 +/- 0.23 x 10(-5) ml O2.mmHg-1.ml-1). The virtually zero delta PVA-independent VO2/delta Emax with vibration indicates a much smaller O2 cost of Emax than that seen with calcium and propranolol inotropism. These mechanoenergetics support the hypothesis that mechanical vibration primarily suppresses cardiac contractility without suppressing E-C coupling.
Impact of extracellular buffer composition on cardioprotective efficacy of Na+/H+ exchanger inhibitors
Authors: Shimada Y. , Hearse D. J. , Avkiran M.
Published: December 2017

There is controversy over whether the cardioprotective effects of Na+/H+ exchanger inhibitors are exerted primarily during ischemia or during subsequent reperfusion, possibly because of interstudy differences in experimental conditions. We studied the impact of perfusate buffer composition on the relative degree of protection afforded by Na+/H+ exchanger inhibition during ischemia vs. reperfusion. Isolated rat hearts (n = 8/group) were perfused (37 degrees C, 75 mmHg) with bicarbonate- or N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium and subjected to 20 min of global zero-flow ischemia and 45 min of reperfusion. One of two structurally distinct Na+/H+ exchanger inhibitors [5-(N,N-dimethyl)amiloride (DMA) or (3-methylsulfonyl-4-piperidinobenzoyl)guanidine methanesulfonate (HOE-694), 10 mumol/l] was transiently (5 min) infused 1) immediately before ischemia, 2) during initial reperfusion, or 3) during both of these periods. With bicarbonate-buffered medium, neither drug improved the postischemic recovery of left ventricular developed pressure (LVDP) when given only during reperfusion. In contrast, HOE-694 improved the postischemic recovery of LVDP from 39 +/- 5% in control to 66 +/- 6% (P < 0.05) when given before ischemia and from 33 +/- 4% in control to 65 +/- 4% (P < 0.05) when given before ischemia plus during reperfusion. With the latter protocol, the cardioprotective effect of HOE-694 occurred in a dose-dependent manner at 0.1-10 mumol/l. In contrast to the results with bicarbonate-buffered medium, in the presence of N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium, DMA and HOE-694 significantly improved recovery of LVDP (from 34 +/- 5% in controls to 56 +/- 3 and 71 +/- 8%, both P < 0.05) when given only during reperfusion. They also provided significant protection when given before ischemia or before ischemia plus during reperfusion; with the latter protocol, HOE-694 produced an almost complete recovery of LVDP (88 +/- 9 vs. 30 +/- 7% in controls, P < 0.05). In conclusion, our results suggest that the influence of Na+/H+ exchanger activity during reperfusion on the extent of functional recovery is modulated significantly by perfusate buffer composition. As a consequence, the cardioprotective efficacy of Na+/H+ exchanger inhibitors may be overestimated under bicarbonate-free conditions.
Cyclic ADP-ribose stimulates sarcoplasmic reticulum calcium release in porcine coronary artery smooth muscle
Authors: Kannan M. S. , Fenton A. M. , Prakash Y. S. , Sieck G. C.
Published: December 2017

Cyclic ADP-ribose (cADPR) was shown to induce calcium release from the endoplasmic reticulum via ryanodine-sensitive pathways. In smooth muscle, two pathways for calcium release from the sarcoplasmic reticulum (SR) have been previously demonstrated: D-myo-inositol 1, 4, 5-trisphosphate-gated and ryanodine-gated. However, evidence for cADPR as a regulator for SR Ca2+ release in smooth muscle is lacking. We used permeabilized porcine coronary artery smooth muscle cells to directly examine the stimulation of SR Ca2+ release by cADPR. The results provide direct evidence that cADPR stimulates SR Ca2+ release and that this response is not inhibited by heparin, by depletion of the caffeine-sensitive Ca2+ pool, or by blockade or ryanodine receptors. These results indicate a novel mechanism for Ca2+ release from the SR of vascular smooth muscle.
Phospholipase D is activated by G protein and not by calcium ions in vascular smooth muscle
Authors: LaBelle E. F. , Fulbright R. M. , Barsotti R. J. , Gu H. , Polyak E.
Published: December 2017

We assessed the sensitivity of phospholipase D (PLD) activity in vascular smooth muscle to cytosolic Ca2+ by increasing cytosolic Ca2+ levels independently of agonist stimulation. When rat tail artery was preloaded with the Ca2+ indicator fluo 3 pentaacetoxymethyl ester, the addition of high extracellular K+, caffeine, or norepinephrine rapidly enhanced cytosolic Ca2+ levels. Neither increased extracellular K+ nor caffeine addition increased phosphatidylethanol production, indicating that cytosolic Ca2+ elevation alone did not stimulate PLD. In contrast, norepinephrine stimulated phosphatidylethanol production in this tissue. In strips of tail artery permeabilized with alpha-toxin and incubated in solutions containing free Ca2+ concentrations observed during physiological stimulation (pCa 6.4), PLD was not stimulated, whereas incubation with guanosine 5'-O-(3-thiotriphosphate) at pCa 7.0 activated this enzyme. Aluminum fluoride (AlF4-) stimulated PLD, and this activity was insensitive to pertussis toxin after stimulation by either norepinephrine or AlF4-. These results indicate that PLD in vascular smooth muscle is activated by norepinephrine via stimulation of a pertussis toxin-insensitive G protein and not via an increase in intracellular Ca2+ levels.
Effect of temperature on myocardial infarction in swine
Authors: Duncker D. J. , Klassen C. L. , Ishibashi Y. , Herrlinger S. H. , Pavek T. J. , Bache R. J.
Published: December 2017

Body core temperature in the normothermic range alters infarct size in rabbits. Moreover, temperature may modulate the protection by adenosine during a coronary artery occlusion. We investigated the effect of core temperature within the normothermic range (35-39 degrees C) on myocardial infarct size produced by a 45-min coronary occlusion in open-chest swine (n = 10), and we determined whether adenosine blockade with 8-phenyltheophylline and adenosine deaminase increased infarct size in the normothermic range (n = 9). After 4 h of reperfusion the area at risk and infarct size were determined with Evans blue dye and triphenyltetrazolium chloride. Infarct size strongly correlated with temperature (r2 = 0.71, P = 0.0001) so that at 35 degrees C no infarction occurred and with each 1 degree C increase in temperature 20% of the area at risk became infarcted. In contrast, neither the low levels of collateral flow (0.03 +/- 0.01 ml.min-1.g-1) nor the rate-pressure product correlated with infarct size. In the normothermic range, adenosine blockade had no effect on infarct size. The data demonstrate that temperature can exert a profound effect on infarct size but fail to demonstrate a protective effect on endogenous adenosine at normothermic temperatures. Our findings emphasize the need for stringent control of core temperature during investigation of interventions aimed at reducing infarct size.
Substrate specific effects of calcium on metabolism of rat heart mitochondria
Authors: Panov A. V. , Scaduto R. C.
Published: December 2017

Oxidative metabolism in the heart is tightly coupled to mechanical work. Because this coupling process is believed to involve Ca2+, the roles of mitochondrial Ca2+ in the regulation of oxidative phosphorylation was studied in isolated rat heart mitochondria. The electrical component of the mitochondrial membrane potential (delta psi) and the redox state of the pyridine nucleotides were determined during the oxidation of various substrates under different metabolic states. In the absence of added adenine nucleotides, the NADP+ redox couple was almost completely reduced, regardless of the specific substrate and the presence of Ca2+, whereas NAD+ couple redox state was highly dependent on the substrate type and the presence of Ca2+. Titration of respiration with ADP, in the presence of excess hexokinase and glucose, showed that both respiration and NAD(P)+ reduction were very sensitive to ADP. The maximal enzyme reaction rate of ADP-stimulated respiration Michaelis constants (Km) for ADP were dependent on the particular substrate employed. delta psi was much less sensitive to ADP. With either alpha-ketoglutarate or glutamate as substrate, Ca2+ significantly increased reduction of NAD(P)+.Ca2+ did not influence NAD(P)+ reduction with either acetylcarnitine or pyruvate as substrate. In the presence of ADP, delta psi was increased by Ca2+ at all metabolic states with glutamate plus malate, 0.5 mM alpha-ketoglutarate plus malate, or pyruvate plus malate as substrates. The data presented support the hypothesis that cardiac respiration is controlled by the availability of both Ca2+ and ADP to mitochondria. The data indicate that an increase in substrate supply to mitochondria can increase mitochondrial respiration at given level of ADP. This effect can be produced by Ca2+ with substrates such as glutamate, which utilize alpha-ketoglutarate dehydrogenase activity for oxidation. Increases in respiration by Ca2+ may mitigate an increase in ADP during periods of increased cardiac work.
Estimation of shear and flow rates in pial arterioles during somatosensory stimulation
Authors: Ngai A. C. , Winn H. R.
Published: December 2017

We tested the hypothesis that a shear stress-dependent mechanism is involved in the dilation of pial arterioles during somatosensory stimulation. In alpha-chloralose-anesthetized rats implanted with cranial windows, we simultaneously measured the diameter and flow velocity of pial arterioles with video and dual-slit methods. Stimulation (0.2-0.3 V, 5 Hz, 0.5 ms pulses for 20 s) of the contralateral sciatic nerve evoked consistent dilator responses in pial arterioles (36 +/- 1 micron diam) without affecting blood pressure. The dilator responses consisted of an initial transient peak dilation of 30 +/- 3%, followed by a sustained dilation of 13 +/- 1% (n = 11). Mean velocity increased by 16.4 +/- 5.7% at 5 s after stimulus onset. Wall shear rate and volume flow were calculated from diameter and velocity data by assuming a parabolic flow profile. There was no significant change in wall shear rate, whereas flow rate increased significantly during sciatic nerve stimulation. The present findings suggest that a flow (shear stress)-mediated mechanism does not play an important role in the dilator response of pial arterioles to sciatic nerve stimulation.
Resolution of the basal plasma membrane calcium flux in vascular smooth muscle cells
Authors: Fayazi A. H. , Lapidot S. A. , Huang B. K. , Tucker R. W. , Phair R. D.
Published: December 2017

Steady-state cytosolic calcium (Ca2+i) concentration in a vascular smooth muscle cell is determined by Ca2+ influx and Ca2+ extrusion across the plasma membrane, yet no means for determining the absolute magnitude of these transmembrane Ca2+ fluxes in the basal state of the resting cell has been devised. We now report a method that combines fluorescence measurement of Ca2+i, 45Ca kinetics, and computer modeling to yield the basal plasma membrane Ca2+ flux in A7r5 vascular smooth muscle cells. Kinetic analysis of basal Ca2+i and Ca2+i transients following chelation of extracellular Ca2+ yields a unique value for the ratio of the rate constant governing Ca2+ pumping into the sarcoplasmic reticulum (SR) to that for plasma membrane Ca2+ extrusion (1.12 +/- 0.06). When this ratio was used to constrain the least-squares fitting of 45Ca efflux data from A7r5 cells, it was possible to determine unique values for the unidirectional, steady-state Ca2+ fluxes across both SR and plasma membranes. The basal unidirectional plasma membrane Ca2+ flux was 0.062 +/- 0.018 fmol . min-1 . cell, and the basal SR Ca2+ flux was 0.069 +/- 0.019 fmol . min-1 . cell-1. These results demonstrate, within the limitations of measuring the absolute value of Ca2+i, the feasibility of measuring previously unresolvable subpicoamp basal Ca2+ fluxes in intact cells under normal physiological conditions.
Evidence for activation of endothelium and monocytes in hypertensive rats
Authors: Liu Y. , Liu T. , McCarron R. M. , Spatz M. , Feuerstein G. , Hallenbeck J. M. , Siren A. L.
Published: December 2017

We have proposed that an interaction between perivascular macrophages and endothelium via cytokines could underlie the increased risk of stroke in hypertension. Therefore, the activation of monocytes, the endothelial expression of intercellular adhesion molecule-1 (ICAM-1), and the numbers of monocytes/macrophages in carotid arteries, as well as the cytokine production in carotid tissue, of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto and Sprague-Dawley rats were studied. The total number of blood monocytes (890 +/- 153 cells/mm3, n = 10) and the number of activated (nitro blue tetrazolium-positive) monocytes (220 +/- 51 cells/mm3, n = 10) were significantly greater (P < 0.05) in SHR than in WKY rats (440 +/- 81 and 40 +/- 16 cells/mm3, respectively, n = 10). Patchy endothelial expression of ICAM-1 was found in 77 +/- 9% of carotid sections from stroke-prone SHR (SHR-SP, n = 5) and in 75 +/- 7% of the sections from SHR (n = 7) but in none of the sections from the two normotensive rat strains (n = 7). The number of endothelium-attached monocytes/macrophages per millimeter of internal elastic lamina was significantly greater in SHR-SP than in SHR [5.1 +/- 0.7 (n = 4) and 3.3 +/- 0.3 (n = 6), P < 0.05], whereas no monocytes were found around the endothelium in either of the normotensive rat strains (n = 7 in each group). Incubation of the carotid arteries with lipopolysaccharide (30-300 ng/ml) induced a concentration-dependent expression of mRNAs for interleukin-1 beta and release of tumor necrosis factor-alpha to a significantly greater degree in the SHR than in the Wistar-Kyoto rats. The results demonstrate that hypertension is associated with activation of monocytes and endothelium and an increased endothelial adhesion and subendothelial accumulation of monocytes/macrophages and with an increased vascular capacity to produce cytokines.
Hypertension, cardiac hypertrophy, and neurohumoral activity in a new animal model of obesity
Authors: Carroll J. F. , Dwyer T. M. , Grady A. W. , Reinhart G. A. , Montani J. P. , Cockrell K. , Meydrech E. F. , Mizelle H. L.
Published: December 2017

Although obesity is a major risk factor for morbidity and mortality, the mechanisms mediating cardiovascular abnormalities in response to weight gain are unclear. One reason for the paucity of information in this area is the lack of appropriate animal models for the study of human obesity. Therefore, the goal of the present study was to develop a small animal model of dietary-induced obesity that mimics many of the characteristics of human obesity. We studied female New Zealand White rabbits fed either a normal (n = 17) or high-fat diet (n = 15) and examined the cardiovascular consequences of obesity, including changes in blood pressure, humoral activation, and end-organ effects such as cardiac hypertrophy. After 12 wk, rabbits on the high-fat diet were 46% heavier than their lean counterparts (5.49 +/- 0.09 vs. 3.77 +/- 0.06 kg, respectively; P = 0.0001). Obese rabbits had higher resting heart rates than lean rabbits (220 +/- 7 vs. 177 +/- 6 beats/min; P = 0.0001) and developed hypertension (96 +/- 2 vs. 85 +/- 1 mmHg; P = 0.0001), hyperinsulinemia (32.5 +/- 3.4 vs. 15.5 +/- 1.0 microU/ml; P = 0.0001), hyperglycemia (162.4 +/- 2.9 vs. 141.9 +/- 2.7 mg/dl; P = 0.0001), and elevated triglycerides (102.3 +/- 9.1 vs. 48.5 +/- 4.0 mg/dl; P = 0.0001). Obese rabbits also developed cardiac hypertrophy, as evidenced by left ventricular (LV) dry weights that were 52% greater in obese than in lean rabbits (P = 0.0003). In addition, LV total protein was increased in proportion to the increase in LV weight. The results of this study suggest that rabbits fed a high-fat diet for a period of 12 wk develop many of the characteristics of human obesity. The obese rabbit should provide a small and relatively inexpensive animal model to investigate mechanisms of obesity-related cardiovascular abnormalities.
Dissociation of negative inotropic effect of carbachol from changes in cAMP and PKA in perfused rat hearts
Authors: Zhang J. Z. , MacLeod K. M.
Published: December 2017

The purpose of this investigation was to determine whether muscarinic receptors are selectively coupled to the pool of adenylyl cyclase that is responsible for the elevation of particulate (membrane-bound) adenosine 3',5'-cyclic monophosphate (cAMP), because this appears to lead to translocation of particulate cAMP-dependent protein kinase A (PKA) to the soluble fraction and the positive inotropic response. Perfusion of hearts with carbachol and isoproterenol concurrently for 1.5 min prevented the increase in left ventricular pressure (LVP) found with isoproterenol alone, although isoproterenol-induced changes in total and particulate cAMP levels and soluble and particulate PKA activity were unaffected. However, perfusion of hearts with carbachol for 1 min then with isoproterenol and carbachol for 1.5 min abolished the isoproterenol-induced increase in LVP and in total and particulate cAMP levels, although changes in total and particulate PKA activity were only partially attenuated. Perfusion of hearts with carbachol for 1 min then carbachol plus forskolin for 2 or 5 min also completely prevented the forskolin-induced increase in LVP without affecting the changes in either total or particulate cAMP levels or soluble or particulate PKA activity produced by this agent. Therefore, muscarinic receptors do not appear to selectively couple to the pool of adenylyl cyclase responsible for elevation of particulate cAMP levels. These data provide further evidence that antagonism of adenylyl cyclase activity is not required for the inhibition by carbachol of positive inotropic responses of ventricular muscle to cAMP generating agents.
A model of the action potential and underlying membrane currents in a rabbit atrial cell
Authors: Lindblad D. S. , Murphey C. R. , Clark J. W. , Giles W. R.
Published: December 2017

We have developed a mathematical model of the rabbit atrial myocyte and have used it in an examination of the ionic basis of the atrial action potential. Available biophysical data have been incorporated into the model to quantify the specific ultrastructural morphology, intracellular ion buffering, and time- and voltage-dependent currents and transport mechanisms of the rabbit atrial cell. When possible, mathematical expressions describing ionic currents identified in rabbit atrium are based on whole cell voltage-clamp data from enzymatically isolated rabbit atrial myocytes. This membrane model is coupled to equations describing Na+, K+, and Ca2+ homeostasis, including the uptake and release of Ca2+ by the sarcoplasmic reticulum and Ca2+ buffering. The resulting formulation can accurately simulate the whole cell voltage-clamp data on which it is based and provides fits to a family of rabbit atrial cell action potentials obtained at 35 degrees C over a range of stimulus rates (0.2–3.0 Hz). The model is utilized to provide a qualitative prediction of the intracellular Ca2+ concentration transient during the action potential and to illustrate the interactions between membrane currents that underlie repolarization in the rabbit atrial myocyte.
Influence of acute-phase proteins on erythrocyte aggregation
Authors: Weng X. , Cloutier G. , Beaulieu R. , Roederer G. O.
Published: December 2017

With the exception of fibrinogen, immunoglobulins, and albumin, little information is available on the effect of acute-phase proteins on erythrocyte aggregation. The objective of this study was to investigate the effects of haptoglobin (Hp), C-reactive protein (CRP), ceruloplasmin (Cp), alpha 1-acid glycoprotein (alpha 1-AGP), and alpha 1-antitrypsin (alpha 1-AT) on the aggregation kinetics and shear resistance of erythrocyte aggregates. The plasma concentration of these proteins was measured in 20 healthy individuals and kept unchanged while the concentration of the protein tested was increased. Adding Hp to concentrations between 2.78 and 4.99 g/l resulted in a significant progressive increase in aggregation kinetics compared with controls. An elevation of the shear resistance of the aggregates was found for CRP at a concentration of 0.438 g/l. By an increase in the concentration of Cp from 4.40 to 9.39 g/l, the aggregation kinetics and the adhesive forces between erythrocytes were significantly increased: No effect on erythrocyte aggregation was observed for alpha 1-AGP, alpha 1-AT, and Cp at concentrations of 2.85, 3.97, and 2.43 g/l, respectively. The molecular mass of the acute-phase proteins, their configuration, and the presence of specific receptors on the erythrocyte membrane are postulated as possible factors influencing erythrocyte aggregation.
Frequency and amplitude of sympathetic discharges by baroreflexes during hypoxia in conscious rabbits
Authors: Malpas S. C. , Bendle R. D. , Head G. A. , Ricketts J. H.
Published: December 2017

Sympathetic nerve activity (SNA) from multifiber preparations exhibits two distinct components: the frequency at which discharges occur and their relative amplitude (reflecting the number of activated nerve fibers within each burst). These two components may respond independently to various afferent inputs, indicating separate central controlling processes. We examined the response in the frequency and amplitude of renal SNA to changes in baroreceptor activity and the effect of two forms of hypoxia on this relationship in nine conscious rabbits. Rabbits breathed either room air or one of two hypoxic gas mixtures (10% O2 or 10% O2 + 3% CO2) for 20 min, during which baroreflexes were stimulated by ramp increases and then decreases in arterial pressure with phenylephrine (0.5 mg/ml iv) and nitroprusside (1 mg/ml) (total arterial pressure range induced was 80 mmHg). Hypoxia with 10% O2 significantly increased the resting frequency of SNA before baroreflex modifications from 2.15 +/- 0.18 to 2.82 +/- 0.25 discharges/s and with 10% O2 + 3% CO2 to 3.20 +/- 21 discharges/s. The amplitude of sympathetic discharges was increased 44 +/- 5% over control levels during 10% O2 but was not further increased by the addition of 3% CO2. The baroreflex curve for total SNA (1-s averages of the integrated neurogram) showed a graded response to the two hypoxic stimuli, with significant increases in the upper plateau, gain, and resting point on the curves. However, the baroreflex curve for the frequency or amplitude of sympathetic discharges did not show graded responses to each hypoxic treatment. The frequency baroreflex curve was sigmoidal and not changed from air during 10% O2. During 10% O2 + 3% CO2, the gain (responsiveness) of the curve was increased although the range of frequencies occurring was unaltered. The baroreflex curve for the amplitude showed similar responses to the two hypoxic stimuli, namely, increases in the upper plateau, gain, and resting point of the curve. We conclude that the frequency and amplitude of sympathetic discharges are able to respond differentially to changes in afferent stimuli. Given that alterations in the frequency and recruitment of sympathetic fibers (amplitude) to the kidney may have differing effects, this phenomenon may provide a previously unknown level of renal hemodynamic control through the interaction of specific afferent inputs to the central nervous system.
Effects of pressure- or volume-overload hypertrophy on passive stiffness in isolated adult cardiac muscle cells
Authors: Kato S. , Koide M. , Cooper G. , Zile M. R.
Published: December 2017

It has been hypothesized that the changes in myocardial stiffness induced by chronic hemodynamic overloading are dependent on changes in the passive stiffness of the cardiac muscle cell (cardiocyte). However, no previous studies have examined the passive constitutive properties of cardiocytes isolated from animals with myocardial hypertrophy. Accordingly, changes in relative passive stiffness of cardiocytes isolated from animals with chronic pressure- or volume-overload hypertrophy were determined by examining the effects of anisosmotic stress on cardiocyte size. Anisosmotic stress was produced by altering superfusate osmolarity. Hypertrophied cardiocytes were enzymatically isolated from 16 adult cats with right ventricular (RV) pressure-overload hypertrophy induced by pulmonary artery banding (PAB) and from 6 adult cats with RV volume-overload hypertrophy induced by creating an atrial septal defect (ASD). Left ventricular (LV) cardiocytes from each cat served as nonhypertrophied, normally loaded, same-animal controls. Superfusate osmolarity was decreased from 305 +/- 3 to 135 +/- 5 mosM and increased to 645 +/- 4 mosM. During anisosmotic stress, there were no significant differences between hypertrophied RV and normal LV cardiocytes in pressure overload PAB cats with respect to percent change in cardiocyte area (47 +/- 2% in RV vs. 48 +/- 2% in LV), diameter (46 +/- 3% in RV vs. 48 +/- 2% in LV), or length (2.4 +/- 0.2% in RV vs. 2.0 +/- 0.3% in LV), or sarcomere length (1.5 +/- 0.1% in RV vs. 1.3 +/- 0.3% in LV). Likewise, there were no significant differences in cardiocyte strain between hypertrophied RV and normal LV cardiocytes from ASD cats. In conclusion, chronic pressure-overload hypertrophy and chronic volume-overload hypertrophy did not alter the cardiocyte response to anisosmotic stress. Thus chronic overload hypertrophy did not alter relative passive cardiocyte stiffness.
Sodium effects on 4-aminopyridine-sensitive transient outward current in canine ventricular cells
Authors: Zygmunt A. C. , Goodrow R. J. , Antzelevitch C.
Published: December 2017

Tetrodotoxin (TTX) or substitution of external Na+ reduces the 4-aminopyridine-sensitive transient outward current (Ito1) in rat ventricular myocytes. We investigated the outcome of reducing external sodium on the kinetics, gating, and selectivity of Ito1 with a dual-patch electrode technique to record whole cell currents and transmembrane potentials independently of the voltage clamp in canine midmyocardial cells. Steps from -80 to 0 mV produced overlapping inward sodium and outward potassium currents, accompanied by a loss of voltage control associated with activation of INa. Substitution of external Na+ or application of TTX abolished INa, restored voltage control, and reduced Ito1. Inactivation of INa with a 10-ms prestep to -45 mV decreased Ito1 to the same extent as external Na+ substitution. The kinetics, gating, and selectivity of Ito1 recorded after inactivation of INa were unaffected by drastic reductions in external Na+. Our findings suggest that a larger Ito1 in the presence of normal external Na+ is due to 1) transient loss of voltage control and concomitant changes in activation of Ito1 and/or 2) facilitation of an outward current by intracellular Na+. We conclude that reduction of external sodium has no direct effect on the kinetics or gating of Ito1, non does Na+ contribute to current flow through Ito1 channels in canine midmyocardial cells.
Endothelial-borne platelet-activating factor and interleukin-8 rapidly immobilize rolling neutrophils
Authors: Rainger G. E. , Fisher A. C. , Nash G. B.
Published: December 2017

The kinetics of the response of integrins to activating signal(s) must be rapid to ensure that rolling neutrophils are localized at the sites of inflammation. From video records, we analyzed the adhesion of individual neutrophils in a flow-based in vitro model of endothelial hypoxia and reoxygenation. There were numerous rolling interactions between flowing neutrophils and P-selectin on human umbilical vein endothelial cells after hypoxia, but 90% lasted for < 1 s, with approximately 30% converted to stationary attachment via beta 2-integrin(s). Interleukin-8 (IL-8) and platelet-activating factor (PAF) were responsible for neutrophil activation in this model [G. E Rainger, A. Fisher, C. Shearman, and G. B. Nash. Am. J. Physiol. 269 (Heart Circ. Physiol. 38): H1398-H1406, 1995]. In the presence of a PAF-receptor antagonist, IL-8 acting alone induced conversion of rolling to stationary adhesion in as little as 80 ms after the initial attachment of a neutrophil, with a median response time of 240 ms. In the presence of a monoclonal antibody that neutralized IL-8 activity, PAF acting alone required a minimum duration of rolling of 560 ms to promote stationary adhesion, with a significantly longer median duration of 720 ms. In a reconstituted model, treatment of endothelial cells with hydrogen peroxide induced short-lived rolling of neutrophils supported by P-selectin. Exogenously added IL-8 and/or PAF bound to the endothelial surface and successfully induced the immobilization of neutrophils. Rapid and distinct kinetics of the conversion to stationary adhesion were observed again for IL-8 or PAF. Thus although endothelial-presented signals differed in their rate of action, neutrophils could be localized within one or two endothelial cell diameters of their initial adhesive contact point.
Left ventricular performance assessed by echocardiographic automated border detection and arterial pressure
Authors: Denault A. Y. , Gorcsan J. , Mandarino W. A. , Kancel M. J. , Pinsky M. R.
Published: December 2017

Automated echocardiographic measures of left ventricular (LV) cavity area are closely correlated with changes in volume and can be coupled with LV pressure (PLV) to construct pressure-area loops in real time. The objective was to rapidly estimate LV contractility from end-systolic relationships of cavity area (as a surrogate for LV volume) and central arterial pressure (Pa) (as a surrogate for PLV) in a canine model using automated algorithms. In eight anesthetized mongrel dogs, we simultaneously measured PLV, LV area, and Pa (fluid-filled catheter). End-systolic pressure-area relationships in terms of pressure-area elastance (E'es)] from pressure-area loops during inferior vena caval occlusions were determined during basal conditions (control), dobutamine infusion (5-10 micrograms.mg-1.min-1), and after bolus propranolol (2 mg/kg) with both PLV and Pa by semiautomated and automated iterative regression methods. E'es increased during dobutamine infusion and decreased after propranolol infusion in all animals and with all iterative methods. Estimates of Ees from Pa were closely correlated with E'es from PLV by both the semiautomated and automated methods (r = 0.93; P < 0.01). The relationship between E'es obtained from Pn for the two methods was also closely correlated. Although the automated methods displayed larger differences from the semiautomated iterative technique by Bland-Altman analysis, the change in E'es with all techniques during dobutamine infusion and after propranolol infusion was of similar magnitude and direction among the three techniques. Greater variability with the dobutamine runs was partially due to abnormally conducted ventricular beats that minimized the number of consecutive beats that could be used for these analyses. We conclude that on-line Pa recordings from fluid-filled catheters can be used with echocardiographic automated border detection to rapidly calculate E'es as a means to estimate LV contractility.
ATP-dependent regulation of a G protein-coupled K+ channel (GIRK1/GIRK4) expressed in oocytes
Authors: Kim D. , Watson M. , Indyk V.
Published: December 2017

Recent studies suggest that activation of the atrial muscarinic K+ current by acetylcholine (ACh) involves an ATP-dependent process that is then inhibited by a cytosolic protein to result in the rapid desensitization. To obtain further evidence in support of such a dually regulated process, we studied the properties of GIRK1 and GIRK4, which, when coexpressed in oocytes, form a heteromultimer that closely resembles the muscarinic K+ channel. ACh activated an inwardly rectifying K+ current that desensitized slowly. In cell-attached patches with ACh in the pipette, the mean open times (tau zero) of GIRK1/GIRK4 were 1.2 +/- 0.1 (28%) and 6.7 +/- 0.8 ms (72%) and did not change significantly with time. However, in inside-out patches, the tau zero of GIRK1/GIRK4 activated with guanosine 5'-O-(3-thiotriphosphate) was 1.3 +/- 0.1 ms (100%), and the channel activity (NP0) was almost fivefold lower. These changes in channel kinetics did not occur in the presence of sodium orthovanadate (3 mM), an inhibitor of phosphatase. Addition of 1 mM ATP, but not adenylimidodiphosphate, to inside-out patches resulted in increases in NP zero (4.8-fold) and the open-time duration of GIRK1/GIRK4, such that tau zero were 1.2 +/- 0.2 (32%) and 6.2 +/- 0.6 ms (68%). Single channel conductances were unchanged (34 +/- 1 pS). Cytosolic extract from atria, but not oocytes, could reverse these effects of ATP. These results provide further evidence that the antagonistic modulation of G protein-gated K+ channels by ATP and the atrial cytosolic protein produces the early rapid desensitization in atrial cells. In oocytes the ATP-dependent step is dominant and thus provides a major component of the total GIRK1/GIRK4 current activated by ACh.
Intracellular calcium-release channels: regulators of cell life and death
Authors: Marks A. R.
Published: December 2017

Intracellular Ca2+-release channels on the sarcoplasmic reticulum of striated muscle [ryanodine receptors (RyRs)] and on the endoplasmic reticulum of almost all types of cells [inositol 1,4,5-trisphosphate receptors (IP3Rs)] comprise a unique family of molecules that are structurally and functionally distinct from all other known ion channels. These channels play crucial roles in Ca2+-mediated signaling that triggers excitation-contraction coupling, T-lymphocyte activation, fertilization, and many other cellular functions. Three forms of RyR have been identified: RyR1, expressed predominantly in skeletal muscle; RyR2, expressed predominantly in cardiac muscle; and RyR3, expressed in specialized muscles and nonmuscle tissues including the brain. RyR channels are tetramers composed of four subunits each with a molecular mass of approximately 560,000 Da. The tetrameric structures of RyR1 and RyR2 are stabilized by a channel-associated protein known as the FK506 binding protein (FKBP). FKBP is the cytosolic receptor for the immunosuppressant drugs FK506 and rapamycin that inhibit the prolyl isomerase activity of FKBP and can dissociate FKBP from RyRs. Rapamycin and FK506 increase the sensitivity of RyRs to agonists such as caffeine and could be a cause of cardiac dysfunction associated with high-dose immunosuppressant therapy by promoting leakage of Ca2+ from the sarcoplasmic reticulum. The role of prolyl isomerase activity of FKBP in regulating RyR function remains uncertain, and several models have been proposed that could explain how the channel is modulated by its association with FKBP. Three forms of IP3Rs (types 1, 2 and 3) have been characterized by cDNA cloning. Most cells have at least one form of IP3R, and many express all three types. Like RyRs, the IP3R channels are tetramers composed of four subunits (approximately 300,000 Da each). IP3R1 function is regulated by at least two major cellular signaling pathways: the second messenger IP3 activates the channel, and phosphorylation by nonreceptor protein tyrosine kinases (e.g., Fyn) increase its open probability. During end-stage human heart failure, RyR2 mRNA and protein are downregulated, whereas IP3R1 is upregulated, suggesting that altered Ca2+-release channel levels may contribute to defects in Ca2+ homeostasis. Cells that are deficient in IP3R1 exhibit defective T cell-receptor signaling and thus cannot be activated by T cell-receptor stimulation. IP3R1-deficient cells are also resistant to induced apoptosis. Thus RyRs and IP3Rs play critical roles in fundamental and diverse signaling phenomena that include excitation-contraction coupling, T-cell activation, and programmed cell death.
An antibody to leukocyte integrins attenuates coronary vascular injury due to ischemia and reperfusion in dogs
Authors: Horwitz L. D. , Kaufman D. , Kong Y.
Published: December 2017

Ischemia and reperfusion cause coronary vascular and myocardial injury, which may be due to leukocyte-mediated processes. Antileukocyte measures have reduced injury after brief reperfusion periods of 1-3 h, but there has been little information on whether benefits are apparent after longer periods of reperfusion. We examined the effect of pretreatment with a monoclonal antibody (R15.7) to the CD18 family of leukocyte adhesion molecules (beta2-integrins) in dogs exposed to regional coronary ischemia for 1 h of left anterior descending coronary artery ligation and then reperfused for 48 h. Coronary microvascular permeability was assessed in vivo by measurement of protein leak index (PLI), using a double-isotope technique with autologous radiolabeled transferrin and erythrocytes. Vasorelaxation was measured in vitro with preconstricted epicardial coronary artery rings subjected to increasing concentrations of the endothelium-dependent vasodilators bradykinin (BK) and ADP and the endothelium-independent vasodilator nitroprusside. At 48 h of reperfusion in untreated dogs there were substantial increases in PLI in the previously ischemic regions, indicative of increased extravascular transferrin. These abnormalities were decreased, but not abolished, in the dogs treated with R15.7. Relaxation of rings from the ischemic/reperfused artery to BK and ADP were blunted in the untreated dogs. R15.7 resulted in improvement in some, but not all, indexes of relaxation in response to BK and ADP. Relaxation to nitroprusside was normal in ischemic/reperfused coronary rings from both treated and untreated dogs. Therefore, after 1 h of regional coronary ischemia and 48 h of reperfusion, coronary endothelial injury, which was manifested by increased coronary microvascular permeability and abnormalities in coronary endothelium-dependent relaxation, was reduced by pretreatment with the anti-CD18 integrin antibody R15.7.
Relationship between sympathetic activity and arterial pressure in conscious spinal rats
Authors: Maiorov D. N. , Weaver L. C. , Krassioukov A. V.
Published: December 2017

Spinal cord injury disrupts regulation of arterial pressure, often resulting in episodic hypertension initiated by spinal reflexes. The contribution of spinally generated sympathetic nerve activity (SNA) to control of resting arterial pressure after cord injury is questionable. The mechanisms responsible for the reflex hypertension also are unresolved. One important question concerns whether or not this hypertension is caused by large spinal sympathetic reflexes or by the known increased vascular sensitivity to norepinephrine and limited effectiveness of baroreceptor reflexes that occur after spinal cord injury. We evaluated the relationship between renal SNA and mean arterial pressure (MAP) in basal conditions and during reflex pressor responses induced by colon distension in conscious rats for 1 wk after midthoracic spinal cord transection (SCT). One day after SCT, MAP (69 +/- 6 mmHg) and SNA(6 +/- 2 microV x s) were lower than the MAP (92 +/- 4 mmHg) and SNA (18 +/- 3 microV x s) in the same anesthetized rats before SCT. At 6 days, MAP increased to 94 +/- 6 mmHg, whereas SNA remained low (4 +/- 1 microV x s). One day after SCT, colon distension increased MAP by 28 +/- 4 mmHg and SNA by 35 +/- 6 microV x s; these responses remained unchanged for 6 days. These data suggest that spinally generated SNA makes no apparent contribution to basal MAP. In contrast, afferent stimulation can produce large excitatory spinal sympathetic reflexes that appear adequate to cause substantial increases in arterial pressure.
Structure and function of cardiac sodium and potassium channels
Authors: Roden D. M. , George A. L.
Published: December 2017

The application of patch-clamp and molecular approaches has resulted in an increasingly refined understanding of the molecular entities underlying cardiac sodium and potassium currents. The sodium current results from expression of a single large alpha-subunit, whereas multiple potassium currents and potassium channel alpha-subunits have been identified. Recapitulation of some ion currents in heterologous expression systems requires not only expression of alpha-subunits but also ancillary (beta) subunits. Domains common to functions such as activation, inactivation, and drug block are now being identified in alpha- and beta-gene products. Variability in the expression or function of individual ion-channel genes is an increasingly recognized source of variability in the ion currents recorded in heart cells under physiological conditions (e.g. during development) as well as in disease.