bluuebunny/crossref_metadata_2025 huggingface dataset:
Angiotensin II and contraction of isolated myocytes from human, guinea pig, and infarcted rat hearts
Authors: Lefroy D. C. , Crake T. , Del Monte F. , Vescovo G. , Dalla Libera L. , Harding S. , Poole-Wilson P. A.
Published: December 2017

The effects of angiotensin II on myocardial contractility were assessed in isolated cardiac myocyte preparations, using video microscopy with a computerized edge-detection system. Angiotensin II (1 nM-10 microM) did not affect the contraction of rat (n = 10), guinea pig (n = 11), or human ventricular myocytes (n = 8) or of human atrial myocytes (n = 12). Isoproterenol or raised extracellular calcium increased the contraction amplitude of the cardiac myocytes to a maximum of between 150 and 560% above basal, and there were corresponding increases in the velocities of contraction and relaxation. In rat and guinea pig ventricular myocytes 1 microM angiotensin II did not affect the inotropic response to isoproterenol. Seven days after left coronary artery ligation in seven rats, the basal contraction amplitude was reduced in myocytes from the infarcted region (4.0 +/- 1.9%) compared with the noninfarcted region (5.0 +/- 2.8%, P = 0.03) and with myocytes from six sham-operated hearts (5.0 +/- 2.8%, P = 0.03). There was a switch in myosin isoform expression from the V1 to the V3 isoform in myocytes from both the infarcted and noninfarcted regions. Angiotensin II (1 nM-10 microM) had no significant effect on the contraction characteristics of myocytes from the infarcted rat hearts. In conclusion, angiotensin II had no significant inotropic effect on isolated cardiac myocyte preparations from guinea pig ventricle, normal and infarcted rat ventricle, human ventricle, and human atrium.
Effects of prolonged exposure to oxygen-derived free radicals in canine pulmonary arteries
Authors: Wiklund L. , McGregor C. G. , Miller V. M.
Published: December 2017

Experiments were designed to evaluate endothelium-dependent responses of pulmonary arteries following prolonged exposure to oxygen-derived free radicals. Rings of canine pulmonary arteries with and without endothelium were suspended for measurement of isometric force in organ chambers and incubated with xanthine (10(-4)M) plus xanthine oxidase (0.015 U/ml) for 1 h in the absence and presence of either superoxide dismutase (SOD, 150 U/ml), catalase (1,200 U/ml), deferoxamine (10(-3)M), or a combination of all three scavengers. Xanthine plus xanthine oxidase caused significantly greater contractions of rings without compared with those with endothelium. In rings with endothelium, contractions were reduced by SOD or catalase but not by deferoxamine. Following 1 h of exposure to xanthine plus xanthine oxidase, endothelium-dependent relaxations to ADP were reduced but not those to bradykinin or the calcium ionophore A-23187 (calcimycin). Relaxations to ADP were not corrected by incubation with the antioxidants used singly or in combination during the exposure to xanthine plus xanthine oxidase. These results suggest that oxygen-derived free radicals generated from exogenously applied xanthine plus xanthine oxidase cause contractions of canine pulmonary arteries. In addition, even when contractions of rings with endothelium were prevented by SOD and catalase, subsequent expression of some but not all endothelium-dependent relaxations were reduced. Therefore, scavenging of oxygen-derived free radicals may prevent some but not all of the vascular injury caused by oxygen-derived free radicals.
Ratiometric measurement of endothelial depolarization in arterioles with a potential-sensitive dye
Authors: Beach J. M. , McGahren E. D. , Xia J. , Duling B. R.
Published: December 2017

A fluorescence ratio technique based on the voltage-sensitive dye 1-(3-sulfonatopropyl)-8-[beta-[2-di-n-butylamino)-6-naphythyl++ +]vinyl] pyridinium betaine (di-8-ANEPPS)has been developed for recording membrane potential changes during vascular responses of arterioles. Perfusion of hamster cheek pouch arterioles with the dye labeled the endothelial cell layer. voltage responses from the endothelium of intact arterioles were determined by analysis of voltage-induced shifts in fluorescence emission wavelengths from dye spectra imaged from the vessel wall. Membrane depolarization caused the dye spectrum to shift toward blue wavelengths, with maximal fluorescence changes near 560 and 620 nm. In isolated nonperfused arterioles, comparison of continuous dual-wavelength recordings with simultaneous microelectrode recordings showed that the ratio of fluorescence intensities (fluorescence at 620 nm to fluorescence at 560 nm) accurately followed changes in membrane potential (6–21 mV) during vasoconstriction. The dye response was linear with respect to potential changes from -56 to -6 mV, with a voltage sensitivity of 9.7% change in the ratio per 100 mV. Membrane potential responses from in vitro and in vivo arterioles after potassium stimulation consisted of rapid ( < 0.5 -s) depolarization followed by slow repolarization over several seconds. Potassium-induced depolarizations were conducted along arterioles, and the values of the electrical length constant for conducted depolarization determined by optical and microelectrode methods were in agreement. We conclude that ratio analysis of di-8-ANEPPS fluorescence emission can be used to accurately record membrane potential changes on the time scale of seconds during vasomotor activity from arterioles.
Regulation of ANG II receptor in hypertension: role of ANG II
Authors: Wang D. H. , Yao A. , Zhao H. , DiPette D. J.
Published: December 2017

To investigate the role of angiotensin II (ANG II) in the development of hypertension induced by reduced renal mass (RRM) and the gene expression of ANG II type 1 (AT1) receptors in the remnant renal tissue, four groups of rats were given 1% NaCl in water and subjected to RRM, RRM+ ramipril, RRM+ losartan, or sham surgery (control). Tail-cuff systolic blood pressure was significantly higher in RRM rats than in the other three groups. Northern blot showed that AT1 gene expression was significantly decreased in RRM, RRM + ramipril, or RRM + losartan vs. control. There was no significant difference among the three RRM groups. Renal transforming growth factor-beta 1 (TGF-beta 1) mRNA levels were increased threefold (P < 0.05) in RRM, RRM+ ramipril, and RRM+ losartan vs. control. There was no significant difference among the three RRM groups. We conclude that the development of RRM hypertension is ANG II dependent but not mediated by AT1 gene expression. RRM downregulates AT1 mRNA and upregulates TGF-beta 1 mRNA in the remnant renal tissue, regardless of blood pressure or plasma levels of ANG II, suggesting that these gene responses are triggered by an effect of local injury.
Myocardial adenosine A1 and A2 receptor activities during juvenile and adult stages of development
Authors: Sawmiller D. R. , Fenton R. A. , Dobson J. G.
Published: December 2017

Myocardial contractile responsiveness to beta-adrenoceptor stimulation is known to be reduced with maturation or aging. The present study was undertaken to determine the role of antiadrenergic A1 and stimulatory A2 adenosine receptors in the modulation of beta-adrenergic-elicited contractile performance of the heart at juvenile (approximately 25 days) and adult (approximately 79 days) stages of maturation. Isoproterenol, a beta-adrenergic agonist, at 10(-7) M produced a greater maximal increase in contractility, assessed as the maximal rate of left ventricular pressure development (+dP/dtmax), in immature than in mature hearts (104 and 80%, respectively), but produced a greater increase in venous adenosine concentration in the mature than in the immature hearts (738 and 277 nM, respectively). Isoproterenol at 10(-9) to 10(-8) M produced similar increases in contractility in the absence or presence of the A1 adenosine receptor antagonist xanthine amine congener (XAC; 0.5 microM) for both immature and mature hearts. In addition, XAC did not alter the isoproterenol-elicited contractile response in the immature heart during hypoperfusion induced by 50% reduction of coronary flow. However, in the mature heart, 10(-8) M isoproterenol elicited a significantly greater increase in +dP/dtmax during hypoperfusion in the presence (79%) vs. the absence (60%) of XAC. In both immature and mature hearts, hypoperfusion enhanced isoproterenol-elicited venous adenosine concentration by similar magnitudes of 76 and 72%, respectively. In further studies, the A2 adenosine receptor antagonist 9-chloro-2-(2-furyl)[1,2,4]-triazolo[1,5-c]quinazolin-5-amine (CGS-15943; 1 microM) reduced the isoproterenol-elicited contractile response of mature but not immature hearts during normal perfusion. These results suggest that myocardial adenosine modulates the beta-adrenergic-elicited contractile response of the adult heart via activation of both A1 and A2 adenosine receptors and that these functions of adenosine become expressed with myocardial maturation.
Elemental composition of Na pump inhibited rabbit aorta VSM cells by electron probe X-ray microanalysis
Authors: Krep H. , Lefurgey A. , Graves S. W. , Hockett D. , Ingram P. , Hollenberg N. K.
Published: December 2017

The Na pump in vascular smooth muscle (VSM) is likely to influence not only intracellular Na content but also the content and distribution of other cations and anions measured by electron probe X-ray microanalysis (EPXMA). The hypothesis we tested was that EPXMA of pump-inhibited VSM would yield a characteristic cellular elemental profile, providing insight into the contribution of the Na pump to the intracellular milieu and an approach to identifying when VSM operates under the constraints of pump inhibition. We assessed the contractile state and elemental EPXMA profile of rabbit aorta that was either quiescent or contracted by serotonin (10(-6) M) or ouabain (10(-6) M). VSM cytoplasm showed the anticipated low Na (28 +/- 2 mM) and high K (182 +/- 5 mM) content. With ouabain, Na rose and K fell to reverse the Na-to-K ratio (0.15 +/- 0.01 vs. 6.6 +/- 0.3; P < 0.01). With serotonin, the ratio rose slightly (0.28 +/- 0.2; P < 0.05). Nuclei and mitochondria showed a similar pattern. CI showed a small increase (56 +/- 2 to 102 +/- 4 mM) with ouabain, a shift that could not be accounted for on the basis of charge redistribution to maintain neutrality because the change in Na and K were essentially offsetting. EPXMA measures total and not ionized Ca. If changes in cytoplasmic Ca occurred, they were too small to be measured by the imaging methods employed. The sustained, myogenic contractile response of VSM to Na pump inhibition shows a characteristic elemental profile that could prove useful in its identification. Direct measurement of membrane potential during the myogenic response to Na pump inhibition should have a high priority.
Reduction of cytochrome-c oxidase copper precedes failing cerebral O2 utilization in fluorocarbon-perfused cats
Authors: Stingele R. , Wagner B. , Kameneva M. V. , Williams M. A. , Wilson D. A. , Thakor N. V. , Traystman R. J. , Hanley D. F.
Published: December 2017

We determined the relationship of the low-potential copper (CuA) redox state of cytochrome-c oxidase to the brain tissue PO2 (PtiO2) and global cerebral O2 consumption (CMRO2) in vivo. The redox state of cytochrome-c oxidase copper was monitored in perfluorocarbon-exchanged cats under normoxic and graded hypoxic conditions with use of near-infrared spectroscopy. Continuous spectra ranging from 730 to 960 nm were acquired, and the change in copper redox state was assessed by the absorption changes at 830 nm. PtiO2 was measured with O2-sensitive electrodes implanted into the cortex, and CMRO2 was determined by sampling arterial and superior sagittal sinus perfusate and by measuring blood flow with radiolabeled microspheres. As PtiO2 decreased with hypoxia, the CuA of cytochrome-c oxidase became progressively reduced, whereas the CMRO2 was unchanged during the initial stages of hypoxia. Only with severe hypoxia, did CMRO2 and the amplitude of somatosensory evoked potentials decrease. We conclude that the CuA site of cytochrome-c oxidase is involved in a regulatory adjustment that helps maintain CMRO2 constant.
Theoretical predictions of end-capillary PO2 in muscles of athletic and nonathletic animals at VO2max
Authors: Roy T. K. , Popel A. S.
Published: December 2017

Characterizing the resistances to O2 transport from the erythrocyte to the mitochondrion is important in understanding potential transport limitations. A steady-state model of this process was developed to predict the minimum (critical) end-capillary PO2 required to prevent hypoxia at maximal O2 consumption (VO2max) in a circular region of tissue surrounding the venular end of a capillary. Capillary density was used as a measure of O2 delivery, and mitochondrial density was used as a measure of O2 consumption. The effects of oxyhemoglobin dissociation kinetics and diffusion facilitation by hemoglobin in the erythrocytes and facilitation by myoglobin in the tissue were taken into account. Calculations made for selected skeletal muscles, diaphragm, and myocardium in three adaptive animal pairs (dog and goat, horse and cow, and pony and calf) yielded values of end-capillary PO2 that were consistent with measured values of mixed venous PO2 in maximally working animals. Values of end-capillary PO2 were found to be uncorrelated with values of VO2max in different muscles. No significant difference in end-capillary PO2 was found between similar muscles of athletic versus nonathletic animals. Predicted intracapillary O2 transport resistance ranged from 18 to 54% of the total transport resistance in the O2 pathway. Further investigation is required to explore the extent to which spatial and temporal heterogeneities in O2 delivery and consumption play a role in O2 transport.
Hyperkalemia alters EDHF-mediated hyperpolarization and relaxation in coronary arteries
Authors: He G. W. , Yang C. Q. , Graier W. F. , Yang J. A.
Published: December 2017

Hyperkalemic solutions are widely used to preserve organs for transplantation and for cardiac surgery. The present study was designed to test the hypothesis that hyperkalemia may alter endothelial function through a non-nitric oxide (NO) pathway, since preliminary studies have shown that the NO pathway may not be affected. Porcine coronary artery rings were studied in organ chambers. After incubation with 20 or 50 mM K+ for 1 h, the indomethacin- and NG-nitro-L-arginine+ (L-NNA)-resistant relaxation induced by A23187 or bradykinin, which could be further inhibited by tetraethylammonium but not glibenclamide, was significantly reduced. Incubation with hyperkalemia also significantly increased the concentration eliciting 50% of the maximal response to A23187 and bradykinin. A23187-induced hyperpolarization of the membrane potential was significantly reduced by hyperkalemic incubation. However, 1-h incubation with hyperkalemia does not affect the endothelial Ca2+ concentration. We conclude that exposure to hyperkalemia reduces the indomethacin- and L-NNA-resistant endothelium-dependent relaxation and endothelium-dependent hyperpolarization. This reduction in the relaxation and hyperpolarization is related to the endothelium-derived hyperpolarizing factor by affecting its effect on the smooth muscle cell, probably through partially depolarizing the membrane, and the Ca2(+)- activated K+ channels rather than by affecting its biosynthesis and/or release in the endothelial cell. Our study may suggest a new mechanism for coronary dysfunction after exposure to hyperkalemic cardioplegia and organ preservation solutions.
Reflex vascular responses to abdominal venous distension in the anesthetized dog
Authors: Doe C. P. , Drinkhill M. J. , Myers D. S. , Self D. A. , Hainsworth R.
Published: December 2017

This was undertaken to determine whether distension of the subdiaphragmatic veins results in reflex vasoconstriction and interacts with the carotid baroreflex. In alpha-chloralose-anesthetized open-chest dogs, a perfusion circuit controlled carotid and thoracic aortic pressures, splanchnic and limb blood flows, and cardiopulmonary blood flows. At carotid sinus pressures below approximately 90 mmHg, increases in splanchnic pressure of 7 mmHg or more resulted in increases in vascular resistance in both the splanchnic and limb circulations; there was no response at higher carotid pressures. At high venous pressures, the average maximum gains of the carotid baroreflex for splanchnic and limb resistance responses were increased by 106 and 67%, respectively. The responses were not abolished by cutting the vagal or phrenic nerves but were prevented by cutting the splanchnic nerves and, for the limb, the sciatic and femoral nerves. These results suggest that splanchnic congestion, by causing vasoconstriction and augmentation of the carotid baroreflex, may be important in the maintenance of blood pressure during gravitational stress.
Nitrite oxidation of myoglobin in perfused myocardium: implications for energy coupling in respiration
Authors: Chung Y. , Xu D. , Jue T.
Published: December 2017

Nitrite oxidation of oxymyoglobin in perfused rat myocardium under nonlimiting oxygen produces a detectable 1H nuclear magnetic resonance metmyoglobin (metMb) signal at -3.9 ppm. When the myocardium is perfused with < 10 mM nitrite, the 1H nuclear magnetic resonance MbO2 gamma CH3 Val E11 signal does not change intensity and the metMb reporter signal at -3.9 ppm is undetectable. However the rate pressure product decreases by 26% from the control level. Phosphocreatine, myocardial oxygen consumption, Pi, ATP, and pH remain constant. With > 10 mM infused nitrite, myoglobin (Mb) oxidation becomes apparent. As the MbO2 gamma CH3 Val E11 signal intensity decreases, the metMb signal intensity at -3.9 ppm increases. At the same time the 31P high-energy phosphate signals, rate pressure product, and lactate formation exhibit significant alterations. Myocardial oxygen consumption, however, remains constant. The data indicate that Mb oxidation does not limit myocardial respiration but does reduce energy production. Pulse-recovery experiments further demonstrate that a transient perfusion with 2 mM infused nitrite depresses the contractile function, which does not recover during reperfusion with oxygenated, nitrite-free buffer. The findings support the view that either Mb mediates energy coupling or nitrite directly uncouples energy production in myocardium. They also reveal a glimpse of the intracellular reductase activity that maintains the Mb in the Fe (II) state.
Enhanced SR function in saponin-treated ventricular trabeculae from rabbits with heart failure
Authors: Denvir M. A. , MacFarlane N. G. , Miller D. J. , Cobbe S. M.
Published: December 2017

Cardiac sarcoplasmic reticulum (SR) Ca(2+)-loading ability was assessed in a coronary artery ligation model of heart failure. Heart failure was produced in New Zealand White rabbits by ligation of the left marginal coronary artery. Sham-operated animals were used as controls. After hemodynamic and echocardiographic assessment 8 wk after coronary ligation, a free-running trabecula was isolated from the left or right ventricle, mounted for isometric tension measurement, and permeabilized with the chemical skinning agent saponin, leaving the SR functionally intact. The SR was Ca2+ loaded by exposure of the preparation to a mock intracellular solution with a Ca2+ concentration ([Ca2+]) of 150-300 nM. The amplitude of the caffeine-induced contracture was used as a measure of Ca2+ loaded by the SR. The same preparation was then treated with Triton X-100 to disrupt all cell membranes, and Ca2+ sensitivity inverted question markexpressed as [Ca2+] required to produce 50% of maximal activation (pCa50) inverted question mark of isometric tension production and maximum Ca2+ activated force (Cmax) were measured. Ligated animals demonstrated enhanced SR Ca(2+)-loading ability that correlated with the degree of left ventricular dysfunction. Enhanced SR Ca2+ loading was associated with evidence of SR Ca2+ overload revealed as spontaneous tension oscillations. Cmax and pCa50 were not significantly different from controls. Increased SR Ca(2+)-loading ability may predispose the SR to Ca2+ overload and could contribute to both contractile dysfunction and arrhythmogenesis in heart failure.
Vasodilatory properties of recombinant maxadilan
Authors: Jackson T. S. , Lerner E. , Weisbrod R. M. , Tajima M. , Loscalzo J. , Keaney J. F.
Published: December 2017

Maxadilan is a peptide from the salivary gland of the sand fly Lutzomyia longipalpis, a vector for leishmaniasis. Cutaneous injection of femtomolar quantities of maxadilan produces long-lasting erythema, making it the most potent vasodilator known. Isolated rabbit thoracic and abdominal aorta, carotid artery, and iliac artery demonstrated dose-dependent arterial relaxation in response to maxadilan with a mean effective concentration (EC50) of 2.7 +/- 1.5, 2.1 +/- 0.5, 2.6 +/- 0.4, and 1.9 +/- 0.5 nM, respectively. Maxadilan proved to be at least sevenfold more potent than nitroglycerin in each arterial bed (EC50 = 25 +/- 12, 32 +/- 9, 37 +/- 10, and 22 +/- 13 nM, respectively; P < 0.05 for each vs. maxadilan). Arterial relaxation to maxadilan was independent of endothelium and was equipotent in the thoracic and abdominal aorta, carotid artery, and iliac artery. Arterial relaxation to maxadilan was not inhibited by K(+)-channel antagonists, methylene blue, quinacrine, or ouabain. Maxadilan-mediated arterial relaxation was found to be adenosine 3',5'-cyclic monophosphate (cAMP) dependent, as it was potentiated by the phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine and theophylline, and it was inhibited by the protein kinase A inhibitor H-89. Consistent with this observation, incubation of thoracic aorta with maxadilan (0.1 microM) produced a time-dependent increase in arterial cAMP content coincident with arterial relaxation. Using rabbit aortic smooth muscle cells, we also observed a time-dependent reduction in intracellular calcium in response to maxadilan. Thus these data indicate that maxadilan, a peptide from the sand fly salivary gland, is a potent vasodilator that reduces intracellular calcium through a cAMP-dependent mechanism.
Matching dicrotic notch and mean pulmonary artery pressures: implications for effective arterial elastance
Authors: Chemla D. , Hebert J. L. , Coirault C. , Salmeron S. , Zamani K. , Lecarpentier Y.
Published: December 2017

It has been suggested that pulmonary artery pressure at the end of ejection is close to mean pulmonary artery pressure, thus contributing to the optimization of external power from the right ventricle. We tested the hypothesis that dicrotic notch and mean pulmonary artery pressures could be of similar magnitude in 15 men (50 +/- 12 yr) referred to our laboratory for diagnostic right and left heart catheterization. Beat-to-beat relationships between dicrotic notch and mean pulmonary artery pressures were studied 1) at rest over 10 consecutive beats and 2) in 5 patients during the Valsalva maneuver (178 beats studied). At rest, there was no difference between dicrotic notch and mean pulmonary artery pressures (21.8 +/- 12.0 vs. 21.9 +/- 11.1 mmHg). There was a strong linear relationship between dicrotic notch and mean pressures 1) over the 10 consecutive beats studied in each patient (mean r = 0.93), 2) over the 150 resting beats (r = 0.99), and 3) during the Valsalva maneuver in each patient (r = 0.98-0.99) and in the overall beats (r = 0.99). The difference between dicrotic notch and mean pressures was -0.1 +/- 1.7 mmHg at rest and -1.5 +/- 2.3 mmHg during the Valsalva maneuver. Substitution of the mean pulmonary artery pressure by the dicrotic notch pressure in the standard formula of the pulmonary vascular resistance (PVR) resulted in an equation relating linearly end-systolic pressure and stroke volume. The slope of this relation had the dimension of a volume elastance (in mmHg/ml), a simple estimate of volume elastance being obtained as 1.06(PVR/T), where T is duration of the cardiac cycle. In conclusion, dicrotic notch pressure was of similar magnitude as mean pulmonary artery pressure. These results confirmed our primary hypothesis and indicated that human pulmonary artery can be treated as if it is an elastic chamber with a volume elastance of 1.06(PVR/T).
Slowing of carotid-cardiac baroreflex with standing and with isometric and dynamic muscle activity
Authors: Sundblad P. , Linnarsson D.
Published: December 2017

We hypothesized that the carotid-cardiac baroreflex becomes slowed in conditions with increased sympathetic activity. Changes in heart rate (HR) and blood pressure in response to 10-s trains of 50-mmHg pulses of neck suction (NS) were studied in six male subjects during supine rest, upright rest, isometric arm exercise at 30% of maximum voluntary contraction, and dynamic leg exercise at 100 W in the sitting position. Estimated mean carotid distending pressure increased by approximately 20 mmHg with 50-mmHg, QRS-triggered, pulsatile NS. Repeated NS sequences were performed in each condition. The amplitude of the bradycardic response was highly variable among the subjects and did not differ significantly between conditions, mean values ranging from 0.3 to 0.6 beats.min-1.mmHg-1. In supine rest, the full bradycardic response appeared within < 1 s, i.e., during or immediately after the R-R interval of the first NS pulse. In the other conditions it took significantly longer, 2-3 s or three to seven R-R intervals, for the full HR responses to develop. Our results support the notion that the carotid-cardiac baroreflex in humans becomes slowed under conditions of concurrent sympathetic stimulation.
Discontinuous conduction at Purkinje-ventricular muscle junction
Authors: Wiedmann R. T. , Tan R. C. , Joyner R. W.
Published: December 2017

Conduction through the cardiac syncytium varies from being nearly continuous, with very well coupled cells, to being clearly discontinuous, with significant conduction delays over very short distances. The Purkinje-ventricular muscle junction (PVJ) sites on the endocardial surface have characteristic delays of conduction and the presence of discrete groups of cells that suggest significant discontinuities of the conduction process at PVJ sites, as compared with the more nearly continuous conduction within either the Purkinje or the ventricular muscle layers of the papillary muscle. The purpose of the present study was to examine the relative sensitivity of conduction at PVJ sites versus conduction within the Purkinje or the ventricular muscle layer of the canine papillary muscle to agents that modulate L-type calcium current. We have used cadmium as a relatively specific blocker of L-type calcium current and isoproterenol as an agent to increase L-type calcium current to test the hypothesis that discontinuous conduction at the PVJ sites would be more sensitive to these agents than would continuous conduction within either the Purkinje layer or the ventricular muscle layer of a canine papillary muscle. Conduction delay at the PVJ sites was significantly increased by cadmium, with some PVJ sites reversibly becoming nonjunctional at 200-400 microM cadmium. Isoproterenol significantly decreased PVJ delay, and this effect was attenuated by carbachol. All of the effects on conduction delay at the PVJ sites were much greater than the effects for the same agents on conduction velocity within either the Purkinje or the ventricular muscle layer of the papillary muscle.
Activation of ATP-sensitive potassium channels contributes to reactive hyperemia in humans
Authors: Banitt P. F. , Smits P. , Williams S. B. , Ganz P. , Creager M. A.
Published: December 2017

Activation of ATP-sensitive potassium (KATP) channels present on vascular smooth muscle cells causes membrane hyperpolarization and vasodilation. The purpose of this study was to determine whether KATP channels contribute to reactive hyperemia in humans. Accordingly, we studied the effect of tolbutamide, a KATP channel inhibitor, on reactive hyperemic forearm blood flow. Forearm blood flow was measured by venous occlusion plethysmography. Forearm ischemia was produced by inflating a sphygmomanometric cuff on the arm to suprasystolic pressures for 5 min. After cuff release, forearm blood flow was measured during the reactive hyperemic phase for 5 min. Tolbutamide (1 mM blood concentration, n = 6) did not affect basal (2.4 +/- 0.2 to 2.2 +/- 0.1 ml.100 ml-1.min-1) or peak reactive hyperemic forearm blood flow (21.9 +/- 3.8 to 22.6 +/- 2.9 ml.100 ml-1.min-1, each P = NS), but it significantly attenuated total hyperemic volume (12.6 +/- 1.7 vs. 9.2 +/- 1.8 ml/100 ml, P < 0.02). Vehicle (n = 6) did not affect basal flow, peak reactive hyperemic flow, or total hyperemia. To determine whether adenosine or endothelium-derived nitric oxide contribute to reactive hyperemia via KATP channels, adenosine (1.5-500 micro grams/min, n = 6) and acetylcholine (30 micrograms/min, n = 6) were infused before and during tolbutamide coinfusion. Tolbutamide did not significantly alter the forearm blood flow response to either adenosine or acetylcholine. In conclusion, KATP channels contribute to vasodilation during reactive hyperemia in humans.
Differential regulation of voltage-activated potassium currents in cultured human atrial myocytes
Authors: Hatem S. N. , Benardeau A. , Rucker-Martin C. , Samuel J. L. , Coraboeuf E. , Mercadier J. J.
Published: December 2017

To examine whether the two components of the voltage-activated outward K+ current, an initially rapidly inactivating component (Ito,1) and a slowly inactivating sustained component (Isus), in human atrial myocytes are distinct currents differentially regulated, we studied their behavior during serum-induced growth of cultured myocytes. Currents were recorded in whole cell patch clamped myocytes. After 1 wk of culture (day 8), membrane capacitance was twice the value in freshly dissociated myocytes (178.7 +/- 23 vs. 83.1 +/- 5.5 pF; P < 0.001). Ito,1 density did not differ from that in freshly dissociated myocytes (at +40 mV: 4.38 +/- 0.8 vs. 3.71 +/- 0.6 pA/pF), whereas that of Isus was markedly increased (at +40 mV: 9.76 +/- 2 vs. 2.21 +/- 0.29 pA/pF; P < 0.001). After inactivation of Ito,1 by a prepulse, sustained depolarization elicited in cultured myocytes an Isus with a density of 10.22 +/- 1.18 pA/pF and an apparent tail current reversal potential of -73.5 +/- 3.2 mV, indicating high K+ selectivity. Isus was highly sensitive to 4-aminopyridine (55.4 +/- 4.4% inhibition in 50 microM) and to D-600 (with a concentration inhibiting 50% of maximal response of 34.2 x 10(-6) M). Addition of 5-10 nM staurosporine at day 3 prevented cell growth and reduced Ito,1 density but not the increase in Isus density, which was inhibited by 10 microM staurosporine. Our results indicate that Ito,1 and Isus are regulated independently during in vitro myocyte growth in human atrial myocytes and that the increase in Isus density is not mediated by a protein kinase C-dependent pathway.
Role of mast cells in oxidized low-density lipoprotein-induced microvascular dysfunction
Authors: Liao L. , Granger D. N.
Published: December 2017

Previous studies demonstrated that human low-density lipoprotein (LDL) oxidized with Cu2+ promotes leukocyte-endothelial cell adhesion, mast cell degranulation, and albumin extravasation in rat mesentery. The objective of this study was to determine whether the mast cell degranulation elicited by oxidized LDL accounts for the accompanying microvascular responses. Leukocyte rolling, adherence, and emigration, fluorescein isothiocyanate-albumin leakage, and mast cell degranulation were monitored in rat mesentery before and during local intra-arterial infusion of either normal LDL (nLDL) or copper-oxidized LDL (CuLDL). Infusion of CuLDL, but not nLDL, elicited significant increases in leukocyte rolling, adherence and emigration, albumin leakage, and mast cell degranulation. Pretreatment with the mast cell-stabilizing agent ketotifen or superfusion of the mesenteric microcirculation with iodoxamide significantly reduced CuLDL-induced mast cell degranulation. The mast cell stabilization was accompanied by attenuated leukocyte-endothelial cell adhesion and albumin leakage responses to CuLDL. The results of this study indicate that 1) CuLDL-induced microvascular dysfunction (albumin leakage) involves the activation of mast cells, and 2) the protective action of mast cell stabilizers may be related to their ability to blunt CuLDL-induced leukocyte-endothelial cell interactions in postcapillary venules.
Neuropeptide Y reduces macromolecule permeability of coronary endothelial monolayers
Authors: Noll T. , Hempel A. , Piper H. M.
Published: December 2017

The effect of neuropeptide Y (NPY) on cellular adenosine 3',5'-cyclic monophosphate (cAMP) contents and macromolecule permeability was studied in cultured monolayers of microvascular coronary endothelial cells from rat. Macromolecule permeability was continuously determined as passage of albumin across the monolayers. NPY (10(-10)-10(-7) M) decreased albumin flux and cellular cAMP content in a dose-dependent manner, with a half-maximal effect on albumin flux at 1.4 x 10(-9) M and on cAMP contents at 0.7 x 10(-9) M. A maximum effect of NPY was observed at 10(-7) M, decreasing albumin flux by 71 +/- 8% and cellular cAMP contents by 80 +/- 9% (mean +/- SD, n = 6, P < 0.05) compared with control. The effect of NPY on albumin flux was not altered in the presence of 10(-5) M indomethacin (an inhibitor of cyclooxygenase) and 10(-5) M NG-nitro-L-arginine (an inhibitor of nitric oxide synthase). NPY (10(-7) M) also antagonized the increase of albumin flux and cAMP content induced by 10(-6) M isoproterenol. Pretreatment of endothelial monolayers with pertussis toxin (1 microgram/ml for 2 h) abolished the effect of NPY on albumin flux and cAMP contents. This study shows that NPY can modulate macromolecule permeability of endothelial monolayers by reducing the cellular cAMP contents. Together with the effect of pertussis toxin, the data suggest that NPY exerts its antiadrenergic effect on cAMP metabolism and endothelial barrier function by receptors linked to adenylyl cyclase via an inhibitory guanosine-binding protein in coronary endothelial cells.
One-day cold perfusion of bimakalim and butanedione monoxime restores ex situ cardiac function
Authors: Stowe D. F. , Graf B. M. , Fujita S. , Gross G. J.
Published: December 2017

Bimakalim (Bim), an opener of ATP-sensitive K+ (KATP) channels, was given alone or with 2,3-butanedione monoxime (BDM), a reversible uncoupler of contractility, to protect myocardial function during 1 day of hypothermia. Left ventricular pressure (LVP), coronary flow (CF), percent O2 extraction (%O2E), and cardiac efficiency were measured in 96 isolated, perfused guinea pig hearts divided into seven groups: 1) cold control (no drugs); 2) BDM; 3) Bim; 4) BDM + Bim; 5) BDM + glibenclamide (Glib, a blocker of KATP channels); 6) BDM + Bim + Glib; and 7) time control (6 h warm perfusion only). Drugs were given before, during, and initially after 22 h of low CF at 3.8 degrees C. At 26 h (cold groups) or 4 h (warm group) LVP (mmHg; means +/- SE) was similar for time control (94 +/- 4) and BDM + Bim (92 +/- 4) groups, lower and equivalent in the BDM (65 +/- 7) and BDM + Bim + Glib (64 +/- 7) groups, but LVP was higher than in the Bim group (46 +/- 3), and lowest in the cold control (30 +/- 8) group. In addition, only in the BDM + Bim group were basal CF, %O2E, and cardiac efficiency returned to values obtained in the time control group. Epinephrine increased LVP to that of the time control (106 +/- 3) group only in the BDM + Bim group (106 +/- 3) after hypothermia, and CF increases with adenosine, 5-hydroxytryptamine, and nitroprusside were similar to that of the time control group only in the BDM + Bim group after hypothermia. All of the effects of Bim were reversed by Glib. These results indicate that Bim, given with BDM, effectively preserves myocardial function and metabolism as well as inotropic and vasodilatory reserve during long-term hypothermic preservation as if the 1-day hypothermic state had not been instituted. Because the beneficial effects of Bim are blocked by Glib, the protective effect of Bim likely results from maintained KATP channel opening. Treatment with exogenous KATP openers may prove useful in preserving cardiac function in the transplanted heart.
Calcium homeostasis in cardiomyocytes isolated from heat-shocked rats
Authors: Cornelussen R. N. , Ver Donck L. , Verellen G. , Borgers M. , van der Vusse G. J. , Reneman R. S. , Snoeckx L. H.
Published: December 2017

The cellular mechanism of heat shock-mediated cardioprotection is still under debate. Because heat pretreatment negatively affects the normoxic left ventricular contractile performance in vitro when the extracellular Ca2+ concentration ([Ca2+]o) is relatively low (0.65-1.25 mM), the intracellular Ca2+ homeostasis was studied in more detail in cardiomyocytes isolated from adult rats 24 h after heat stress (42 degrees C for 15 min) or anesthesia (control). Sensitivity to Ca2+ overload was assessed by exposure to veratridine (quiescent cells) or to [Ca2+]o ranging from 0.125 to 20 mM in quiescent and paced cardiomyocytes. The fraction of irreversibly hypercontracted cells was not different between groups. The fura-2 fluorescence ratio (I340/I380), which was used as a measure for cytoplasmic Ca2+ concentration ([Ca2+]i) in quiescent cells after exposure to [Ca2+]o (0.5-10 mM), was also not different between groups. Myofilament Ca2+ sensitivity was assessed in paced (0.5 Hz) cells by simultaneous measurement of [Ca2+]i transients and cell shortening. At stepwise increases of [Ca2+]o from 1 to 10 mM, these parameters were comparable between groups. The diastolic cell length shortened progressively and equally in both groups after increasing [Ca2+]o. However, within 2 min of return from 10 to 1 mM [Ca2+]o, cells from heat-shocked rats retained the same length, whereas cells from control rats contracted further (P = 0.05). These data suggest that heat stress improves relaxation after challenge with high [Ca2+]o.
Ischemic preconditioning attenuates postischemic leukocyte adhesion and emigration
Authors: Akimitsu T. , Gute D. C. , Korthuis R. J.
Published: December 2017

Intravital microscopy was used to determine whether ischemic preconditioning (IPC; 5 min ischemia and 10 min reperfusion) would attenuate leukocyte adhesion and emigration induced by subsequent prolonged ischemia (60 min) and reperfusion (60 min) (I/R) in murine cremaster muscle and whether adenosine produced during IPC and/or reperfusion contributed to these beneficial effects. I/R elicited a marked increase in the number of adherent and emigrated leukocytes compared with the nonischemic control muscles, an effect that was largely prevented by IPC. Superfusion of the cremaster with adenosine deaminase only during IPC or only during 60-min reperfusion attenuated the inhibitory effect of IPC on postischemic leukocyte adhesion and emigration. However, the beneficial effects of IPC were mimicked in cremaster muscles preconditioned with adenosine (topical application for 10 min beginning 20 min before the onset of prolonged ischemia). Similar results were obtained in experiments in which adenosine was topically applied to the cremaster only during the 60-min reperfusion period. Our findings suggest that the ability of IPC to attenuate postischemic leukocyte adhesion and emigration may be mediated by adenosine released during IPC and during reperfusion after prolonged ischemia.
Temporal evaluation of left ventricular remodeling and function in rats with chronic volume overload
Authors: Brower G. L. , Henegar J. R. , Janicki J. S.
Published: December 2017

The left ventricle (LV) significantly dilates and hypertrophies in response to chronic volume overload. However, the temporal responses in LV mass, volume, and systolic/diastolic function secondary to chronic volume overload induced by an infrarenal arteriovenous (A-V) fistula in rats have not been well characterized. To this end, LV end-diastolic pressure, size, and function (i.e., isovolumetric pressure-volume relationships in the blood-perfused isolated heart) were assessed at 1, 2, 3, 5, and 8 wk post-A-V fistula and compared with age-matched control animals. Progressive hypertrophy (192% at 8 wk), ventricular dilatation (172% at 8 wk), and a decrease in ventricular stiffness (257% at 8 wk) occurred in the fistula groups. LV end-diastolic pressure increased from a control value of 4.2 +/- 3.1 mmHg to a peak value of 15.7 +/- 3.6 mmHg after 3 wk of volume overload. A subsequent decline in LVEDP to 11.0 +/- 6.0 mmHg together with further LV dilation (169%) corresponded to a significant decrease in LV stiffness (222%) at 5 wk post-A-V fistula. Myocardial contractility, as assessed by the isovolumetric pressure-volume relationship, was significantly reduced in all A-V fistula groups; however, the compensatory remodeling induced by 8 wk of chronic biventricular volume overload tended to preserve systolic function.
Cardiomyocyte DNA synthesis and binucleation during murine development
Authors: Soonpaa M. H. , Kim K. K. , Pajak L. , Franklin M. , Field L. J.
Published: December 2017

Cardiomyocyte DNA synthesis and binucleation indexes were determined during murine development. Cardiomyocyte DNA synthesis occurred in two temporally distinct phases. The first phase occurred during fetal life and was associated exclusively with cardiomyocyte proliferation. The second phase occurred during early neonatal life and was associated with binucleation. Collectively, these results suggest that cardiomyocyte reduplication ceases during late fetal life. Northern and Western blot analyses identified several candidate genes that were differentially expressed during the reduplicative and binucleation phases of cardiomyocyte growth.
Effect of nitric oxide and potassium channel agonists and inhibitors on basilar artery diameter
Authors: Sobey C. G. , Faraci F. M.
Published: December 2017

The first goal of this study was to examine the hypothesis that dilatation of the basilar artery in response to activation of ATP-sensitive K+ channels is mediated by nitric oxide (NO). Diameter of the basilar artery (209 +/- 5 microns, mean +/- SE) was measured using a cranial window in anesthetized rats. Aprikalim (a direct activator of ATP-sensitive K+ channels) dilated the basilar artery under control conditions. Inhibition of endogenous NO production with NG-nitro-L-arginine (L-NNA, 10(-4) M) did not alter responses to aprikalim. The second goal was to determine whether vasodilatation in response to NO is dependent on activation of calcium-activated K+ channels. Tetraethylammonium (TEA, 10(-3) M), an inhibitor of calcium-activated K+ channels, did not affect dilator responses to sodium nitroprusside (an NO donor) under control conditions. Responses to nitroprusside (10(-8) and 10(-7) M) were augmented more than twofold during application of L-NNA. In the presence of L-NNA, the augmented portion of the response to nitroprusside was inhibited by TEA and iberiotoxin (5 x 10(-8) M, a highly selective inhibitor of calcium-activated K+ channels), but it was not inhibited by glibenclamide (10(-6) M), an inhibitor of ATP-sensitive K+ channels. These findings suggest that dilator responses of the basilar artery to an activator of ATP-sensitive potassium channels are not mediated by NO. Calcium-activated K+ channels may not normally contribute to dilator responses of the basilar artery to nitroprusside. The effects of TEA and iberiotoxin suggest that when endogenous production of NO is inhibited, sodium nitroprusside causes the opening of calcium-activated K+ channels, contributing to an augmented vasodilator response.
Anterior and posterior left ventricular sarcomere lengths behave similarly during ejection
Authors: Guccione J. M. , O'Dell W. G. , McCulloch A. D. , Hunter W. C.
Published: December 2017

Previous studies of regional differences in myocardial deformation between the anterior and posterior walls of the canine left ventricle were based on strain, which is not an absolute measure of deformation. We thus compared sarcomere lengths at anterior and posterior sites during ejection in isolated dog hearts. Cineradiographic imaging of regional deformation with radiopaque markers implanted near the midwall in five hearts and just below the epicardium in six hearts, combined with postmortem histology, allowed sarcomere length reconstruction throughout the cardiac cycle. The amount of sarcomere shortening accompanying left ventricular ejection was similar in both walls of the left ventricle for sarcomeres located at epicardial and midwall sites. The mean sarcomere length (taken at the middle of the ejecting range) was also similar between the anterior and posterior sites when averaged over all hearts. The similarity of sarcomere function held not only at end systole but throughout ejection and over wide ranges of ventricular pre- and afterloads. Hence functional measurements of relative myocardial shortening may not be indicative of regional sarcomere length heterogeneity.
Chronic heart failure induced by coronary artery ligation in Lewis inbred rats
Authors: Liu Y. H. , Yang X. P. , Nass O. , Sabbah H. N. , Peterson E. , Carretero O. A.
Published: December 2017

Rat models of heart failure (HF) secondary to myocardial infarction (MI) are useful in studying the progression of cardiac dysfunction and in testing therapeutic approaches. Sprague-Dawley rats are frequently used; however, this model is hampered by high mortality and a marked variability in infarct size and cardiac dysfunction, necessitating large numbers of rats and prolonged follow-up when studying the progression of dysfunction. In the present work, we developed a model of HF utilizing Lewis inbred rats. Ligation of the left anterior descending coronary artery in Lewis rats produced more uniform and larger infarcts (40 +/- 1.7 vs. 28 +/- 2.3%; P < 0.001) and lower mortality (16 vs. 36%; P < 0.001) than in Sprague-Dawley rats. Using this rat model, we further studied the course of left ventricular (LV) dysfunction and enlargement from 1 wk to 6 mo after MI with cineventriculography. LV end-systolic volume and end-diastolic volume were determined with the area-length method. LV ejection fraction ranged between 0.57 and 0.62 in control rats; after MI, it decreased significantly to 0.48 +/- 0.04 at 1 wk, 0.36 +/- 0.02 at 2 wk, 0.48 +/- 0.02 at 1 mo, 0.35 +/- 0.03 at 2 mo, 0.30 +/- 0.02 at 3 mo, 0.31 +/- 0.02 at 4 mo, and 0.24 +/- 0.02 at 6 mo (P < 0.001, MI vs. sham). LV end-diastolic volume in control rats ranged between 0.32 and 0.42 ml; it increased to 0.48 +/- 0.04 ml at 1 wk, 0.46 +/- 0.02 ml at 2 wk, and 0.46 +/- 0.03 ml at 1 mo. It markedly increased to 0.79 +/- 0.03, 0.79 +/- 0.06, 0.78 +/- 0.03, and 0.80 +/- 0.05 ml at 2, 3, 4, and 6 mo, respectively, after MI (P < 0.001 vs. sham). LV end-diastolic pressure was significantly elevated at all time points. Thus coronary ligation in Lewis inbred rats produces uniformly large infarcts with low mortality, progressive LV dysfunction, and increased LV chamber size. This model may be useful in studying chronic HF secondary to MI.