bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of cardiotrophin-1 on hemodynamics and endocrine function of the heart
Authors: Hamanaka Ichiro , Saito Yoshihiko , Nishikimi Toshio , Magaribuchi Tatsuo , Kamitani Shigeki , Kuwahara Koichiro , Ishikawa Masahiro , Miyamoto Yoshihiro , Harada Masaki , Ogawa Emiko , Kajiyama Noboru , Takahashi Nobuki , Izumi Takehiko , Shirakami Gotaro , Mori Kenjiro , Inobe Yoshito , Kishimoto Ichiro , Masuda Izuru , Fukuda Kazuhiko , Nakao Kazuwa
Published: December 2017

Cardiotrophin-1 (CT-1), a member of the interleukin-6 superfamily of cytokines, possesses hypertrophic actions and atrial natriuretic peptide (ANP)-producing activity in vitro. The goal of our study is to elucidate whether CT-1 affects the cardiovascular system in vivo. Intravenous injection of CT-1 (4–100 μg/kg) in conscious rats evoked significant declines in blood pressure and reflex increases in heart rate (HR) in a dose-dependent manner. CT-1 induced no significant change in cardiac output (from 260.7 ± 11.0 to 264.7 ± 26.6 ml ⋅ min−1⋅ kg−1, P = not significant), which was compatible with the results from isolated perfused rat hearts; HR, change in pressure over time, left ventricular developed pressure, and perfusion pressure were unaffected. Northern blot and RT-PCR analyses revealed that CT-1 increased expression of inducible nitric oxide synthase (iNOS) in lung and aorta but not in heart or liver. Pretreatment with aminoguanidine, a specific iNOS inhibitor, inhibited both iNOS mRNA production and the depressor effect of CT-1. Interestingly, CT-1 increased ventricular expression of ANP and brain natriuretic peptide (BNP). The data demonstrate that CT-1 elicits its hypotensive effect via a nitric oxide-dependent mechanism and that CT-1 induces ANP and BNP mRNA expression in vivo.
SHR Y chromosome enhances the nocturnal blood pressure in socially interacting rats
Authors: Caplea Ann , Seachrist Darcie , Dunphy Gail , Ely Daniel
Published: December 2017

Our objective was to test the hypothesis that nocturnal mean arterial pressure (MAP), heart rate (HR), and activity would be increased in 1) colony over individually caged rats and 2) the spontaneously hypertensive rat (SHR) Y chromosome strain (SHR/y colony) compared with Wistar-Kyoto (WKY) rats. MAP, HR, and activity were monitored using radiotelemetry. The nocturnal MAP rise expressed as the percentage change in MAP from light to dark was increased ( P < 0.05) in the SHR/y colony. The SHR Y chromosome increased MAP in both the colony and caged groups compared with WKY ( P < 0.001). The SHR/y colony animals spent 23% of a 24-h period at a MAP >120 mmHg, whereas the WKY colony animals spent 2% of a 24-h period in this range. The MAP of the SHR/y colony on clonidine was reduced ( P < 0.001) to WKY baseline values. Activity but not HR was increased ( P < 0.01) in the WKY and SHR/y colonies compared with caged animals. In conclusion, colony housing and the SHR Y chromosome increased MAP compared with individually caged housing.
Mechanism of effect of extracellular pH on L-type Ca2+ channel currents in human mesenteric arterial cells
Authors: Smirnov Sergey V. , Knock Gregory A. , Belevych Andriy E. , Aaronson Philip I.
Published: December 2017

Extracellular pH (pHo) influences vasoconstriction partly by modulating Ca2+ influx through voltage-gated Ca2+ channels in the vasculature. The mechanism of this effect of pHo is, however, controversial. Using the whole cell voltage-clamp technique, we examined the influence of pHo on L-type Ca2+ channel currents in isolated human mesenteric arterial myocytes. Acidification to pH 6.2 and alkalinization to 8.2 from 7.2 decreased by ∼50% and increased by 25–30%, respectively, the peak amplitude of Ca2+ and Ba2+ currents (1.5 and 10 mM), with an apparent p K a of 6.8. Activation and inactivation of Ca2+ and Ba2+ currents were shifted toward positive membrane voltages during acidification and in the opposite direction during alkalinization. The relationship between the current amplitude and shifts in the gating parameters in solutions of different pHo conformed closely to that predicted by the Gouy-Chapman model, in which the divalent cation concentration at the outer surface of the membrane varies with the extent to which protons neutralize the membrane surface potential.
Arteriolar wall Po 2 and nitric oxide release during sympathetic vasoconstriction in the rat intestine
Authors: Sauls Bryan A. , Boegehold Matthew A.
Published: December 2017

Endothelium-derived nitric oxide (NO) attenuates arteriolar constriction in the rat small intestine during periods of increased sympathetic nerve activity. This study was undertaken to test the hypothesis that a flow-dependent fall in arteriolar wall Po 2 serves as the stimulus for endothelial NO release under these conditions. Sympathetic nerve stimulation at 3–16 Hz induced frequency-dependent arteriolar constriction, with arteriolar wall O2 tension (Po 2) falling from 67 ± 3 mmHg to as low as 41 ± 6 mmHg. Arteriolar responses to nerve stimulation were enhanced after inhibition of NO synthase with N G-monomethyl-l-arginine (l-NMMA). Under a high-O2 (20%) superfusate, the fall in wall Po 2 was significantly attenuated, arteriolar constrictions were increased by 57 ± 9 to 66 ± 12%, and these responses were no longer sensitive tol-NMMA. The high-O2 superfusate had no effect on vascular smooth muscle responsiveness to NO (as judged by arteriolar responses to sodium nitroprusside) or on arteriolar wall oxidant activity (as determined by the reduction of tetranitroblue tetrazolium dye). These results indicate that a flow-dependent fall in arteriolar wall Po 2 may serve as a stimulus for the release of endothelium-derived NO during periods of increased sympathetic nerve activity.
Hyperventilation alters arterial baroreflex control of heart rate and muscle sympathetic nerve activity
Authors: Van de Borne Philippe , Mezzetti Silvia , Montano Nicola , Narkiewicz Krzysztof , Degaute Jean Paul , Somers Virend K.
Published: December 2017

Interactions between mechanisms governing ventilation and blood pressure (BP) are not well understood. We studied in 11 resting normal subjects the effects of sustained isocapnic hyperventilation on arterial baroreceptor sensitivity, determined as the α index between oscillations in systolic BP (SBP) generated by respiration and oscillations present in R-R intervals (RR) and in peripheral sympathetic nerve traffic [muscle sympathetic nerve activity (MSNA)]. Tidal volume increased from 478 ± 24 to 1,499 ± 84 ml and raised SBP from 118 ± 2 to 125 ± 3 mmHg, whereas RR decreased from 947 ± 18 to 855 ± 11 ms (all P < 0.0001); MSNA did not change. Hyperventilation reduced arterial baroreflex sensitivity to oscillations in SBP at both cardiac (from 13 ± 1 to 9 ± 1 ms/mmHg, P < 0.001) and MSNA levels (by −37 ± 5%, P < 0.0001). Thus increased BP during hyperventilation does not elicit any reduction in either heart rate or MSNA. Baroreflex modulation of RR and MSNA in response to hyperventilation-induced BP oscillations is attenuated. Blunted baroreflex gain during hyperventilation may be a mechanism that facilitates simultaneous increases in BP, heart rate, and sympathetic activity during dynamic exercise and chemoreceptor activation.
Vasomotion in critically perfused muscle protects adjacent tissues from capillary perfusion failure
Authors: Rücker M. , Strobel O. , Vollmar B. , Roesken F. , Menger M. D.
Published: December 2017

We analyzed the incidence and interaction of arteriolar vasomotion and capillary flow motion during critical perfusion conditions in neighboring peripheral tissues using intravital fluorescence microscopy. The gracilis and semitendinosus muscles and adjacent periosteum, subcutis, and skin of the left hindlimb of Sprague-Dawley rats were isolated at the femoral vessels. Critical perfusion conditions, achieved by stepwise reduction of femoral artery blood flow, induced capillary flow motion in muscle, but not in the periosteum, subcutis, and skin. Strikingly, blood flow within individual capillaries was decreased ( P < 0.05) in muscle but was not affected in the periosteum, subcutis, and skin. However, despite the flow motion-induced reduction of muscle capillary blood flow during the critical perfusion conditions, functional capillary density remained preserved in all tissues analyzed, including the skeletal muscle. Abrogation of vasomotion in the muscle arterioles by the calcium channel blocker felodipine resulted in a redistribution of blood flow within individual capillaries from cutaneous, subcutaneous, and periosteal tissues toward skeletal muscle. As a consequence, shutdown of perfusion of individual capillaries was observed that resulted in a significant reduction ( P < 0.05) of capillary density not only in the neighboring tissues but also in the muscle itself. We conclude that during critical perfusion conditions, vasomotion and flow motion in skeletal muscle preserve nutritive perfusion (functional capillary density) not only in the muscle itself but also in the neighboring tissues, which are not capable of developing this protective regulatory mechanism by themselves.
Insulin resistance and the modulation of rat cardiac K+ currents
Authors: Shimoni Y. , Severson D. , Ewart H. S.
Published: December 2017

K+ currents were measured using a whole cell voltage-clamp method in enzymatically isolated rat ventricular myocytes obtained from two hyperinsulinemic, insulin-resistant models. Fructose-fed rats as well as genetically obese rats, both of which are resistant to the metabolic effects of insulin, were used. The normal augmentation of a calcium-independent sustained K+ current was reduced or abolished in insulin-resistant states. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadyl sulfate (3–4 wk treatment or after 5–6 h in vitro) enhanced the sustained K+ current. The in vitro effect of vanadyl was blocked by cycloheximide. Insulin resistance of the K+current was not reversed by vanadyl sulfate. The results show that insulin resistance is expressed in terms of insulin actions on ion channels, in addition to its actions on metabolism. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadate compounds, which mimic the effects of insulin on metabolism, also mimic the augmenting effects of insulin on a cardiac K+ current in a manner suggesting synthesis of new channels.
A spontaneously active focus drives a model atrial sheet more easily than a model ventricular sheet
Authors: Joyner Ronald W. , Wang Yang-Gan , Wilders Ronald , Golod David A. , Wagner Mary B. , Kumar Rajiv , Goolsby William N.
Published: December 2017

Tachycardias can be produced when focal activity at ectopic locations in either the atria or the ventricles propagates into the surrounding quiescent myocardium. Isolated rabbit atrioventricular nodal cells were coupled by an electronic circuit to a real-time simulation of an array of cell models. We investigated the critical size of an automatic focus for the activation of two-dimensional arrays made up of either ventricular or atrial model cells. Over a range of coupling conductances for the arrays, the critical size of the focus cell group for successful propagation was smaller for activation of an atrial versus a ventricular array. Failure of activation of the arrays at smaller focus sizes was due to the inhibition of pacing of the nodal cells. At low levels of coupling conductance, the ventricular arrays required larger sizes of the focus due to failure of propagation even when the focus was spontaneously active. The major differences between activation of the atrial and ventricular arrays is due to the higher membrane resistance (lower inward rectifier current) of the atrial cells.
Presynaptic β2-adrenoceptors mediate nicotine-induced NOergic neurogenic dilation in porcine basilar arteries
Authors: Lee Tony J. F. , Zhang W. , Sarwinski S.
Published: December 2017

We previously reported that nicotine-induced nitric oxide (NO)-mediated cerebral neurogenic vasodilation was dependent on intact sympathetic innervation. We hypothesized that nicotine acted on sympathetic nerve terminals to release norepinephrine (NE), which then acted on adrenoceptors located on the neighboring nitric oxidergic (NOergic) nerve terminals to release NO, resulting in vasodilation. The adrenoceptor subtype in mediating nicotine-induced vasodilation in isolated porcine basilar arterial rings denuded of endothelium was therefore examined pharmacologically and immunohistochemically. Results from using an in vitro tissue bath technique indicated that propranolol and preferential β2-adrenoceptor antagonists (ICI-118,551 and butoxamine), in a concentration-dependent manner, blocked the relaxation induced by nicotine (100 μM) without affecting the relaxation elicited by transmural nerve stimulation (TNS, 8 Hz). In contrast, preferential β1-adrenoceptor antagonists (atenolol and CGP-20712A) did not affect either nicotine- or TNS-induced relaxation. Results of double-labeling studies indicated that β2-adrenoceptor immunoreactivities and NADPH diaphorase reactivities were colocalized in the same nerve fibers in basilar and middle cerebral arteries. These findings suggest that NE, which is released from sympathetic nerves upon application of nicotine, acts on presynaptic β2-adrenoceptors located on the NOergic nerve terminals to release NO, resulting in vasodilation. In addition, nicotine-induced relaxation was enhanced by yohimbine, an α2-adrenoceptor antagonist, which, however, did not affect the relaxation elicited by TNS. Prazosin, an α1-adrenoceptor antagonist, on the other hand, did not have any effect on relaxation induced by either nicotine or TNS. The predominant facilitatory effect of β2-adrenoceptors in releasing NO may be compromised by presynaptic α2-adrenoceptors.
Fluorescent HPLC assay for 20-HETE and otherP-450 metabolites of arachidonic acid
Authors: Maier Kristopher G. , Henderson Lisa , Narayanan Jayashree , Alonso-Galicia Magdalena , Falck John R. , Roman Richard J.
Published: December 2017

This study describes a fluorescent HPLC assay for measuring 20-hydroxyeicosatetraenoic acid (20-HETE) and other cytochrome P-450 metabolites of arachidonic acid in urine, tissue, and interstitial fluid. An internal standard, 20-hydroxyeicosa-6( Z),15( Z)-dienoic acid, was added to samples, and the lipids were extracted and labeled with 2-(2,3-naphthalimino)ethyl trifluoromethanesulfonate. P-450 metabolites were separated on a C18 reverse-phase HPLC column. Coelution and gas chromatography-mass spectrometry studies confirmed the identity of the 20-HETE peak. The 20-HETE peak can be separated from those for dihydroxyeicosatrienoic acids, other HETEs, and epoxyeicosatrienoic acids. Known amounts of 20-HETE were used to generate a standard curve (range 1–10 ng, r2= 0.98). Recovery of 20-HETE from urine averaged 95%, and the intra-assay variation was <5%. Levels of 20-HETE were measured in 100 μl of urine and renal interstitial fluid or 0.1 mg of renal tissue. The assay was evaluated by studying the effects of 1-aminobenzotriazole (ABT) on the excretion of 20-HETE in rats. ABT reduced excretion of 20-HETE by >65% and inhibited the formation of 20-HETE by renal microsomes. The availability of this assay should facilitate work in this field.
Comparison of blood-brain barrier permeability in mice and rats using in situ brain perfusion technique
Authors: Murakami Hideyasu , Takanaga Hitomi , Matsuo Hirotami , Ohtani Hisakazu , Sawada Yasufumi
Published: December 2017

Here we present a method for measuring the permeability coefficient-surface area product ( PS) values at the blood-brain barrier in mice, using the in situ brain perfusion technique originally developed for rats by Takasato et al. ( Am J Physiol Heart Circ Physiol 247: H484–H493, 1984). Retrograde infusion into the right external carotid artery increased the carotid perfusion pressure in proportion to the perfusion rate. Intravascular volume and cerebral perfusion fluid flow at a perfusion rate of 1.0 ml/min in mice were similar to those in rats. In addition, the contribution of systemic blood to total flow in the hemisphere was small (only 3.2%). These findings indicated that this perfusion rate is suitable for mice. The PS values of more than 20 different compounds were determined in mice by using the in situ brain perfusion technique, and comparisons were made with data from rats. There was a close relationship (1:1) between the PS values in mice and rats, indicating that brain capillary permeabilities are similar in mice and rats.
Increase in peripheral blood flow due to extraocular direct irradiation of visible light in rats
Authors: Kobayashi Keisuke , Kobayashi Yoshiko , Hashida-Okumura Akiko , Iimori Sonoe , Nagai Katsuya , Nakashima Hisao
Published: December 2017

We have conducted experiments to clarify the existence of extraretinal photosensitivity in mammals through the measurements of skin blood flow variation due to light irradiation. We found that blood flow shows a synchronized transient increase with a irradiation-nonirradiation sequence. The action spectrum of the phenomenon was found to show peaks at ∼410–420 nm, 540–550 nm, and 570– 580 nm. These peaks coincide with the specific optical absorption peaks of B and Q (α,β) bands in sixfold coordinated ferruos-heme complexes such as nitric oxide (NO)-Hb. The blood flow increase in the irradiated duration disappears when the rats are intraperitoneally injected with 1H-[1,2,3]oxydiazolo[4,3-a] quinoxalin-1-one (ODQ), which is an inhibitor of guanylate cyclase, and NG-monomethyl-l-arginine acetate and NG-nitro-l-arginine methyl ester, which are inhibitors of NO synthase. On the basis of the present results, we propose a photochemical model of the photosensitivity mechanism where optical absorption of the sixfold coordinated ferrous heme-NO complex plays a main role.
Amlodipine inhibits thapsigargin-sensitive Ca2+stores in thrombin-stimulated vascular smooth muscle cells
Authors: Stepien Olivier , Marche Pierre
Published: December 2017

Ca2+channel blockers, such as amlodipine, inhibit vascular smooth muscle cell (VSMC) growth through interactions with targets other than L-type Ca2+channels. The effects of amlodipine on Ca2+movements in thrombin- and thapsigargin-stimulated VSMCs were therefore investigated by determining the variations of intracellular free Ca2+concentration in fura 2-loaded cultured VSMCs. Results indicated that 10–1,000 nM amlodipine inhibited 1) thrombin-induced Ca2+mobilization from a thapsigargin-sensitive pool and 2) thapsigargin-induced Ca2+responses, including Ca2+mobilization from internal stores and store-operated Ca2+entry. These effects of amlodipine do not involve L-type Ca2+channels and could not be reproduced with 100 nM isradipine, diltiazem, or verapamil. The inhibition by amlodipine of Ca2+mobilization appears therefore to be a specific property of the drug, in addition to its Ca2+channel-blocking property. It is suggested that amlodipine acts in this capacity by interacting with Ca2+-ATPases of the sarcoplasmic reticulum, thus modulating the enzyme activity. This mechanism might participate in the inhibitory effect of amlodipine on VSMC growth.
Renal SNA as the primary mediator of slow oscillations in blood pressure during hemorrhage
Authors: Malpas Simon C. , Burgess Don E.
Published: December 2017

Blood pressure contains a distinct low-frequency oscillation often termed the Mayer wave. This oscillation is caused by the action of the sympathetic nervous system on the vasculature and results from time delays in the baroreflex feedback loop for the control of sympathetic nerve activity (SNA) in response to changes in blood pressure. In this study, we used bilateral renal denervation to test the hypothesis that it is SNA to the kidney that contributes a large portion of the vascular resistance associated with changes in the strength of the slow oscillation in blood pressure. In conscious rabbits, SNA and blood pressure were measured during hemorrhage (blood withdrawal at 1.35 ml · min−1 · kg−1 for 20 min). Spectral analysis identified a strong increase in power at 0.3 Hz in SNA and blood pressure in the initial compensatory phase of hemorrhage before blood pressure started to fall. However, in a separate group of renal denervated rabbits, although the power of the 0.3-Hz oscillation under control conditions in blood pressure was similar, it was not altered during hemorrhage. Wavelet analysis revealed the development of low-frequency oscillations at 0.1 Hz in both intact and denervated animals. In conclusion, we propose that changes in the strength of the oscillation at 0.3 Hz in arterial pressure during hemorrhage are primarily mediated by sympathetic activity directed to the kidney.
Myosin light chain replacement in the heart
Authors: Sanbe Atsushi , Gulick James , Hayes Eric , Warshaw David , Osinska Hanna , Chan Chi-Bew , Klevitsky Raisa , Robbins Jeffrey
Published: December 2017

Myosin-actin cross-bridge kinetics are an important determinant for cardiac systolic and diastolic function. We compared the effects of myosin light chain substitutions on the ability of the fibers to contract in response to calcium and in their ability to produce power. Transgenesis was used to effect essentially complete replacement of the target contractile protein isoform specifically in the heart. Atrial and ventricular fibers derived from the various transgenic (TG) lines were skinned, and the force-velocity relationships, unloaded shortening velocities, and Ca2+-stimulated Mg2+-ATPase activities were determined. Replacement with an ectopic isoform resulted in significant changes in cross-bridge cycling kinetics but without any overt effects on morbidity or mortality. To confirm that this result was not light chain specific, a modified α-myosin heavy chain isoform that resulted in significant changes in force development was also engineered. The animals appeared healthy and have normal lifespans, and the changes in force development did not result in significant remodeling or overt hypertrophy. We conclude that myosin light chains can control aspects of cross-bridge cycling and alter force development. The myosin heavy chain data also show that changes in the kinetics of force development and power output do not necessarily lead to activation of the hypertrophic response or significant cardiac remodeling.
Intact endothelial and smooth muscle function in small resistance arteries after 48 h in vessel culture
Authors: Bolz Steffen-Sebastian , Pieperhoff Susanne , De Wit Cor , Pohl Ulrich
Published: December 2017

Long-term culture of resistance vessels allows introduction of molecular biology techniques for use in microvascular research. The aim of the present study was to establish a culture protocol that preserved vascular integrity and function in microvessels for 48 h in culture. Skeletal muscle resistance arteries were excised from the hamster gracilis muscle. Segments were assigned to immediate functional tests or to vessel culture, during which segments were perfused and superfused at a transmural pressure of 45 mmHg with Leibovitz (L15) medium containing 15% fetal calf serum and antibiotics for 48 h. Cultured and freshly isolated vessels showed similar levels of spontaneous tone, myogenic responses, changes in smooth muscle intracellular calcium (Cai 2+) (fura 2), and vascular diameter (video microscopy) in response to 0.3 M norepinephrine and similar concentration-response curves for acetylcholine (endothelium dependent, ± N ω-nitro-l-arginine) and sodium nitroprusside (endothelium independent). Measurements of endothelial Cai 2+ revealed similar acetylcholine-induced increases in endothelial Cai 2+ in both groups. It is concluded that vascular function can be preserved while maintaining vessels in culture. Thus it is possible to utilize protocols that require long-term treatment.
Fiber type-specific differential expression of angiogenic factors in response to chronic hindlimb ischemia
Authors: Cherwek D. Hunter , Hopkins M. Benjamin , Thompson Michael J. , Annex Brian H. , Taylor Doris A.
Published: December 2017

Alterations in endogenous levels of the angiogenic proteins basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) were assessed in rabbit hindlimb muscles subjected to 1, 5, or 21 days of ischemia. In the glycolytic [tibialis anterior (TA)] and the oxidative [soleus (SOL)] muscles from the ischemic and contralateral (control) hindlimb, bFGF and VEGF protein expression was determined by ELISA and immunoblot analysis. Total VEGF protein expression was greater in oxidative than in glycolytic muscles after 5 days of hindlimb ischemia. In SOL muscle, total VEGF detected by ELISA in ischemic limbs was increased to 137, 300, and 220% of control at 1, 5, and 21 days, respectively. However, in TA, total VEGF expression by ELISA was increased only at 1 and 5 days of ischemia to 140 and 134% of control, respectively. By immunoblotting, the expression of the 165-amino acid isoform (VEGF165) was initially decreased to 55% of control in ischemic SOL at 1 day but was increased to 250% of control at day 5 and remained at 155% at day 21. In TA, VEGF165was increased to 260% of control at 1 day of ischemia but only to 150% of control by day 5. The only significant change in bFGF expression in either the oxidative or glycolytic muscles was a small increase (129% of control) at 21 days in SOL. This study demonstrates that the magnitude and direction of change in VEGF protein expression depend on VEGF subtype, muscle fiber type, and duration of ischemia. These findings suggest that strategies in therapeutic angiogenesis may need to differ depending on muscle fiber type.
Mechanisms of endothelial cell swelling from lactacidosis studied in vitro
Authors: Behmanesh S. , Kempski O.
Published: December 2017

One of the early sequelae of ischemia is an increase of circulating lactic acid that occurs in response to anaerobic metabolism. The purpose of the present study was to investigate whether lactic acidosis can induce endothelial swelling in vitro under closely controlled extracellular conditions. Cell volume of suspended cultured bovine aortic endothelial cells was measured by use of an advanced Coulter technique employing the “pulse area analysis” signal-processing technique (CASY1). The isosmotic reduction of pH from 7.4 to 6.8 had no effect on cell volume. Lowering of pH to 6.6, 6.4, or 6.0, however, led to significant, pH-dependent increases of cell volume. Swelling was more pronounced in bicarbonate-buffered media than in HEPES buffer. Specific inhibition of Na+/H+exchange by ethylisopropylamiloride completely prevented swelling in HEPES-buffered media. Pretreatment with ouabain to partially depolarize the cells did not affect the degree of acidosis-induced swelling. In bicarbonate-buffered media, the inhibition of transmembrane HCO3 − transport by DIDS reduced swelling to a level comparable with that seen in the absence of bicarbonate ions. Lactacidosis-induced endothelial swelling, therefore, is a result of intracellular pH regulatory mechanisms, namely, Na+/H+ exchange and bicarbonate-transporting carriers.
Na+/H+exchange inhibition-induced cardioprotection in dogs: effects on neutrophils versus cardiomyocytes
Authors: Gumina Richard J. , Auchampach John , Wang Rongang , Buerger Erich , Eickmeier Christian , Moore Jeannine , Daemmgen Juergen , Gross Garrett J.
Published: December 2017

Numerous studies have examined the effect of Na+/H+exchanger (NHE) inhibition on the myocardium; however, the effect of NHE-1 inhibition on neutrophil function has not been adequately examined. An in vivo canine model of myocardial ischemia-reperfusion injury in which 60 min of left anterior descending coronary artery occlusion followed by 3 h of reperfusion was used to examine the effect of NHE-1 inhibition on infarct size (IS) and neutrophil function. BIIB-513, a selective inhibitor of NHE-1, was infused before ischemia. IS was expressed as a percentage of area at risk (IS/AAR). NHE-1 inhibition significantly reduced IS/AAR and reduced neutrophil accumulation in the ischemic myocardium. NHE-1 inhibition attenuated both phorbol 12-myristate 13-acetate- and platelet-activating factor-induced neutrophil respiratory burst but not CD18 upregulation. Furthermore, NHE-1 inhibition directly protected cardiomyocytes against metabolic inhibition-induced lactate dehydrogenase release and hypercontracture. This study provides evidence that the cardioprotection induced by NHE-1 inhibition is likely due to specific protection of cardiomyocytes and attenuation of neutrophil activity.
Virtual sources associated with linear and curved strands of cardiac cells
Authors: Tung Leslie , Kléber André G.
Published: December 2017

Transmembrane potential ( V m) responses in cardiac strands with different curvature were characterized during uniform electric-field stimulation with the use of modeling and experimental approaches. Linear and U-shaped strands (width 100–150 μm) were stained with voltage-sensitive dye. V m was measured by optical mapping across the width and at sites of beginning curvature. Field pulses were applied transverse to the strands during the action-potential plateau. For linear strands, V mcontained 1) a rapid passive component ( V m ar) nearly linear and symmetric across the width, 2) a slower hyperpolarizing component ( V m as) greater and faster on the anodal side, and 3) at high field strengths a delayed depolarizing component ( V m ad) greater on the anodal side. For U-shaped strands, V m at sites of beginning curvature also contained rapid and slow components ( V m br and V m bs, respectively) that included contributions from the linear strand response and from the fiber curvature. V m ar, V m br, and part of V m bs could be attributed to passive behavior that was modeled, and V m as, V m ad, and part of V m bs could be attributed to active membrane currents. Thus curved strands exhibit field responses separable into components with characteristic amplitude, spatial, and temporal signatures.
Effect of hypercholesterolemia on Ca2+-dependent K+ channel-mediated vasodilatation in vivo
Authors: Jeremy Richmond W. , McCarron Hugh
Published: December 2017

Nitric oxide (NO)-mediated and NO-independent mechanisms of endothelium-dependent vasodilatation involve Ca2+-dependent K+ (KCa) channels. We examined the role in vivo of KCa channels in NO-independent vasodilatation in hypercholesterolemia. Hindlimb vascular conductance was measured at rest and after aortic injection of ACh, bradykinin (BK), and sodium nitroprusside in anesthetized control and cholesterol-fed rabbits. Conductances were measured before and after treatment with the NO synthase antagonist N ω-nitro-l-arginine methyl ester (l-NAME, 10 mg/kg) or KCa blockers tetraethylammonium (30 mg/kg), charybdotoxin (10 μg/kg), and apamin (50 μg/kg). The contribution of NO to basal conductance was greater in control than in cholesterol-fed rabbits [2.2 ± 0.4 vs. 1.1 ± 0.3 (SE) ml · min−1 · kg−1 · 100 mmHg−1, P < 0.05], but the NO-independent KCa channel-mediated component was greater in the cholesterol-fed than in the control group (1.1 + 0.4 vs. 0.3 ± 0.1 ml · min−1 · kg−1 · 100 mmHg−1, P < 0.05). Maximum conductance response to ACh and BK was less in cholesterol-fed than in control rabbits, and the difference persisted after l-NAME (ACh: 7.7 ± 0.7 vs. 10.1 ± 0.5 ml · min−1 · kg−1 · 100 mmHg−1, P < 0.005). Blockade of KCa channels with tetraethylammonium or charybdotoxin + apamin almost completely abolished l-NAME-resistant vasodilatation after ACh or BK. The magnitude of KCa-mediated vasodilatation after ACh or BK was impaired in hypercholesterolemic rabbits. Vasodilator responses to nitroprusside did not differ between groups. In vivo , hypercholesterolemia is associated with an altered balance between NO-mediated and NO-independent KCa channel contributions to resting vasomotor tone and impairment of both mechanisms of endothelium-dependent vasodilatation.
Reduced contractile response to insulin and IGF-I in ventricular myocytes from genetically obese Zucker rats
Authors: Ren Jun , Sowers James R. , Walsh Mary F. , Brown Ricardo A.
Published: December 2017

Obesity plays a pivotal role in the pathophysiology of metabolic and cardiovascular diseases. Resistance to insulin is commonly seen in metabolic disorders such as obesity and diabetes. Insulin-like growth factor-I (IGF-I) mimics insulin in many tissues and has been shown to enhance cardiac contractile function and growth. Because IGF-I resistance often accompanies resistance to insulin, we sought to determine whether IGF-I-induced myocardial contractile was elevated and whether heart and kidney size were enlarged in obese compared with lean rats. The myocyte contraction profile in the obese rats showed a decreased peak shortening associated with prolonged relengthening and normal shortening duration, a pattern similar to that observed in diabetes. IGF-I (1–500 ng/ml) caused a dose-dependent increase in peak shortening in lean but not obese animals, but it did not alter the duration of shortening and relengthening. Consistent with contractile data, IGF-I induced a dose-dependent increase in Ca2+transients only in myocytes of lean rats. IGF-I receptor mRNA levels were significantly reduced in obese rat hearts. These results suggest that the IGF-I-induced cardiac contractile responses are attenuated in the Zucker model of obesity. The mechanisms underlying this alteration may be related to the decreased receptor number and/or changes in intracellular Ca2+handling in these animals.
Prior exercise training increases collateral-dependent blood flow in rats after acute femoral artery occlusion
Authors: Yang H. T. , Laughlin M. Harold , Terjung Ronald L.
Published: December 2017

We evaluated whether prior training would improve collateral blood flow (BF) to the calf muscles after acute-onset occlusion of the femoral artery. Exercise training was performed in the absence of any vascular occlusion. Adult male Sprague-Dawley rats (∼325 g) were kept sedentary ( n = 14), limited to cage activity, or exercise trained ( n = 14) for 6 wk by treadmill running. Early in the day of measurement, animals were surgically prepared for BF determination, and the femoral arteries were occluded bilaterally. Four to five hours later, collateral BF was determined twice during treadmill running with the use of 141Ce and85Sr microspheres: first, at a demanding speed and, second, after a brief rest and at a higher speed. The absence of any further increase in BF at the higher speed indicated that maximal collateral BF was measured. Prior training increased calf muscle BF by ∼70% compared with sedentary animals; however, absolute BF remained below values previously observed in animals with a well-developed collateral vascular tree. Thus prior training appeared to optimize the use of the existing collateral circuit. This implies that altered vasoresponsiveness induced in normal nonoccluded vessels with exercise training serves to improve collateral BF to the periphery.
Cardioprotection with κ-opioid receptor stimulation is associated with a slowing of cross-bridge cycling
Authors: Pyle W. G. , Smith T. D. , Hofmann P. A.
Published: December 2017

Opioid and α-adrenergic receptor activation protect the heart from ischemic damage. One possible intracellular mechanism to explain this is that an improvement in ATP availability contributes to cardioprotection. We tested this hypothesis by correlating postischemic left ventricular developed pressure (LVDP) and myofibrillar Ca2+-dependent actomyosin Mg2+-ATPase from isolated rat hearts treated with the κ-opioid receptor agonist U-50488H (1 μM) or the α-adrenergic receptor agonist phenylephrine (10 μM) + propranolol (3 μM). Preischemic treatment with U-50488H or phenylephrine + propranolol improved postischemic LVDP recovery by 25–30% over control hearts. Ca2+-dependent actomyosin Mg2+-ATPase was found to be 20% lower in both U-50488H- and phenylephrine + propranolol-treated hearts compared with control hearts. The κ-opioid receptor antagonist nor-binaltorphimine (1 μM) abolished the effects of U-50488H on postischemic LVDP and actomyosin Mg2+-ATPase activity. Reduced actomyosin ATP utilization was also suggested in single ventricular myocytes treated with either U-50488H or the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), because U-50488H and PMA lowered maximum velocity of unloaded shortening by 15–25% in myocytes. U-50488H and phenylephrine + propranolol treatment both resulted in increased phosphorylation of troponin I and C protein. These findings are consistent with the hypothesis that κ-opioid and α-adrenergic receptors decrease actin-myosin cycling rate, leading to a conservation of ATP and cardioprotection during ischemia.
Endotoxin infusion in rats induces apoptotic and survival pathways in hearts
Authors: McDonald Treena E. , Grinman Michelle N. , Carthy Chris M. , Walley Keith R.
Published: December 2017

Inflammatory mediators of sepsis induce apoptosis in many cell lines. We tested the hypothesis that lipopolysaccharide (LPS) injection in vivo results in induction of early apoptotic and survival pathways as well as evidence of late-stage apoptosis in the heart. Hearts were collected from control rats and at 6, 12, and 24 h after LPS injection (4 mg/kg). Activation of an apoptotic pathway was identified by a 1,000-fold increase in caspase-3 activity at 24 h ( P < 0.05). Confirmation of these results occurred when terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining identified myocardial cells undergoing DNA fragmentation with significant levels at 24 h post-LPS injection. LPS also caused early proapoptotic mRNA (Bax) to increase (16% at 24 h, P < 0.05), whereas the Bax protein initially decreased (35% at 6 h, P < 0.05) and then returned to baseline values by 24 h. Six hours after LPS injection, Bcl-2 (early prosurvival) mRNA levels increased, whereas its protein levels decreased (70%, P < 0.05) and then returned to baseline levels by 24 h. Mitochondrial cytochrome c levels decreased, suggestive of mitochondrial involvement. Thus involvement of proapoptotic and prosurvival pathways in the heart occurs during a septic inflammatory response.
Inhibition of NHE protects reoxygenated cardiomyocytes independently of anoxic Ca2+overload and acidosis
Authors: Schäfer C. , Ladilov Y. V. , Schäfer M. , Piper H. M.
Published: December 2017

We investigated the question of whether inhibition of the Na+/H+exchanger (NHE) during ischemia is protective due to reduction of cytosolic Ca2+accumulation or enhanced acidosis in cardiomyocytes. Additionally, the role of the Na+-HCO3−symporter (NBS) was investigated. Adult rat cardiomyocytes were exposed to simulated ischemia and reoxygenation. Cytosolic pH [2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)], Ca2+(fura 2), Na+[sodium-binding benzolfuran isophthatlate (SBFI)], and cell length were measured. NHE was inhibited with 3 μmol/l HOE 642 or 1 μmol/l 5-( N-ethyl- N-isopropyl)-amiloride (EIPA), and NBS was inhibited with HEPES buffer. During anoxia in bicarbonate buffer, cells developed acidosis and intracellular Na and Ca (Naiand Cai, respectively) overload. During reoxygenation cells underwent hypercontracture (44.0 ± 4.1% of the preanoxic length). During anoxia in bicarbonate buffer, inhibition of NHE had no effect on changes in intracellular pH (pHi), Nai, and Cai, but it significantly reduced the reoxygenation-induced hypercontracture (HOE: 61.0 ± 1.4%, EIPA: 68.2 ± 1.8%). The sole inhibition of NBS during anoxia was not protective. We conclude that inhibition of NHE during anoxia protects cardiomyocytes against reoxygenation injury independently of cytosolic acidification and Caioverload.
Hemodynamic changes in apolipoprotein E-knockout mice
Authors: Hartley Craig J. , Reddy Anilkumar K. , Madala Sridhar , Martin-McNulty Baby , Vergona Ronald , Sullivan Mark E. , Halks-Miller Meredith , Taffet George E. , Michael Lloyd H. , Entman Mark L. , Wang Yi-Xin
Published: December 2017

Apolipoprotein E-knockout (ApoE-KO) mice develop advanced atherosclerotic lesions by 1 yr of age and have been well characterized pathologically and morphologically, but little is known regarding their cardiovascular physiology and hemodynamics. We used noninvasive Doppler ultrasound to measure aortic and mitral blood velocity and aortic pulse-wave velocity in 13-mo-old ApoE-KO and wild-type (WT) mice anesthetized with isoflurane. In other mice from the same colony, we measured systolic blood pressure, body weight, heart weight, cholesterol, and hematocrit. Heart rate and blood pressure were comparable ( P = not significant) between ApoE-KO and WT mice, but significant decreases ( P < 0.001) were found in body weight (−22%) and hematocrit (−11%), and significant increases were found in heart weight (+23%), aortic velocity (+60%), mitral velocity (+81%) (all P < 0.001), and pulse-wave velocity (+13%, P < 0.05). We also found inflections in the aortic arch velocity signal consistent with enhanced peripheral wave reflection. Thus ApoE-KO mice have phenotypic alterations in indexes of peripheral vascular resistance and compliance and significantly elevated cardiac outflow velocities and heart weight-to-body weight ratios.
Changes in venous return parameters associated with univentricular Fontan circulations
Authors: Macé Loïc , Dervanian Patrice , Bourriez Armand , Mazmanian Guy M. , Lambert Virginie , Losay Jean , Neveux Jean-Yves
Published: December 2017

To clarify the physiology of venous return (Qvr) in Fontan circulations, venous return conductance ( Gvr) and mean circulatory filling pressure (Pmcf) were determined in pentobarbital sodium-anesthetized pigs. Relationships between Qvrand right (biventricular, n = 8) or left (Fontan, n = 8) filling pressures are described by straight lines with significant correlation coefficients. Estimated Pmcfvalues were correlated with observed Pmcfvalues in either circulations ( P ≤ 0.02). Gvrwas smaller in Fontan than in biventricular circulations (4.51 ± 0.36 vs. 7.83 ± 0.69 ml · min−1· kg−1· mmHg−1, P = 0.002) and inversely correlated with pulmonary vascular resistances in Fontan circulations ( P = 0.01). Estimated Pmcf(20.5 ± 1.4 vs. 11.1 ± 0.9 mmHg, P = 0.001) and observed Pmcf(21.8 ± 1.3 vs. 10.6 ± 0.8 mmHg, P < 0.001) were higher in Fontan versus biventricular circulations, respectively. Pulmonary artery pressure in Fontan circulations was correlated with either Pmcf( P ≤ 0.04). We conclude that in Fontan circulations 1) pulmonary vascular resistances induce a proportional decrease in Gvr; and 2) volume loading, while increasing Pmcf(similar to pulmonary artery pressure), allows the gradient for Qvrto increase and maintains systemic blood flow at a biventricular level.
Nitric oxide-dependent pulmonary vasodilation in polycythemic rats
Authors: Walker Benjimen R. , Resta Thomas C. , Nelin Leif D.
Published: December 2017

Polycythemia causes increased vascular production of nitric oxide (NO), most likely secondary to an effect of elevated vascular shear stress to enhance expression of endothelial nitric oxide synthase (eNOS). Because both polycythemia and increased eNOS expression are associated with chronic hypoxia-induced pulmonary hypertension, experiments were performed to test the hypothesis that increased hematocrit leads to upregulation of pulmonary eNOS and enhanced vascular production of NO independent of hypoxia. Rats were administered human recombinant erythropoietin (rEpo; 48 U/day) or vehicle for 2 wk. At the time of study, hematocrit was significantly greater in the rEpo-treated group than in the vehicle group (65.8 ± 0.7% vs. 45.1 ± 0.5%), although mean pulmonary artery pressure did not differ between treatments. Experiments on isolated, saline-perfused lungs demonstrated similar vasodilatory responses to the endothelium-derived NO-dependent agonist ionomycin in each group. Additional experiments showed that the vasoconstrictor response to the thromboxane mimetic U-46619 was diminished at lower doses in lungs from the rEpo group compared with the vehicle group. However, perfusate nitrite/nitrate concentration after 90 min of perfusion in isolated lungs was not different between groups. Additionally, no difference was detected between groups in lung eNOS levels by Western blot. We conclude that the predicted increase in shear stress associated with polycythemia does not result in altered pulmonary eNOS expression.
Partitioning of pyruvate between oxidation and anaplerosis in swine hearts
Authors: Panchal Ashish R. , Comte Blandine , Huang Hazel , Kerwin Todd , Darvish Ahmed , Rosiers Christine Des , Brunengraber Henri , Stanley William C.
Published: December 2017

The goal of this study was to measure flux through pyruvate carboxylation and decarboxylation in the heart in vivo. These rates were measured in the anterior wall of normal anesthetized swine hearts by infusing [U-13C3]lactate and/or [U-13C3] pyruvate into the left anterior descending (LAD) coronary artery. After 1 h, the tissue was freeze-clamped and analyzed by gas chromatography-mass spectrometry for the mass isotopomer distribution of citrate and its oxaloacetate moiety. LAD blood pyruvate and lactate enrichments and concentrations were constant after 15 min of infusion. Under near-normal physiological concentrations of lactate and pyruvate, pyruvate carboxylation and decarboxylation accounted for 4.7 ± 0.3 and 41.5 ± 2.0% of citrate formation, respectively. Similar relative fluxes were found when arterial pyruvate was raised from 0.2 to 1.1 mM. Addition of 1 mM octanoate to 1 mM pyruvate inhibited pyruvate decarboxylation by 93% without affecting carboxylation. The absence of M1 and M2 pyruvate demonstrated net irreversible pyruvate carboxylation. Under our experimental conditions we found that pyruvate carboxylation in the in vivo heart accounts for at least 3–6% of the citric acid cycle flux despite considerable variation in the flux through pyruvate decarboxylation.
Altered β-adrenergic signal transduction in nonfailing hypertrophied myocytes from Dahl salt-sensitive rats
Authors: Nagata Kohzo , Communal Catherine , Lim Chee C. , Jain Mohit , Suter Thomas M. , Eberli Franz R. , Satoh Naoya , Colucci Wilson S. , Apstein Carl S. , Liao Ronglih
Published: December 2017

Desensitization of the β-adrenergic receptor (β-AR) response is well documented in hypertrophied hearts. We investigated whether β-AR desensitization is also present at the cellular level in hypertrophied myocardium, as well as the physiological role of inhibitory G (Gi) proteins and the L-type Ca2+channel in mediating β-AR desensitization. Left ventricular (LV) myocytes were isolated from hypertrophied hearts of hypertensive Dahl salt-sensitive (DS) rats and nonhypertrophied hearts of normotensive salt-resistant (DR) rats. Cells were paced at a rate of 300 beats/min at 37°C, and myocyte contractility and intracellular Ca2+concentration ([Ca2+]i) were simultaneously measured. In response to increasing concentrations of isoproterenol, DR myocytes displayed a dose-dependent augmentation of cell shortening and the [Ca2+]i transient amplitude, whereas hypertrophied DS myocytes had a blunted response of both cell shortening and the [Ca2+]i transient amplitude. Interestingly, inhibition of Gi proteins did not restore β-AR desensitization in DS myocytes. The responses to increases in extracellular Ca2+ and an L-type Ca2+ channel agonist were also similar in both DS and DR myocytes. Isoproterenol-stimulated adenylyl cyclase activity, however, was blunted in hypertrophied myocytes. We concluded that compensated ventricular hypertrophy results in a blunted contractile response to β-AR stimulation, which is present at the cellular level and independent of alterations in inhibitory G proteins and the L-type Ca2+ channel.