bluuebunny/crossref_metadata_2025 huggingface dataset:
Degradation of α-actin filaments in venous smooth muscle cells in response to mechanical stretch
Authors: Goldman Jeremy , Zhong Lin , Liu Shu Q.
Published: March 2015

Mechanical stretch has been shown to induce the degradation of α-actin filaments in smooth muscle cells (SMC) of experimental vein grafts. Here, we investigate the possible role of ERK1/2 and p38 MAPK in regulating this process using an ex vivo venous culture model that simulates an experimental vein graft. An exposure of a vein to arterial pressure induced a significant increase in the medial circumferential strain, which induced rapid α-actin filament disruption, followed by degradation. The percentage of SMC α-actin filament coverage was reduced significantly under arterial pressure (91 ± 1%, 43 ± 13%, 51 ± 5%, 28 ± 3%, and 19 ± 5% at 1, 6, 12, 24, and 48 h, respectively), whereas it did not change significantly in specimens under venous pressure at theses times. The degradation of SMC α-actin filaments paralleled an increase in the relative activity of caspase 3 (3.0 ± 0.7- and 1.7 ± 0.4-fold increase relative to the control level at 6 and 12 h, respectively) and a decrease in SMC density (from the control level of 1,368 ± 66 cells/mm2 at time 0 to 1,205 ± 90, 783 ± 129, 845 ± 61, 637 ± 55, and 432 ± 125 cells/mm2 at 1, 6, 12 , 24, and 48 h of exposure to arterial pressure, respectively). Treatment with a p38 MAPK inhibitor (SB-203580) significantly reduced the stretch-induced activation of caspase 3 at 6 h (from 3.0 ± 0.7- to 2.2 ± 0.3-fold) in conjunction with a significant rescue of α-actin filament degradation (from 43 ± 13% to 69 ± 15%) at the same time. Treatment with an inhibitor for the ERK1/2 activator (PD-98059), however, did not induce a significant change in the activity of caspase 3 or the percentage of SMC α-actin filament coverage. These results suggest that p38 MAPK and caspase 3 may mediate stretch-dependent degradation of α-actin filaments in vascular SMCs.
Remodeling of the adventitia during coronary arteriogenesis
Authors: Cai Wei-Jun , Koltai Sophie , Kocsis Elisabeth , Scholz Dimitri , Kostin Sawa , Luo Xuegang , Schaper Wolfgang , Schaper Jutta
Published: March 2015

We studied the role of the adventitia in adaptive arteriogenesis during the phase of active growth of coronary collateral vessels (CV) induced by chronic occlusion of the left circumflex coronary artery in canine hearts. We used electron microscopy and immunoconfocal (IF) labeling for bFGF, matrix metalloproteinase (MMP)-2, MMP-9, tissue-type plasminogen activator (tPA), its inhibitor (PAI-1), fibronectin (FN), and Ki-67. Proliferation of smooth muscle cells and adventitial fibroblasts was evident. Quantitative IF showed that adventitial MMP-2, MMP-9, and FN were 9.2-, 7.5-, and 8.6-fold, bFGF was 5.1-fold, and PAI-1 was 3.4-fold higher in CV than in normal vessels (NV). The number of fibroblasts was 5-fold elevated in CV, but the elastic fiber content was 25-fold greater in NV than in CV. Perivascular myocyte damage and induction of endothelial nitric oxide synthase in peri-CV capillaries indicate expansion of CV. It was concluded that adventitial activation is associated with the development of CV through cell proliferation, production of growth factors, and induction of extracellular proteolysis thereby contributing to remodeling during adaptive arteriogenesis.
Alterations in ET-1, not nitric oxide, in 1-week-old lambs with increased pulmonary blood flow
Authors: Ovadia Boaz , Reinhartz Olaf , Fitzgerald Robert , Bekker Janine M. , Johengen Michael J. , Azakie Anthony , Thelitz Stephan , Black Stephen M. , Fineman Jeffrey R.
Published: March 2015

Altered pulmonary vascular reactivity is a source of morbidity and mortality for children with congenital heart disease and increased pulmonary blood flow. Nitric oxide (NO) and endothelin (ET)-1 are important mediators of pulmonary vascular reactivity. We hypothesize that early alterations in endothelial function contribute to the altered vascular reactivity associated with congenital heart disease. The objective of this study was to characterize endothelial function in our lamb model of increased pulmonary blood flow at 1 wk of life. Eleven fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt) and were studied 7 days after delivery. The pulmonary vasodilator response to both intravenous ACh (endothelium dependent) and inhaled NO (endothelium independent) was similar in shunted and control lambs. In addition, tissue NOx, NO synthase (NOS) activity, and endothelial NOS protein levels were similar. Conversely, the vasodilator response to both ET-1 and 4Ala-ET-1 (an ETBreceptor agonist) were attenuated in shunted lambs, and tissue ET-1 concentrations were increased ( P < 0.05). Associated with these changes were an increase in ET-converting enzyme-1 protein and a decrease in ETBreceptor protein levels ( P < 0.05). These data demonstrate that increased pulmonary blood flow induces alterations in ET-1 signaling before NO signaling and suggest an early role for ET-1 in the altered vascular reactivity associated with increased pulmonary blood flow.
OxLDL stimulates cell proliferation through a general induction of cell cycle proteins
Authors: Zettler Marjorie E. , Prociuk Michele A. , Austria J. Alejandro , Massaeli Hamid , Zhong Guangming , Pierce Grant N.
Published: March 2015

Oxidized low-density lipoprotein (oxLDL) may be involved in atherosclerosis by stimulating proliferation of cells in the vessel wall. The purpose of this study was to identify the mechanism by which oxLDL induces proliferation. Quiescent human fibroblasts and rabbit smooth muscle cells were treated with 0, 10, or 50 μg/ml oxLDL for 24–48 h. This resulted in significant increases in total cell counts at both concentrations of oxLDL, at both time points, for both types of cells. Western blot analysis revealed that oxLDL-stimulated cell proliferation was associated with significant increases in the expression of proteins that regulate entry into and progression through the cell cycle [cell division cycle 2, cyclin-dependent kinase (cdk) 2, cdk 4, cyclin B1, cyclin D1, and PCNA]. Surprisingly, the expression of cell cycle inhibitors (p21 and p27) was stimulated by oxLDL as well, but this was to a lesser extent than the effects on cell cycle-activating proteins. OxLDL also induced nuclear localization of all cell cycle proteins examined. The similar effects of oxLDL on the translocation and expression of both cell cycle-activating and -inhibiting proteins may explain the controlled proliferative phenomenon observed in atherosclerosis as opposed to the more rapid proliferative event characteristic of cancer.
Modulation of collateral artery growth in a porcine hindlimb ligation model using MCP-1
Authors: Voskuil Michiel , van Royen Niels , Hoefer Imo E. , Seidler Randolph , Guth Brian D. , Bode Christoph , Schaper Wolfgang , Piek Jan J. , Buschmann Ivo R.
Published: March 2015

For an appropriate extrapolation to patients with peripheral arterial obstructive disease, we tested the efficacy of monocyte chemoattractant protein 1 (MCP-1) treatment in a porcine hindlimb ligation model. In 40 minipigs, a femoral artery ligation was performed. Control animals were examined immediately after ligation ( n = 4) or after 2 wk of intra-arterial infusion of PBS ( n = 11). A second group of animals was evaluated after intra-arterial infusion of 2.0 μg/h of MCP-1 for 48 h (followed by 12 days of PBS; n = 13) or 2 wk continuously ( n = 12). In the terminal experiment after 2 wk, resting flow to the leg and peripheral arterial pressures were assessed without vasodilatation. Subsequently, vascular conductance was determined by using a pump-driven extracorporal circulation during maximal vasodilatation. The results showed that resting blood flow to the hindlimb was 53% of the normal after 2 wk of infusion of PBS, compared with 81% in both MCP-1 treatment groups ( P < 0.05). Collateral conductance was 645 ± 346 ml · min−1 · mmHg−1after 2 wk of infusion with PBS, compared with 1,070 ± 530 and 1,158 ± 535 ml · min−1 · mmHg−1after 48 h and 2 wk treatment with MCP-1, respectively ( P < 0.05). Modulation of the process of arteriogenesis is feasible in this large animal model via intra-arterial infusion of the Cys-Cys-chemokine MCP-1.
Oxidized low-density lipoprotein and 15-deoxy-Δ12,14-PGJ2increase mitochondrial complex I activity in endothelial cells
Authors: Ceaser Erin K. , Ramachandran Anup , Levonen Anna-Liisa , Darley-Usmar Victor M.
Published: March 2015

Oxidized lipids are capable of initiating diverse cellular responses through both receptor-mediated mechanisms and direct posttranslational modification of proteins. Typically, exposure of cells to low concentrations of oxidized lipids induces cytoprotective pathways, whereas high concentrations result in apoptosis. Interestingly, mitochondria can contribute to processes that result in either cytoprotection or cell death. The role of antioxidant defenses such as glutathione in adaptation to stress has been established, but the potential interaction with mitochondrial function is unknown and is examined in this article. Human umbilical vein endothelial cells (HUVEC) were exposed to oxidized LDL (oxLDL) or the electrophilic cyclopentenone 15-deoxy-Δ12,14-PGJ2(15d-PGJ2). We demonstrate that complex I activity, but not citrate synthase or cytochrome- c oxidase, is significantly induced by oxLDL and 15d-PGJ2. The mechanism is not clear at present but is independent of the induction of GSH, peroxisome proliferator-activated receptor (PPAR)-γ, and PPAR-α. This response is dependent on the induction of oxidative stress in the cells because it can be prevented by nitric oxide, probucol, and the SOD mimetic manganese(III) tetrakis(4-benzoic acid) porphyrin chloride. This increased complex I activity appears to contribute to protection against apoptosis induced by 4-hydroxynonenal.
Role of AT2receptor in the brain in regulation of blood pressure and water intake
Authors: Li Zhen , Iwai Masaru , Wu Lan , Shiuchi Tetsuya , Jinno Toyohisa , Cui Tai-Xing , Horiuchi Masatsugu
Published: March 2015

The effects of intracerebroventricular (ICV) injection of angiotensin II (ANG II) on blood pressure and water intake were examined with the use of ANG II receptor-deficient mice. ICV injection of ANG II increased systolic blood pressure in a dose-dependent manner in wild-type (WT) mice and ANG type 2 AT2receptor null (knockout) (AT2KO) mice; however, this increase was significantly greater in AT2KO mice than in WT mice. The pressor response to a central injection of ANG II in WT mice was inhibited by ICV preinjection of the selective AT1receptor blocker valsartan but exaggerated by the AT2receptor blocker PD-123319. ICV injection of ANG II also increased water intake. It was partly but significantly suppressed both in AT2KO and AT1aKO mice. Water intake in AT2/AT1aKO mice did not respond to ICV injection of ANG II. Both valsartan and PD-123319 partly inhibited water intake in WT mice. These results indicate an antagonistic action between central AT1a and AT2receptors in the regulation of blood pressure, but they act synergistically in the regulation of water intake induced by ANG II.
Role of xanthine oxidoreductase and NAD(P)H oxidase in endothelial superoxide production in response to oscillatory shear stress
Authors: McNally J. Scott , Davis Michael E. , Giddens Don P. , Saha Aniket , Hwang Jinah , Dikalov Sergey , Jo Hanjoong , Harrison David G.
Published: March 2015

Oscillatory shear stress occurs at sites of the circulation that are vulnerable to atherosclerosis. Because oxidative stress contributes to atherosclerosis, we sought to determine whether oscillatory shear stress increases endothelial production of reactive oxygen species and to define the enzymes responsible for this phenomenon. Bovine aortic endothelial cells were exposed to static, laminar (15 dyn/cm2), and oscillatory shear stress (±15 dyn/cm2). Oscillatory shear increased superoxide ([Formula: see text]) production by more than threefold over static and laminar conditions as detected using electron spin resonance (ESR). This increase in [Formula: see text] was inhibited by oxypurinol and culture of endothelial cells with tungsten but not by inhibitors of other enzymatic sources. Oxypurinol also prevented H2O2production in response to oscillatory shear stress as measured by dichlorofluorescin diacetate and Amplex Red fluorescence. Xanthine-dependent [Formula: see text] production was increased in homogenates of endothelial cells exposed to oscillatory shear stress. This was associated with decreased xanthine dehydrogenase (XDH) protein levels and enzymatic activity resulting in an elevated ratio of xanthine oxidase (XO) to XDH. We also studied endothelial cells lacking the p47phoxsubunit of the NAD(P)H oxidase. These cells exhibited dramatically depressed [Formula: see text] production and had minimal XO protein and activity. Transfection of these cells with p47phoxrestored XO protein levels. Finally, in bovine aortic endothelial cells, prolonged inhibition of the NAD(P)H oxidase with apocynin decreased XO protein levels and prevented endothelial cell stimulation of [Formula: see text] production in response to oscillatory shear stress. These data suggest that the NAD(P)H oxidase maintains endothelial cell XO levels and that XO is responsible for increased reactive oxygen species production in response to oscillatory shear stress.
Glycation end-product cross-link breaker reduces collagen and improves cardiac function in aging diabetic heart
Authors: Liu Jing , Masurekar Malthi R. , Vatner Dorothy E. , Jyothirmayi Garikiparthy N. , Regan Timothy J. , Vatner Stephen F. , Meggs Leonard G. , Malhotra Ashwani
Published: March 2015

Aging and diabetes mellitus (DM) both affect the structure and function of the myocardium, resulting in increased collagen in the heart and reduced cardiac function. As part of this process, hyperglycemia is a stimulus for the production of advanced glycation end products (AGEs), which covalently modify proteins and impair cell function. The goals of this study were first to examine the combined effects of aging and DM on hemodynamics and collagen types in the myocardium in 12 dogs, 9–12 yr old, and second to examine the effects of the AGE cross-link breaker phenyl-4,5-dimethylthazolium chloride (ALT-711) on myocardial collagen protein content, aortic stiffness, and left ventricular (LV) function in the aged diabetic heart. The alloxan model of DM was utilized to study the effects of DM on the aging heart. DM induced in the aging heart decreased LV systolic function (LV ejection fraction fell by 25%), increased aortic stiffness, and increased collagen type I and type III protein content. ALT-711 restored LV ejection fraction, reduced aortic stiffness and LV mass with no reduction in blood glucose level (199 ± 17 mg/dl), and reversed the upregulation of collagen type I and type III. Myocardial LV collagen solubility (%) increased significantly after treatment with ALT-711. These data suggest that an AGE cross-link breaker may have a therapeutic role in aged patients with DM.
Scaling vs. nonscaling methods of assessing autonomic tone in streptozotocin-induced diabetic rats
Authors: Perlstein Itay , Sapir Nir , Backon Joshua , Sapoznikov Dan , Karasik Roman , Havlin Shlomo , Hoffman Amnon
Published: March 2015

We studied heart rate variability in rats by power scaling spectral analysis (PSSA), autoregressive modeling (AR), and detrended fluctuation analysis (DFA), assessed stability by coefficient of variation between consecutive 6-h epochs, and then compared cross-correlation among techniques. These same parameters were checked from baseline conditions through acute and chronic disease states (streptozotocin-induced diabetes) followed by therapeutic intervention (insulin). Cross-correlation between methods over the entire time period was r = 0.94 (DFA and PSSA), r = 0.81 (DFA and AR), and r = 0.77 (AR and PSSA). Under baseline conditions the scaling parameter measured by DFA and PSSA and the high-frequency (HF) component measured by AR fluctuated around an average value, but these fluctuations were different for the three methods. After diabetes induction, a strong correlation was found between the HF power and the short-term scaling parameter. Despite their differences in methodology, DFA and PSSA assess changes in parasympathetic tone as detected by autoregressive modeling.
Glutamate causes a loss in human cerebral endothelial barrier integrity through activation of NMDA receptor
Authors: Sharp Christopher D. , Hines I. , Houghton J. , Warren A. , Jackson T. H. , Jawahar A. , Nanda A. , Elrod J. W. , Long A. , Chi A. , Minagar A. , Alexander J. S.
Published: March 2015

l-Glutamate is a major excitatory neurotransmitter that binds ionotropic and metabotropic glutamate receptors. Cerebral endothelial cells from many species have been shown to express several forms of glutamate receptors; however, human cerebral endothelial cells have not been shown to express either the N-methyl-d-aspartate (NMDA) receptor message or protein. This study provides evidence that human cerebral endothelial cells express the message and protein for NMDA receptors. Human cerebral endothelial cell monolayer electrical resistance changes in response to glutamate receptor agonists, antagonists, and second message blockers were tested. RT-PCR and Western blot analysis were used to demonstrate the presence of the NMDA receptor. Glutamate and NMDA (1 mM) caused a significant decrease in electrical resistance compared with sham control at 2 h postexposure; this response could be blocked significantly by MK-801 (an NMDA antagonist), 8-( N,N-diethylamino)- n-octyl-3,4,5-trimethyoxybenzoate (an intracellular Ca2+antagonist), and N-acetyl-l-cystein (an antioxidant). Trans(±)-1-amino-1,3-cyclopentanedicarboxylic acid, a metabotropic receptor agonist (1 mM), did not significantly decrease electrical resistance. Our results are consistent with a model where glutamate, at excitotoxic levels, may lead to a breakdown in the blood brain barrier via activation of NMDA receptors.
Shift in metabolic substrate uptake by the heart during development of alloxan-induced diabetes
Authors: Linke Axel , Zhao Gong , Recchia Fabio A. , Williams Jeffrey , Xu Xiaobin , Hintze Thomas H.
Published: March 2015

Inhibition of endothelial nitric oxide (NO) synthase (eNOS) is associated with an increase in glucose uptake by the heart. We have already shown that Type I diabetes also causes a decrease in eNOS protein expression and altered NO control of both coronary vascular resistance and oxygen consumption. Therefore, we predict that the increase in plasma glucose and the reduction in eNOS during diabetes together would result in a large increase in cardiac glucose uptake. Arterial (A) and coronary sinus (C) plasma levels of glucose, free fatty acid (FFA), β-hydroxybutyric acid (β-HBA), and lactate were measured, and myocardial uptake was calculated before and at week 1, 2, 3, and 4 of alloxan-induced diabetes. The heart of healthy dogs consumed FFA (19.2 ± 2.6 μeq/min) and lactate (19.7 ± 3.4 μmol/min). Dogs in the late stage of diabetes (at week 4) had elevated arterial β-HBA concentrations (1.6 ± 0.7 μmol/l) that were accompanied by an increased β-HBA uptake (0.3 ± 0.2 μmol/min). In contrast, myocardial lactate (–4.8 ± 3.0 μmol/min) and FFA uptake (2.5 ± 1.9 μeq/min) were significantly reduced in diabetic animals. Despite a marked hyperglycemia (449 ± 25 mg/dl), the heart did not take up glucose (–7.9 ± 4.1 mg/dl). Our results indicate significant changes in the myocardial substrate utilization in dogs only in the late stage of diabetes, at a time when myocardial NO production is already decreased.
Neurokinin-1 receptor-expressing cells regulate depressor region of rat ventrolateral medulla
Authors: Wang Hong , Weston Matthew C. , McQuiston Travis J. , Stornetta Ruth L. , Guyenet Patrice G.
Published: March 2015

Intraparenchymal injection of the saporin conjugate [Sar9, Met (O2)11] substance P-saporin (SSP-SAP) into the ventrolateral medulla (VLM) destroys neurokinin-1 receptor-immunoreactivity (NK1R-ir) neurons selectively. This treatment attenuates the hypotension caused by injection of dl-homocysteic acid (DLH) into the caudal VLM (CVLM). Here we ask whether SSP-SAP creates this deficit by destroying the CVLM GABAergic interneurons that mediate the sympathetic baroreflex (baroactivated depressor neurons) or by destroying other VLM neurons. Two weeks after unilateral SSP-SAP treatment (97% loss of VLM NK1R-ir neurons) DLH-induced hypotension and sympathetic tone inhibition were blunted on the lesioned side. Unlesioned or unilaterally lesioned rats received phenylephrine (PE) while awake to identify CVLM baroactivated depressor neurons by the presence of Fos-ir nuclei. Although CVLM Fos-ir cells were not NK1R-ir, their number was reduced ∼60–70% on the SSP-SAP-injected side. SSP-SAP spared VLM neurons devoid of NK1R-ir, such as the catecholaminergic cells and the precerebellar glutamatergic neurons. In the pre-Bötzinger region of the VLM the toxin killed glutamatergic neurons while sparing glycinergic and GABAergic inhibitory neurons. In the CVLM region ∼26% of the inhibitory cells were destroyed. In conclusion, the baroactivated depressor neurons of the CVLM do not appear to express NK1Rs but their activity is probably modulated by a population of excitatory NK1R-ir cells located in the VLM. The results also suggest that a region located below the CVLM (subCVLM) may contain an unrelated population of GABAergic depressor neurons that are NK1R-ir but are either not barosensitive or do not express Fos during baroreceptor stimulation.
Load-induced focal adhesion kinase activation in the myocardium: role of stretch and contractile activity
Authors: Domingos Priscila P. , Fonseca Priscila M. , Nadruz Wilson , Franchini Kleber G.
Published: March 2015

We investigated the influence of stretch and contractile activity on load-induced activation of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK)1/2 in isolated rat hearts. Increases of diastolic pressure from ∼0 to ∼15 mmHg rapidly increased FAK tyrosine phosphorylation (maximum: 2.3-fold) and binding to c-Src (maximum: 2.8-fold) and Grb2 (maximum: 3.6-fold). This was paralleled by activation (maximum: 2.8-fold) and binding of ERK1/2 to FAK. FAK and ERK1/2 were immunolocalized at sarcolemmal sites of cardiac myocytes and in the nuclei, in the case of ERK1/2. Balloon inflation to raise ventricular pressure in hearts perfused with cardioplegic solution also activated FAK and ERK1/2. However, increases in contractile activity induced by increasing calcium concentration in the perfusate (from 0.5 to 5 mM) did not activate the FAK multicomponent signaling complex or ERK1/2 in the myocardium. These results indicate that stretch rather than contractile activity induces FAK and ERK1/2 activation in the myocardium. In addition, the activation and binding of ERK1/2 to FAK suggest that FAK drives the load-induced activation of ERK1/2.
Mechanisms of make and break excitation revisited: paradoxical break excitation during diastolic stimulation
Authors: Nikolski Vladimir P. , Sambelashvili Aleksandre T. , Efimov Igor R.
Published: March 2015

10.1152/ajpheart.00544.2001. Onset and termination of electric stimulation may result in “make” and “break” excitation of the heart tissue. Wikswo et al. (30) explained both types of stimulations by virtual electrode polarization. Make excitation propagates from depolarized regions (virtual cathodes). Break excitation propagates from hyperpolarized regions (virtual anodes). However, these studies were limited to strong stimulus intensities. We examined excitation during weak near-threshold diastolic stimulation. We optically mapped electrical activity from a 4 × 4-mm area of epicardium of Langendorff-perfused rabbit hearts ( n = 12) around the pacing electrode in the presence ( n = 12) and absence ( n = 2) of 15 mM 2,3-butanedione monoxime. Anodal and cathodal 2-ms stimuli of various intensities were applied. We imaged an excitation wavefront with 528-μs resolution. We found that strong stimuli (×5 threshold) result in make excitation, starting from the virtual cathodes. In contrast, near-threshold stimulation resulted in break excitation, originating from the virtual anodes. Characteristic biphasic upstrokes in the virtual cathode area were observed. Break and make excitation represent two extreme cases of near-threshold and far-above-threshold stimulations, respectively. Both mechanisms are likely to contribute during intermediate clinically relevant strengths.
Time-dependent systolic and diastolic function in mice overexpressing calcineurin
Authors: Semeniuk L. M. , Severson D. L. , Kryski A. J. , Swirp S. L. , Molkentin J. D. , Duff H. J.
Published: March 2015

Echocardiograms have been assessed only at 56 days in mice overexpressing calcineurin (CN mice). Age-dependent echocardiographic changes were evaluated because the development of sudden death is time dependent. Because cyclosporin A (CsA) reverses hypertrophy in CN mice, its effects on the time course of the development of sudden death and cardiac dysfunction were assessed. In wild-type (WT) mice, the left ventricular (LV) internal end-diastolic dimension (LVIDd) increased and the LV mass index (LVMI) decreased with age. In CN mice, two distinct phases of pathophysiology were found. After 14 days, in CN mice, the LVIDd and LVMI were significantly increased, but sudden death had not occurred. After 28 days, in CN mice, relative dilation of the left ventricle occurred, whereas the LVMI decreased. Sudden death developed during progressive dilation associated with systolic and diastolic dysfunction. CsA treatment reversed hypertrophy in CN mice but did not reverse systolic and diastolic dysfunction and exaggerated sudden death. Sudden cardiac death was associated with systolic and diastolic dysfunction but was not related to isolated cardiac hypertrophy in CN mice.
Direct effect of PaCO2 on respiratory sinus arrhythmia in conscious humans
Authors: Sasano Nobuko , Vesely Alex E. , Hayano Junichiro , Sasano Hiroshi , Somogyi Ron , Preiss David , Miyasaka Kiyoyuki , Katsuya Hirotada , Iscoe Steve , Fisher Joseph A.
Published: March 2015

Respiratory sinus arrhythmia (RSA) may improve the efficiency of pulmonary gas exchange by matching the pulmonary blood flow to lung volume during each respiratory cycle. If so, an increased demand for pulmonary gas exchange may enhance RSA magnitude. We therefore tested the hypothesis that CO2directly affects RSA in conscious humans even when changes in tidal volume (VT) and breathing frequency ( F B), which indirectly affect RSA, are prevented. In seven healthy subjects, we adjusted end-tidal Pco 2 (Pet CO2 ) to 30, 40, or 50 mmHg in random order at constant VT and F B. The mean amplitude of the high-frequency component of R-R interval variation was used as a quantitative assessment of RSA magnitude. RSA magnitude increased progressively with Pet CO2 ( P < 0.001). Mean R-R interval did not differ at Pet CO2 of 40 and 50 mmHg but was less at 30 mmHg ( P < 0.05). Because VT and F B were constant, these results support our hypothesis that increased CO2directly increases RSA magnitude, probably via a direct effect on medullary mechanisms generating RSA.
Pressure-dependent myogenic constriction of cerebral arteries occurs independently of voltage-dependent activation
Authors: Lagaud G. , Gaudreault N. , Moore E. D. W. , van Breemen C. , Laher I.
Published: March 2015

Pressure-induced decreases in arterial diameter are accompanied by membrane depolarization and Ca2+ entry via voltage-gated Ca2+ channels. Recent evidence also suggests the involvement of Ca2+ sensitization of the contractile proteins. Both PKC and Rho kinase are candidate second messengers for the mediation of the sensitization process. We investigated the signaling pathways of pressure-induced decreases in rat cerebral artery diameter in vessels that were depolarized with a 60 mM potassium-physiological salt solution (KPSS). Arteries were mounted on a pressure myograph, and pressure-induced constrictions were recorded. In some experiments simultaneous changes in intracellular Ca2+ concentration ([Ca2+]i) were recorded by using fura 2 fluorescence photometry. Pressure increases induced constriction with significant changes in [Ca2+]i at high pressures (60–100 mmHg). The ratio of the change in diameter to change in [Ca2+]i was greater for pressure-induced constriction compared with constriction produced by depolarization with 60 mM KPSS, suggesting that in addition to increases in [Ca2+]i, enhanced myofilament Ca2+ sensitivity occurs during pressure-induced decreases in arterial diameter. Depolarizing the membrane with 60 mM KPSS increased [Ca2+]i via a Ca2+influx pathway insensitive to PKC inhibition. Cerebral arteries were able to maintain their diameters in the continued presence of 60 mM KPSS. Pressure-induced constriction under these conditions was not associated with further increases in Ca2+ but was abolished by selective inhibitors of PLC, PKC, and Rho kinase. We report for the first time that in rat cerebral arteries, pressure-induced decreases in arterial diameter are not only due to increases in voltage-gated Ca2+ influx but also to accompanying increases in myofilament sensitivity to Ca2+ mediated by PKC/Rho kinase activation.
Nonlinear methods of biosignal analysis in assessing terbutaline-induced heart rate and blood pressure changes
Authors: Kuusela Tom A. , Jartti Tuomas T. , Tahvanainen Kari U. O. , Kaila Timo J.
Published: March 2015

The aim of this study was to characterize how different nonlinear methods characterize heart rate and blood pressure dynamics in healthy subjects at rest. The randomized, placebo-controlled crossover study with intravenous terbutaline was designed to induce four different stationary states of cardiovascular regulation system. The R-R interval, systolic arterial blood pressure, and heart rate time series were analyzed with a set of methods including approximate entropy, sample entropy, Lempel-Ziv entropy, symbol dynamic entropy, cross-entropy, correlation dimension, fractal dimensions, and stationarity test. Results indicate that R-R interval and systolic arterial pressure subsystems are mutually connected but have different dynamic properties. In the drug-free state the subsystems share many common features. When the strength of the baroreflex feedback loop is modified with terbutaline, R-R interval and systolic blood pressure lose mutual synchrony and drift toward their inherent state of operation. In this state the R-R interval system is rather complex and irregular, but the blood pressure system is much simpler than in the drug-free state.
Is microvascular protection by cariporide and ischemic preconditioning causally linked to myocardial salvage?
Authors: Reffelmann Thorsten , Kloner Robert A.
Published: March 2015

Two independent cardioprotective interventions, Na+/H+ exchange inhibition and ischemic preconditioning (PC), were investigated with respect to differential effects on microvascular and myocardial salvage in anesthetized rabbits (30 min of ischemia, 180 min of reperfusion). Cariporide (Car, 300 μg/kg) administered before occlusion and PC reduced infarct size (IS) as measured by triphenyltetrazolium staining [control, 46.0 ± 4.2% of risk area (RA); Car, 17.6 ± 3.7% ( P< 0.01); PC, 27.5 ± 4.1% ( P < 0.01)] and concomitantly decreased the area of anatomic no reflow (ANR) as measured by thioflavin S staining [control, 40.4 ± 3.7%; Car, 19.0 ± 2.9% ( P < 0.01); PC, 26.9 ± 3.4% ( P < 0.05)]. Regional myocardial blood flow (RMBF, measured by radioactive microspheres) in the RA, which deteriorated between 30 and 180 min of reperfusion (control, from 79 ± 6 to 26 ± 2% of nonischemic flow), was shifted to higher values with both treatments [Car, from 110 ± 12 to 49 ± 7% ( P < 0.05); PC, from 109 ± 8 to 38 ± 6% ( P < 0.05)]. However, neither intervention uncoupled the close relationship between IS and ANR ( r= 0.92–0.95) or RMBF. Car given at reperfusion did not alter IS, ANR, RMBF, or the close interrelationships. Because size and spatial distribution of no reflow and myocardial necrosis remained closely coupled with independent cardioprotective interventions, a potential causal connection between microvascular and myocardial salvage is discussed.
Contributions of heart rate and contractility to myocardial oxygen balance during exercise
Authors: Colin Patrice , Ghaleh Bijan , Monnet Xavier , Su Jinbo , Hittinger Luc , Giudicelli Jean-François , Berdeaux Alain
Published: March 2015

The respective contributions of heart rate (HR) reduction and left ventricular (LV) negative inotropy to the effects of antianginal drugs are debated. Accordingly, eight instrumented dogs were investigated during exercise at spontaneous and paced HR (250 beats/min) after administration of either saline, atenolol, or ivabradine (selective pacemaker current channel blocker). During exercise, atenolol and ivabradine (both 1 mg/kg iv) similarly reduced HR (−30% from 222 ± 5 beats/min), and LV mean ejection wall stress was not altered. LV dP/d t max was reduced by atenolol but not ivabradine. Diastolic time (DT) was increased by atenolol versus saline (195 ± 6 vs. 123 ± 4 ms, respectively) and to a greater extent by ivabradine (233 ± 11 ms). Myocardial oxygen consumption (MV˙o 2) was lower under ivabradine and atenolol versus saline (6.7 ± 0.6 and 4.7 ± 0.4 vs. 8.1 ± 0.6 ml/min, respectively, P < 0.05). Under pacing, DT and MV˙o 2 were similar between ivabradine and saline but significantly reduced with atenolol. Thus HR reduction and negative inotropy equally contribute to the reduction in MV˙o 2 during exercise in the normal heart. The negative inotropy limits the increase in DT afforded by HR reduction.
Slow rate during AF improves ventricular performance by reducing sensitivity to cycle length irregularity
Authors: Popović Zoran B. , Mowrey Kent A. , Zhang Youhua , Zhuang Shaowei , Tabata Tomotsugu , Wallick Don W. , Grimm Richard A. , Thomas James D. , Mazgalev Todor N.
Published: March 2015

Atrial fibrillation (AF) is characterized by short and irregular ventricular cycle lengths (VCL). While the beneficial effects of heart rate slowing (i.e., the prolongation of VCL) in AF are well recognized, little is known about the impact of irregularity. In 10 anesthetized dogs, R-R intervals, left ventricular (LV) pressure, and aortic flow were collected for >500 beats during fast AF and when the average VCL was prolonged to 75%, 100%, and 125% of the intrinsic sinus cycle length by selective atrioventricular (AV) nodal vagal stimulation. We used the ratio of the preceding and prepreceding R-R intervals (RRp/RRpp) as an index of cycle length irregularity and assessed its effects on the maximum LV power, the minimum of the first derivative of LV pressure, and the time constant of relaxation by using nonlinear fitting with monoexponential functions. During prolongation of VCL, there was a pronounced decrease in curvature with the formation of a plateau, indicating a lesser dependence on RRp/RRpp. We conclude that prolongation of the VCL during AF reduces the sensitivity of the LV performance parameters to irregularity.
Alterations of β-adrenergic signaling and cardiac hypertrophy in transgenic mice overexpressing TGF-β1
Authors: Rosenkranz Stephan , Flesch Markus , Amann Kerstin , Haeuseler Claudia , Kilter Heiko , Seeland Ute , Schlüter Klaus-Dieter , Böhm Michael
Published: March 2015

Transforming growth factor-β1(TGF-β1) promotes or inhibits cell proliferation and induces fibrotic processes and extracellular matrix production in numerous cell types. Several cardiac diseases are associated with an increased expression of TGF-β1mRNA, particularly during the transition from stable cardiac hypertrophy to heart failure. In vitro studies suggest a link between TGF-β1signaling and the β-adrenergic system. However, the in vivo effects of this growth factor on myocardial tissue have been poorly identified. In transgenic mice overexpressing TGF-β1(TGF-β), we investigated the in vivo effects on cardiac morphology, β-adrenergic signaling, and contractile function. When compared with nontransgenic controls (NTG), TGF-β mice revealed significant cardiac hypertrophy (heart weight, 164 ± 7 vs. 130 ± 3 mg, P < 0.01; heart weight-to-body weight ratio, 6.8 ± 0.3 vs. 5.1 ± 0.1 mg/g, P < 0.01), accompanied by interstitial fibrosis. These morphological changes correlated with an increased expression of hypertrophy-associated proteins such as atrial natriuretic factor (ANF). Furthermore, overexpression of TGF-β1led to alterations of β-adrenergic signaling as myocardial β-adrenoceptor density increased from 7.3 ± 0.3 to 11.2 ± 1.1 fmol/mg protein ( P < 0.05), whereas the expression of β-adrenoceptor kinase-1 and inhibitory G proteins decreased by 56 ± 9.7% and 58 ± 7.6%, respectively ( P < 0.05). As a consequence of altered β-adrenergic signaling, hearts from TGF-β showed enhanced contractile responsiveness to isoproterenol stimulation. In conclusion, we conclude that TGF-β1induces cardiac hypertrophy and enhanced β-adrenergic signaling in vivo. The morphological alterations are either induced by direct effects of TGF-β1or may at least in part result from increased β-adrenergic signaling, which may contribute to excessive catecholamine stimulation during the transition from compensated hypertrophy to heart failure.
Temperature-sensitive intracellular Mg2+ block of L-type Ca2+ channels in cardiac myocytes
Authors: Yamaoka Kaoru , Yuki Tsunetsugu , Kawase Kayoko , Munemori Makoto , Seyama Issei
Published: March 2015

We examined the concentration-dependent blocking effects of intracellular Mg2+ on L-type Ca2+ channels in cardiac myocytes using the whole cell patch-clamp technique. The increase of L-type Ca2+ channel current ( I Ca) (due to relief of Mg2+ block) occurred in two temporal phases. The rapid phase (runup) transiently appeared early (<5 min) in dialysis of the low-Mg2+ solution; the slow phase began later in dialysis (>10 min). Runup was not blocked by intracellular GTP (GTPi). The late phase of the I Ca increase (late I Ca) was suppressed by GTPi (0.4 mM) and was observed in myocytes of the guinea pig or frog at higher (32 or 24°C, respectively) rather than lower temperatures (24 or 17.5°C, respectively). At pMg = 6.0, raising the temperature from 24 to 32°C evoked late I Ca with a Q10 of 14.5. Restoring the temperature to 24°C decreased I Ca with a Q10 of only 2.4. The marked difference in the Q10 values indicated that late I Ca (pMg = 5–6) is an irreversible phenomenon. Phosphorylation suppressed the intracellular [Mg2+] dependency of late I Ca. This effect of phosphorylation together with the inhibitory action of GTPi on Mg2+-dependent blocking of I Ca are common properties of mammalian and amphibian cardiomyocytes.
Transient transcapillary exchange of water driven by osmotic forces in the heart
Authors: Kellen Michael R. , Bassingthwaighte James B.
Published: March 2015

Osmotic transient responses in organ weight after changes in perfusate osmolarity have implied steric hindrance to small-molecule transcapillary exchange, but tracer methods do not. We obtained osmotic weight transient data in isolated, Ringer-perfused rabbit hearts with NaCl, urea, glucose, sucrose, raffinose, inulin, and albumin and analyzed the data with a new anatomically and physicochemically based model accounting for 1) transendothelial water flux, 2) two sizes of porous passages across the capillary wall, 3) axial intracapillary concentration gradients, and 4) water fluxes between myocytes and interstitium. During steady-state conditions ∼28% of the transcapillary water flux going to form lymph was through the endothelial cell membranes [capillary hydraulic conductivity ( Lp) = 1.8 ± 0.6 × 10–8cm · s–1· mmHg–1], presumably mainly through aquaporin channels. The interendothelial clefts (with Lp= 4.4 ± 1.3 × 10–8cm · s–1· mmHg–1) account for 67% of the water flux; clefts are so wide (equivalent pore radius was 7 ± 0.2 nm, covering ∼0.02% of the capillary surface area) that there is no apparent hindrance for molecules as large as raffinose. Infrequent large pores account for the remaining 5% of the flux. During osmotic transients due to 30 mM increases in concentrations of small solutes, the transendothelial water flux was in the opposite direction and almost 800 times as large and was entirely transendothelial because no solute gradient forms across the pores. During albumin transients, gradients persisted for long times because albumin does not permeate small pores; the water fluxes per milliosmolar osmolarity change were 200 times larger than steady-state water flux. The analysis completely reconciles data from osmotic transient, tracer dilution, and lymph sampling techniques.
Effects of hypoxia-reoxygenation on rat blood-brain barrier permeability and tight junctional protein expression
Authors: Witt Ken A. , Mark Karen S. , Hom Sharon , Davis Thomas P.
Published: March 2015

Cerebral microvessel endothelial cells that form the blood-brain barrier (BBB) have tight junctions (TJs) that are critical for maintaining brain homeostasis. The effects of initial reoxygenation after a hypoxic insult (H/R) on functional and molecular properties of the BBB and TJs remain unclear. In situ brain perfusion and Western blot analyses were performed to assess in vivo BBB integrity on reoxygenation after a hypoxic insult of 6% O2for 1 h. Model conditions [blood pressure, blood gas chemistries, cerebral blood flow (CBF), and brain ATP concentration] were also assessed to ensure consistent levels and criteria for insult. In situ brain perfusion revealed that initial reoxygenation (10 min) significantly increased the uptake of [14C]sucrose into brain parenchyma. Capillary depletion and CBF analyses indicated the perturbations were due to increased paracellular permeability rather than vascular volume changes. Hypoxia with reoxygenation (10 min) produced an increase in BBB permeability with associated alterations in tight junctional protein expression. These results suggest that H/R leads to reorganization of TJs and increased paracellular diffusion at the BBB, which is not a result of increased CBF, vascular volume change, or endothelial uptake of marker. Additionally, the tight junctional protein occludin had a shift in bands that correlated with functional changes (i.e., increased permeability) without significant change in expression of claudin-3, zonula occludens-1, or actin. H/R-induced changes in the BBB may result in edema and/or associated pathological outcomes.
Increased expression of cardiotrophin-1 during ventricular remodeling in hypertensive rats
Authors: Takimoto Yoshihito , Aoyama Takeshi , Iwanaga Yoshitaka , Izumi Toshiaki , Kihara Yasuki , Pennica Diane , Sasayama Shigetake
Published: March 2015

Cardiotrophin-1 (CT-1) stimulates longitudinal myocardial cell hypertrophy. We examined the expression of CT-1, leukemia inhibitory factor (LIF), and gp130 by competitive RT-PCR and Western blotting in Dahl salt-sensitive (DS) rats with a high-salt diet, which showed a distinct transition from left ventricular hypertrophy (LVH) to congestive heart failure (CHF). The expression levels of CT-1 mRNA and protein were significantly increased at the CHF stage compared with the LVH stage and age-matched Dahl salt-resistant (DR) rats ( n = 6 for each group). mRNA expression of LIF was not changed in the left ventricle at any stage by RT-PCR. gp130 mRNA and protein levels of DS rats at 11 and 17 wk were significantly increased compared with age-matched DR rats. The isolated myocyte length of DS rats at 17 wk was the longest among the four groups of rats. The LV end-diastolic dimension (LVDd) of DS rats, determined by echocardiography, was significantly increased at the CHF stage. There was a significant correlation between the CT-1 protein level and LVDd. CT-1 may play a role in ventricular remodeling during transition from LVH to CHF in the rat hypertensive model.
Myofilament properties comprise the rate-limiting step for cardiac relaxation at body temperature in the rat
Authors: Janssen Paul M. L. , Stull Linda B. , Marbán Eduardo
Published: March 2015

The majority of studies aimed at characterizing basic contractile mechanisms have been conducted at room temperature. To elucidate the mechanism of cardiac relaxation under more physiological conditions, we investigated contractile function and calcium handling in ultrathin rat cardiac trabeculae. Active developed tension was unaltered between 22.5 and 30.0°C (from 89 ± 10 to 86 ± 11 mN/mm2, P = not significant) but steeply declined at 37.5°C (30 ± 5 mN/mm2). Meanwhile, the speed of relaxation (time from peak force to 50% relaxation) declined from 22.5 to 30.0°C (from 360 ± 40 to 157 ± 17 ms) and further declined at 37.5°C to 76 ± 13 ms. Phase-plane analysis of calcium versus force revealed that, with increasing temperature, the relaxation phase is shifted rightward, indicating that the rate-limiting step of relaxation tends to depend more on calcium kinetics as temperature rises. The force-frequency relationship, which was slightly negative at 22.5°C (0.1 vs. 1 Hz: 77 ± 12 vs. 66 ± 7 mN/mm2), became clearly positive at 37.5°C (1 vs. 10 Hz: 30 ± 5 vs. 69 ± 9 mN/mm2). Phase-plane analyses indicated that, with increasing frequency, the relaxation phase is shifted leftward. We conclude that temperature independently affects contraction and relaxation, and cross-bridge cycling kinetics become rate limiting for cardiac relaxation under experimental conditions closest to those in vivo.
Alkaline pH shifts Ca2+sparks to Ca2+waves in smooth muscle cells of pressurized cerebral arteries
Authors: Heppner Thomas J. , Bonev Adrian D. , Santana L. Fernando , Nelson Mark T.
Published: March 2015

The effects of external pH (7.0–8.0) on intracellular Ca2+signals (Ca2+sparks and Ca2+waves) were examined in smooth muscle cells from intact pressurized arteries from rats. Elevating the external pH from 7.4 to 7.5 increased the frequency of local, Ca2+transients, or “Ca2+sparks,” and, at pH 7.6, significantly increased the frequency of Ca2+waves. Alkaline pH-induced Ca2+waves were inhibited by blocking Ca2+release from ryanodine receptors but were not prevented by inhibitors of voltage-dependent Ca2+channels, phospholipase C, or inositol 1,4,5-trisphosphate receptors. Activating ryanodine receptors with caffeine (5 mM) at pH 7.4 also induced repetitive Ca2+waves. Alkalization from pH 7.4 to pH 7.8–8.0 induced a rapid and large vasoconstriction. Approximately 82% of the alkaline pH-induced vasoconstriction was reversed by inhibitors of voltage-dependent Ca2+channels. The remaining constriction was reversed by inhibition of ryanodine receptors. These findings indicate that alkaline pH-induced Ca2+waves originate from ryanodine receptors and make a minor, direct contribution to alkaline pH-induced vasoconstriction.
Pericardium modulates left and right ventricular stroke volumes to compensate for sudden changes in atrial volume
Authors: Kroeker Carol A. Gibbons , Shrive Nigel G. , Belenkie Israel , Tyberg John V.
Published: March 2015

The pericardium may modulate acute compensatory changes in stroke volumes seen with sudden changes in cardiac volume, but such a mechanism has never been clearly demonstrated. In eight open-chest dogs, we measured left and right ventricular pressures, diameters, stroke volumes, and pericardial pressures during rapid (∼300 ms) systolic infusions or withdrawals of ∼25 ml blood into and out of the left atrium and right atrium. Control beats, the infusion/withdrawal beat, and 4–10 subsequent beats were studied. With infusions, ipsilateral ventricular end-diastolic transmural pressure, diameter, and stroke volume increased. With the pericardium closed, there was a compensatory decrease in contralateral transmural pressure, diameter, and stroke volume, mediated by opposite changes in transmural end-diastolic pressures. The sum of the ipsilateral increase and contralateral decrease in stroke volume approximated the infused volume. Corresponding changes were seen with blood withdrawals. This direct ventricular interaction was diminished when pericardial pressure was <5 mmHg and absent when the pericardium was opened. Pericardial constraint appears essential for immediate biventricular compensatory responses to acute atrial volume changes.