bluuebunny/crossref_metadata_2025 huggingface dataset:
CK inhibition accelerates transcytosolic energy signaling during rapid workload steps in isolated rabbit hearts
Authors: Harrison Glenn J. , van Wijhe Michiel H. , de Groot Bas , Dijk Francina J. , van Beek Johannes H. G. M.
Published: December 2017

The effect of graded creatine kinase (CK) inhibition on the response time of mitochondrial O2consumption to dynamic workload jumps ( tmito) was studied in isolated rabbit hearts. Tyrode-perfused hearts ( n = 7/group) were exposed to 15 min of 0, 0.1, 0.2, or 0.4 mM iodoacetamide (IA) (CK activity = 100, 14, 6, and 3%, respectively). Pretreatment tmitowas similar across groups at 6.5 ± 0.5 s (mean ± SE). The increase observed over time in control hearts (33 ± 8%) was progressively reversed to 16 ± 6, −20 ± 6 ( P< 0.01 vs. control), and −46 ± 6 ( P < 0.01 vs. control) % in the 0.1, 0.2 and 0.4 mM IA groups, respectively. The faster response times occurred without reductions in mitochondrial oxidative capacity (assessed in vitro) or myocardial O2consumption of the whole heart during workload steps. Isovolumic contractile function assessed as rate-pressure product (RPP) and contractile reserve (increase in RPP during heart rate steps) were significantly reduced by IA. We conclude that CK in the myofibrils and/or cytosol does not speed up transfer of the energy-related signal to the mitochondria but rather acts as an energetic buffer, effectively slowing the stimulus between myofibrils/ion pumps and oxidative phosphorylation. This argues against the existence of an obligatory creatine phosphate energy shuttle, because CK is effectively bypassed.
Induction of 72-kDa heat shock protein does not produce second window of ischemic preconditioning in rat heart
Authors: Qian Yong-Zhen , Bernardo Nelson L. , Nayeem Mohammed A. , Chelliah Jeya , Kukreja Rakesh C.
Published: December 2017

Ischemic preconditioning (PC) induces delayed phase of protection, known as the second window of protection (SWOP). We investigated this phenomenon in rat and correlated it with the expression of 72-kDa heat shock protein (HSP 72). Rats were preconditioned with 1, 2, and 3 cycles of 5-min left anterior descending artery occlusions, each separated by a 10-min reperfusion (PC × 1, PC × 2 and PC × 3, respectively). Another group of rats was preconditioned with heat shock (HS) by raising temperature to 42°C for 15 min. Twenty-four hours later, rats were given sustained ischemia for 30 min and 90 min of reperfusion. Infarct sizes (%risk area) were 40.0 ± 7.5, 37.6 ± 5.6, and 47.6 ± 2.4 (mean ± SE) for PC × 1, PC × 2, and PC × 3 hearts, respectively, which were not different from the sham (49.9 ± 3.9, P > 0.05). In contrast, infarct size was reduced from 47.5 ± 3.8% in sham to 4.7 ± 2.3% ( P < 0.01) 24 h after HS. Additionally, early PC significantly reduced infarct size from 47.5 ± 3.8% in controls to 6.0 ± 1.2 and 5.0 ± 1.1% with PC × 1 and PC × 3. Repeated PC cycles induced over a threefold increase in HSP 70 mRNA after 2 h compared with sham ( P < 0.05). HSP 72, which increased 24 h after PC or HS, was not significantly different between the two PC stimuli. We conclude that PC does not induce SWOP in rat heart despite enhanced expression of HSP 72. In contrast, HS-induced delayed protection was associated with enhanced accumulation of HSP 72. It is possible that SWOP and HS have distinct mechanisms of protection that may not be exclusively related to HSP 72 expression.
Mechanism of Ca2+release and entry during contraction elicited by norepinephrine in rat resistance arteries
Authors: Lagaud G. J. L. , Randriamboavonjy V. , Roul G. , Stoclet J. C. , Andriantsitohaina R.
Published: December 2017

The intracellular Ca2+stores and the mechanisms of Ca2+entry produced by norepinephrine (NE) were investigated in small mesenteric resistance arteries of the rat. In Ca2+-free medium, NE (10 μM) elicited a transient increase in both intracellular free Ca2+concentration ([Ca2+]i) and tension that were both drastically reduced by caffeine and only partially reduced by the two sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) blockers thapsigargin and cyclopiazonic acid, despite the presence of SERCA2a and SERCA2b isoforms in the medial smooth muscle layer of the artery. After depletion of intracellular Ca2+stores with 10 μM NE, addition of exogenous CaCl2(2.5 mM) produced large and sustained increases in both [Ca2+]iand contraction of the arteries provided that the agonist was continuously present. In these conditions, the responses to CaCl2were inhibited by the voltage-dependent Ca2+entry blocker nitrendipine (1 μM), the putative inhibitor of receptor-operated Ca2+entry SKF-96365 (30 μM), and NiCl2(1 mM). The inhibition produced by SKF-96365 and NiCl2was greater than that of nitrendipine. Also, the responses to CaCl2were greatly reduced or abolished in the presence of the Na+/Ca2+exchanger inhibitors 1,3-dimethyl-2-thiourea, 3′,4′-dichlorobenzamil, MgCl2, and amiloride or after omission of NaCl in the medium. Also, protein kinase C inhibitors, calphostin C and staurosporine, and tyrosine kinase inhibitors, genistein and tyrphostin 23, both reduced the responses to CaCl2. The inhibitory effect of protein kinase C inhibitor and tyrosine kinase were additive. These results suggest that NE releases Ca2+from intracellular stores that are caffeine sensitive and partially sensitive to SERCA inhibitors. They indicate that in addition to Ca2+influx via nitrendipine-sensitive and SKF-96365-sensitive channels, Na+/Ca2+exchanger participates in the CaCl2-induced contraction produced in NE-exposed vessels. The pathway leading to Ca2+entry probably involves tyrosine kinase and protein kinase C. All the above mechanisms require ongoing receptor stimulation.
Changes in cardiac ANG II postmyocardial infarction in rats: effects of nephrectomy and ACE inhibitors
Authors: Leenen Frans H. H. , Skarda Vaclav , Yuan Baoxue , White Roselyn
Published: December 2017

We evaluated in rats the time course of changes in cardiac versus plasma ANG I and II postmyocardial infarction (MI) and the effects of nephrectomy and angiotensin-converting enzyme (ACE) inhibitors on the early changes post-MI. Acute coronary artery ligation was induced in conscious rats using the two-stage model, and plasma and cardiac tissue were obtained shortly (6 h, 1 and 3 days) and chronically (1, 4, and 8–9 wk) after MI. In an additional group of rats, bilateral nephrectomy was performed 18 h before the coronary artery ligation, and samples were obtained at 6 h post-MI. Furthermore, in two additional groups of rats, treatment with enalapril and quinapril was started 3 days before the ligation, and samples were obtained at 1 or 3 days post-MI. In these groups of rats, plasma and left ventricular (LV) (infarct and infarct free) ANG I and II were measured by RIA after separation on HPLC. In control rats, plasma ANG I and II showed a clear increase at 6 h post-MI but subsequently only minor increases were observed. In contrast, LV ANG II showed major increases at 6 h and 1 day post-MI, which had returned to normal by 3 days in the infarct-free LV and after 1(–2) wk in the infarct LV. LV ANG I showed a more gradual increase and remained elevated in the infarct up to 8–9 wk. Nephrectomy preceding the MI lowered ANG I and II in plasma but enhanced their increases in the heart at 6 h post-MI. Both ACE inhibitors decreased plasma ANG II associated with large increases in plasma ANG I. They also inhibited the increases in LV ANG II in both the infarct and infarct-free LV at 1 and 3 days post-MI with however no significant increase in LV ANG I. In conclusion, induction of a MI in conscious rats leads to rapid and marked, but only short-lived, increases in cardiac tissue ANG II in both the infarct and infarct-free parts of the LV. Pretreatment with ACE inhibitors, but not nephrectomy, blocks this increase. Local production appears to play a major role in the increases in cardiac ANG II post-MI.
Effect of angiotensin-converting enzyme inhibition on protein kinase C and SR proteins in heart failure
Authors: Takeishi Yasuchika , Bhagwat Ajit , Ball Nancy A. , Kirkpatrick Darryl L. , Periasamy Muthu , Walsh Richard A.
Published: December 2017

We tested the hypothesis that activation of protein kinase C (PKC) isoforms in pressure-overload heart failure was prevented by angiotensin-converting enzyme (ACE) inhibition, resulting in normalization of cardiac sarcoplasmic reticulum (SR) Ca2+ATPase (SERCA) 2a and phospholamban protein levels and improvement in intracellular Ca2+handling. Aortic-banded and control guinea pigs were given ramipril (5 mg ⋅ kg−1⋅ day−1) or placebo for 8 wk. Ramipril-treated banded animals had lower left ventricular (LV) and lung weight, improved survival, increased isovolumic LV mechanics, and improved cardiomyocyte Ca2+transients compared with placebo-treated banded animals. This was associated with maintenance of SERCA2a and phospholamban protein expression. Translocation of PKC-α and -ε was increased in placebo-treated banded guinea pigs compared with controls and was attenuated significantly by treatment with ramipril. We conclude that ACE inhibition attenuates PKC translocation and prevents downregulation of Ca2+cycling protein expression in pressure-overload hypertrophy. This represents a mechanism for the beneficial effects of this therapy on LV function and survival in heart failure.
Adaptation to hypoxia alters energy metabolism in rat heart
Authors: Rumsey William L. , Abbott Brian , Bertelsen Darci , Mallamaci Michael , Hagan Kevin , Nelson David , Erecinska Maria
Published: December 2017

The present study characterized metabolic changes in the heart associated with long-term exposure to hypoxia, a potent stimulus for pulmonary hypertension and right ventricular hypertrophy. When anesthetized rats adapted to chronic hypoxia spontaneously respired room air, their mean right intraventricular peak systolic pressure (RVSP) was twice that in normal control animals with the same arterial [Formula: see text]. RVSP was linearly related to right ventricular mass ( r = 0.78). Oxidative capacity (O2consumption) of homogenates of right and left ventricles from both groups of rats was measured with one of the following substrates: pyruvate, glutamate, acetate, and palmitoyl-l-carnitine. Oxidation of all substrates was significantly greater in the left than in the right ventricle in normal rats but not in hypoxia-adapted animals, where it was the same, within the experimental error. O2consumption by the left ventricle was greater in control than in experimental rats, but right ventricular O2consumption was similar in the two groups. Maximal reaction velocity of cytochrome- c oxidase was about the same in the two ventricles, and there were no significant differences between control and hypoxia-adapted animals. HPLC analyses showed significantly higher aspartate levels and aspartate-to glutamate concentration ratios in both ventricles of hypoxic rats than in corresponding tissues from controls, indicative of a decreased flux through the malate-aspartate shuttle under conditions of O2limitation. Myocardial glutamine levels were lower in hypoxic rats, and glutamine-to-glutamate concentration ratios decreased, although primarily in the pressure-overloaded right ventricle. These findings indicate that normal energy metabolism in the left ventricle differs from that in the right and that the differences, particularly those of amino acid metabolism, are markedly influenced by chronic exposure to hypoxia.
TransmembraneI Ca contributes to rate-dependent changes of action potentials in human ventricular myocytes
Authors: Li Gui-Rong , Yang Baofeng , Feng Jianlin , Bosch Ralph F. , Carrier Michel , Nattel Stanley
Published: December 2017

The mechanism of action potential abbreviation caused by increasing rate in human ventricular myocytes is unknown. The present study was designed to determine the potential role of Ca2+ current ( I Ca) in the rate-dependent changes in action potential duration (APD) in human ventricular cells. Myocytes isolated from the right ventricle of explanted human hearts were studied at 36°C with whole cell voltage and current-clamp techniques. APD at 90% repolarization decreased by 36 ± 4% when frequency increased from 0.5 to 2 Hz. Equimolar substitution of Mg2+ for Ca2+ significantly decreased rate-dependent changes in APD (to 6 ± 3%, P < 0.01). Peak I Ca was decreased by 34 ± 3% from 0.5 to 2 Hz ( P < 0.01), and I Ca had recovery time constants of 65 ± 12 and 683 ± 39 ms at −80 mV. Action potential clamp demonstrated a decreasing contribution of I Ca during the action potential as rate increased. The rate-dependent slow component of the delayed rectifier K+current ( I Ks) was not observed in four cells with an increase in frequency from 0.5 to 3.3 Hz, perhaps because the I Ks is so small that the increase at a high rate could not be seen. These results suggest that reduction of Ca2+influx during the action potential accounts for most of the rate-dependent abbreviation of human ventricular APD.
Hypertrophic response to hemodynamic overload: role of load vs. renin-angiotensin system activation
Authors: Koide Masaaki , Carabello Blase A. , Conrad Chester C. , Buckley John M. , DeFreyte Gilberto , Barnes Mary , Tomanek Robert J. , Wei Chih-Chang , Dell’Italia Louis J. , Cooper George , Zile Michael R.
Published: December 2017

Myocardial hypertrophy is one of the basic mechanisms by which the heart compensates for hemodynamic overload. The mechanisms by which hemodynamic overload is transduced by the cardiac muscle cell and translated into cardiac hypertrophy are not completely understood. Candidates include activation of the renin-angiotensin system (RAS) and angiotensin II receptor (AT1) stimulation. In this study, we tested the hypothesis that load, independent of the RAS, is sufficient to stimulate cardiac growth. Four groups of cats were studied: 14 normal controls, 20 pulmonary artery-banded (PAB) cats, 7 PAB cats in whom the AT1was concomitantly and continuously blocked with losartan, and 8 PAB cats in whom the angiotensin-converting enzyme (ACE) was concomitantly and continuously blocked with captopril. Losartan cats had at least a one-log order increase in the ED50of the blood pressure response to angiotensin II infusion. Right ventricular (RV) hypertrophy was assessed using the RV mass-to-body weight ratio and ventricular cardiocyte size. RV hemodynamic overload was assessed by measuring RV systolic and diastolic pressures. Neither the extent of RV pressure overload nor RV hypertrophy that resulted from PAB was affected by AT1blockade with losartan or ACE inhibition with captopril. RV systolic pressure was increased from 21 ± 3 mmHg in normals to 68 ± 4 mmHg in PAB, 65 ± 5 mmHg in PAB plus losartan and 62 ± 3 mmHg in PAB plus captopril. RV-to-body weight ratio increased from 0.52 ± 0.04 g/kg in normals to 1.11 ± 0.06 g/kg in PAB, 1.06 ± 0.06 g/kg in PAB plus losartan and 1.06 ± 0.06 g/kg in PAB plus captopril. Thus 1) pharmacological modulation of the RAS with losartan and captopril did not change the extent of the hemodynamic overload or the hypertrophic response induced by PAB; 2) neither RAS activation nor angiotensin II receptor stimulation is an obligatory and necessary component of the signaling pathway that acts as an intermediary coupling load to the hypertrophic response; and 3) load, independent of the RAS, is capable of stimulating cardiac growth.
Vasoconstrictor effect of endothelin-1 in human skin: role of ETAand ETBreceptors
Authors: Lipa Joan E. , Neligan Peter C. , Perreault Therese M. , Baribeau Johanne , Levine Ronald H. , Knowlton Robert J. , Pang Cho Y.
Published: December 2017

The aim of this project was to investigate the role of ETAand ETBreceptors in the mediation of endothelin (ET)-1-induced vasoconstriction in human skin. This information should provide important insights into the design of pharmacological intervention against skin vasospasm induced by ET-1 in peripheral vascular disease or surgical trauma. Vasoconstriction in response to intra-arterial drug infusion in isolated perfused human skin flaps (8 × 18 cm) derived from dermolipectomy specimens was assessed by studying changes in skin perfusion and perfusion pressure under constant flow rate in each drug treatment ( n = 4). It was observed that ET-1 (10−10to 10−8M) and norepinephrine (NE, 10−8to 10−5M) caused skin vasoconstriction in a concentration-dependent manner, with the vasoconstrictor potency of ET-1 ∼200-fold higher than NE. The ETA-receptor antagonist BQ-123 but not the ETB-receptor antagonist BQ-788 blocked the vasoconstrictor effect of ET-1. This observation was confirmed by studying skin perfusion using the dermofluorometry technique. In addition, ETB-receptor agonists BQ-3020 and sarafotoxin S6c (10−9to 10−6M) did not evoke skin vasoconstriction. BQ-3020 also did not elicit skin vasoconstriction even in the presence of 10−5M of Nω-nitro-l-arginine methyl ester and indomethacin. Furthermore, results from saturable and competitive ET-1 radioligand membrane receptor binding assays revealed that high-affinity and capacity binding sites are predominantly the ETAreceptor subtype in endothelium-denuded skin arteries and veins of 0.5–1.5 mm diameter, with an ETA-to-ETBreceptor ratio of 83:17 in arteries ( n= 5) and 78:22 in veins ( n = 7). Results from the present functional and radioligand receptor binding studies clearly indicate that ET-1 is a very potent vasoconstrictor in human skin and its vasoconstrictor effect is primarily mediated by ETAreceptors, with no significant participation from ETBreceptors.
Electrical interactions among real cardiac cells and cell models in a linear strand
Authors: Wagner Mary B. , Namiki Takao , Wilders Ronald , Joyner Ronald W. , Jongsma Habo J. , Verheijck E. Etienne , Kumar Rajiv , Golod David A. , Goolsby William N. , van Ginneken Antoni C. G.
Published: December 2017

Previous work with model systems for action potential conduction have been restricted to conduction between two real cells or conduction between a model cell and a real cell. The inclusion of additional elements to make a linear strand has allowed us to investigate the interactions between cells at a higher level of complexity. When, in the simplest case of a linear strand of three elements, the conductance between elements 2 and 3( G C2) is varied, this affects the success or failure of propagation between elements 1 and 2 (coupled by G C1) as well as the success or failure of propagation between elements 2 and 3. Several major features were illustrated. 1) When G C1 was only slightly greater than the coupling conductance required for successful propagation between a model cell and a real cell, addition of a third element of the strand either prevented conduction from element 1 to element 2 (when G C2 was high) or allowed conduction from element 1 to element 2 but not conduction from element 2 to element 3 (when G C2 was low). 2) For higher levels of G C1, there was an allowable “window” of values of G C2 for successful conduction from element 1 through to element 3. The size of this allowable window of G C2 values increased with increasing values of G C1, and this increase was produced by increases in the upper bound of G C2 values. 3) When the size of the central element of the strand was reduced, this facilitated conduction through the strand, increasing the range of the allowable window of G C2 values. The overall success or failure of conduction through a structure of cells that has a spatially inhomogeneous distribution of coupling conductances cannot be predicted simply by the average or the minimum value of coupling conductance but may depend on the actual spatial distribution of these conductances.
Cytochrome P-450 ω-hydroxylase senses O2 in hamster muscle, but not cheek pouch epithelium, microcirculation
Authors: Lombard Julian H. , Kunert Mary Pat , Roman Richard J. , Falck John R. , Harder David R. , Jackson William F.
Published: December 2017

The goal of this study was to investigate the role of cytochrome P-450 ω-hydroxylase in mediating O2-induced constriction of arterioles in the microcirculation of the hamster. Male Golden hamsters were anesthetized with pentobarbital sodium, and the cremaster muscle or cheek pouch was prepared for observation by intravital microscopy. Arteriolar diameters were measured during elevations of superfusate[Formula: see text] from ∼5 to 150 mmHg. Arteriolar responses to elevated [Formula: see text] were determined in the cremaster muscle, in the retractor muscle where it inserts on the cheek pouch, and in the epithelial portion of the cheek pouch. Elevation of superfusion solution[Formula: see text] caused a vigorous constriction of arterioles in the cremaster and retractor muscles and in the epithelial portion of the cheek pouch. Superfusion with 10 μM 17-octadecynoic acid, a suicide substrate inhibitor of cytochrome P-450 ω-hydroxylase, and intravenous infusion of N-methylsulfonyl-12,12-dibromododec-11-enamide, a mechanistically different and highly selective inhibitor of cytochrome P-450 ω-hydroxylase, caused a significant reduction in the magnitude of O2-induced constriction of arterioles in the cremaster and retractor muscles. However, arteriolar constriction in response to elevated[Formula: see text] was unaffected by 17-octadecynoic acid or N-methylsulfonyl-12,12-dibromododec-11-enamide in the epithelial portion of the cheek pouch. These data confirm that there are regional differences in the mechanism of action of O2 on the microcirculation and indicate that cytochrome P-450 ω-hydroxylase senses O2 in the microcirculation of hamster skeletal muscle, but not in the cheek pouch epithelium.
Electrical and mechanical responses of rat middle cerebral arteries to reduced P O 2 and prostacyclin
Authors: Lombard Julian H. , Liu Yanping , Fredricks Kim T. , Bizub Donna M. , Roman Richard J. , Rusch Nancy J.
Published: December 2017

Isolated rat middle cerebral arteries were perfused and superfused with physiological salt solution equilibrated with a control (∼140 mmHg) or reduced (∼35–40 mmHg)[Formula: see text]. In other experiments, cerebral arteries were isolated and prostacyclin release was determined by radioimmunoassay for 6-ketoprostaglandin F1α. Equilibration of the vessels with reduced[Formula: see text] (35 mmHg) solution caused a significant increase in prostacyclin release relative to control[Formula: see text] (140 mmHg) conditions. Exposure of middle cerebral arteries to reduced[Formula: see text] caused vascular smooth muscle (VSM) hyperpolarization and vessel relaxation, which could be blocked by 1 μM glibenclamide, an inhibitor of the ATP-sensitive K+ channel, but not by 1 mM tetraethylammonium (TEA), an inhibitor of the Ca2+-activated K+ channel. Glibenclamide also inhibited VSM hyperpolarization and vasodilation in response to the stable prostacyclin analog iloprost, but TEA did not affect iloprost-induced dilation of the vessel. Endothelial removal eliminated the electrical and mechanical responses of the arteries to reduced[Formula: see text], but vessel responses to iloprost were similar to those of intact vessels. The results of this study are consistent with the hypothesis that hypoxic dilation of rat middle cerebral arteries is due to VSM hyperpolarization mediated by prostacyclin-induced activation of glibenclamide-sensitive K+ channels.
Role of phospholipase C, protein kinase C, and calcium in VEGF-induced venular hyperpermeability
Authors: Wu H. mac , Yuan Yuan , Zawieja David C. , Tinsley John , Granger Harris J.
Published: December 2017

We previously demonstrated that vascular endothelial growth factor (VEGF)-elicited increase in the permeability of coronary venules was blocked by the nitric oxide (NO) synthase inhibitor NG-monomethyl-l-arginine (l-NMMA). The aim of this study was to delineate in more detail the signaling pathways upstream from NO production in VEGF-induced venular hyperpermeability. The apparent permeability coefficient of albumin ( Pa) and endothelial cytosolic Ca2+concentration ([Ca2+]i) were measured in intact perfused porcine coronary venules using fluorescence microscopy. VEGF (10−10M) induced a two- to threefold increase in Pa, which was blocked by a monoclonal antibody directed against the VEGF receptor Flk-1/KDR, the phospholipase C (PLC) antagonist U-73122, or the protein kinase C (PKC) antagonist bisindolylmaleimide (BIM). In 12 venules that displayed the [Ca2+]iresponse to bradykinin (10−6M) and ionomycin (10−6M), only 4 vessels responded to VEGF with a transient increase in [Ca2+]i. Furthermore, Western blot analysis of cultured human umbilical vein endothelial cells showed that VEGF increased tyrosine phosphorylation of PLC-γ and serine phosphorylation of endothelial constitutive NO synthase (ecNOS). The hyperphosphorylation of PLC-γ was greatly attenuated by the KDR receptor antibody and U-73122, but not by BIM orl-NMMA. In contrast, U-73122 and BIM were able to inhibit VEGF-elicited serine phosphorylation of ecNOS. The results suggest that VEGF induces venular hyperpermeability through a KDR receptor-mediated activation of PLC. In turn, ecNOS is activated by PLC-mediated PKC and/or cytosolic Ca2+elevation stimulation.
Laminar fiber architecture and three-dimensional systolic mechanics in canine ventricular myocardium
Authors: Costa Kevin D. , Takayama Yasuo , McCulloch Andrew D. , Covell James W.
Published: December 2017

Previous studies suggest that the laminar architecture of left ventricular myocardium may be critical for normal ventricular mechanics. However, systolic three-dimensional deformation of the laminae has never been measured. Therefore, end-systolic finite strains relative to end diastole, from biplane radiography of transmural markers near the apex and base of the anesthetized open-chest canine anterior left ventricular free wall ( n = 6), were referred to three-dimensional laminar microstructural axes reconstructed from histology. Whereas fiber shortening was uniform [−0.07 ± 0.04 (SD)], radial wall thickening increased from base (0.10 ± 0.09) to apex (0.14 ± 0.13). Extension of the laminae transverse to the muscle fibers also increased from base (0.08 ± 0.07) to apex (0.11 ± 0.08), and interlaminar shear changed sign [0.05 ± 0.07 (base) and −0.07 ± 0.09 (apex)], reflecting variations in laminar architecture. Nevertheless, the apex and base were similar in that at each site laminar extension and shear contributed ∼60 and 40%, respectively, of mean transmural thickening. Kinematic considerations suggest that these dual wall-thickening mechanisms may have distinct ultrastructural origins.
Protein kinase C translocation and PKC-dependent protein phosphorylation during myocardial ischemia
Authors: Albert Carolyn J. , Ford David A.
Published: December 2017

The present study demonstrates that the α, ε, and ι isozymes of protein kinase C (PKC) are translocated to particulate fractions from the cytosol during brief intervals of global ischemia as well as reperfusion of ischemic rat myocardium. In contrast, phorbol ester treatment of perfused hearts resulted in the translocation of the α, δ, and ε isozymes of PKC to particulate fractions. Additionally, the α, δ, and ε isozymes of PKC are translocated to particulate fractions in phorbol ester-stimulated, isolated adult rat cardiac myocytes. Concomitant with the translocation of PKC isozymes to particulate fractions during myocardial ischemia, increased protein phosphorylation was observed, which was blocked by pretreatment of hearts with the selective PKC inhibitor bisindolylmaleimide I (50 nM). In particular, ischemia resulted in the phosphorylation of 26-, 20-, and 17-kDa particulate-associated proteins. Taken together, the present findings are the first to demonstrate that specific PKC isozymes are translocated to particulate fractions in the ischemic and the reperfused ischemic rat heart, resulting in the phosphorylation of specific particulate-associated proteins.
Intracellular gradients of O2supply to mitochondria in actively respiring single cardiomyocyte of rats
Authors: Takahashi Eiji , Endoh Hiroshi , Doi Katsuhiko
Published: December 2017

We demonstrated in a previous study [Takahashi, E., K. Sato, H. Endoh, Z.-L. Xu, and K. Doi. Am. J. Physiol. 275 ( Heart Circ. Physiol. 44): H225–H233, 1998] that significant radial gradients of intracellular [Formula: see text] may be produced in an uncoupled actively respiring, single isolated cardiomyocyte of the rat. The present study was designed to further determine whether such intracellular [Formula: see text] gradients can be a limiting factor of oxidative metabolism in uncoupled cardiomyocytes. The NAD(P)H fluorescence of a single cardiomyocyte was captured by a digital charge-coupled device camera and quantitated with a subcellular spatial resolution by a ratio-imaging technique. In the conditions that we demonstrated significant radial[Formula: see text] gradients (cells treated with 1 μM carbonyl cyanide m-chlorophenylhydrazone and superfused with 2.09% or 3.14% O2gas at 27°C), we demonstrated significant augmentation of NAD(P)H fluorescence near the core of an individual cell. The heterogeneous fluorescence pattern was not found in the control cell, whereas fluorescence intensity averaged over the cell was increased by hypoxia. These results suggest the possibility that oxidative phosphorylation near the core of actively respiring, uncoupled cardiomyocytes may be severely suppressed due to insufficient diffusional oxygen supply (hypoxic core) even if regions near the sarcolemma are adequately oxygenated.
Estrogen increases Ca2+efflux from female porcine coronary arterial smooth muscle
Authors: Prakash Y. S. , Togaibayeva A. A. , Kannan M. S. , Miller V. M. , Fitzpatrick L. A. , Sieck G. C.
Published: December 2017

Acute estrogen administration relaxes vascular smooth muscle by decreasing intracellular Ca2+ concentration ([Ca2+]i). In the present study, we examined the hypothesis that this reduction in [Ca2+]iis mediated in part by enhanced Ca2+ efflux. Coronary artery smooth muscle cells were isolated from gonad-intact, sexually mature female pigs. The [Ca2+]iresponse to endothelin-1 was measured using fluo 3 and confocal microscopy. 17β-Estradiol (E2β), but not 17α-estradiol or triamcinolone acetonide, caused a concentration-dependent (IC50 = 10 nM) decrease in the [Ca2+]iresponse to endothelin-1. This decrease was blocked by the specific estrogen receptor antagonist ICI-182780. Under conditions in which Ca2+ influx and sarcoplasmic reticulum Ca2+ reuptake were blocked, E2β still decreased [Ca2+]i. The response was blocked by extracellular lanthanum. These data indicate that E2β decreases [Ca2+]iin coronary artery smooth muscle by affecting Ca2+ efflux via a receptor-mediated mechanism.
Coronary microvascular protection with Mg2+: effects on intracellular calcium regulation and vascular function
Authors: Matsuda Naruto , Tofukuji Motohisa , Morgan Kathleen G. , Sellke Frank W.
Published: December 2017

The use of Mg2+-supplemented hyperkalemic cardioplegia preserves microvascular function. However, the mechanism of this beneficial action remains to be elucidated. We investigated the effects of Mg2+supplementation on the regulation of intracellular calcium concentration ([Ca2+]i) and vascular function using an in vitro microvascular model. Ferret coronary arterioles (80–150 μm in diameter) were studied in a pressurized (40 mmHg) no-flow, normothermic (37°C) state. Simultaneous monitoring of internal luminal diameter and [Ca2+]iusing fura 2 were made with microscopic image analysis. The microvessels ( n = 6 each group) were divided into four groups according to the content of MgCl2(nominally 0, 1.2, 5.0, and 25.0 mM) in a hyperkalemic cardioplegic solution ([K+] 25.0 mM). After baseline measurements, vessels were subjected to 60 min of hypoxia with hyperkalemic cardioplegia (equilibrated with 95% N2-5% CO2) containing each concentration of Mg2+([Mg2+]) and were then reoxygenated. During hyperkalemic cardioplegia, [Ca2+]iincreased in a time-dependent manner in all groups. In the lower [Mg2+] cardioplegia groups, [Ca2+]iwas significantly increased at the end of the 60-min cardioplegic period (247 ± 44 nM and 236 ± 49 nM in [Mg2+] 0 and 1.2 mM groups, respectively; both P < 0.05 vs. baseline) with 19.6–17.2% vascular contraction. Conversely, there was no significant [Ca2+]iincrease in the higher [Mg2+] cardioplegia groups and less vascular contraction (5.4–4.1%, both P < 0.05 vs. [Mg2+] 1.2 mM group). After reperfusion, agonist (U-46619, thromboxane A2analog)-induced vascular contraction was significantly enhanced in the lower [Mg2+] cardioplegia groups (both P < 0.05 vs. control) but was normalized in the higher [Mg2+] cardioplegia groups. Intrinsic myogenic contraction was significantly decreased in the lower [Mg2+] cardioplegia groups (both P < 0.05 vs. control) but was preserved in the higher [Mg2+] cardioplegia groups. These results suggest that supplementation of the solution with >5.0 mM [Mg2+] may prevent hyperkalemic cardioplegia-related intracellular Ca2+overloading and preserve vascular contractile function in coronary microvessels.
C-peptide induces a concentration-dependent dilation of skeletal muscle arterioles only in presence of insulin
Authors: Jensen Michael E. , Messina Edward J.
Published: December 2017

In this study we tested the hypothesis that C-peptide alone or in conjunction with insulin may cause a dilation of skeletal muscle arterioles. First-order arterioles (88 μm) isolated from rat cremaster muscles were pressurized (65 mmHg), equilibrated in a Krebs bicarbonate-buffered solution (pH 7.4), gassed with 10% O2(balance 5% CO2, 85% N2), and studied in a no-flow state. C-peptide administered at concentrations of 0.3, 1, 3, 10, 100, 300, and 1,000 ng/ml evoked arteriolar dilation that was not concentration dependent. In contrast, the administration of the four lower physiological concentrations of C-peptide to arterioles exposed to a nondilating concentration of insulin evoked a significant concentration-dependent increase in arteriolar diameter from 8.6 to 42.3% above control. The arteriolar dilation to C-peptide in the presence of insulin was completely inhibited by administration of NG-nitro-l-arginine (10−4M). Responses to ACh and adenosine were not enhanced when these drugs were administered in the presence of insulin. These results indicate that C-peptide has the capacity to evoke arteriolar dilation in skeletal muscle via a nitric oxide-mediated mechanism that appears to be enhanced by an interaction with insulin. Furthermore, the effects of insulin appear to be specific for C-peptide and are not the result of a general enhancement of endothelium-dependent or endothelium-independent dilation.
Sympathovagal balance is major determinant of short-term blood pressure variability in healthy subjects
Authors: Laitinen Tomi , Hartikainen Juha , Niskanen Leo , Geelen Ghislaine , Länsimies Esko
Published: December 2017

Short-term blood pressure variability (BPV) has been suggested to provide important information about cardiovascular regulation. However, the background of BPV, its determinants, and physiological correlates have remained obscure. The aim of this study was to characterize physiological correlates of BPV and to investigate associations between BPV and neural and hormonal regulatory systems at rest in healthy subjects. We studied 117 healthy, normal-weight, nonsmoking male and female subjects aged 23–77 yr. Spectral analysis of BPV and heart rate variability (HRV) was performed from 5-min blood pressure (Finapres) and electrocardiogram recordings during controlled breathing. Baroreflex sensitivity (BRS) was measured using the phenylephrine method. In addition, plasma concentrations of norepinephrine, epinephrine, and arginine vasopressin and plasma renin activity were measured. We found that the ratio between the low- and high-frequency components of HRV, an index of cardiac sympathovagal balance, correlated positively with total power and very low- and low-frequency components of systolic and diastolic BPV and inversely with high-frequency components of systolic and diastolic BPV. BRS, predominantly a measure of cardiac vagal regulation, correlated inversely with BPV. Furthermore, age, gender, body mass index, and systolic blood pressure contributed to BPV. Vasoactive hormones were not significant correlates of BPV. We conclude that sympathovagal balance of cardiovascular regulation is the major determinant of BPV. Other factors associated with BPV are age, gender, body mass index, blood pressure, and BRS.
Estradiol modulates vascular response to melatonin in rat caudal artery
Authors: Doolen Suzanne , Krause Diana N. , Duckles Sue P.
Published: December 2017

The purpose of this study was to determine whether estrogen modulates the function of vascular melatonin receptors. We used the rat caudal artery and found that the contractile effects of melatonin were influenced by the estrous cycle, ovariectomy, and estrogen replacement. In arterial ring segments isolated from female rats, melatonin potentiated, in a concentration-dependent manner, contractions produced either by adrenergic nerve stimulation or by phenylephrine. Constrictor responses to melatonin were smaller in arteries from female rats in proestrus compared with other stages of the estrous cycle and after ovariectomy. Administration of 17β-estradiol to ovariectomized female rats also resulted in decreased constriction of isolated arteries to melatonin; however, in vitro addition of 17β-estradiol (10−7 M) had no effect. In the caudal artery, melatonin appears to act on two receptor subtypes that mediate contraction and relaxation, respectively. The selective melatonin MT2-receptor antagonist 4-phenyl-2-propionamidotetraline (4P-PDOT) enhanced constrictor responses to melatonin in arterial segments from intact female rats, consistent with the inhibition of MT2 receptor-mediated relaxation. In contrast, 4P-PDOT had no significant effect in arteries from ovariectomized female rats. However, when estradiol was replaced in vivo, the effect of 4P-PDOT on melatonin responses was restored. Thus circulating estradiol appears to enhance MT2 melatonin-receptor function in the thermoregulatory caudal artery of the female rat resulting in increased vasodilatation in response to melatonin.
Delayed ischemic preconditioning is mediated by opening of ATP-sensitive potassium channels in the rabbit heart
Authors: Bernardo Nelson L. , D’Angelo Michael , Okubo Shinji , Joy Archi , Kukreja Rakesh C.
Published: December 2017

Cardioprotection from preconditioning reappears 24 h after the initial stimulus. This phenomenon is called the second window of protection (SWOP). We hypothesized that opening of the ATP-sensitive potassium (KATP) channel mediates the protective effect of SWOP. Rabbits were preconditioned (PC) with four cycles of 5-min regional ischemia each followed by 10 min of reperfusion. Twenty-four hours later, the animals were subjected to sustained ischemia for 30 min followed by 180 min of reperfusion (I/R). Glibenclamide (Glib, 0.3 mg/kg ip) or 5-hydroxydecanoate (5-HD, 5 mg/kg iv) was used to block the KATP channel function. Infarct size was reduced from 41.2 ± 2.6% in sham-operated rabbits to 11.6 ± 1.0% in PC rabbits, a 71% reduction ( n = 11, P < 0.01). Treatment with Glib or 5-HD before I/R increased the infarct size to 43.4 ± 2.6 and 37.8 ± 1.9%, respectively ( P < 0.01 vs. PC group, n = 12/group). Sham animals treated with either Glib or 5-HD had an infarct size of 39.0 ± 3.4 and 37.8 ± 1.5%, respectively, which was not different from control (40.0 ± 3.8%) or sham (41.2 ± 2.6%) I/R hearts. Monophasic action potential duration (APD) at 50% repolarization significantly shortened by 28.7, 26.6, and 23.3% in sham animals during 10, 20, and 30 min of ischemia. However, no further augmentation in the shortening of APD was observed in PC hearts. Glib and 5-HD significantly suppressed ischemia-induced epicardial APD shortening, suggesting that 5-HD may not be a selective blocker of the mitochondrial KATP channel in vivo. We conclude that SWOP is mediated by a KATP channel-sensitive mechanism that may have occurred because of the opening of the sarcolemmal KATP channel in vivo.
Physiological doses of estradiol decrease nocturnal blood pressure in normotensive postmenopausal women
Authors: Cagnacci Angelo , Rovati Lucio , Zanni Annalisa , Malmusi Stefania , Facchinetti Fabio , Volpe Annibale
Published: December 2017

The effect of a 2-mo treatment with transdermal estradiol (50 μg/day) versus placebo on 24 h of blood pressure rhythm was investigated in 18 normotensive healthy postmenopausal women. Whereas daytime blood pressure was not modified, nighttime blood pressure was reduced by estradiol. Estradiol magnified the nocturnal decrement of systolic (14.3 ± 7.2 vs. 9.8 ± 6.7 mmHg, P = 0.0033), diastolic (11.6 ± 5.0 vs. 7.5 ± 7.3 mmHg, P = 0.028), and mean (10.8 ± 5.6 vs. 7.2 ± 4.5 mmHg, P = 0.011) blood pressure. As a consequence, the 24-h rhythm of mean blood pressure was restored in 50% of the subjects ( P = 0.045) in whom it was absent and was amplified in the remaining 50% of the subjects. Body mass index was an independent determinant of blood pressure values being directly related to the amplitude of the 24-h mean blood pressure rhythm ( r2= 0.38; P = 0.0067). In normotensive postmenopausal women, physiological doses of estradiol amplify the nocturnal decline of blood pressure.
Bradykinin-stimulated protein synthesis by myocytes is dependent on the MAP kinase pathway and p70S6K
Authors: Ritchie Rebecca H. , Marsh James D. , Schiebinger Rick J.
Published: December 2017

Bradykinin (BK) has a direct hypertrophic effect on rat ventricular cardiomyocytes (VCM) as defined by an increase in protein synthesis and an increase in atrial natriuretic peptide mRNA and secretion. In the current study, we have examined the dependence of BK-induced protein synthesis on activation of 90-kDa ribosomal S6 kinase (p90rsk) and 70-kDa S6 kinase (p70S6K). Both of these kinases possess the ability to phosphorylate the ribosomal protein S6, which plays an important role in initiating mRNA translation. Stimulation of adult VCM with 10 μM BK increased p90rsk activity by 2.5 ± 0.3-fold and increased p70S6Kactivity by 2.0 ± 0.3-fold. p90rsk is a terminal kinase in the mitogen-activated protein (MAP) kinase pathway. Inhibition of MAP kinase kinase activation by Raf in the MAP kinase pathway with PD-098059 (25 μM) blocked BK-stimulated activation of p90rsk by 70% and unexpectedly blocked p70S6K by 72%. Rapamycin inhibited BK-stimulated p70S6Kactivity by 93% but had no effect on p90rsk activation by BK. Inhibition of the MAP kinase pathway and p70S6K with PD-098059 was paralleled by changes in protein synthesis. BK (10 μM) increased [3H]phenylalanine incorporation by 27 ± 3 and 39 ± 6% in cultured adult and neonatal VCM, respectively. Treatment with PD-098059 or rapamycin abolished the increase in protein synthesis stimulated by BK. These results suggest that 1) BK activates p70S6K and p90rsk; 2) although both p70S6K and p90rsk have the potential to phosphorylate the ribosomal S6 protein, p70S6K and not p90rsk is the predominant kinase involved in increasing protein synthesis by BK; and 3) p70S6K activation is dependent on stimulation of the MAP kinase pathway at a point distal to Raf.
NOS gene transfer inhibits expression of cell cycle regulatory molecules in vascular smooth muscle cells
Authors: Sharma Ram V. , Tan Enqing , Fang Shengyun , Gurjar Milind V. , Bhalla Ramesh C.
Published: December 2017

The mechanisms of nitric oxide (NO)-mediated inhibition of vascular smooth muscle (VSM) cell proliferation are still obscure. Cyclins A and E in association with cyclin-dependent kinase 2 (cdk2) serve as positive regulators for mammalian cell cycle progression through the G1/S checkpoint of the cell cycle and subsequent cell proliferation. Therefore, we have tested the effect of adenovirus-mediated transfection of the endothelial nitric oxide synthase (eNOS) gene into guinea pig coronary VSM cells on platelet-derived growth factor (BB homodimer) (PDGF-BB)-stimulated cell proliferation and the expression of cell cycle regulatory molecules. Transfection of the eNOS gene ( eNOS) into VSM cells significantly inhibited ( P < 0.05) [3H]thymidine incorporation into the DNA in response to PDGF-BB stimulation compared with lacZ-transfected control cells. The eNOS transfer significantly inhibited ( P < 0.05) PDGF-BB-induced proliferating cell nuclear antigen (PCNA) and cyclin A expression in VSM cells compared with cells transfected with the control vector. The time course of cyclin E expression in response to PDGF-BB stimulation was delayed in eNOS-transfected cells. Levels of cyclin-dependent kinase inhibitors p21 and p27 were not significantly affected by eNOStransfer. eNOS transfer did not decrease PDGF-β receptor number, affinity, and autophosphorylation measured by radioreceptor assay and Western analysis. These results suggest that inhibition of PDGF-stimulated expression of cyclin A, cyclin E, and PCNA is the target of NO action. These findings could explain, at least in part, NO-mediated inhibition of VSM cell proliferation.
AMP deaminase in piglet cardiac myocytes: effect on nucleotide metabolism during ischemia
Authors: Hohl Charlene M.
Published: December 2017

The purpose of this study was to examine in situ regulation of AMP deaminase in newborn piglet cardiac myocytes and to determine its role in nucleotide metabolism during ischemia. When a rapid deenergization paradigm was used to assay AMP deaminase, enzyme activity depended on the hormonal and metabolic status of cells just before deenergization. Inosine 5′-monophosphate (IMP) formation was increased 150% in deenergized myocytes pretreated with phorbol 12-myristate 13-acetate (PMA; EC50= 4.7 × 10−8M). This effect was 90% blocked with the protein kinase C (PKC) inhibitor staurosporine. In addition, the β-adrenergic agonist isoproterenol stimulated AMP deaminase activity (EC50= 1.5 × 10−8M), and IMP formation was directly correlated to intracellular cAMP levels ( r2= 0.9). Furthermore, adenosine increased IMP formation, whereas nonrespiring, glycolyzing piglet myocytes had reduced AMP deaminase activity. Pretreatment of perfused piglet hearts with adenosine, but not PMA, before exposure to global ischemia resulted in enhanced conversion of AMP to IMP during the ischemic period. Similar results were obtained in piglet myocytes preincubated with adenosine or PMA before exposure to simulated ischemia. These results may be relevant to the preconditioning phenomenon.
Properties and expression of Ca2+-activated K+ channels in H9c2 cells derived from rat ventricle
Authors: Wang Wei , Watanabe Makino , Nakamura Takeshi , Kudo Yoshihisa , Ochi Rikuo
Published: December 2017

H9c2 is a clonal myogenic cell line derived from embryonic rat ventricle that can serve as a surrogate for cardiac or skeletal muscle in vitro. Using whole cell clamp with H9c2 myotubes, we observed that depolarizing pulses activated slow outward K+ currents and then slow tail currents. The K+ currents were abolished in a Ca2+-free external solution, indicating that they were Ca2+-activated K+ currents. They were blocked by apamin, a small-conductance Ca2+-activated K+ (SK) channel antagonist (IC50 = 6.2 nM), and by d-tubocurarine (IC50 = 49.4 μM). Activation of SK channels exhibited a bell-shaped voltage dependence that paralleled the current-voltage relation for L-type Ca2+ currents ( I Ca,L). I Ca,L exhibited a slow time course similar to skeletal I Ca,L, were unaffected by apamin, and were only slightly depressed by d-tubocurarine. RT-PCR analysis of the mRNAs revealed that rSK3, but not rSK1 or rSK2, was expressed in H9c2 myotubes but not in myoblasts. These results suggest that rSK3 channels are expressed in H9c2 myotubes and are primarily activated by I Ca,L directly or indirectly via Ca2+-induced Ca2+ release from sarcoplasmic reticulum.