bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of tetrahydrobiopterin biosynthesis impairs endothelium-dependent relaxations in canine basilar artery
Authors: Kinoshita H. , Milstien S. , Wambi C. , Katusic Z. S.
Published: December 2017

Tetrahydrobiopterin is an essential cofactor in biosynthesis of nitric oxide. The present study was designed to determine the effect of decreased intracellular tetrahydrobiopterin levels on endothelial function of isolated cerebral arteries. Blood vessels were incubated for 6 h in minimum essential medium (MEM) in the presence or absence of a GTP cyclohydrolase I inhibitor, 2,4-diamino-6-hydroxypyrimidine (DAHP, 10(-2) M). Rings with and without endothelium were suspended for isometric force recording in the presence of a cyclooxygenase inhibitor, indomethacin (10(-5) M). In arteries with endothelium, DAHP significantly reduced intracellular levels of tetrahydrobiopterin. DAHP in combination with a precursor of the salvage pathway of tetrahydrobiopterin biosynthesis, sepiapterin (10(-4) M), not only restored but increased levels of tetrahydrobiopterin above control values. In DAHP-treated arteries, endothelium-dependent relaxations to bradykinin (10(-10)-10(-6) M) or calcium ionophore A23187 (10(-9)-10(-6) M) were significantly reduced, whereas endothelium-independent relaxations to a nitric oxide donor, 3-morpholinosydnonimine (10(-9)-10(-4) M), were not affected. When DAHP-treated arteries with endothelium were incubated with sepiapterin (10(-4) M) or superoxide dismutase (150 U/ml), relaxations to bradykinin and A23187 were restored to control levels. In contrast, superoxide dismutase did not affect endothelium-dependent relaxations in arteries incubated in MEM. A nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (10(-4) M), abolished relaxations to bradykinin or A23187 in control arteries and in DAHP-treated arteries. These studies demonstrate that in cerebral arteries, decreased intracellular levels of tetrahydrobiopterin can reduce endothelium-dependent relaxations. Production of superoxide anions during activation of dysfunctional endothelial nitric oxide synthase appears to be responsible for the impairment of endothelial function.
Sympathetic nervous system and hypertension during prolonged TxA2/PGH2 receptor activation in rats
Authors: Gao H. , Welch W. J. , DiBona G. F. , Wilcox C. S.
Published: December 2017

The thromboxane A2 (TxA2)/prostaglandin H2 (PGH2) receptor mimetic U-46619 (0.6 microgram.kg-1.min-1) was infused into conscious rats receiving a high-salt diet. U-46619 increased the mean arterial pressure (MAP) over 13 days by 25 +/- 2 mmHg, whereas the MAP of vehicle-infused controls did not change (-2 +/- 2 mmHg). In subgroups infused with U-46619, cardiac output was unchanged, whereas renal blood flow was reduced (before: 8.5 +/- 0.8; day 4: 5.7 +/- 0.7 ml/min; P < 0.01). Ifetroban (a specific TxA2/PGH2 receptor antagonist) reduced MAP to basal levels in the group receiving U-46619 when infused intravenously (1-100 micrograms/kg) but not intracerebroventricularly (1-100 ng/kg). Hexamethonium (10 mg/kg i.v., a ganglionic blocking agent) and prazosin (0.1 mg/kg, an alpha-adrenergic antagonist) decreased MAP significantly (P < 0.05) more in the experimental group (hexamethonium, U-46619: -55 +/- 3 vs. vehicle: -43 +/- 4 mmHg; and prazosin, U-46619: 28 +/- 3 vs. vehicle: 17 +/- 2 mmHg). In conclusion, hypertension during prolonged infusions of U-46619 into conscious, salt-loaded rats is accompanied by an increase in total and renal vascular resistance and is dependent on peripheral but not central TxA2/PGH2 receptors and on the autonomic and alpha 1-adrenergic peripheral sympathetic nervous systems.
Ischemic preconditioning of human myocardium: protein kinase C mediates a permissive role for alpha 1-adrenoceptors
Authors: Cleveland J. C. , Meldrum D. R. , Rowland R. T. , Cain B. S. , Meng X. , Gamboni-Robertson F. , Banerjee A. , Harken A. H.
Published: December 2017

The purposes of this study were to determine whether ischemic preconditioning (IPC) in human atrial trabeculae is mediated by alpha 1-adrenoceptors and protein kinase C (PKC) and whether the protection of IPC is replicated with alpha 1-adrenoceptor stimulation [alpha 1-adrenoceptor preconditioning (alpha 1-PC)]. Atrial trabeculae were obtained during coronary bypass surgery. The trabeculae were suspended in organ baths containing Tyrode solution and field stimulated at 1 Hz, and developed force was recorded. The trabeculae underwent 45 min of simulated ischemia (SI) and 120 min of reperfusion (I/R injury). IPC trabeculae received transient SI before I/R injury, alpha 1-Adrenoceptor blockade with BE-2254 and PKC inhibition with chelerythrine were independently combined with IPC before I/R injury. alpha 1-PC before I/R was examined with alpha 1-adrenergic agonist (phenylephrine) pre-treatment. Improved recovery of developed force and higher tissue creatine kinase activity were present in IPC trabeculae, and the protective effect of IPC was eliminated with either alpha 1-adrenoceptor blockade or PKC inhibition. alpha 1-PC trabeculae also exhibited enhanced functional recovery after I/R injury but lacked preservation of tissue creatine kinase activity. PKC inhibition eliminated the functional protection of alpha 1-PC. These results suggest that, in human atrial trabeculae, alpha 1-adrenoceptors and PKC mediate, in part, the functional and tissue CK preservation conferred by IPC, but alpha 1-PC does not replicate the protection of IPC.
Left atrial systolic and diastolic function after cessation of pacing in tachycardia-induced heart failure
Authors: Hoit B. D. , Shao Y. , Gabel M. , Pawloski-Dahm C. , Walsh R. A.
Published: December 2017

Studies in the rapid-pacing model of heart failure have shown that left ventricular (LV) systolic function normalizes on cessation of pacing and LV diastolic dysfunction persists, but there is no information regarding atrial function under these conditions. To determine the effects of cessation of pacing on left atrial (LA) systolic and diastolic function, ten dogs with rapid pacing-induced heart failure (250 beats/min for 3-4 wk), six dogs with regression of heart failure (4 wk after cessation of rapid pacing), and seven control dogs were instrumented with LA sonomicrometers and micromanometers. At matched LA pressure, LA ejection (10.2 +/- 3.0 vs. 17.4 +/- 5.5%), reservoir volume fractions (19 +/- 8 vs. 35 +/- 11%), and heart rate-corrected mean normalized systolic ejection rate (1.25 +/- 0.33 vs. 1.60 +/- 0.44 EF/s) were significantly less, and the volume-normalized diastolic stiffness constant (4.9 +/- 0.8 vs. 3.2 +/- 1.1) was significantly greater, in regression versus control dogs; these changes were associated with incomplete regression of LA hypertrophy and a persistent 77.4% increase in beta-myosin heavy chain (beta-MHC) in the LA body. LV systolic function and weight were not significantly different, whereas the time constant of LV relaxation was longer (52.5 +/- 4.4 vs. 40.8 +/- 7.6 ms; P < 0.05) and LV end-diastolic pressure was greater (12.2 +/- 1.8 vs. 7.1 +/- 2.0 mmHg; P < 0.05) in regression compared with control dogs. Thus, unlike the normalization of LV systolic function observed with cessation of rapid pacing, LA systolic function is persistently abnormal, owing in part to persistent LV diastolic dysfunction, residual LA hypertrophy, and MHC isoform switches.
Disparate effects of preconditioning and MLA on 5'-NT and adenosine levels during coronary occlusion
Authors: Przyklenk K. , Hata K. , Zhao L. , Kloner R. A. , Elliott G. T.
Published: December 2017

Ischemic preconditioning has been proposed to protect the heart against infarction by increasing 5'-nucleotidase (5'-NT) activities and augmenting adenosine levels during sustained coronary artery occlusion. To test this theory, anesthetized dogs received four 5-min episodes of preconditioning ischemia, pretreatment with the pharmacological "preconditioning mimetic" monophosphoryl lipid A (MLA, 35 micrograms/kg i.v.) or no intervention before coronary artery ligation. At 20 min into occlusion (the crucial time at which myocyte death begins in this model), myocardial samples were obtained for measurement (by high-performance liquid chromatography) of ectosolic and cytosolic 5'-NT activity and adenosine levels. Preconditioning and MLA pretreatment limit infarct size in the canine model by 75 and 50%, respectively. However, only MLA augmented 5'-NT activity [i.e., cytosolic 5'-NT in the ischemic subendocardium was 26 +/- 1, 39 +/- 7, and 26 +/- 6 nmol. mg protein-1. min-1 in preconditioned, MLA, and control groups (P < 0.05), respectively]. Moreover, adenosine levels (in nmol/mg protein) were increased with MLA treatment (2.30 +/- 0.44) but attenuated in preconditioned dogs (1.11 +/- 0.23; P < 0.05) versus controls (1.87 +/- 0.29). Thus 5'-NT and adenosine levels need not be increased beyond control values during sustained occlusion to elicit cardioprotection.
Ito1 dictates behavior of ICl(Ca) during early repolarization of canine ventricle
Authors: Zygmunt A. C. , Robitelle D. C. , Eddlestone G. T.
Published: December 2017

The contributions of the 4-aminopyridine (4-AP)-sensitive transient outward potassium conductance (Ito1) and the calcium-activated chloride conductance (ICl(Ca)] to cardiac action potentials were investigated in canine ventricular myocytes. Action potentials or currents were recorded at 37 degrees C using standard whole cell or amphotericin B perforated-patch-clamp techniques. Inhibition of Ito1 by 1 mM 4-AP prolonged phase 1 repolarization, elevated the action potential notch, and depressed the plateau. Action potential voltage clamp revealed that 4-AP blocked a rapidly decaying outward current during phase 1 without affecting plateau or diastolic currents. These results suggested that depression of the plateau was not a direct result of Ito1 inhibition but followed from delayed phase 1 repolarization. Calcium current (ICa) at the peak of the action potential dome was reduced 60 +/- 4% when the rate of phase 1 repolarization was reduced. ICl(Ca) measured by action potential clamp reversed over the course of the action potential. Chloride fluxes associated with outward and inward components of the 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid-sensitive current were +130 +/- 17 and -184 +/- 20 (pA.ms)/pF, respectively. The effects of selective inhibition of ICl(Ca) on the action potential were dependent on the rate of early repolarization and the prominence of the notch. Inhibition of ICl(Ca) elevated the plateau and slightly abbreviated action potential duration when the notch was prominent. When repolarization was prolonged and the notch was shallow, inhibition of ICl(Ca) elevated the notch and the plateau and abbreviated duration. We have shown that Ito1 and ICl(Ca) contribute to canine ventricular action potentials. The extent of overlap between Ito1 and ICl(Ca) during the action potential is largely determined by the amplitude of Ito1 and the depth of the notch. Regional differences in the density of Ito1, or interventions that moderate phase 1 repolarization by reducing this current, will have considerable effect on the time course of ICa and calcium-dependent conductances.
Interstitial norepinephrine level by cardiac microdialysis correlates with ventricular contractility
Authors: Kawada T. , Yamazaki T. , Akiyama T. , Shishido T. , Miyano H. , Sato T. , Sugimachi M. , Alexander J. , Sunagawa K.
Published: December 2017

Although a cardiac microdialysis technique has made it possible to estimate myocardial interstitial norepinephrine (NE) levels, whether such levels reflect the local NE concentration that would regulate ventricular contractility remains unknown. If such levels indicate locally regulating NE concentration, then ventricular contractility should be a unique function of the interstitial NE level regardless of how the latter is altered. To examine this hypothesis, we altered the interstitial NE level endogenously by stimulating the cardiac sympathetic nerves at 1 and 2 Hz while monitoring ventricular contractility. We also altered the interstitial NE level exogenously by means of intravenous NE infusions at 10 and 40 micrograms.kg-1.h-1. The basal NE levels did not differ between the stimulation and the infusion experiments (42.9 +/- 11.2 vs. 40.1 +/- 6.2 pg/ml, means +/- SE). The slopes of regression lines relating ventricular contractility and interstitial NE level were also not different between the two experiments [1.13 +/- 0.20 vs. 1.17 +/- 0.20%/(pg/ml), means +/- SE]. We conclude that the interstitial NE level estimated by cardiac microdialysis reflects the local NE concentration regulating ventricular contractility.
Role of passive electrical properties during action potential restitution in intact heart
Authors: Laurita K. R. , Girouard S. D. , Rudy Y. , Rosenbaum D. S.
Published: December 2017

Action potential duration (APD) restitution is classically attributed to membrane ionic currents; however, the role of cell-to-cell coupling in restitution is poorly understood. To test the hypothesis that passive electrical properties of multicellular preparations influence restitution, spatial gradients of transmembrane voltage were measured with high spatial (0.83 mm), voltage (1 mV), and temporal (0.5 ms) resolutions using voltage-sensitive dye in Langendorff-perfused guinea pig ventricle. At short premature coupling intervals, APD failed to shorten in cells located near (< 3 mm) the site of pacing corresponding to the site of earliest repolarization, deviating from classical restitution. In contrast, APD shortened exponentially with increasing stimulus prematurity when pacing was remote from the identical recording site. The mechanism responsible for nonexponential restitution was investigated in a one-dimensional propagation model using the dynamic Luo-Rudy formulation of the ventricular cell and was found to be attributable to depolarizing axial current present in regions of steep repolarization gradients. Moreover, axial current loading attenuated spatial gradients of repolarization that were prominent in the absence of cell-to-cell coupling. These data demonstrate that 1) in contrast to restitution in isolated cells, restitution in multicellular tissue is influenced by axial current from neighboring cells, and 2) in normal myocardium, axial current between cells attenuates dispersion of repolarization during premature stimulation of the heart.
Heat stress protects aged hypertrophied and nonhypertrophied rat hearts against ischemic damage
Authors: Cornelussen R. N. , Garnier A. V. , Vork M. M. , Geurten P. , Reneman R. S. , van der Vusse G. J. , Snoeckx L. H.
Published: December 2017

To explore the effects of heat stress (HS) in aged hypertrophied and nonhypertrophied rat hearts, postischemic recovery was investigated 15 mo after aortic constriction (AoB) or sham operation (Sham). Twenty-four hours after HS (42 degrees C; 15 min) or control treatment (normothermia), global ischemia was induced for 20 min in isolated AoB hearts and for 20 or 30 min in Sham hearts. After HS, postischemic recovery after 20-min ischemia in AoB hearts and 30-min ischemia in Sham hearts, respectively, was significantly better than in corresponding controls. In AoB hearts, cardiac output (CO), left ventricular developed pressure (LVDP), and the positive maximal first derivative of left ventricular pressure (+dP/dtmax) recovered to 33 +/- 26 (means +/- SD), 87 +/- 5, and 72 +/- 12%, respectively, after HS and to 5 +/- 8, 22 +/- 39, and 17 +/- 29% of preischemic values, respectively, in controls. Postischemic arrhythmias were significantly reduced in HS hypertrophied hearts, but creatine kinase (CK) loss was not reduced. In Sham hearts subjected to 30 min ischemia, CO, LVDP, and +dP/dtmax recovered to 20 +/- 20, 75 +/- 8, and 59 +/- 15%, respectively, after HS and to 3 +/- 8, 21 +/- 32, and 16 +/- 32% of preischemic values, respectively, in controls. Duration of arrhythmias and CK loss were not reduced in the heated hearts. When Sham hearts were subjected to only 20-min ischemia, functional recovery was not different in HS and control hearts, indicating that HS pretreatment extends the ischemic interval before irreversible injury occurs in the heart. In all HS Sham hearts, the myocardial 72-kDa HS protein (HSP 70) content was significantly increased. However, in HS AoB hearts, HSP 70 levels were not significantly different from the values in the control hearts. These results indicate that HS pretreatment induces cardioprotection in aged hypertrophied and nonhypertrophied rat hearts, which, however, cannot be unequivocally related to increased HSP 70 tissue contents.
Blood pressure variability responses to tilt are buffered by cardiac autonomic control
Authors: Sloan R. P. , DeMeersman R. E. , Shapiro P. A. , Bagiella E. , Chernikhova D. , Kuhl J. P. , Zion A. S. , Paik M. , Myers M. M.
Published: December 2017

Variability in blood pressure (BPV) is influenced by vascular sympathetic drive as well as autonomic control of the heart. Evidence suggests that elimination of cardiac autonomic control, as measured by heart period variability (HPV), produces a reduction in BPV at rest but an increase in BPV during challenge. We recently showed that the BPV response to psychological challenge, which principally produces cardiac parasympathetic withdrawal, was inversely related to the subject's level of cardiac control. In the current study we examined the BPV response to orthostatic tilt, a sympathetic stressor. Subjects were 22 healthy men and women who differed in cardiac control due in part to differences in aerobic capacity. HPV and BPV were measured noninvasively on a beat-to-beat basis. Tilt produced significant increases in heart rate and diastolic blood pressure and a significant decrease in high frequency HPV. As predicted, changes in BPV in response to tilt were inversely related to resting HPV. Results are interpreted in terms of a model of cardiovascular control which holds that BPV originates from feedforward effects of central control of the heart, feedback effects mediated through the baroreflexes, and direct sympathetic vascular effects.
Ryanodine and left ventricular function in intact dogs: dissociation of force-based and velocity-based indexes
Authors: Prabhu S. D. , Rozek M. M. , Murray D. R. , Freeman G. L.
Published: December 2017

After anesthesia and autonomic blockade, nine dogs chronically instrumented with left ventricular (LV) micromanometers and piezoelectric dimension crystals were studied before and after the intravenous administration of 4 micrograms/kg ryanodine, a specific inhibitor of the sarcoplasmic reticulum Ca2+ release channel. Ryanodine prolonged LV contraction and relaxation (P < 0.001) without changing heart rate, end-diastolic volume (EDV), or end-systolic pressure. Velocity-dependent mechanical parameters were significantly depressed, including the maximal rate of LV pressure rise (dP/dtmax; P < 0.002), the mean velocity of circumferential fiber shortening (P < 0.002), the slope of the dP/dtmax-EDV relation (P < 0.05), and the time constant of LV relaxation (P < 0.01). In contrast, the slopes of the end-systolic pressure-volume (PES-VES) and stroke work (SW)-EDV relations, both force-based parameters, were increased (P < 0.05) or maintained, respectively. Ryanodine reduced overall LV contractile performance, evidenced by significant rightward shifts of the PES-VES, dP/dtmax-EDV, and SW-EDV relations and reduced SW at constant preload (P < 0.02). Thus, in the closed-chest dog, low-dose ryanodine resulted in 1) generalized slowing of LV mechanical events without changes in heart rate or load, 2) dissociation of velocity-based and force-based measures of LV function, with depression of the former but enhancement or maintenance of the latter, and 3) reduced overall LV inotropic performance. These effects are consistent with ryanodine-induced alterations of the Ca2+ transient and altered sarcoplasmic reticulum Ca2+ availability.
Sustained cardiomyocyte DNA synthesis in whole embryo cultures lacking the TSC2 gene product
Authors: Pajak L. , Jin F. , Xiao G. H. , Soonpaa M. H. , Field L. J. , Yeung R. S.
Published: December 2017

Tuberous sclerosis complex (TSC) is characterized by the appearance of nonmalignant tumors that affect a wide spectrum of organs, including the heart. TSC disease-causing genes have been identified on chromosomes 9 (TSC1) and 16 (TSC2). This study examined the impact of the TSC2 gene product on cardiomyocyte proliferation and terminal differentiation. We took advantage of the observation that Eker rats carry a germ-line TSC2 mutation. Rats heterozygous for the mutation (TSC2EK/+) are predisposed to renal carcinoma, whereas animals homozygous for the mutation (TSC2EK/EK) die in utero during midgestation. Spontaneously contractile cardiomyocytes were observed after multiple passages of whole embryo cultures prepared from embryonic day 12.5 TSC2EK/EK fetuses but not from TSC2EK/+ or wild-type fetuses. The TSC2EK/EK cardiomyocytes continued to actively synthesize DNA after as many as eight passages. Cytological, ultrastructural, and molecular analyses indicated that the TSC2EK/EK cardiomyocytes retained a highly differentiated phenotype similar to that observed for normal rat cardiomyocytes during late embryonic and early neonatal life. These results suggested that the TSC2 gene product is required for normal cardiomyocyte cell-cycle withdrawal and terminal differentiation.
Role of β1- and β2-adrenergic receptors in regulation of Cl−and Ca2+channels in guinea pig ventricular myocytes
Authors: Hool Livia C. , Harvey Robert D.
Published: December 2017

The role of β1- and β2-adrenergic receptor stimulation in modulating adenosine 3′,5′-cyclic monophosphate (cAMP)-regulated Cl−and Ca2+currents was investigated with use of guinea pig ventricular myocytes. Activation of the Cl−current by the nonselective β-receptor agonist isoproterenol (Iso) was not affected by the β2-receptor antagonist ICI-118,551 (ICI), but it was blocked by the β1-receptor antagonist atenolol. The inability of β2-receptor stimulation to activate the Cl−current was confirmed by the lack of response to the selective β2-receptor agonists salbutamol and zinterol. Responses to β2-adrenergic receptor stimulation were also looked for in pertussis toxin (PTX)-treated myocytes because PTX increases the sensitivity of responses to Iso, and PTX has been reported to increase the responsiveness to β2- but not β1-receptor stimulation. PTX treatment increased the sensitivity of the Cl−current to activation by Iso in the presence of ICI, indicating that PTX increases β1-receptor responsiveness. PTX treatment also resulted in the ability of salbutamol to activate the Cl−current. However, the response to salbutamol was blocked by atenolol but not by appropriate concentrations of ICI, suggesting that salbutamol was activating β1-receptors. These results indicate that PTX treatment increases the sensitivity to β1-receptor stimulation, without affecting β2-responsiveness. To verify that the lack of response to β2-receptor stimulation was not unique to the Cl−current, the effects of β2-receptor agonists on the L-type Ca2+current were also examined. The Ca2+current was only affected by high concentrations of zinterol or salbutamol, and such responses were blocked by atenolol, but not by ICI, suggesting that activation of β1-receptors was involved. These results indicate that β1- but not β2-adrenergic receptor stimulation plays an important role in modulating the cAMP-regulated Cl−and Ca2+currents in guinea pig ventricular myocytes.
Dual effects of endothelins on the muscarinic K+current in guinea pig atrial cells
Authors: Yamaguchi Hiroshi , Sakamoto Naoya , Watanabe Yasuhide , Saito Toshihiro , Masuda Yoshiaki , Nakaya Haruaki
Published: December 2017

Effects of endothelins (ETs) on the acetylcholine receptor-operated K+current ( IK ACh) were examined in isolated guinea pig atrial cells using patch-clamp techniques. ET-1 or ET-3 produced a transient activation of IK AChin atrial cells held at −40 mV. When IK AChwas preactivated by 1 μM carbachol, however, both ETs produced a transient potentiation followed by a sustained inhibition of the current. When IK AChwas maximally activated by 10 μM carbachol or 100 μM adenosine, these ETs produced only a sustained inhibition of the IK ACh. Their inhibitory effects on the preactivated IK AChwere concentration dependent, and the half-maximal effective concentrations were 314 pM for ET-1 and 1.13 nM for ET-3. The inhibitory effect of ET-1 was antagonized by BQ-485, a specific ETAreceptor antagonist, but not by BQ-788, a specific ETBreceptor antagonist, indicating that the ET-1 effect is mediated by ETAreceptors. On the other hand, the inhibitory effect of ET-3 was antagonized by BQ-788 and more effectively by BQ-485, suggesting the involvement of “atypical” ET receptors. Both ETs partly reversed the carbachol-induced shortening of the action potential recorded in the current-clamp mode. Inhibitory effects of ET-1 and ET-3 on the preactivated IK AChmay contribute to the positive inotropic and chronotropic effects of ETs in atrial tissues.
Modulation of Kv4 channels, key components of rat ventricular transient outward K+ current, by PKC
Authors: Nakamura Tomoe Y. , Coetzee William A. , Vega-Saenz De Miera Eleazar , Artman Michael , Rudy Bernardo
Published: December 2017

Current evidence suggests that members of the Kv4 subfamily may encode native cardiac transient outward current ( I to). Antisense hybrid-arrest with oligonucleotides targeted to Kv4 mRNAs specifically inhibited rat ventricular I to, supporting this hypothesis. To determine whether protein kinase C (PKC) affects I to by an action on these molecular components, we compared the effects of PKC activation on Kv4.2 and Kv4.3 currents expressed in Xenopus oocytes and rat ventricular I to. Phorbol 12-myristate 13-acetate (PMA) suppressed both Kv4.2 and Kv4.3 currents as well as native I to, but not after preincubation with PKC inhibitors (e.g., chelerythrine). An inactive stereoisomer of PMA had no effect. Phenylephrine or carbachol inhibited Kv4 currents only when coexpressed, respectively, with α1C-adrenergic or M1 muscarinic receptors (this inhibition was also prevented by chelerythrine). The voltage dependence and inactivation kinetics of Kv4.2 were unchanged by PKC, but small effects on the rates of inactivation and recovery from inactivation of native I to were observed. Thus Kv4.2 and Kv4.3 proteins are important subunits of native rat ventricular I to, and PKC appears to reduce this current by affecting the molecular components of the channels mediating I to.
Cytoskeleton modulates coupling between availability and activation of cardiac sodium channel
Authors: Maltsev Victor A. , Undrovinas Albertas I.
Published: December 2017

The aim of this study was to investigate modulation of voltage-dependent steady-state activation and availability from inactivation of the cardiac Na+ channel by the cytoskeleton. As an experimental approach, we used long-lasting monitoring [63 ± 5 (SE) min] of the half-point potentials of the steady-state availability curve ( V 1/2A ) and normalized conductance curve ( V 1/2G) in 116 rat ventricular cardiomyocytes by whole cell patch clamp at 22–24°C. Both half-point potentials shifted in the negative direction with time as an exponentially saturating change, with the shift of V 1/2G being smaller and faster. An F-actin disrupter, cytochalasin D (Cyto-D, 20 μM), accelerated the rate of the V 1/2A shift but decreased the range of the V 1/2G shift. An F-actin stabilizer, phalloidin (100 μM), temporarily (for 28.2 ± 2.2 min, n = 15) prevented the V 1/2A shift but did not influence the V 1/2G shift. The best fit for the V 1/2G- V 1/2Arelationship in untreated cells (1,021 data points measured in 51 cells) was a second-degree (2.06) power function. Cytoskeleton-directed agents modified the relationship. In Cyto-D-treated cells, the V 1/2G- V 1/2Arelationship was shifted (by 2.5 mV) toward positive V 1/2G. On the contrary, a microtubule stabilizer, taxol (100 μM), shifted the relationship toward negative V 1/2G (by 12.2 mV). We conclude that coupling between availability and activation is modulated by F-actin-based and microtubular cytoskeleton.
Components of acetylcholine-induced dilation in isolated rat arterioles
Authors: Bakker Erik N. T. P. , Sipkema Pieter
Published: December 2017

Acetylcholine-induced dilation was studied in cannulated resistance arteries of rat cremaster muscle. Pressurized arteriolar segments (internal diameter: 175 ± 2 μm) developed spontaneous tone (90 ± 2 μm). Application of acetylcholine (0.1 and 0.3 μM) resulted in a transient dilation followed by a steady-state dilatory response. In the presence of N G-nitro-l-arginine (l-NNA) ∼70% of the transient dilation was resistant to nitric oxide inhibition, whereas the steady-state response was abolished. Further experiments using 0.1 μM acetylcholine (no l-NNA present) were aimed to inhibit synthesis or action of the mediator of the transient component (amplitude: 39 ± 2.8 μm). A high-potassium buffer (30–50 mM) abolished this transient dilation (1.3 ± 1.3 μm), suggesting that the dilation is mediated by an endothelium-derived hyperpolarizing factor (EDHF). This putative EDHF-mediated dilation is strongly reduced by cytochrome P-450 inhibitors miconazole (11 ± 1.3 μm) and SKF-525a (4.8 ± 4.5 μm). The transient component is inhibited by tetraethylammonium but not by glibenclamide, indicating it is mediated by opening of Ca2+-activated K+ channels. Interestingly, inhibition of the transient component was followed by a subsequent decrease of the nitric oxide-mediated part of the response to acetylcholine. Thus a transient dilation, mediated by a cytochrome P-450 metabolite, precedes and possibly stimulates nitric oxide-mediated dilation in acetylcholine-induced dilation.
Endothelial cell adhesion molecule expression in gene-targeted mice
Authors: Eppihimer Michael J. , Russell Janice , Anderson Donald C. , Wolitzky Barry A. , Granger D. Neil
Published: December 2017

Gene-targeted mice are now routinely employed as tools for defining the contribution of different leukocyte and endothelial cell adhesion molecules to the leukocyte recruitment and tissue injury associated with acute and chronic inflammation. The objective of this study was to determine whether gene-targeted mice that are deficient in CD11/CD18, intracellular adhesion molecule-1 (ICAM-1), or P-selectin exhibit an altered constitutive or induced expression of the endothelial cell adhesion molecules E- and P-selectin. The gene-targeted mice were all developed in the 129Sv mouse strain and backcrossed into C57Bl/6J mice. The number of backcrosses ranged between 8 (P-selectin) and 10 (CD18 and ICAM-1) generations. The dual-radiolabeled monoclonal antibody technique was used to quantify E- and P-selectin expression in different vascular beds. In the unstimulated state, E-selectin expression was significantly elevated (relative to wild-type mice) in the stomach, large intestine, and brain of mutants deficient in ICAM-1. In general, constitutive expression of P-selectin did not differ between wild-type, ICAM-1-deficient, and CD11/CD18-deficient mutants. In CD11/CD18-deficient mice, tumor necrosis factor-α (TNF-α) administration elicited a more profound upregulation of P-selectin in several vascular beds, compared with wild-type and ICAM-1-deficient mice. E-selectin expression in brain of TNF-α-stimulated, ICAM-1-deficient, and P-selectin-deficient mice was attenuated compared with wild-type mice. These findings indicate that chronic deficiency of some of the adhesion glycoproteins that mediate leukocyte recruitment alters basal and induced surface expression of other adhesion molecules on endothelial cells.
Taurine depletion, a novel mechanism for cardioprotection from regional ischemia
Authors: Allo Simon N. , Bagby Lillian , Schaffer Stephen W.
Published: December 2017

Three processes that have been implicated in ischemic injury are impaired Ca2+movement, altered osmoregulation, and membrane remodeling. Because the amino acid, taurine, affects all three processes, it seemed logical that changes in the myocardial content of taurine might affect ischemic injury. To test this hypothesis, infarct size and areas at risk were compared in isolated hearts from control and taurine-depleted rats after a 45-min ligation of the left anterior descending coronary artery and 2 h of reperfusion. Hearts of rats treated for 4 wk with the taurine inhibitor, β-alanine, exhibited a 57% reduction in the infarct size-to-risk area ratio. The degree of cardioprotection was found to correlate ( r = 0.85) with the extent of taurine depletion, the latter dependent on the length of β-alanine feeding. When the taurine-depleted rats were fed taurine, myocardial taurine levels were restored and the cardioprotection was lost. However, addition of neither β-alanine (3%) nor taurine (20 mM) to the perfusion medium altered infarct size. We conclude that taurine depletion renders the heart resistant to injury caused by regional ischemia.
Carbachol promotes Na+ entry and augments Na/Ca exchange current in guinea pig ventricular myocytes
Authors: Saeki Tomoaki , Shen Jian-Bing , Pappano Achilles J.
Published: December 2017

The effect of carbachol (CCh) on the Na/Ca exchange current ( I Na/Ca) was studied in voltage-clamped ventricular myocytes isolated from guinea pig hearts and superfused with Tyrode solution at 35°C. CCh (100 μM) increased outward current during depolarizations (10–200 ms) from −45 mV and tail current amplitude on repolarization; CCh had no effect on the L-type Ca2+current. Amplitudes of the outward and tail currents declined with increasing duration of the depolarizing clamp pulse. Ouabain produced similar current changes that are suppressed by intrapipette ethylene glycol-bis(β-aminoethyl ether)- N, N, N′, N′-tetraacetic acid and are characteristic of I Na/Ca. Depolarization from −80 to −30 mV elicited the rapid Na+ current followed by a slowly decaying inward I Na/Ca (J. C. Gilbert, T. Shirayama, and A. J. Pappano. Circ. Res. 69: 1632–1639, 1991.) that was reversibly increased by CCh. Atropine (1–3 μM) prevented the CCh effect. All procedures that suppressed I Na/Caalso suppressed the CCh effect. Sarcoplasmic reticulum (SR) Ca2+ release participated in generating I Na/Cabecause 10 mM caffeine or 1 μM ryanodine blocked I Na/Ca and the effect of CCh. Rapid superfusion of 10 mM caffeine induced inward I Na/Ca at −75 mV; a caffeine-induced charge transfer gives an SR Ca2+ content of 67 μM. CCh increased caffeine-induced current; SR Ca2+ content rose to 98 μM. CCh also augmented the amplitude of steady-state intracellular Ca2+ transients and contractions during a train of voltage-clamp pulses (−75 to 30 mV for 200 ms) at 1 Hz. CCh elevated intracellular Na+ (M. Korth and V. Kühlkamp. Pflügers Arch.403: 266–272, 1985) by inducing a background Na+ current [K. Matsumoto and A. J. Pappano. J. Physiol. (Lond.)415: 487–502, 1989]. Together with these data, the present results are consistent with the hypothesis that CCh, via muscarinic receptors, eventually promotes I Na/Ca at the sarcolemma through a mechanism that requires the SR and that this action accounts for the increased contractions.
Echocardiographic changes after myocardial infarction in a model of left ventricular diastolic dysfunction
Authors: Pennock Gregory D. , Yun Douglas D. , Agarwal Poonam G. , Spooner Peter H. , Goldman Steven
Published: December 2017

To determine the early and late effects of myocardial infarction on left ventricular (LV) diastolic function in the rabbit postinfarction model, male New Zealand White rabbits were randomly assigned to ligation of the circumflex artery or sham operation. Serial echocardiographic and Doppler studies were performed on both groups of animals at baseline and 1 h and 3 wk after surgery ( n = 10 for each group) after verification of the reproducibility and repeatability of the measurements. At 1 h postinfarction, decreases in early mitral inflow velocity (E wave) and mitral inflow velocity with atrial contraction (A wave) and increases in the mean pulmonary venous systolic-to-diastolic ratio and A wave reversal velocities were observed, without changes in LV geometry. By 3 wk postinfarction, increases in the mitral E-to-A ratio (1.1 ± 0.3 vs. 2.9 ± 0.9, P < 0.001) and left atrial area (131 ± 23 vs. 510 ± 72 mm2, P < 0.001) and decreases in the pulmonary venous systolic-to-diastolic ratio (0.56 ± 0.20 vs. 0.79 ± 0.14, P = 0.008) were consistent with severe diastolic abnormalities (restricted physiology). The findings of this study demonstrate that coronary artery ligation in the rabbit provides a reproducible echocardiographic and Doppler model of LV diastolic dysfunction that is consistent with abnormalities found in humans with previous myocardial infarction, symptoms of heart failure, and preserved LV systolic function.
Left ventricular pressure response to small-amplitude, sinusoidal volume changes in isolated rabbit heart
Authors: Campbell Kenneth B. , Wu Yiming , Kirkpatrick Robert D. , Slinker Bryan K.
Published: December 2017

The objective was to determine the dynamics of contractile processes from pressure responses to small-amplitude, sinusoidal volume changes in the left ventricle of the beating heart. Hearts were isolated from 14 anesthetized rabbits and paced at 1 beats/s. Volume was perturbed sinusoidally at four frequencies ( f ) (25, 50, 76.9, and 100 Hz) and five amplitudes (0.50, 0.75, 1.00, 1.25, and 1.50% of baseline volume). A prominent component of the pressure response occurred at the f of perturbation [in-frequency response,[Formula: see text] ( t)]. A model, based on cross-bridge mechanisms and containing both pre- and postpower stroke states, was constructed to interpret[Formula: see text] ( t). Model predictions were that[Formula: see text] ( t) consisted of two parts: a part with an amplitude rising and falling in proportion to the pressure around that which[Formula: see text] ( t) occurred [Pr( t)], and a part with an amplitude rising and falling in proportion to the derivative of Pr( t) with time. Statistical analysis revealed that both parts were significant. Additional model predictions concerning response amplitude and phase were also confirmed statistically. The model was further validated by fitting simultaneously to all[Formula: see text] ( t) over the full range of f and ΔV in a given heart. Residual errors from fitting were small ( R 2 = 0.978) and were not systematically distributed. Elaborations of the model to include noncontractile series elastance and distortion-dependent cross-bridge detachment did not improve the ability to represent the data. We concluded that the model could be used to identify cross-bridge rate constants in the whole heart from responses to 25- to 100-Hz sinusoidal volume perturbations.
Myocardial dysfunction is associated with activation of Na+/H+exchange immediately during reperfusion
Authors: Maddaford Thane G. , Pierce Grant N.
Published: December 2017

Amiloride analogs block Na+/H+exchange and thereby protect the heart from myocardial ischemia-reperfusion injury. It is unclear whether drugs must be present before ischemia to be cardioprotective. After 60 min of global ischemia in the coronary-perfused right ventricular wall (RVW), as little as 1 min of exposure to dimethyl amiloride (DMA) immediately at the time of reperfusion protected the RVW. Delaying the drug attenuated the cardioprotection. If DMA was introduced in an ischemic solution near the end of ischemia, the cardioprotective effects were augmented. If the drug was washed out of the RVW vascular space before ischemia, cardioprotection was not observed. In contrast, in whole hearts, preischemic perfusion of the drug was necessary for cardioprotection and the cardioprotection remained even if the drug was washed out before ischemia. We conclude that Na+/H+exchange is active and contributes to contractile dysfunction during the first seconds of reperfusion. This is difficult to detect in the perfused whole heart, and the washout data suggest that this may be due to a limitation in drug delivery across the vascular wall. The data also suggest that the exchanger is not as active during ischemia itself as it is during reperfusion.
ATP-sensitive potassium channel mediates delayed ischemic protection by heat stress in rabbit heart
Authors: Hoag Jeffrey B. , Qian Yong-Zhen , Nayeem Mohammed A. , D’Angelo Michael , Kukreja Rakesh C.
Published: December 2017

Heat shock protects against myocardial ischemia-reperfusion injury possibly via increased expression of heat shock proteins. The direct evidence of heat shock protein protection in vivo remains circumstantial, and no other new mechanism of protection has been proposed. Recent studies suggest that opening of ATP-sensitive K+ channels (KATP channels) plays an important role in ischemic preconditioning; however, it is not known whether this channel is also important in delayed protection conferred by heat shock. Anesthetized rabbits underwent heat shock treatment by raising core temperature to 42°C for 15 min. Twenty-four hours later, the animals were reanesthetized and subjected to regional ischemia-reperfusion. The specific KATP channel blockers glibenclamide (0.3 mg/kg ip) and sodium 5-hydroxydecanoate (5HD; 5 mg/kg iv) were used to block the channel function. The drugs were administered at two different times, either pre-heat stress or preischemia. Infarct size was determined by triphenyltetrazolium chloride staining. The 72-kDa heat shock protein (HSP 72) was measured by Western blots. Our results show that heat shock produced a marked reduction in infarct size (39.4 ± 8.1 to 14.3 ± 2.5% of risk area, P < 0.05). Glibenclamide and 5HD completely abolished heat shock-induced reduction in infarct size (42.3 ± 0.32 and 33.7 ± 4.8%) when given before ischemia-reperfusion; however, these antagonists failed to block protection when administered before the onset of heat shock. Furthermore, the enhanced expression of HSP 72 in heat shock groups was not diminished by glibenclamide or 5HD, suggesting a lack of a direct role of this protein in conferring cardiac protection by heat shock. The complete blockade of cardiac protection by glibenclamide and 5HD strongly suggests that opening of this channel is a very important component of heat shock-induced ischemic protection in rabbit hearts.
Dose-dependent reduction of cardiac transmembrane potential by high-intensity electrical shocks
Authors: Neunlist Michel , Tung Leslie
Published: December 2017

Cardiac tissue dysfunction can result from high-intensity electrical shocks and is manifested as changes in transmembrane potential ( V m). Ten-millisecond shock pulses (SPs) of varying intensity and polarity were applied to frog ventricle in diastole, and V m was quantified directly under the stimulating electrode by an optical method using voltage-sensitive dye. As SP intensities were increased, the shock-induced action potential (AP) plateau and AP amplitude (APAs) decreased sigmoidally toward 75–85% of the control AP amplitude (APAc) and zero, respectively. APAswas shifted toward lower current densities for anodal compared with cathodal SPs (half-maximal values 185 and 238 mA/cm2, respectively; P = 0.02). Recovery of APAs was marginally significant 1 s after SP delivery ( P = 0.063). The peak change in V mduring SP (across all intensity levels) was −200% APAc for anodal and +125% APAc for cathodal pulses. In conclusion, we show that SP reduces APA in a sigmoidal fashion at strengths >10–20 × diastolic threshold and is more deleterious for anodal polarities.
Effect of a 14-day hindlimb suspension on cytosolic Ca2+ concentration in rat portal vein myocytes
Authors: Morel Jean-Luc , Boittin François-Xavier , Halet Guillaume , Arnaudeau Serge , Mironneau Chantal , Mironneau Jean
Published: December 2017

Effects of a 14-day hindlimb suspension were examined on increases in cytosolic Ca2+ concentration ([Ca2+]i) evoked by vasoactive compounds and on Ca2+ channels in rat portal vein myocytes. The maximal increases in [Ca2+]ielicited by caffeine, norepinephrine, and angiotensin II were reduced by 30–50% in suspended rats, and complete recovery was obtained 4 days after suspension removal. In contrast, voltage-gated Ca2+ channels were unaffected by hindlimb suspension. Using both confocal microscopy and the patch-clamp technique, we measured local increases in [Ca2+]iwhich corresponded to activation of a small number of ryanodine-sensitive Ca2+-release channels (Ca2+ sparks) andd- myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]-gated Ca2+ channels. After hindlimb suspension, these local Ca2+events, as well as the Ca2+sensitivity of ryanodine-sensitive Ca2+ release channels, remained unchanged. In contrast, the propagated Ca2+ responses (Ca2+ waves) were significantly reduced in parallel with a noticeable inhibition of [3H]ryanodine binding to vascular membranes. Taken together, these results suggest that inhibition of the vasoconstrictor-induced increases in [Ca2+]iduring long-term suspension may be related to a reduction of the number of functional ryanodine-sensitive and Ins(1,4,5)P3-gated channels in the sarcoplasmic reticulum of rat portal vein myocytes.
Alterations in cardiac SR Ca2+-release channels during development of heart failure in cardiomyopathic hamsters
Authors: Ueyama Takeshi , Ohkusa Tomoko , Hisamatsu Yuji , Nakamura Yasuma , Yamamoto Takeshi , Yano Masafumi , Matsuzaki Masunori
Published: December 2017

The cardiomyopathic Syrian hamster develops a progressive cardiomyopathy characterized by cellular necrosis, hypertrophy, cardiac dilatation, and congestive heart failure. This study aimed to identify alterations in cardiac mechanical function and in the cellular content of sarcoplasmic reticulum (SR) Ca2+-release channels (ryanodine receptors, RyR) in the heart of the UM-X7.1 cardiomyopathic hamster during the development of heart failure. Experimental and healthy control hamsters were examined at 8, 18, and 28 wk of age. The UM-X7.1 hamsters had developed left ventricular (LV) hypertrophy at 8 wk and a marked LV dilatation at 18–28 wk. During the latter stage, the UM-X7.1 hamster hearts showed global hypokinesis. Equilibrium binding assays of high-affinity sites for [3H]ryanodine were performed in ventricular homogenate preparations. There was no significant difference between the two groups in the maximum number of [3H]ryanodine binding sites (Bmax) at either 8 or 18 wk of age, although the cardiac pump function was impaired in UM-X7.1 hamsters at 18 wk of age. By 28 wk, Bmaxwas significantly lower in the UM-X7.1 hamsters. Quantitative immunoblot assay revealed that the content of RyR protein in cardiomyopathic hearts, which was increased at the early stage, declined to below normal as heart failure advanced. These results suggest that the number of RyR in the UM-X7.1 cardiomyopathic hamsters was preserved at both the hypertrophic and early stages of heart failure with a possibly compensatory increase in the level of protein expression, although the cardiac function already showed a tendency to be impaired.