bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of feeding and ambient temperature on thermoregulation in newborn lambs
Authors: Clarke L , Heasman L , Firth K , Symonds ME
Published: December 2014

This study examined the effect of ambient temperature and feeding on brown adipose tissue (BAT) function and thermoregulation in lambs born either vaginally at term or by Caesarean section close to term. Immediately after birth lambs were placed in a warm (30 degrees C) or cool (15 degrees C) ambient temperature and measurements of colonic temperature and heat production recorded for 6 h. Lambs were fed 50 ml of colostrum when 5 h old. The amount of uncoupling protein and level of guanosine 5'diphosphate (GDP) binding in BAT was higher in vaginally delivered lambs than in lambs delivered by Caesarean section. For each delivery group, GDP binding was greater in lambs maintained at 30 degrees C than in lambs maintained at 15 degrees C. O2 consumption, CO2 production and colonic temperature only increased after feeding in lambs born by Caesarean section and maintained at 30 degrees C, a response that was accompanied by a decreased incidence of shivering. Irrespective of delivery temperature, plasma thyroid hormone concentrations and noradrenaline content of BAT were lower in lambs born by Caesarean section than in those born vaginally. Plasma cortisol concentrations were higher in lambs delivered by Caesarean section, as was adrenaline content of BAT in these lambs maintained at 30 degrees C. It is concluded that the thermoregulatory response to feeding in terms of changes in both recruitment of shivering and colonic temperature were observed only in lambs delivered by Caesarean section.
The effects of buspirone on perceived exertion and time to fatigue in man
Authors: Marvin G , Sharma A , Aston W , Field C , Kendall MJ , Jones DA
Published: December 2014

Male subjects exercised at 80% maximal rate of O2 uptake (VO2,max) following oral administration of either placebo or the partial 5‐HT1A agonist buspirone (45 mg), using a paired design. Ratings of perceived exertion were higher following buspirone and time to volitional fatigue (median and inter‐quartile range) fell significantly by approximately a third from 26 min (24‐30 min) on placebo to 16 min (11‐19 min) following buspirone. Serum prolactin was significantly elevated following buspirone administration, indicating increased hypothalamic 5‐HT1A receptor stimulation. There were no significant differences in blood lactate or serum glucose between the trials. This study supports the possible central modulation of exercise tolerance by serotonergic pathways, although a role for dopamine cannot be excluded.
The enzymic potential of tissue kallikrein (rK1) in rat submandibular saliva depends on whether it was secreted via constitutive or regulated pathways
Authors: Proctor GB , Zhang XS , Garrett  , Shori DK , Chan KM , Chao J
Published: December 2014

The enzymic activity and immunoreactivity of rat tissue kallikrein (rK1) secreted at rest by granular duct cells of unstimulated submandibular glands has been compared with that secreted on autonomic nerve stimulation. Although a direct vesicular, constitutive secretory pathway operates for rK1 secretion from granular duct cells of unstimulated and parasympathetically stimulated glands the rK1 was not present in a pro‐form and actually showed a greater enzymic activity per unit immunoreactive protein than the granule‐derived rK1 in sympathetically evoked saliva. Constitutively secreted rK1 was found to be in a single chain molecular form by reducing SDS gel electrophoresis. In contrast rK1 secreted from the storage granule pool of granular duct cells on sympathetic nerve stimulation was present in much higher amounts and occurred in both one‐chain and two‐chain forms as revealed by SDS gel electrophoresis under reducing conditions. The lower enzymic potential of rK1 in sympathetically evoked saliva might be accounted for by its conversion to a two‐chain form.
Fluid uptake by the renal medullary vasa recta: an estimate based on a quantitative analysis of the distribution of fenestrae in the vasa recta of young Sprague‐Dawley rats
Authors: MacPhee PJ
Published: December 2014

Transmission electron microscopic techniques were used to carry out a quantitative analysis of the density of fenestration in the inner medullary vasa recta of the rat kidney. Measurements were made at 200 microns intervals from the tip to the base of the papilla (1800 microns from the tip). Fenestral diaphragms were estimated to be 65.4 +/− 0.78 nm in diameter (mean +/− S.E.M.), and were arranged in plaques with a mean interfenestral distance of 114.8 +/− 2.6 nm. Near the tip of the papilla there was no correlation between vessel size and degree of fenestration; density of fenestration, however, began to decrease about 1400 microns from the tip. The ratio of fenestrated to non‐fenestrated profiles of vasa recta was found to be linear with respect to distance from the tip (r = 0.991), with values ranging from about 40:1 near the tip to 2:1 near the base of the papilla. We have estimated the proportion of the total surface area of a fenestrated vasa recta occupied by fenestral diaphragms to be 0.057 at 1000 microns from the tip. The total potential conductance (K) of a 200 microns segment of fenestrated vessel at 1000 microns from the tip was calculated to be 0.319 microns 3 s‐1 cmH2O‐1, giving a hydraulic conductivity (Lp) of 0.030 micron s‐1 cmH2O‐1. We have also examined the reverse question of the conductance of a single fenestra if all the fluid flux across the vessel wall occurred through the fenestrae and none via the intercellular clefts or water channels; single fenestral conductance was estimated to be 1.94 x 10(‐3) microns 3 s‐1 cmH2O‐1.
The effect of temperature on the rate‐dependent decrease of the rat ventricular calcium current
Authors: McMorn SO , Harrison SM , Boyett MR
Published: December 2014

We have investigated the effect of temperature upon the rate‐dependent decrease in the L‐type Ca2+ current (iCa) in isolated rat ventricular myocytes. Increasing the rate of stimulation from 0.5 to 3.0 Hz for 30s induced a reversible decrease in iCa which was temperature dependent. Compared to control (0.5 Hz), the first beat at 3 Hz was decreased by 38 +/− 7% at 22 degrees C and by 9 +/− 1% at 37 degrees C (mean +/− S.E.M., n = 5, P < 0.05) and, after 30 s of 3 Hz stimulation, iCa was reduced by a further 26 +/− 4 and 21 +/− 2% at 22 and 37 degrees C, respectively. The magnitude of this secondary decline was not significantly different at the two temperatures (P = 0.29). Corroboratory results were obtained from cell‐attached patches which also illustrated that the rate‐dependent decrease in iCa resulted from a reduction of open channel probability. Paired pulse experiments showed that the greater initial rate‐dependent decrease in iCa at 22 degrees C occurred as a result of slower recovery from fast inactivation processes at 22 than at 37 degrees C. Recovery of the channel from fast inactivation was very temperature sensitive with a Q10 of 5.6. In contrast, the secondary, progressive decrease in iCa, which results from incomplete recovery from ultra‐slow voltage‐dependent inactivation, was similar at the two temperatures and appears to be much less temperature dependent.
Changes in skeletal muscle sarcoplasmic reticulum function and force production following myocardial infarction in rats
Authors: Williams JH , Ward CW
Published: December 2014

In patients following myocardial infarction (MI), exercise tolerance and muscular strength are often markedly reduced. The purpose of this investigation was to determine if calcium (Ca2+) uptake and release by skeletal muscle sarcoplasmic reticulum (SR) are altered following MI and if such changes are associated with diminished muscular performance. SR vesicles were isolated from rat gastrocnemius muscle at 6 and 12 weeks following MI (via left coronary artery ligation) or sham surgery. At both post‐surgery intervals, the rates of Ca2+ uptake (measured using fura‐2) were 35% greater in the MI group. In addition, the rates of Ca2+ release were increased in the MI group by 10 and 30% at 6 and 12 weeks, respectively. At 12 weeks post‐surgery, animals of the MI group showed significant reduction in in situ twitch and tetanic forces and significant elevations in the rates of tension increase and decrease. These data indicate that SR Ca2+ exchange is altered following MI. In addition, changes in SR function are associated with changes in force production by the whole muscle.
The effects of sodium substitution on currents determining the resting potential in guinea‐pig ventricular cells
Authors: Spindler AJ , Noble SJ , Noble D , LeGuennec JY
Published: December 2014

It has recently been shown that a sodium background current, ib,Na, exists in cardiac muscle cells whose effect is to depolarize the membrane so that the resting potential, Vm, is positive to the potassium equilibrium potential, EK. In ventricular cells, where ib,Na is smallest, Vm is about 10 mV positive to EK (EK = ‐87 mV at 37 degrees C). Yet, replacement of Na+ ions by large impermeant cations does not cause the expected hyperpolarization. We have studied this problem in guinea‐pig myocytes using a single microelectrode recording technique in combination with a rapid external solution switch. Cells depolarized < or = 0.5 mV from potentials between ‐80 and ‐73 mV and hyperpolarized up to 5 mV from potentials between ‐73 and ‐64 mV when 70 mM choline chloride or N‐methyl‐D‐glucamine chloride were used to replace 70 mM Na+ in the bathing solution. Replacement by 70 mM lithium chloride, however, only caused hyperpolarization in very depolarized cells when the voltage change was much smaller. The changes were complete almost as soon as the solution change, i.e. within 250 ms, indicating that the actions are attributable to the external solution change rather than to secondary changes in intracellular concentrations. Patch clamp recording was used to investigate the mechanism involved. These experiments showed that the presence or absence of the inward rectifier current iK1 determines in which direction Na+ removal acts. In the absence of iK1 the changes are attributable to removal of ib,Na, whereas in the presence of iK1 the changes resemble the i(V) relation for iK1, implying that Na+ regulates iK1 in a way that can mask the changes in ib,Na. These results explain why removal of Na+ does not lead to hyperpolarization in ventricular cells as would be expected if changes in ib,Na were solely responsible. Computer reconstruction shows that the effects may be attributed to actions of sodium removal on the conductance and gating of iK1.
The effects of skin brushing on H reflex amplitude in normal human subjects
Authors: Wood L , Nicol DJ , Thulin CE
Published: December 2014

Experiments were performed on twenty‐two neurologically normal subjects in order to investigate the effects of skin brushing on H reflex excitability in triceps surae. H reflex amplitude was observed to decrease during brushing of a 2 cm x 10 cm area of skin overlying triceps surae, returning to control levels when brushing ceased. Alterations in the duration of the brushing period did not affect the magnitude of the H reflex inhibition, although increased frequency of brush strokes per minute slightly increased the amount of inhibition observed. Brushing of smaller skin areas overlying the muscle only sometimes resulted in H reflex inhibition. Brushing over other skin areas of the lower limb produced only slight effects on triceps surae H reflex amplitude. Removal of cutaneous input from the skin overlying triceps surae abolished any effects of brushing in this area on H reflex amplitude. These results demonstrate an inhibitory effect of brushing on H reflex excitability in normal subjects. If such results are confirmed in subjects with neurological deficit, they could have implications for the use of brushing in clinical practice.
Adenosine and hypoxanthine transport in horse erythrocytes: evidence for a polymorphism in the transport of hypoxanthine via a sodium‐dependent cotransporter
Authors: Jarvis SM , Harris RC
Published: December 2014

The inward transport of two purines, adenosine and hypoxanthine, at 37 degrees C by horse erythrocytes was compared. No mediated transport of adenosine was detected in horse erythrocytes, nor was saturable, high‐affinity binding of the potent facilitated‐diffusion inhibitor nitrobenzylthioinosine demonstrable in horse erythrocyte membranes. In contrast, erythrocytes from most horses possessed a saturable sodium‐dependent hypoxanthine transporter (apparent K(m), 100 +/− 28 microM; Vmax, 0.20 +/− 0.08 mmol (l cells)‐1 h‐1; means +/− S.E.M., n = 5). Guanine inhibited hypoxanthine influx (apparent Ki, 24 +/− 6 microM), but adenine and xanthine had no effect. Unlike human erythrocytes, no sodium‐independent hypoxanthine transporter was detected in horse erythrocytes. There are, however, a small number of animals (approximately 15%) whose erythrocytes fail to transport hypoxanthine. This variation appears to be under genetic control, but the precise nature of the control is unknown.
Mitochondrial carrier proteins can reversibly change their transport mode: the cases of the aspartate/glutamate and the phosphate carrier
Authors: Kramer R
Published: December 2014

A number of mitochondrial carrier systems function both in homologous and in heterologous exchange mode, which, in the case of the phosphate carrier is a homologous Pi(‐)‐Pi‐ and a heterologous Pi(‐)‐OH‐ exchange. In addition, we showed that mitochondrial carriers, e.g. the aspartate/glutamate and the phosphate carrier, can undergo a functional shift from coupled antiport to uncoupled uniport after modification of cysteine residues. In this transport mode a mixture of carrier‐ and channel‐type properties is observed. To address this question on the molecular level, the phosphate carrier from yeast (S. cerevisiae) mitochondria was expressed in E. coli, solubilized, purified and functionally reconstituted. From three cysteine residues present in the yeast phosphate carrier at positions 28, 134 and 300, only one single cysteine residue (C28) was found responsible for the functional switch from antiport to uniport. Upon replacement by a serine residue, this interconversion was blocked. After incorporation of the carrier into giant liposomes, electrophysiological methods (patch clamp) were applied. Under these conditions, a fourth transport mode of the phosphate carrier was observed, namely an action as anion‐selective channel, which could be reversibly blocked by phosphate.
Temperature dependence of mechanical power output in mammalian (rat) skeletal muscle
Authors: Ranatunga KW
Published: December 2014

Force‐velocity data at different temperatures (range, 10–35 degrees C) from intact fibre bundles are analysed to determine the temperature dependence of the maximal mechanical power output of fast and slow rat muscles. At 35 degrees C, the maximal mechanical power was approximately 250 kW m(−3) (=250 microW mm(−3)) in fast (probably an underestimate) and approximately 100 kW m(−3) in slow muscle. Within the more physiological temperature range (25–35 degrees C), the temperature coefficient (Q10) of maximum power was 2–2.5. In both muscles, the maximal power at 10 degrees C was only about 3–5% of that at 35 degrees C, the decrease being particularly pronounced at temperatures below 20 degrees C (Q10 of 5–7).
Vasorelaxant effect of thiopentone in isolated human epigastric arteries
Authors: Olele NE , Ehigiegba AE , Ebeigbe AB
Published: December 2014

The experiments were designed to elucidate the mechanism of thiopentone‐induced inhibition of contractile responses in isolated human epigastric arteries. Segments of human epigastric arteries were obtained from patients who underwent elective or emergency caesarean section, placed in standard physiological salt solution (PSS), cut into rings at 3 mm intervals and suspended in organ baths for recording of isometric contractions at 37 degrees C, and pH 7.4. Three protocols were employed to examine the inhibitory effect of thiopentone: (a) concentration‐dependent effect on 10(‐7) M noradrenaline (NA)‐ or high‐K+ (40 mM)‐induced contractions: (b) effect on NA‐induced extra‐and intracellular Ca(2+)‐dependent contractions and (c) effect on the dose‐response curve when Ca2+ is restored to Ca(2+)‐depleted rings in Ca(2+)‐free 40 mM K(+)‐depolarizing medium. Thiopentone (1 x 10(‐6) ‐4 x 10(‐3) M) caused concentration‐dependent relaxation of both NA‐ and high‐K(+)‐induced contractions. The magnitudes of both precontractions were not significantly different but the IC50 values for thiopentone relaxation of high‐K+ contractions were significantly lower than for NA contractions. Thiopentone (10(‐4) M) significantly attenuated the phasic (intracellular Ca2+ dependent) contractile responses to 10(‐5) M NA in Ca(2+)‐free PSS as well as the tonic (extracellular Ca2+ dependent) contractions upon restoration of Ca2+. In contrast, nifedipine (1 microM) did not modify the phasic response but significantly attenuated the tonic response. Thiopentone (10(‐4) M) also almost completely abolished concentration‐dependent Ca(2+)‐induced contractions in K(+)‐depolarized Ca(2+)‐depleted rings. The results suggest that in the smooth muscle of human epigastric arteries, thiopentone‐induced relaxation is non‐specific and is associated with impairment of Ca2+ supply from both extracellular and intracellular pools.
The influence of streptozotocin‐induced diabetes and the antihyperglycaemic agent metformin on the contractile characteristics and the membrane potential of the rat diaphragm
Authors: McGuire M , MacDermott M
Published: December 2014

After 2 months of streptozotocin‐induced diabetes in rats, the membrane potential of the diaphragm muscle when measured in vitro at 30 degrees C was unchanged but the tetanic tension, the half‐relaxation time of the isometric twitch and the fatigue resistance were each reduced. Treatment of the diabetic rats with the antihyperglycaemic agent metformin prevented the decrease in half‐relaxation time and the greater degree of fatigue in the diaphragms. The possibility that changes in H+ and cyclic AMP concentrations in the diabetic muscles contributed to the decreased contractile function and that metformin acted by attenuating these changes is discussed.
Long‐term administration of L‐arginine did not influence blood pressure, heart rate, cardiac hypertrophy or arterial wall thickness of spontaneously hypertensive rats
Authors: Kristek F
Published: December 2014

The aim of this study was to evaluate whether long‐term administration of L‐arginine, a physiological substrate for the production of nitric oxide, improved blood pressure, heart rate, cardiac hypertrophy and particularly structural changes in the coronary and carotid artery of spontaneously hypertensive rats (SHR). The experiments started with three groups of 10‐week‐old animals: control Wistar rats, untreated SHR and SHR treated with L‐arginine (SHR + L‐arginine). L‐Arginine was administered to SHR in a daily dose of 300 mg kg‐1 intraperitoneally for 6 weeks. Blood pressure and heart rate were recorded each week. At the end of the experiment in one‐half of each group heart weight and body weight were determined and the heart weight/body weight index was calculated. In the other animals, the cardiovascular system was perfused via the left ventricle with a glutaraldehyde fixative at 120 mmHg and the coronary and carotid arteries were processed for transmission electron microscopy. The inner diameter and wall thickness (tunica intima and tunica media) were measured on semithin sections. The reliability of the genetic feature in the SHR group was proved by the increased heart weight, heart weight/body weight index, wall thickness and wall thickness/inner diameter ratio of coronary and carotid arteries in comparison to the group of control Wistar rats. Long‐term administration of L‐arginine did not significantly influence blood pressure and heart rate in comparison with untreated SHR. Neither were any differences found in cardiac hypertrophy or the geometry of the coronary and carotid arteries (thickness of arterial wall, inner diameter, wall/diameter ratio). In conclusion, the changes in the cardiovascular system in SHR were not reversed, or even alleviated, by chronic treatment with L‐arginine.
Novel form of L‐aromatic amino acid decarboxylase mRNA in rat antral mucosa
Authors: Djali PK , Dimaline R , Dockray GJ
Published: December 2014

Gut endocrine cells possess the capacity to take up and decarboxylate biogenic amine precursors. Decarboxylation is mediated by aromatic L‐amino acid decarboxylase (AADC) which is encoded by mRNAs differing in their 5' untranslated regions (UTR) depending on the usage of alternative first exons, 1a and 1b, each with its own acceptor site (−13 and −8 bases relative to the translation start site, respectively). We describe here a novel splice variant of exon 1a‐AADC mRNA in rat antral mucosa. Both exon 1a and 1b mRNAs were expressed in rat antral mucosa, but the 1a form was spliced into the acceptor site usually associated with exon 1b (−8). An enteroendocrine cell line (STC‐1) expressed exon 1a or exon 1b mRNAs spliced into the ‐8 acceptor site of exon 2. Transient transfection of a range of cell lines with reporter constructs revealed that all three 5' UTRs efficiently supported expression of the Luciferase reporter. There is therefore a novel, functional 57' UTR of AADC mRNA in rat antral mucosa; alternative AADC splice variants could provide the capacity for control at the level of mRNA translation.
K+ transport in colonocytes isolated from the chick: effect of anisosmotic buffers
Authors: Calonge ML , Cano M , Ilundain AA
Published: December 2014

Potassium transport was measured in isolated chicken colonocytes using 85Rb+ as a tracer for K+. Rb+ was determined by atomic absorption spectrometry. The results revealed that net K+ uptake occurred via at least four mechanisms: (i) Na+,K(+)‐ATPase, (ii) K(+)‐ATPase, (iii) Na(+)‐K(+)‐2Cl‐ cotransport system and (iv) a mechanism(s) which is resistant to both ouabain and bumetanide. The rate of K+(Rb+) efflux is stimulated by the calcium ionophore A23187, inhibited by either quinine, verapamil or Ba2+, and unaffected by either apamin, 3,4‐diaminopyridine (3,4‐DAP), H2‐DIDS or bumetanide. The A23187‐induced increase in K+(Rb+) efflux was abolished by apamin. These findings suggest that K+(Rb+) efflux from chicken colonocytes occurs at least in part through Ca(2+)‐activated K+ channels. The present results also show that all these K+ transport systems are involved in cell volume regulation. Thus, external hyposmolarity decreased net K+(Rb+) uptake mediated by Na+,K(+)‐ATPase, K(+)‐ATPase and the Na(+)‐K(+)‐2Cl‐ cotransporter and increased K+(Rb+) efflux rate. The opposite was observed under hyperosmotic conditions.
Regulation of spontaneous rhythmic contractions in rat pregnant myometrium by corticotrophin‐releasing factor
Authors: Dobashi Y , Kanno T , Suga S , Saito Y , Wakui M
Published: December 2014

To elucidate the role of corticotrophin‐releasing factor (CRF) in the spontaneous rhythmic contractions of pregnant myometrium, isometric contractions of longitudinal myometrial preparations taken from Sprague‐Dawley rats (18‐21 days gestation) were measured. CRF (0.03‐30 nM) significantly increased the amplitude (117 +/− 4% of control at 30 nM, mean +/− S.E.M.) and significantly decreased the frequency (74 +/− 5%) in a concentration‐dependent manner. The area under the tension curve did not increase (89 +/− 8%). Such effects of CRF were not observed in preparations pretreated with the RP diastereomer of adenosine cyclic 3',5'‐phosphorothioate (Rp‐cAMPS, 10 microM), an inhibitor of protein kinase A. In preparations pretreated with indomethacin (1 microM), CRF caused little change in the amplitude but significantly decreased the frequency of the contractions. Intracellular cAMP levels in the preparations, measured by enzyme immunoassay, rose when CRF was applied at 30 nM. These results suggest that the slight positive inotropic action of CRF is due to activation of both cAMP and prostaglandin pathways, whereas the negative chronotropic action is due solely to the cAMP signalling pathway.
Depletion of acinar secretory granules in the ferret parotid gland: effects of substance P and vasoactive intestinal peptide
Authors: Ekstrom J , Ekstrom PF
Published: December 2014

The acinar cells of the ferret parotid gland are supplied with parasympathetic nerve fibres containing vasoactive intestinal peptide (VIP) and substance P. In this study intracarotid infusions of the two peptides (0.5–1.0 microgram kg‐1 min‐1 of each for 40 min) in the pentobarbitone‐anaesthetized ferret, treated with atropine and adrenoceptor antagonists, induced a loss of acinar secretory granules from this gland, by 32 % in response to VIP and by 46 % in response to substance P. Stimulation of the parasympathetic auriculo‐temporal nerve (40 Hz, in the presence of adrenoceptor antagonists) caused a larger loss of acinar granules from the gland than stimulation of the sympathetic superior cervical ganglion (intermittently, 50 Hz for 1 s every 10th second, in the presence of atropine) over 40 min (52 % versus 10 %). A 27 % granular loss in response to parasympathetic stimulation followed upon atropinization. The parasympathetic response was not further diminished by the tachykinin antagonist Spantide ((d‐Arg1, d‐Pro2, d‐Trp7,9, Leu)‐substance P). Thus, despite the large exocytotic response to the infusion of substance P, the parasympathetic non‐adrenergic, non‐cholinergic secretion of storage granules seemed, under the present experimental conditions, to occur independently of the action of substance P.
Regional differences in action potential characteristics and membrane currents of guinea‐pig left ventricular myocytes
Authors: Main MC , Bryant SM , Hart G
Published: December 2014

Regional differences in action potential characteristics and membrane currents were investigated in subendocardial, midmyocardial and subepicardial myocytes isolated from the left ventricular free wall of guinea‐pig hearts. Action potential duration (APD) was dependent on the region of origin of the myocytes (P < 0.01, ANOVA). Mean action potential duration at 90 % repolarization (APD90) was 237 +/− 8 ms in subendocardial (n = 30 myocytes), 251 +/− 7 ms in midmyocardial (n = 30) and 204 +/− 7 ms in subepicardial myocytes (n = 36). L‐type calcium current (ICa) density and background potassium current (IK1) density were similar in the three regions studied. Delayed rectifier current (IK) was measured as deactivating tail current, elicited on repolarization back to ‐45 mV after 2 s step depolarizations to test potentials ranging from ‐10 to +80 mV. Mean IK density (after a step to +80 mV) was larger in subepicardial myocytes (1.59 +/− 0.16 pA pF−1, n = 16) than in either subendocardial (1.16 +/− 0.12 pA pF−1, n = 17) or midmyocardial (1. 13 +/− 0.11 pA pF−1, n = 21) myocytes (P < 0.05, ANOVA). The La3+‐insensitive current (IKs) elicited on repolarization back to ‐45 mV after a 250 ms step depolarization to +60 mV was similar in the three regions studied. The La3+‐sensitive tail current, (IKr) was greater in subepicardial (0.50 +/− 0.04 pA pF−1, n = 11) than in subendocardial (0.25 +/− 0.05 pA pF−1, n = 9) or in midmyocardial myocytes (0.38 +/− 0.05 pA pF−1, n = 11, P < 0.05, ANOVA). The contribution of a Na+ background current to regional differences in APD was assessed by application of 0.1 microM tetrodotoxin (TTX). TTX‐induced shortening of APD90 was greater in subendocardial myocytes (35.7 +/− 7.1 %, n = 11) than in midmyocardial (15.7 +/− 3. 8 %, n = 10) and subepicardial (20.2 +/− 4.3 %, n = 11) myocytes (P < 0.05, ANOVA). Regional differences in action potential characteristics between subendocardial, midmyocardial, and subepicardial myocytes isolated from guinea‐pig left ventricle are attributable, at least in part, to differences in IK and Na+‐dependent currents.
Afterload‐induced left ventricular diastolic dysfunction during myocardial ischaemia and reperfusion
Authors: Diakos Nikolaos A. , Pozios Iraklis , Katsaros Lampros , Vakrou Styliani , Sventzouri Stefania , Michelinakis Nikolaos , Tseliou Eleni , Bonios Michael , Malliaras Konstantinos , Papalois Apostolos , Anastasiou‐Nana Maria , Terrovitis John V.
Published: December 2014

New Findings

What is the central question of this study?

While the load dependence of the diastolic function is established for the normal heart, little is known about the response of the acutely ischaemic and reperfused myocardium to alterations in afterload.

What is the main finding and its importance?

Using a model that simulates the clinical scenario of acute ischaemia–reperfusion, we show that increased afterload aggravates diastolic dysfunction during both acute ischaemia and reperfusion. In addition, increased afterload induces diastolic dyssynchrony, which might be the underlying mechanism of the diastolic dysfunction of the ischaemic myocardium. These findings provide us with new information regarding how better to manage patients who undergo revascularization therapy after acute myocardial infarction.

The effects of changes in left ventricular (LV) afterload on diastolic function of acutely ischaemic and reperfused myocardium have not been studied in depth. We examined the following factors: (i) the consequences of increasing the LV afterload on LV diastolic function during acute ischaemia and reperfusion; (ii) whether the myocardial response to afterload elevation is stable throughout a 2 h reperfusion period; and (iii) the role of LV wall synchrony in the development of afterload‐induced diastolic dysfunction. We instrumented 12 anaesthetized, open‐chest pigs with Millar pressure catheters and piezoelectric crystals before ligating mid‐left anterior descending coronary artery for 1 h, followed by reperfusion for 2 h. Six of the animals survived throughout the 2 h of reperfusion, and their data were used for comparisons across the different experimental phases. Left ventricular afterload was increased by inflating an intra‐aortic balloon. Data were recorded at baseline, after 20 min of coronary occlusion and at 30 and 90 min of myocardial reperfusion. The increased afterload for 2 min lengthened the isovolumic relaxation during ischaemia and during early and late reperfusion but had no significant effect on isovolumic relaxation before coronary artery occlusion. Increasing the afterload aggravated LV diastolic dyssynchrony during coronary artery occlusion, but not during reperfusion. The afterload‐induced prolongation of isovolumic relaxation was positively correlated with afterload‐induced diastolic dyssynchrony. These observations indicate that, during myocardial ischaemia and throughout reperfusion, LV diastolic function is afterload dependent. Afterload‐induced diastolic dyssynchrony might be an underlying mechanism of diastolic dysfunction during acute ischaemia.
Reduction of Multibody Dynamic Models in Automotive Systems Using the Proper Orthogonal Decomposition
Authors: Masoudi Ramin , Uchida Thomas , McPhee John
Published: December 2014

The proper orthogonal decomposition (POD) is employed to reduce the order of small-scale automotive multibody systems. The reduction procedure is demonstrated using three models of increasing complexity: a simplified dynamic vehicle model with a fully independent suspension, a kinematic model of a single double-wishbone suspension, and a high-fidelity dynamic vehicle model with double-wishbone and trailing-arm suspensions. These three models were chosen to evaluate the effectiveness of the POD given systems of ordinary differential equations (ODEs), algebraic equations (AEs), and differential-algebraic equations (DAEs), respectively. These models are also components of more complicated full vehicle models used for design, control, and optimization purposes, which often involve real-time simulation. The governing kinematic and dynamic equations are generated symbolically and solved numerically. Snapshot data to construct the reduced subspace are obtained from simulations of the original nonlinear systems. The performance of the reduction scheme is evaluated based on both accuracy and computational efficiency. Good agreement is observed between the simulation results from the original models and reduced-order models, but the latter simulate substantially faster. Finally, a robustness study is conducted to explore the behavior of a reduced-order system as its input signal deviates from the reference input that was used to construct the reduced subspace.
Conceptual Design and Performance Analysis of SOFC/Micro Gas Turbine Hybrid Distributed Energy System
Authors: Dang Zheng , Zhao Hua , Xi Guang
Published: December 2014

A numerical model has been developed for the performance analysis of solid oxide fuel cell (SOFC)/micro gas turbine (MGT) hybrid systems with prereforming of natural gas, in which a quasi two-dimensional model has been built up to simulate the cell electrochemical reaction, heat and mass transfer within tubular SOFC. The developed model can be used not only to predict the overall performance of the SOFC/MGT hybrid system but also to reveal the nonuniform temperature distribution within SOFC unit. The effects of turbine inlet temperature (TIT) and pressure ratio (PR) on the performance of the hybrid system have been investigated. The results show that selecting smaller TIT or PR value will lead to relative higher system efficiency and lower CO2 emission ratio; however, this will raise the risk to destroy SOFC beyond the limitation temperature of electrolyte.
Single vs. Two Stage High Pressure Turbine Design of Modern Aero Engines
Authors: Ahmad Fathi , Mirzamoghadam Alexander V.
Published: December 2014

In this paper, the two-stage shrouded HPT engine configuration rated at 22000 lbs thrust is used as the baseline from which a single stage HPT unshrouded design is systematically derived to evaluate the potential weight and cost advantage. The baseline thermodynamic cycle at the rated thrust level was modified in order to optimize the turbine inlet temperature, overall pressure ratio, and core flow with a single stage HPT and deliver competitive performance. The comparative study, although preliminary in depth, has led to the advantages and disadvantages associated with an unshrouded single versus a two-stage shrouded HPT design. The results compare design configuration, secondary air system, weight, safety, life, specific fuel consumption (SFC), and future thrust growth capability. The main advantages of the single stage application are reductions in cost and complexity of design, lower turbine gas temperature, and ease of maintenance. The main disadvantages are in reduced turbine polytropic/isentropic efficiency for HPC pressure ratio greater than 9, increased SFC, higher rim speed, higher HPT exit Mach number, higher bypass ratio to achieve the desired thrust level, and possibly higher weight. A quantitative statement on the reduction of engine cost/weight is premature until a detailed design and the associated cost-benefit is performed. The paper concludes by recommending that the design philosophy of the modern unmixed turbofan engine (single or two-stage HPT) leads to a balance between the selected turbine gas temperature versus the by-pass ratio in order to minimize cost and maximize the thrust-to-weight ratio and the cycle efficiency. In either ease, the expected high reliability and reduced engine cost/weight in the context of future thrust-growth capability need to be demonstrated by proven technology which seem to favor the two-stage HPT configuration.
Environomic Optimization for Combined Plants Including CO2 Influence
Authors: Santarelli M. , Borchiellini R. , Massardo A. F.
Published: December 2014

In the paper two environomic procedures for the analysis and the optimization of energy systems, where environmental considerations are taken into account together with thermodynamic and economic ones, are presented. The aim is the assignment to energy plants of costs linked to their pollutant activities. The problem is faced with two different environomic approaches: (a) a method assigning a cost to the pollutant emissions (environmental cost); (b) a method assigning a cost to the exergy destroyed inside the system and rejected in the biosphere with the plant wastes (efficiency penalty).

As an example the environomic analysis is developed considering the pollutant emissions (CO, NOx and SOx) of an existing 700 MW combined power plant. Finally, a procedure to determine an efficiency penalty to the emitted CO2 is presented, and a comparison is developed between the results obtained by the two environomic approaches.
Industrial Trent Combustor — Combustion Noise Characteristics
Authors: Scarinci Thomas , Halpin John L.
Published: December 2014

Thermoacoustic resonance is a difficult technical problem that is experienced by almost all lean-premixed combustors. The Industrial Trent combustor is a novel dry-low-emissions (DLE) combustor design, which incorporates three stages of lean premixed fuel injection in series. The three stages in series allow independent control of two stages — the third stage receives the balance of fuel to maintain the desired power level — at all power conditions. Thus, primary zone and secondary zone temperatures can be independently controlled. This paper examines how the flexibility offered by a 3-stage lean premixed combustion system permits the implementation of a successful combustion noise avoidance strategy at all power conditions and at all ambient conditions. This is because at a given engine condition (power level and day temperature) a characteristic “noise map” can be generated on the engine, independently of the engine running condition. The variable distribution of heat release along the length of the combustor provides an effective mechanism to control the amplitude of longitudinal resonance modes of the combustor. This approach has allowed the Industrial Trent combustion engineers to thoroughly “map out” all longitudinal combustor acoustic modes and design a fuel schedule that can navigate around regions of combustor thermoacoustic resonance. Noise mapping results are presented in detail, together with the development of noise prediction methods (frequency and amplitude) that have allowed the noise characteristics of the engine to be established over the entire operating envelope of the engine.
Exergy Analysis of Combined Cycles Using Latest Generation Gas Turbines
Authors: Facchini Bruno , Fiaschi Daniele , Manfrida Giampaolo
Published: December 2014

The potential performance of optimized gas-steam combined cycles built around latest-generation gas turbine engines is analyzed, by means of energy/exergy balances.

The options here considered are the reheat gas turbine and the H-series with closed-loop steam blade cooling. Simulations of performance were run using a well-tested Modular Code developed at the Department of Energy Engineering of Florence and subsequently improved to include the calculation of exergy destruction of all types (heat transfer, friction, mixing and chemical irreversibilities). The blade cooling process is analyzed in detail as it is recognized to be of capita] importance for performance optimization.

The distributions of the relative exergy destruction for the two solutions — both capable of achieving energy/exergy efficiencies in the range of 60% — are compared and the potential for improvement is discussed.
A Simplified Equation to Obtain the Complex Heat Transfer Distribution in an Internal Duct of a Semi-Cooled Turbine Blade
Authors: Visser Jan A.
Published: December 2014

Due to the three-dimensional shape of the internally cooling channels of a modern gas turbine blade, the heat transfer rate varies substantially between the different sides of the channels. This detailed heat flux and resulting temperature distribution on the walls are important to improve the design of the blade as well as to determine the durability of the blade. This detail heat transfer data is usually obtained by means of a complex three-dimensional simulation of the blade configuration. Therefore, for design purposes, the heat transfer data on the channel surfaces is often assumed to be the average heat transfer rate on the channel walls. The average heat transfer rate can be obtained by using a simplified heat transfer equation, based on the average Reynolds number in the channel. This paper presents a simplified formula that can be used to obtain the detailed heat transfer rate in square and non-square cooling channels of a stationary, as well as a rotating turbine blade. The simplified formula is based on results obtained from three-dimensional simulations of the heat transfer in the channels and was compared to simulated and experimental data over a range in flow rates and channel geometries. In general, it can be concluded that the formulation produces fast and accurate results over a wide range of applications.
Actively Controlled Bearing Dampers for Aircraft Engine Applications
Authors: Vance John M. , Ying Daniel , Nikolajsen Jorgen L.
Published: December 2014

This paper describes some of the requirements for bearing dampers to be used in an aircraft engine and briefly discusses the pros and cons of various types of dampers that were considered as candidates for active control in aircraft engines. A disk type of electrorheological (ER) damper was chosen for further study and testing. The paper explains how and why the choice was made. For evaluating potential applications to aircraft engines, an experimental development engine (XTE-45) was used as an example for this study.

Like most real aircraft engines, the XTE-45 ran through more than one critical speed in its operating speed range. There are some speeds where damping is desirable and other speeds where it is not. Thus, the concept of a damper with controllable forces appears attractive. The desired equivalent viscous damping at the critical speeds along with the available size envelope were two of the major criteria used for comparing the dampers.

Most previous investigators have considered the ER damper to produce a purely Coulomb type of damping force and this was the assumption used by the present authors in this study. It is shown in a companion paper (Vance and San Andres, 1999), however, that a purely Coulomb type of friction cannot restrain the peak vibration amplitudes at rotordynamic critical speeds and that the equivalent viscous damping for rotordynamics is different from the value derived by previous investigators for planar vibration. Control laws for Coulomb damping are derived in Vance and San Andres, (1999) to achieve minimum rotor vibration amplitudes in a test rig while avoiding large bearing forces over a speed range that includes a critical speed. The type of control scheme required and its effectiveness was another criterion used for comparing the dampers in this paper.
Dynamic Coefficients of Stepped Labyrinth Gas Seals
Authors: Kwanka K.
Published: December 2014

Rotor-fluid interactions can cause self-excited shaft vibrations of high density turbomachinery. Often the amplitude of the vibrations reaches unacceptably high amplitudes and the scheduled power or running speed cannot be achieved. One of the most important sources of excitation is the flow through labyrinth seals. For a reliable design it is necessary to predict these forces exactly, including not only stiffness but also damping coefficients.

As the forces in labyrinth gas seals are rather small only minimal experimental data is available for the comparison and validation of calculations. Meanwhile a new and easy-to-handle identification procedure enables the investigation of numerous seal geometrys. The paper presents dynamic coefficients obtained with a stepped labyrinth and the comparison with other seal concepts.
Unsteady Aerodynamic Analysis of an Oscillating Cascade at Large Incidence
Authors: Liu Jong-Shang , Murthy Durbha V.
Published: December 2014

The flutter analysis capability of the quasi-3D aeroelastic computational fluid dynamic (CFD) code UNSFLO is evaluated by comparing to unsteady pressure results in an oscillating cascade. The geometry is two-dimensional and the oscillation is well-controlled. Time unsteady UNSFLO results are compared with data at inlet Mach number from 0.2 to 0.8 with incidence 0° and 10°. Three reduced frequencies, 0.4, 0.8, and 1.2 with inter-blade phase angle of 180 degrees were tested. The calculated steady state loadings show good agreement with data at zero incidence. The correlations become worse for high incidence angles because of the separation. The calculated aerodynamic work capture the chordwise distribution except in the near leading edge region. The correlations become also worse for high incidence from the leading edge to midchord especially at high Mach number.
Full-Annulus Simulations of Airfoil Clocking in a 1-1/2 Stage Axial Compressor
Authors: Dorney D. J. , Sondak D. L. , Cizmas P. G. A. , Saren V. E. , Savin N. M.
Published: December 2014

Axial compressors have inherently unsteady flow fields because of relative motion between rotor and stator airfoils. This relative motion leads to viscous and inviscid (potential) interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of stators or rotors can change these interactions, leading to different unsteady forcing functions on airfoils and different compressor efficiencies. In addition, as the Mach number increases the interaction between blade rows can be intensified due to potential effects.

It has been shown, both experimentally and computationally, that airfoil clocking can be used to improve the efficiency and reduce the unsteadiness in multiple-stage axial turbomachines with equal blade counts in alternate blade rows. While previous investigations have provided an improved understanding of the physics associated with airfoil clocking, more research is needed to determine if airfoil clocking is viable for use in modern gas-turbine compressors. This paper presents the results of a combined experimental/computational research effort to study the physics of airfoil clocking in a high-speed axial compressor. Computational simulations have been performed for eight different clocking positions of the stator airfoils in a 1-1/2 stage high-speed compressor. To accurately model the experimental compressor, full-annulus simulations were conducted using 34 IGV, 35 rotor and 34 stator airfoils. It is common practice to modify blade counts to reduce the computational work required to perform turbomachinery simulations, and this approximation has been made in all computational clocking studies performed to date. A simulation was also performed in the present study with 1 inlet guide vane, 1 rotor airfoil, and 1 stator airfoil to model blade rows with 34 airfoils each in order to examine the effects of this approximation. Time-averaged and unsteady data (including performance and boundary layer quantities) were examined. The predicted results indicate that simulating the full annulus gives better qualitative agreement with the experimental data, as well as more accurately modeling the interaction between adjacent blade rows.