bluuebunny/crossref_metadata_2025 huggingface dataset:
Adenosine affects the release of Ca2+ from the sarcoplasmic reticulum via A2A receptors in ferret skinned cardiac fibres
Authors: Hleihel W. , Lafoux A. , Ouaini N. , Divet A. , Huchet‐Cadiou C.
Published: April 2006

In this study, it was shown that adenosine potentiates caffeine‐induced Ca2+ release. It was then proposed that the enhancement of the caffeine‐induced Ca2+ release might occur by a direct effect on the ryanodine Ca2+ release channel or on other Ca2+ regulation mechanisms. Furthermore, A2A receptors may be functional on the ferret cardiac sarcoplasmic reticulum. Using chemically skinned fibres, experiments were conducted on ferret cardiac muscle to find out whether adenosine and the A1 and A2A adenosine receptor agonists (CCPA and CGS 21680) and antagonists (DPCPX and ZM 241385) affected caffeine‐induced Ca2+ release and the Ca2+ sensitivity of contractile proteins. Changes in the caffeine‐induced contracture brought about by adenosine and by adenosine‐receptor agonists and antagonists were recorded in saponin‐skinned fibres (50 μg ml−1). Tension–pCa relationships were then obtained by exposing Triton X‐100‐skinned fibres (1% v/v) sequentially to solutions of decreasing pCa. Adenosine (1–100 nm) and the specific A2A receptor agonist CGS 21680 (1–50 nm) produced a concentration‐dependant potentiation of the caffeine‐induced Ca2+ release from saponin‐skinned fibres. The data plotted versus adenosine and CGS 21680 concentrations displayed sigmoid relationships (Hill relationship), with potentiation of Ca2+ release by 22.2 ± 1.6 (n= 6) and 10.9 ± 0.4% (n= 6), respectively. In addition, the potentiation of caffeine‐induced Ca2+ release by adenosine (50 nm; 15.3 ± 1.0%; n= 6) and by CGS 21680 (50 nm; 11.2 ± 0.4%; n= 6) was reduced by the specific A2A receptor antagonist ZM 241385 (50 nm) to 8.0 ± 1.4 (n= 4) and 5.4 ± 1.2% (n= 4), respectively. The A1 receptor agonist CCPA (1–50 nm) and antagonist DPCPX (50 nm) had no significant effects on caffeine responses. In Triton X‐100‐skinned fibres, the maximal Ca2+‐activated tension of the contractile proteins (41.3 ± 4.1 mN mm−2; n= 8), the Hill coefficient (nH= 2.2 ± 0.1; n= 8) and the pCa50(6.15 ± 0.05; n= 8) were not significantly modified by adenosine (100 nm) or by CGS 21680 (50 nm).
The rapidly adapting receptors in mammalian airways and their responses to changes in extravascular fluid volume
Authors: Kappagoda C. Tissa , Ravi Krishnan
Published: April 2006

In this short review, we shall focus on some recent findings on the physiological stimulus for the rapidly adapting receptors (RAR) of the airways. They are readily activated by a sustained inflation of the lungs and they are usually identified by their rapid adaptation to this stimulus. They are also activated by both tactile stimuli and irritant gases applied to the epithelium of the airways. The investigations reviewed here suggest that these receptors are activated by changes in extravascular fluid volume. The principal factors governing fluid flux from the microcirculation are identified in the Starling equation. These are the hydrostatic pressure, plasma oncotic pressure and capillary permeability. Findings from recent studies suggest that all these factors increase the activity of RAR. In addition, these receptors are also activated by obstruction of lymph drainage from the lung. Evidence is presented to show that manipulation of Starling forces also increases the extravascular fluid volume of the airways in areas where the RAR are located. On the basis of these findings, it is suggested that, along with mechanosensitivity to stimuli such as stretch, inflation and deflation, another physiological stimulus to the RAR is a change in extravascular fluid volume in the regions of the airways where these receptors are located.
Tyrosine kinase and phosphatase regulation of slow delayed‐rectifier K+ current in guinea‐pig ventricular myocytes
Authors: Missan Sergey , Linsdell Paul , McDonald Terence F.
Published: April 2006

The objective of this study was to investigate the involvement of tyrosine phosphorylation in the regulation of the cardiac slowly activating delayed‐rectifier K+ current (IKs) that is important for action potential repolarization. Constitutive IKs recorded from guinea‐pig ventricular myocytes was suppressed by broad‐spectrum tyrosine kinase (TK) inhibitors tyrphostin A23 (IC50, 4.1 ± 0.6 μm), tyrphostin A25 (IC50, 12.1 ± 2.1 μm) and genistein (IC50, 64 ± 4 μm), but was relatively insensitive to the inactive analogues tyrphostin A1, tyrphostin A63, daidzein and genistin. IKs was unaffected by AG1478 (10 μm), an inhibitor of epidermal growth factor receptor TK, and was strongly suppressed by the Src TK inhibitor PP2 (10 μm) but not by the inactive analogue PP3 (10 μm). The results of experiments with forskolin, H89 and bisindolylmaleimide I indicate that the suppression of IKs by TK inhibitors was not mediated via inhibition of (IKs‐stimulatory) protein kinases A and C. To evaluate whether the suppression was related to lowered tyrosine phosphorylation, myocytes were pretreated with TK inhibitors and then exposed to the phosphotyrosyl phosphatase inhibitor orthovanadate (1 mm). Orthovanadate almost completely reversed the suppression of IKs induced by broad‐spectrum TK inhibitors at concentrations around their IC50 values. We conclude that basal IKs is strongly dependent on tyrosine phosphorylation of Ks channel (or channel‐regulatory) protein.
Reflex regulation of airway sympathetic nerves in guinea‐pigs
Authors: Oh Eun Joo , Mazzone Stuart B. , Canning Brendan J. , Weinreich Daniel
Published: April 2006

Sympathetic nerves innervate the airways of most species but their reflex regulation has been essentially unstudied. Here we demonstrate sympathetic nerve‐mediated reflex relaxation of airway smooth muscle measuredin situin the guinea‐pig trachea. Retrograde tracing, immunohistochemistry and electrophysiological analysis identified a population of substance P‐containing capsaicin‐sensitive spinal afferent neurones in the upper thoracic (T1–T4) dorsal root ganglia (DRG) that innervate the airways and lung. After bilateral vagotomy, atropine pretreatment and precontraction of the trachealis with histamine, nebulized capsaicin (10–60 μm) evoked a 63 ± 7% reversal of the histamine‐induced contraction of the trachealis. Either the β‐adrenoceptor antagonist propranolol (2 μm,administered directly to the trachea) or bilateral sympathetic nerve denervation of the trachea essentially abolished these reflexes (10 ± 9% and 6 ± 4% relaxations, respectively), suggesting that they were mediated primarily, if not exclusively, by sympathetic adrenergic nerve activation. Cutting the upper thoracic dorsal roots carrying the central processes of airway spinal afferents also markedly blocked the relaxations (9 ± 5% relaxation). Comparable inhibitory effects were observed following intravenous pretreatment with neurokinin receptor antagonists (3 ± 7% relaxations). These reflexes were not accompanied by consistent changes in heart rate or blood pressure. By contrast, stimulating the rostral cut ends of the cervical vagus nerves also evoked a sympathetic adrenergic nerve‐mediated relaxation that were accompanied by marked alterations in blood pressure. The results indicate that the capsaicin‐induced reflex‐mediated relaxation of airway smooth muscle following vagotomy is mediated by sequential activation of tachykinin‐containing spinal afferent and sympathetic efferent nerves innervating airways. This sympathetic nerve‐mediated response may serve to oppose airway contraction induced by parasympathetic nerve activation in the airways.
Temporal profile of rat skeletal muscle capillary haemodynamics during recovery from contractions
Authors: Ferreira Leonardo F. , Padilla Danielle J. , Musch Timothy I. , Poole David C.
Published: April 2006

In skeletal muscle capillaries, red blood cell (RBC) flux (FRBC), velocity (VRBC) and haematocrit (HctCAP) are key determinants of microvascular O2 exchange. However, the mechanisms leading to the changes in FRBC, VRBC and HctCAP during muscle contractions and recovery thereafter are not fully understood. To address this issue we used intravital microscopy to investigate the temporal profile of the rat spinotrapezius muscle (n= 5) capillary haemodynamics during recovery from 3 min of twitch muscle contractions (1 Hz, 4–6 V). Specifically, we hypothesized that (1) during early recovery FRBC and VRBC would decrease rapidly and FRBC would display a biphasic response (consistent with a muscle pump effect on capillary haemodynamics), and (2) there would be a dynamic relationship between changes (Δ) in VRBC and HctCAP. The values at rest (R) and end‐recovery (ER) were significantly lower (P < 0.05) than at end‐contraction (EC) for FRBC (in cells s−1, R = 30.1 ± 7.8, EC = 46.2 ± 7.3 and ER = 26.0 ± 6.1), VRBC (in μm s−1, R = 368 ± 83, EC = 497 ± 62 and ER = 334 ± 59) and HctCAP(R = 0.193 ± 0.016, EC = 0.214 ± 0.023 and ER = 0.185 ± 0.019). The first data point where a significant decrease in FRBC, HctCAP and VRBC occurred was at 5, 5 and 20 s post‐contraction, respectively. The decrease in FRBC approximated a monoexponential response (half‐time of ∼26 s). The relationship between ΔVRBC and ΔHctCAP was not significant (P > 0.05). Based on the early decrease in FRBC(within 5 s), overall dynamic profile of FRBC and the ∼20 s ‘delay’ to the decrease in VRBC we conclude that the muscle pump does not appear to contribute substantially to the steady‐state capillary haemodynamics in the contracting rat spinotrapezius muscle. Moreover, our findings suggest that alterations in VRBC do not obligate proportional changes in HctCAP within individual capillaries following muscle contractions.
Changes in corticospinal drive to spinal motoneurones following visuo‐motor skill learning in humans
Authors: Perez Monica A. , Lundbye‐Jensen Jesper , Nielsen Jens B.
Published: April 2006

We have previously demonstrated an increase in the excitability of the leg motor cortical area in relation to acquisition of a visuo‐motor task in healthy humans. It remains unknown whether the interaction between corticospinal drive and spinal motoneurones is also modulated following motor skill learning. Here we investigated the effect of visuo‐motor skill training involving the ankle muscles on the coupling between electroencephalographic (EEG) activity recorded from the motor cortex (Cz) and electromyographic (EMG) activity recorded from the left tibialis anterior (TA) muscle in 11 volunteers. Coupling in the time (cumulant density function) and frequency domains (coherence) between EEG–EMG and EMG–EMG activity were calculated during tonic isometric dorsiflexion before and after 32 min of training a visuo‐motor tracking task involving the ankle muscles or performing alternating dorsi‐ and plantarflexion movements without visual feedback. A significant increase in EEG–EMG coherence around 15–35 Hz was observed following the visuo‐motor skill session in nine subjects and in only one subject after the control task. Changes in coherence were specific to the trained muscle as coherence for the untrained contralateral TA muscle was unchanged. EEG and EMG power were unchanged following the training. Our results suggest that visuo‐motor skill training is associated with changes in the corticospinal drive to spinal motorneurones. Possibly these changes reflect sensorimotor integration processes between cortex and muscle as part of the motor learning process.
Rapid inhibition of neural excitability in the nucleus tractus solitarii by leptin: implications for ingestive behaviour
Authors: Williams K. W. , Smith B. N.
Published: April 2006

The fat‐derived peptide leptin regulates cellular activity in areas of the CNS related to feeding, and application of leptin to the fourth ventricle or the nucleus tractus solitarii (NTS) inhibits food intake and weight gain. The hypothesis that leptin modulates cellular activity in the NTS was tested using whole‐cell patch‐clamp recordings in brainstem slices. Leptin caused a rapid membrane hyperpolarization in 58% of rat NTS neurones, including neurones receiving tractus solitarius input (i.e. viscerosensory) and those involved in regulating output to the stomach, identified after gastric inoculation with a transneuronal retrograde viral label. The hyperpolarization was accompanied by a decrease in input resistance and cellular responsiveness, reversed near the K+ equilibrium potential, and was prevented by intracellular Cs+. Perfusion of tolbutamide (200 μm) or wortmannin (100–200 nm) prevented the hyperpolarization, indicating activation of an ATP‐sensitive K+ channel via a PI3 kinase‐dependent mechanism. Constant latency tractus solitarius‐evoked EPSCs were decreased in amplitude by leptin, and the paired‐pulse ratio was increased, suggesting effects on evoked EPSCs involved activation of receptors on vagal afferent terminals. Leptin reduced the frequency of spontaneous and miniature EPSCs, whereas IPSCs were largely unaffected. Leptin's effects were observed in neurones from lean, but not obese, Zucker rats. Neurones that expressed enhanced green fluorescent protein (EGFP) in a subpopulation of putative GABAergic neurones in transgenic mice did not respond to leptin, whereas unlabelled murine neurones responded similarly to rat neurones. Leptin therefore directly and rapidly suppresses activity of excitatory NTS neurones likely to be involved in viscerosensory integration and/or premotor control of the stomach.
Developmental remodelling of the lemniscal synapse in the ventral basal thalamus of the mouse
Authors: Arsenault Dany , Zhang Zhong‐wei
Published: April 2006

Synapse elimination occurs throughout the nervous system during development, and is essential for the formation of neural circuits. The mechanisms underlying synapse elimination in the brain, however, remain largely unknown. Using whole‐cell patch‐clamp recording in a slice preparation, we examined synaptic refinement at the somatosensory relay synapse (lemniscal synapse) in the ventral basal thalamus of the mouse during postnatal development. At 1 week old, each neuron in the ventral basal thalamus is innervated by multiple lemniscal fibres, as revealed by multiple increments of the synaptic response. By 16 days after birth (P16), the majority of neurons showed an all‐or‐none response, suggesting a single fibre innervation. In addition to synapse elimination, extensive modifications in synaptic properties occur during the second week after birth. The ratio of AMPA to NMDA component of the synaptic current tripled between P7 and P17. The decay constant of the NMDA component decreased by about 70% between P7 and P17; ifenprodil (3 μm) reduced the NMDA component by about 40% in neurons at P7–9, but was much less effective at P20–24. On the other hand, there was little change in the inward rectification of AMPA component between P11 and P24. Paired‐pulse ratios, measured at −70 and +40 mV, were stable between P7 and P24. Whisker deprivation from P5 through P19 had no effect on the elimination or the maturation of the lemniscal synapse. These results suggest that the lemniscal synapse in the ventral basal thalamus undergoes extensive refinement during the second week, and that sensory experience has a rather limited role in this process.
Maximal exercise and muscle oxygen extraction in acclimatizing lowlanders and high altitude natives
Authors: Lundby Carsten , Sander Mikael , Van Hall Gerrit , Saltin Bengt , Calbet José A. L.
Published: April 2006

The tight relation between arterial oxygen content and maximum oxygen uptake within a given person at sea level is diminished with altitude acclimatization. An explanation often suggested for this mismatch is impairment of the muscle O2 extraction capacity with chronic hypoxia, and is the focus of the present study. We have studied six lowlanders during maximal exercise at sea level (SL) and with acute (AH) exposure to 4100 m altitude, and again after 2 (W2) and 8 weeks (W8) of altitude sojourn, where also eight high altitude native (Nat) Aymaras were studied. Fractional arterial muscle O2 extraction at maximal exercise was 90.0 ± 1.0% in the Danish lowlanders at sea level, and remained close to this value in all situations. In contrast to this, fractional arterial O2 extraction was 83.2 ± 2.8% in the high altitude natives, and did not change with the induction of normoxia. The capillary oxygen conductance of the lower extremity, a measure of oxygen diffusing capacity, was decreased in the Danish lowlanders after 8 weeks of acclimatization, but was still higher than the value obtained from the high altitude natives. The values were (in ml min−1 mmHg−1) 55.2 ± 3.7 (SL), 48.0 ± 1.7 (W2), 37.8 ± 0.4 (W8) and 27.7 ± 1.5 (Nat). However, when correcting oxygen conductance for the observed reduction in maximal leg blood flow with acclimatization the effect diminished. When calculating a hypothetical leg at altitude using either the leg blood flow or the O2 conductance values obtained at sea level, the former values were almost completely restored to sea level values. This would suggest that the major determinant for not to increase with acclimatization is the observed reduction in maximal leg blood flow and O2 conductance.
Topographical heterogeneity of KIR currents in pericyte‐containing microvessels of the rat retina: effect of diabetes
Authors: Matsushita Kenji , Puro Donald G.
Published: April 2006

Although inwardly rectifying potassium (KIR) channels are known to have important functional roles in arteries and arterioles, knowledge of these channels in pericyte‐containing microvessels is limited. A working hypothesis is that KIR channel activity affects the membrane potential and thereby the contractile tone of abluminal pericytes whose contractions and relaxations may regulate capillary perfusion. Because pericyte function is thought to be particularly important in the retina, we used the perforated‐patch technique to monitor the ionic currents of pericytes located on microvessels freshly isolated from the rat retina. In addition, because changes in ion channel function may contribute to microvascular dysfunction in the diabetic retina, we also recorded from pericyte‐containing microvessels of streptozotocin‐injected rats. Using barium to identify KIR currents, we found that there is a topographical heterogeneity of these currents in the pericyte‐containing microvasculature of the normal retina. Specifically, the KIR current detected at distal locations is strongly rectifying, but the proximal KIR current is weakly rectifying and has a smaller inward conductance. However, soon after the onset of diabetes, these differences diminish as the rectification and inward conductance of the proximal KIR current increase. These diabetes‐induced changes were reversed by an inhibitor of polyamine synthesis and could be mimicked by spermine, whose concentration is elevated in the diabetic eye. Hence, spermine is a candidate for mediating the effect of diabetes on the function of microvascular KIR channels. In addition, our findings raise the possibility that functional changes in KIR channels contribute to blood flow dysregulation in the diabetic retina.
Creatine supplementation augments the increase in satellite cell and myonuclei number in human skeletal muscle induced by strength training
Authors: Olsen Steen , Aagaard Per , Kadi Fawzi , Tufekovic Goran , Verney Julien , Olesen Jens L. , Suetta Charlotte , Kjær Michael
Published: April 2006

The present study investigated the influence of creatine and protein supplementation on satellite cell frequency and number of myonuclei in human skeletal muscle during 16 weeks of heavy‐resistance training. In a double‐blinded design 32 healthy, male subjects (19–26 years) were assigned to strength training (STR) while receiving a timed intake of creatine (STR‐CRE) (n= 9), protein (STR‐PRO) (n= 8) or placebo (STR‐CON) (n= 8), or serving as a non‐training control group (CON) (n= 7). Supplementation was given daily (STR‐CRE: 6–24 g creatine monohydrate, STR‐PRO: 20 g protein, STR‐CON: placebo). Furthermore, timed protein/placebo intake were administered at all training sessions. Muscle biopsies were obtained at week 0, 4, 8 (week 8 not CON) and 16 of resistance training (3 days per week). Satellite cells were identified by immunohistochemistry. Muscle mean fibre (MFA) area was determined after histochemical analysis. All training regimes were found to increase the proportion of satellite cells, but significantly greater enhancements were observed with creatine supplementation at week 4 (compared to STR‐CON) and at week 8 (compared to STR‐PRO and STR‐CON) (P < 0.01–0.05). At week 16, satellite cell number was no longer elevated in STR‐CRE, while it remained elevated in STR‐PRO and STR‐CON. Furthermore, creatine supplementation resulted in an increased number of myonuclei per fibre and increases of 14–17% in MFA at week 4, 8 and 16 (P < 0.01). In contrast, STR‐PRO showed increase in MFA only in the later (16 week, +8%) and STR‐CON only in the early (week 4, +14%) phases of training, respectively (P < 0.05). In STR‐CRE a positive relationship was found between the percentage increases in MFA and myonuclei from baseline to week 16, respectively (r= 0.67, P < 0.05). No changes were observed in the control group (CON). In conclusion, the present study demonstrates for the first time that creatine supplementation in combination with strength training amplifies the training‐induced increase in satellite cell number and myonuclei concentration in human skeletal muscle fibres, thereby allowing an enhanced muscle fibre growth in response to strength training.
Effects of female steroid hormones on A‐type K+currents in murine colon
Authors: Beckett Elizabeth A. H. , McCloskey Conor , O'Kane Neil , Sanders Kenton M. , Don Koh Sang
Published: April 2006

Idiopathic constipation is higher in women of reproductive age than postmenopausal women or men, suggesting that female steroid hormones influence gastrointestinal motility. How female hormones affect motility is unclear. Colonic motility is regulated by ion channels in colonic myocytes. Voltage‐dependent K+channels serve to set the excitability of colonic muscles. We investigated regulation of Kv4.3 channel expression in response to acute or chronic changes in female hormones. Patch clamp experiments and quantitative PCR were used to compare outward currents and transcript expression in colonic myocytes from male, non‐pregnant, pregnant and ovariectomized mice. Groups of ovariectomized mice received injections of oestrogen or progesterone to investigate the effects of hormone replacement. The capacitance of colonic myocytes from non‐pregnant females was larger than in males. Net outward current density in male and ovariectomized mice was higher than in non‐pregnant females and oestrogen‐treated ovariectomized mice. Current densities in late pregnancy were lower than in female controls. Progesterone had no effect on outward currents. A‐type currents were decreased in non‐pregnant females compared with ovariectomized mice, and were further decreased by pregnancy or oestrogen replacement. Kv4.3 transcripts did not differ significantly between groups; however, expression of the potassium channel interacting protein KChIP1 was elevated in ovariectomized mice compared with female controls and oestrogen‐treated ovariectomized mice. Delayed rectifier currents were not affected by oestrogen. In the mouse colon, oestrogen suppresses A‐type currents, which are important for regulating excitability. These observations suggest a possible link between female hormones and altered colonic motility associated with menses, pregnancy and menopause.
Cartilage elasticity resides in shape module decoran and aggrecan sumps of damping fluid: implications in osteoarthrosis
Authors: Scott John E. , Stockwell Robin A.
Published: April 2006

Cartilage ultrastructure is based on collagen fibrils tied together by proteoglycans (PGs). Interfibrillar orthogonal PG bridges (‘shape modules’) were located by electron histochemistry using Cupromeronic blue methodology. Their frequency and size, similar to those in tendon, cornea, etc., were compatible with biochemical estimates of tissue decoran (formerly decorin), the PG component of shape module bridges. Digestion by hyaluronanase and chondroitinase AC helped to identify aggrecan and decoran and exemplified the destruction of shape modular organization by glycan‐splitting agents. The anionic glycosaminoglycan (AGAG) of decoran, dermochondan sulphate (DS, formerly dermatan sulphate), contains l‐iduronate, an elastic sugar unit. Chondroitan, keratan (present in aggrecan) and hyaluronan are not similarly elastic but can participate in sliding‐filament reversible deformability. Mechanical properties predicted for the interfibrillar bridges accord with anisotropic stress/strain responses of articular cartilage to compressive or tensile stresses. We propose that fluid from pericellular aggrecan‐rich domains moves under pressure into the interterritorial fibrillar arrays against the elastic resistance of the shape modules, which return the fluid, post‐compression, to its original position. Cartilage is tendon‐like, with the addition of expansile aggrecan‐rich reservoirs of aqueous shock absorber fluid. Rupture or loss of interfibrillar ties would allow expansile PG to force the collagenous matrix apart, imbibing water, increasing swelling and fissuring – characteristic manifestations of osteoarthrosis (OA), a joint disease of major economic importance. Decoran may be a primary target of the OA disease process.
Startle responses elicited by whiplash perturbations
Authors: Blouin Jean‐Sébastien , Inglis J. Timothy , Siegmund Gunter P.
Published: April 2006

The human startle response produces muscle contractions throughout the body but the most brisk and synchronized contractions appear in the neck muscles. This response, which is greatest with the first exposure to a startling stimulus, could produce excessive and inappropriately directed muscle contractions that could explain the higher incidence of whiplash injuries in people who are unprepared for the collision. This study seeks neurophysiological evidence of startle responses in the neck muscles of 120 healthy subjects exposed to between 1 and 16 rear‐end impacts or forward perturbations of different speeds. Startle responses were quantified by the synchronous electromyographic (EMG) activity between 10 and 20 Hz in bilaterally homologous sternocleidomastoid, scalene and cervical paraspinal neck muscles. Coherence analyses of EMGs from the left and right muscles were used to estimate synchrony for: (i) the first unexpected trial, (ii) subsequent habituated trials, and (iii) the superposition of habituated trials and a loud acoustic stimulus (40 ms, 124 dB sound). The peak in coherent EMG activity between contralateral muscle pairs in the 10–20 Hz bandwidth was related to startle. Synchrony in this bandwidth was observed between the left and right muscles during the first impact or whiplash‐like perturbation. This synchrony decreased significantly in the habituated trials, but reappeared when the loud acoustic stimulus was introduced. Its presence in the first trial indicates that startle is part of the neuromuscular response to an unexpected rear‐end impact. This startle component of the neuromuscular response could play a role in the aetiology of whiplash injuries.
Influence of ipsilateral transcranial magnetic stimulation on the triphasic EMG pattern accompanying fast ballistic movements in humans
Authors: Irlbacher Kerstin , Voss Martin , Meyer Bernd‐Ulrich , Rothwell John C.
Published: April 2006

Fast ballistic flexion movements of the wrist are produced by a triphasic pattern of electromyographic (EMG) activity in flexor and extensor muscle. Whereas it is generally accepted that the primary motor cortex generates the first agonist burst (AG1), its contribution to the following antagonist burst (ANT) and second agonist burst (AG2) is unresolved. We applied single pulses of suprathreshold transcranial magnetic stimulation (TMS) at different times to the motor cortex ipsilateral to wrist flexion. This produced interhemispheric inhibition of the opposite motor cortex and a silent period in the ballistic EMG pattern that started about 30 ms after the stimulus and lasted for a further 30 ms. If the silence was timed to start within the first 30 ms of AG1, then timing of the subsequent ANT and AG2 bursts was delayed. However, if the silence began later, then the timing of the ANT burst was not changed. A similar effect on the onset latency of the AG2 was seen if the silence began in the first part of the ANT burst. The results are compatible with a model in which the triphasic pattern is not triggered as a single entity. Instead we suggest that each burst has its own trigger that occurs about 30–40 ms after the start of AG1 (or ANT). If AG1 (or ANT) is interrupted within this time period then this trigger, and hence later bursts, are delayed. If the interruption occurs after 30–40 ms it has no effect on the onset of later bursts since they have already been triggered.
Heat stress enhances arterial baroreflex control of muscle sympathetic nerve activity via increased sensitivity of burst gating, not burst area, in humans
Authors: Keller D. M. , Cui J. , Davis S. L. , Low D. A. , Crandall C. G.
Published: April 2006

The relationship between muscle sympathetic nerve activity (MSNA) and diastolic blood pressure has been used to describe two sites for arterial baroreflex control of MSNA. By determining both the likelihood of occurrence for sympathetic bursts and the area of each burst for a given diastolic blood pressure, both a ‘gating’ and an ‘area’ control site has been described in normothermic humans. Assessing the effect of heat stress on these mechanisms will improve the understanding of baroreflex control of arterial blood pressure under this thermal condition. Therefore, the purpose of this study was to test the hypothesis that heat stress enhances arterial baroreflex control of burst gating and area. In 10 normotensive subjects (age, 32 ± 2 years; mean ±s.e.m.), MSNA (peroneal) was assessed using standard microneurographic techniques. Five minute periods of data were examined during normothermic and whole‐body heating conditions. The burst incidence (i.e. number of sympathetic bursts per 100 cardiac cycles) and the area of each burst were determined for each cardiac cycle and were placed into 3 mmHg intervals of diastolic blood pressure. During normotheric conditions, there was a moderate, negative relationship between burst incidence and diastolic blood pressure (slope =−2.49 ± 0.38; r2= 0.73 ± 0.06; mean ±s.e.m.), while area per burst relative to diastolic blood pressure exhibited a less strong relationship (slope =–1.13 ± 0.46; r2= 0.45 ± 0.09). During whole‐body heating there was an increase in the slope of the relationship between burst incidence and diastolic blood pressure (slope =–4.69 ± 0.44; r2= 0.84 ± 0.03) compared to normothermia (P < 0.05), while the relationship between area per burst and diastolic blood pressure was unchanged (slope =–0.92 ± 0.29; r2= 0.41 ± 0.08) (P= 0.50). The primary finding of this investigation is that, at rest, whole‐body heating enhanced arterial baroreflex control of MSNA through increased sensitivity of a ‘gating’ mechanism, as indicated by an increase in the slope of the relationship between burst incidence and diastolic blood pressure. This occurrence is likely to afford protection against potential decreases in arterial blood pressure in an effort to preserve orthostatic tolerance during heat stress.
Glucagon activates Ca2+ and Cl− channels in rat hepatocytes
Authors: Aromataris Edoardo C. , Roberts Michael L. , Barritt Greg J. , Rychkov Grigori Y.
Published: April 2006

Glucagon is one of the major hormonal regulators of glucose metabolism, counteracting the hepatic effects of insulin when the concentration of glucose in the bloodstream falls below a certain level. Glucagon also regulates bile flow, hepatocellular volume and membrane potential of hepatocytes. It is clear that changes in cell volume and membrane potential cannot occur without significant ion fluxes across the plasma membrane. The effects of glucagon on membrane currents in hepatocytes, however, are not well understood. Here we show, by patch‐clamping of rat hepatocytes, that glucagon activates two types of currents: a small inwardly rectifying Ca2+ current with characteristics similar to those of the store‐operated Ca2+ current and a larger outwardly rectifying Cl− current similar to that activated by cell swelling. We show that the mechanism of glucagon action on membrane conductance involves phospholipase C and adenylyl cyclase. Contribution of the adenylyl cyclase‐dependent pathway to activation of the currents depended on Epac (exchange protein directly activated by cAMP), but not on protein kinase A. The activation of Ca2+ and Cl− channels is likely to play a key role in the mechanisms by which glucagon regulates hepatocyte metabolism and volume.
Parametric Analysis of Combined Cycles Equipped With Inlet Fogging
Authors: Bhargava R. , Bianchi M. , Melino F. , Peretto A.
Published: April 2006

In recent years, deregulation in the power generation market worldwide combined with significant variation in fuel prices and a need for flexibility in terms of power augmentation specially during periods of high electricity demand (summer months or noon to 6:00 p.m.) has forced electric utilities, cogenerators and independent power producers to explore new power generation enhancement technologies. In the last five to ten years, inlet fogging approach has shown more promising results to recover lost power output due to increased ambient temperature compared to the other available power enhancement techniques. This paper presents the first systematic study on the effects of both inlet evaporative and overspray fogging on a wide range of combined cycle power plants utilizing gas turbines available from the major gas turbine manufacturers worldwide. A brief discussion on the thermodynamic considerations of inlet and overspray fogging including the effect of droplet dimension is also presented. Based on the analyzed systems, the results show that high pressure inlet fogging influences performance of a combined cycle power plant using an aero-derivative gas turbine differently than with an advanced technology or a traditional gas turbine. Possible reasons for the observed differences are discussed.
Combining Classification Techniques With Kalman Filters for Aircraft Engine Diagnostics
Authors: Dewallef P. , Romessis C. , Léonard O. , Mathioudakis K.
Published: April 2006

A diagnostic method consisting of a combination of Kalman filters and Bayesian Belief Network (BBN) is presented. A soft-constrained Kalman filter uses a priori information derived by a BBN at each time step, to derive estimations of the unknown health parameters. The resulting algorithm has improved identification capability in comparison to the stand-alone Kalman filter. The paper focuses on a way of combining the information produced by the BBN with the Kalman filter. An extensive set of fault cases is used to test the method on a typical civil turbofan layout. The effectiveness of the method is thus demonstrated, and its advantages over individual constituent methods are presented.
Transient Analysis of Solid Oxide Fuel Cell Hybrids—Part I: Fuel Cell Models
Authors: Magistri Loredana , Trasino Francesco , Costamagna Paola
Published: April 2006

The main goal of this work is the transient analysis of hybrid systems based on solid oxide fuel cells (SOFC). The work is divided into three parts: in the first, the fuel cell transient models are presented and discussed, whereas in the subsequent parts of the paper the anodic recirculation system (Part B: Ferrari, M.L., Traverso, A., Massardo, A.F., 2004, ASME Paper No. 2004-GT-53716) and the entire hybrid transient performance (Part C: Magistri, L., Ferrari, M.L., Traverso, A., Costamagna, P., Massardo, A.F., 2004, ASME Paper No. 2004-GT-53845) are investigated. In this paper the transient behavior of a solid oxide fuel cell is analyzed through the use of two different approaches: macroscopic and detailed SOFC models. Both models are presented in this paper, and their simulation results are compared to each other and to available experimental data. As a first step the transient response of the fuel cell was studied using a very detailed model in order to completely describe this phenomenon and to highlight the critical aspects. Subsequently, some modifications were made to this model to create an apt simulation tool (macroscopic fuel cell model) for the whole plant analysis. The reliability of this model was verified by comparing several transient responses to the results obtained with the detailed model. In the subsequent papers (Parts B and C), the integration of the macroscopic fuel cell model into the whole plant model will be described and the transient study of the hybrid plant will be presented.
Modeling and Simulation of a Gas Turbine Engine for Power Generation
Authors: Al-Hamdan Qusai Z. , Ebaid Munzer S. Y.
Published: April 2006

The gas turbine engine is a complex assembly of a variety of components that are designed on the basis of aerothermodynamic laws. The design and operation theories of these individual components are complicated. The complexity of aerothermodynamic analysis makes it impossible to mathematically solve the optimization equations involved in various gas turbine cycles. When gas turbine engines were designed during the last century, the need to evaluate the engines performance at both design point and off design conditions became apparent. Manufacturers and designers of gas turbine engines became aware that some tools were needed to predict the performance of gas turbine engines especially at off design conditions where its performance was significantly affected by the load and the operating conditions. Also it was expected that these tools would help in predicting the performance of individual components, such as compressors, turbines, combustion chambers, etc. At the early stage of gas turbine developments, experimental tests of prototypes of either the whole engine or its main components were the only method available to determine the performance of either the engine or of the components. However, this procedure was not only costly, but also time consuming. Therefore, mathematical modelling using computational techniques were considered to be the most economical solution. The first part of this paper presents a discussion about the gas turbine modeling approach. The second part includes the gas turbine component matching between the compressor and the turbine which can be met by superimposing the turbine performance characteristics on the compressor performance characteristics with suitable transformation of the coordinates. The last part includes the gas turbine computer simulation program and its philosophy. The computer program presented in the current work basically satisfies the matching conditions analytically between the various gas turbine components to produce the equilibrium running line. The computer program used to determine the following: the operating range (envelope) and running line of the matched components, the proximity of the operating points to the compressor surge line, and the proximity of the operating points at the allowable maximum turbine inlet temperature. Most importantly, it can be concluded from the output whether the gas turbine engine is operating in a region of adequate compressor and turbine efficiency. Matching technique proposed in the current work used to develop a computer simulation program, which can be served as a valuable tool for investigating the performance of the gas turbine at off-design conditions. Also, this investigation can help in designing an efficient control system for the gas turbine engine of a particular application including being a part of power generation plant.
Experimental Study on Homogeneous Charge Compression Ignition Combustion With Fuel of Dimethyl Ether and Natural Gas
Authors: Yao Mingfa , Zheng Zunqing , Qin Jin
Published: April 2006

The homogeneous charge compression ignition (HCCI) combustion fueled by dimethyl ether (DME) and compressed natural gas (CNG) was investigated. The experimental work was carried out on a single-cylinder diesel engine. The results show that adjusting the proportions of DME and CNG is an effective technique for controlling HCCI combustion and extending the HCCI operating range. The combustion process of HCCI with dual fuel is characterized by a distinctive two-stage heat release process. As CNG flow rate increases, the magnitude of peak cylinder pressure and the peak heat release rate in the second stage goes up. As DME flow rate increases, the peak cylinder pressure, heat release rate, and NOx emissions increase while THC and CO emissions decrease.
Optimal Design of Gas Turbine Cogeneration Plants in Consideration of Discreteness of Equipment Capabilities
Authors: Yokoyama Ryohei , Ito Koichi
Published: April 2006

To attain the highest economic and energy-saving characteristics of gas turbine cogeneration plants, it is necessary to rationally determine capacities and numbers of gas turbines and auxiliary equipment in consideration of their operational strategies corresponding to seasonal and hourly variations in energy demands. Some optimization approaches based on the mixed-integer linear programing have been proposed to this design problem. However, equipment capacities have been treated as continuous variables, and correspondingly, performance characteristics and capital costs of equipment have been assumed to be continuous functions with respect to their capacities. This is because if equipment capacities are treated discretely, the number of integer variables increases drastically and the problem becomes too difficult to solve. As a result, the treatment of equipment capacities as continuous variables causes discrepancies between existing and optimized values of capacities and expresses the dependence of performance characteristics and capital costs on capacities with worse approximations. In this paper, an optimal design method is proposed in consideration of discreteness of equipment capacities. A formulation for keeping the number of integer variables as small as possible is presented to solve the optimal design problem easily. This method is applied to the design of a gas turbine cogeneration plant, and its validity and effectiveness are clarified.
Gas Turbine Compressor Washing: Historical Developments, Trends and Main Design Parameters for Online Systems
Authors: Mund Friederike C. , Pilidis Pericles
Published: April 2006

By being exposed to atmospheric conditions gas turbines are inevitably subjected to sources of fouling. The resulting degradation can be partially recovered by cleaning the compressor. Based on open literature and patents, the different approaches leading to the most advanced method of compressor online washing have been compiled. The origins of online washing and the development trends over the decades are outlined, and the current systems are categorized. The introduction of system categories has been justified by a field survey. Additionally, the main design parameters of online washing systems are summarized.
Conserving a Volatile Metabolite: a Role for Carboxysome-Like Organelles in
Salmonella enterica
Authors: Penrod Joseph T. , Roth John R.
Published: April 2006

Salmonellae can use ethanolamine (EA) as a sole source of carbon and nitrogen. This ability is encoded by an operon (
eut
) containing 17 genes, only 6 of which are required under standard conditions (37°C; pH 7.0). Five of the extra genes (
eutM
, -
N
, -
L
, -
K
, and -
G
) become necessary under conditions that favor loss of the volatile intermediate, acetaldehyde, which escapes as a gas during growth on EA and is lost at a higher rate from these mutants. The
eutM
,
-N
,
-L
, and -
K
genes encode homologues of shell proteins of the carboxysome, an organelle shown (in other organisms) to concentrate CO
2
. We propose that carboxysome-like organelles help bacteria conserve certain volatile metabolites—CO
2
or acetaldehyde—perhaps by providing a low-pH compartment. The EutG enzyme converts acetaldehyde to ethanol, which may improve carbon retention by forming acetals; alternatively, EutG may recycle NADH within the carboxysome.
Transcriptional Analysis of Long-Term Adaptation ofYersinia enterocoliticato Low-Temperature Growth
Authors: Bresolin Geraldine , Neuhaus Klaus , Scherer Siegfried , Fuchs Thilo M.
Published: April 2006

To analyze the transcriptional response ofYersinia enterocoliticacells to prolonged growth at low temperature, a collection ofluxCDABEtransposon mutants was cultivated in parallel at optimal (30°C) and suboptimal (10°C) temperatures and screened for enhanced promoter activities during growth until entering stationary phase. Among 5,700Y. enterocoliticamutants, 42 transcriptional units were identified with strongly enhanced or reduced promoter activity at 10°C compared to 30°C, and changes in their transcriptional levels over time were measured. Green fluorescent protein fusions to 10 promoter regions confirmed the data. The temporal order of induction of the temperature-responsive genes ofY. enterocoliticawas deduced, starting with the expression of cold shock genescspAandcspBand the elevated transcription of a glutamate-aspartate symporter. Subsequently, cold-adapted cells drastically up-regulated genes encoding environmental sensors and regulators, such as UhpABC, ArcA, and methyl-accepting chemotaxis protein I (MCPI). Among the most prominent cold-responsive elements that were transcriptionally induced during growth in early and middle exponential phase are the insecticidal toxin genestcaAandtcaB, as well as genes involved in flagellar synthesis and chemotaxis. The expression pattern of the late-exponential- to early-stationary-growth phase is dominated by factors involved in biodegradative metabolism, namely, a histidine ammonia lyase, three enzymes responsible for uptake and utilization of glycogen, the urease complex, and a subtilisin-like protease. Double-knockout mutants and complementation studies demonstrate inhibitory effects of MCPI and UhpC on the expression of a putative hemolysin transporter. The data partially delineate the spectrum of gene expression ofY. enterocoliticaat environmental temperatures, providing evidence that an as-yet-unknown insect phase is part of the life cycle of this human pathogen.
TheErwinia chrysanthemi3937 PhoQ Sensor Kinase Regulates Several Virulence Determinants
Authors: Venkatesh Balakrishnan , Babujee Lavanya , Liu Hui , Hedley Pete , Fujikawa Takashi , Birch Paul , Toth Ian , Tsuyumu Shinji
Published: April 2006

The PhoPQ two-component system regulates virulence factors inErwinia chrysanthemi, a pectinolytic enterobacterium that causes soft rot in several plant species. We characterized the effect of a mutation inphoQ, the gene encoding the sensor kinase PhoQ of the PhoPQ two-component regulatory system, on the global transcriptional profile ofE. chrysanthemiusing cDNA microarrays and further confirmed our results by quantitative reverse transcription-PCR analysis. Our results indicate that a mutation inphoQaffects transcription of at least 40 genes, even in the absence of inducing conditions. Enhanced expression of several genes involved in iron metabolism was observed in the mutant, including that of theacsoperon that is involved in achromobactin biosynthesis and transport. This siderophore is required for full virulence ofE. chrysanthemi, and its expression is governed by the global repressor protein Fur. Changes in gene expression were also observed for membrane transporters, stress-related genes, toxins, and transcriptional regulators. Our results indicate that the PhoPQ system governs the expression of several additional virulence factors and may also be involved in interactions with other regulatory systems.