bluuebunny/crossref_metadata_2025 huggingface dataset:
Impaired Microvascular Function in Normal Children: Effects of Adiposity and Poor Glucose Handling
Authors: Khan Faisel , Green Fiona C. , Forsyth J. Stewart , Greene Stephen A. , Morris Andrew D. , Belch Jill J. F.
Published: August 2003

Clustering of cardiovascular risk factors is thought to occur early in life. The endothelium is an important regulator of microvascular function. We investigated the relationship between microvascular function and cardiovascular risk factors in 145 normal, healthy children aged 11‐14 years. Skin microvascular responses, measured using laser Doppler imaging, to iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP), were negatively correlated with percentage body fat (r=−0.20, P < 0.05 and r=−0.18, P < 0.05, respectively). Subjects were stratified into quintiles based on 2‐h, post‐feeding glucose levels. Subjects in the upper glucose quintile (range 7.4‐11.4 mmol l−1) showed significantly lower vasodilatation to both ACh (P < 0.005) and SNP (P < 0.02) than those in the lower quintile (range 3.9‐4.9 mmol l−1). Waist‐to‐hip ratio and the fasting insulin resistance index were significantly greater in subjects in the upper quintile than those in the lower quintile (P < 0.001 and P < 0.05, respectively). Additionally, in subjects in the upper glucose quintile, fasting triglyceride correlated with fasting insulin (r= 0.59, P < 0.001) and with the fasting insulin resistance index (r= 0.49, P < 0.009), and plasma levels of cholesterol and 2‐h glucose were also correlated (r= 0.40, P < 0.05). In a cross‐section of normal children, microvascular function was negatively associated with adiposity. Additionally, in a subgroup of subjects, there was a clustering of high post‐feeding glucose, impaired microvascular function, increased insulin resistance and higher central fat distribution. These findings suggest that risk factors for adult cardiovascular disease begin to cluster in normal children, which might have important consequences for development of atherosclerosis later in life.
Novel modulatory mechanisms revealed by the sustained application of nicotine in the guinea‐pig hippocampus in vitro
Authors: Mann Edward O. , Greenfield Susan A.
Published: August 2003

The α7 nicotinic acetylcholine receptor (nAChR) has been implicated widely in behavioural functions and dysfunctions related to the hippocampus, but the detailed mechanisms by which this receptor contributes to these behavioural processes have yet to be elucidated. In the present study, sustained application (5 min) of nicotine significantly lowered the threshold for synaptic plasticity, and thus a long‐lasting potentiation was induced by a stimulus that would normally evoke only a short‐term potentiation. This effect appeared to be mediated by α7 nAChRs, as it was inhibited by the α7 nAChR‐specific antagonist α‐bungarotoxin (100 nm), but not by mecamylamine (50 μm) or dihydro‐β‐erythroidine (DHβE; 1 μm) at concentrations known to be selective for non‐α7 nAChRs. Further pharmacological dissection revealed that the effect was also abolished by the NMDA receptor antagonist, D‐(‐)‐2‐amino‐5‐phosphonopentanoic acid (D‐AP5; 50 μm). This blockade, however, unmasked a slowly developing nicotine‐induced potentiation of field excitatory postsynaptic potential that appeared to be dependent on both α7 nAChR activation and non‐α7 nAChR desensitisation. This secondary effect of nicotine was blocked by a combination of picrotoxin (50 μm) and saclofen (100 μm), and thus appeared to be mediated via GABAergic interneurons. The important implication of this study was that the sustained application of α7 nAChR agonists could modulate the conditions for synaptic plasticity through multiple transduction pathways, and not simply the inactivation of α7 nAChRs. These α7‐nAChR‐dependent mechanisms could reconcile the discrepancies between the previously reported behavioural versus electrophysiological effects of nicotine in the hippocampus.
Suppression of skeletal muscle lipoprotein lipase activity during physical inactivity: a molecular reason to maintain daily low‐intensity activity
Authors: Bey Lionel , Hamilton Marc T.
Published: August 2003

We have examined the regulation of lipoprotein lipase (LPL) activity in skeletal muscle during physical inactivity in comparison to low‐intensity contractile activity of ambulatory controls. From studies acutely preventing ambulatory activity of one or both the hindlimbs in rats, it was shown that ≈90–95 % of the heparin‐releasable (HR) LPL activity normally present in rat muscle with ambulatory activity is lost, and thus dependent on local contractile activity. Similarly, ≈95 % of the differences in LPL activity between muscles of different fibre types was dependent on ambulatory activity. The robustness of the finding that physical inactivity significantly decreases muscle LPL activity was evident from confirmatory studies with different models of inactivity, in many rats and mice, both sexes, three muscle types and during both acute and chronic (11 days) treatment. Inactivity caused a local reduction of plasma [3H]triglyceride uptake into muscle and a decrease in high density lipoprotein cholesterol concentration. LPL mRNA was not differentially expressed between ambulatory controls and either the acutely or chronically inactive groups. Instead, the process involved a rapid loss of the HR‐LPL protein mass (the portion of LPL largely associated with the vascular endothelium) by an actinomycin D‐sensitive signalling mechanism (i.e. transcriptionally dependent process). Significant decreases of intracellular LPL protein content lagged behind the loss of HR‐LPL protein. Treadmill walking raised LPL activity ≈8‐fold (P < 0.01) within 4 h after inactivity. The striking sensitivity of muscle LPL to inactivity and low‐intensity contractile activity may provide one piece of the puzzle for why inactivity is a risk factor for metabolic diseases and why even non‐vigorous activity provides marked protection against disorders involving poor lipid metabolism.
Carotid baroreflex responsiveness to head‐up tilt‐induced central hypovolaemia: effect of aerobic fitness
Authors: Ogoh Shigehiko , Volianitis Stefanos , Nissen Peter , Wray D. Walter , Secher Niels H. , Raven Peter B.
Published: August 2003

This investigation examined the interaction between carotid baroreflex (CBR) responsiveness during head‐up tilt (HUT)‐induced central hypovolaemia and aerobic fitness. Seven average fit (AF) individuals, with a mean maximal oxygen uptake (V̇O2max) of 49 ± 1 (ml O2) kg−1min−1, and seven high fit (HF) individuals, with a V̇O2max of 61 ± 1 (ml O2) kg−1 min−1, voluntarily participated in the investigation. After 10‐15 min supine, each subject was exposed to nine levels of progressively increasing HUT by 10 deg increments from −20 deg to +60 deg. During the final 3 min of each stage of HUT, the CBR responsiveness was measured using a rapid pulse (500 ms) train of neck pressure (NP) and neck suction (NS) ranging from +40 to −80 Torr. The maximal gain of the carotid‐HR (Gmax‐HR) and carotid‐MAP (Gmax‐MAP) baroreflex function curves was identified as measures of CBR responsiveness. During HUT‐induced decreases in thoracic admittance, an index of central blood volume (CBV), the Gmax‐HR and Gmax‐MAP of the AF subjects increased more than the Gmax‐HR and Gmax‐MAP of the HF subjects (P < 0.05). The data demonstrate that the increase in the CBR responsiveness during a tilt‐induced progressive unloading of the cardiopulmonary baroreceptors was attenuated in endurance‐trained subjects. These findings provide an explanation for the predisposition to orthostatic hypotension and intolerance in well‐trained athletes.
Cyclo‐oxygenase‐2 mediated prostaglandin release regulates blood flow in connective tissue during mechanical loading in humans
Authors: Langberg H. , Boushel R. , Skovgaard D. , Risum N. , Kjær M.
Published: August 2003

Mechanical loading is known to increase connective tissue blood flow of human tendons and to cause local release of vasodilatory substances. The present study investigated the importance of prostaglandins (PG) formed by cyclo‐oxygenase isoforms (COX‐1 and 2) for the exercise‐related increase in blood flow in connective tissue. Healthy individuals (n= 24, age: 23‐31 years) underwent 30 min of intermittent, isometric, plantarflexion with both calf muscles either without (n= 6, Control, C) or with blockade of PG formation, either COX‐2 specific (n= 10, Celecoxib 2 x 100 mg day−1 for 3 days prior to the experiment) or COX unspecific (n= 8, indomethacin 100 mg (12 and 1 h pre‐experiment) and acetyl salicylic acid 500 mg day−1 for 3 days pre‐experiment). Prostaglandin E2 (PGE2) concentration was determined by microdialysis and blood flow by 133Xe washout. In C, interstitial PGE2 rose from (0.8 ± 0.2 (rest) to 1.4 ± 0.5 ng ml−1 (exercise), P < 0.05), whereas during unspecific COX inhibition, tissue PGE2 was completely inhibited at rest and during exercise. COX‐2 specific blockade did not inhibit tissue PGE2 at rest, but totally abolished the exercise induced increase. Blood flow was similar in the three groups at rest (P > 0.05), whereas the increase in flow with exercise was reduced by 35 and 43 % with COX‐2 specific blockade (3.2 ± 0.7 to 6.1 ± 1.5 ml (100 g tissue)−1 min−1 or COX unspecific blockade (3.0 ± 0.8 to 7.6 ± 1.6), respectively, compared to C (2.7 ± 0.8 to 10.2 ± 2.0)(P < 0.05). The findings indicate that COX‐2 specific mechanisms are responsible for the exercise‐induced increase in prostaglandin synthesis, and that increase in tissue prostaglandin plays an important role for blood flow in peritendinous connective tissue during physical loading in vivo.
Extracellular Signal‐Regulated Kinases and Contractile Responses in Ovine Adult and Fetal Cerebral Arteries
Authors: Zhao Yu , Long Wen , Zhang Lubo , Longo Lawrence D.
Published: August 2003

Accumulating evidence suggests that extracellular signal‐regulated kinases (ERK1/2) play a key role in regulating vascular tone. To test the hypotheses that ERK1/2 modulate cerebral artery agonist‐induced contraction, and that this changes with developmental age, we measured both total and phosphorylated ERK1/2 in adult and fetal ovine cerebral arteries. In middle cerebral arteries (MCA) we also examined tension and [Ca2+]i responses to phenylephrine (PHE), in the absence and presence of the ERK1/2 inhibitor U‐0126 and the mitogen‐activated protein kinase kinase (MAPKK or MEK) inhibitor PD‐98059. In the fetus, but not adult, U‐0126 potentiated PHE‐induced contraction. In both age groups, inhibition by U‐0126, but not PD‐98059, decreased the PHE‐induced [Ca2+]i increase; in fact for adult, this eliminated any significant [Ca2+]i increase. In turn in the adult, but not fetus, protein kinase C (PKC) inhibition by staurosporine (3 × 10−8 M) prior to ERK1/2 inhibition by U‐0126 (10−5 M) prevented this elimination of [Ca2+]i increase. In adult and fetal cerebral arteries basal total ERK1/2 levels were similar. However, in fetal arteries the basal phosphorylated ERK1/2 levels were significantly less than in adult. In fetal, but not adult, cerebral arteries, 10−6‐10−4m PHE increased ERK1/2 phosphorylation in a concentration‐ and time‐dependent manner. The ERK1/2 inhibitor U‐0126, but not the MEK inhibitor PD‐98059, lowered basal activated ERK1/2 levels in vessels of both age groups. These results suggest that basal levels of phosphorylated ERK1/2 play an important role in suppressing Ca2+ sensitivity, perhaps by PKC inhibition. The developmental increase in cerebral artery basal phosphorylated ERK levels from fetus to adult, suggests a transition in the regulation of contraction from Ca2+ sensitivity in the fetal arteries to Ca2+ concentration in the adult vessels.
Nociception attenuates parasympathetic but not sympathetic baroreflex via NK1 receptors in the rat nucleus tractus solitarii
Authors: Pickering Anthony E. , Boscan Pedro , Paton Julian F. R.
Published: August 2003

Somatic noxious stimulation can evoke profound cardiovascular responses by altering activity in the autonomic nervous system. This noxious stimulation attenuates the cardiac vagal baroreflex, a key cardiovascular homeostatic reflex. This attenuation is mediated via NK1 receptors expressed on GABAergic interneurones within the nucleus of the solitary tract (NTS). We have investigated the effect of noxious stimulation and exogenous substance P (SP) on the sympathetic component of the baroreflex. We recorded from the sympathetic chain in a decerebrate, artificially perfused rat preparation. Noxious hindlimb pinch was without effect on the sympathetic baroreflex although the cardiac vagal baroreflex gain was decreased (56 %, P < 0.01). Bilateral NTS microinjection of SP (500 fmol) produced a similar selective attenuation of the cardiac vagal baroreflex gain (62 %, P < 0.005) without effect on the sympathetic baroreflex. Recordings from the cardiac sympathetic and vagal nerves confirmed the selectivity of the SP inhibition. Control experiments using a GABAA receptor agonist, isoguvacine, indicated that both components of the baroreflex (parasympathetic and sympathetic) could be blocked from the NTS injection site. The NTS microinjection of a NK1 antagonist (CP‐99,994) in vivo attenuated the tachycardic response to hindlimb pinch. Our data suggest that noxious pinch releases SP within the NTS to selectively attenuate the cardiac vagal, but not the sympathetic, component of the baroreflex. This selective withdrawal of the cardiac vagal baroreflex seems to underlie the pinch‐evoked tachycardia seen in vivo. Further, these findings confirm that baroreflex sympathetic and parasympathetic pathways diverge, and can be independently controlled, within the NTS.
Mg2+ dependence of halothane‐induced Ca2+ release from the sarcoplasmic reticulum in rat skeletal muscle
Authors: Duke Adrian M. , Hopkins Philip M. , Steele Derek S.
Published: August 2003

The effect of cytosolic Mg2+ on halothane‐induced Ca2+ release from the sarcoplasmic reticulum (SR) was investigated in mechanically skinned fibres from the rat extensor digitorum longus (EDL) muscle. Preparations were perfused with solutions mimicking the intracellular milieu and changes in [Ca2+] were detected using Fura‐2 fluorescence. In the presence of 1 mm Mg2+, brief (500 ms) applications of 40 mm halothane failed to induce Ca2+ release from the SR. However, Ca2+ release became detectable when [Mg2+] was reduced to 0.4 mm, and the amplitude of the response increased progressively as [Mg2+] was further reduced to 0.2 and 0.1 mm. Lower halothane concentrations within the range found during anaesthesia or induction (0.1–1.2 mm) failed to induce SR Ca2+ release at 0.2 or 0.4 mm Mg2+. However, in further experiments, preparations were exposed to 1 mm halothane for 2‐3 min under conditions where the volume of solution surrounding the preparation was restricted by stopping the flow. In the absence of perfusion, 1 mm halothane induced Ca2+ release from the SR at 0.4 mm Mg2+ in two out of six preparations, and release was observed consistently at 0.2 and 0.1 mm Mg2+. Responses to 1 mm halothane induced in the presence of 0.4 and 0.2 mm Mg2+ were typically delayed in onset and involved a localised release of Ca2+ that propagated along the fibre. These results suggest that halothane‐induced Ca2+ release is strongly inhibited at normal physiological levels of Mg2+. However, when Mg2+‐induced inhibition of the ryanodine receptor (RYR) is reduced, levels of halothane within the range found during anaesthesia can induce a marked efflux of Ca2+ from the SR. This may be of relevance to the condition of malignant hyperthermia, where the inhibition of RYRs by Mg2+ is reportedly reduced.
Baroreflex‐induced sympathetic activation does not alter cerebrovascular CO2 responsiveness in humans
Authors: LeMarbre Gabrielle , Stauber Shannon , Khayat Rami N. , Puleo Dominic S. , Skatrud James B. , Morgan Barbara J.
Published: August 2003

We investigated the effect of baroreflex‐induced sympathetic activation, produced by lower body negative pressure (LBNP) at −40 mmHg, on cerebrovascular responsiveness to hyper‐ and hypocapnia in healthy humans. Transcranial Doppler ultrasound was used to measure blood flow velocity (CFV) in the middle cerebral artery during variations in end‐tidal carbon dioxide pressure (PET,CO2) of +10, +5, 0, −5, and −10 mmHg relative to eupnoea. The slopes of the linear relationships between PET,CO2 and CFV were computed separately for hyper‐ and hypocapnia during the LBNP and no‐LBNP conditions. LBNP decreased pulse pressure, but did not change mean arterial pressure. LBNP evoked an increase in ventilation that resulted in a 9 ± 2 mmHg decrease in PET,CO2, which was corrected by CO2 supplementation of the inspired air. LBNP did not affect cerebrovascular CO2 response slopes during steady‐state hypercapnia (3.14 ± 0.24 vs. 2.96 ± 0.26 cm s−1 mmHg−1) or hypocapnia (1.31 ± 0.18 vs. 1.32 ± 0.19 cm s−1 mmHg−1), or the CFV responses to voluntary apnoea (+51 ± 19 vs.+50 ± 18 %). Thus, cerebrovascular CO2 responsiveness was not altered by baroreflex‐induced sympathetic activation. Our data challenge the concept that sympathetic activation restrains cerebrovascular responses to alterations in CO2 pressure.
A Short Latency Vestibulomasseteric Reflex Evoked by Electrical Stimulation Over the Mastoid in Healthy Humans
Authors: Deriu Franca , Tolu Eusebio , Rothwell C.
Published: September 2003

We describe EMG responses recorded in active masseter muscles following unilateral and bilateral electrical vestibular stimulation (EVS, current pulses of 5 mA intensity, 2 ms duration, 3 Hz frequency). Averaged responses in unrectified masseter EMG induced by unilateral EVS were examined in 16 healthy subjects; effects induced by bilateral (transmastoid) stimulation were studied in 10 subjects. Results showed that unilateral as well as bilateral EVS induces bilaterally a clear biphasic response (onset latency ranging from 7.2 to 8.8 ms), that is of equal amplitude and latency contra‐ and ipsilateral to the stimulation site. In all subjects, unilateral cathodal stimulation induced a positive—negative response termed p11/n15 according to its mean peak latency; the anodal stimulation induced a response of opposite polarity (n11/p15) in 11/16 subjects. Cathodal responses were significantly larger than anodal responses. Bilateral stimulation induced a p11/n15 response significantly larger than that induced by the unilateral cathodal stimulation. Recordings from single motor units showed that responses to cathodal stimulation corresponded to a brief (2–4 ms) silent period in motor unit discharge rate. The magnitude of EVS‐induced masseter response was linearly related to current intensity and scaled with the mean level of EMG activity. The size of the p11/n15 response was asymmetrically modulated when subjects were tilted on both sides; in contrast head rotation did not exert any influence. Control experiments excluded a possible role of cutaneous receptors in generating the masseter response. We conclude that transmastoid electrical stimulation evokes vestibulomasseteric reflexes in healthy humans at latencies consistent with a di‐trisynaptic pathway.
Convergent control of synaptic GABA release from rat dorsal horn neurones by adenosine and GABA autoreceptors
Authors: Hugel Sylvain , Schlichter Rémy
Published: August 2003

Perforated patch clamp recordings were performed on cultured superficial neonatal rat dorsal horn (DH) spinal cord neurones in order to study the presynaptic modulation of GABA release at unitary synaptic connections. Since ATP can be coreleased with GABA at about two‐thirds of GABAergic synapses between DH neurones, and can be rapidly metabolized to adenosine in the extracellular space, we investigated the potential role of A1 adenosine receptors and GABAB receptors which might function as inhibitory autoreceptors. Adenosine and GABAB receptor agonists reduced the amplitude of electrically evoked GABAergic inhibitory postsynaptic currents (eIPSCs) as well as the frequency of GABAergic miniature IPSCs, suggesting a presynaptic action of these substances. The actions of adenosine were blocked by the A1 receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX). The effects of adenosine and GABAB agonists were occlusive, indicating a functional convergence of the signalling pathways engaged by A1 and GABAB receptors. A1 and GABAB antagonists increased the amplitude of eIPSCs in a supra‐additive manner, suggesting a tonic activation of these receptors by ambient adenosine and GABA. Moreover, using trains of electrical stimulations, we were able to unravel a phasic (activity‐dependent) activation of presynaptic A1 and GABAB autoreceptors only in the case of neurones coreleasing ATP and GABA, despite the presence of functional presynaptic A1 and GABAB receptors on all GABAergic DH neurones. This selective, convergent and activity‐dependent inhibition of GABA release by A1 and GABAB autoreceptors might modulate the integrative properties of postsynaptic DH neurones under physiological conditions and/or during the development of pathological pain states.
Cardiac vanilloid receptor 1‐expressing afferent nerves and their role in the cardiogenic sympathetic reflex in rats
Authors: Zahner Matthew R. , Li De‐Pei , Chen Shao‐Rui , Pan Hui‐Lin
Published: August 2003

Myocardial ischaemia causes the release of metabolites such as bradykinin, which stimulates cardiac sensory receptors to evoke a sympathoexcitatory reflex. However, the molecular identity of the afferent neurons and fibres mediating this reflex response is not clear. In this study, we tested the hypothesis that the cardiogenic sympathoexcitatory reflex is mediated by capsaicin‐sensitive afferent fibres. Enhanced immunofluorescence labelling revealed that vanilloid receptor 1 (VR1)‐containing afferent nerve fibres were present on the epicardial surface of the rat heart. Resiniferatoxin (RTX), a potent analogue of capsaicin, was used to deplete capsaicin‐sensitive afferent fibres in rats. Depletion of these fibres was confirmed by a substantial reduction of VR1 immunoreactivity in the epicardium and dorsal root ganglia. The thermal sensitivity was also diminished in RTX‐treated rats. Renal sympathetic nerve activity (RSNA) and blood pressure were recorded in anaesthetized rats during epicardial application of bradykinin or capsaicin. In vehicle‐treated rats, epicardial bradykinin (10 μg ml−1) or capsaicin (10 μg ml−1) application produced a significant increase in RSNA and arterial blood pressure. The RSNA and blood pressure responses caused by bradykinin and capsaicin were completely abolished in RTX‐treated rats. Furthermore, epicardial application of iodo‐RTX, a highly specific antagonist of VR1 receptors, blocked capsaicin‐ but not bradykinin‐induced sympathoexcitatory responses. Thus, these data provide important histological and functional evidence that the heart is innervated by VR1‐expressing afferent nerves and these afferent nerves are essential for the cardiogenic sympathoexcitatory reflex during myocardial ischaemia.
GABA Mediates Autoreceptor Feedback Inhibition in the Rat Carotid Body Via Presynaptic GABAB Receptors and TASK‐1
Authors: Fearon Ian M. , Zhang Min , Vollmer Cathy , Nurse Colin A.
Published: September 2003

Background K+ channels exert control over neuronal excitability by regulating resting potential and input resistance. Here, we show that GABAB receptor‐mediated activation of a background K+ conductance modulates transmission at rat carotid body chemosensory synapses in vitro. Carotid body chemoreceptor (type I) cells expressed GABAB(1) and GABAB(2) subunits as well as endogenous GABA. The GABAB receptor agonist baclofen activated an anandamide‐ and Ba2+‐sensitive TASK‐1‐like background K+ conductance in chemoreceptor cell clusters, but was without effect on voltage‐gated Ca2+ channels. Hydroxysaclofen (50 μm), 5‐aminovaleric acid (100 μm) and CGP 55845 (100 nm), selective GABAB receptor blockers, potentiated the hypoxia‐induced receptor potential; this effect was abolished by pre‐treatment with pertussis toxin (PTX; 500 ng ml‐1), an inhibitor of Gi, or by H‐89 (50 μm), a selective inhibitor of protein kinase A. The protein kinase C inhibitor chelerythrine chloride (100 μm) was without effect on this potentiation. GABAB receptor blockers also caused depolarisation of type I cells in clusters, and enhanced spike discharge in spontaneously firing cells. In functional co‐cultures of type I clusters and petrosal sensory neurones, GABAB receptor blockers potentiated hypoxia‐induced postsynaptic chemosensory responses mediated by the fast‐acting transmitters ACh and ATP. Thus GABAB receptor‐mediated activation of TASK‐1 or a related channel provides a presynaptic autoregulatory feedback mechanism that modulates fast synaptic transmission in the rat carotid body.
Focal adhesion kinase mediates porcine venular hyperpermeability elicited by vascular endothelial growth factor
Authors: Wu Mack H. , Guo Mingzhang , Yuan Sarah Y. , Granger Harris J.
Published: September 2003

Focal adhesion kinase (FAK) is known to mediate endothelial cell adhesion and migration in response to vascular endothelial growth factor (VEGF). The aim of this study was to explore a potential role for FAK in VEGF regulation of microvascular endothelial barrier function. The apparent permeability coefficient of albumin (Pa) was measured in intact isolated porcine coronary venules. Treating the vessels with VEGF induced a time‐ and concentration‐dependent increase in Pa. Inhibition of FAK through direct delivery of FAK‐related non‐kinase (FRNK) into venular endothelium did not alter basal barrier function but significantly attenuated VEGF‐elicited hyperpermeability. Furthermore, cultured human umbilical vein endothelial monolayers displayed a similar hyperpermeability response to VEGF which was greatly attenuated by FRNK. Western blot analysis showed that VEGF promoted FAK phosphorylation in a time course correlating with that of venular hyperpermeability. The phosphorylation response was blocked by FRNK treatment. In addition, VEGF stimulation caused a significant morphological change of FAK from a punctate pattern to an elongated, dash‐like staining that aligned with the longitudinal axis of the cells. Taken together, the results suggest that FAK contributes to VEGF‐elicited vascular hyperpermeability. Phosphorylation of FAK may play an important role in the signal transduction of vascular barrier response to VEGF.
Compensatory Increase of the Cervico‐Ocular Reflex with Age in Healthy Humans
Authors: Kelders W. P. A. , Kleinrensink G. J. , van der Geest J. N. , Feenstra L. , de Zeeuw C. I. , Frens M. A.
Published: September 2003

The cervico‐ocular reflex (COR) is an ocular stabilization reflex that is elicited by rotation of the neck. It works in conjunction with the vestibulo‐ocular reflex (VOR) and the optokinetic reflex (OKR) in order to prevent visual slip over the retina due to self‐motion. The gains of the VOR and OKR are known to decrease with age. We have investigated whether the COR, a reflexive eye movement elicited by rotation of the neck, shows a compensatory increase and whether a synergy exists between the COR and the other ocular stabilization reflexes. In the present study 35 healthy subjects of varying age (20–86 years) were rotated in the dark in a trunk‐to‐head manner (the head fixed in spaced with the body passively rotated under it) at peak velocities between 2.1 and 12.6 deg s−1 as a COR stimulus. Another 15 were subjected to COR, VOR and OKR stimuli at frequencies between 0.04 and 0.1 Hz. Three subjects participated in both tests. The position of the eyes was recorded with an infrared recording technique. We found that the COR‐gain increases with increasing age and that there is a significant covariation between the gains of the VOR and COR, meaning that when VOR increases, COR decreases and vice versa. A nearly constant phase lag between the COR and the VOR of about 25 deg existed at all stimulus frequencies.
Renin: origin, secretion and synthesis
Authors: Persson Pontus B.
Published: September 2003

Renin is a central hormone in the control of blood pressure and various other physiological functions. In spite of the very early discovery of renin over 100 years ago, we have only recently gained a deeper understanding of the origin of renin‐producing cells and of the mechanisms responsible for renin synthesis and secretion. The main source of renin is the juxtaglomerular cells (JGCs), which release renin from storage granules. Besides the renin‐angiotensin system (RAS) in the JGCs, there exist local RASs in various tissues. JGCs originate in situ within the metanephric kidney from mesenchymal cells that are not related to smooth muscle lineages, as hitherto assumed. The previous notion that JGCs stem from vascular smooth muscle cells may be explained by JGC differentiation: they acquire smooth muscle markers that are maintained throughout adulthood. It has become clear that increasing intracellular free [Ca2+] inhibits renin secretion in JGCs. In contrast, cAMP stimulates renin release. Over the last decade, numerous studies on isolated JGCs and intact animals have provided contradictory results as to whether cGMP has a stimulatory or inhibitory action on renin release. More recent results strongly suggest that the effects of cGMP on renin release from JGCs involve the degradation of cAMP, which is modulated by cGMP. Finally, it has been found that not only is the production of renin modulated by enhancing or attenuating renin transcription, but renin mRNA stability is controlled by various proteins present in renin‐producing cells.
Pharmacological Modulation of Cortical Excitability Shifts Induced by Transcranial Direct Current Stimulation in Humans
Authors: Nitsche M. A. , Fricke K. , Henschke U. , Schlitterlau A. , Liebetanz D. , Lang N. , Henning S. , Tergau F. , Paulus W.
Published: September 2003

Transcranial direct current stimulation (tDCS) of the human motor cortex results in polarity‐specific shifts of cortical excitability during and after stimulation. Anodal tDCS enhances and cathodal stimulation reduces excitability. Animal experiments have demonstrated that the effect of anodal tDCS is caused by neuronal depolarisation, while cathodal tDCS hyperpolarises cortical neurones. However, not much is known about the ion channels and receptors involved in these effects. Thus, the impact of the sodium channel blocker carbamazepine, the calcium channel blocker flunarizine and the NMDA receptor antagonist dextromethorphane on tDCS‐elicited motor cortical excitability changes of healthy human subjects were tested. tDCS‐protocols inducing excitability alterations (1) only during tDCS and (2) eliciting long‐lasting after‐effects were applied after drug administration. Carbamazepine selectively eliminated the excitability enhancement induced by anodal stimulation during and after tDCS. Flunarizine resulted in similar changes. Antagonising NMDA receptors did not alter current‐generated excitability changes during a short stimulation, which elicits no after‐effects, but prevented the induction of long‐lasting after‐effects independent of their direction. These results suggest that, like in other animals, cortical excitability shifts induced during tDCS in humans also depend on membrane polarisation, thus modulating the conductance of sodium and calcium channels. Moreover, they suggest that the after‐effects may be NMDA receptor dependent. Since NMDA receptors are involved in neuroplastic changes, the results suggest a possible application of tDCS in the modulation or induction of these processes in a clinical setting. The selective elimination of tDCS‐driven excitability enhancements by carbamazepine proposes a role for this drug in focussing the effects of cathodal tDCS, which may have important future clinical applications.
Blunted Sympathetic Vasoconstriction in Contracting Skeletal Muscle of Healthy Humans: is Nitric Oxide Obligatory?
Authors: Dinenno Frank A. , Joyner Michael J.
Published: September 2003

We tested the hypothesis that nitric oxide (NO) is responsible for blunting sympathetic α‐adrenergic vasoconstriction in the active muscles of humans (functional sympatholysis). We measured forearm blood flow (Doppler ultrasound) and calculated the reductions in forearm vascular conductance (FVC) in response to α‐adrenergic receptor stimulation during rhythmic handgrip exercise and during a control non‐exercise vasodilator condition (intra‐arterial adenosine), before and after local NO synthase (NOS) inhibition in healthy men. The forearm vasoconstrictor responses to endogenous noradrenaline release (intra‐arterial tyramine) were significantly blunted during moderate exercise compared with adenosine, and these vasoconstrictor responses were not restored by NOS inhibition withNG‐monomethyl‐l‐arginine (l‐NMMA;n= 6) orNG‐nitro‐l‐arginine methyl ester (l‐NAME;n= 8). Similarly,l‐NAME did not restore the vasoconstrictor responses to tyramine in contracting muscle during heavy rhythmic handgrip exercise (n= 4). In four additional subjects, we also found that the vasoconstrictor responses evoked by tyramine during exercise or adenosine were repeatable in the absence of NOS inhibition (i.e. time control). Finally, in five subjects the forearm vasoconstrictor responses to direct α1‐adrenergic (phenylephrine) and α2‐adrenergic (clonidine) receptor stimulation were blunted during moderate exercise compared with adenosine; these responses were also unaffected byl‐NAME. Taken together, our results demonstrate that NO is not obligatory for functional sympatholysis in contracting skeletal muscles of healthy men.
Capsaicin‐sensitive neurogenic sensory vasodilatation in the dura mater of the rat
Authors: Dux Mária , Sántha Péter , Jancsó Gábor
Published: September 2003

The neurogenic sensory vascular responses of the dura mater encephali are considered to contribute significantly to the mechanisms of meningeal nociception and headache. Although the fundamental role of capsaicin‐sensitive afferent nerves in the development of the neurogenic inflammatory responses of a variety of tissues is well established, their participation in meningeal vascular reactions is unclear. In the present study, the effects of the topical application of capsaicin on the dural blood flow and on the morphology of the dural nerve fibres were examined in control and capsaicin‐pretreated rats by means of laser Doppler flowmetry and electron microscopy, respectively. In the control rats, the dural application of capsaicin at concentrations of 50 and 100 nm induced significant increases in blood flow in the branches of the medial meningeal artery. This capsaicin‐induced vasodilatation was abolished by capsazepine, a transient receptor potential vanilloid 1 (TRPV1) receptor antagonist, and by hCGRP8–37, a calcitonin gene‐related peptide (CGRP) receptor antagonist. Administration of capsaicin at higher concentrations (1 and 10 μm) resulted in marked, dose‐dependent decreases in dural blood flow. The capsaicin‐induced vasodilatation was abolished, whereas vasoconstriction was augmented, by systemic pretreatment of the animals with capsaicin. Electron microscopy revealed degenerating unmyelinated axons in the dura mater after an acute exposure to capsaicin (10 μm), providing support for the existence and possible functional role of capsaicin‐sensitive dural afferent nerves. The results indicate that capsaicin‐induced vasodilatation in the rat dura mater is mediated by the release of CGRP from the sensory nerves, whereas the vasoconstrictor response may be attributed to a direct action of capsaicin on the vascular smooth muscle. The present study demonstrates for the first time that capsaicin‐sensitive nociceptive afferent nerves contribute significantly to the dural vasodilatory responses and suggests an important role in meningeal nociception.
Myocardial Infarction Causes Increased Expression But Decreased Activity of the Myocardial Na+—Ca2+ Exchanger in the Rabbit
Authors: Quinn F. R. , Currie S. , Duncan A. M. , Miller S. , Sayeed R. , Cobbe S. M. , Smith G. L.
Published: September 2003

Na+—Ca2+ exchanger (NCX) protein levels and activity were measured in myocardium from the basal region of the left ventricle of rabbit hearts with significant left ventricular dysfunction (LVD), 8‐9 weeks after an apical infarction. NCX protein abundance was higher in the tissue homogenates (121 ± 11 %) and purified membrane fractions (143 ± 12 %) in the LVD compared to the sham‐operated (sham) group. NCX mRNA was also higher in the LVD group (126 %). Lower NCX protein expression was observed in the membrane fractions from the epicardium compared to the endocardium in both the sham and LVD groups. Transmembrane currents were recorded in isolated cardiomyocytes by single‐electrode voltage clamp; [Ca2+]i was measured using Fura‐2. Rapid application of 10 mmol l−1 caffeine was used to induce Ca2+ release from the sarcoplasmic reticulum. The subsequent NCX‐mediated Ca2+ efflux rate constant was lower (70 % of sham) in the LVD group. NCX currents were measured in cardiomyocytes dialysed with 250 nm Ca2+ (50 mmol l−1 EGTA). A lower NCX current (75 % of sham) was observed in the LVD group. Lower NCX activity was also observed in cardiomyocytes isolated from the epicardium compared to the endocardium; a transmural difference that was also seen in the LVD group. Reduced activity despite increased protein expression may result from reduced Ca2+ sensitivity of the allosteric regulation of NCX. However, measurements indicated increased Ca2+ sensitivity in the LVD group. Cardiomyocytes from LVD hearts displayed a marked reduction in the transverse tubule area (59 % of sham) and the surface area/volume ratio (80 % of sham). Disrupted transverse tubule structure may contribute to the decrease in NCX activity despite increased protein expression in LVD.
The effect of light on outer segment calcium in salamander rods
Authors: Matthews Hugh R. , Fain Gordon L.
Published: September 2003

Calcium acts as a second messenger in vertebrate rods, regulating the recovery phase of the light response and modulating sensitivity during light‐adaptation. Since light not only decreases the outer segment calcium concentration ([Ca2+]i) by closing cyclic nucleotide‐gated channels but can also increase [Ca2+]i by releasing Ca2+ from buffer sites or intracellular stores, we examined in detail the effect of light and circulating current on [Ca2+]i by making simultaneous measurements of suction pipette current and [Ca2+]i from isolated rods of the salamander Ambystoma tigrinum after incorporation of the fluorescent dye fluo‐5F. When the release of Ca2+ is measured in 0 Ca2+−0 Na+ solution, minimising fluxes of Ca2+ across the plasma membrane, it is substantial only for light bright enough to bleach a significant fraction of the photopigment and is restricted to the part of the outer segment in which the bleach occurred. It is unlikely, therefore, to make a large contribution to [Ca2+]i for most of the physiological operating range of the rod. Nevertheless, since release is half‐maximal for a bleach of less than 10 %, it cannot be produced by a simple mechanism such as a change in the affinity of a binding site on rhodopsin itself but must instead require some more complex interaction. In Ringer solution, the Ca2+ in the light‐releasable pool can be discharged merely by the decrease in [Ca2+]i that occurs as the outer segment channels close. In steady background light or after exposure to saturating illumination, the fraction of Ca2+ in the pool decreases essentially in proportion to [Ca2+]i as if Ca2+ were being removed from a buffer site within the cytoplasm. Furthermore, [Ca2+]i itself changes in proportion to the circulating current, with little evidence for a contribution from Ca2+ release or other mechanisms of Ca2+ homeostasis. This indicates that flux of Ca2+ across the plasma membrane is the major determinant of outer segment Ca2+ concentration within the rod's normal operating light intensity range. Once Ca2+ has been discharged from the releasable pool, it is restored following dim illumination apparently as the simple result of the subsequent restoration of dark [Ca2+]i and the rebinding of Ca2+ to its release site, but after brighter light perhaps also as a consequence of regeneration of the photopigment.
Syntaxin 1A Co‐Associates with Native Rat Brain and Cloned Large Conductance, Calcium‐Activated Potassium Channels in situ
Authors: Ling Shizhang , Sheng Jian‐Zhong , Braun Janice E. A. , Braun Andrew P.
Published: September 2003

Large conductance, calcium‐activated potassium channels (BKCa channels) are regulated by several distinct mechanisms, including phosphorylation/dephosphorylation events and protein‐protein interactions. In this study, we have examined the interaction between BKCa channels and syntaxin 1A, a soluble N‐ethylmaleimide‐sensitive factor attachment protein receptor (SNARE) that is reported to modulate the activity and/or localization of different classes of ion channels. Using a reciprocal co‐immunoprecipitation strategy, we observed that native BKCa channels in rat hippocampus co‐associate with syntaxin 1A, but not the closely related homologue syntaxin 3. This BKCa channel‐syntaxin 1A interaction could be further demonstrated in a non‐neuronal cell line (human embryonic kidney (HEK) 293 cells) following co‐expression of rat syntaxin 1A and BKCa channels cloned from either mouse brain or bovine aorta. However, co‐expression of these same channels with syntaxin 3 did not lead to a detectable protein‐protein interaction. Immunofluorescent co‐staining of HEK 293 cells expressing BKCa channels and syntaxin 1A demonstrated overlapping distribution of these two proteins in situ. Functionally, co‐expression of BKCa channels with syntaxin 1A, but not syntaxin 3, was observed to enhance channel gating and kinetics at low concentrations (1–4 μm) of free cytosolic calcium, but not at higher concentrations (≤ 10 μm), as judged by macroscopic current recordings in excised membrane patches. Interactions between BKCa channels and neighbouring membrane proteins may thus play important roles in regulating the activity and/or distribution of these channels within specialized cellular compartments.
ATP modulates intracellular Ca2+ and firing rate through a P2Y1 purinoceptor in cane toad pacemaker cells
Authors: Ju Yue‐kun , Huang Wenbing , Jiang Lele , Barden Julian A. , Allen David G.
Published: September 2003

The effect of extracellular ATP (10–100 μm) on intracellular Ca2+ concentration ([Ca2+]i) and firing rate has been studied in single pacemaker cells isolated from the sinus venosus of cane toads. In spontaneously firing cells, ATP initially increased peak [Ca2+]i by 43 ± 5 %, increased diastolic [Ca2+]i by 20 + 3 % and increased the firing rate by 58 ± 8 %. These early effects were followed by a late phase in which both the peak [Ca2+]i and the firing rate declined. Adenosine, and UTP (respectively, P1‐ and P2Y2,4,6‐selective agonists) caused no significant change in [Ca2+]i or firing rate, while αβ‐methylene ATP (a P2X1,3 agonist) caused a small increase in firing rate but no changes in [Ca2+]i. In contrast the P2Y1‐selective agonist 2‐MesADP (1 μm) mimicked the biphasic effects of ATP and these effects were inhibited by the purinoceptor antagonists suramin and PPADS and by the P2Y1‐selective antagonist MRS 2179. Immunohistochemistry established that P2Y1 purinoceptors were present on the cell surface. Western blotting analysis demonstrated that the P2Y1 antibody recognised a 57 kDa protein. After sarcoplasmic reticulum Ca2+ release was prevented with caffeine or ryanodine, ATP no longer had any effect on [Ca2+]i or firing rate. Furthermore, the SR Ca2+ store content was decreased during the late phase of 2‐MesADP application. The effect of ATP was coupled to phospholipase C (PLC) activity because the PLC inhibitor U‐73122 eliminated the effects of ATP. Our study shows that in toad pacemaker cells, the biphasic effects of ATP on pacemaker activity are mainly through P2Y1 purinoceptors, which are able to modulate Ca2+ release from the SR Ca2+ store.
Maximum Amplification of Blade Response due to Mistuning: Localization and Mode Shape Aspects of the Worst Disks
Authors: Rivas-Guerra Alejandro J. , Mignolet Marc P.
Published: August 2003

This paper focuses on the determination and study of the maximum amplification of the steady state forced response of bladed disks due to mistuning. First, an optimization strategy is proposed in which partially mistuned bladed disks are considered as physical approximations of the worst case disk and the mistuned properties are sought to maximize the response of a specific blade. This approach is exemplified on both a reduced order model of a blisk and a single-degree-of-freedom per blade disk model an extensive parametric study of which is conducted with respect to blade-to-blade coupling, damping, and engine order. A mode shape-based formulation of the amplification factor is then developed to clarify the findings of the parametric study in the strong coupling/small damping limit. In this process, the upper bound of Whitehead is recovered for all engine orders and number of blades and the conditions under which this limit is exactly achieved or closely approached are clarified. This process also uncovers a simple yet reliable approximation of the resonant mode shapes and natural frequencies of the worst disk.
Gradient Elasticity Theory for Mode III Fracture in Functionally Graded Materials—Part I: Crack Perpendicular to the Material Gradation
Authors: Paulino G. H. , Fannjiang A. C. , Chan Y.-S.
Published: August 2003

Anisotropic strain gradient elasticity theory is applied to the solution of a mode III crack in a functionally graded material. The theory possesses two material characteristic lengths, l and l′, which describe the size scale effect resulting from the underlining microstructure, and are associated to volumetric and surface strain energy, respectively. The governing differential equation of the problem is derived assuming that the shear modulus is a function of the Cartesian coordinate y, i.e., G=Gy=G0eγy, where G0 and γ are material constants. The crack boundary value problem is solved by means of Fourier transforms and the hypersingular integrodifferential equation method. The integral equation is discretized using the collocation method and a Chebyshev polynomial expansion. Formulas for stress intensity factors, KIII, are derived, and numerical results of KIII for various combinations of l,l′, and γ are provided. Finally, conclusions are inferred and potential extensions of this work are discussed.
An Improved Streamline Curvature Approach for Off-Design Analysis of Transonic Axial Compression Systems
Authors: Boyer Keith M. , O’Brien Walter F.
Published: August 2003

A streamline curvature throughflow numerical approach is assessed and modified to better approximate the flow fields of transonic axial compression systems. Improvements in total pressure loss modeling are implemented, central to which is a physics-based shock model, to ensure accurate and reliable off-design performance prediction. The new model accounts for shock geometry changes, with shock loss estimated as a function of inlet relative Mach number, blade section loading (flow turning), solidity, leading edge radius, and suction surface profile. Data from a single-stage, isolated rotor provide the basis for experimental comparisons. Improved performance prediction is shown. The importance of properly accounting for shock geometry and loss changes with operating conditions is demonstrated.