bluuebunny/crossref_metadata_2025 huggingface dataset:
Mediation by 5‐hydroxytryptamine of the femoral vasoconstriction induced by acid challenge of the rat gastric mucosa
Authors: Wachter Christof H. , Heinemann Ákos , Donnerer Josef , Pabst Maria A. , Holzer Peter
Published: September 2004

Gastric mucosal barrier disruption in the presence of luminal acid causes femoral vasoconstriction via a pathway that appears to be stimulated by messengers generated in the injured gastric mucosa. This study was undertaken to analyse the gastric factors that are responsible for the femoral vasoconstrictor response.

Gastric mucosal barrier disruption in the presence of luminal acid was induced by perfusing the stomach of urethane‐anaesthetized rats with ethanol (15 %) in 0.01‐0.15 M HCl. Blood flow in the left gastric and right femoral artery was estimated by the ultrasonic transit time shift technique.

Gastric perfusion of ethanol in HCl caused loss of H+ ions from the gastric lumen, decreased the HCO3− concentration in hepatic portal vein blood, induced macroscopic histological damage to the gastric mucosa, dilated the left gastric artery and constricted the femoral artery. These responses were related to the HCl concentration in the ethanol‐containing perfusion medium.

The femoral vasoconstriction was also seen when, instead of ethanol, taurocholate (20 mM) was used to disrupt the gastric mucosal barrier in the presence of 0.15 M HCl.

The femoral vasoconstriction evoked by gastric perfusion of ethanol in HCl was left unaltered by pharmacological blockade of gastrin and histamine receptors. In contrast, the 5‐hydroxytryptamine 5‐HT1/2 receptor antagonist methiothepin, but not the 5‐HT2A receptor antagonist ketanserin or the 5‐HT3 receptor antagonist granisetron, inhibited the ability of both 5‐hydroxytryptamine and gastric acid back‐diffusion to constrict the femoral artery.

Gastric acid back‐diffusion caused release of 5‐hydroxytryptamine into the gastric lumen, which was related to the HCl concentration in the ethanol‐containing perfusion medium.

These data show that femoral vasoconstriction evoked by gastric mucosal barrier disruption depends on back‐diffusion of acid into the mucosa. The acid‐induced damage results in release of 5‐hydroxytryptamine from the gastric mucosa, and the pathway leading to constriction of the femoral artery involves 5‐hydroxytryptamine acting via 5‐HT1/2 receptors as a messenger molecule.
Absence of early resetting of coronary baroreceptors in anaesthetized dogs
Authors: McMahon Nicholas C. , Drinkhill Mark J. , Hainsworth Roger
Published: September 2004

Both carotid and aortic arch baroreceptors have been shown to reset after as little as 20 min exposure to a different conditioning pressure; the mid‐point of the stimulus‐response curve is displaced towards the conditioning pressure.

Coronary baroreceptors operate over much lower pressures and induce slower reflex vasoconstriction than the other baroreceptors and this investigation was designed to determine whether their resetting characteristics are also different.

In chloralose anaesthetized dogs, a perfusion circuit allowed independent control of pressures distending carotid, aortic and coronary baroreceptors. Stimulus‐response curves were obtained for carotid and coronary baroreceptors after maintaining the distending pressure at 60 or 180 mmHg for 20 min.

Neither the magnitude of the responses nor the baroreceptor pressure corresponding to 50 % of the response (BP50) of the coronary curves was changed by the conditioning regime. In contrast, conditioning carotid baroreceptors with the same regime produced significant shifts in the BP50 towards the conditioning pressure.

No changes were obtained after conditioning the coronary baroreceptors at 60 or 120 mmHg for 40 min.

These results confirm early resetting of carotid baroreceptors but show that coronary baroreceptors do not reset over a period of at least 40 min.
Premature bifurcation of the apical dendritic trunk of vibrissa‐responding pyramidal neurones of X‐irradiated rat neocortex
Authors: Ito Muneyuki , Kato Miyuki , Kawabata Masao
Published: September 2004

Electrophysiological and morphological experiments were performed on the pyramidal neurones of the somatosensory neocortex of the adult rat that had been exposed in utero to 200 rad of X‐irradiation. Under urethane anaesthesia, evoked gross potentials, extracellular and intracellular neuronal responses, and laminar field potentials were recorded. The evoked epicortical potential to deflection of a single whisker was a long‐lasting positive wave which contrasted with a biphasic positive‐negative complex in unirradiated controls. Neurones were initially tested during extracellular recording for responses to whisker deflections. This was followed by intracellular injection with horseradish peroxidase (HRP), and the HRP‐stained neuronal elements were visualized using diaminobenzidine as a chromagen.

Fifty neurones were recorded and stained through the soma. The mean response latency was 15.1 ms. Of these, thirty‐six showed premature bifurcation of the apical dendrite. The angle of bifurcation of the apical dendrite was measured in the coronal plane and was found to be a function of the depth at which the soma was located and the distance between the soma and bifurcation point. It was suggested that the apical dendrites of these neurones underwent premature bifurcation due to an imbalance between the growth of neurones and skull.

Fifteen neurones were recorded and stained through the presumed apical dendritic shaft. The mean response latency was 19.5 ms. The electrode track left in the histological specimen pointed to the stained apical dendrite. Dendritic elements distal to the entry point were preferentially filled with HRP. In no cases were somata stained. There was, in turn, no evidence of recording from dendritic elements distal to the bifurcation since no electrode track was found to point to these elements. That dendritic spike responses may not travel beyond the bifurcation was further substantiated by laminar analysis of field potentials.
Role of endogenous endothelin in the regulation of basal coronary tone in the rat
Authors: Goodwin Andrew T. , Amrani Mohamed , Gray Caroline C. , Jayakumar Jay , Yacoub Magdi H.
Published: September 2004

Coronary vascular tone is a vital factor that regulates the delivery of oxygen to cardiac muscle. We tested the hypothesis that basal coronary tone may depend on the release of an endogenous vasoconstrictor peptide, endothelin (ET).

Using an isolated, Krebs solution‐perfused rat heart we measured the changes in coronary flow following the administration over a 30 min period of the ET antagonists Ro61‐0612 (mixed ETA/ETB), PD155080 (ETA) and BQ788 (ETB).

In a second series of experiments, hearts were randomly assigned to perfusion with plain Krebs solution, or with Krebs solution to which L‐NAME and/or indomethacin had been added. The effect on coronary flow following the addition of Ro61‐0612 was then measured.

Perfusion with Ro61‐0612 (10−4 M) alone increased coronary flow by 57.8 %vs. control (P= 0.00001). PD155080 (10−4 M) increased coronary flow by 28.9 % (P= 0.009), whereas BQ788 had no effect on coronary flow.

In the second series of experiments, Ro61‐0612 increased coronary flow by 6.6 ± 0.8 ml min−1 in hearts perfused with plain Krebs solution, by 3.8 ± 0.8 ml min−1 in hearts to which both L‐NAME and indomethacin had been added, by 3.3 ± 0.7 ml min−1 in hearts to which L‐NAME had been added, and by 6.9 ± 0.5 ml min−1 in hearts to which indomethacin had been added to the Krebs buffer.

In hearts perfused with Krebs solution alone, nitric oxide (NO) release into the coronary sinus increased from 219.8 to 544.9 pmol min−1 g−1 following the addition of Ro61‐0612 (P= 0.06). There was no detectable release of NO from hearts perfused with L‐NAME alone or in combination with indomethacin either before or after the addition of Ro61‐0612.

We conclude that endogenous ET plays a role in coronary tone mediated via ETA receptors. This vasodilatation is partially due to an increase in endogenous NO release. However, a significant vasodilatation is still seen following the inhibition of NO synthesis. We propose that basal coronary tone depends on a balance between the endogenous release of vasodilators such as NO and vasoconstrictors such as ET.
Activation of α‐ and β‐adrenoceptors by sympathetic nerve stimulation in the large intestine of the rat
Authors: Luckensmeyer Greta B. , Keast Janet R.
Published: September 2004

The effects of sympathetic nerve stimulation on the motility of the circular and longitudinal muscle of the large intestine were investigated in vitro, and the involvement of various adrenoceptor subtypes determined. A comparison between the sympathetic supply arising from the prevertebral and pelvic ganglia was also made.

In the longitudinal muscle of the distal colon, sympathetic nerve stimulation caused responses which were contractile (0.1–2 Hz), biphasic (5–10 Hz) or purely inhibitory (20–30 Hz). All contractile responses were removed with phentolamine (3 μM), whereas the inhibitory responses were significantly diminished by propranolol (0.1 μM) and completely abolished by alprenolol (3 μM) or nadolol (300 μM).

In the longitudinal muscle of the proximal colon, the effects of sympathetic nerve stimulation were predominantly inhibitory. Some of this inhibition was removed by propranolol (0.1 μM), but was largely unaffected by alprenolol (3 μM). The remainder of the inhibitory response was probably non‐noradrenergic as it was not removed by a combination of phentolamine (3 μM) and alprenolol (3 μM).

In the circular muscle of both the proximal and distal colon, sympathetic stimulation caused a strong contractile response which was completely removed by phentolamine (3 μM) to reveal an inhibitory response. This inhibitory response was unchanged by propranolol (0.1 μM) but was removed by alprenolol (3 μM), following which a weak non‐noradrenergic contractile response was unmasked.

Stimulation of the hypogastric nerve to activate pelvic sympathetic pathways had no effect on the motility of the longitudinal muscle, but caused a contractile response in the circular muscle which was completely removed by phentolamine (3 μM).

We conclude that sympathetic nerves innervate adrenoceptors of different types in the various muscle layers and regions of the colon. They innervate a mixture of α‐, and β3‐adrenoceptors in the longitudinal muscle of the proximal colon, α‐, classical β‐ and β3‐adrenoceptors in the distal colon, and primarily α‐adrenoceptors with a few β3‐adrenoceptors in the circular muscle. In addition, the pelvic sympathetic innervation of the rectum differs from the prevertebral supply by innervating only excitatory α‐adrenoceptors.
Extrinsic neural control of nitric oxide synthase expression in the myenteric plexus of rat jejunum
Authors: Nakao Koji , Takahashi Toku , Utsunomiya Joji , Owyang Chung
Published: September 2004

The role of extrinsic innervation in the expression of nitric oxide synthase (NOS) in the myenteric plexus remains unknown. In this study, we investigated the effect of extrinsic denervation on NOS expression in rat jejunum.

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G‐nitro‐L‐arginine methyl ester (L‐NAME)‐sensitive non‐adrenergic, non‐cholinergic (NANC) relaxations induced by transmural nerve stimulation were significantly increased in muscle strips obtained from rats treated with splanchnic ganglionectomy or 6‐hydroxy‐dopamine (6‐OH‐dopamine). Truncal vagotomy or treatment of the coeliac ganglia with capsaicin did not significantly affect NANC relaxations.

The number of NOS‐immunopositive cells in the myenteric plexus was significantly increased in tissues obtained from rats treated with splanchnic ganglionectomy or 6‐OH‐dopamine.

Western blot analysis and Northern blot analysis showed a significant increase in the density of the immunoreactive NOS band and the NOS mRNA band, respectively, of the tissues obtained from rats treated with splanchnic ganglionectomy or 6‐OH‐dopamine.

Truncal vagotomy or treatment of the coeliac ganglia with capsaicin did not significantly affect the density of NOS band or NOS mRNA band.

It is concluded that neuronal NOS expression in the myenteric plexus is independent of vagus nerve and is negatively regulated by the splanchnic nerves in the rat small intestine.
Transepithelial electrochemical gradients in the proximal convoluted tubule during potassium depletion in the rat
Authors: Shirley D. G. , Walter S. J. , Folkerd E. J. , Unwin R. J. , Bailey M. A.
Published: September 2004

In order to examine the electrochemical gradient for potassium reabsorption across the S2 segment of the proximal convoluted tubule, transepithelial potential differences and transepithelial potassium concentrations were measured in anaesthetized potassium‐replete and potassium‐depleted rats.

Potassium‐depleted rats were markedly hypokalaemic (plasma potassium, 1.4 ± 0.1 vs. 4.1 ± 0.1 mmol l−1 in potassium‐replete rats) and had a significantly reduced muscle potassium content. In confirmation of previous reports, glomerular filtration rate was slightly reduced, while fractional reabsorption in the proximal convoluted tubule was enhanced.

In potassium‐replete animals, the transepithelial potential difference (PD) at the late proximal convoluted tubule was +2.1 ± 0.3 mV (lumen positive) and the tubular fluid to plasma ultrafiltrate concentration ratio for potassium (TFK/UFK) at the same site was 1.03 ± 0.01. In potassium‐depleted rats, there was a striking reversal of the transepithelial PD (to −4.0 ± 0.4 mV), while the TFK/UFK was increased to 1.19 ± 0.03.

The data from both potassium‐replete and potassium‐depleted animals are consistent with accumulating evidence that potassium reabsorption in the proximal convoluted tubule is passive in nature and depends partly on diffusion down an electrochemical gradient.
Effect of transverse‐tubular chloride conductance on excitability in skinned skeletal muscle fibres of rat and toad
Authors: Coonan J. R. , Lamb G. D.
Published: September 2004

The influence of the transverse‐tubular (T‐) system Cl− conductance on membrane excitability in skeletal muscle fibres of toad and rat was examined because of conflicting conclusions of previous studies on Cl− conductance. A mechanically skinned fibre preparation was used that permitted investigation of Ca2+ release via the normal T‐system voltage‐sensor mechanism after complete removal of the surface membrane, which thereby allowed estimation of the T‐system potential from force measurements.

When a skinned fibre was bathed in a high‐[K+] solution, the sealed T‐system became polarized and could be rapidly depolarized by replacing the K+ with Na+, thereby eliciting Ca2+ release from the sarcoplasmic reticulum. In rat skinned fibres, addition of 20 mM Cl− to the ‘myoplasm’ (i.e. bathing solution) partially depolarized the T‐system, inducing Ca2+ release and subsequent voltage‐sensor inactivation. These effects were completely abolished with 100 μM of the Cl− channel blocker 9‐anthracene carboxylic acid (9‐AC). Voltage‐sensor inactivation increased in a graded manner over the range 3‐20 mM myoplasmic Cl−.

In toad fibres, voltage‐sensor inactivation was only detectable at > 10 mM myoplasmic Cl−, and 20 mM Cl− was only able to depolarize the T‐system sufficiently to trigger Ca2+ release if the myoplasmic [K+] was reduced by 50 %. In toad fibres, 100 μM 9‐AC caused little if any block of the T‐system Cl− conductance.

It was also found that when skinned fibres were obtained from muscles that had been bathed in a zero Cl− extracellular solution, the initial Na+ substitutions were more effective at depolarizing the T‐system. This is consistent with Cl− trapped in the sealed T‐system exerting a polarizing effect on T‐system potential.

These results unequivocally demonstrate that there is a large 9‐AC‐sensitive Cl− conductance in the T‐system of rat fibres, and a smaller, though still appreciable, Cl− conductance in the T‐system of toad fibres, which is relatively insensitive to 9‐AC. The results are important for understanding the basis of the Cl− channel aberration in myotonia.
Carbachol‐induced oscillations in membrane potential and [Ca2+]i in guinea‐pig ileal smooth muscle cells
Authors: Kohda M. , Komori S. , Unno T. , Ohashi H.
Published: September 2004

Cytosolic free Ca2+ concentration ([Ca2+]i) and membrane potential were simultaneously recorded from single smooth muscle cells of guinea‐pig ileum, using a combination of nystatin‐perforated patch clamp and fura‐2 fluorimetry techniques.

Carbachol (CCh, 2 μM) produced oscillatory changes in [Ca2+]i and membrane potential which coincided well in time with each other, and peaks of membrane potential oscillations reached a saturated level of around −7 mV. Thapsigargin (1 μM) abolished these effects of 2 μM CCh. La3+ (3 μM) immediately prevented the discharge of spike potentials, but allowed both on‐going oscillatory responses to persist for a while.

CCh (0.25‐0.75 μM) caused membrane potential and [Ca2+]i to oscillate in some 20 % of cells studied. Every membrane potential oscillation was preceded by the discharge of single or multiple spike potentials. The effects of CCh were readily abolished by La3+ (3 μM).

In cells exhibiting no oscillatory response to 0.25‐0.75 μM CCh, an electrically evoked action potential usually generated changes in [Ca2+]i and membrane potential similar to those following spontaneously evoked action potentials, and sometimes it did so only after [Ca2+]i or InsP3 had been slightly elevated by repeatedly evoking action potentials or by increasing CCh concentration in the bath medium.

The results suggest that in ileal smooth muscle cells, the oscillations of [Ca2+]i and membrane potential arising from muscarinic stimulation result from release of Ca2+ from internal stores and that there is a Ca2+‐induced potentiation of coincidently elicited cation channel openings. Under weak muscarinic stimulation, Ca2+ entry upon action potential discharge can trigger such a release of stored Ca2+, resulting in synchronous generation of a large rise in [Ca2+]i and a slow, large membrane depolarization.
Central role of heterocellular gap junctional communication in endothelium‐dependent relaxations of rabbit arteries
Authors: Chaytor A. T. , Evans W. H. , Griffith T. M.
Published: September 2004

The contribution of gap junctions to endothelium‐dependent relaxation was investigated in isolated rabbit conduit artery preparations pre‐constricted by 10 μM phenylephrine (PhE).

Acetylcholine (ACh) relaxed the thoracic aorta by ≈60 % and the superior mesenteric artery (SMA) by ≈90 %. A peptide possessing sequence homology with extracellular loop 2 of connexin 43 (Gap 27, 300 μM) inhibited relaxation by ≈40 % in both artery types. Gap 27 also attenuated the endothelium‐dependent component of the relaxation induced by ATP in thoracic aorta but did not modify force development in response to PhE.

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G‐nitro‐L‐arginine methyl ester (L‐NAME, 300 μM), an inhibitor of NO synthase, attenuated ACh‐induced relaxation by ≈90 % in the aorta but only by ≈40 % in SMA (P < 0.05). Residual L‐NAME‐insensitive relaxations were almost abolished by 300 μM Gap 27 in aorta and inhibited in a concentration‐dependent fashion in SMA (≈50 % at 100 μM and ≈80 % at 10 mM). Gap 27 similarly attenuated the endothelium‐dependent component of L‐NAME‐insensitive relaxations to ATP in aorta.

Responses to cyclopiazonic acid, which stimulates endothelium‐dependent relaxation through a receptor‐independent mechanism, were also attenuated by Gap 27, whereas this peptide exerted no effect on the NO‐mediated relaxation induced by sodium nitroprusside in preparations denuded of endothelium.

ACh‐induced relaxation of ‘sandwich’ mounts of aorta or SMA were unaffected by Gap 27 but completely abolished by L‐NAME.

We conclude that direct heterocellular communication between the endothelium and smooth muscle contributes to endothelium‐dependent relaxations evoked by both receptor‐dependent and ‐independent mechanisms. The inhibitory effects of Gap 27 peptide do not involve homocellular communication within the vessel wall or modulation of NO release or action.
The hypoxic response of neurones within the in vitro mammalian respiratory network
Authors: Ramirez J. M. , Quellmalz U. J. A. , Wilken B. , Richter D. W.
Published: September 2004

The transverse brainstem slice preparation containing the pre‐Bötzinger complex (PBC) was used in mice to study developmental changes of the response of the in vitro respiratory network to hypoxia. This preparation generates at different postnatal stages (postnatal days (P) 0‐22) spontaneous rhythmic activity in hypoglossal (XII) rootlets that occur in synchrony with periodic bursts of neurones in the PBC.

In slices from P0‐4 mice, hypoxia did not significantly affect the amplitude of rhythmic synaptic drive potentials in four of five inspiratory neurones. Hypoxia reduced, but did not suppress, the amplitude of synaptic drive potentials in only one inspiratory neurone. Spike discharge and phasic ‘inspiratory’ hyperpolarizations of six expiratory neurones were suppressed during hypoxia revealing a phasic ‘inspiratory’ depolarization.

The coupling between rhythmic activity in PBC neurones and XII bursts occurred under control conditions in preparations from P0‐4 mice in a 1:1 manner (n= 11) and from mice older than P5 in a 3:1 manner (n= 9). During hypoxia, PBC and XII activity were linked in a 1:1 manner in all slices.

In six of fourteen inspiratory PBC neurones, the amplitude of synaptic drive potentials of slices from mice older than P8 was increased during the period of augmentation, reduced during the period of depression and suppressed during a hypoxic response which we refer to as central apnoea. Augmentation led to a weak‐to‐moderate membrane depolarization which on average was 4.8 ± 3.7 mV. This depolarization was followed by a hyperpolarization of 6.2 ± 4.1 mV only in four inspiratory neurones. In the majority of neurones (n= 9), however, membrane depolarization remained stable and was not followed by hyperpolarization. In expiratory neurones (n= 12) from this age group hypoxia suppressed phasic hyperpolarizations that occurred in synchrony with XII bursts. As similarly seen in inspiratory neurones, membrane potentials were depolarized by 5.1 ± 4.1 mV during the period of hypoxic augmentation.

The hypoxic response of respiratory neurones within the pre‐Bötzinger complex resembles the response of neurones that were previously described under in vivo conditions. Thus we conclude that the ‘transverse rhythmic slice’ is a good model for studying the hypoxic response of the respiratory network under in vitro conditions.
Necessity of acetylcholine for retinal directionally selective responses to drifting gratings in rabbit
Authors: Grzywacz Norberto M. , Amthor Franklin R. , Merwine David K.
Published: September 2004

A model for retinal directional selectivity postulates that GABAergic inhibition of responses to motions in the null (anti‐preferred) direction underlies this selectivity. An alternative model postulates that besides this inhibition, there exists an asymmetric, nicotinic acetylcholine (ACh) input from starburst amacrine cells. It is possible for the latter but not the former model that stimuli could exist such that nicotinic blockade eliminates directional selectivity. Such stimuli would drive the cholinergic but not the GABAergic system well.

So far, attempts to eliminate directional selectivity with nicotinic blockade have failed, but they always used isolated, moving bars as the stimulus. We confirmed this failure for On‐Off directionally selective (DS) ganglion cells in our preparation of the rabbit's retina.

However, while recording from these cells, we discovered that nicotinic blockade eliminated directional selectivity to drifting, low spatial frequency sine‐ and square‐wave gratings.

This effect was not just due to the smallness of the responses under nicotinic blockade. NMDA blockade caused even smaller responses, but no loss of directional selectivity.

This result is consistent with a two‐asymmetric‐pathways model of directional selectivity, but inconsistent with an asymmetric‐GABA‐only model.

We conclude that asymmetric nicotinic inputs extend the range of stimuli that can elicit directional selectivity to include moving textures, that is, those with multiple peaks in their spatial luminance profile.
Focally recorded single sympathetic postganglionic neuronal activity supplying rat lateral tail vein
Authors: Johnson Christopher D. , Gilbey Michael P.
Published: September 2004

In anaesthetized rats, using a focal recording technique, activity was recorded from single sympathetic postganglionic neurones innervating the lateral tail veins. On‐going activity was examined in order to determine whether it had similar or different characteristics to those recorded from the caudal ventral artery in a previous study.

Animals were artificially ventilated, vagotomized, paralysed and given a pneumothorax.

The discharges of fourteen out of seventeen sympathetic postganglionic neurones were rhythmic. Such units had a mean firing frequency of 1.62 ± 0.70 Hz. The mean frequency of the dominant sympathetic rhythm under control conditions was 0.82 ± 0.05 Hz.

The frequency of the dominant sympathetic rhythm was different from that of the phrenic rhythm in nine out of fourteen cases.

The mean frequency of the dominant sympathetic rhythm was: (i) not influenced significantly by hypocapnic apnoea, (ii) decreased by hyperthermia, which increased the frequency of the phrenic rhythm, (iii) in all cases different from that of the artificial ventilation cycle.

The above characteristics are similar to those recorded from the sympathetic supply to the caudal ventral artery of the same vascular bed under comparable conditions.
Mechanisms of Ca2+ sensitization of force production by noradrenaline in rat mesenteric small arteries
Authors: Buus Carsten L. , Aalkjær Christian , Nilsson Holger , Juul Birte , Møller Jesper V. , Mulvany Michael J.
Published: September 2004

Mechanisms of Ca2+ sensitization of force production by noradrenaline were investigated by measuring contractile responses, intracellular Ca2+ concentration ([Ca2+]i) and phosphorylation of the myosin light chain (MLC) in intact and α‐toxin‐permeabilized rat mesenteric small arteries.

The effects of noradrenaline were investigated at constant membrane potential by comparing fully depolarized intact arteries in the absence and presence of noradrenaline. Contractile responses to K‐PSS (125 mM K+) and NA‐K‐PSS (K‐PSS + 10 μM noradrenaline) were titrated to 30 and 75 %, respectively, of control force, by adjusting extracellular Ca2+ ([Ca2+]o). At both force levels, [Ca2+]i was substantially lower with NA‐K‐PSS than with K‐PSS. With K‐PSS, the proportion of MLC phosphorylated (≈30 %) was similar at 30 and 75 % of control force; with NA‐K‐PSS, MLC phosphorylation was greater at the higher force level (40 vs. 34 %).

In α‐toxin‐permeabilized arteries, the force response to 1 μM Ca2+ was increased by 10 μM noradrenaline, and MLC phosphorylation was increased from 35 to 45 %. The protein kinase C (PKC) inhibitor calphostin C (100 nM) abolished the noradrenaline‐induced increase in MLC phosphorylation and contractile response, without affecting the contraction in response to Ca2+. Treatment with ATPγS in the presence of the MLC kinase inhibitor ML‐9 increased the sensitivity to Ca2+ and abolished the response to noradrenaline.

The present results show that in rat mesenteric small arteries noradrenaline‐induced Ca2+ sensitization is associated with an increased proportion of phosphorylated MLC. The results are consistent with a decreased MLC phosphatase activity mediated through PKC. Furthermore, while MLC phosphorylation is a requirement for force production, the results show that other factors are also involved in force regulation.
Buffering of blood pressure variability by the renin‐angiotensin system in the conscious dog
Authors: Just Armin , Kirchheim Hartmut R. , Ehmke Heimo
Published: September 2004

The renin‐angiotensin system (RAS) participates in the compensation of major blood pressure disturbances such as haemorrhage and is involved in the tonic long‐term (> 1 day) maintenance of mean arterial blood pressure (MABP). Since its contribution to the short‐term (< 1 h) buffering of normal blood pressure variability is not known, this was investigated in resting conscious dogs.

The regulatory efficiency and the response time of the RAS were studied by an acute step reduction of renal artery pressure to 70 mmHg for 1 h using a suprarenal aortic cuff. After a delay of at least 100 s, MABP rose exponentially by 22 ± 5 mmHg in normal dogs (n= 4), by 6 ± 3 mmHg after angiotensin converting enzyme (ACE) inhibition (n= 4), and by 25 ± 5 mmHg after ganglionic blockade (n= 4). MABP returned to control after release of the cuff with similar time courses. The time constants of the MABP responses were in the range of 20 min. Thus, possible feedback oscillations of the RAS would be expected around 0.0025 Hz (1/(4 × 100 s)); a buffering effect would be possible below this frequency.

Blood pressure variability was investigated by spectral analysis of MABP from 3.75 h recordings in the frequency ranges of 0.002–0.003 Hz (feedback oscillations) and below 0.002 Hz (buffering effect).

ACE inhibition (n= 7) decreased MABP by 11 ± 2 mmHg (P < 0.05), but in both frequency ranges integrated spectral density was not affected. ACE inhibition also failed to significantly change spectral density in either of the two frequency ranges under the following conditions: (1) during ganglionic blockade (n= 7), (2) during a low‐sodium diet (except for a very slight elevation below 0.002 Hz) (n= 7), and (3) when the fall of MABP induced by ACE inhibition was compensated by an angiotensin II infusion (n= 7).

It is concluded that in spite of its high regulatory efficiency with an adequate response time the RAS does not directly contribute to the short‐term buffering of blood pressure variability, nor does it give rise to feedback oscillations under normal resting conditions. Even if the RAS is stimulated by sodium restriction its contribution to short‐term blood pressure buffering is only marginal.
Shortening‐induced force depression in human adductor pollicis muscle
Authors: De Ruiter C. J. , De Haan A. , Jones D. A. , Sargeant A. J.
Published: September 2004

The effects of single isovelocity shortening contractions on force production of the electrically stimulated human adductor pollicis muscle were investigated in seven healthy male subjects.

Redeveloped isometric force immediately following isovelocity shortening was always depressed compared with the isometric force recorded at the same muscle length but without preceding shortening. The maximal isometric force deficit (FD) was (mean ± s.e.m.) 37 ± 2 % after 38 deg of shortening at 6.1 deg s−1.

The FD was positively correlated with angular displacement (r2 > 0.98) and decreased with increasing velocity of the shortening step. Stimulation at 20 Hz instead of 50 Hz reduced absolute force levels during the contractions to about 73 % and the FD was decreased to a similar extent. Eighty‐nine per cent of the velocity‐related variation in the FD could be explained by the absolute force levels during shortening.

FD was largely abolished by allowing the muscle to relax briefly (approximately 200 ms), a time probably too short for significant metabolic recovery.

At all but the highest velocities there was a linear decline in force during the latter part of the isovelocity shortening phase, suggesting that the mechanisms underlying FD were active during shortening.

Our results show that shortening‐induced force deficit is a significant feature of human muscle working in situ and is proportional to the work done by the muscle‐tendon complex. This finding has important implications for experimental studies of force‐velocity relationships in the intact human.
Role of insulin‐like growth factor binding proteins in human post‐nephrectomy proximal tubule cells
Authors: Johnson David W. , Saunders Heather J. , Field Michael J. , Pollock Carol A.
Published: September 2004

In order to determine the role of the insulin‐like growth factor‐I (IGF‐I)/IGF binding protein (IGFBP) axis in the augmentation of tubule growth and function following reductions in nephron mass, primary cultures of human proximal tubule cells (PTCs) were generated from the histologically normal sections of ten surgically removed kidneys.

PTC hypertrophy (cellular protein content), DNA synthesis (thymidine incorporation) and apical sodium‐hydrogen exchange (NHE) activity (ethylisopropylamiloride‐sensitive apical 22Na+ uptake) were measured following 24 h incubation in media supplemented with 10 % pre‐ or post‐nephrectomy sera obtained from these patients. The results were compared with the effects of pre‐ and post‐operative control sera collected from seven patients undergoing retroperitoneal operations not involving removal of renal tissue.

Day 1 post‐nephrectomy sera promoted a significant 73 % increase in apical NHE activity, which was accompanied by a significant increase in PTC binding of 125I‐IGF‐I (post‐ vs. pre‐nephrectomy, 163 ± 6 vs. 142 ± 4 fmol (mg protein)−1; P < 0.05). Subsequent post‐nephrectomy sera significantly stimulated PTC protein content and thymidine incorporation, peaking at day 7 (127.7 ± 14.0 and 118.4 ± 9.0 % of pre‐nephrectomy values, respectively; P < 0.05). The growth effects were cell specific, as they were not observed with renal cortical fibroblasts. No change was detected in any of these measured variables following exposure to control sera.

Serum IGF‐I and IGFBP‐1 levels did not significantly change over time or between groups. IGFBP‐3 levels progressively decreased in both control and nephrectomized sera from pre‐operative values of 3580 ± 305 and 3360 ± 217 ng ml−1, respectively, to 2670 ± 341 and 2600 ± 347 ng ml−1 at 1 week post‐operation. Serum IGFBP‐2 levels increased to a comparable extent in both controls (day 0 vs. day 7, 2940 ± 1024 vs. 7010 ± 2520 ng ml−1; P < 0.01) and nephrectomized patients (day 0 vs. day 7, 3070 ± 656 vs. 9130 ± 2010 ng ml−1; P < 0.01).

The results indicate that nephrectomy engenders the elaboration of one or more humoral factor(s), which promotes increased binding of IGF‐I to PTCs and which may in turn specifically stimulate PTC Na+ transport and growth.
Modification of Cl− transport in skeletal muscle of Rana temporaria with the arginine‐binding reagent phenylglyoxal
Authors: Skydsgaard Jørgen M.
Published: September 2004

The effect of membrane modification by the arginine‐binding reagent phenylglyoxal (PG) on Cl− permeability was studied in thin bundles of twitch fibres from frog muscle. The bundles were modified by a method that yields stable PG binding to outer arginyl residues in erythrocyte membranes.

PG almost eliminated the pH‐dependent fraction of 36Cl− efflux under conditions of Cl− equilibrium in depolarized bundles: the fluxes at pH 7.2 and 8.5 were strongly inhibited approaching an apparent baseline value close to the normal flux at pH 6 which per se was not inhibited.

The uninhibited flux at pH 6 in modified bundles maintained the normally high sensitivity to DNDS), and the reduction of fluxes at pH > 7 coincided with increased DNDS sensitivity, suggesting a selective blocking of the pH‐dependent flux fraction that has a low DNDS sensitivity.

In normal Ringer solution the modified fibres showed normal resting membrane potentials (Vm) with normal sensitivity to [K+]o but sensitivity to changes of [Cl−]o was almost eliminated, suggesting a normal resting Na+ : K+ conductance ratio (gNa/gK) and that the main influence of modification on the resting membrane conductance (gm) was a loss of Cl− conductance (gCl).

The modified fibres were not excitable, possibly due to arginine modification in the voltage sensor (S4) of the Na+ channels.

These results suggest that positively charged arginines are important for the activity of the pH‐dependent Vm‐stabilizing Cl− channels and that PG may isolate a pH‐independent ‘basal’ flux fraction which normally dominates the Cl− flux at low pH.
Compensatory and excess retrieval: two types of endocytosis following single step depolarizations in bovine adrenal chromaffin cells
Authors: Engisch Kathrin L. , Nowycky Martha C.
Published: September 2004

Endocytosis following exocytosis evoked by single step depolarizations was examined in bovine adrenal chromaffin cells using high resolution capacitance measurements in perforated‐patch voltage clamp recordings.

Endocytosis was detected as a smooth exponential decline in membrane capacitance to either the pre‐stimulus level (‘compensatory retrieval’) or far below the pre‐stimulus level (‘excess retrieval’). During excess retrieval, > 10 % of the cell surface could be internalized in under 5 s.

Compensatory retrieval was equal in magnitude to stimulus‐evoked exocytosis for membrane additions > 100 fF (about fifty large dense‐cored vesicles). In contrast, excess retrieval surpassed both the stimulus‐evoked exocytosis, and the initial capacitance level recorded at the onset of phase‐tracking measurements. Cell capacitance was not maintained at the level achieved by excess retrieval but slowly returned to pre‐stimulus levels, even in the absence of stimulation.

A large percentage of capacitance increases < 100 fF, usually evoked by 40 ms depolarizations, were not accompanied by membrane retrieval.

Compensatory retrieval could occur with any amount of Ca2+ entry, but excess retrieval was never triggered below a threshold Ca2+ current integral of 70 pC.

The kinetics of compensatory and excess retrieval differed by an order of magnitude. Compensatory retrieval was usually fitted with a single exponential function that had a median time constant of 5.7 s. Excess retrieval usually occurred with double exponential kinetics that had an extremely fast first time constant (median, 670 ms) and a second time constant indistinguishable from that of compensatory retrieval.

The speed of compensatory retrieval was Ca2+ dependent: the largest mono‐exponential time constants occurred for the smallest amounts of Ca2+ entry and decreased with increasing Ca2+ entry. The Ca2+ dependence of mono‐exponential time constants was disrupted by cyclosporin A (CsA), an inhibitor of the Ca2+‐ and calmodulin‐dependent phosphatase calcineurin.

CsA also reduced the proportion of responses with excess retrieval, but this action was caused by a shift in Ca2+ entry values below the threshold for activation. The lower total Ca2+ entry in the presence of CsA was due to an increase in the rate of Ca2+ current inactivation rather than a reduction in peak amplitude.

Our data suggest that compensatory and excess retrieval represent two independent, Ca2+‐regulated mechanisms of rapid membrane internalization in bovine adrenal chromaffin cells. Alternatively, there is a single membrane internalization mechanism that can switch between two distinct modes of behaviour.
Voluntary activation of human elbow flexor muscles during maximal concentric contractions
Authors: Gandevia S. C. , Herbert R. D. , Leeper J. B.
Published: September 2004

To measure voluntary activation of human elbow flexor muscles during maximal concentric contractions, the twitch interpolation method was modified to enable detection of torque increments evoked by single stimuli during contractions of up to 300 deg s−1. Subjects flexed the elbow to rotate a loaded beam ‘as fast as possible’ (load typically 23–58 N m) from 70 deg below to 70 deg above the horizontal. Electrical stimuli were delivered to biceps brachii when the beam passed through the horizontal. Voluntary activation was estimated from the amplitude of the interpolated twitch, which was expressed as a percentage of the twitch produced by relaxed muscles shortening at the same velocity.

In eleven subjects, the level of voluntary activation during repeated maximal concentric contractions (median 99.4 %) did not differ significantly from that during maximal isometric contractions (98.0 %). Voluntary activation during maximal contractions did not depend on shortening velocity and was the same when tested at two angles 30 deg apart.

To induce fatigue, five subjects repeatedly lifted and lowered a heavy load at about 30 deg s−1, and continued for ten to twelve contractions after they needed assistance to continue lifting. All maintained the capacity to attain maximal levels of activation.

It is concluded that voluntary drive to elbow flexor muscles during maximal concentric contractions is usually maximal or near‐maximal, and that this level of drive can be maintained during development of peripheral fatigue.
Slow recovery of impaired phrenic responses to hypoxia following perinatal hyperoxia in rats
Authors: Ling Liming , Olson E. Burt , Vidruk Edward H. , Mitchell Gordon S.
Published: September 2004

Previous studies demonstrated that both ventilatory and phrenic nerve responses to acute hypoxia are greatly attenuated in adult rats (3–5 months old) previously exposed to 1 month of perinatal hyperoxia (60 % O2; perinatal treated rats). The present study tested the hypothesis that this functional impairment recovers spontaneously with advancing age in perinatal treated rats.

Hypoxia‐induced chemoreflexes were examined by measuring integrated phrenic responses to strictly controlled isocapnic hypoxia in urethane‐anaesthetized, vagotomized, paralysed and ventilated rats at different ages.

At 50 mmHg Pa,O2 (arterial O2 partial pressure), the hypoxia‐induced increase in minute phrenic activity was significantly attenuated in both 3‐ to 5‐month‐old (166 ± 15 % of baseline) and 6‐month‐old (130 ± 17 %) perinatal treated rats, relative to 3‐ to 6‐month‐old, untreated control rats (279 ± 28 %; both P < 0.05). However, at 40 mmHg Pa,O2, the hypoxic minute phrenic activity response was attenuated only in 3‐ to 5‐month‐old (154 ± 33 %), but not 6‐month‐old (232 ± 33 %) perinatal treated rats versus control rats (293 ± 30 %).

The minute phrenic activity response to hypoxia was not significantly different between geriatric perinatal treated rats (14–15 months) and untreated geriatric control rats at either 50 mmHg (treated: 250 ± 20 %versus control: 274 ± 23 %) or 40 mmHg Pa,O2 (treated: 292 ± 19 %versus control: 315 ± 36 %).

These data suggest that partial spontaneous recovery may occur in 6‐month‐old perinatal treated rats and that full recovery occurs by 15 months of age.
Antioxidant‐oxidant balance in the glomerulus and proximal tubule of the rat kidney
Authors: Gwinner Wilfried , Deters‐Evers Ute , Brandes Ralf P. , Kubat Birgit , Koch Karl‐Martin , Pape Michael , Olbricht Christoph J.
Published: September 2004

Antioxidant and oxidative enzymes were examined in renal glomeruli and proximal tubules of healthy young rats (10‐12 weeks old), and results were related to the superoxide anion generation of these tissues.

Activities of superoxide dismutases, catalase, and glutathione peroxidase were 3‐ to 6‐fold higher in proximal tubules than in glomeruli. Similarly, enzyme levels and mRNA levels of superoxide dismutases and catalase were significantly higher in proximal tubules.

NADH‐ and NADPH‐dependent oxidase activity and xanthine oxidase activity were not different in glomeruli and proximal tubules.

Measurements with lucigenin‐enhanced chemiluminescence in vital tissues indicated 10‐fold higher rates of superoxide anion in glomeruli than in tubules.

Compared with the young rats, tubules of 8‐month‐old rats had significantly higher superoxide anion rates and lower superoxide dismutase activity, whereas NADH‐ and NADPH‐dependent oxidase activities were unchanged.

We conclude that considerable differences in the antioxidant‐oxidant balance exist between the glomerulus and proximal tubule. Results from experiments using chemiluminescence in vital tissues suggest that changes in the antioxidant‐oxidant balance have an effect on oxygen radical levels. The relevance of the observed differences to glomerular and tubulo‐interstitial disease remains to be determined, but a greater susceptibility of the glomerulus to oxidant stress might be anticipated.
In vivo measurements of the triceps surae complex architecture in man: implications for muscle function
Authors: Maganaris Constantinos N. , Baltzopoulos Vasilios , Sargeant Anthony J.
Published: September 2004

The objectives of this study were to (1) quantify experimentally in vivo changes in pennation angle, fibre length and muscle thickness in the triceps surae complex in man in response to changes in ankle position and isometric plantarflexion moment and (2) compare changes in the above muscle architectural characteristics occurring in the transition from rest to a given isometric plantarflexion intensity with the estimations of a planimetric muscle model assuming constant thickness and straight muscle fibres.

The gastrocnemius medialis (GM), gastrocnemius lateralis (GL) and soleus (SOL) muscles of six males were scanned with ultrasonography at different sites along and across the muscle belly at rest and during maximum voluntary contraction (MVC) trials at ankle angles of −15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg. Additional images were taken at 80, 60, 40 and 20 % of MVC at an ankle angle of 0 deg.

In all three muscles and all scanned sites, as ankle angle increased from −15 to +30 deg, pennation increased (by 6–12 deg, 39–67 %, P < 0.01 at rest and 9–16 deg, 29–43 %, P < 0.01 during MVC) and fibre length decreased (by 15–28 mm, 32–34 %, P < 0.01 at rest and 8–10 mm, 27–30 %, P < 0.05 during MVC). Thickness in GL and SOL increased during MVC compared with rest (by 5–7 mm, 36–47 %, P < 0.01 in GL and 6–7 mm, 38–47 %, P < 0.01 in SOL) while thickness of GM did not differ (P > 0.05) between rest and MVC.

At any given ankle angle the model underestimated changes in GL and SOL occurring in the transition from rest to MVC in pennation angle (by 9–12 deg, 24–38 %, P < 0.01 in GL and 9–14 deg, 25–28 %, P < 0.01 in SOL) and fibre length (by 6–15 mm, 22–39 %, P < 0.01 in GL and 6–8 mm, 23–24 %, P < 0.01 in SOL).

The findings of the study indicate that the mechanical output of muscle as estimated by the model used may be unrealistic due to errors in estimating the changes in muscle architecture during contraction compared with rest.
The arginine vasopressin and corticotrophin‐releasing hormone gene transcription responses to varied frequencies of repeated stress in rats
Authors: Ma Xin‐Ming , Lightman Stafford L.
Published: September 2004

Rats habituate to repeated exposure to homotypic stressors. The present studies were designed to define how altered frequency of exposure to a stressor affects the development of habituation and how this habituation is reflected in alterations in basal expression and responsiveness of hypothalamic corticotrophin‐releasing hormone (CRH) and arginine vasopressin (AVP) messenger and heteronuclear RNA (hnRNA).

Rats were exposed to a 60 min period of restraint stress every 7th day, every 3rd day, alternate days or daily for 2 weeks and their response to a final episode of stress on day 15 was compared with that of a control group of unstressed rats.

The response of plasma corticosterone to the final stressor on day 15 was diminished in animals which had been stressed on only two previous occasions, 7 days apart, and diminished further with increasing frequency of previous stressors until it failed to respond at all in animals stressed daily.

The pattern of CRH hnRNA and mRNA responses were similar, decreasing with increasing frequency of exposure to the stressor, while AVP mRNA responses increased in response to repeated stress.

The gradual emergence of increased AVP transcription at a time of diminishing CRH response suggests that repeated stress results in a specific facilitation of AVP gene expression, perhaps by impairment of corticosterone feedback.