bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of rapid changes in plasma sugar concentration on the brush‐border potential difference in rat jejunum
Authors: Sharp PA , Debnam ES
Published: December 2014

The effect of infusion (2 h) of various sugars (20%, w/v) or early diabetes mellitus (2 h following injection of streptozotocin) on the potential difference (PD) across the brush border of rat jejunum has been studied in vitro. Infusion of glucose or galactose resulted in hyperpolarization of the brush‐border PD (‐55.2 and ‐54.9 mV respectively) compared with mannitol‐infused animals (‐47.7 mV). Infusion of fructose and alpha‐methyl glucoside was without effect on PD. Ion substitution experiments showed that the glucose infusion‐induced hyperpolarization was due either to a decrease in Cl‐ conductance and/or increased K+ conductance of the brush‐border membrane. Na+ conductance appeared to be unaltered in these experiments. Since galactose infusion hyperpolarized PD without elevating plasma glucose or insulin levels, it seems that neither glucose nor insulin alone is responsible for the significantly greater PD. Treatment with streptozotocin produced glycosuria and hyperglycaemia within approximately 90 min and animals were used 30‐60 min later. PD in streptozotocin‐treated animals (‐51.8 mV) was significantly greater than that measured in diluent‐injected animals (‐45.3 mV, P < 0.001). However, unlike the situation with sugar infusion, ion substitution experiments showed that the hyperpolarization seen in diabetic animals was due to a decreased Na+ conductance of the brush‐border membrane. Since the magnitude of the brush‐border PD dictates the electrochemical driving force for Na(+)‐sugar cotransport, our data represent the first evidence for an effect of acute hyperglycaemia on the capacity for brush border sugar uptake. However, the enterocyte and systemic factors responsible for the membrane hyperpolarization are unclear.
The effect of ryanodine on the contraction of isolated frog atrial trabeculae is triggered by caffeine
Authors: Tunstall J , Chapman RA
Published: December 2014

Ryanodine is without effect on the contraction of frog atrial muscle when applied alone. However, if agents which bring about Ca2+ release from the sarcoplasmic reticulum (SR), e.g. caffeine, hypertonic fluid or rapid cooling, are applied together with or up to 1 h after exposure to ryanodine, subsequent effects upon contraction are evident. These include a complete inhibition of the contractures evoked by caffeine, rapid cooling or hypertonic solutions applied in Na(+)‐deficient media and a shift in the relationship between [Ca2+]o and the strength of the heart beat to a higher [Ca2+]o. The contractures evoked by Na+ withdrawal are unaffected. These results have been interpreted as an action of ryanodine to maintain the open state of the SR Ca(2+)‐release channels, thereby inhibiting Ca2+ accumulation by the SR. In this respect the response of the frog heart resembles mammalian heart, but differs in that this action is not triggered by the normal heart beat. These results add support to the notion that, although contraction can be activated in frog atrial muscle by release of Ca2+ from the SR, it is not a major source of Ca2+ during the normal heart beat.
The effects of oesophageal distension on diaphragm and laryngeal muscle activity in the anaesthetized cat
Authors: Jones JF , McKeogh D , Nolan P , O'Regan RG
Published: December 2014

The electromyographic (EMG) activities of diaphragm and laryngeal muscles were recorded during oesophageal distension in anesthetized cats. The responses to distension of the thoracic oesophagus differed from those evoked by distension of the cervical oesophagus. The crural component of the diaphragm (CD) was inhibited by distension of the thoracic oesophagus; distension of the cervical oesophagus did not affect CD EMG. Thyroarytenoid (TA) muscle EMG increased markedly and consistently in response to distension of the cervical oesophagus. Distension of the thoracic oesophagus only produced statistically significant increases in TA EMG with high distending volume (10 ml) at the level of the gastro‐oesophageal junction. The main abductor of the vocal cords, the posterior cricoarytenoid (PCA) was either unchanged or decreased by oesophageal distension. The electrical activities of left paratendinous diaphragm, left costal diaphragm, internal intercostal and external intercostal muscles remained unchanged. The entire pattern would appear to constitute a means to aid passage of a bolus into the stomach, and simultaneously guard the respiratory tract from reflux or aspiration.
Inhibitory effect of milk fat on milk secretion in the mouse: a re‐examination
Authors: Peaker M , Taylor E
Published: December 2014

Lactating mice were treated I.P. with cow milk, skim milk, milk lipid extract, preparations of milk fat globule membranes and fat globule‐enriched milk (cream). Milk, but not skim milk, inhibited litter growth significantly. None of the fractions of milk fat globules had any apparent effect on litter growth. Litter growth was reduced markedly and maternal health adversely affected by cream. It is concluded that previous studies in which milk was injected I.P. cannot be taken to indicate that milk contains a lipid or lipid‐soluble inhibitor of milk secretion in addition to the protein inhibitor discovered in milk more recently.
The contribution of ischaemia and deformation to the conduction block generated by compression of the cat sciatic nerve
Authors: Fern R , Harrison PJ
Published: December 2014

The pattern of conduction block induced in cat peripheral nerve by compression has been investigated electrophysiologically by recording unitary action potentials. A degree of compression, associated with chronic compression disorders in man, was applied to the cat sciatic nerve and resulted in a conduction block typified by early failure of the slow conducting myelinated axons. By contrast, a greater degree of compression, a degree more likely to result in acute compression lesions, produced a different pattern of effect, inducing early conduction failure in the fast conducting myelinated axons. These results are related to earlier studies which have shown that nerve deformation during compression has a differential action upon fast myelinated axons, while nerve ischaemia has a differential action upon slow myelinated axons.
Developmental and gestational changes of phosphoethanolamine and taurine in rat brain, striated and smooth muscle
Authors: Turner O , Phoenix J , Wray S
Published: December 2014

Concentrations of taurine and phosphoethanolamine in rat smooth (intestinal and uterine), skeletal and cardiac muscle, and brain have been determined, using high‐performance liquid chromatography (HPLC), to examine possible interrelationships in their tissue content. Concentrations were determined in fetal and neonatal samples, as well as in adult tissue, to investigate whether phosphoethanolamine and taurine levels are influenced by developmental state. The effect of gestational state was also studied. A marked decrease in cerebral phosphoethanolamine concentration during development was found together with a concomitant decrease in striated muscle but not in the two smooth muscles studied. A rise in uterine phosphoethanolamine during the early postpartum period confirmed previous NMR data. This occurred only in the uterus, suggesting it is specific to the process of involution within the myometrium. Taurine concentrations showed no consistent pattern of change with postnatal development. In adult animals, the highest levels of taurine were found in cardiac muscle. Pregnancy was associated with a fall in taurine concentration in all tissues, suggesting an influence of steroid hormones. As taurine is cotransported with Na+ in many systems it may be related to the increased water retention seen in pregnancy. It is concluded that marked changes in phosphoethanolamine and taurine levels occur during development and gestation, but that the changes are not interdependent, i.e., the changes are tissue specific.
Interaction of aldosterone and oxytocin to influence renal sodium excretion in rats
Authors: Musabayane CT , Ndhlovu CE , Forsling ML , Balment RJ
Published: December 2014

The possibility of an interaction between oxytocin and aldosterone to influence renal Na+ excretion was investigated in Inactin‐anaesthetized male Sprague‐Dawley rats. Endogenous plasma concentrations of aldosterone were suppressed by either adrenalectomy or bicarbonate infusion. The effects of 2 h intravenous administration of oxytocin (0.04 pmol/min) and/or aldosterone (42 pmol/min) on renal Na+ handling were studied in 0.077 M NaCl‐infused adrenalectomized (Adx) rats and groups of intact animals that were infused with 0.077 M NaHCO3. Aldosterone alone significantly (P < 0.01) reduced Na+ excretion from pretreatment peak value of 5.0 +/− 1.0 to 1.5 +/− 0.4 mumol/min in Adx animals (n = 8) and 9.2 +/− 1.2 to 5.2 +/− 1.2 mumol/min in NaHCO3‐infused rats (n = 8) by 2 h after the start of administration. However, combined administration of aldosterone and oxytocin was associated with a significantly (P < 0.01) increased Na+ excretion rate from a peak pretreatment value of 6.8 +/− 0.7 mumol/min to a peak value of 11.5 +/− 1.1 mumol/min by 1 h 40 min after the start of treatment in Adx rats (n = 7). In bicarbonate‐infused rats (n = 8) Na+ excretion rose within 20 min of the start of treatment from a pretreatment peak of 9.0 +/− 0.8 mumol/min to a peak value of 13.5 +/− 0.8 mumol/min in response to combined hormone administration. In conclusion, we have shown that concomitant administration of aldosterone and oxytocin increased the rate of excretion of Na+ in two different preparations, which supports the idea of an interaction between the steroid and oxytocin to promote Na+ loss.
The effect of a hyposmotic shock on amino acid efflux from lactating rat mammary tissue: stimulation of taurine and glycine efflux via a pathway distinct from anion exchange and volume‐activated anion channels
Authors: Shennan DB , McNeillie SA , Curran DE
Published: December 2014

We have examined the effect of a hyposmotic shock, and thus cell swelling, upon the efflux of amino acids, SO4(2‐) and I‐ from lactating mammary tissue. A hyposmotic challenge increased the efflux of taurine and glycine via a 4,4'‐diisothiocyanatostilbene‐2,2'‐ disulphonic acid (DIDS)‐sensitive pathway. It appears that these amino acids do not exit via an anion‐exchange mechanism following cell swelling because sulphate efflux, which uses a DIDS‐sensitive exchange mechanism, was unaffected. The hyposmotic‐induced efflux of taurine was not dependent upon the Na+ gradient and was not influenced by the nature of the anion in the incubation medium. In addition, taurine efflux was stimulated by incubating mammary tissue in an isosmotic medium that contained urea, suggesting that cell swelling is the stimulating factor rather than a decrease in osmolality per se. The results suggest that mammary tissue uses taurine and glycine as a means of regulating cell volume following swelling. In contrast, the efflux of glutamic acid, alanine and alpha‐aminoisobutyric acid was unaffected by a hyposmotic challenge. Similarly, the efflux of I‐ was unaffected by such a challenge. The results suggest that volume‐activated amino acid transport in lactating rat mammary tissue is distinct from volume‐regulated anion channels.
Indirect measurement of saliva secretion in sheep fed diets of different structures and the effect of such diets on ruminal fluid kinetics and fermentation pattern
Authors: Duric M , Zhao GY , Orskov ER , Chen XB
Published: December 2014

Four Suffolk x Dorset sheep were allocated in a 4 x 4 Latin square design and received a hay‐barley‐molasses diet in one of four different physical structures: (1) pelleted; (2) pelleted:chopped (60:40); (3) chopped:pelleted (60:40); or (4) chopped. The animals were penned individually and the diet was restricted to provide 20 g of dry matter (DM) per kilogram live weight daily. The effects of the diets on rumen fluid kinetics, fermentation pattern and microbial nitrogen (MN) supply were examined. Saliva secretion was estimated using an indirect method based on water balance in the rumen. When the animals were fed the chopped diet, the salivation rate, rumen fluid volume and rumen liquid outflow were all increased significantly (P < 0.05 to P < 0.01). No consistent effect of dietary structure on rumen fluid dilution rate, purine derivative (PD) excretion or MN supply was observed. Dietary structure had no effect on the rumen fermentation pattern, digestibility of DM or nitrogen.
A linear relationship between ATP degradation and fatigue during high‐intensity dynamic exercise in rat skeletal muscle
Authors: de Haan A , Koudijs JC
Published: December 2014

The relationship between changes in work output (fatigue) and metabolite concentrations was measured in rat skeletal muscle during the course of dynamic exercise (10 s). After 4 s, work output decreased rapidly to approximately 30% at 8 s. In contrast to the changes in phosphocreatine and lactate, the change in ATP concentration paralleled the reduction in work output. A strong linear relationship (r = 0.95) was found between the relative decrease in ATP and the extent of fatigue. Possible mechanisms underlying this relationship are discussed.
The role of the sarcoplasmic reticulum in the response of isolated ferret cardiac muscle to beta‐adrenergic stimulation
Authors: Shah N , Than N , White E , Bennett KL , Orchard CH
Published: December 2014

beta‐Adrenergic stimulation of cardiac muscle leads to an increase in the strength of contraction and an abbreviation of its time course. We have investigated the role of the sarcoplasmic reticulum in these changes by monitoring force and cytoplasmic [Ca2+] in ferret papillary muscles, and the Ca2+ current in isolated ferret myocytes, during the application of isoprenaline in the absence and presence of the sarcoplasmic reticulum inhibitor ryanodine (10(‐6) mol/l). Isoprenaline (10(‐6) mol/l) led to a marked increase in the size of both the twitch and Ca2+ transient, and a decrease in their duration. In the presence of ryanodine, application of isoprenaline had no significant effect on either the size or the time course of the twitch. However, the increase in the Ca2+ current in response to isoprenaline was the same in the absence and presence of ryanodine. Increasing bathing [Ca2+] led to a prolongation of both the twitch and the Ca2+ transient. In the presence of ryanodine, increasing bathing [Ca2+] still increased the size, but decreased the duration, of the twitch. These data provide direct evidence that both the inotropic and lusitropic effects of isoprenaline are mediated via the sarcoplasmic reticulum.
Mechanosensitive fibroblasts in the sino‐atrial node region of rat heart: interaction with cardiomyocytes and possible role
Authors: Kohl P , Kamkin AG , Kiseleva IS , Noble D
Published: December 2014

The positive chronotropic response of the heart to stretch of the right atrium is one of the major mechanisms adjusting the heart rate to variations in venous return on a beat‐by‐beat basis. The precise pathway of this mechano‐electric feedback and its cellular basis are uncertain. In this study, a possible contribution of mechanosensitive fibroblasts, abundant in the sino‐atrial node region, was investigated using a mathematical model of the electrical interaction of a mechanosensitive fibroblast and a sino‐atrial pacemaker cell. Electrophysiological evidence for a bio‐electrical interaction of mechanosensitive fibroblasts with surrounding cardiomyocytes has been studied in (i) the isolated spontaneously beating atrium of rat hearts, and (ii) cell cultures of the neonatal rat heart. These investigations were performed using (i) double‐barrelled floating microelectrodes for intracellular potential registrations, and (ii) the double whole cell patch‐clamp technique. It was shown that cardiac fibroblasts and surrounding cardiomyocytes can be either electrically well isolated from each other, or coupled both capacitively and electrotonically. The electrophysiological data obtained were incorporated into the OXSOFT HEART program. Assuming that equivalent coupling may occur between mechanosensitive fibroblasts and sino‐atrial pacemaker cells, a heterologous cell pair consisting of one fibroblast and one sino‐atrial node myocyte connected by ten to thirty single gap junctional channels with a conductance of 30 pS was modelled. The model of the electrotonic interaction of these cells showed that stretch of the fibroblast during atrial diastole, simulating increased atrial wall tension during atrial filling, can raise the spontaneous depolarization rate of the pacemaker cell in a stretch‐dependent manner by up to 24%. These results show that cardiac mechanosensitive fibroblasts could form a cellular basis for the positive chronotropic response of the heart to stretch of the right atrium.
Estimation of intracellular calcium activity in confluent monolayers of primary cultures of quail medullary bone osteoclasts
Authors: Arkle S , Wormstone IM , Bascal ZA , Dacke CG
Published: December 2014

The present study was concerned with an investigation of the relative utilities of the fluorescent indicators fura‐2 and fluo‐3 for spectrofluorimetric estimation of the intracellular calcium concentration ([Ca2+]i) in confluent osteoclast monolayers that had been isolated from medullary bone of quail hens and maintained in tissue culture for 6–8 days. Additionally, we have determined the effects of raised extracellular calcium ([Ca2+]o) and chicken calcitonin (CT) on [Ca2+]i in this preparation. Relative to fura‐2, fluo‐3 was poorly incorporated into the osteoclasts and had a high apparent equilibrium binding constant (Kd) for Ca2+ binding (809 nM). The osteoclasts were only weakly sensitive to the calcium ionophore, ionomycin. It is concluded that fura‐2 is of greater utility than furo‐3 in this preparation. In contrast to its lack of effect in freshly isolated cells, elevated [Ca2+]o up to 20 mM stimulated a concentration‐dependent increase in [Ca2+]i in cultured osteoclasts, but CT was without effect. These findings further support the idea that quail osteoclasts are able to acquire a Ca2+ sensor or 'receptor' and thus to respond to [Ca2+]o in a similar manner to mammalian osteoclasts when they are removed from the bone microenvironment, but retain a refractoriness to CT under these conditions.
Control of gastric emptying in the pig: influence of cholecystokinin, somatostatin and prokinetic agents
Authors: Gregory PC , McFadyen M , Rayner DV
Published: December 2014

The influence of systemic arterial infusions of cholecystokinin octapeptide (CCK8) and somatostatin, and injections of cisapride, metoclopramide and atropine on gastric emptying were studied in eight pigs. Gastric emptying of dry matter (DM) and liquids (Cr‐EDTA as marker) was measured, in pigs fitted with a gastric cannula, by evacuation of gastric contents either immediately after the pigs had finished feeding, or 3 h after being fed a meal containing 1200 g of a finely ground barley diet mixed with 2.41 water. Gastric emptying of DM and liquids during the feeding period was not significantly altered by cisapride (0.15 and 0.3 mg kg‐1‐1), metoclopramide (0.2 mg kg‐1), CCK8 (250 ng kg‐1 h‐1) or somatostatin (1.8 and 4.5 micrograms kg‐1 h‐1); atropine (0.06 mg kg‐1) slowed emptying of DM (by 53 +/− 6%; P < 0.001) and of liquids (by 51 +/− 7%, P < 0.01). In contrast, the amount of DM emptied within 3 h of feeding was significantly reduced with CCK8 (250 ng kg‐1 h‐1; by 14 +/− 3%, P < 0.001) and with somatostatin (1.8 microgram kg‐1 h‐1; by 10 +/− 4%; P < 0.001). There was no increase in emptying of DM or liquids with cisapride or metoclopramide; indeed, there was actually a reduction in liquid emptying (by 13 +/− 6%; P < 0.05) with cisapride (0.3 mg kg‐1).(ABSTRACT TRUNCATED AT 250 WORDS)
Comparison of synovial PO2 and sympathetic vasoconstrictor responses in normal and acutely inflamed rabbit knee joints
Authors: Najafipour H , Ferrell WR
Published: December 2014

Experiments were performed to assess the effect of acute inflammation of the rabbit knee joint on the partial pressure of oxygen in synovial fluid (Ps,O2) and nerve‐mediated vasoconstrictor responses of articular blood vessels. With the hypodermic needle oxygen electrode sited within the synovial cavity in the posterior region of the knee joint, mean (+/‐ S.E.M.). Ps,O2 was 37.4 +/‐ 3.6 mmHg (n = 10) in the inflamed group, which differed significantly (P < 0.05) from that occurring in the normal group from a different series (48.2 +/‐ 3.1 mmHg; n = 18). Ps,O2 was found to decrease with increasing depth of penetration of the oxygen electrode into the joint cavity of the inflamed knee, as in the normal knee. The lowest values were observed close to articular cartilage. Absolute blood flow was measured using radiolabelled microspheres whilst relative changes in blood flow were assessed using laser Doppler flowmetry. The former technique showed that the inflamed joints had a significantly higher blood flow. Electrical stimulation of the posterior articular nerve (PAN) of the knee resulted in vasoconstriction of knee joint blood vessels, which was accompanied by a reduction in Ps,O2. The frequency‐response and voltage‐response profiles to electrical stimulation of the PAN, although differing in magnitude, showed a high degree of correlation between blood flow and Ps,O2. The frequency‐response profile to electrical stimulation of the PAN shifted to the right in inflamed joints compared with normal joints, suggesting a reduction in the efficacy of the sympathetic nervous system in regulating blood flow to the inflamed joints. Although the inflamed joint had a higher blood flow, Ps,O2 was lower compared with the normal joint. The results of this study show significantly altered blood flow, Ps,O2 and nerve‐mediated constrictor responses in the acutely inflamed joint. These are related to the inflammatory response and may contribute to the pathogenesis of arthritis.
Recognition of a pharyngo‐oesophageal sphincter inhibitory reflex in dogs and its role in deglutition
Authors: Shafik A
Published: December 2014

The present study describes the 'pharyngo‐oesophageal sphincter inhibitory reflex' and its clinical significance. The study was performed on twelve anaesthetized dogs. A balloon‐tipped catheter was placed within the pharyngo‐oesophageal sphincter (POS) and another in the pharynx. The POS response to distension of the pharynx with a balloon filled with 2, 4 or 6 ml of water was recorded before and after application of local anaesthetic to the POS, and after successive section of the anatomical constituents of the POS. Upon pharyngeal distension, POS pressure was reduced; the greater the distension, the greater the pressure reduction. The anaesthetized POS did not respond to pharyngeal distension. Section of the cricopharyngeus muscle did not influence the resting POS pressure or the POS response to pharyngeal distension. The POS pressure dropped significantly (P < 0.0001) and was unresponsive to pharyngeal distension after section of both the cricopharyngeus muscle and the oesophageal circular muscle bundles. This shows that the cricopharyngeus muscle is not involved in the upper oesophagus sphincter mechanism.
Responses to reduced water intake, including dehydration natriuresis, in sheep excreting sodium predominantly in urine or in faeces
Authors: Michell AR , Moss P
Published: December 2014

Sheep which were predominantly urinary excretors (U) or faecal excretors (F) of sodium were exposed to a 75% reduction of water intake for 72 h. The experiment was performed on moderate, low or high sodium intakes (0.4, 0.05 or 1.2 mmol kg‐1 day‐1) to test the hypothesis that dehydration natriuresis was not a cause of sodium depletion but a defence against hypernatraemia. Dehydration caused elevation of plasma sodium concentration, osmolality, antidiuretic hormone (ADH) and oxytocin but, as in other experiments, a fall in haematocrit. The two higher levels of sodium intake were associated with dehydration natriuresis but also a smaller increase in faecal sodium excretion in both U and F sheep. On low sodium intake, however, neither urinary nor faecal sodium excretion increased in either group of sheep although the rise in plasma sodium concentration caused by dehydration was similar. Thus, when there is a risk of sodium depletion, due to low sodium intake, dehydration natriuresis does not occur, consistent with the hypothesis. Active sodium transport inhibitor (ASTI) and atrial natriuretic peptide (ANP) fell rather than rose during dehydration. Since aldosterone is suppressed by the higher levels of sodium intake, none of these hormones is likely to mediate dehydration natriuresis in sheep. F sheep showed more effective renal and faecal water conservation when dehydrated. During water restriction, the urinary potassium excretion of U sheep was significantly reduced, unlike that of F sheep; moreover, the latter maintained an identical plasma potassium concentration between baseline and restriction period, whereas in U sheep it was 0.3 mmol l‐1 higher during water restriction. Increased drinking rather than reduced urine output was the basis of rehydration when ad lib. water intake was restored.
Opioid tolerance and dependence in the magnocellular oxytocin system: a physiological mechanism?
Authors: Russell JA , Leng G , Bicknell RJ
Published: December 2014

At the neurosecretory terminals in the neural lobe, oxytocin secretion is restrained by co‐secreted endogenous opioids, which act via kappa‐receptors. The co‐secreted opioids include products of pro‐dynorphin (released by both vasopressin and oxytocin terminals) and proenkephalin (released by oxytocin terminals). In morphine‐tolerant rats this opioid mechanism is more effective, but in late pregnancy it is less effective. Opioids also act directly on oxytocin cell bodies, via separate mu‐ and kappa‐receptors, inhibiting excitation by all stimuli tested, and also exert presynaptic and more distal actions on afferent systems. During chronic morphine exposure, tolerance and dependence develop in oxytocin neurones; the former involves reduction in mu‐opioid receptor density, while the latter may involve compensatory upregulation of mechanisms regulating Ca2+ influx. In mid‐pregnancy, the effectiveness of opioid mechanisms in the neural lobe increases, assisting the accumulation of oxytocin stores in advance of parturition, but by the end of pregnancy the effectiveness of these mechanisms is reduced. At this time, a separate endogenous opioid system, acting via mu‐receptors, actively restrains the electrical activity of oxytocin neurones. Release of this endogenous opioid inhibition may contribute to the increase in activity during parturition analogous to that occurring during morphine withdrawal excitation. Central opioid mechanisms retain the ability to control oxytocin neurones during parturition, and can interrupt established parturition by inhibiting oxytocin neurone firing rate in disadvantageous environmental circumstances.
Prolonged alteration of vasoconstrictor and vasodilator responses in rat knee joints by adjuvant monoarthritis
Authors: McDougall JJ , Karimian SM , Ferrell WR
Published: December 2014

Both neurogenic influences and the regulatory neuropeptide substance P (SP) have been implicated in the development of joint inflammation. Using the laser Doppler perfusion imaging technique to quantify relative changes in joint blood flow, the effects of nerve stimulation and topical SP application were examined in normal and chronically inflamed rat knee joints. Synovial inflammation was induced by unilateral intra‐articular injection of Freund's complete adjuvant and experiments were carried out 1 week and 3 weeks later. Normal knees showed a frequency‐dependent vasoconstriction in response to saphenous nerve stimulation over the range of 5–30 Hz and a dose‐dependent vasodilation in response to SP administration. These vasoactive responses were completely abolished in the chronically inflamed knee joint, the abolition persisting throughout the investigation. Since articular cartilage is critically dependent on synovial fluid formation for its nutrition, loss of neurovascular control of the synovial microcirculation could contribute to the degenerative changes that commonly accompany chronic inflammatory joint diseases.
Activity‐induced facilitation of L‐type Ca2+ current in cardiomyocytes isolated from guinea‐pig ventricles
Authors: Kaspar SP , Pelzer DJ
Published: December 2014

The facilitation of L‐type Ca2+ current (ICa), which sometimes occurs with an increase in stimulation frequency, was investigated in single guinea‐pig ventricular cardiomyocytes using whole‐cell recording and K(+)‐free solutions. With a holding potential of ‐80 mV, an increase in frequency from 0.5 to 1, 2, 3 or 4 Hz caused either a small or large initial reduction, or a transient enhancement (facilitation) of peak ICa, which developed rapidly and was followed by a reduction of ICa. Reducing the frequency to 0.1 or 0.2 Hz caused a depression of ICa on the first pulse that was followed by a slower increment. Transient facilitation and depression were entirely absent when either Ba2+ or Na+ was used as the charge carrier in Ca(2+)‐free solutions. High concentrations of isoprenaline (1‐3 microM), forskolin (1‐3 microM), or 8‐(4‐chlorophenylthio)‐cAMP (150 microM) suppressed but did not abolish the incidence and size of facilitation; employing a holding potential of ‐40 mV also suppressed the incidence of ICa facilitation. Lower isoprenaline concentrations (0.1 and 0.3 microM) greatly enhanced the incidence and magnitude of the transient facilitation occurring with an increase in stimulation rate, but did not diminish the magnitude of the ensuing reduction. When facilitation occurred with 0.1 mM EGTA in the dialysate, or the usual 5 mM EGTA with 0.01 microM extracellular isoprenaline, it developed more slowly after an increase in frequency. In the presence of the phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine, an increase in stimulation rate from 0.5 to 1, 2 or 3 Hz sometimes caused a large and sustained facilitation of ICa, which developed over tens of seconds, declined slowly with continued stimulation and was maintained after returning to 0.5 Hz. It is concluded that the levels of intracellular cAMP and Ca2+ mediate the initial sensitivity of ICa to changes in stimulation rate, to the extent that they determine whether or not transient facilitation will occur. Because the reduction of ICa was relatively constant, facilitation dictates the level of steady‐state ICa that will be reached at the higher rate. Taken together with the fact that facilitation can be modulated, the results argue for separate mechanisms of facilitation and reduction for ICa. It is suggested that the mechanism of facilitation is partly enzymatic, insofar as sustained facilitation could be a manifestation of a stimulatory Ca(2+)‐dependent process, which is normally counteracted by the action of phosphodiesterases.(ABSTRACT TRUNCATED AT 400 WORDS)
Swelling‐activated conductances for chloride, potassium and amino acids in the rat colon: a whole‐cell study
Authors: Diener M , Scharrer E
Published: December 2014

Cell swelling induced by superfusion with a hypotonic medium (152 mosmol l‐1) induced a reversible membrane depolarization of 13.8 +/− 5.3 mV in isolated colonic crypts during whole‐cell recording using nystatin‐permeabilized patches. This depolarization was concomitant with an increase in Cl‐ current as shown by anion substitution. In the absence of Cl‐ ions, the effect of the hypotonic medium was reversed into a hyperpolarization, which was associated with an increase in membrane outward (K+) current. The hyperpolarization was dependent on the presence of Ca2+ ions. It was blocked by TMB‐8 ((N,N‐diethylamino)‐octyl‐3,4,5‐trimethoxy‐benzoate hydrochloride; 10(‐5) mol l‐1), an inhibitor of intracellular Ca2+ release, but not by a Ca2+ channel blocker, verapamil (5 x 10(‐5) mol l‐1). Using butyrate as a stimulus for cell swelling, it was investigated whether swelling induces a conductance for an amino acid, glutamate. In the absence of Cl‐ ions, superfusion with butyrate induced a reversible depolarization when glutamate was present in the intracellular medium, and a reversible hyperpolarization when glutamate was present in the extracellular medium. This response was blocked by the lipoxygenase inhibitor, NDGA (nordihydroguaiaretic acid, 10(‐5) mol l‐1), and was markedly attenuated when glutamate was replaced by the poorly permeable anion, gluconate. Measurements of the membrane current during voltage clamping revealed a modest increase in membrane current carried by glutamate during cell swelling. These results demonstrate that the dominant effect of cell swelling in rat colonic crypts is an increase in Cl‐ conductance, a smaller increase in K+ conductance and a modest increase in conductance of amino acids, such as glutamate.
The effects of MM‐creatine kinase deficiency on sustained force production of mouse fast skeletal muscle
Authors: de Haan A , Koudijs JC , Wevers RA , Wieringa B
Published: December 2014

Twitch force production was normal in muscles of mice which lack MM‐creatine kinase, but the tetanic force:twitch force ratio was lower than in control muscles (3.60 vs 4.27; P < 0.05). In a series of repeated tetanic contractions the force in the second contraction was already markedly depressed (20–50%), while subsequently only small changes were observed. The effect was greater in exercise that would require a higher metabolic peak flux. The depressed force production was not accompanied by a slowing of relaxation, indicating that enough ATP was present to sustain myofibrillar ATPase and Ca(2+)‐ATPase activity.
Muscle cell function during prolonged activity: cellular mechanisms of fatigue
Authors: Allen DG , Lannergren J , Westerblad H
Published: December 2014

Muscle performance declines during prolonged and intense activity; important components are a reduction in force production and shortening velocity and a prolongation of relaxation. In this review we consider how the changes in metabolites (particularly H+, inorganic phosphate (Pi), ATP and ADP) and changes in sarcoplasmic reticulum Ca2+ release lead to the observed changes in force, shortening velocity and relaxation. The reduced force is caused by a combination of reduced maximum force‐generating capacity, reduced myofibrillar Ca2+ sensitivity and reduced Ca2+ release. The reduced maximum force and Ca2+ sensitivity are largely explained by the effects of H+ and Pi that have been observed in skinned fibres. At least three different forms of reduced Ca2+ release can be recognized but the mechanisms involved are incompletely understood. The reduced shortening velocity can be partly explained by the effects of H+ that have been observed in skinned fibres. In addition it is proposed that ADP, which depresses shortening velocity, increases during contractions to a level that is considerably higher than existing measurements suggest. Changes in Ca2+ release are probably unimportant for the reduced shortening velocity. The prolongation of relaxation can arise both from slowing of the rate of decline of myoplasmic calcium concentration and from slowing of cross‐bridge detachment rates. A method of analysis which separates these components is described. The increase in H+ and the other metabolite changes during fatigue can independently affect both components. Finally we show that reduced force, shortening velocity and slowed relaxation all contribute to the decline in muscle performance during a working cycle in which the muscle first shortens actively and then is stretched passively by an antagonist muscle.
The secretion of parathyroid hormone‐related protein in the saliva of sheep and its effects on the salivary clearance of phosphate, calcium, magnesium, potassium and sodium ions
Authors: Dua K , Abbas SK , Care AD
Published: December 2014

Parathyroid hormone‐related protein (PTHrP(1–34)) was infused into five sheep, each fitted with a large rumen cannula. After infusion, significant increases were observed in the total and ionized calcium concentrations in plasma but not in saliva. In contrast, significant decreases in the plasma concentrations of phosphate and potassium and corresponding increases in their salivary concentrations and clearance rates were observed. The salivary concentration of endogenous PTH1P(1–34) was significantly greater than that in plasma sampled simultaneously, but during the infusion of PTHrP(1–34) both plasma and salivary concentrations of PTHrP(1–34) increased.
Insulin stimulates cationic amino acid transport activity in the isolated perfused rat pancreas
Authors: Munoz M , Sweiry JH , Mann GE
Published: December 2014

The effects of exogenous insulin, glucagon and streptozotocin‐diabetes on influx (15 s) of L‐lysine via a cationic amino acid transporter resembling system y+ were investigated in the isolated perfused rat pancreas. In non‐diabetic pancreata, transport of L‐lysine was saturable with an apparent Km of 2.11 +/‐ 0.29 mM and Vmax of 2.21 +/‐ 0.20 mumol min‐1 g‐1 (n = 6). Bovine insulin (100 mu u ml‐1) increased the maximal transport rate (Vmax = 3.49 +/‐ 0.30 mumol min‐1 g‐1, n = 4, P < 0.05) for L‐lysine 1.6‐fold without altering the Km. L‐Lysine transport was not elevated significantly in diabetic pancreata, although insulin (100 mu u ml‐1) enhanced transport to values measured in non‐diabetic preparations. Human glucagon (1.5 x 10(‐9) M) had no stimulatory effect on L‐lysine transport. These findings provide the first evidence that exogenous insulin stimulates cationic amino acid transport activity in the exocrine pancreatic epithelium. Activation of the cationic pancreatic amino acid transporter may provide a mechanism to enhance the supply of L‐arginine and thus sustain nitric oxide‐mediated pancreatic secretion in response to islet hormones and secretagogues.
Hypoxic and metabolic regulation of voltage‐gated K+ channels in rat pulmonary artery smooth muscle cells
Authors: Yuan XJ , Tod ML , Rubin LJ , Blaustein MP
Published: December 2014

Inhibition of voltage‐gated K+ (Kv) channels by 4‐aminopyridine (4‐AP) depolarizes pulmonary artery (PA) smooth muscle cells, induces Ca(2+)‐dependent action potentials and increases [Ca2+]i. Neither charybdotoxin, which blocks Ca(2+)‐activated K+ channels, nor glibenclamide, which blocks ATP‐sensitive K+ channels, has such effects on membrane potential (Em) and [Ca2+]i. Hypoxia reversibly decreases the 4‐AP‐sensitive KV currents (IK(V)) in PA myocytes. The resulting membrane depolarization caused by decreased IK(V) induces Ca(2+)‐dependent action potentials and thereby raises [Ca2+]i. Thus, KV channel activity plays a critical role in: (a) regulating Em and [Ca2+]i under physiological conditions; and (b) sensing O2 alteration and transducing the hypoxic stimulus to changes of Em and [Ca2+]i. The metabolic inhibitors 2‐deoxy‐D‐glucose (2‐DOG; 10 mM) and carbonyl cyanide‐p‐trifluoromethoxyphenyl‐hydrazone (FCCP; 3‐5 microM), the reducing agent reduced glutathione and inhibitors of cytochrome P‐450, all mimic the effects of hypoxia on IK(V) and Em in PA myocytes. Furthermore, hypoxia and 2‐DOG negligibly affect IK(V) and Em in mesenteric artery smooth muscle cells. These results suggest that hypoxia, perhaps via a localized reduction of ATP, triggers the block of KV channels and depolarizes PA myocytes. This blockade may also be mediated by a change in cellular redox status, perhaps via a conformational change of a haem‐ (or metal‐) containing regulatory moiety that is attached to the channel protein.
The role of nitric oxide in the control of protein secretion in the submandibular gland of the cat
Authors: Buckle AD , Parker SJ , Bloom SR , Edwards AV
Published: December 2014

Submandibular salivary responses to stimulation of the parasympathetic chorda lingual innervation have been investigated in anaesthetized cats in the presence and absence of N omega‐arginine‐L‐methyl ester (L‐NAME) to block the synthesis of nitric oxide. Stimulation either at 2 Hz continuously or at 20 Hz for 1 s at 10 s intervals produced an abrupt fall in submandibular vascular resistance and initiated a flow of submandibular saliva. Neither of these responses differed significantly from the other but the output of protein was significantly potentiated (P < 0.05) when the high‐frequency intermittent pattern of stimulation was employed. This potentiation of protein output was abolished in the presence of L‐NAME, when the output of protein from the gland was closely similar, whichever pattern of stimulation was employed. Additional administration of atropine completely blocked all submandibular responses to parasympathetic stimulation showing that, in the presence of L‐NAME, each response was due to release of acetylcholine acting on muscarinic receptors. The intermittent pattern of chorda lingual nerve stimulation produced a significant rise in the output of vasoactive intestinal peptide (VIP) from the gland (P < 0.01) and this response was significantly reduced following administration of L‐NAME (P < 0.05). The results are consistent with the contention that stimulation of the parasympathetic innervation in bursts, which increases the amount of VIP released from the postganglionic nerve terminals, enhances the output of protein in submandibular saliva in the cat. The mechanism involves nitric oxide (NO), which may act, at least in part, presynaptically by modulating VIP release.
Rat pancreas after long‐term treatment with the somatostatin analogue octreotide
Authors: von Schonfeld J , Meisse F , Muller MK
Published: December 2014

Somatostatin is a potent inhibitor of endocrine and exocrine pancreatic secretion. However, it is not clear whether it also inhibits pancreatic growth. Therefore we treated male Wistar rats with a somatostatin analogue, octreotide (12‐192 micrograms/(kg body wt.day)), over a period of 14 days. In a dose‐dependent manner, this potent and long‐acting analogue caused a reduction in weight of the pancreas and a reduction in pancreatic content of protein, DNA, trypsin, chymotrypsin, amylase and lipase, as well as pancreatic content of insulin‐, glucagon‐ and somatostatin‐like immunoreactivities. When growth of rat pancreas was induced by oral administration of camostate (200 mg/(kg body wt. day) or by subcutaneous administration of cholecystokinin (2 x 10 micrograms/(kg body wt. day)) over a period of 14 days, octreotide (12‐192 micrograms/(kg body wt.day)) had the same effects, but these were even more pronounced. We conclude that somatostatin is an important regulator of pancreatic growth.
Electrophysiological and ultrastructural events evoked by methacholine and intracellular photolysis of caged compounds in cultured ovine trachea submucosal gland cells
Authors: Griffin A , Newman TM , Scott RH
Published: December 2014

Cultured ovine trachea submucosal gland cells release lysozyme in response to extracellular application of secretagogues, including the muscarinic receptor agonist methacholine (20 microM). Investigation of the ultrastructure has shown that these cells contain electron‐dense cored granules, which differ from the intact tissue, but appear to be released in response to the application of methacholine and can be arrested during exocytosis by the application of tannic acid. The release process appears to be linked to electrophysiological events activated by methacholine. Extracellular application of methacholine and intracellular photorelease of Ca2+ from DM‐nitrophen evoked similar events suggesting that a rise in intracellular Ca2+ may occur following muscarinic receptor activation. Measurements of the reversal potential and the inhibitory action of the chloride channel blocker niflumic acid (10 microM) indicated that Ca(2+)‐activated Cl‐ channel activity underlies these events. Some of the cultured submucosal gland cells also responded similarly to intracellular photorelease of inositol 1,4,5‐trisphosphate, suggesting a possible link between muscarinic receptor occupation by agonist, release of calcium from stores, and activation of Ca(2+)‐activated Cl‐ current. Secretion of lysozyme, methacholine‐activated currents and currents evoked by intracellular photorelease of Ca2+ were also attenuated by the potent bronchodilator Ro 31‐6930 (1 microM). We conclude that Ca(2+)‐activated Cl‐ conductances play an important role in secretory processes in cultured submucosal gland cells. This may have a bearing on both physiological control of secretory events and regulation of the nature of airway surface liquid. Ca(2+)‐activated Cl‐ channels may offer a potential target site for novel therapeutic agents.
The role of reflex activity in the regulation of muscle tone in rats
Authors: Ossowska K , Lorenc-Koci E , Schulze G , Konieczny J , Wolfarth S , Bojarski M , Coper H
Published: December 2014

The aim of the study was to assess the contribution of reflex activity to the regulation of muscle tone in rats. The experiment was carried out on young Wistar male and female rats. The hindfoot of a rat was flexed or extended at the ankle joint by 25 deg over 250 ms. The resistance of the foot to passive movements, as well as the electromyographic (EMG) activity in the gastrocnemius and the tibialis anterior muscles, were recorded simultaneously. During passive movements, reflex EMG activity developed simultaneously in both antagonistic muscles of the foot. Three components were distinguished: a short‐latency EMG‐A (within the first 0‐20 ms of a movement), long‐latency EMG‐B (within 60‐160 ms), and EMG‐C (within 220‐340 ms). When the amplitudes of EMG‐B and EMG‐C components of the gastrocnemius muscle reflex response were greater than 50 microV, a significant correlation was found between them and the maximum resistance of the hindfoot (MMGmax) during flexion, whereas no such correlation was observed for the tibialis anterior muscle. No correlation was found when the amplitudes of the log‐latency components of the gastrocnemius muscle were less than 50 microV. Moreover, no correlation was observed between the EMG‐A and the MMG(max). The above results suggest that: (1) the muscle tone of the gastrocnemius muscle in rats seems to be regulated by long‐latency (supraspinal) reflexes only when the level of EMG activity exceeds a critical threshold of ca 50 microV; (2) when the level of EMG activity is lower, a major role in the resistance of hindlimb muscles is played by some non‐neuronal factors; and (3) the proposed animal model emphasizes new aspects of the reflex which may be useful in a search for basic mechanisms underlying changes in the muscle tone.
Natriuresis caused by blood volume expansion in dogs is not mediated by the renal nerves
Authors: Drake‐Holland AJ , Song G , Belcher PR , Noble MI
Published: December 2014

The influence of renal denervation on the renal response to rapid blood volume expansion was investigated by measurement of urine volume, sodium and osmolar excretion rates, sodium p‐aminohippurate and free water clearances, and systemic haemodynamic and plasma hormone (atrial natriuretic peptide, arginine vasopressin and plasma renin activity (PRA)) changes in ten control and ten renal‐denervated chloralose‐anaesthetized mongrel dogs. Following renal denervation, blood volume expansion caused a similar increase in sodium excretion to that in the control group. Renal denervation resulted in systemic vasodilatation and decreased PRA. During fluid loading the right atrial pressure and pulmonary capillary wedge pressure were significantly higher in the control group. In the control group, volume expansion caused a large fall in PRA, whereas in the renal‐denervated dogs, PRA remained suppressed. We conclude, from the fact that natriuresis is preserved after renal denervation, that this response is not mediated by a reflex with efferent limb in the renal nerves.