bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of Ca2+ release in rat atrophied gastrocnemius muscle
Authors: Rassier DE , Tubman LA , MacIntosh BR
Published: December 2014

Contractile parameters of a twitch contraction and changes in these parameters during repetitive stimulation are modified by muscle atrophy induced by tetrodotoxin (TTX). These altered parameters included developed tension (DT), contraction time (tC), half‐relaxation time (tR, 1/2), average rate of force development (DT tC‐1) and peak rate of relaxation (DTdtmin‐1). These modifications may be related to different Ca2+ concentration transients in the myoplasm during muscle stimulation. We have used dantrolene sodium (DS) in TTX‐treated rat gastrocnemius muscle to test this hypothesis. In situ isometric contractile responses of rat gastrocnemius muscle during repetitive stimulation at 10 Hz were analysed before and after administration of DS. After DS administration, twitch amplitude, tC, tR, 1/2 and DT tC‐1 decreased and DTdtmin‐1 relative to DT increased in atrophied muscle. During repetitive stimulation, a progressive enhancement developed tension (staircase) was absent in atrophied muscle, but DT increased to 171 +/ࢤ 4%, presenting a staircase response after DS treatment. This potentiation was accompanied by an increase in DT tC‐1 to 175.6 +/ࢤ 7%. Inhibition of Ca2+ release in atrophied muscle resulted in twitch contractile parameters and contractile responses to 10 Hz stimulation that were similar, in many respects, to those responses in control (non‐atrophied) muscles.
Hyperbaric‐induced enhancement of noradrenaline‐evoked contraction in rat thoracic aorta
Authors: Guerrero F , Lucciano M , Joanny P , Jammes Y
Published: December 2014

The aim of this study was to investigate the effects of a high ambient pressure of He on vascular contraction induced by noradrenaline and to distinguish the effects of ambient pressure per se from those of increased pressure of inert gas. Rings of thoracic aorta were isolated from male Wistar rats. Isometric tension was measured in preparations exposed to 7.1 MPa (absolute pressure) of He. Dose‐response curves for noradrenaline and contractions elicited by 120 mM KCl were compared with time‐matched experiments performed at atmospheric pressure. The same protocol was also carried out under 7.1 MPa of N2. At the high pressure of He, the contraction elicited by noradrenaline was increased with no change in the response to K(+)ࢤevoked depolarization. The tension developed in response to noradrenaline also increased under 7.1 MPa of N2 but the effects were less marked than during the He experiments. Moreover, the response to KCl was reduced in this circumstance. Hyperbaric conditions enhance the noradrenaline‐induced contraction of rat aorta in vitro. This effect probably results from an action of pressure per se on activation of adrenoceptors. However, the hyperbaric‐induced increase in vascular smooth muscle contraction is partially counteracted by high pressures of inert gases (N2, but also probably He), which impair the efficiency of the contractile machinery.
Secretory interactions between the sympathetic and parasympathetic innervations of the submandibular gland in the anaesthetized cat
Authors: Edwards AV , Garrett  , Proctor GB
Published: December 2014

Interactions between the sympathetic and parasympathetic innervations of the submandibular gland have been investigated in the anaesthetized cat. At low frequencies of chorda lingual (parasympathetic) stimulation, simultaneous stimulation of the ascending cervical sympathetic nerve in bursts (20 Hz for 1 s at 10 s intervals) increased the flow of submandibular saliva, but the effect was never more than additive. The output of protein was consistently reduced by simultaneous stimulation of both the sympathetic and parasympathetic innervations, below that evoked by stimulation of either alone. Sympathetic stimulation was more effective than parasympathetic stimulation in promoting the secretion of tissue kallikrein and peroxidase in the submandibular saliva. The output of the latter enzyme, in response to sympathetic stimulation, was significantly reduced by simultaneous stimulation of the parasympathetic innervation at frequencies greater than 1 Hz, but nevertheless exceeded the amount secreted during chorda stimulation alone. Thus, this protocol provided no evidence of synergy between the two divisions of the autonomic nervous system with respect to any submandibular secretory function that was recorded. However, following the administration of a small dose of atropine (2‐15 micrograms kg‐1 i.v.), sufficient to block secretion during chorda stimulation alone, the flow of saliva, in response to sympathetic stimulation, was potentiated when superimposed on a background of parasympathetic stimulation at all frequencies that were employed. This effect was abolished by larger doses of atropine, indicating that it was dependent upon activation of muscarinic receptors, only some of which could have been blocked by the initial dose.
An investigation into the relative merits of pituitary adenylate cyclase‐activating polypeptide (PACAP‐27) and vasoactive intestinal polypeptide as vagal neuro‐transmitters in exocrine pancreas of rats
Authors: Wheeler S , Eardley JE , McNulty KF , Sutcliffe CP , Morrison JD
Published: December 2014

Pancreatic exocrine secretions were collected over 15 min periods and analysed in terms of weight of juice, total HCO3‐ and total protein in anaesthetized and pithed rats. Pituitary adenylate cyclase‐activating polypeptide (PACAP) (i.v.) evoked a serous HCO3‐ secretion which contained relatively little protein, together with a marked vasodepressor action. The latter was still maximal at lower doses of PACAP, which evoked diminished pancreatic secretions. The effects of PACAP were similar to those evoked by the same dose of VIP and by cervical vagal stimulation, while secretion evoked a much larger secretion of fluid and HCO3‐. The time courses of the PACAP‐evoked secretions were significantly delayed compared with those of VIP. In the pithed rat, PACAP caused the same level of pancreatic secretions as in the anaesthetized rat, though this was now accompanied by a substantial pressor response which was blocked by phentolamine or prazosin, indicating that it was alpha 1‐adrenoceptor mediated. VIP caused a depressor response in the pithed rat, as well as the same level of pancreatic secretions as in the anaesthetized rat. The putative VIP antagonist [Lys1,Pro25,Arg3,4,Tyr6]‐VIP (abbreviated as VIPi) caused a selective and significant reduction in the HCO3‐ secretion evoked by VIP and blocked the vasodepressor response caused by VIP. By contrast, VIPi did not antagonize either the secretory or vasodepressor actions of PACAP. Unilateral electrical stimulation of the cervical vagus nerve evoked significant increases in the weight of juice, total protein and total HCO3‐ secreted. When preceded by injection of VIPi, vagally evoked secretions were unchanged in terms of weight of juice and total protein but had a significantly reduced HCO3‐ content. These results are consistent with the release of VIP, though not PACAP, as a vagal neurotransmitter in the exocrine pancreas.
Changes in the maternal and fetal renin‐angiotensin systems in response to angiotensin II type 1 receptor blockade and angiotensin‐converting enzyme inhibition in pregnant sheep during late gestation
Authors: Forhead AJ , Pipkin FB , Sutherland MF , Fowden AL
Published: December 2014

The effects of maternal administration of either an angiotensin II type 1 (AT1) receptor antagonist (GR138950) or an angiotensin‐converting enzyme (ACE) inhibitor (captopril) on the renin‐angiotensin system (RAS) were investigated in chronically catheterized ewes and their fetuses during late gestation. From 127 +/ࢤ 1 days of gestation until parturition at 145 +/ࢤ 2 days, each ewe received daily i.v. injections of GR138950 (3 mg kg‐1, n = 10 animals) or captopril (3 mg kg‐1, n = 6) or an equivalent volume of vehicle solution (0.9% NaCl, n = 10). On the first day of treatment, plasma renin concentrations in the pregnant ewe increased within 2 h of administration of either GR138950 (median change followed by lower and upper quartiles (25%, 75%): +38.3 ng ml‐1 h‐1 (15.6, 80.7); P < 0.05) or captopril (+22.1 ng ml‐1 h‐1 (19.2, 28.8); P < 0.05). Maternal plasma concentrations of angiotensin II (AII) also increased by 871 pg ml‐1 (555, 1340; P < 0.05) in the GR138950‐treated ewes. In the fetuses of both groups of drug‐treated animals, an increase in plasma renin concentration was observed within 2 h of maternal treatment with either GR138950 (+11.6 ng ml‐1 h‐1 (1.2, 18.6); P < 0.05) or captopril (+59.3 ng ml‐1 h‐1 (41.7, 74.6); P < 0.05). These short‐term changes in circulating renin and AII concentrations observed in the pregnant ewe were sustained after 1 week of GR138950 administration. In addition, 1 week of GR138950 treatment decreased plasma angiotensinogen (Ao) concentrations in both the ewe (‐0.36 microgram ml‐1 (‐0.58, ‐0.16); P < 0.05) and the fetus (‐0.43 microgram ml‐1 (‐0.59, ‐0.09); P < 0.05). A long‐term reduction in maternal plasma AII, and an increase in fetal plasma renin concentration, were associated with 1 week of captopril administration. Neither drug had any consistent effect on plasma ACTH or cortisol concentrations in the pregnant ewe or fetus. These findings show that, during ovine pregnancy, antagonism of maternal AII activity, either by blockade of the AT1 receptor or by inhibition of AII synthesis, induces changes in the circulating components of the RAS in the mother and fetus. In both the pregnant ewe and fetus, the RAS is shown to be activated by suppression of AII activity.
Effects of 8h of eucapnic and poikilocapnic hypoxia on middle cerebral artery velocity and heart rate in humans
Authors: Clar C , Pedersen ME , Poulin MJ , Tansley JG , Robbins PA
Published: December 2014

This study examines the effects of prolonged hypoxia, with and without control of end‐tidal CO2 partial pressure (PET,CO2), on the intensity‐weighted mean velocity of blood flow in the middle cerebral artery (VIWM) and on heart rate (HR). Specifically, the time course of the responses, their reversibility with brief periods of hyperoxia and the recovery phase following prolonged hypoxia were all investigated. Twelve subjects were studied, of whom nine provided satisfactory data. A purpose‐built chamber was used for the prolonged control of the end‐tidal gases, and an end‐tidal forcing system was used for generating the brief variations in end‐tidal gases. Three 16 h protocols were employed: (1) 8 h eucapnic (average PET,CO2 = 39 mmHg) hypoxia (end‐tidal O2 partial pressure, PET,O2 = 55 mmHg) followed by 8 h eucapnic euoxia (PET,O2 = 100 mmHg); (2) 8 h poikilocapnic (average PET,CO2 4 mmHg below eucapnia) hypoxia (PET,O2 = 55 mmHg) followed by 8 h poikilocapnic euoxia (PET,O2 = 100 mmHg); and (3) control (air inspired throughout). VIWM (using Doppler ultrasound) and HR were measured during brief exposures to hypoxic/euoxic and hyperoxic conditions with PET,CO2 held 1‐2 mmHg above eucapnia, at 0, 20, 240 and 480 min in the first 8 h, and at the same times in the second 8 h. There were no significant trends in VIWM under hypoxic conditions for either hypoxic protocol (ANOVA) and no significant differences between the three protocols for VIWM in hyperoxia (ANOVA). In contrast to VIWM, there was a significant increase in HR over time during both hypoxic exposures (P < 0.01, ANOVA). HR increased to a similar extent for the two types of hypoxia, and there was some suggestion that HR remained elevated after the relief of hypoxia. The results suggest that, with the level of hypoxia employed, progressive changes in HR occur, but that this level and duration of hypoxia has little sustained effect on VIWM.
Reversal of fusimotor reflex responses during locomotion in the decerebrate cat
Authors: Murphy PR , Hammond GR
Published: December 2014

The effect of brief trains of electrical stimulation, at 2, 3 and 20 x threshold (T), of cutaneous afferents in the medial plantar nerve on the discharges of single medial gastrocnemius static and dynamic gamma‐efferents has been investigated at rest and during locomotion in a decerebrate cat preparation. The units were classified as dynamic (10 units) or static (10 units) indirectly on the basis of their resting and locomotor discharge characteristics. Responses were assessed by calculating the change in mean gamma‐rate during the 100 ms after stimulus onset compared with a control period. At rest, most dynamic neurones were inhibited by stimulation at 2T (9 of 10 units) and above. In contrast, the resting responses of most static neurones were excitatory at 2T (9 of 10 units) and 3T, while 20T produced static gamma‐effects that varied in sign. During locomotion the responses of both types of gamma‐efferent were phase related. Two patterns were observed with dynamic units. For seven dynamic neurones, at stimulus levels of 2T (7 units) and above, responses during electromyogram (EMG) bursts were inhibitory while those between bursts were not significantly different from zero. However, for three other dynamic units, a phase‐related reversal of reflex responses was observed at some stimulus intensities (always 2T, 3 units) comprising inhibition during, and excitation between, EMG bursts. For static neurones, inhibitory (never excitatory) responses occurred during walking at stimulus intensities of 2T (10 units) and above. The locomotor responses of static units were maximum during (3 units) or between (7 units) EMG bursts and were minimum in the opposite phase of EMG activity. A task‐related reversal of reflex responses was thus generally apparent (9 of 10 units) to low intensity stimulation (2T) for static gamma‐efferents during locomotion (inhibition) compared with rest (excitation). During locomotion there was a significant linear relation between the magnitude of response and the background gamma‐rate for static units and those dynamic units that did not exhibit phase‐related reflex reversal (total, 17 units). For dynamic gamma‐efferents, inhibition at rest and during locomotion occurred at short (spinal) latencies which were not significantly different and are consistent with the involvement of the same interneuronal pathway. We conclude that pathways of opposite sign may dominate the responses of fusimotor neurones to low threshold cutaneous afferents from the plantar surface of the foot depending on behavioural context. Furthermore, the cutaneous reflex responses of both types of gamma‐motoneurones during locomotion appear to vary with the source of the afferent input and do not constitute a general excitatory drive. The results are discussed in relation to the role and reflex control of the fusimotor system.
Glomerular haemodynamics during renal artery clamping and haemorrhage in the dog
Authors: Heller J , Horacek V
Published: December 2014

The influence of gradual decline in renal perfusion pressure (RPP) due either to renal artery clamping (C) or to haemorrhagic hypotension (HH) was studied using micropuncture techniques in anaesthetized dogs. The decrease in renal blood flow (RBF) was more profound and set in earlier during HH than during C, where perfect autoregulation was observed down to a mean arterial blood pressure of 85 mmHg. Glomerular filtration rate (GFR) was also only slightly decreased during C, with no change in filtration fraction (FF); again, a much greater decrease in GFR with an increase in FF was seen in HH. The excretion of water, electrolytes and urea were also more decreased during HH than during C. Similar changes were seen at the single nephron (SN) level. Opposite changes were observed in arteriolar resistances: during C a decrease in total arteriolar resistance (RT) amounting to ‐22% at a RPP of 84 mmHg and ‐13% at 60 mmHg was seen, due exclusively to a drop in afferent resistance (RA), but during HH there was a significant increase in RT by +36% at RPP of 110 mmHg, +39% at 85 mmHg and +68% at 60 mmHg. This increase was mainly due to an increase in efferent resistance (RE) rather than in RA: +42 vs. +31%, respectively, at 110 mmHg and +67 vs +19% respectively, at 85 mmHg. It was not until a RPP of 60 mmHg was reached that this difference between RE and RA disappeared, being +67% for RE and +69% for RA. The ultrafiltration coefficient, Kf, did not change during C and only decreased slightly with the biggest drop in RPP during HH (2.84 microliters mmHg‐1 min‐1 during HH vs. 4.19 microliters mmHg‐1 min‐1 before HH). The SNGFR/GFR ratio remained unchanged during C but declined with decreasing RPP during HH, which probably indicates a 'redistribution' of RBF to the deeper regions of the renal cortex. In conclusion, major differences in renal function were observed between C and HH whose cause is unknown.
Adipose tissue development during early postnatal life in ewe‐reared lambs
Authors: Clarke L , Buss DS , Juniper DT , Lomax MA , Symonds ME
Published: December 2014

This study examines the precise time course that brown adipose tissue (BAT) takes to adopt the characteristics of white adipose tissue in postnatal lambs. Perirenal adipose tissue was sampled from ewe‐reared lambs within 1 h of birth and at 1, 2, 4, 7, 14, 21 and 30 days of age and analysed for the amount of mRNA for uncoupling protein (UCP), the amount and activity of UCP, and protein, mitochondrial protein and lipid content. This was combined with measurements of colonic temperature and jugular venous plasma concentrations of thyroid hormones and insulin‐like growth factor‐1 (IGF‐1). Over the first 4‐7 days of age, large quantities of UCP mRNA were associated with a peak in plasma triiodothyronine concentration at 2 days of age followed by a maximal amount and activity of UCP at 4 days and a basal colonic temperature of 39.3 degrees C. Between 7 and 30 days there was a large increase in lipid deposition as the amount and activity of UCP and the amount of UCP mRNA declined to basal values and colonic temperature was maintained at 40 degrees C. A significant positive relationship between perirenal adipose tissue lipid content and plasma IGF‐1 concentration was observed throughout the study period. It is concluded that ovine adipose tissue maturation occurs in two distinct phases over the first month of life. The precise time scale of this process could be regulated in part by the lamb's body temperature which determines whether adipose tissue is required for heat production (i.e. BAT) or as an endogenous energy source (i.e. white adipose tissue).
The effect of sodium citrate ingestion on the metabolic response to intense exercise following diet manipulation in man
Authors: Ball D , Maughan RJ
Published: December 2014

Feeding a high‐carbohydrate (CHO) diet and administration of alkalinizing agents have both been shown to improve performance in high‐intensity exercise. The effect of these treatments in combination was investigated in the present study. Six healthy male subjects exercised to exhaustion on an electrically braked cycle ergometer at a power output equivalent to 100% of their maximum oxygen uptake (VO2,max) on four separate occasions. Each subject consumed either a diet with the same composition as his normal diet (termed the experimental normal (N) diet; 54 +/ࢤ 7% CHO, 13 +/ࢤ 2% protein, 33 +/ࢤ 7% fat) or a high‐CHO diet (81 +/ࢤ 2% CHO, 13 +/ࢤ 2% protein, 6 +/ࢤ 1% fat) that had the same energy and protein content for the 3 days prior to the exercise tests. Subjects then ingested either a placebo (CaCO3) or trisodium citrate (0.3 g (kg body mass)‐1) 3 h before exercise. Time to fatigue was not different between experimental conditions. Consumption of the high‐CHO diet had no effect on blood acid‐base status, but the ingestion of sodium citrate induced a mild metabolic alkalosis after both the N diet and the high‐CHO diet. This alkalinizing effect was also evident after exercise, since blood pH, plasma bicarbonate and blood base excess were higher (P < 0.05) after the ingestion of sodium citrate than under the placebo conditions. The changes in blood lactate, pyruvate and glucose and plasma glycerol after exercise were similar for all experimental conditions. Blood lactate, glucose and pyruvate and plasma glycerol concentrations increased from resting values (P < 0.01) following exercise but this increase was similar under all experimental conditions. These data demonstrate that when the energy and protein content of the diets is the same, exercise capacity and the metabolic response to intense exercise are similar following consumption either of a high‐CHO diet or a more normal diet. Acute ingestion of sodium citrate prior to exercise resulted in a reduction in post‐exercise acidosis despite a blood lactate concentration that was similar to that observed after the ingestion of a placebo, but did not affect exercise performance under the conditions of this study.
Modulation of Ca2+ and K+ permeabilities by oxotremorine‐m (Oxo‐m) in rodent pancreatic B‐cells
Authors: Bordin S , Carneiro EM , Boschero AC
Published: December 2014

The effects of the muscarinic agonist oxotremorine‐m (Oxo‐m) on 45Ca and 86Rb fluxes, insulin secretion, cytoplasmic Ca2+ concentration ([Ca2+]i) and membrane potential in pancreatic B‐cells were studied. Oxo‐m (40–200 microM) increased the [Ca2+]i by about 250 nM, irrespective of the glucose concentration present in the medium (2.8–22 mM). This effect was reduced by 50% upon the addition of EGTA. Oxo‐m (50 microM) increased the 45Ca efflux from islets perifused in the absence or presence of [Ca2+]o, although under the former condition this efflux was transient. The difference between effluxes measured in the absence and presence of [Ca2+]o represents the sustained second component, which presumably reflects Ca2+ influx. In both the absence and presence of 11.2 mM glucose. Oxo‐m (50 microM) transiently increased 86Rb efflux. In the presence of glucose, Oxo‐m provoked a transient polarization of the B‐cell membrane associated with an increase in the K+ permeability values. K+ permeability returned to basal values (no Oxo‐m) after 1–2 min. These results indicate that the initial phase of Oxo‐m‐induced insulin secretion depends partially on intracellular Ca2+ release, and that the sustained enhancement of release depends on Ca2+ influx. The participation of a calcium release‐activated current (ICRAC) is proposed to explain the sustained small changes in membrane potential.
Influence of cerebral blood flow on the ventilatory response to hypoxia in humans
Authors: Poulin MJ , Robbins PA
Published: December 2014

The purpose of this study was to quantify the possible reduction in ventilation that could be attributed to changes in cerebral blood flow (CBF) with hypoxia to determine whether it could be of sufficient magnitude to underlie hypoxic ventilatory decline (HVD). Six subjects underwent 20 min of isocapnic hypoxia (end‐tidal PO2, 50 mmHg). An index of CBF was obtained using transcranial Doppler ultrasound of the middle cerebral artery. The CBF sensitivities to hypoxia and hypercapnia were obtained from the percentage changes in CBF between the last 3 min of the hypoxic or hypercapnic exposure and the 3 min period prior to the exposure. The magnitude of HVD during hypoxia was estimated by fitting a simple model of the ventilatory response to the hypoxic stimulus. The predicted fall in expiratory ventilation (VE) due to a reduction in brain PCO2 generated by the increase in CBF with hypoxia in all subjects was less than the measured magnitude of HVD (33%). Thus, the results from this study suggest that, in awake humans, changes in CBF during acute isocapnic hypoxia are quantitatively insufficient to underlie HVD in humans.
Effects of short chain fatty acids and carbon dioxide on magnesium transport across sheep rumen epithelium
Authors: Leonhard-Marek S , Gabel G , Martens H
Published: December 2014

Short chain fatty acids (SCFAs) and CO2 have been shown to stimulate net Mg2+ efflux from the isolated reticulorumen in vivo. To investigate the underlying mechanisms of Mg2+ transport we performed Ussing chamber and microelectrode experiments and measured 28Mg2+ fluxes across sheep rumen epithelium in vitro. In the presence of SCFAs mucosal‐to‐serosal Mg2+ flux (Jm‐sMg) amounted to 82.3 +/− 7.8 nmol cm‐2 h‐1 and serosal‐to‐mucosal Mg2+ flux (Js‐mMg) to 3.2 +/− 0.7 nmol cm‐2 h‐1. Replacing SCFAs with gluconate caused a 50% reduction of Jm‐sMg, whereas Js‐mMg was not affected. Among the SCFAs, n‐butyrate was more effective in stimulating Jm‐sMg than acetate, propionate or iso‐butyrate. Eliminating HCO3(‐)‐CO2 from SCFA‐containing solutions did not affect Mg2+ fluxes, whereas the same replacement in SCFA‐free solutions led to a further reduction in Jm‐sMg. Jm‐sMg decreased after the addition of ethoxyzolamide to SCFA‐free, bicarbonate buffered solutions. Decreasing mucosal pH from 6.4 to 5.4 increased Jm‐sMg in SCFA‐free, bicarbonate buffered solutions. SCFAs had no effect on the apical membrane potential of rumen epithelial cells. The experiments show that both SCFAs and CO2 stimulate Mg2+ transport through an increase in Jm‐sMg, most probably via stimulation of a Mg(2+)‐2H+ exchange mechanism. SCFAs may have additional metabolic effects on Mg2+ transport.
The relation between local cerebral blood flow and extracellular glucose concentration in rat striatum
Authors: Fillenz M , Lowry JP
Published: December 2014

The effect of anaesthetics on the relation between local cerebral blood flow (rCBF) and extracellular glucose was studied in rat striatum. Cerebral blood flow was measured using the hydrogen clearance method and extracellular glucose using an implanted glucose oxidase‐based biosensor. Rats were given an intraperitoneal (i.p.) injection of either sodium pentobarbitone (60 mg kg‐1) or chloral hydrate (350 mg kg‐1). The effect of the i.p. injection, as demonstrated by an i.p. saline injection, was a brief increase in rCBF accompanied by a decrease in glucose. Sodium pentobarbitone produced a decrease in both rCBF and glucose, whereas chloral hydrate caused a decrease in glucose but an increase in rCBF. These findings show a dissociation between rCBF and extracellular glucose and suggest that glucose in the extracellular compartment is not derived directly from the blood vascular compartment.
Glucose transport inhibitors protect against 1,2‐cyclohexanedione‐produced potassium loss from human red blood cells
Authors: Baker GF , O'Gorman R , Baker P
Published: December 2014

It has been suggested that the glucose transport system of human erythrocytes contains an arginine shield to prevent the leak of potassium through the transporter. To investigate this suggestion we treated human erythrocytes with the specific arginine reagent 1,2‐cyclohexanedione. Under conditions which produce a covalent reaction between arginine and the reagent, a steady leak of potassium occurs. If glucose, maltose or the inhibitor phloretin are present during the reaction the extent of the leak is reduced. These findings support the view that arginines have a role in preventing potassium loss through the glucose transporter.
Channelling free energy into work in biological processes
Authors: Krupka RM
Published: December 2014

The process by which free energy from ATP or an ion gradient is coupled to work‐‐either osmotic work, by a membrane pump, or mechanical work, by a molecular motor‐‐as well as the development of force by a molecular motor, can be explained by mechanisms dependent on substrate binding energy. Coupling involves a reaction sequence that combines the driving and driven reactions and that is controlled at switch points where the mobility of the coupling protein and its specificity in binding and catalysis can be abruptly altered; the altered state is an intermediate (or transition state) in the coupled reaction, the unaltered state an intermediate in the uncoupled reaction (slippage). The balance between these states, which is determined by the increase in substrate binding energy in the transformation, decides the relative importance of the coupled and uncoupled paths. On this basis a general expression for switching may be derived: the tightness of coupling is limited by a ratio of substrate dissociation constants before and after a controlling change in state: Rate(coupled)/Rate(uncoupled) < or = Kinitial state/Kfinal state. When binding energy is used in this way to distort the conformation of a protein, mechanical work is done; the work is internal but becomes external if the protein is connected to an external load. External work, force F multiplied by distance d, is then limited by a ratio of substrate dissociation constants before and after the conformational change: W = Fd < RT In(Kinitial state/Kfinal state). The ratios of dissociation constants, estimated from published values of the force exerted by molecular motors, are > 1 x 10(4) for myosin and > 2 x 10(4) for kinesin. From the tightness of coupling of the anion exchange carrier of red cells the ratio of constants for coupling is > or = 4 x 10(4). These increments can be accounted for by conversion of a surface complex to an enclosed complex, as in chelate formation. The work done by an ATP‐driven motor is limited by the free energy of ATP hydrolysis, but the force developed is independent of the ATP reaction, and comes from binding energy with either the driving or driven substrate.
Electrocholecystogram: a study of the electromechanical activity of the gall bladder in a canine model
Authors: Shafik A
Published: December 2014

To characterize an ‘electrocholecystogram’ (EChG) for the normal gall bladder (GB) that might act as a standard for the evaluation of pathological electrocholecystograms of the diseased GB, ten mongrel dogs (14.4+/−3.2 kg) were studied. Under anaesthesia, the abdomen was opened and three silver‐silver chloride electrodes were sutured to the GB serosa. The GB pressure was measured by a perfused catheter introduced through the fundus. The response of the myoelectrical activity of the GB to balloon distension was tested and the direction of electrical waves was defined by GB myotomies. Pacesetter potentials (PPs) were recorded exhibiting the same frequency, amplitude and velocity of conduction from the three electrodes of each dog on all test days. Action potentials (APs) followed the PPs randomly and were associated with a rise of the GB pressure. Balloon distension of the GB caused increased PP and AP frequency. The electrical waves showed proximally but not distally to GB myotomy, indicating that they propagate proximo‐distally towards the cystic duct. To conclude, the GB possesses electrical waves which are probably initiated from a ‘pacemaker’ at the GB fundus. A normal EChG could be characterized in the canine model. It is suggested that this EChG might show changes in gall bladder diseases and might thus act as an investigative tool, provided it can be developed to be performed percutaneously.
Measurement of nitric oxide concentration in human skin in vivo using dermal microdialysis
Authors: Clough GF , Bennett AR , Church MK
Published: December 2014

Using microdialysis, we measured nitric oxide (NO) levels in healthy human skin, in vivo, before and during the local inflammatory response to histamine. Basal dialysate NO concentration, assayed using an amperometric technique, was 0.49+/−0.06 microM (mean+/−S.E.M., 21 probes, 14 subjects). Histamine injection produced transient increases in NO concentration within both the weal and flare which was blocked by the NO synthase inhibitor, NG‐nitro‐L‐arginine‐methyl ester (L‐NAME). Dialysate NO concentration also increased following transdermal delivery of the nitrosovasodilator, glyceryl trinitrate. Thus, using microdialysis, it is possible to quantify NO production in human skin in vivo and study its modulation during the acute inflammatory response.
Intracellular Mg2+ regulation in voltage‐clamped Helix aspersa neurones measured with mag‐fura‐2 and Mg(2+)‐sensitive microelectrodes
Authors: Kennedy HJ
Published: December 2014

The extrusion mechanism for intracellular Mg2+ was investigated in voltage‐clamped snail neurones using Mg(2+)‐sensitive microelectrodes and mag‐fura‐2. The intracellular free magnesium ion concentration ([Mg2+]1) of snail neurones voltage clamped to ‐60 mV was estimated to be 0.57 +/− 0.06 mM (mean +/− S.E.M.; n = 12) using Mg(2+)‐sensitive microelectrodes and 0.62 +/− 0.05 mM (n = 15) using mag‐fura‐2. Raising extracellular MgCl2 from 5 to 20 mM caused an average increase in [Mg2+]1 of 0.25 +/− 0.04 mM (n = 7). In three experiments, removing extracellular Mg Cl2 caused an average decrease in [Mg2+]1 of 0.1 mM. Replacing extracellular Na+ with N‐methyl‐D‐glucamine (NMDG) caused a rise in [Mg2+]1 of 1.8 +/− 0.5 mM (n = 7); [Mg2+]1 recovered to resting levels when extracellular Na+ was restored. Iontophoretic injections of MgCl2 were used to raise [Mg2+]1. The rate of recovery from such increases in [Mg2+]1 inverted question markcalculated from the slope of the recovery was inhibited by 85‐100% (n = 5) in the absence of extracellular Na2+ compared with control conditions. Raising extracellular Ca2+ from 7 to 35 mM caused a reversible rise in [Mg 2+]1 of 0.4 +/− 0.05 mM (mean +/− S.E.M., n = 7). It was concluded that in snail neurones the main mechanism for [Mg2+]1 extrusion is a Na(+)‐Mg2+ exchanger which may be partially inhibited be high extracellular Ca2+ concentrations.
Glucose 6‐phosphate alters rat skeletal muscle contractile apparatus and sarcoplasmic reticulum function
Authors: Williams JH , Ward CW , Spangenburg EE , Nelson R , Stavrianeas S , Klug GA
Published: December 2014

We investigated the effects of glucose 6‐phosphate (G6P) on skeletal muscle contractile apparatus and sarcoplasmic reticulum (SR) function. Using rat extensor digitorum longus fibres, the presence of 5 mM G6P decreased the Ca2+ sensitivity of both force production and actomyosin ATPase (AM‐ATPase) activity. Conversely, maximal Ca(2+)−activated force was unaffected while maximal AM‐ATPase activity was increased by 37%. In SR vesicles isolated from rat gastrocnemius, G6P markedly altered Ca2+ handling. It increased Ca(2+)‐stimulated Ca(2+)‐ATPase activity but depressed the net rate of Ca2+ uptake. This latter effect appears to be due to G6P‐stimulated Ca2+ release. When G6P was added to Ca(2+)‐loaded vesicles, a small, transient release of Ca2+ was elicited. In addition, G6P lowered the threshold for Ca(2+)‐induced Ca2+ release but depressed the net rates of both AgNO3‐ and caffeine‐induced releases. It is possible that the accumulation of G6P during muscular activity may adversely affect muscle force production and contribute to the fatigue process via its action on the contractile apparatus and SR.
Salt overload does not modify plasma atrial natriuretic peptide or vasopressin during pregnancy in rats
Authors: Carvalho EG , Franci CR , Antunes-Rodrigues J , Gutkowska J , Favaretto AL
Published: December 2014

The present study was carried out to determine whether the increased salt intake induce by increased specific sodium appetite in pregnant rats modifies water‐salt homeostasis throughout pregnancy. Two groups of pregnant rats were used, one fed ad libitum with a normal sodium (NS) diet consisting of standard rat chow and distilled water, and the other fed with a high‐sodium (HS) diet with free access to chow, distilled water plus saline solution (1.5% NaCl). Virgin rats in dioestrus were also studied as non‐pregnant controls. Pregnant animals were studied on days 4, 9, 14, 20 and 21 of gestation at which time body weight, water and saline intake, sodium excretion, plasma atrial natriuretic peptide (ANP) and arginine vasopressin (AVP) concentrations, as well as plasma osmolality were determined. Data showed that water intake was higher in the NS group, but total fluid intake (water plus saline) was higher in the HS group throughout pregnancy. Dietary sodium intake was the same for both groups but total sodium intake (chow plus saline) was 60‐98% higher in the HS rats. Pregnant HS rats excreted more fluid (35‐50%) and sodium (up to 100%) compared with NS rats, indicating that the animals could change their renal excretion in response to a 2.5‐fold higher dietary sodium intake compared with the control level. Salt satiety during pregnancy did not modify plasma ANP concentration. In both groups of pregnant rats ANP levels increased 3‐fold on day 14 without significant alteration in sodium excretion, suggesting that the natriuretic action of ANP is attenuated at least after the second week of pregnancy. High sodium intake did not change plasma AVP concentration or osmolality and both groups showed the same gradual decrease in plasma osmolality (approximately 8 mosmol kg‐1) at the end of pregnancy that was not accompanied by decreased plasma AVP concentration. The present data show that rats maintain the special homeostatic equilibrium that occurs in normal pregnancy even when they are allowed to increase sodium intake to satisfy their salt appetite during this period of the reproductive cycle.
Secretory response to cholera toxin in the porcine jejunum under different types of general anaesthesia
Authors: Maltbaek JS , Grondahl ML , Berggreen P , Nielsen CG , Thorboll JE , Skadhauge E , Hansen MB
Published: December 2014

Investigations of intestinal secretion are often performed under anaesthesia. This study evaluates the influence of anaesthetic agents on the intestinal secretion induced by cholera toxin (CT) in the pig. CT was instilled for 4 h in ligated jejunal loops under anaesthesia with halothane, saffan, alpha‐chloralose, or propofol. Cardiovascular parameters, blood gas data, plasma cortisol levels, net fluid accumulation, intraluminal mediators (serotonin (5‐HT), prostaglandin E2 (PGE2)) and electrolyte concentrations in the accumulated fluid were determined. The systolic blood pressure and heart rate was highest for saffan‐anaesthetized pigs (blood pressure: saffan > alpha‐chloralose > propofol = halothane; heart rate: saffan > alpha‐chloralose = propofol = halothane), while blood gases and cortisol levels were within the same range. CT induced a dose‐dependent fluid accumulation under all four anaesthetics. The fluid accumulation was significantly higher in pigs treated with saffan, alpha‐chloralose and propofol than in halothane‐treated pigs (saffan = alpha‐chloralose > propofol > halothane). There was no significant difference in electrolyte concentrations in the accumulated fluid or in the luminal content of 5‐HT and PGE2 between anaesthetics. The results demonstrate that anaesthetic agents profoundly influence the secretory response in the small intestine and indicate the importance of the choice of anaesthetic in this type of experiment.
Non‐adrenergic, non‐cholinergic reflex secretion of parotid saliva in rats elicited by mastication and acid applied on the tongue
Authors: Ekstrom J
Published: December 2014

Chewing and acid on the tongue evoked a flow of saliva from the duct‐cannulated parotid gland of the conscious rat despite pretreatment with atropine and adrenoceptor antagonists. This non‐adrenergic, non‐cholinergic (NANC) response depended on an intact parasympathetic innervation and was abolished by a tachykinin antagonist. The present findings are consistent with a physiological role for the secretory NANC mechanisms of the salivary glands.
Effects of intracellular N+, M2+ and metabolites on C2+−activated K+ channels in pulmonary and ear arterial smooth muscle cells of the rabbit
Authors: Lee SH , Ho WK , Earm YE
Published: December 2014

Hypoxic pulmonary vasoconstriction (HPV) is an important mechanism for matching the ventilation/perfusion ratio in the lung, but the signal transduction pathway through which hypoxia induces vasoconstriction remains unclear. We hypothesized that the decrease in K+ current induced by hypoxia is a key mechanism for HPV, and examined the effects of the substances which are expected to accumulate during hypoxia on the activity of large conductance Ca2+‐activated K+ (BKCa) channels. Pulmonary and ear arterial smooth muscle cells were isolated from the rabbit using enzymatic digestion, and large conductance Ca2+−activated K+ current (IBK,Ca) was recorded in symmetrical K+ concentrations using the inside‐out mode of the patch‐clamp technique. Increasing the Na+ concentration on the intracellular side suppressed IBK,Ca dose dependently: 4.6, 20.9, 35.5 and 44.6 % reduction with 4, 8, 12 and 16 mM Na+, respectively. Mg2+ also reduced IBK,Ca, and the maximum reduction was obtained at 0.5 mM. Lactate, adenosine, ADP and ATP did not significantly affect IBK,Ca. There was no difference between pulmonary and ear arterial smooth muscle cells in their response to the above substances; this finding rules out modulation of BKCa channels by the various factors thought to accumulate during hypoxia as a major mechanism involved in the decrease in the K+ conductance of pulmonary arteries in hypoxia.
Triple projections of neurones located in S1 and S2 segments of the cat spinal cord to the C6 segment, the cerebellum and the reticular formation
Authors: Grottel K , Krutki P , Mrowczynski W
Published: December 2014

Electrophysiological investigation of neurones in sacral segments of the spinal cord was performed in alpha‐chloralose‐anaesthetized cats in order to establish whether at least some ascending tract neurones could diverge to three different centres located in the brainstem, the cerebellum or the spinal cord. Recordings of antidromic action potentials from cells in S1 and S2 segments were taken following stimulation of the contralateral gigantocellular nucleus, contralateral restiform body and ipsi‐ and contralateral grey matter of the C6 spinal segment. Antidromic responses allowed identification of several types of neurones that differed in their pattern of supraspinal or propriospinal projections. In eighteen out of a total of sixty‐three neurones triple projections to all the above structures were found. In the majority of cells investigated their axons divided into two branches ascending both ipsi‐ and contralaterally in the lateral funiculi of the spinal cord. Their cell bodies were distributed in laminae VII‐VIII except for a minor group of neurones that projected to the C6 segment only, which were located in laminae V‐VI. The latter group also displayed lower values of axonal conduction velocities. Comparison of conduction velocities in proximal and distal parts of axons revealed significant slowing in most, raising the possibility that additional collaterals were present to other spinal or supraspinal centres. Dual and triple projections from most cells in this study suggest that such a divergence may be a more common feature of ascending tract neurones than has been reported before.
Conduction velocity and gap junction resistance in hypertrophied, hypoxic guinea‐pig left ventricular myocardium
Authors: Cooklin M , Wallis WR , Sheridan DJ , Fry CH
Published: December 2014

The passive and active electrical properties of left ventricular myocardium were measured, using conducted action potentials and current clamp of isolated myocytes. The objective was to quantify changes of intracellular resistivity, Ri, during hypertrophic growth and the simultaneous imposition of cellular hypoxia. Ri was estimated from the time course of the rising phase of a conducted action potential using a solution of the two‐dimensional cable equation. The thoracic aorta of guinea‐pigs was constricted to induce left ventricular hypertrophy (LVH) and myocardium used 50 and 150 days post‐operation. Conduction velocity increased in the earlier stage of LVH and declined in the later stage, compared with age‐matched controls. Hypoxia reduced conduction velocity in all experimental groups. Ri increased only in the later stage of hypertrophy (253 +/− 39 Omega cm to 544 +/− 130 Omega cm) and was additionally increased by hypoxia in all groups (e.g. control myocardium 252 +/− 39 Omega cm to 506 +/− 170 Omega cm). The magnitude of the increase of Ri in hypertrophied, hypoxic myocardium can create conditions required to generate re‐entrant arrhythmias.
Effect of glucose‐dependent insulinotropic polypeptide on whole‐body glucose utilization in sheep
Authors: Rose MT , Itoh F , Takahashi Y
Published: December 2014

Four adult Corriedale sheep were used in an experiment divided into three parts. In part 1 a primed continuous infusion of [6, 6‐2H2]glucose was infused for 7 h. The first 3 h was the control period, from 3 to 7 h glucose‐dependent insulinotropic polypeptide (GIP) was infused, and from 5 to 7 h somatostatin was infused. Part 2 of the experiment was the same as for part 1 except that insulin was infused between 3 h and 7 h and GIP was infused between 5 and 7 h. Coincident with the insulin infusion, normal glucose was also infused at a variable rate in order to keep the plasma glucose at basal levels. In part 3 of the experiment [6,6‐2H2]glucose was infused for 5 h and somatostatin was infused between 3 and 5 h. Measurements of glucose turnover were made in the last 40 min of the control, GIP only, insulin only, somatostatin only, GIP plus somatostatin and GIP plus insulin infusion periods. Plasma insulin levels were reduced to the limit of detection by the somatostatin infusion; under such conditions whole‐body glucose uptake should be entirely non‐insulin‐mediated (NIMGU). Expressing glucose disposal as glucose metabolic clearance rate demonstrated that elevated, but still physiological GIP levels had no effect on NIMGU but significantly increased insulin‐mediated glucose uptake when plasma insulin levels were similar to levels typically observed after a meal. These results indicate that in sheep, GIP may enhance insulin action with respect to glucose disposal following a meal, but has no effect on glucose disposal pathways not responsive to insulin.
Systolic coronary flow impediment in the dog: role of ventricular pressure and contractility
Authors: Pagliaro P , Gattullo D , Linden RJ , Losano G , Westerhssof N
Published: December 2014

The present study was planned to investigate the effect of left ventricular pressure and inotropic state on coronary arterial inflow in systole in the anaesthetized dog. A wide range of left ventricular systolic pressures, including the physiological range, were studied. Experiments were done under conditions of maximal vasodilatation and low perfusion pressure in order to avoid vascular autoregulative interference and to keep the microvascular pressure within the normal range. In five anaesthetized dogs, perfused with extracorporeal circulation system, ventricular volume was changed from 20 to 50 ml in steps of 10 ml by filling an intraventricular latex balloon, and the related changes in left ventricular pressure and coronary flow were measured. The volume was then extended to 70 ml to obtain an overstretch which induced a transient decrease in cardiac contractility. During the period of low cardiac contractility the volume was brought back to 20 ml in steps of 10 ml. Systolic ventricular pressure changed with volume but was lower during the period of low contractility. For systolic pressures below 100 mmHg there was no significant relationship between pressure and coronary systolic flow, but the relationship shifted to higher flows during low contractility. For systolic pressures above 100 mmHg systolic coronary flow decreased significantly when systolic pressure increased. In this case the slopes of the relationships were not significantly different before and after the reduction in contractility. These findings suggest that for systolic pressures less than 100 mmHg (i.e. below the physiological range) the shielding effect of the contracting ventricle prevents the ventricular pressure from being transmitted in the myocardial wall. When systolic pressure exceeds 100 mmHg the shielding effect is overcome and the amplitude of the systolic flow reduction varies with ventricular pressure.