bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluo‐3 signals associated with potassium contractures in single amphibian muscle fibres.
Authors: Caputo C , Bolaños P
Published: December 2014

1. The calcium‐sensitive dye fluo‐3 AM was used to obtain fluorescence signals and calcium transients associated with K+ contractures, twitches and tetani, in intact single muscle fibres of the tropical toad Leptodactylus insularis. 2. The changes in free calcium concentration in the myoplasm ([Ca2+]i) were calculated using the values of the ‘off’ (k‐ = 33.5 s‐1) and ‘on’ (k+ = 13.1 microM‐1 s‐1) rate constants for the binding of calcium to the dye (dissociation constant, Kd = k‐/k+). The mean (+/‐ S.E.M., n = 7) peak [Ca2+]i value during twitches or tetani was 3.9 +/‐ 0.3 or 4.1 +/‐ 0.3 microM, respectively, while during maximal K+ contractures, it was 10.3 +/‐ 0.8 microM. The threshold [Ca2+]i for tension development was about 1 microM. 3. For responses elicited with high [K+]o (80‐190 mM), the calcium transients decayed faster than tension. At lower [K+]o (30‐70 mM), the decay was slower, and relaxation was complete when [Ca2+]i was still above contractile threshold values. 4. Following a K+ contracture, recovery of the calcium transients associated with twitches occurred before recovery of tension, indicating an apparent dissociation between [Ca2+]i and tension output. This apparent dissociation between calcium and tension output could be attributed to the desensitization of the contractile proteins to calcium, or, more probably, to the non‐uniform behaviour of calcium release and/or uptake sites, leading to an unhomogeneous distribution of active sarcomeres along the fibre length and localized sarcomere relaxation.
Aminophylline enhances resting Ca2+ concentrations and twitch tension by adenosine receptor blockade in Rana pipiens.
Authors: Clark K I , Barry S R
Published: December 2014

1. We hypothesized that the xanthine aminophylline acts to block adenosine receptors on the surface of skeletal muscle fibres, thereby inhibiting a depressant action of endogenous adenosine. We further hypothesized that this action results in increased concentrations of intracellular resting Ca2+ and enhanced twitch tension upon muscle stimulation. 2. Peak twitch tension (Pt) of the semitendinosus muscle in normal frog Ringer solution (NFR) ranged from 6.8 to 9.4 g. Intracellular Ca2+ concentrations in control resting fibres ranged from 67 to 70 nM. Aminophylline at 100 microM produced increases of 26 and 22% in Pt and Ca2+ concentrations, respectively. 3. The adenosine receptor antagonists 8‐phenyltheophylline (8‐PT) and 1,3‐dipropyl‐7‐methylxanthine (1,3‐d‐7‐M) both increased Pt by 32% over values in NFR. In addition, 1,3‐d‐7‐M increased resting Ca2+ concentrations by 29% over control levels. 4. Adenosine deaminase increased twitch tension and resting intracellular Ca2+ concentrations by 22 and 26% over controls, respectively. 5. N6‐(2‐phenylisopropyl)adenosine (R‐PIA, 1 microM), a potent adenosine analogue, partially blocked both the increase in Pt and intracellular Ca2+ concentrations induced by the xanthines, possibly by competing for the adenosine receptor. 6. The data herein provide support for the existence of adenosine receptors on the membranes of skeletal muscle fibres and suggest a possible role for adenosine receptors in the regulation of twitch tension.
Increase of sympathetic discharge to skeletal muscle but not to skin during mild lower body negative pressure in humans.
Authors: Vissing S F , Scherrer U , Victor R G
Published: December 2014

1. Haemodynamic studies in humans have concluded that the cutaneous circulation is regulated by cardiopulmonary baroreceptors. In contrast, neurophysiological studies have indicated that skin sympathetic outflow, unlike muscle sympathetic outflow, is unaffected by perturbations in baroreceptor activity. 2. Thus, in an attempt to resolve this discrepancy, both muscle and skin sympathetic nerve activity was recorded during unloading of mainly cardiopulmonary afferents with non‐hypotensive lower body negative pressure (LBNP) performed in both normothermic and hyperthermic conditions. The function of the sympathetic activity was studied by estimations of skin blood flow (laser Doppler velocimetry), of calf blood flow (plethysmography) and of sudomotor activity (electrodermal responses). 3. A level of LBNP that caused robust increases in sympathetic outflow and vascular resistance in the skeletal muscle of the lower leg had no effect on sympathetic activity and vascular resistance in the skin of the same region in the same subjects. Both at normothermia and during hyperthermia LBNP decreased electrodermal activity. Experiments performed during sham LBNP and with skin temperature kept constant suggest that the electrodermal response was due to a decrease in skin temperature produced by the LBNP. 4. In conclusion, these findings challenge the concept that the cutaneous circulation participates importantly in the peripheral circulatory adjustments to unloading of cardiopulmonary afferents during orthostatic stress in humans. During non‐hypotensive LBNP, the skeletal muscle bed accounts for all of the reflex vasoconstriction in the calf.
Mediation of excitatory neurotransmission by the release of ATP and noradrenaline in sheep mesenteric lymphatic vessels.
Authors: Hollywood M A , McHale N G
Published: December 2014

1. Spontaneous isometric contractions were measured in rings of sheep mesenteric lymphatics. Field stimulation at short pulse widths increased the frequency of spontaneous contractions and this response was blocked by 3 x 10(‐7) M omega‐conotoxin and by 10(‐6) M guanethidine. 2. Rings that had been incubated with [3H]noradrenaline release 3H in response to field stimulation in a frequency‐dependent manner. 3. Exogenous ATP mimicked the response to field stimulation and this was blocked by 10(‐4) M suramin but not by prior desensitization with 10(‐6) M alpha, beta‐methylene ATP. Exogenous noradrenaline was not blocked by 10(‐4) M suramin. 4. The excitatory response to field stimulation was not blocked by 10(‐4) M suramin but a combination of 10(‐4) M suramin and 3 x 10(‐6) M phentolamine did block the response. 5. In rings taken from sheep that had been pretreated with reserpine, 10(‐4) M suramin alone blocked the response to field stimulation. 6. The results of this study suggest that the excitatory response to stimulation of intramural nerves in sheep mesenteric lymphatics is mediated by the release of both ATP and noradrenaline.
Depression of Renshaw recurrent inhibition by activation of corticospinal fibres in human upper and lower limb.
Authors: Mazzocchio R , Rossi A , Rothwell J C
Published: December 2014

1. This study tested whether the recurrent inhibition of soleus and wrist flexor motoneurones could be modified by transcranial magnetic stimulation in human subjects. 2. Magnetic stimulation was given through a circular coil centred at the vertex. The intensity of the magnetic stimulus was subthreshold for evoking a motor response in the active soleus and wrist flexor muscles. The recurrent inhibition brought about by a conditioning H1 reflex discharge was estimated by a test H' reflex. The modifications of the recurrent inhibition after cortical stimulation were distinguished from the motoneuronal changes by comparing H' to a reference H reflex. 3. In the soleus motoneurones, the reference H reflex was inhibited at a minimum conditioning‐test interval of ‐2 ms (H reflex stimulus before magnetic stimulation). In contrast, the H' reflex was facilitated at minimum conditioning‐test intervals of +1 ms. In the wrist flexor motoneurones, both H' and reference H reflexes were facilitated. However, at lower cortical stimulus intensities, only the H' reflex was facilitated at minimum conditioning‐test intervals of +1 ms. 4. In both motoneurone pools, H' facilitation started 3‐4 ms later than the earliest changes in the reference H reflex. Also, the threshold of H' facilitation was lower than that of reference H reflex. 5. It is concluded that facilitation of the H' reflex is produced by corticospinal inhibition of Renshaw cells via a short interneuronal chain in both the upper and lower limb.
Response of arm flexor muscles to magnetic and electrical brain stimulation during shortening and lengthening tasks in man.
Authors: Abbruzzese G , Morena M , Spadavecchia L , Schieppati M
Published: December 2014

1. The responses of the brachioradialis and biceps brachii muscles to non‐invasive magnetic and electrical stimulation of the human motor cortex have been investigated during performance of different tasks. 2. Both muscles were simultaneously active during elbow flexor isometric torque, or forearm flexion lifting a weight (shortening contraction), or extension breaking the fall of the weight (lengthening contraction). The forearm extensor triceps brachii muscle was not engaged in any task. By using different weights, comparable levels of EMG activity were obtained in the same muscle across tasks. 3. Both magnetic (7 subjects) and electrical (3 subjects) brain stimulation (at about 1.5 times the motor threshold) produced larger responses during shortening, and smaller responses during lengthening, in the brachioradialis muscle with respect to isometric contractions, in spite of equal background EMG levels. Responses evoked in the biceps brachii by either stimulation mode were smaller during lengthening but not significantly enhanced during shortening. No consistent differences in the task‐related modulation of the responses were present between electrical or magnetic stimulations. No significant changes in the evoked responses occurred during passive elbow flexion or extension. 4. In three subjects, the H reflex was evoked in the brachioradialis by stimulation of the radial nerve during performance of the same tasks. The pattern of task‐related modulation of the reflex amplitude paralleled that obtained for brain stimulation. 5. The opposite modulation induced by the shortening and lengthening tasks both in magnetically and electrically evoked motor responses, and in the H reflex, suggests that task‐related changes in excitability of the cortical neurones play a minor role.(ABSTRACT TRUNCATED AT 250 WORDS)
Different regulation by pHi and osmolarity of the rabbit ileum brush‐border and parietal cell basolateral anion exchanger.
Authors: Nader M , Lamprecht G , Classen M , Seidler U
Published: December 2014

1. The purpose of this study was to look for evidence of a pH‐sensitive modifier site on the parietal cell basolateral anion exchanger, determine the pH range in which allosteric regulation takes place, investigate the effect of the osmolarity on internal pH (pHi) dependence and compare it with that of the ileum brush‐border anion exchanger. 2. When the pHi in parietal cell basolateral membrane (BLM) vesicles was increased, the rate of Cl(‐)‐gradient‐driven 36Cl‐ uptake increased from 6.03 +/‐ 2.24 to 38.09 +/‐ 3.33 nmol (mg protein)‐1 with the steep increase in anion exchange rates occurring within a narrow pH range between pHi 7.0 and 7.5. This was due to allosteric activation by internal OH‐ and not due to a change in driving force, since the driving force for maximal exchange rates was provided by the outwardly directed Cl‐ gradient. 3. The pHi dependency curve of parietal cell BLM anion exchange rates was shifted to the left by 0.25 pH units by increasing the osmolarity of the intra‐ and extravesicular solutions from 300 to 380 mosmol l‐1. Thus cell shrinking may activate the parietal cell anion exchanger without a change in pHi and without phosphorylation of the anion exchanger protein. 4. In ileum brush‐border membranes, the pHi‐dependent increase in the rate of Cl(‐)‐gradient‐driven 36Cl‐ uptake was more gradual and the half‐maximal anion exchange rate was attained at lower pHi (pH 6.5). Increasing the osmolarity from 300 to 500 mosmol l‐1 had no effect on pH dependence. 5. We conclude that the parietal cell basolateral and ileum brush‐border anion exchangers possess an internal modifier site for allosteric activation by OH‐, but the pH range in which allosteric regulation occurs differs between the two exchangers, as does the effect of an increase in osmolarity. Since current evidence suggests that both the parietal cell basolateral and the ileum brush‐border anion exchanger are encoded by the AE2 gene, the differences in pHi dependence between the two may be due to alternative splicing, post‐transcriptional modification, or the different membrane environment. 6. The pHi range for allosteric activation found in this study would suggest that for both the ileum and the parietal cell anion exchanger, but especially for the latter, a potentiating effect of the allosteric activation and the HCO3‐ availability occurs within the physiological pHi range and can cause dramatic increases in maximal anion exchange rates with increasing pHi.
Presynaptic actions of morphine: blockade of cholecystokinin‐induced noradrenaline release in the rat supraoptic nucleus.
Authors: Onaka T , Luckman S M , Guevara-Guzman R , Ueta Y , Kendrick K , Leng G
Published: December 2014

1. This study aimed to establish the site at which morphine acts to inhibit oxytocin release in response to peripheral administration of cholecystokinin (CCK). 2. Conscious rats were given morphine or vehicle followed by CCK or vehicle (I.V.). Fos immunoreactivity was apparent 90 min after CCK injection in the supraoptic nucleus of vehicle‐ but not morphine‐pretreated animals. 3. In the dorsomedial (C2/A2) and the ventrolateral (C1/A1) regions of the brainstem, about half of the cells immunoreactive for tyrosine hydroxylase (TH) expressed Fos‐like protein after CCK injection. In the C2/A2 region, 20% of the Fos‐positive cells also showed TH immunoreactivity, whereas in the C1/A1 region 68% did so. Morphine treatment did not significantly change the number of cells expressing Fos immunoreactivity, or the percentage of TH‐positive cells expressing Fos‐like protein. 4. Amine release was measured in the supraoptic nucleus of urethane‐anaesthetized rats using a microdialysis probe. An I.V. injection of CCK increased the concentrations in the dialysate of noradrenaline and serotonin, but not of either adrenaline or dopamine. Pretreatment with morphine (I.V.) blocked the effects of CCK in a naloxone‐reversible manner. 5. Inclusion of morphine in the dialysate also blocked the increase in noradrenaline and serotonin in response to CCK in a naloxone‐reversible manner. 6. These observations indicate that morphine acts near or within the supraoptic nucleus to block CCK‐evoked noradrenaline release presynaptically. This presynaptic action of morphine may be a cause of the blockade of oxytocin release after CCK.
cAMP accelerates the decay of stretch‐activated inward currents in guinea‐pig urinary bladder myocytes.
Authors: Wellner M C , Isenberg G
Published: December 2014

1. Myocytes from the urinary bladder were stretched longitudinally by 5‐20%. At ‐50 mV, stretch induced whole‐cell inward currents (Iin) between ‐100 and ‐600 pA. Iin decayed slowly with time to 93 +/‐ 20% (mean +/‐ S.E.M., n = 6) of the initial value in 1 min. The mechanisms of this ‘adaptation’ and its modulation by dibutyryl cAMP (dBcAMP) were analysed with whole‐cell and single channel currents. 2. When the cells were internally perfused with 100 microM 8‐bromo‐cAMP (8BrcAMP), stretch induced an Iin of the usual amplitude that decayed completely within 40 +/‐ 13 s. When 200 microM dBcAMP was bath applied 10 s after the start of the stretch, Iin decayed to zero within 85 +/‐ 18 s. 3. dBcAMP increased the K+ current through Ca(2+)‐activated BK channels (IK(Ca)) at 0 mV with a time course that correlated well with the decay of Iin, and block of IK(Ca) by TEA suppressed the dBcAMP‐induced decay of Iin. In the presence of intracellular BAPTA, dBcAMP increased the stretch‐induced Iin. The results suggest that adaptation is caused by superimposition of IK(Ca) which is increased through elevation of near‐membrane [Ca2+] and by cAMP‐dependent phosphorylation. 4. Single channel analysis was carried out with 140 mM KCl electrode solution and at ‐50 mV. Stretch‐activated channels (SACs) were recorded during pulses of negative pressures between ‐2 and ‐5 kPa. Activity (NPo) of SACs was constant for at least 4 min, e.g. evidence for adaptation was missing. dBcAMP (200 microM) increased NPo of SACs by 142 +/‐ 35% (n = 16). 5. dBcAMP increased NPo via frequency of openings and channel open time. In five of sixteen patches, dBcAMP induced openings without suction. Similar effects were induced by the catalytic subunit of cAMP‐dependent protein kinase (PKAc), applied to inside‐out patches. 6. NPo, normalized by its maximum, increased with more negative pressure along an S‐shaped curve. dBcAMP increased the sensitivity of SACs to stretch by shifting the point of half‐maximal activity from ‐3.2 to ‐2.6 kPa. 7. The augmentation of NPo by dBcAMP is attributed to the phosphorylation of SACs promoting their opening. Adaptation of Iin is discussed as a ‘secondary’ effect of stretch‐activated channels: Ca2+ influx through SACs increases the Ca2+ concentration that activates BK channels whose Ca2+ sensitivity is increased by cAMP.
Effects of neurotensin on rat supraoptic nucleus neurones in vitro.
Authors: Kirkpatrick K , Bourque C W
Published: December 2014

1. The electrophysiological actions of neurotensin on magnocellular neurosecretory cells (MNCs) were examined during intracellular recording from seventy‐three supraoptic nucleus neurones in superfused explants of rat hypothalamus. 2. Application of neurotensin tridecapeptide (NT(1‐13); 1 nM to 3 microM) caused a membrane depolarization and reversibly attenuated the after‐hyperpolarization (AHP) which followed current‐evoked spike trains. This effect was accompanied by increased firing frequency during depolarizing current pulses evoked from a fixed potential. 3. The effects of neurotensin could be mimicked by the C‐terminal fragment, NT(8‐13), but not by the N‐terminal fragment, NT(1‐8). 4. Depolarizing responses to NT(1‐13) or NT(8‐13), retained during K+ channel blockade with internal Cs+, were accompanied by increased membrane conductance. Current‐ and voltage‐clamp analyses revealed that neurotensin‐evoked depolarizations result partly from the activation of a non‐selective cationic conductance reversing near ‐34 mV. 5. Depolarizing responses to neurotensin were retained in the presence of TTX or in Ca(2+)‐free solutions, indicating the involvement of receptors located on the plasma membrane of MNCs themselves. 6. Through these effects endogenously released neurotensin may modulate excitability, activity patterns and secretion from the hypothalamo‐neurohypophysial axis.
Recovery of power output and muscle metabolites following 30 s of maximal sprint cycling in man.
Authors: Bogdanis G C , Nevill M E , Boobis L H , Lakomy H K , Nevill A M
Published: December 2014

1. The recovery of power output and muscle metabolites was examined following maximal sprint cycling exercise. Fourteen male subjects performed two 30 s cycle ergometer sprints separated by 1.5, 3 and 6 min of recovery, on three separate occasions. On a fourth occasion eight of the subjects performed only one 30 s sprint and muscle biopsies were obtained during recovery. 2. At the end of the 30 s sprint phosphocreatine (PCr) and ATP contents were 19.7 +/‐ 1.2 and 70.5 +/‐ 6.5% of the resting values (rest), respectively, while muscle lactate was 119.0 +/‐ 4.6 mmol (kg dry wt)‐1 and muscle pH was 6.72 +/‐ 0.06. During recovery, PCr increased rapidly to 65.0 +/‐ 2.8% of rest after 1.5 min, but reached only 85.5 +/‐ 3.5% of rest after 6 min of recovery. At the same time ATP and muscle pH remained low (19.5 +/‐ 0.9 mmol (kg dry wt)‐1 and 6.79 +/‐ 0.02, respectively). Modelling of the individual PCr resynthesis using a power function curve gave an average half‐time for PCr resynthesis of 56.6 +/‐ 7.3 s. 3. Recovery of peak power output (PPO), peak pedal speed (maxSp) and mean power during the initial 6 s (MPO6) of sprint 2 did not reach the control values after 6 min of rest, and occurred in parallel with the resynthesis of PCr, despite the low muscle pH. High correlations (r = 0.71‐0.86; P < 0.05) were found between the percentage resynthesis of PCr and the percentage restoration of PPO, maxSp and MPO6 after 1.5 and 3 min of recovery. No relationship was observed between muscle pH recovery and power output restoration during sprint 2 (P > 0.05). 4. These data suggest that PCr resynthesis after 30 s of maximal sprint exercise is slower than previously observed after dynamic exercise of longer duration, and PCr resynthesis is important for the recovery of power during repeated bouts of sprint exercise.
Neurotransmitter release evoked by nerve impulses without Ca2+ entry through Ca2+ channels in frog motor nerve endings.
Authors: Silinsky E M , Watanabe M , Redman R S , Qiu R , Hirsh J K , Hunt J M , Solsona C S , Alford S , MacDonald R C
Published: December 2014

1. The requirement for extracellular Ca2+ in the process of evoked acetylcholine (ACh) release by nerve impulses was tested at endplates in frog skeletal muscle. Ca(2+)‐containing lipid vesicles (Ca2+ liposomes) were used to elevate cytoplasmic Ca2+ concentrations under conditions in which Ca2+ entry from the extracellular fluid was prevented. 2. In an extracellular solution containing no added Ca2+ and 1 mM Mg2+ (‘Ca(2+)‐free’ solution), Ca2+ liposomes promoted the synchronous release of ACh quanta, reflected electrophysiologically as endplate potentials (EPPs), in response to temporally isolated nerve impulses. 3. Motor nerve stimulation generated EPPs during superfusion with Ca2+ liposomes in Ca(2+)‐free solutions containing the Ca2+ channel blocker Co2+ (1 mM), and the Ca2+ chelator EGTA (2 mM). As a physiological control for Ca2+ leakage from the liposomes to the extracellular fluid, the effect of Ca2+ liposomes on asynchronous evoked ACh release mediated by Ba2+ was examined. In contrast to the effects of 0.2‐0.3 mM extracellular Ca2+, which generated EPPs but antagonized Ba(2+)‐mediated asynchronous ACh release, Ca2+ liposomes generated EPPs but did not reduce asynchronous release mediated by Ba2+. The effects of Ca2+ liposomes were thus not due to leakage of Ca2+ from the liposome to the extracellular fluid. 4. Morphological studies using fluorescently labelled liposomes in conjunction with a confocal microscope demonstrate that lipid is transferred from the liposomes to nerve endings and liposomal contents are delivered to the nerve terminal cytoplasm. 5. The results suggest that when intracellular Ca2+ is elevated using liposomes as a vehicle, evoked ACh release can occur in the absence of Ca2+ entry via Ca2+ channels.
Quantal puffs of intracellular Ca2+ evoked by inositol trisphosphate in Xenopus oocytes.
Authors: Yao Y , Choi J , Parker I
Published: December 2014

1. Ca2+ liberation induced in Xenopus oocytes by a poorly metabolized derivative of inositol 1,4,5‐trisphosphate (3‐deoxy‐3‐fluoro‐D‐myo‐inositol 1,4,5‐trisphosphate; 3‐F‐InsP3) was visualized using a video‐rate confocal microscope to image fluorescence signals reported by the indicator dye calcium green‐1. 2. Low (10‐30 nM) intracellular concentrations of 3‐F‐InsP3 evoked Ca2+ release as localized transient ‘puffs’. Progressively higher concentrations (30‐60 nM) gave rise to abortive Ca2+ waves triggered by puffs, and then (> 60 nM) to a sustained elevation of Ca2+ followed by the appearance of propagating Ca2+ waves. At concentrations up to that giving waves, the frequency of puffs increased as about the third power of [InsP3], whereas their amplitudes increased only slightly. 3. The rise of cytosolic Ca2+ during a puff began abruptly, and peaked within about 50 ms. The peak free Ca2+ level was about 180 nM, and the total amount of Ca2+ liberated was several attomoles (10(‐18) mol), too much to be accounted for by opening of a single InsP3‐gated channel. The subsequent decline of Ca2+ occurred over a few hundred milliseconds, determined largely by diffusion of Ca2+ away from the release site, rather than by resequestration. Lateral spread of Ca2+ was restricted to a few micrometres, consistent with an effective diffusion coefficient for Ca2+ ions of about 27 microns2 s‐1. 4. The peak amplitudes of puffs recorded at a given site were distributed in a roughly Gaussian manner, and a small proportion of sites consistently gave puffs much larger than the main population. Intervals between successive puffs at a single site were exponentially distributed, except for a progressive fall‐off in puffs seen at intervals shorter than about 10 s. Thus, triggering of puffs appeared to be stochastically determined after recovery from a refractory period. 5. There was little correlation between the occurrence of puffs at sites more than a few micrometres apart, indicating that puff sites can function autonomously, but closely (ca 2 microns) adjacent sites showed highly correlated behaviour. 6. Puffs arose from sites‐present at a density of about 1 per 30 microns2 in the animal hemisphere, located within a narrow band about 5‐7 microns below the plasma membrane. 7. We conclude that Ca2+ puffs represent a ‘quantal’ unit of InsP3‐evoked Ca2+ liberation, which may arise because local regenerative feedback by cytosolic Ca2+ ions causes the concerted opening of several closely clustered InsP3 receptor channels.
Raphe magnus and reticulospinal actions on primary afferent depolarization of group I muscle afferents in the cat.
Authors: Quevedo J , Eguibar J R , Jiménez I , Rudomin P
Published: December 2014

1. In the anaesthetized cat, electrical stimulation of the bulbar reticular formation produced a short latency (2.1 +/‐ 0.3 ms) positive potential in the cord dorsum. In contrast, stimulation of the nucleus raphe magnus with strengths below 50 microA evoked a slow negative potential with a mean latency of 5.5 +/‐ 0.6 ms that persisted after sectioning the contralateral pyramid and was abolished by sectioning the ipsilateral dorsolateral funiculus. 2. The field potentials evoked by stimulation of the bulbar reticular formation and of the nucleus raphe magnus had a different intraspinal distribution, suggesting activation of different sets of segmental interneurones. 3. Stimulation of these two supraspinal nuclei produced primary afferent depolarization (PAD) in single Ib fibres and inhibited the PAD elicited by group I volleys in single Ia fibres. The inhibition of the PAD of Ia fibres produced by reticulospinal and raphespinal inputs appears to be exerted on different interneurones along the PAD pathway. 4. It is concluded that, although reticulospinal and raphespinal pathways have similar inhibitory effects on PAD of Ia fibres, and similar excitatory effects on the PAD of Ib fibres, their actions are conveyed by partly independent pathways. This would allow their separate involvement in the control of posture and movement.
Immunoglobulin E receptor‐activated calcium conductance in rat mast cells.
Authors: Zhang L , McCloskey M A
Published: December 2014

1. The nystatin perforated‐patch method was used to record macroscopic currents from anti‐trinitrophenyl (TNP) immunoglobulin E (IgE)‐sensitized rat basophilic leukaemia (RBL‐2H3) cells at 37 degrees C. 2. An inwardly rectifying Ca2+ current (ICa) was activated upon stimulation with the multivalent antigen trinitrophenylated bovine serum albumin (TNP‐BSA). Induction of ICa was not observed at room temperature. ICa was reversed and reinduced upon cyclical addition of the monovalent hapten dinitrophenyl (DNP)‐lysine and multivalent antigen, indicating that a specific interaction of antigen with IgE was required to elicit ICa. 3. The antigen‐induced current was also carried by Ba2+ or Sr2+, and to a lesser extent by Na+, in the nominal absence of Ca2+. ICa did not exhibit time‐dependent opening (< or = 1 ms) in response to hyperpolarizing voltage steps to ‐100 mV, although it did accumulate steady‐state inactivation of approximately 40‐50% over 100 ms. 4. Two inorganic blockers of antigen‐stimulated 45Ca2+ influx and secretion, La3+ and Zn2+, inhibited ICa by approximately 50% at concentrations known to produce 50% block of 45Ca2+ influx. In contrast, cromolyn sodium (0.5 mM) and the L‐type Ca2+ channel antagonist nitrendipine (5 microM) had no effect on ICa. 5. ICa also was induced by the intracellular Ca2+ mobilizer thapsigargin. Because the actions of thapsigargin and antigen were not additive, IgE receptor cross‐linkage appears to activate the recently described capacitative Ca2+ entry channels.
Cellular basis of temporal synaptic signalling: an in vitro electrophysiological study in rat auditory thalamus.
Authors: Hu B
Published: December 2014

1. The cellular mechanisms underlying temporal synaptic signalling of tectothalamic pathways were investigated in rat medial geniculate body (MGB) maintained in vitro. Stimulation of the brachium of the inferior colliculus elicited either a short latency, single‐ (or dual‐) spike or a long latency (10‐80 ms) burst in MGB neurones. The delayed burst response was found in most non‐lemniscal or caudodorsal MGB (MGd) neurones, whereas single‐spike units were mainly seen in the lemniscal ventral MGB (MGv). Population latency analysis revealed that the overall relay time of tectothalamic transmission is approximately 50 ms, with at least two excitation peaks occurring around 8 and 15 ms, respectively. 2. Intracellular recordings showed that the delayed burst responses in MGd neurones were mediated by an EPSP‐triggered low threshold spike (LTS). Small variations in either the membrane voltage or in EPSP amplitude induced significant shifts of LTS latency. 3. Compared with MGv cells, MGd neurones exhibited a more negative resting membrane potential and a prolonged EPSP; they lacked an apparent hyperpolarization‐activated inward rectifier (Ih). These factors seem to lead collectively to a dominant occurrence of long latency burst response in the MGd. In the majority of single‐spiking MGv cells that expressed a clear Ih, application of Cs+ consistently hyperpolarized the cell, which transformed a single‐spike synaptic response into an EPSP‐LTS burst or a subthreshold EPSP. 4. Taken together, these data suggest that the monosynaptic tectothalamic pathways are capable of introducing a ventrodorsal gradient in auditory response time. This synaptic activity pattern is probably dominantly regulated by a set of membrane conductances expressed endogenously in thalamocortical neurones.
Synaptic integration in layer IV of the ferret striate cortex.
Authors: Hirsch J A
Published: December 2014

1. Whole‐cell patch recording were made with dye‐filled electrodes from layer IV in slices of the ferret striate cortex. Projections from the thalamus and layer VI provide most of the extralaminar input to layer IV. Interactions between these two pathways are thought to play a role in the generation of suppressive non‐linearities such as end‐inhibition. Thus, synaptic responses evoked by stimulating each pathway individually were compared with those produced by activating both projections together. 2. Spiny stellate cells are the majority population in layer IV and were the most frequently patched neurons (n = 23); all fired adapting trains of large, fast action potentials. About half of those tested (n = 13) were progressively inhibited by strengthening the stimulus to layer VI, while the rest became more excited. For the former, the response evoked by stimulating both pathways in coincidence was often more hyperpolarizing than would have been predicted by summing the responses to either projection alone (n = 4). Hence, the inputs from the thalamus and layer VI are integrated by circuits that can produce strong and non‐linear inhibition. 3. Recordings from various basket cells, which are inhibitory, have provided a first view of the suppressive circuits in layer IV (n = 5). Two cells were excited by stimulation of both pathways. The remaining three cells were mainly excited by activation of thalamic afferents but were largely inhibited by stimulation of layer VI. Thus, inhibition seen at the level of the spiny stellate cells could result from two mechanisms operating via presynaptic smooth cells: convergent excitation provided by both ascending pathways on the one hand, and a push‐pull relationship between pathways on the other.
Evidence for the involvement of cGMP in neural bronchodilator responses in humal trachea.
Authors: Ward J K , Barnes P J , Tadjkarimi S , Yacoub M H , Belvisi M G
Published: December 2014

1. We have investigated the correlation between relaxation and changes in cyclic nucleotide content of human tracheal smooth muscle (HTSM) in vitro following inhibitory non‐adrenergic non‐cholinergic (i‐NANC) neural bronchodilator responses evoked by electrical field stimulation (EFS), and compared these with changes seen with sodium nitroprusside (SNP), 3‐morpholinosydnonimine (SIN‐1) and vasoactive intestinal peptide (VIP). The effects of N omega‐nitro‐L‐arginine methyl ester (L‐NAME), Methylene Blue and alpha‐chymotrypsin (alpha‐CT) were studied. 2. EFS (10 Hz, 1 ms, 40 V for 30 s) evoked a time‐dependent relaxation accompanied by a concurrent rise in cGMP, both of which were maximal at 30 s and unaffected by epithelium removal. Levels of cAMP were more variable than those of cGMP and were not significantly changed at any time point. 3. SIN‐1 (1 mM) and SNP (100 microM) also produced time‐dependent relaxations which were maximal between 2 and 8 min, accompanied by concomitant rises in cGMP; however, these changes were larger than those associated with i‐NANC relaxations. cAMP levels were unchanged at all time points. 4. EFS‐evoked i‐NANC relaxations and cGMP increases (time, t = 30 s) were inhibited by L‐NAME. The effects were partially reversed by L‐arginine (1 mM), but not by D‐arginine. D‐NAME and alpha‐CT (2 u ml‐1) had no effect on either relaxation or cGMP accumulation. Tetrodotoxin (TTX, 3 microM) inhibited both relaxation and cGMP accumulation. 5. VIP (1 microM) also produced a time‐dependent relaxation associated with a concurrent rise in cAMP levels with no change in cGMP levels. 6. Methylene Blue (10 microM) partially inhibited EFS (10 Hz)‐evoked i‐NANC relaxation and cGMP accumulation, and almost completely inhibited both relaxation and cGMP accumulation evoked by SIN‐1 (1 mM). Methylene Blue had no significant effect on relaxation or cGMP accumulation evoked by SNP (100 microM). 7. Neural i‐NANC relaxations in HTSM are associated with a concurrent selective accumulation of cGMP which is unaffected by epithelium removal. This is inhibited in a stereoselective manner by L‐NAME and mimicked by SNP and SIN‐1; however, cGMP accumulation was greatly increased with SNP and SIN‐1 suggesting compartmentalized changes in cGMP content. VIP also caused relaxation associated with an increase of cAMP; however, no evidence was found for VIP being involved in i‐NANC relaxation. Hence nitric oxide (NO), or a NO‐containing complex, appears to mediate i‐NANC responses in human trachea in vitro.
Evidence for two different heat transduction mechanisms in nociceptive primary afferents innervating monkey skin.
Authors: Treede R D , Meyer R A , Raja S N , Campbell J N
Published: December 2014

1. Mechano‐ and heat‐sensitive A fibre nociceptors (AMHs) and C fibre nociceptors (CMHs) in hairy skin (forty‐six AMHs and twenty‐one CMHs) and in glabrous skin (fifty‐nine AMHs and ten CMHs) of anaesthetized monkeys were tested with a 30 s, 53 degrees C heat stimulus, delivered by a laser thermal stimulator (0.1 s rise time, 7.5 mm diameter). 2. Two types of heat response were observed in hairy skin AMHs. Type I AMHs had a peak discharge towards the end of the stimulus, response latencies to heat of up to several seconds, a median heat threshold greater than 53 degrees C, and a mean conduction velocity of 25 m s‐1 (n = 33). Type II AMHs had a peak discharge within 1‐3 s, a mean response latency of 120 ms, a median heat threshold of 46 degrees C, and a mean conduction velocity of 15 m s‐1 (n = 13). Type I AMH fibres were sensitized to heat, whereas heat responses of type II AMHs were suppressed following the intense heat stimulus. 3. In glabrous skin, only type I AMHs were found. The absence of type II AMHs is consistent with the absence of first pain to heat in glabrous skin. 4. C fibre nociceptors in hairy skin had a peak discharge near stimulus onset, a mean response latency of 100 ms and a median heat threshold of 41 degrees C. Heat responses of CMHs in glabrous skin were not significantly different from those in hairy skin. 5. Only type II AMHs had response latencies that were short enough to explain first pain to heat. Heat thresholds of type II AMHs were significantly higher than those of CMHs. 6. These results suggest two different heat transduction mechanisms in nociceptive afferents. For one, heat energy is quickly transduced into action potentials, and the peak discharge is reached soon after stimulus onset. For the other, the transduction of heat is distinctly slower, and the peak discharge occurs near the end of the stimulus. Chemically mediated sensitization may be involved in the second transduction mechanism.
Dipeptide transport and hydrolysis in isolated loops of rat small intestine: effects of stereospecificity.
Authors: Lister N , Sykes A P , Bailey P D , Boyd C A , Bronk J R
Published: December 2014

1. Isolated jejunal loops of rat small intestine were perfused by a single pass of bicarbonate Krebs‐Ringer solution containing either D‐ or L‐phenylalanine or one of eight dipeptides formed from D‐ or L‐alanine plus D‐ or L‐phenylalanine. 2. At 0.5 mM L‐phenylalanyl‐L‐alanine increased serosal phenylalanine appearance to forty times the control rate giving a value similar to that found with 0.5 mM free L‐phenylalanine. No serosal dipeptide could be detected. 3. Perfusions with the two mixed dipeptides with N‐terminal D‐amino acids (D‐alanyl‐L‐phenylalanine and D‐phenylalanyl‐L‐alanine) gave rise to the appearance of intact dipeptides in the serosal secretions although there were substantial differences in their rates of absorption and subsequent hydrolysis. 4. L‐Alanyl‐D‐phenylalanine was absorbed from the lumen three to five times as fast as L‐phenylalanyl‐D‐alanine. At 1 mM L‐alanyl‐D‐phenylalanine transferred D‐phenylalanine across the epithelial layer at more than seven times the rate found with the same concentration of the free D‐amino acid. 5. Perfusions with D‐alanyl‐D‐phenylalanine or D‐phenylalanyl‐D‐alanine showed that these two dipeptides are poor substrates for both transport and hydrolysis by the rat small intestine. 6. Analysis of mucosal tissue extracts after perfusion with the two mixed dipeptides with N‐terminal D‐amino acids revealed that both dipeptides were accumulated within the mucosa and suggested that exit across the basolateral membrane was rate limiting for transepithelial dipeptide transport.
Subatmospheric closing pressures in individual microvessels of rats and frogs.
Authors: MacPhee P J , Michel C C
Published: December 2014

1. We have investigated the hypothesis that ascending vasa recta (AVR) in the rat renal medulla are able to remain open when the external pressure is greater than the internal. 2. Individual vasa recta were cannulated in anaesthetized rats with Evans Blue albumin solution and then occluded downstream prior to the first branchpoint. When the intraluminal pressure was lowered, the lumina collapsed at a mean pressure of approximately ‐4.0 cmH2O for both AVR and descending vasa recta. 3. The studies were extended to include microvessels from rat spinotrapezius muscle and mesentery and frog mesentery; mean closing pressures were ‐3.2, ‐4.2 and ‐5.3 cmH2O, respectively. 4. Subatmospheric closing pressures may allow small differences in hydrostatic pressure alone to drive fluid uptake into the AVR.
Different mechanisms for use‐dependent depression of two GABAA‐mediated IPSCs in rat hippocampus.
Authors: Pearce R A , Grunder S D , Faucher L D
Published: December 2014

1. The mechanisms involved in the use‐dependent depression of GABAA,fast and GABAA,slow, two GABAA‐mediated IPSCs in the rat hippocampal slice preparation, were investigated by observing the effects of paired‐pulse depression and of baclofen and CGP 35348 on monosynaptic inhibitory currents recorded from CA1 pyramidal neurons. 2. The second of a pair of evoked responses that consisted of both inhibitory components was depressed and decayed more rapidly compared to the first at an interpulse interval (IpI) of 200 ms. This effect was due to a decrease in the amplitude of GABAA,slow, with no effect on the time constant of decay or on the amplitude or time constant of GABAA,fast. 3. The time course of paired‐pulse depression of both components at IpIs ranging from 5 to 2560 ms was compared. GABAA,slow was depressed maximally by 55% at IpIs of 80‐160 ms. GABAA,fast was depressed maximally by 38% at 5 ms, and recovered exponentially with a time constant of 130 ms. 4. GABAA,slow was more sensitive than GABAA,fast to depression by baclofen. GABAA,slow was susceptible to complete block, with an ED50 of approximately 200 nM for (+/‐)‐baclofen and 100 nM for the active enantiomer, (R)‐(+)‐baclofen. GABAA,fast was blocked by only 50% by the highest concentrations of baclofen tested (10‐100 microM (R)‐(+)‐baclofen), with an ED50 of approximately 2 microM for (+/‐)‐baclofen and 1 microM for (R)‐(+)‐baclofen. Paired‐pulse depression of GABAA,fast was not occluded by 10 or 100 microM (R)‐(+)‐baclofen. 5. The GABAB antagonist CGP 35348 (0.4‐1 mM), prevented paired‐pulse depression of GABAA,slow at IpIs of 160 to 200 ms, and reversed the depression of GABAA,fast by baclofen, but had no effect on paired‐pulse depression of GABAA,fast at IpIs of 20 to 40 ms. 6. It is concluded that use‐dependent depression of GABAA,slow, but not GABAA,fast, is mediated by a presynaptic GABAB receptor. It is speculated that use‐dependent depression of GABAA,fast, which occurs only over a much faster time scale, may be due to rapid postsynaptic GABAA receptor desensitization.
A monovalent cationic conductance that is blocked by extracellular divalent cations in Xenopus oocytes.
Authors: Arellano R O , Woodward R M , Miledi R
Published: December 2014

1. Native Xenopus oocytes were voltage clamped and exposed to Ringer solutions containing low concentrations of divalent cations. Oocytes, held at ‐60 mV, developed a reversible non‐inactivating smooth inward current (Ic) associated with an increase in membrane conductance. 2. Ic was selectively carried by cations (Na+, K+), indicating that the current was not the result of a non‐specific membrane breakdown, but was due instead to removal of a blocking effect of divalent cations on a specific population of endogenous ionic channels located in the oocyte membrane. 3. The blocking effects of Ca2+ and Mg2+ were voltage dependent, implying action at a binding site within the pore of the cationic channel. For example, the half‐maximal inhibition (IC50) of Ic by Ca2+ was 61 microM in oocytes held at ‐60 mV and 212 microM in oocytes held at 0 mV. 4. The Ic channels could be unblocked by depolarization of the membrane even in the presence of physiological concentrations of Ca2+ or Mg2+. The unblocking of the channels was observed as a slowly developing outward current. 5. The novel cationic current was substantially reduced following in vitro maturation of oocytes by treatment with progesterone (10 microM, 4‐5 h). 6. The physiological role of Ic channels remains to be elucidated. Nonetheless, their characteristics explain the ionic basis of the sensitivity of oocytes to reductions in extracellular divalent cations and raise the possibility that the channels play a role in calcium homeostasis.
Volume‐activated chloride channels in rat parotid acinar cells.
Authors: Arreola J , Melvin J E , Begenisich T
Published: December 2014

1. Rat parotid acinar cells undergo a regulatory volume decrease in response to hypotonically induced cell swelling that is sensitive to K+ and Cl‐ gradients. To investigate the potential mechanisms involved, the whole‐cell patch‐clamp technique was used to characterize a volume‐sensitive Cl‐ channel in rat parotid acinar cells. 2. Exposure of cells to a hyposmotic gradient induced large Cl‐ currents that exhibited outward rectification and were not affected by membrane potential or the absence of intracellular Ca2+. Low external pH increased the currents at all potentials without affecting current kinetics. These currents were nearly abolished when the cells were in hypertonic conditions. This decrease in the current amplitude was correlated with a decrease in the cell size. 3. The volume‐sensitive currents displayed little or no time dependence, whereas Ca(2+)‐activated Cl‐ channels, present in the same cells, displayed slow activation kinetics and large, time‐dependent tail currents upon repolarization to the holding potential. 4. The reversal potential of the osmotically activated channels was close to the predicted chloride equilibrium potential and was sensitive to the physiological extracellular Cl‐ concentration ([Cl‐]o). The relationship between reversal potential and [Cl‐]o was fitted to a modified Nernst equation with a slope of 51 mV per decade, consistent with a Cl‐ selective conductance. 5. The anion permeability sequence of the channel, obtained from the shifts of the reversal potentials of the volume‐sensitive Cl‐ current, was: SCN‐ > I‐ > NO‐3 > Br‐ > Cl‐ > formate > propionate = methanesulphonate = acetate > or = F‐ > or = butyrate > valerate > gluconate = glucuronate = glutamate. 6. The current through the volume‐sensitive channels was inhibited by the Cl‐ channel blocker SITS (4‐acetamido‐4'‐isothiocyanatostilbene‐2,2'‐disulphonic acid) in a voltage‐dependent manner. 7. We conclude that rat parotid acinar cells express an outwardly rectifying Cl‐ current that can be activated by swelling under hypotonic conditions. This Cl‐ conductance may be an element of the cellular mechanisms of volume regulation in exocrine glands.
Localization of chemosensitive structures in the isolated brainstem of adult guinea‐pig.
Authors: Morin-Surun M P , Boudinot E , Schäfer T , Denavit-Saubié M
Published: December 2014

1. Central respiratory chemosensitivity has been intensively examined but some questions remain unsolved; namely, what is the nature of the stimulus (fixed acid and/or CO2) and where is the site of brainstem chemosensitivity (near the ventral medullary surface or structures deeper within the brainstem)? To examine these questions, we used the in vitro isolated brainstem of adult guinea‐pig perfused independently through the basilar artery and the bath. 2. Respiratory motor output was recorded with a suction electrode from cranial hypoglossal (XII) roots. Changes in pH and CO2 in the Krebs perfusate were made by changing either the bicarbonate concentration or the PCO2 saturating the Krebs solution. 3. Changes in basilar artery perfusate consisting of (i) an acidifying increase in PCO2 (hypercapnic acidic Krebs solution), (ii) an increase in PCO2 with no change in pH (hypercapnic Krebs solution), or (iii) a decrease in pH with no change in PCO2 (acidic Krebs solution) evoked increases in respiratory frequency and a concomitant decrease in inspiratory burst amplitude. 4. Bath superfusion with hypercapnic acidic Krebs solution increased the inspiratory burst amplitude with no effect on respiratory burst frequency. 5. Bath superfusion with hypercapnic non‐acidic Krebs solution increased the inspiratory burst amplitude and decreased the respiratory frequency, while normocapnic acidic Krebs solution increased the respiratory frequency with no change in burst amplitude. 6. These results show that respiratory responses to changes in CO2 and pH depend upon the sites of action. While a CO2 increase or a pH decrease affected the respiratory frequency in the deep brainstem structures (perfused through the basilar artery), CO2 respiratory chemosensitivity at the ventral surface could be differentiated from the hydrogen ion chemosensitivity. This suggests that different mechanisms mediated respiratory responses when deep versus superficial brainstem structures were stimulated.