bluuebunny/crossref_metadata_2025 huggingface dataset:
Regenerative and non‐regenerative calcium transients in hamster eggs triggered by inositol 1,4,5‐trisphosphate.
Authors: Galione A , Swann K , Georgiou P , Whitaker M
Published: December 2014

1. Inositol 1,4,5‐trisphosphate (InsP3) injected into unfertilized golden hamster eggs elicits a hyperpolarizing response (HR) that is due to stimulation of calcium‐activated potassium channels in the egg plasma membrane. 2. A single injection of InsP3 gave a single HR above a threshold value of 0.3 nM. At 5 nM and above, InsP3 induced HRs with no detectable latency. At concentrations between these two values a latency was observed. The amplitude of the HR was independent of InsP3 concentration. 3. A second HR could be elicited by injection of InsP3, but five times more InsP3 was required to trigger a second HR, and 10‐100 times more to give an HR of similar magnitude to the first, and there was no latency. 4. The increase in [Ca2+]i in response to an initial injection of 1 nM InsP3 could be resolved into two distinct components: a slow, early rise immediately after InsP3 injection (phase I) followed by a larger and more rapid increase (phase II). The initiation of an HR coincided with the second component of the [Ca2+]i increase. 5. Further injection of InsP3 resulted only in slow, smaller increases in [Ca2+]i that resembled phase I and often did not cause an HR. Phase II appeared to be absent. However, 100‐fold greater InsP3 concentrations gave slow, larger Ca2+ transients (and HRs) with no detectable latency. 6. If large amounts of InsP3 were allowed to leak into the eggs constantly from a pipette, repetitive calcium transients were seen. Unlike the sustained repetitive responses seen at fertilization, they were often smaller than the initial transient and less well sustained. However, a subsequent transient could still be elicited on injection of very large concentrations of InsP3. 7. InsP3 can induce regenerative, all‐or‐none [Ca2+]i increase (CICR) in hamster eggs, often with a long latency, as well as non‐regenerative increases. InsP3 injections desensitize CICR and cannot mimic all the features of Ca2+ signalling at fertilization in the hamster egg, in particular, the sensitization of CICR caused by the sperm.
Muscarinic amplification of fast excitation in hilar neurones and inhibition in granule cells in the guinea‐pig hippocampus.
Authors: Brunner H , Misgeld U
Published: December 2014

1. Effects of the cholinergic agonist, carbachol (CCh), or the acetylcholinesterase inhibitor, eserine, on presumed inhibitory hilar neurones and on inhibition in granule cells were studied by intracellular recording in guinea‐pig hippocampal slices. 2. CCh (1‐5 microM) strongly enhanced the discharge activity of hilar neurones and spontaneous and evoked IPSPs in granule cells. 3. Eserine, in an atropine‐sensitive manner, increased the excitability of hilar neurones through effects on membrane properties and on excitatory synaptic barrage. EPSPs readily triggered long‐duration burst discharges. In granule cells, the amplitudes of evoked GABAA and GABAB receptor‐mediated IPSPs were enhanced. 4. In the presence of eserine and antagonists for glutamatergic and GABAergic synaptic transmission, train stimulation evoked atropine‐sensitive slow EPSPs. In contrast to those in granule cells, slow EPSPs in hilar neurones were invariably preceded by a strong burst‐after‐hyperpolarization. 5. We suggest that acetylcholine, released from septo‐hippocampal fibres, amplifies fast synaptic excitation of inhibitory hilar neurones and inhibition of granule cells. In the dentate area, muscarinic receptor‐mediated effects are faster than anticipated from the time course of the slow EPSP.
Comparison of neuronal nicotinic receptors in rat sympathetic neurones with subunit pairs expressed in Xenopus oocytes.
Authors: Covernton P J , Kojima H , Sivilotti L G , Gibb A J , Colquhoun D
Published: December 2014

1. The agonist sensitivity of nicotinic acetylcholine receptors in rat superior cervical ganglion (SCG) neurones was compared with that of cloned receptors expressed in Xenopus oocytes by pairwise injections of alpha 3‐beta 2 or alpha 3‐beta 4 neuronal nicotinic subunit combinations. 2. Agonist responses in rat SCG neurones indicated that cytisine was the most potent agonist and lobeline the least potent (rank order of potency: cytisine > dimethylphenylpiperazinium iodide (DMPP) > nicotine > ACh > carbachol > lobeline). 3. Receptors expressed in oocytes by injection of alpha 3 and beta 2 subunits had a relatively high sensitivity to DMPP and low sensitivity to cytisine (rank order of potency: DMPP > ACh > lobeline > carbachol > nicotine > cytisine), whereas receptors composed of alpha 3 and beta 4 subunits had a high sensitivity to cytisine and low sensitivity to DMPP (rank‐order of potency: cytisine > nicotine approximately ACh > DMPP > carbachol > lobeline). 4. With the exception of responses to DMPP, agonist sensitivity measurements suggest that nicotinic receptors in the rat SCG are composed of alpha 3 and beta 4 subunits. The results are discussed in terms of the receptor subunit mRNAs known to be expressed in the rat SCG and previous evidence of functional heterogeneity of rat SCG nicotinic acetylcholine receptors.
Ionic conductances contributing to spike repolarization and after‐potentials in rat medial vestibular nucleus neurones.
Authors: Johnston A R , MacLeod N K , Dutia M B
Published: December 2014

1. Intracellular recordings were made from 123 tonically active medial vestibular nucleus (MVN) neurones in a horizontal slice preparation of the dorsal brainstem of the rat. On the basis of their averaged action potential shapes, the cells were classified as either type A, having a single deep after‐hyperpolarization (AHP; 40/123 cells, 33%), or type B, having an early fast AHP and a delayed slow AHP (83/123 cells, 67%). The two cell types were distributed throughout the rostrocaudal extent of the MVN. 2. In type A cells TEA reduced the single deep AHP and decreased the rate of spike repolarization. Depolarizing current pulses from a hyperpolarized membrane potential elicited spikes with short plateau potentials in TEA. These persisted in Ca(2+)‐free medium but were abolished along with the spontaneous activity in TTX. Ca(2+)‐free medium did not affect the initial rate of repolarization but reduced the deep AHP. Apamin and carbachol had little effect. 4‐Aminopyridine (4‐AP) slowed spike repolarization and the AHP amplitude by a small amount. Thus, in type A cells spike repolarization and AHP appear to be mediated largely by a TEA‐sensitive potassium current (presumably IK) and an apamin‐insensitive Ca(2+)‐activated potassium current (presumably IC). 3. The early fast AHP in type B cells was readily abolished in TEA. In seven of ten type B cells tested, the spontaneous spikes developed plateau potentials of 100‐120 ms duration in 10 mM TEA, which then became 7‐9 s long in Ca(2+)‐free medium. In the remaining three cells, the spontaneous plateaux were 1.75‐2 s long in TEA, and were reduced to 30‐100 ms in Ca(2+)‐free medium. TTX abolished the spontaneous spikes and plateaux. The delayed AHP was abolished by apamin, which induced irregular firing. 4‐AP slowed spike repolarization and abolished the fast AHP, but did not induce plateaux. Thus, in type B cells spike repolarization involves a TEA‐sensitive current (presumably IK) as well as IC and the 4‐AP‐sensitive potassium current IA, while the apamin‐sensitive potassium current IAHP is responsible for the delayed AHP. 4. The tonic activity in type B cells appears to be regulated mainly by interactions between a persistent Na+ current, which in most cells is large enough to generate plateaux when repolarization is impeded in TEA, and the hyperpolarization mediated by IAHP. About 30% of type B cells have an additional inward Ca2+ current.(ABSTRACT TRUNCATED AT 400 WORDS)
Mediation of baroreceptor inhibition of sympathetic nerve activity via both a brainstem and spinal site in rats.
Authors: Lewis D I , Coote J H
Published: December 2014

1. The possible involvement of a spinal site of sympatho‐inhibitory action in the baroreceptor reflex pathways was investigated by determining the effect of phenylephrine‐induced, baroreceptor‐mediated inhibition on a spinally evoked excitatory response of renal nerve activity before, during and after removal of tonic descending excitatory drive from the rostral ventrolateral medulla (RVLM). 2. Stimulation of descending excitatory axons at the C4 vertebral level evoked a highly reproducible excitatory response (mean variance, 2.2 +/‐ 0.6%) in a renal sympathetic nerve with a latency of 72 +/‐ 5.7 ms and duration of 211 +/‐ 32 ms. 3. Following baroreceptor activation, the magnitude of this spinally evoked response was reduced by 33.5 +/‐ 4.2% compared with control spinal response. 4. To remove tonic descending excitatory drive, glycine was microinjected bilaterally into the RVLM (RVLM block); this briefly and reversibly abolished spontaneous sympathetic nerve activity. 5. Following RVLM block, the spinally evoked response in a renal sympathetic nerve was inhibited by 16.9 +/‐ 4.4% during baroreceptor activation. 6. Intrathecal administration of the glycine antagonist strychnine to the lower thoracic segments of the spinal cord virtually abolished this inhibition. 7. It was concluded that baroreceptor inhibition of sympathetic activity occurs at a spinal site as well as a supraspinal one. Glycine is a likely mediator of the inhibition at the spinal site.
The role of ascending excitatory and descending inhibitory pathways in peristalsis in the isolated guinea‐pig small intestine.
Authors: Waterman S A , Tonini M , Costa M
Published: December 2014

1. The effects of experimental manipulations to alter the activation of ascending excitatory and descending inhibitory reflexes on peristalsis were studied in isolated segments of guinea‐pig small intestine. 2. The normal site of initiation of the peristaltic contraction, the oral end, was always shifted to a point just anal to a crush which interrupted enteric neuronal pathways. 3. Shortening the functional length of the intestine by a series of crushes, thus effectively reducing the length of enteric neuronal reflex pathways, led to a progressive increase in the threshold distension for triggering the peristaltic contraction. 4. A sleeve placed around the intestine to prevent it from being distended by fluid led to a shift in the site of initiation of the peristaltic contraction to a point just anal to the sleeve. Furthermore, sleeves placed in the anal half of the intestine were able to stop propagation of the contraction. 5. The effect of these manipulations on peristalsis suggests that ascending excitatory and descending inhibitory enteric pathways, activated by distension, determine the pattern of peristaltic activity. The peristaltic contraction is initiated at the oral end as a result of the summation of ascending excitatory inputs and the relative absence of inputs from descending inhibitory pathways at this point. The magnitude of the distension for triggering this contraction is determined by a balance between ascending excitatory and descending inhibitory inputs to the circular muscle. Propagation of the circular muscle contraction requires the activation of ascending excitatory pathways at each point along the intestine and the sequential inactivation of the descending inhibitory reflex pathways anal to the contraction. The propagation of the circular muscle contraction stops when there is no longer a sufficient distension stimulus ahead.
Gating mode conversion by proteolysis in a large‐conductance K+ channel from embryonic rat telencephalon.
Authors: Mienville J M
Published: December 2014

1. In situ patch‐clamp recordings of early embryonic large‐conductance K+ channels consistently revealed (86% of patches) a complex behaviour characterized by noisy fluctuations between open and closed states of relatively short duration. 2. This behaviour is similar to the buzz mode, a type of gating observed only very rarely in some channels. Its prevalence in proliferative neuroepithelium may thus constitute a criterion of immaturity. 3. In 89% of patches, the buzz mode was converted to a ‘normal’ mode by intracellular exposure to trypsin. 4. These observations suggest that the immature channel protein includes (or is affected by) a cytoplasmic component, the presence or absence of which determines certain sets of conformational transitions.
Inhibitory effect of adenosine on electrical activity of frog melanotrophs mediated through A1 purinergic receptors.
Authors: Mei Y A , Vaudry H , Cazin L
Published: December 2014

1. The effects of adenosine were studied in cultured frog melanotrophs by the patch‐clamp technique. 2. In cell‐attached experiments, most cells responded to adenosine (50 microM) by a reversible inhibition of action current discharges without any apparent desensitization. 3. In whole‐cell experiments, adenosine provoked a hyperpolarization accompanied by a depression of spontaneous action potentials and a decrease in membrane resistance. When adenosine was repeatedly applied, tachyphylaxis was observed. Addition of GTP (100 microM) in the intracellular solution augmented the percentage of cells hyperpolarized by adenosine, and the duration and amplitude of the hyperpolarization, and prevented the tachyphylaxis. 4. Pretreatment with pertussis toxin (1 microgram ml‐1) blocked adenosine‐induced inhibition. 5. In cells dialysed with the non‐hydrolysable GTP analogue GTP gamma S (100 microM), adenosine caused a sustained, strong hyperpolarization and an irreversible inhibition of spikes. 6. The effect of adenosine was mimicked by the A1 receptor agonist R‐PIA (R‐N6‐phenylisopropyl‐adenosine; 50 microM) and blocked by the A1 receptor antagonist CPDPX (8‐cyclopentyl‐1,3‐dipropylxanthine, 50 microM). The A2 receptor antagonist CGS15943 (9‐chloro‐2‐(2‐furanyl)‐5,6‐dihydro‐1,2,4‐triazolo[1,5‐c] quinazoline‐5‐imine; 50 microM) did not affect the adenosine‐induced response. 7. The results suggest that, in frog melanotrophs, adenosine exerts a direct hyperpolarizing effect accompanied by blockage of spontaneous action potentials. The effect of adenosine is mediated through A1 receptors coupled to a Gi/o protein.
Calcium channel currents in bovine adrenal chromaffin cells and their modulation by anaesthetic agents.
Authors: Charlesworth P , Pocock G , Richards C D
Published: December 2014

1. The calcium channel currents of bovine adrenal chromaffin cells were characterized using a variety of voltage pulse protocols and selective channel blockers before examination of their modulation by anaesthetic agents. 2. All the anaesthetics studied (halothane, methoxyflurane, etomidate and methohexitone) inhibited the calcium channel currents in a concentration‐dependent manner and increased the rate of current decay. 3. The anaesthetics did not shift the current‐voltage relation nor did they change the voltage for half‐maximal channel activation derived from analysis of the voltage dependence of the tail currents. None of the anaesthetics appeared to alter the time constant of tail current decay. 4. To complement earlier studies of the inhibitory actions of anaesthetics on K(+)‐evoked catecholamine secretion and the associated Ca2+ uptake, the IC50 values for etomidate and methohexitone were determined using a biochemical assay. The IC50 values for anaesthetic inhibition of calcium channel currents corresponded closely with those for inhibition of K(+)‐evoked calcium uptake and catecholamine secretion. 5. The inhibitory effect of the volatile anaesthetics and etomidate is best explained by dual action: a reduction in the probability of channel opening coupled with an increase in the rate of channel inactivation. Methohexitone appeared to inhibit the currents by a use‐dependent slow block.
Central interleukin‐1 beta stimulation of vasopressin release into the rat brain: activation of an antipyretic pathway.
Authors: Wilkinson M F , Horn T F , Kasting N W , Pittman Q J
Published: December 2014

1. Arg8‐vasopressin (AVP)‐containing neurones of the bed nucleus of the stria terminalis (BST), which terminate in the ventral septal area (VSA) of the rat brain, provide a pathway which controls body temperature during fever. The present study was conducted to test the hypothesis that interleukin‐1 beta (IL‐1 beta) may trigger the antipyretic response by evoking AVP release from BST neurones projecting into the VSA. 2. The push‐pull perfusion technique and radioimmunoassay were utilized to determine the AVP concentrations of retrieved VSA perfusion fluid in urethane‐anaesthetized rats following BST infusion of vehicle or IL‐1 beta (125 or 500 pg (2 microliters)‐1). 3. Ventral septal AVP levels significantly increased from basal levels, in a dose‐related manner, in response to IL‐1 beta (0‐500 pg). Electrical stimulation of the same areas of the BST also evoked AVP release into the VSA. 4. IL‐1 beta infusions and electrical stimulation of the BST resulted in significant increases in rectal temperature. In IL‐1 beta‐treated animals (500 pg), the change in body temperature and VSA AVP release were negatively correlated (P < 0.001). However, external heating of the animals to approximately the same levels as electrically stimulated or IL‐1 beta treated rats did not affect basal AVP release. 5. These data show that IL‐1 beta is a potent stimulus for AVP release from BST neurones and supports BST involvement in neuro‐immune interactions. We propose, that in addition to febrogenesis, IL‐1 beta is also a key component in the process of endogenous antipyresis by activating vasopressinergic BST neurones to release AVP during fever.
Storage and release of mechanical energy by contracting frog muscle fibres.
Authors: Cavagna G A , Heglund N C , Harry J D , Mantovani M
Published: December 2014

1. Stretching a contracting muscle leads to greater mechanical work being done during subsequent shortening by its contractile component; the mechanism of this enhancement is not known. 2. This mechanism has been investigated here by subjecting tetanized frog muscle fibres to ramp stretches followed by an isotonic release against a load equal to the maximum isometric tension, T(o). Shortening against T(o) was taken as direct evidence of an absolute increase in the ability to do work as a consequence of the previous stretch. 3. Ramp stretches (0.5‐8.6% sarcomere strain, confined to the plateau of the isometric tension‐length relationship) were given at different velocities of lengthening (0.03‐1.8 sarcomere lengths s‐1). Isotonic release to T(o) took place immediately after the end of the ramp, or 5‐800 ms after the end of the largest ramp stretches. The length changes taking place after release were measured both at the fibre end and on a tendon‐free segment of the fibre. The experiments were carried out at 4 and 14 degrees C. 4. After the elastic recoil of the undamped elastic elements, taking place during the fall in tension at the instant of the isotonic release, a well‐defined shortening took place against T(o) (transient shortening against T(o)). 5. The amplitude and time course of transient shortening against T(o) were similar at the fibre end and in the segment, indicating that it is due to a properly of the sarcomeres and not due to stress relaxation of the tendons. 6. Transient shortening against T(o) increased with sarcomere stretch amplitude up to about 8 nm per half‐sarcomere independent of stretch velocity. 7. When a short delay (5‐20 ms) was introduced between the end of the stretch and the isotonic release, the transient shortening against T(o) did not change; after longer time delays, the transient shortening against T(o) decreased in amplitude. 8. The velocity of transient shortening against T(o) increased with temperature with a temperature coefficient, Q10, of approximately 2.5. 9. It is suggested that transient shortening against T(o) results from the release of mechanical energy stored within the damped element of the cross‐bridges. The cross‐bridges are brought into a state of greater potential energy not only during the ramp stretch, but also immediately afterwards, during the first phase of stress relaxation.
Down‐regulation of A1 adenosine receptors coupled to muscarinic K+ current in cultured guinea‐pig atrial myocytes.
Authors: Bünemann M , Pott L
Published: December 2014

1. Muscarinic K+ current (IK(ACh)) was measured in cultured atrial myocytes from hearts of adult guinea‐pigs using whole‐cell voltage clamp. IK(ACh) was activated by superfusion with solutions containing either acetylcholine (ACh) or adenosine (Ado), in saturating concentrations of 2 microM (ACh) and 1 mM (Ado), respectively. 2. In freshly isolated cells the amplitude of the current activated by Ado (IK(Ado)) was 58% (mean) of the current that was induced by ACh. In serum‐free culture this relation, but also the absolute density of IK(ACh), remained fairly constant for up to 8 days. 3. If the culture medium was supplemented with fetal calf serum (FCS, 5%) the relation IK(Ado)/IK(ACh) gradually decayed, reaching a value of less than 0.1 on days 7‐8, whereas the response to ACh remained stable over this period of time. 4. After treatment of cells with FCS‐containing medium, no recovery was observed upon FCS withdrawal for up to 4 days. 5. The effect of FCS on responsiveness to Ado was half‐maximal at about 1% (v/v). The active principle can be dialysed (mol. mass exclusion: 10 kDa). It is not identical with an albumin‐associated factor that has been shown to be a potent activator of atrial IK(ACh) upon acute superfusion. Loss of responsiveness to Ado was paralleled by a reduction of binding sites to the A1 adenosine receptor‐specific radioligand 8‐cyclopentyl‐1,3‐dipropylxanthine ([3H]CPX). 6. It is concluded that FCS contains a factor that causes down‐regulation of A1 Ado receptors. The signalling pathway that leads to an increased opening activity of IK(ACh) channels and other receptors, such as the M2 muscarinic receptor, linked to this signalling pathway are not affected by this factor.
Factors controlling changes in intracellular Ca2+ concentration produced by noradrenaline in rat mesenteric artery smooth muscle cells.
Authors: Baró I , Eisner D A
Published: December 2014

1. The intracellular Ca2+ concentration ([Ca2+]i) was measured in mesenteric artery smooth muscle cells using the fluorescent indicator indo‐1. 2. Noradrenaline (1‐10 microM) produced a transient increase in [Ca2+]i. This response was unaffected by the removal of external calcium suggesting that the bulk of the increase in [Ca2+]i produced by noradrenaline is due to release from an intracellular store. 3. The maintained application of caffeine (10 mM) produced a transient rise in [Ca2+]i. The rate of relaxation was slower than that of the noradrenaline response. If caffeine was removed at the peak of the rise in [Ca2+]i then [Ca2+]i recovered more quickly than was the case in both the maintained response to noradrenaline and that to caffeine. 4. In the presence of noradrenaline, caffeine or thapsigargin elevated [Ca2+]i. However, if thapsigargin or caffeine was added first, the subsequent application of noradrenaline did not increase [Ca2+]i, suggesting that only part of the caffeine‐sensitive store is sensitive to noradrenaline. 5. The recovery of [Ca2+]i during the application of caffeine was unaffected by the removal of external sodium suggesting that Na+‐Ca2+ exchange is not important in the reduction in [Ca2+]i. The addition of lanthanum (1 mM) did, however, greatly slow [Ca2+]i recovery. 6. We conclude that the three major factors responsible for removing Ca2+ ions from the cytoplasm are: (i) a caffeine‐ and noradrenaline‐sensitive store (43%), (ii) a caffeine‐sensitive but noradrenaline‐insensitive store (36%), and (iii) a sarcolemmal Ca(2+)‐ATPase (16%). Finally, a 5% contribution remains to be accounted for.
Dendritic glutamate receptor channels in rat hippocampal CA3 and CA1 pyramidal neurons.
Authors: Spruston N , Jonas P , Sakmann B
Published: December 2014

1. Properties of dendritic glutamate receptor (GluR) channels were investigated using fast application of glutamate to outside‐out membrane patches isolated from the apical dendrites of CA3 and CA1 pyramidal neurons in rat hippocampal slices. CA3 patches were formed (15‐76 microns from the soma) in the region of mossy fibre (MF) synapses, and CA1 patches (25‐174 microns from the soma) in the region of Schaffer collateral (SC) innervation. 2. Dual‐component responses consisting of a rapidly rising and decaying component followed by a second, substantially slower, component were elicited by 1 ms pulses of 1 mM glutamate in the presence of 10 microM glycine and absence of external Mg2+. The fast component was selectively blocked by 2‐5 microM 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and the slow component by 30 microM D‐2‐amino‐5‐phosphonopentanoic acid (D‐AP5), suggesting that the fast and slow components were mediated by the GluR channels of the L‐alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) and NMDA type, respectively. The peak amplitude ratio of the NMDA to AMPA receptor‐mediated components varied between 0.03 and 0.62 in patches from both CA3 and CA1 dendrites. Patches lacking either component were rarely observed. 3. The peak current‐voltage (I‐V) relationship of the fast component was almost linear, whereas the I‐V relationship of the slow component showed a region of negative slope in the presence of 1 mM external Mg2+. The reversal potential for both components was close to 0 mV. 4. Kainate‐preferring GluR channels did not contribute appreciably to the response to glutamate. The responses to 100 ms pulses of 1 mM glutamate were mimicked by application of 1 mM AMPA, whereas 1 mM kainate produced much smaller, weakly desensitizing currents. This suggests that the fast component is primarily mediated by the action of glutamate on AMPA‐preferring receptors. 5. The mean elementary conductance of AMPA receptor channels was about 10 pS, as estimated by non‐stationary fluctuation analysis. The permeability of these channels to Ca2+ was low (approximately 5% of the permeability to Cs+). 6. The elementary conductance of NMDA receptor channels was larger, with a main conductance state of about 45 pS. These channels were 3.6 times more permeable to Ca2+ than to Cs+.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for a critical role of nitric oxide in the tonic excitation of rabbit renal sympathetic preganglionic neurones.
Authors: Hakim M A , Hirooka Y , Coleman M J , Bennett M R , Dampney R A
Published: December 2014

1. A large proportion of sympathetic preganglionic neurones contain nitric oxide synthase. The purpose of this study was to determine the effects of facilitation and inhibition of nitric oxide synthesis within the lower thoracic spinal cord (which contains the majority of renal preganglionic neurones) on renal sympathetic nerve activity (rSNA). 2. In anaesthetized rabbits, rSNA was recorded before and after intrathecal injection (50 microliters of 0.5 M solution) of either L‐arginine, a precursor of nitric oxide, or N omega‐nitro‐L‐arginine methyl ester (L‐NAME), an inhibitor of nitric oxide synthase, into the lower thoracic spinal cord. Spinal cord sections were also stained for the presence of NADPH diaphorase, a marker of nitric oxide synthesizing neurones. 3. A high density of NADPH diaphorase‐containing neurones was found within the intermediolateral cell column of the lower thoracic spinal cord. 4. Intrathecal injection of L‐arginine and L‐NAME resulted in a large increase (113 +/‐ 25%) and decrease (43 +/‐ 8%), respectively, in rSNA. In contrast, injection of the inactive isomers D‐arginine and D‐NAME had no significant effect on rSNA. 5. The results indicate that endogenous nitric oxide in the lower thoracic spinal cord (1) has a potent excitatory action on renal sympathetic preganglionic neurones, and (2) helps to maintain the tonic activity of renal sympathetic nerves under resting conditions.
Identification of an ATP‐dependent copper transport system in endoplasmic reticulum vesicles isolated from rat liver.
Authors: Bingham M J , Burchell A , McArdle H J
Published: December 2014

1. This paper identifies and characterizes an ATP‐dependent copper transport system in endoplasmic reticulum vesicles isolated from male rat liver. 2. The transporter has a Km of 2.5 +/‐ 1.2 mumol 1(‐1) copper glutathione (CuGSH) and a Vmax of 4.5 +/‐ 1.3 nmol (mg protein)‐1 (5 min)‐1 for copper. 3. At a copper concentration of 2 mumol l‐1, ATP dependence reaches saturation, with a Km for ATP of 4.7 +/‐ 2.4 mmol l‐1 and a Vmax of 2.8 +/‐ 0.6 nmol (mg protein)‐1 (5 min)‐1. 4. The uptake is dependent on ATP hydrolysis, since a low energy analogue of ATP, adenosine 5'‐[beta‐gamma‐methylene] triphosphate tetralithium (AMP.PCP), has no effect on copper uptake. 5. The transporter is a P‐type ATPase, since vanadate inhibits uptake with a high degree of specificity (100 mumol l‐1 inhibits uptake by 50% at a copper concentration of 2 mumol l‐1).
Imagination of dynamic exercise produced ventilatory responses which were more apparent in competitive sportsmen.
Authors: Wuyam B , Moosavi S H , Decety J , Adams L , Lansing R W , Guz A
Published: December 2014

1. The cardiorespiratory response to imagination of previously performed treadmill exercise was measured in six competitive sportsmen and six non‐athletic males. This was compared with the response to a control task (imaging letters) and a task not involving imagination (‘treadmill sound only’). 2. In athletes, imagined exercise produced increases in ventilation which varied within and between subjects. The mean maximal increase (11.71 min‐1) was approximately 20% of the ventilatory response to actual exercise. This was primarily due to treadmill speed‐related increases in respiratory frequency (mean maximal increase, 14.8 breaths min‐1) and resulted in significant reductions in end‐tidal PCO2 (mean maximal fall, 7 mmHg). These effects were greater (P < 0.01) than any observed during the control tasks. 3. Changes in heart rate (mean increase, 12 beats min‐1) were not significantly different from those observed during the control tasks (P > 0.2). 4. In non‐athletes, imagination of exercise produced no changes in cardiorespiratory variables. No significant differences were detected in subjective assessments of movement imagery ability between athletes and non‐athletes (P = 0.17). 5. This study demonstrates that ventilatory effects, when observed, are specific to imagination of exercise. The greater likelihood of generating ventilatory responses in highly trained athletes, experienced in ‘rhythmic’ sports, may be related to awareness of breathing and its role in exercise imagination strategy. A volitional component of the response cannot be discounted.
Volume‐activated chloride currents associated with the multidrug resistance P‐glycoprotein.
Authors: Higgins C F
Published: December 2014

The ability to regulate volume is an important property of most, if not all cells. In epithelial cells, amongst others, cell volume‐activated chloride channels are central to this response. The molecular identities of these channels are not yet known. Expression of the human multidrug resistance P‐glycoprotein (P‐gp) has been associated with cell volume‐regulated chloride currents, although the nature of this association is the subject of debate. Recent data indicate that P‐gp acts by regulating the activation of an endogenous channel protein. In this review, evidence associating P‐gp with cell volume‐activated chloride currents, and the possible mechanisms by which this might be achieved, are discussed.
Length dependence of Ca2+ sensitivity of tension in mouse cardiac myocytes expressing skeletal troponin C.
Authors: McDonald K S , Field L J , Parmacek M S , Soonpaa M , Leiden J M , Moss R L
Published: December 2014

1. Beat‐to‐beat performance of myocardium is highly dependent on sarcomere length. The physiological basis for this effect is not well understood but presumably includes alterations in the extent of overlap between thick and thin filaments. Sarcomere length dependence of activation also appears to be involved since length‐tension relationships in cardiac muscle are usually steeper than those in skeletal muscle. 2. An explanation recently proposed to account for the difference between length‐tension relationships is that the cardiac isoform of troponin C (cTnC) has intrinsic properties that confer greater length‐dependent changes in the Ca2+ sensitivity of tension than does skeletal troponin C (sTnC), presumably due to greater length‐dependent changes in the Ca(2+)‐binding affinity of cTnC. To test this hypothesis, transgenic mice were developed in which fast sTnC was expressed ectopically in the heart. This allowed a comparison of the length dependence of the Ca2+ sensitivity of tension between myocytes having thin filaments that contained either endogenous cTnC or primarily sTnC. 3. In myocytes from both transgenic and normal mice, the Ca2+ sensitivity of tension increased similarly when mean sarcomere length was increased from approximately 1.83 to 2.23 microns. In both cases, the mid‐point (pCa50) of the tension‐pCa (i.e. ‐log[Ca2+]) relationship shifted 0.12 +/‐ 0.01 pCa units (mean +/‐ S.E.M.) in the direction of lower Ca2+. 4. We conclude that the Ca2+ sensitivity of tension in myocytes changes as a function of sarcomere length but is independent of the isoform of troponin C present in the thin filaments.
Effects of creatine phosphate and inorganic phosphate on the sarcoplasmic reticulum of saponin‐treated rat heart.
Authors: Steele D S , McAinsh A M , Smith G L
Published: December 2014

1. Ventricular trabeculae from rat heart were permeabilized by treatment with saponin. In the presence of 150 nM Ca2+, application of 20 mM caffeine released Ca2+ from the sarcoplasmic reticulum (SR), resulting in a transient contracture. Ca2+ released from the SR was detected using fura‐2 fluorescence. The amplitudes of the caffeine‐induced Ca2+ transients were used to assess SR Ca2+ content. 2. In the absence of creatine phosphate (CP), introduction of 5‐30 mM inorganic phosphate (Pi) caused a net release of Ca2+ from the SR. Subsequent caffeine‐induced Ca2+ and tension transients were smaller in the presence of Pi. Under these conditions, 30 mM Pi decreased the caffeine‐induced Ca2+ transients by 45 +/‐ 3.1% (mean +/‐ S.D., n = 14). On removal of Pi, the [Ca2+] transiently decreased and the caffeine‐induced Ca2+ transients returned to control levels over 4‐6 min. 3. In the presence of CP (5‐15 mM), the Ca2+ transients were unaffected by the introduction of Pi (5‐30 mM) or slightly increased in amplitude. Pi (30 mM) significantly increased the caffeine‐induced Ca2+ transients by 7 +/‐ 8.8% (mean +/‐ S.D., n = 19, P < 0.05) in the presence of 15 mM CP. The release of Ca2+ on addition of Pi and decrease in [Ca2+] on Pi withdrawal was less pronounced or absent completely in the presence of CP. The inhibitory effects of Pi on caffeine‐induced Ca2+ release became apparent as the [CP] was decreased from 5 to 0 mM. 4. In the presence of the creatine phosphokinase inhibitor dinitro‐fluorobenzene (DNFB) the effects of Pi (in the presence of CP) were qualitatively similar to the results obtained in the absence of CP, although the decrease in caffeine‐induced Ca2+ release was less pronounced. 5. These results suggest that the rise in [Pi]i during ischaemia or anoxia will have little effect on the regulation of Ca2+ by the SR while the [CP]i remains above 5 mM. However, as the [CP] decreases below 5 mM, the accumulation of Pi within the cytosol will progressively reduce the SR Ca2+ content. CP may act in conjunction with endogenous creatine phosphokinase to modify the response of the SR to Pi, and possible mechanisms are considered.
Central inhibitory effects of muscimol and bicuculline on the milk ejection reflex in the anaesthetized rat.
Authors: Voisin D L , Herbison A E , Poulain D A
Published: December 2014

1. In order to determine whether GABAergic mechanisms are involved in the control of the milk ejection reflex in the rat, we examined the effects of central administration of a GABAA receptor agonist (muscimol) and antagonist (bicuculline) on the milk ejection reflex in the urethane‐anaesthetized rat. 2. Intracerebroventricular (i.c.v.) injection of both muscimol (n = 17), at doses of 5, 10 and 20 ng, and bicuculline (n = 15), at doses of 0.01, 0.1 and 0.3 microgram, inhibited the milk ejection reflex in a dose‐dependent manner. The bicuculline‐induced inhibition was accompanied by desynchronization of the electroencephalogram and, at the highest dose, by alteration in the sensitivity of the mammary gland to oxytocin. No significant effect on the milk ejection reflex was seen with i.c.v. isotonic saline (n = 5). 3. Injection of 20 (n = 5) or 40 ng (n = 2) muscimol or 0.1 microgram bicuculline (n = 5) i.c.v. did not significantly alter the rise in intramammary pressure evoked by electrical stimulation of the neurohypophysis. 4. Bilateral 400 nl microinfusions directly into the supraoptic nuclei of either muscimol (20‐100 ng microliter(‐1); n = 10) or bicuculline (0.15 micrograms microliter(‐1); n = 5) [corrected] resulted in an inhibition of the milk ejection reflex, which was not accompanied by desynchronization of the electroencephalogram. 5. The effects of i.c.v. injections of muscimol (15 and 20 ng) and bicuculline (0.01, 0.12 and 0.3 microgram) on the electrical activity of twenty‐seven antidromically identified supraoptic magnocellular neurones were examined. Both compounds resulted in an inhibition of the background firing of oxytocinergic and vasopressinergic cells, and delayed the occurrence of high frequency bursts in oxytocin neurones. In five supraoptic neurones, bicuculline induced a transient activation before inhibition. 6. The powerful inhibitory action on the milk ejection reflex of both muscimol and bicuculline provides evidence for the importance of GABA neurones in maintaining the functional integrity of the mechanisms which allow the intermittent and pulsatile release of oxytocin during suckling.
Inhibitory effect of sympathetic stimulation on activities of masseter muscle spindles and the jaw jerk reflex in rats.
Authors: Matsuo R , Ikehara A , Nokubi T , Morimoto T
Published: December 2014

1. To evaluate sympathetic effects on jaw muscles, the discharges of masseter muscle spindle afferents, jaw muscle electromyographic (EMG) activities and blood flow changes were compared in anaesthetized decerebrate rats before and during electrical stimulation of the cervical sympathetic trunk. 2. To eliminate the possibility of efferent control from the trigeminal motoneurones, muscle spindle activity was recorded from the cut peripheral end of the masseter nerve. The absence of a sympathetic component in the masseter nerve was confirmed by the horseradish peroxidase method. 3. Electrical stimulation of the sympathetic nerve at frequencies within the physiological range reduced muscle spindle afferent discharges evoked by passive jaw opening. 4. Sympathetic stimulation also reduced the EMG activity evoked by the jaw jerk reflex, which may reflect a sympathetic effect on spindle afferents. After cessation of stimulation, a transient increase in EMG activity was observed, which may be due to efferent supply from the trigeminal motoneurones. During rhythmical jaw movements, no sympathetic effect on EMG activity was detected. 5. The above sympathetic effect on muscle spindle afferents and EMG activity was independent of blood flow changes.
Step phase‐related excitability changes in spino‐olivocerebellar paths to the c1 and c3 zones in cat cerebellum.
Authors: Apps R , Hartell N A , Armstrong D M
Published: December 2014

1. Chronically implanted microwires were used to record extracellular field potentials generated in the c1 and c3 zones in the cortex of lobules V and VI of the cerebellum by non‐noxious stimuli delivered to the superficial radial nerve in the ipsilateral forelimb. Responses due to input via climbing fibre afferents were studied; their latency and other characteristics identified them as mediated mainly via the dorsal funiculus spino‐olivocerebellar path (DF‐SOCP). 2. Responses at individual sites were studied repeatedly with a range of stimulus intensities and during two different behaviours: quiet rest and steady walking on an exercise belt. For responses during walking, step histograms were constructed showing response mean size during different tenths of the step cycle in the ipsilateral forelimb, both in absolute terms and relative to mean size during rest. 3. Step histograms for the same site on different days or different stimulus intensities varied appreciably in form but in both cases the timing of the largest response was usually the same or shifted by only one step tenth. 4. In both zones the largest responses during walking occurred overwhelmingly during the E1 step phase when the limb is extended forwards and down to establish footfall. Least responses were much less uniform in timing but were mostly during stance, particularly its early (E2) part. 5. In many histograms the smallest responses were smaller in mean size than the responses during rest while the largest were larger. These changes were not paralleled by changes in nerve volley size, so presumably reflect step‐related central changes in pathway excitability. Facilitations and depressions were differently affected by stimulus intensity and sometimes occurred independently, suggesting generation by separate mechanisms. 6. In both zones there were differences between recording sites which suggests that different DF‐SOCP subcomponents innervate different parts of the zones. However, no systematic differences could be firmly established between the medial and lateral subzones of the c1 zone. 7. The results are discussed in relation to the hypothesis that the DF‐SOCP constitutes the afferent limb of a transcerebellar mechanism involved in adapting the evolving step.
Proton conductance and intracellular pH recovery from an acid load in chicken enterocytes.
Authors: Peral M J , Ilundáin A A
Published: December 2014

1. Chicken enterocytes present a Na(+)‐independent proton transport mechanism involved in pHi recovery from an acid load. In the current study the nature of this proton transport system is investigated. 2. The pHi of acid‐loaded cells increased when transferred to Na(+)‐free, pH 7.4 buffers, both at 6 and 65 mM extracellular potassium concentration. Addition of nigericin accelerated the rate of cell alkalinization. 3. When acid‐loaded cells were transferred to a Na(+)‐free, pH 6.5 buffer, the cells acidified further, regardless of the extracellular potassium concentration. The addition of nigericin increased the rate of acidification at 6 mM K+ but produced an alkalinization at 65 mM K+. 4. The rate of the Na(+)‐independent regulatory cell alkalinization was inhibited by SCH 28080, DCCD, NBD‐Cl, rotenone or Zn2+. Addition of valinomycin reversed the inhibition induced by SCH 28080, DCCD and NBD‐Cl but not that induced by Zn2+ or rotenone. Zn2+ inhibition was abolished by the metal chelator DTPA. 5. Cytosolic acidification increased the rate of Na(+)‐independent regulatory cell alkalinization. 6. The results suggest that the Na(+)‐independent proton transport system is a Zn(2+)‐sensitive proton‐conducting pathway which is regulated by the cytosolic proton concentration.
Synaptic excitation in the thoracic spinal cord from expiratory bulbospinal neurones in the cat.
Authors: Kirkwood P A
Published: December 2014

1. Synaptic actions in the thoracic spinal cord of individual expiratory bulbospinal neurones were studied in anaesthetized cats by the use of two techniques: (i) the monosynaptic connections to motoneurones were assessed by cross‐correlations between the discharges of the neurones and efferent discharges in the internal intercostal nerves of several segments bilaterally; and (ii) distributions of terminal and focal synaptic potentials were measured by extracellular spike‐triggered averaging in the thoracic ventral horn. 2. Monosynaptic connections were identified by both the durations and timings of observed cross‐correlation peaks, taking into account accurate conduction velocity measurements derived from collision tests and from spike‐triggered averaging. Discrimination was made against peaks resulting from presynaptic synchronization. 3. Monosynaptic connections to motoneurones were identified for twenty‐three out of twenty‐seven neurones. The connections to nerves on the side ipsilateral to the cell somata were, on average, about 36% of the strength of those on the contralateral side. The overall strength of the connections was about twice as strong as previous estimates for similar connections from inspiratory bulbospinal neurones to phrenic motoneurones. The monosynaptic pathway was calculated to be able to provide most of the depolarization for the motoneurones concerned and therefore was likely to be the main determinant of their firing patterns under the conditions of these experiments. 4. However, taking into account previous measurements it is considered possible that these connections may only involve a minority of motoneurones, perhaps only 10% of the expiratory population. Thus, in general, the control of the whole pool of expiratory motoneurones, despite the strong monosynaptic connections measured here, is suggested to be mainly dependent on spinal interneurones, as has been concluded previously for inspiratory motoneurones. 5. Spike‐triggered averaging revealed that nearly all neurones gave signs of collaterals in each of the segments investigated (T7, T8 or T9), as shown by the presence of terminal potentials or focal synaptic potentials, but the projection within a given thoracic segment was non‐uniform, in that large‐amplitude potentials were more common in the rostral than the caudal part of the segment. This non‐uniformity could be a factor involved in the apparently non‐heterogeneous connections to the motoneurones.
Contribution of ATP‐sensitive potassium channels to the electrophysiological effects of adenosine in guinea‐pig atrial cells.
Authors: Li G R , Feng J , Shrier A , Nattel S
Published: December 2014

1. Adenosine caused dose‐dependent action potential abbreviation in multicellular guinea‐pig atrial preparations, an action antagonized by glyburide (IC50, 31 microM) in both physiological and low‐chloride superfusate. 2. When 5 mM ATP was included in pipettes for whole‐cell voltage clamp of isolated guinea‐pig atrial myocytes, adenosine (10 microM) increased the holding current at ‐40 mV from 41 +/‐ 8 to 246 +/‐ 31 pA (mean +/‐ S.E.M., P < 0.01), and glyburide (20 microM) returned the holding current to 69 +/‐ 11 pA (P < 0.01 vs. adenosine alone). Acetylcholine (10 microM) also increased the holding current, but its effects were not altered by glyburide. 3. Both adenosine and acetylcholine induced an additional current component in response to 500 ms voltage steps. Glyburide partially inhibited the adenosine‐induced current, but did not alter the effect of acetylcholine. In the presence of maximally effective acetylcholine concentrations, adenosine increased membrane conductance (P < 0.01), although to a lesser extent than in the absence of acetylcholine. 4. Single K+ channel activity was seen in only one of eight cell‐attached patches in the absence of adenosine or acetylcholine (0.5 mM Ba2+ in bath and pipette solutions). With acetylcholine (10 microM) in the pipette, inwardly rectifying channels (conductance, 41 +/‐ 5 pS) were seen in five of six patches. With adenosine (10 microM) in the pipette, single‐channel activity was seen in twelve of fourteen patches with two populations of channels, one similar to that induced by acetylcholine and another higher‐conductance channel (72 +/‐ 5 pS) that showed less inward rectification. Glyburide (20 microM) suppressed the high‐conductance channel (68 +/‐ 2 pS) leaving a single channel type with a conductance of 36 +/‐ 5 pS and strong inward rectification. 5. We conclude that K+ATP channels contribute to the electrophysiological actions of adenosine on guinea‐pig atrium in the presence of physiological intracellular ATP levels, and may therefore play a role in the cardiac electrophysiological effects of adenosine in the absence of myocardial ischaemia.