bluuebunny/crossref_metadata_2025 huggingface dataset:
Galanin‐induced hyperpolarization and decreased membrane excitability of neurones in mudpuppy cardiac ganglia.
Authors: Konopka L M , McKeon T W , Parsons R L
Published: December 2014

1. Membrane hyperpolarization and decreased excitability produced by galanin were investigated in vitro on parasympathetic postganglionic neurones in the cardiac ganglion of the mudpuppy, Necturus maculosus. 2. Galanin produced a slowly developing hyperpolarization which, in 2.5 mM‐KCl, reversed at ‐105.4 +/‐ 2.7 mV. The reversal potential was shifted by 38.7 +/‐ 4.9 mV following a fourfold elevation of the extracellular potassium concentration. 3. Galanin inhibited action potential firing in spontaneously active neurones and decreased the number of spikes in a train produced by long (500‐680 ms) depolarizing current pulses. Both effects were independent of the galanin‐induced hyperpolarization. 4. Galanin increased the threshold for spike generation, prolonged the spike hyperpolarizing after‐potential and decreased the maximum rate of rise, amplitude and maximum rate of fall of the sodium spike. These effects occurred independently of the galanin‐induced hyperpolarization. 5. Galanin decreased the amplitude and duration of TTX‐insensitive spikes initiated in cells maintained in a solution containing 9 mM‐calcium, 20 mM‐TEA and 1.5 microM‐TTX. 6. These results suggest that a galanin‐like peptide may act as an inhibitory transmitter in the mudpuppy cardiac ganglion.
The role of interconnection between supraoptic nucleus and anterior third ventricular region in osmoregulation in the rat.
Authors: Chaudhry M A , Dyball R E , Honda K , Wright N C
Published: December 2014

1. To determine the importance of the region of the hypothalamus anterior and ventral to the third ventricle (AV3V) in the osmotic regulation of neurohypophysial hormone release, extracellular recordings were made in the urethane‐anaesthetized rat from neurones in the supraoptic nucleus (SON) and in the AV3V using a ventral surgical approach. 2. In the first series of experiments, recordings were made from SON cells (n = 41) which could be antidromically activated from the neural stalk in control rats and rats 2 weeks after electrolytic destruction of the AV3V (n = 74). Destruction of AV3V significantly (P less than 0.01) reduced the responsiveness of SON cells to an osmotic challenge (1 ml of 1.5 M‐NaCl I.P.). 3. In the second series of experiments recordings were made in the AV3V region while stimulus pulses were applied to the region of the SON. The cells recorded could be divided into five groups; those which were inhibited (presumably synaptically; OD‐; n = 97), those which were excited (also presumably synaptically; OD+; n = 73), those which could be antidromically activated (AD; n = 50), those which showed a complex cycle of excitation and inhibition after the stimulus (n = 40) and those which did not respond to the stimulus (n = 47). 4. The characteristic response of OD‐ cells to an osmotic challenge was inhibition (six out of ten cells) and that of OD+ cells was excitation (thirteen out of seventeen cells). No AD cells showed excitation following I.P. NaCl injection (nine out of nine). 5. Our experiments provide clear evidence that the AV3V region is important for the normal responsiveness of the cells of the SON to raised plasma osmolality and for an interaction between the SON and the AV3V region. 6. Our results also suggest, contrary to our expectation, that the SON exerts both excitatory and inhibitory influences on the AV3V. Since the cells which project from the AV3V to the SON region are not osmoresponsive, the importance of the direct projection from the AV3V to SON may be to maintain the responsiveness of SON neurones rather than to provide osmotic drive.
Calcium‐sensitive and insensitive transient outward current in rabbit ventricular myocytes.
Authors: Hiraoka M , Kawano S
Published: December 2014

1. A suction pipette whole‐cell voltage‐clamp technique was used to record membrane currents and potentials of isolated ventricular myocytes from rabbit hearts. 2. Transient outward current (Ito) was activated by voltage steps positive to ‐20 mV, increasing in amplitude with further depolarization to reach a maximum around +70 mV. The current attained its peak within 10 ms and then it inactivated for 100‐200 ms. 3. A large portion of Ito still remained after the calcium current (ICa) was blocked when depolarizing pulses were applied at a frequency of 0.1 Hz or less. Therefore, this current component is referred to as calcium‐insensitive Ito or It. 4. It showed voltage‐ and time‐dependent inactivation similar to that observed in Purkinje fibres and other cardiac preparations. 5. The reversal potential of It depended on external K+ concentration, [K+]o, with a slope of 32 mV per 10‐fold change in the presence of a normal [Na+]o (143 mM), while the slope was 48 mV per 10‐fold change in low [Na+]o (1.0 mM). 6. It was completely inhibited by 2‐4 mM‐4‐aminopyridine. Ito in the presence of ICa was also partially blocked by 4‐aminopyridine and the remainder was abolished by 5 mM‐caffeine. 7. The calcium‐insensitive and caffeine‐sensitive Ito differed in their decay rates as well as in their recovery time courses. The former was predominantly available at a slow pulsing rate, while the latter increased its amplitude with high‐frequency depolarization. 8. The caffeine‐sensitive Ito was inhibited by a blockade of ICa, by replacing Ca2+ with Sr2+, by external application of ryanodine and by internal application of EGTA. This indicates that the current is calcium‐sensitive and is dependent on increased myoplasmic Ca2+ through Ca2+ influx via the sarcolemma and Ca2+ release from the sarcoplasmic reticulum. The current is therefore designated as IK, Ca. 9. The physiological functions of IK, Ca and It are indicated by their contribution to ventricular repolarization at fast and slow heart rates, respectively.
Studies on the regenerated carotid sinus nerve of the rabbit.
Authors: Ponte J , Sadler C L
Published: December 2014

1. The central end of the distally cut left carotid sinus nerve was sutured to the tunica media of the external carotid artery, 1 cm cranial to the carotid bifurcation, in nineteen rabbits. The carotid body was removed in fourteen of these rabbits but left in situ in the remaining five. After 56‐165 days of recovery a neuroma was identified at the site of the suture. Ventilatory reflexes mediated by both sinus nerves were tested and afferent activity recorded from the regenerated nerve. 2. Ventilatory reflex responses to hypoxia and sodium cyanide were abolished on sectioning the right sinus nerve, whilst the hypercapnic response was maintained. 3. Electrical stimulation of the regenerated sinus nerve caused hypotension and hyperventilation. These responses were attenuated compared to stimulation of the right sinus nerve. 4. A level of afferent activity equivalent to that found in non‐regeneration experiments was recorded from all regenerated sinus nerves. Whole‐nerve afferent activity was modulated by changes in carotid sinus blood pressure but not by changes in Pa,O2, Pa,CO2 (arterial O2 and CO2 pressures) or intracarotid injection of sodium cyanide. 5. A minimum of thirty single afferent fibres was identified in each experiment, the vast majority of which were mechanoreceptors. In only nine experiments were chemoreceptor fibres found and only twelve chemoreceptor fibres (1.7% of total) were identified in these nine experiments. In ten experiments no chemoreceptor fibres could be found. Leaving the carotid body in situ increased the incidence of chemoreceptive preparations. A small number of fibres unresponsive to mechanical stimulation and asphyxia was also identified. 6. The responses of regenerated chemoreceptor fibres to physiological and pharmacological stimuli were generally similar to those found in control carotid body preparations. Fibres unresponsive to mechanical stimulation and asphyxia did not respond to sodium cyanide, dopamine or isoprenaline; some of these fibres were excited by nicotine. 7. The receptive fields of mechanosensitive fibres were localized on or up to 2 cm away from the neuroma. Surface application of 20‐40 microliters sodium cyanide (200 micrograms ml‐1) was used to localize the receptive fields of seven of the twelve chemoreceptor fibres. All seven were localized to the site of the carotid body. 8. The neuroma and site of the carotid body were examined under light and electron microscopy. Glomus tissue was absent from the neuroma but was found at the site of the carotid body. 9. In conclusion, recovery of chemoreceptor function after carotid sinus nerve section appears to be associated with reinnervation of glomus tissue.
Characterization of three types of potassium current in cultured neurones of rat supraoptic nucleus area.
Authors: Cobbett P , Legendre P , Mason W T
Published: December 2014

1. Whole‐cell, voltage‐clamp recordings were obtained from neurones of the supraoptic area of neonatal rats in dissociated cell culture. Recordings were made from neurones having the same morphology as those which were vasopressin or oxytocin immunoreactive. 2. Three types of voltage‐activated K+ current were identified on the basis of their kinetics, voltage sensitivities, Ca2+ dependence and pharmacology. The currents corresponded to the delayed rectifier current (IK), the A‐current (IA), and the Ca2+‐dependent current (IK(Ca] described in other neurones. 3. IK had a threshold of ‐40 mV, a sigmoidal time course of activation, and was sustained during voltage steps lasting less than 300 ms. The underlying conductance was voltage dependent reaching a maximum at +30 mV (mean maximum conductance 4.09 nS). The activation time constant was also voltage dependent declining exponentially from 4.5 ms at ‐30 mV to 1.8 ms at +50 mV. 4. IA was transient, and was activated from holding potentials negative to ‐70 mV; the maximum conductance (mean 5.9 nS) underlying the current was obtained at +10 mV. The activation and inactivation time constants were voltage dependent: the activation time constant declined exponentially between ‐40 mV (2.2 ms) and +40 mV (0.65 ms). 5. IK and IA were attenuated by the K+ channel blockers tetraethylammonium (TEA) and 4‐aminopyridine (4‐AP). TEA blocked the conductance underlying IK but appeared to alter the kinetics of IA. In contrast, 4‐AP blocked the conductance underlying IA and, to a lesser extent, IK. 6. IK and IA were activated independently of external Ca2+ and the voltage activation of Ca2+ channels since these currents were recorded in the presence of Co2+, a Ca2+ channel blocker. 7. IK(Ca) was recorded only when Ca2+ (2 mM) was present in the external medium. From a holding potential of ‐30 mV, IK(Ca) had a threshold of ‐20 mV, was maximal at about +20 mV and declined at more positive potentials. This current was sustained during voltage steps lasting 100 ms and was abolished by addition of Co2+ (2 mM) to the medium. 8. The possible roles of the three K+ currents in regulating the characteristic firing behaviour of supraoptic neurones previously recorded in vivo and in vitro are discussed.
Desynchronized respiratory rhythms and their interactions in cats with split brain stems.
Authors: Eldridge F L , Paydarfar D
Published: December 2014

1. The effects on activities and rhythms of the two opposing phrenic nerves (C5 roots) of mid‐line sagittal splitting of the medulla were determined in anaesthetized or decorticate, vagotomized, paralysed and ventilated cats. 2. Splitting the medulla above the obex led to marked decreases of phrenic activity on both sides, but no desynchronization of the two phrenic rhythms occurred. Further splitting to more than 3 mm below the obex led to desynchronized phrenic rhythms in fourteen of the fifteen animals that survived the necessary surgery, although it was often necessary to increase respiratory drive by means of hypercapnia, stimulatory drugs or electrical stimulation of the mesencephalon to cause the rhythms to occur. 3. When only the brain stem had been split, the two desynchronized rhythms showed interactions that led to modulations of amplitude of phrenic bursts, both being larger when in phase than when out of phase. In addition each side modulated the rhythm of the opposite side, demonstrating a ‘magnet’ effect. 4. Both types of modulation were eliminated after additional splitting of the spinal cord at the level (C5‐C6) of the phrenic motoneurone pools. 5. Potential explanations for the amplitude modulations include cross‐over of activity from one phrenic motoneurone pool to the opposite side and cross‐over from the medulla of one side to the opposite phrenic motoneurone pool at the phrenic level. 6. Since the rhythm generators were independent in our preparation and located in the split halves of the medulla and since peripheral sensory feed‐back was not important in these paralysed animals, we propose that the phase modulations must be due to a corollary discharge, an afferent feed‐back driven by phrenic motoneurone activity that crosses the mid‐line at C5‐C6, ascends to the brain and affects respiratory rhythm in the opposite medullary half.
The contribution of atrial systole to mitral diastolic blood flow increases during exercise in humans.
Authors: Channer K S , Jones J V
Published: December 2014

1. The change in the relative contribution of the early passive and later active phases of transmitral flow to left ventricular filling was studied using Doppler echocardiography in ten normal male subjects during mild exercise. 2. The peak velocity of passive flow increased during exercise by a mean of 16% whereas peak velocity of active flow increased by a mean of 89%. Hence the ratio of the peak velocities decreased in a linear fashion with a correlation coefficient of r = ‐0.95. 3. The ratio of the Doppler‐derived velocity‐time integrals (equivalent to the ratio of flow) of the two phases of transmitral flow also showed a significant negative linear correlation of r = ‐0.97. 4. Active atrial transport (atrial systole) progressively increases its contribution to overall transmitral blood flow with increasing heart rate during mild exercise. This effect is mainly mediated by an increase in flow velocity which is related to increased atrial contractility.
A study of synchronization of quantal transmitter release from mammalian motor endings by the use of botulinal toxins type A and D.
Authors: Molgó J , Siegel L S , Tabti N , Thesleff S
Published: December 2014

1. The effects of botulinum toxin (BoTx) types A and D on spontaneous and evoked phasic transmitter release were studied in the isolated extensor digitorum longus muscle of the rat or the levator auris longus muscle of mice. 2. The toxins were injected subcutaneously into the hindleg of adult rats or the dorsal aspect of the neck of mice. At various times after the injection the muscles were removed from the anaesthetized animal and neuromuscular transmission examined in vitro by conventional intracellular techniques. 3. Both toxins reduced spontaneous transmitter release recorded as the frequency of miniature end‐plate potentials but BoTx type D was less effective in that respect than the type A toxin. 4. With both toxins the block of evoked phasic transmitter release, recorded as end‐plate potentials, was almost complete. As previously reviewed by Simpson (1986) the block produced by BoTx type A was partially reversed by procedures which elevate the intraterminal level of calcium ions. However, in BoTx type D‐paralysed muscles such procedures failed to restore phasic transmitter release but caused a period of high‐frequency asynchronous transmitter release following each nerve impulse. 5. To investigate if the lack of synchronization of evoked transmitter release observed in BoTx type D‐paralysed muscles was due to alterations in presynaptic currents we examined, by perineural recordings, the Na+, fast K+, slow K+, K+‐Ca2+‐dependent and the Ca2+ currents in BoTx type D‐paralysed muscles. These presynaptic currents were not altered as compared to unpoisoned controls. 6. We suggest that there exists a presynaptic process, which in addition to Ca2+ influx participates in transmitter synchronization and which is a main target for BoTx type D action.
Comparison between sympathetic adrenergic and purinergic transmission in the dog mesenteric artery.
Authors: Muramatsu I , Ohmura T , Oshita M
Published: December 2014

1. Electrical transmural stimulation evoked a sympathetic contraction in the isolated dog mesenteric artery. This contraction consisted of adrenergic and purinergic components, which were separately observed under conditions where postjunctional P2 purinoceptors were desensitized with alpha, beta‐methylene ATP or postjunctional alpha 1 adrenoceptors were blocked by prazosin, respectively. 2. The purinergic component was transient and developed immediately after the start of stimulation and declined rapidly after a peak. In contrast, the adrenergic contraction slowly developed and lasted longer than the purinergic component. Thus, the purinergic and adrenergic components predominantly contributed to the early and later phases of the total sympathetic response, respectively. 3. The peak amplitudes of contraction of both components were similar at 1 Hz, but the adrenergic component occurred more dominantly in the responses to higher frequency stimulation. 4. Cocaine, a neuronal uptake inhibitor of noradrenaline, potentiated the adrenergic component but attenuated the purinergic component. This attenuation was reversed by DG‐5128, a prejunctional alpha 2 adrenoceptor antagonist. Treatment with DG‐5128 alone augmented both adrenergic and purinergic components. 5. 8‐Phenyltheophylline, a P1 purinoceptor antagonist, potentiated the purinergic component without affecting the adrenergic component. 6. Exogenous noradrenaline produced a sustained contraction, which was potentiated by cocaine and was competitively inhibited by prazosin. alpha, beta‐Methylene ATP and 8‐phenyltheophylline had no effect on the response to noradrenaline. Exogenous ATP produced a transient contraction, which was abolished under conditions where postjunctional P2 purinoceptors were desensitized with alpha, beta‐methylene ATP. 8‐Phenyltheophylline potentiated but cocaine or prazosin did not affect the ATP response. 7. Electrical stimulation produced an increase in 3H efflux from the sympathetic nerve terminals in the mesenteric arteries pre‐incubated with [3H]noradrenaline. The evoked efflux was significantly augmented by cocaine or DG‐5128 and was inhibited by guanethidine or tetrodotoxin. alpha, beta‐Methylene ATP and 8‐phenyltheophylline were without effect. Adenosine reduced the 3H efflux and the inhibition was suppressed by 8‐phenyltheophylline. 8. These results suggest that sympathetic contraction of the dog mesenteric artery is caused through not only adrenergic but also purinergic mechanisms, and that both the sympathetic transmissions are predominantly modulated through prejunctional adrenergic mechanisms.
Possible involvement of prostaglandin E in development of ACTH response in rats induced by human recombinant interleukin‐1.
Authors: Morimoto A , Murakami N , Nakamori T , Sakata Y , Watanabe T
Published: December 2014

1. Intravenous (I.V.) injection of human recombinant interleukin‐1 alpha (IL‐1 alpha) produced dose‐dependent monophasic fevers in rats. Moreover, the I.V. injection of IL‐1 alpha produced dose‐dependent rises in the plasma concentrations of adrenocorticotrophic hormone (ACTH) 30 min after injections with dosages of 5 micrograms/kg and 15 micrograms/kg of IL‐1 alpha. 2. The febrile responses induced by the I.V. injection of IL‐1 alpha (15 micrograms/kg) were completely abolished, and conversely hypothermia occurred, when the animals were pre‐treated with a cyclo‐oxygenase inhibitor, indomethacin (INDO). Pre‐treatment with INDO also inhibited the increase in the plasma concentrations of ACTH induced by I.V. injection of IL‐1 alpha (15 micrograms/kg), indicating that enhancement of plasma concentrations of ACTH induced by I.V. injection of IL‐1 alpha is processed through the action of prostaglandins. 3. Intrapreoptic injection of prostaglandin E2 produced a dose‐dependent fever with a rapid onset at doses of 25 and 100 ng. Moreover, the intrapreoptic injection of prostaglandin E2 increased the plasma concentrations of ACTH in a dose‐dependent manner 30 min after injections. 4. The intrapreoptic injection of IL‐1 alpha (20 ng) caused slow monophasic fever. However, no significant elevation of plasma concentrations of ACTH was observed 30, 90 and 180 min after the intrapreoptic injection of IL‐1 alpha, as compared with the ACTH levels at each time in the control group which received an intrapreoptic injection of saline. 5. These results suggest that intrapreoptic prostaglandin E plays an important role in the ACTH response by inducing the release of corticotrophin‐releasing factor (CRF).
Characteristics of GABA‐activated chloride channels in mammalian dorsal root ganglion neurones.
Authors: Robertson B
Published: December 2014

1. The properties of gamma‐aminobutyric acid (GABA)‐activated chloride channels in dorsal root ganglion (DRG) neurones obtained from rats and cats were examined using the single‐electrode voltage clamp in conjunction with suction‐electrode techniques. 2. GABA‐evoked currents showed voltage‐sensitive kinetics. Time constants (tau D) were measured from voltage‐jump relaxations and tau D became briefer with membrane hyperpolarization. tau D was 33 ms at ‐120 mV with 60 microM‐GABA and changed e‐fold for 188 mV. tau D decreased as GABA concentration was increased ‐ the extrapolated tau D at ‘zero’ GABA concentration was approximately equal to 50 ms at ‐120 mV. 3. The steady‐state current in GABA was curvilinear, rectifying at negative potentials. The instantaneous current was linear with symmetrical chloride concentrations (140 mM) on both sides of the cell membrane. 4. Muscimol was a more effective agonist than GABA, while piperidine‐4‐sulphonic acid and ethylenediamine monocarbamate were only weakly effective agonists. Taurine and glycine had no detectable agonist activity. 5. Ion substitution experiments revealed the permeability sequence I‐ greater than Br‐ greater than Cl‐ greater than F‐ greater than propionate (1.88 greater than 1.21 greater than 1.0 approximately equal to 0.1 approximately equal to 0.1). 6. The presence of iodide and bromide ions externally caused an increase in chloride efflux at membrane potentials more negative than ‐40 mV, and caused a prolongation of voltage‐jump relaxations. Relaxations in fluoride and propionate solutions were faster than those seen in chloride.
Electromyographic reflexes evoked in human wrist flexors by tendon extension and by displacement of the wrist joint.
Authors: Cody F W , Plant T
Published: December 2014

1. The electromyographic (EMG) reflexes evoked in the wrist flexor muscle, flexor carpi radialis (FCR), by percutaneous extension of its tendon and by forcible extension of the wrist joint have been studied. Reflexes were elicited during steadily maintained voluntary flexor contraction of 10% of each subject's maximum. 2. Tendon extension, using ‘ramp and hold’ displacements, evoked fairly prolonged (ca 50 ms) increases in EMG activity. These responses were usually subdivided into two main excitatory peaks of respectively short (SL, ca 20 ms) and long (LL, ca 45 ms) latency. This pattern contrasted with that observed following brief tendon taps when only a single, SL peak was elicited. 3. ‘Stretch’ reflexes evoked by ‘ramp and hold’ wrist extensions, as has been noted by numerous earlier investigators, were also protracted and comprised two main excitatory components. These responses resembled those produced by tendon extension both in their general form and in their behaviour upon altering the velocity of mechanical stimuli. Quantitatively, however, two main differences were evident. The reflexes evoked by wrist extension, including their SL and LL peaks, were generally somewhat larger. Additionally, when parameters of the two modes of stimulation were adjusted to elicit SL responses of equivalent amplitude, the LL responses elicited by tendon extension were regularly smaller and of shorter duration than those elicited by wrist extension. 4. Termination of the two forms of mechanical stimulation, by releasing tendon or wrist extension, each elicited a SL reduction in EMG activity. Such troughs were more pronounced and more consistently observed upon release of wrist extension. 5. Neither local anaesthesia of the skin overlying the flexor tendons at the wrist nor ischaemia of the hand and lower forearm produced any systematic modification of reflex response patterns. 6. It is concluded that intramuscular receptors (presumably muscle spindles) in FCR mediate both the SL and LL reflexes evoked in this muscle by extension of its tendon. Intramuscular receptors also seem certain to be very largely responsible for the EMG responses generated in this muscle by wrist extension.
A short‐latency crossed pathway from cutaneous afferents to rat hindlimb motoneurones.
Authors: Edgley S A , Wallace N A
Published: December 2014

1. A novel pathway is described which mediates excitation of hindlimb moto‐neurones from contralateral afferents. Stimulation of contralateral limb nerves evoked short‐latency (less than 5 ms) EPSPs in 55% of motoneurones tested. 2. The EPSPs were evoked by fast‐conducting contralateral afferents activated by electrical stimuli of 1.04‐2.5 times nerve threshold. Stimulation of contralateral muscle nerves did not evoke short‐latency EPSPs, whereas nerves which contain afferents from distal skin territories (sural, superficial peroneal, tibial and saphenous nerves) did. 3. Central latencies were determined for the EPSPs from the arrival of the earliest components of the afferent volleys at the spinal cord. The earliest latencies were very brief (1.5 ms). These are comparable to the latencies of disynaptic inhibition in rat motoneurones from ipsilateral group I muscle afferents (1.5‐1.7 ms). We conclude that a disynaptic relay is likely to be responsible for the earliest of the crossed EPSPs. 4. Short‐latency crossed EPSPs were found in all types of motoneurone tested (including both flexor and extensor motoneurones) except in six cells innervating intrinsic foot muscles. In view of the origin and distribution of the crossed EPSPs, their possible functional role is discussed.
Vasopressin‐induced natriuresis in the conscious rat: role of blood pressure, renal prostaglandin synthesis and the peptide ANF.
Authors: Lote C J , Thewles A , Wood J A
Published: December 2014

1. The response to arginine vasopressin (AVP) at doses of 5 and 10 pmol (100 g body weight)‐1 h‐1 was studied in conscious rats during the infusion of 1% (w/v) dextrose at 11.6 ml h‐1 with and without pre‐treatment with indomethacin. 2. In the absence of indomethacin AVP infusion induced dose‐related increases in sodium output that were positively correlated with increases in mean arterial blood pressure (MAP) and plasma atrial natriuretic factor (ANF) immunoreactivity. Increases in renal prostaglandin E2 (PGE2) synthesis were also associated with AVP infusion. 3. Indomethacin pre‐treatment abolished the AVP‐induced increases in renal PGE2 synthesis and also the dose‐related differences in ANF immunoreactivity. Increases in MAP and sodium output were unaffected at the 10 pmol (100 g body weight)‐1 h‐1 dose of AVP and only slightly attenuated for the 5 pmol (100 g body weight)‐1 h‐1 dose. 4. For both series AVP induced marked falls in glomerular filtration rate (GFR) but only small transient falls in effective renal plasma flow. The observed falls in GFR support the view that the natriuresis is due to changes in tubular handling and not in the filtered load of sodium. 5. It is concluded that the natriuresis elicited by AVP is closely related to the pressor action of the hormone but renal PGE2 synthesis and plasma ANF are not responsible for mediating this response.
Effects of halothane and enflurane on firing threshold of frog myelinated axons.
Authors: Butterworth J F , Raymond S A , Roscoe R F
Published: December 2014

1. Firing thresholds and conduction latencies of single myelinated axons in frog sciatic nerves were monitored during impulse activity in vitro. Resting threshold and the activity dependence of threshold were studied as a function of the concentration of two inhalational anaesthetic agents, halothane and enflurane. 2. At concentrations comparable to those obtained during general anaesthesia both agents produced biphasic effects on the resting threshold. A step increase in the partial pressure of anaesthetic was followed first by a transient lowering of threshold, then by a slow rise to a steady‐state level above the original baseline. Step decreases in anaesthetic were followed by transient rises before threshold dropped. Transients lasted 20‐30 min. During these threshold transients, the average latency of impulse conduction changed monotonically. The prolongation of latency following an increase in anaesthetic was progressive, reaching steady state concurrently with threshold (20 min to greater than 1 h). 3. The anaesthetics reduced the long‐lasting increased threshold (‘depression’) which normally follows repetitive impulse activity in axon membrane. 4. These actions of halothane at concentrations of 0.25‐2.7% (0.14‐1.54 mM) and enflurane at concentrations of 0.62‐3.08% (0.35‐1.73 mM) on resting threshold and on the activity‐dependent increase in threshold increased monotonically with anaesthetic concentration. 5. The effects on excitability at steady state are consistent with block of voltage‐dependent Na+ and K+ channels by these inhalational agents. Reduced depression may occur because the anaesthetics reduce the net ion transfer per impulse, slowing the substrate‐driven Na+‐K+‐ATPase and thereby reducing electrogenic hyper‐polarization. 6. The finding that general anaesthetics inhibit depression at clinically relevant concentrations supports the possibility that general anaesthesia is produced by inhibition of processes that modulate excitability of nerve membrane. We suggest that general anaesthetics produce unconsciousness and amnesia because they disrupt activity‐dependent processes, which may thus remove temporal ‘context’ essential for interpreting nerve impulse patterns.
Demonstration of H+‐ and Na+‐coupled co‐transport of beta‐alanine by luminal membrane vesicles of rabbit proximal tubule.
Authors: Jessen H , Jørgensen K E , Røigaard‐Petersen H , Sheikh M I
Published: December 2014

1. The characteristics of renal transport of beta‐alanine by luminal membrane vesicles isolated from either the proximal convoluted part (pars convoluta) or the proximal straight part (pars recta) of rabbit proximal tubule were investigated. 2. In vesicles from pars convoluta two transport systems have been characterized: (1) a Na+‐dependent system with intermediate affinity (half‐saturation 2.7 mM), and (2) a Na+‐independent system, which in the presence of a H+ gradient (extravesicular greater than intravesicular) can drive the uphill transport of beta‐alanine into these vesicles. This is the first demonstration of H+‐beta‐alanine co‐transport across luminal membrane of rabbit kidney proximal convoluted tubule. 3. By contrast, in membrane vesicles from pars recta, transport of beta‐alanine was strictly dependent on Na+ and occurred via a dual transport system, namely a high‐affinity (half‐saturation 0.16 mM) and a low‐affinity system (half‐saturation 9.3 mM). 4. The demonstration of competition between the Na+‐gradient‐dependent uptake of beta‐alanine and taurine, without appreciable inhibition by alpha‐amino acids in vesicles from pars convoluta as well as from pars recta, strongly suggests that the luminal membrane of proximal tubule has transport systems for the reabsorption of beta‐amino acids which are distinct from alpha‐amino acid transport systems.
Haemodynamic and renal tubular responses to low‐dose infusion or bolus injection of the peptide ANF in anaesthetized rats.
Authors: Harris P J , Skinner S L , Zhuo J
Published: December 2014

1. Renal haemodynamic and tubular transport responses to low‐dose infusions (0.1‐5.0 ng min‐1) and injections (50‐200 ng) of atrial natriuretic factor (ANF) were studied in anaesthetized rats (average body weight, 300 g). 2. The lowest infusion dose (average, 0.3 ng kg‐1 min‐1) was above threshold for significant hypotension (‐11 mmHg), increased glomerular filtration (20%), urine flow (104%) and sodium output (191%). 3. Compared with the lowest rate of infusion of ANF, the smallest injection dose (50 ng) was less effective in reducing blood pressure, caused no change in glomerular filtration rate but induced similar diuresis and natriuresis. Based on total dose administered, sensitivity to injection was only one‐tenth that of infusion. 4. Absolute proximal reabsorption, derived from lithium clearance measurements, did not increase in parallel with filtration rate during infusions, and fractional proximal reabsorption was markedly depressed. Proximal glomerulo‐tubular balance was only 50% effective at 0.1 ng min‐1, falling to 16% at 5 ng min‐1. 5. Despite complete recovery of filtration rate and filtration fraction 30 min after terminating infusions, diuresis, natriuresis and depressed fractional proximal reabsorption persisted. Time‐control animals displayed no changes in renal function. 6. It is proposed that disruption of glomerulo‐tubular balance occurred in these experiments from inhibition of endogenous angiotensin II‐stimulated proximal sodium reabsorption by ANF. Persistence of this action may be due to accumulation of intracellular messengers or to sequestration of biologically active ANF bound to ‘clearance receptors’.
Giant miniature end‐plate potentials at the untreated and emetine‐treated frog neuromuscular junction.
Authors: Alkadhi K A
Published: December 2014

1. Intracellular recordings from the cutaneous pectoris muscle fibres of the frog showed that giant miniature end‐plate potentials (gMEPPs) occurred in untreated preparations. Emetine (10 microM), after a 15‐20 min delay, increased the frequency of gMEPPs. In both cases gMEPPs disappeared in the presence of (+)‐tubocurarine. 2. There was no correlation between the frequency of gMEPPs and the frequency of normal MEPPs (nMEPPs) in untreated or emetine‐treated fibres. 3. Tetraphenylborate (TPB, 50 microM) applied to muscles pre‐treated with emetine caused the frequency and amplitude of both nMEPPs and gMEPPs to decrease gradually. All MEPPs disappeared in about 10 min. 4. Chloride permeability was modified by changing the pH of the Ringer solution. Changing the pH from 7.2 to 8.2 or 6.2, which in both cases caused marked increases in nMEPP frequency, had no significant effect on gMEPP frequency in untreated muscles. 5. Decreasing the pH from 7.2 to 6.2 blocked the ability of emetine to increase gMEPP frequency. Increasing the pH from 7.2 to 8.2 had no significant effect on emetine ability to increase gMEPP frequency. 6. Treatment with the Cl‐ channel blocker SITS (0.5 mM) had no effect on gMEPPs in untreated muscle or on the ability of emetine to increase the frequency of these potentials. 7. The Ca2+ sensitivity of gMEPPs in untreated or emetine‐treated muscles was tested by treatments which are known to alter intracellular Ca2+. Raising extracellular Ca2+ (10 mM), treatment with Mn2+ (10 mM), Mg2+ (10 mM), K+ (7.5 mM), hypotonic solution, ouabain (0.2 mM) or ethanol (0.5 M), although causing profound changes in nMEPP frequency had no significant effect on gMEPP frequency in untreated fibres or on the ability of emetine to increase gMEPP frequency. 8. It is concluded that at the frog neuromuscular junction generation of the normally occurring or emetine‐induced gMEPPs is independent of Ca2+ and does not seem to be influenced by changing membrane C1‐ permeability.
Receptive fields and in‐field afferent inhibition of neurones in the cat's lateral cervical nucleus.
Authors: Brown A G , Maxwell D J , Short A D
Published: December 2014

1. Extracellular microelectrode recordings were made from projection neurones of the lateral cervical nucleus (LCN) in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. The receptive fields of eight‐five units were analysed. Most units had excitatory receptive fields similar in size and shape to those of spinocervical tract (SCT) cells. A few (14%) had either very large fields or 'stocking‐like' fields. The majority of the LCN neurones (fifty‐five, 65%) were excited by hair movement and, in addition, by noxious mechanical stimulation within the skin area responding to hair movement. Twenty‐five units (29%) were excited by hair movement alone. For seven of these twenty‐five neurones, noxious mechanical stimulation within the excitatory receptive field produced inhibition of the background discharge. One unit was excited by noxious mechanical stimulation and for the remaining four units no receptive field could be found. In six units inhibitory receptive fields outside the excitatory field were found. 3. Air‐jet stimuli were used to define the excitatory profiles of the units' receptive fields to hair movement. In general, receptive fields had single regions of greatest sensitivity usually at or near the centre of the field, where that was oval in shape, with the sensitivity declining towards the field's circumference. In some units with very large fields that included parts of one or two limbs and the trunk there could be more than one highly sensitive region. 4. Pairs of air‐jet stimuli were used to investigate in‐field afferent inhibition in LCN cells. One jet was used to condition the responses to another jet located at a different position within the excitatory receptive field and occurring 200 ms later. Sixteen units were tested and significant in‐field inhibition was observed in all sixteen. 5. The in‐field afferent inhibition was organized spatially in the sense that inhibition was generally strongest when the conditioning and testing stimuli were close together and became weaker as they were moved apart. The afferent inhibition was not simply a function of the response produced by the conditioning stimulus. Furthermore, increasing the strength of the stimuli did not in general lead to larger areas from which the inhibition could be produced. The inhibitory areas defined in these experiments were generally less than 120 mm in length in units with receptive fields much longer than 100 mm.(ABSTRACT TRUNCATED AT 400 WORDS)
On the transduction mechanism for muscarine‐induced inhibition of M‐current in cultured rat sympathetic neurones.
Authors: Brown D A , Marrion N V , Smart T G
Published: December 2014

1. Dissociated adult or fetal rat superior cervical ganglion cells were voltage‐clamped through a single patch pipette. The voltage‐dependent K+ current, IM (M‐current), was maintained by including MgATP in the pipette solution and by buffering the solution pH to 6.7. 2. Bath‐applied muscarine (0.4 microM) produced a reversible inhibition of IM. 3. Addition of Gpp(NH)p (200 microM) or GTP‐gamma‐S (500 microM) to the pipette solution induced a slowly developing inhibition of IM and prevented recovery from subsequent muscarine‐induced inhibition. 4. Addition of GDP‐beta‐S (500 microM) to the pipette solution reduced the amount of IM inhibition produced by 0.4 microM‐muscarine by 42% and reduced the associated inward shift of the holding current by 56%. 5. Cells responded normally to muscarine after pre‐treatment for 4‐27 h with 500 ng ml‐1 pertussis toxin (PTx). 6. IM was not diminished by extracellular addition of 1 mM‐dibutyryl cyclic AMP, 8‐bromo‐cyclic AMP or dibutyryl cyclic GMP, or of 10 microM‐forskolin. 7. IM was not reduced by inclusion of Li+ (2 mM) or inositol 1,4,5‐trisphosphate (IP3, 100 microM) in the patch pipette, nor by ionophoretic injection of IP3 from an inserted micropipette. 8. Addition of 4‐beta‐phorbol 12,13‐dibutyrate (PDBu, 0.5‐2 microM) to the extracellular medium partly inhibited IM and reduced an additional component of resting membrane current. This effect was not replicated by 4‐alpha‐phorbol 12,13‐didecanoate. 9. It is concluded that the inhibition of IM by muscarine is mediated through activation of a PTx‐insensitive GTP‐binding protein. The effect of muscarine appears not to be mediated by cyclic nucleotides or IP3 but may possibly involve the generation of diacylglycerols and activation of protein kinase C.
Regulation of N‐methyl‐D‐aspartate receptors revealed by intracellular dialysis of murine neurones in culture.
Authors: MacDonald J F , Mody I , Salter M W
Published: December 2014

1. The whole‐cell patch clamp recording technique was employed to investigate the intracellular regulation of N‐methyl‐D‐aspartate (NMDA) receptors in cultured murine hippocampal neurones. Excitatory amino acids were repeatedly applied at regular intervals during intracellular dialysis with solutions of various composition. 2. Currents evoked by L‐aspartate, an agonist of NMDA receptors, gradually ‘washed out’ to approximately 50% of their initial amplitude during dialysis with an intracellular solution containing CsCl and EGTA as a calcium buffer. In contrast, responses to kainate did not wash out. The wash‐out of L‐aspartate currents followed an exponential time course with a time constant of about 150 s. Wash‐out did not appear to be related to desensitization of NMDA receptors. 3. Following wash‐out, L‐aspartate responses were blocked by Mg2+, ketamine or D‐2‐amino‐5‐phosphonovalerate indicating that these responses were still mediated by NMDA receptors. Furthermore, responses to NMDA itself showed wash‐out to the same extent and with a time course similar to that for L‐aspartate responses. 4. Neither the time course nor the extent of the wash‐out of responses to L‐aspartate was affected when the Ca2+ concentration of the dialysate was varied from zero to 1.5 x 10(‐5) M. In addition, wash‐out was unaffected by substitution of BAPTA for EGTA, indicating that wash‐out was not a consequence of changes in intracellular pH related to the binding of Ca2+ to the buffer or to the kinetics of this binding. Therefore, the wash‐out of NMDA currents could not be attributed to a gradual elevation of the concentration of intracellular Ca2+. 5. The extent of the wash‐out of L‐aspartate currents was similar for cells held at +40 versus ‐60 mV although the rate of wash‐out was slower at the depolarized potential. In addition, the reversal potential of these currents was not altered, demonstrating that a change in driving force did not account for a component of the wash‐out. 6. Inclusion of an ATP regeneration solution (Forscher & Oxford, 1985) in the dialysate prevented the wash‐out of L‐aspartate currents. ATP alone was less effective in preventing wash‐out whereas phosphocreatine and creatine phosphokinase were ineffective by themselves. Wash‐out also occurred when ATP was replaced with the non‐hydrolysable analogue, beta, gamma‐methyleneATP, or with GTP. In cells where wash‐out of L‐aspartate currents had been established, subsequent dialysis with the ATP regenerating solution partially reversed this wash‐out.(ABSTRACT TRUNCATED AT 400 WORDS)
Identification of ionic currents at presynaptic nerve endings of the lizard.
Authors: Lindgren C A , Moore J W
Published: December 2014

1. Ionic currents associated with the invasion of an action potential into the motor nerve ending of the lizard, Anolis carolinensis, were measured with a focal extracellular electrode at several locations along the nerve ending. 2. These experimentally observed currents could be matched with computer simulations of action potential propagation into the nerve ending. They revealed that while Na+ channels are the major ionic current pathway in the heminode, K+ channels provide the major pathway in the terminal branches and boutons. 3. Calcium current in the presynaptic ending was unmasked by the application of tetraethylammonium (TEA). This current was blocked by: (a) cadmium, (b) omega‐conotoxin GVIA and (c) nifedipine, but was unaffected by nickel at concentrations less than or equal to 100 microM. Nifedipine's action became more definitive when the duration of the action potential was greatly extended by pre‐treatment with TEA. The effect of Bay K 8644 was inconsistent. 4. Transmitter release, as measured by postsynaptic current, had a pharmacological response profile similar to that of the Ca2+ current, with the exception that transmitter release was increased reliably and reversibly by Bay K 8644. 5. This pharmacological response profile is identical to that of the L type Ca2+ channel identified by Fox, Nowycky & Tsien (1987 alpha) in chick dorsal root ganglion neurones. We saw no evidence for more than a single type of Ca2+ channel in lizard motor nerve endings. 6. A calcium‐activated K+ current IK(Ca) was revealed by application of 3,4‐diaminopyridine (DAP), a delayed‐rectifier K+ channel blocker. This K(Ca) current was blocked by TEA, charybdotoxin and by substitution of cobalt for extracellular calcium.
Cellular mechanism of the modulation of contractile function by coronary perfusion pressure in ferret hearts.
Authors: Kitakaze M , Marban E
Published: December 2014

1. Isovolumic left ventricular pressure was measured at various coronary arterial pressures in Langendorff‐perfused ferret hearts. The concentrations of phosphorus‐containing metabolites were measured using 31P nuclear magnetic resonance (NMR). Intracellular free calcium concentration ([Ca2+]i), was measured with 19F NMR in a group of hearts that were loaded with the calcium indicator 5F‐BAPTA. 2. Developed pressure increased when coronary arterial pressure was raised from the control value of 80 to 100‐160 mmHg and decreased when coronary pressure was lowered to 40‐70 mmHg. The changes were reversible. 3. Coronary flow varied directly with coronary pressure over the entire range from 40 to 160 mmHg. 4. The concentrations of phosphorus‐containing metabolites and the efflux of lactate from the heart remained unchanged at coronary pressures of 60 mmHg or higher. Below 60 mmHg, intracellular pH decreased, while inorganic phosphate concentration and lactate efflux increased. 5. In contrast to the developed pressure during twitch contractions, maximal Ca2+‐activated pressure remained constant at coronary pressures of 60‐160 mmHg. Only below a coronary pressure of 60 mmHg did maximal Ca2+‐activated pressure decline. 6. An increase in coronary pressure produced an increase in developed pressure even in hearts stretched to the peak of the Frank‐Starling relation. 7. When coronary pressure was lowered from 80 to 60 mmHg, [Ca2+]i decreased during systole; the opposite effect was apparent when coronary pressure was raised from 80 to 120 mmHg. 8. We conclude that coronary perfusion (pressure or flow) modulates intracellular calcium and, consequently, contractile force. Ischaemia cannot fully explain this phenomenon, nor can changes in sarcomere length.
Intracellular calcium mobilization triggered by a glutamate receptor in rat cultured hippocampal cells.
Authors: Furuya S , Ohmori H , Shigemoto T , Sugiyama H
Published: December 2014

1. Intracellular free calcium ([Ca2+]i) was monitored by means of Fura‐2 fluorescence measurements in hippocampal cells in primary cultures from newborn rats. 2. In external media containing 200 microM‐DL‐2‐amino‐5‐phosphonovalerate and 1 mM‐kynurenate, but no added Ca2+, an increase in [Ca2+]i was observed in 30‐40% of cells examined in response to quisqualate or L‐glutamate. 3. Under such conditions, [Ca2+]i often increased gradually with a latency of a few seconds after application of the agonists. 4. Pre‐treatment of the cultured cells with pertussis toxin reduced the extent of quisqualate‐stimulated [Ca2+]i increase in Ca2+‐free media, but the percentage of the responsive cells was not affected appreciably. 5. It is concluded that quisqualate and L‐glutamate can trigger the release of Ca2+ from intracellular Ca2+ stores, most likely by activating a glutamate receptor coupled to a pertussis toxin‐sensitive G‐protein.