bluuebunny/crossref_metadata_2025 huggingface dataset:
Afferent inhibition and facilitation of transmission through the spinocervical tract in the anaesthetized cat.
Authors: Short A D , Brown A G , Maxwell D J
Published: December 2014

1. Extracellular microelectrode recordings were made from single spinocervical tract (SCT) neurones in the lumbosacral spinal cord of cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. Pairs of air‐jet stimuli, 60 ms in duration, were used to investigate in‐field afferent inhibition in SCT cells. One jet was used to condition the responses to another jet located at a different position within the excitatory receptive field and occurring at times from 100 to 1800 ms later. Fifteen neurones were tested and significant in‐field inhibition was observed in all of them. 3. The in‐field afferent inhibition was organized spatially in the sense that inhibition was generally strongest when conditioning and testing stimuli were close together and became weaker as they were moved apart. There was also a weak effect due to the strength of the conditioning response; when conditioning produced a strong response, from near the most excitable part of the receptive field, there was often a weak reduction in the test response from distant sites. The inhibitory areas defined in these experiments were generally less than 100 mm in length in units with excitatory receptive fields much longer than this. 4. The in‐field afferent inhibition had a time course that lasted from 300 to about 1000 ms. 5. Afferent inhibition was also evoked by applying either air‐jet stimuli to hairy skin outside, but close to, the excitatory receptive field or by applying a vibratory stimulus from a piezoelectric transducer (200 Hz) to glabrous skin of the toe pads or the central foot pad. These conditioning stimuli had durations of 20 or 60 ms. For convenience we call this inhibition ‘out‐of‐field’ afferent inhibition. 6. Out‐of‐field afferent inhibition was evoked from both glabrous and hairy skin areas outside the excitatory receptive field. It was common in neurones with receptive fields on the toes and of twenty‐eight such neurones tested it was observed in twenty‐four. This inhibition had a short latency (usually about 10 ms or less but occasionally up to 30 ms) and lasted for about the duration of the test stimulus (30 or 80 ms when the test stimulus was 20 or 60 ms respectively). It was often followed by a further period of inhibition, with a latency of between 50 and 100 ms and lasting for 60 up to 130 ms. 7. In thirteen SCT neurones more complex effects were seen.(ABSTRACT TRUNCATED AT 400 WORDS)
Competitive antagonists and partial agonists at the glycine modulatory site of the mouse N‐methyl‐D‐aspartate receptor.
Authors: Henderson G , Johnson J W , Ascher P
Published: December 2014

1. Kynurenate (Kyn), 7‐chlorokynurenate (7‐Cl‐Kyn), 3‐amino‐1‐hydroxypyrrolid‐2‐one (HA‐966) and D‐cycloserine are known to bind to the glycine site that modulates the N‐methyl‐D‐aspartate (NMDA) response of vertebrate central neurones. The effects of these compounds were investigated with patch‐clamp and fast‐perfusion techniques on mouse cortical neurones in primary culture in an effort to establish whether they act as antagonists, partial agonists and/or inverse agonists of glycine. A fast drug application method allowed the study of both steady‐state and transient responses. 2. The analysis of steady‐state responses indicates that the main effects of Kyn and 7‐Cl‐Kyn are those expected from competitive antagonists of glycine, with a dissociation constant of 15 microM for Kyn, and of 0.3 microM for 7‐Cl‐Kyn. Concentration jumps indicate that at all concentrations of glycine, and in particular in the absence of added glycine, the blockade by Kyn and 7‐Cl‐Kyn develops at a rate which is close to the rate of dissociation of glycine from its binding site and is independent of antagonist concentration. 3. The main effects of D‐cycloserine and of HA‐966 are those of partial agonists of high and low efficacy, respectively. In the absence of added glycine, D‐cycloserine always produced a potentiation, while HA‐966 produced either a potentiation or an inhibition. This can be explained by assuming the presence of a variable level of contaminating glycine. With both D‐cycloserine and HA‐966, concentration jumps produced biphasic relaxations in which the onset rate of the slow component was, here again, close to the rate of dissociation of glycine from its binding site. 4. These results can be interpreted by assuming that (1) Kyn and 7‐Cl‐Kyn are competitive antagonists of glycine, (2) HA‐966 and D‐cycloserine are partial agonists, (3) in the absence of added glycine some glycine is present in the extracellular solution and (4) the response in the total absence of glycine is very small or negligible.
Quantal analysis of inhibitory synaptic transmission in the dentate gyrus of rat hippocampal slices: a patch‐clamp study.
Authors: Edwards F A , Konnerth A , Sakmann B
Published: December 2014

1. Synaptically connected neurones were identified in the granule cell layer of slices of 17‐ to 21‐day‐old rat hippocampus. Whole‐cell current recording using the patch‐clamp technique revealed synaptic currents ranging from less than 10 to 200 pA in symmetrical Cl‐ conditions, at a holding potential of ‐50 mV. These currents were blocked by 2 microM‐bicuculline, indicating that they result from the activation of postsynaptic gamma‐aminobutyric acid receptor (GABAA‐receptor) channels. 2. Addition of tetrodotoxin (TTX, 1 microM) resulted in the loss of most currents of more than 40 pA in amplitude. Currents which disappeared after TTX treatment were assumed to be the result of spontaneous presynaptic action potentials. The currents seen in the absence of TTX are referred to as spontaneously occurring inhibitory postsynaptic currents (IPSCs); those remaining in the presence of TTX were defined as miniature IPSCs. 3. Similar currents were observed when recording in the whole‐cell configuration while extracellular stimulation was applied to a nearby neurone. These currents were also completely blocked by 2 microM‐bicuculline and by 0.5 microM‐TTX. They were thus defined as stimulus‐evoked IPSCs. 4. The half rise time of both miniature and stimulus‐evoked IPSCs was fast (less than 1 ms). The time course of decay of both miniature IPSCs and stimulus‐evoked IPSCs could be well fitted with the sum of two exponentials. At a membrane potential of ‐50 mV, the mean decay time constants of the two components were 2.0 +/‐ 0.38 and 54.4 +/‐ 18 ms (mean +/‐ S.D.) for miniature IPSCs (six cells) and 2.2 +/‐ 1.3 and 66 +/‐ 20 ms (three cells) for stimulus‐evoked IPSCs. 5. Stimulus‐evoked IPSCs varied in amplitude from less than ten to hundreds of picoamperes. In eight of eleven cells histograms of IPSC amplitudes showed several clear peaks which, when fitted with the sum of Gaussian curves, were found to be equidistant. This is consistent with the view that stimulus‐evoked IPSC amplitudes vary in a quantal fashion. The quantal size varied between 7 and 20 pA, at a membrane potential of ‐50 mV. 6. Decreasing the Ca2+ and increasing the Mg2+ concentration in the extracellular solution decreased the number of peaks in the IPSC amplitude histogram but did not affect the size of the quantal event.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanical, electrical and cyclic nucleotide responses to peptide VIP and inhibitory nerve stimulation in rat stomach.
Authors: Ito S , Kurokawa A , Ohga A , Ohta T , Sawabe K
Published: December 2014

1. Effects of apamin on electrical and mechanical activities and cyclic nucleotide accumulation in response to vasoactive intestinal peptide (VIP) and intramural nerve stimulation were investigated in isolated circular strips of the rat stomach in the presence of atropine and guanethidine. 2. Circular muscles generated rhythmic contractions and slow waves in the antrum but not in the fundus. Intramural nerve stimulation and VIP caused frequency‐ and dose‐dependent relaxation of fundic strips and inhibition of spontaneous contractions of antral strips. Apamin partly reduced the responses to intramural nerve stimulation but not those to VIP. 3. In the antrum, apamin reduced inhibitory junction potentials (IJPs) evoked at the nadir of slow waves but not at their zenith. In the fundus, apamin partly decreased the amplitude of IJPs. Repetitive nerve stimulation was associated with an apamin‐sensitive hyperpolarization and apamin‐resistant decrease in the slow wave amplitude in the antrum. 4. VIP caused a dose‐dependent hyperpolarization of fundic circular muscle membrane. In the antrum, VIP inhibited spike potentials superimposed on slow waves and it decreased the slow wave amplitude in about half of the preparations. These electrical responses to VIP were resistant to apamin. 5. Intramural nerve stimulation evoked an apamin‐resistant output of VIP from muscle strips, which no longer occurred after tetrodotoxin or removal of extracellular Ca2+. 6. Intramural nerve stimulation and VIP elicited apamin‐resistant increases in cyclic AMP and cyclic GMP accumulations. The effects of VIP on cyclic AMP were greater than those on cyclic GMP. The effects of intramural nerve stimulation on cyclic GMP were faster in onset than those of cyclic AMP. 7. It is suggested that VIP is a neurotransmitter of the intramural inhibitory nerves concerned in the apamin‐resistant relaxation of the rat stomach.
Irreversible desensitization of ATP responses in developing chick skeletal muscle.
Authors: Thomas S A , Hume R I
Published: December 2014

1. In developing chick skeletal muscle, extracellular adenosine 5'‐triphosphate (ATP) elicits an early excitatory conductance increase followed by a late potassium conductance increase. Both of these responses desensitize profoundly. Intracellular recordings and whole‐cell voltage‐clamp recordings were made in order to examine the time course and mechanism of desensitization and the recovery from desensitization. 2. Most of the loss of responsiveness to ATP occurred during the first minute of exposure to ATP. For the excitatory conductance, the loss of responsiveness to ATP resulted in part from long‐lasting activation of the ATP‐sensitive channels and in part from entrance into an inactive (non‐conducting) state. In contrast, desensitization of the potassium conductance was entirely the result of a relatively fast transition to an inactive state. 3. Recovery from desensitization took many hours for both responses and was quite sensitive to temperature. 4. Recovery from desensitization for both responses was prevented by preincubation with the glycosylation inhibitor, tunicamycin. Several lines of evidence suggest that tunicamycin treatment blocked the delivery of new ATP receptors to the cell surface. 5. The recovery of the early response to ATP following exposure to two non‐competitive inhibitors of the ATP response was also examined. These two compounds are thought to covalently modify the receptor. After exposure to either of these inhibitors, responsiveness to ATP returned over a time course that was similar to the time course of recovery from desensitization. 6. These results indicate that, following activation, ATP receptors do not become available for reactivation, and that recovery from desensitization is due to the insertion of newly synthesized receptors into the plasma membrane.
Ionic mechanisms in spontaneous vasomotion of the rat basilar artery in vivo.
Authors: Fujii K , Heistad D D , Faraci F M
Published: December 2014

1. The goal of this study was to examine ionic mechanisms that modulate spontaneous rhythmic changes in vascular calibre or ‘vasomotion’ in the basilar artery in vivo. 2. Diameter of the basilar artery was measured through a craniotomy in anaesthetized rats under control conditions and during topical application of antagonists or alteration in the ionic composition of artificial cerebrospinal fluid (CSF). 3. Both Ca2(+)‐free CSF and the Ca2+ channel blocker, nimodipine, produced moderate dilatation of the basilar artery and abolished vasomotion. Increasing the concentration of Ca2+ in CSF from 1.7 to 5.0 mM did not affect the frequency of vasomotion, although the amplitude was increased slightly. 4. Both K(+)‐free CSF and ouabain produced mild to moderate vasoconstriction and abolished vasomotion. In contrast, increasing the concentration of K+ in CSF produced vasodilatation of the basilar artery and decreased or abolished vasomotion depending on the degree of vasodilatation. 5. Tetrodotoxin had no effect on vasomotion. 6. These results suggest that vasomotion of the basilar artery in vivo is dependent on extracellular Ca2+ and K+, and on the activity of Na(+)‐K(+)‐ATPase, and not dependent on Na+ channel.
Gating in the spino‐olivocerebellar pathways to the c1 zone of the cerebellar cortex during locomotion in the cat.
Authors: Lidierth M , Apps R
Published: December 2014

1. The field potentials evoked in the cerebellar cortical c1 zone by single‐pulse, non‐noxious stimulation of the superficial radial nerve have been recorded with tungsten‐in‐glass microelectrodes in awake cats. Responses that were due to transmission in the spino‐olivocerebellar pathways (SOCPs), which terminate in the cortex as climbing fibres, were identified and studied while the cat walked on a moving belt. 2. The size of the climbing fibre‐evoked potentials varied systematically during the step cycle. They were invariably largest in mid‐ to late swing of the ipsilateral forelimb and, at most recording sites (5/6), they were smallest during the first half of stance. 3. With low stimulus strength, the probability of evoking a measurable response also varied. The probability was greatest in mid‐ to late swing and least in early stance. 4. Similar variations were shown to occur when the analysis was restricted to responses evoked by a single functionally homogenous SOCP, the dorsal funiculus SOCP. 5. It is proposed that these variations reflect the operation of a gating mechanism which modulates the excitability of the SOCPs and prevents them transmitting self‐generated tactile inputs to the cerebellum while facilitating transmission when unexpected inputs are most likely to arise. 6. The present data are compared with those from a similar study of the c2 zone SOCPs (Apps, Lidierth & Armstrong, 1990) and are discussed in relation to a study of the effects of unexpected mechanical perturbations of stepping (Andersson & Armstrong, 1987).
The contractile response during steady lengthening of stimulated frog muscle fibres.
Authors: Lombardi V , Piazzesi G
Published: December 2014

1. Steady lengthenings at different velocities (0.025‐1.2 microns/s per half‐sarcomere; temperature 2‐5.5 degrees C) were imposed on isolated frog muscle fibres at the isometric tetanus plateau by means of a loudspeaker motor. The lengthening at the sarcomere level was measured by means of a striation follower either in fixed‐end or in length‐clamp mode. The force response was measured by a capacitance gauge transducer (resonance frequency 50 kHz). Preparations showing gross non‐homogeneity during lengthening were excluded. 2. A steady tension was in all cases reached after about 20 nm per half‐sarcomere of lengthening. Tension during this steady phase rose with speed of elongation up to 0.25‐0.4 micron/s per half‐sarcomere, when tension was 1.9‐2 times isometric tetanic force (T0). Further increase in speed produced only very little increase in the steady tension. 3. During the transitory phase, before steady tension was reached, the tension rose monotonically if speed of lengthening was less than 0.25‐0.3 micron/s per half‐sarcomere; at higher speed the tension rose above the steady level, reaching a peak when extension was 10‐14 nm per half‐sarcomere, and then fell to the steady level. Tension at the peak continued to rise with speed of lengthening above 0.3 micron/s per half‐sarcomere. 4. During the tension rise within the transitory phase of force response the segment elongated at a speed 15‐20% lower than that imposed on the whole fibre, as a consequence of tendon compliance. 5. During the steady phase, non‐homogeneity of lengthening speed began above a speed of lengthening which varied from fibre to fibre. At speeds below this value, segments elongated at the same speed as that imposed on the fibre. 6. Tension responses to large step stretches (up to 12 nm per half‐sarcomere), applied at the plateau of isometric tetanus, showed that the instantaneous elasticity of contractile machinery is not responsible for the limit in force attained with high‐speed lengthening. 7. Instantaneous stiffness was determined during the steady state of force response by superposing small steps (less than 1.5 nm per half‐sarcomere) on steady lengthening at different velocities. Stiffness was 10‐20% larger during lengthening than at the plateau of isometric tetanus and remained practically constant, independent of lengthening velocity, in the range of velocities used. 8. The results indicate that steady lengthening of a tetanized fibre induces a cross‐bridge cycle characterized by fast detachment of the cross‐bridge extended beyond a critical level.(ABSTRACT TRUNCATED AT 400 WORDS)
Membrane depolarization and intracellular Ca2+ increase caused by high external Ca2+ in a rat calcitonin‐secreting cell line.
Authors: Yamashita N , Hagiwara S
Published: December 2014

1. Calcitonin secretion is regulated by the external Ca2+ concentration ([Ca2+]o) via a rise in intracellular Ca2+ concentration ([Ca2+]i). The mechanism which couples an increase in [Ca2+]o to an increase in [Ca2+]i was explored in a rat calcitonin‐secreting cell line (rMTC 44‐2). [Ca2+]i was monitored using Fura‐2 AM, and the membrane potential or current was simultaneously measured. 2. Using the conventional whole‐cell clamp, tetrodotoxin‐sensitive voltage‐gated Na+ channels, T‐ and L‐type Ca2+ channels, and three types of K+ channels, the delayed K+ channel, the A‐channel and the inward‐rectifying channel were observed. 3. Using the nystatin‐perforated whole‐cell‐clamp technique, the resting potential measured under current clamp in standard extracellular medium was ‐59.0 +/‐ 5.0 mV (mean +/‐ S.D., n = 25), and the input resistance was 3.9 +/‐ 1.9 G omega (n = 10). In 0.5 mM [Ca2+]o most cells (22/25) showed spontaneous action potentials. 4. An increase in [Ca2+]o depolarized the cell membrane and elevated [Ca2+]i even in the presence of 10 microM‐tetrodotoxin. The rise in [Ca2+]i was greatly reduced when action potentials were inhibited by applying hyperpolarizing current. The increase in [Ca2+]i saturated with 3‐4 mM [Ca2+]o. In 3 mM [Ca2+]o, [Ca2+]i was 188.9 +/‐ 40.5% (n = 12) of that in 0.5 mM [Ca2+]o. 5. In high [Ca2+]o the duration of action potentials was prolonged, but the action potential frequency did not always increase. In some cases it even decreased in high [Ca2+]o. 6. Two types of action potential were observed in high [Ca2+]o, one with a shorter duration and the other with a longer duration. [Ca2+]i transiently increased in association with the long‐duration action potentials. These long‐duration action potentials were also accompanied by a larger after‐hyperpolarization. 7. Under voltage clamp, high [Ca2+]o caused a membrane conductance increase to Na+ ions. 8. Even when the membrane potential was clamped at a level below the threshold for Ca2+ channel activation, high [Ca2+]o provoked an increase of [Ca2+]i which was composed of an initial transient increase followed by a sustained increase, indicating an involvement of mechanisms other than Ca2+ influx through voltage‐gated channels. The sustained increase was more frequently observed than the initial transient increase. The amplitude of the sustained phase was dependent on [Ca2+]o, and in 5 mM [Ca2+]o it was 120.9 +/‐ 18.9% (103‐194%) (n = 58) of that in 0.5 mM [Ca2+]o.(ABSTRACT TRUNCATED AT 400 WORDS)
Properties of a hyperpolarization‐activated cation current and its role in rhythmic oscillation in thalamic relay neurones.
Authors: McCormick D A , Pape H C
Published: December 2014

1. The physiological and functional features of time‐dependent anomalous rectification activated by hyperpolarization and the current which underlies it, Ih, were examined in guinea‐pig and cat thalamocortical relay neurones using in vitro intracellular recording techniques in thalamic slices. 2. Hyperpolarization of the membrane from rest with a constant‐current pulse resulted in time‐dependent rectification, expressed as a depolarizing sag of the membrane potential back towards rest. Under voltage clamp conditions, hyperpolarizing steps to membrane potentials negative to approximately ‐60 mV were associated with the activation of a slow inward current, Ih, which showed no inactivation with time. 3. The activation curve of the conductance underlying Ih was obtained through analysis of tail currents and ranged from ‐60 to ‐90 mV, with half‐activation occurring at ‐75 mV. The time course of activation of Ih was well fitted by a single‐exponential function and was strongly voltage dependent, with time constants ranging from greater than 1‐2 s at threshold to an average of 229 ms at ‐95 mV. The time course of de‐activation was also described by a single‐exponential function, was voltage dependent, and the time constant ranged from an average of 1000 ms at ‐80 mV to 347 ms at ‐55 mV. 4. Raising [K+]o from 2.5 to 7.5 mM enhanced, while decreasing [Na+]o from 153 to 26 mM reduced, the amplitude of Ih. In addition, reduction of [Na+]o slowed the rate of Ih activation. These results indicate that Ih is carried by both Na+ and K+ ions, which is consistent with the extrapolated reversal potential of ‐43 mV. Replacement of Cl‐ in the bathing medium with isethionate shifted the chloride equilibrium potential positive by approximately 30‐70 mV, evoked an inward shift of the holding current at ‐50 mV, and resulted in a marked reduction of instantaneous currents as well as Ih, suggesting a non‐specific blocking action of impermeable anions. 5. Local (2‐10 mM in micropipette) or bath (1‐2 mM) applications of Cs+ abolished Ih over the whole voltage range tested (‐60 to ‐110 mV), with no consistent effects on instantaneous currents. Barium (1 mM, local; 0.3‐0.5 mM, bath) evoked a steady inward current, reduced the amplitude of instantaneous currents, and had only weak suppressive effects on Ih. 6. Block of Ih with local application of Cs+ resulted in a hyperpolarization of the membrane from the resting level, a decrease in apparent membrane conductance, and a block of the slow after‐hyperpolarization that appears upon termination of depolarizing membrane responses, indicating that Ih contributes substantially to the resting and active membrane properties of thalamocortical relay neurones.(ABSTRACT TRUNCATED AT 400 WORDS)
Submandibular responses to stimulation of the parasympathetic innervation in bursts in the anaesthetized ferret.
Authors: Tobin G , Ekström J , Edwards A V
Published: December 2014

1. Submandibular salivary and vascular responses to different patterns of stimulation of the parasympathetic innervation have been investigated in anaesthetized ferrets in the presence and absence of atropine. 2. At low stimulus frequencies likely to fall within the physiological range (0.5‐2.0 Hz continuously; 5.0‐20.0 Hz in 1 s bursts at 10 s intervals) secretion of fluid and protein were both potentiated by the bursting pattern of stimulation and the latency of the secretory response was reduced. Over a somewhat lower range (0.5‐1.0 Hz continuously; 5.0‐10.0 Hz in bursts) the submandibular vascular response was also significantly potentiated by employing this intermittent pattern of stimulation. Above these frequency ranges no such potentiation occurred. 3. Pre‐treatment with atropine (2.0 mg kg‐1) blocked the submandibular secretory responses to stimulation of the chorda‐lingual nerve at these low frequencies and the residual responses at higher frequencies were not significantly affected by changing the pattern of stimulation. The vascular response was somewhat reduced after atropine but that which persisted was enhanced by stimulating in bursts. 4. It is concluded that the release of some transmitter from postganglionic terminals in the submandibular gland of the ferret must be potentiated by the arrival of action potentials at short intervals and possible mechanisms are considered.
Is increased metabolism in rats in the cold mediated by the thyroid?
Authors: Whitaker E M , Hussain S H , Hervey G R , Tobin G , Rayfield K M
Published: December 2014

1. In the rat variation of metabolic heat production is the principal effector of thermoregulation. There is a continuous relationship between ambient temperature and metabolic rat over the whole range of tolerable environmental temperature. The mechanism that controls metabolic rate is unknown; this paper reports an attempt to test whether thyroid hormones provide the controlling pathway. 2. First, the changes in metabolic rate and in the plasma concentrations of thyroid stimulating hormone (TSH), triiodothyronine (T3) and thyroxine (T4) were measured in rats living in a controlled environment, first at 23 degrees C and then at 6 degrees C. Metabolic rate increased from approximately 290 to 470 kJ day‐1 when the temperature was lowered, a factor of ca 1.6, and the diurnal rhythm disappeared. The concentration of TSH increased from approximately 320 to 450 ng ml‐1 (with loss of diurnal rhythm) and of T3 from ca 0.7 to 1.0 nmol l‐1, a factor of ca 1.4 in each case. T4 concentration did not change. 3. Next, a dose schedule of T3 was found that, when injected I.V. via indwelling jugular cannulae in the same rats in an environment at 23 degrees C, maintained an increase in T3 concentration rather greater than had been found at 6 degrees C. 4. This dose of T3, given to the same rats at 23 degrees C, did not affect metabolic rate (or its diurnal pattern). 5. It is therefore unlikely that the increase in T3 concentration evoked the increase in metabolic rate when ambient temperature was changed from 23 to 6 degrees C; and therefore that the thyroid controls variation of metabolic rate in ‘everyday’ thermoregulation in the rat.
Rat splanchnic net oxygen consumption, energy implications.
Authors: Casado J , Fernández-López J A , Esteve M , Rafecas I , Argilés J M , Alemany M
Published: December 2014

1. The blood flow, PO2, pH and PCO2 have been estimated in portal and suprahepatic veins as well as in hepatic artery of fed and overnight starved rats given an oral glucose load. From these data the net intestinal, hepatic and splanchnic balances for oxygen and bicarbonate were calculated. The oxygen consumption of the intact animal has also been measured under comparable conditions. 2. The direct utilization of oxygen balances as energy equivalents when establishing the contribution of energy metabolism of liver and intestine to the overall energy expenses of the rat, has been found to be incorrect, since it incorporates the intrinsic error of interorgan proton transfer through bicarbonate. Liver and intestine produced high net bicarbonate balances in all situations tested, implying the elimination (by means of oxidative pathways, i.e. consuming additional oxygen) of high amounts of H+ generated with bicarbonate. The equivalence in energy output of the oxygen balances was then corrected for bicarbonate production to 11‐54% lower values. 3. Intestine and liver consume a high proportion of available oxygen, about one‐half in basal (fed or starved) conditions and about one‐third after gavage, the intestine consumption being about 15% in all situations tested and the liver decreasing its oxygen consumption with gavage.
Water permeability of acinar cell membranes in the isolated perfused rabbit mandibular salivary gland.
Authors: Steward M C , Seo Y , Rawlings J M , Case R M
Published: December 2014

1. The diffusive water permeability of epithelial cell membranes in the perfused rabbit mandibular salivary gland was measured at 37 degrees C by a 1H nuclear magnetic resonance relaxation method using an extracellular relaxation reagent, gadolinium diethylenetriaminepentaacetic acid (Gd(DTPA)). 2. In glands perfused with a HEPES‐buffered solution containing 10 mmol l‐1 Gd(DTPA), the spin‐lattice (T1) relaxation of the water protons showed two exponential components. The water compartment responsible for the slower component corresponded in magnitude to 71 +/‐ 5% of the wet weight of the gland, and was attributed to the exchangeable intracellular water of the acinar cells. 3. The rate constant for water efflux from the cells was estimated to be 4.1 +/‐ 0.1 s‐1 which would be consistent with a diffusive membrane permeability (Pd) of approximately 3 x 10(‐3) cm s‐1. Stimulation with acetylcholine (10(‐6) mol l‐1) did not cause any detectable change in membrane water permeability. 4. Since the basolateral membrane probably provides the main pathway for water efflux, the osmotic water permeability of this barrier (expressed per gland) was estimated to be less than 6.2 cm3 s‐1. This would be insufficient to account for the generation of a near‐isosmotic fluid at the flow rates observed during secretion, and suggests that a substantial fraction of the flow of water occurs via a paracellular route.
Capsaicin and sensory neuropeptide stimulation of goblet cell secretion in guinea‐pig trachea.
Authors: Kuo H P , Rohde J A , Tokuyama K , Barnes P J , Rogers D F
Published: December 2014

1. We studied the effect of capsaicin and sensory neuropeptides on tracheal goblet cell secretion in anaesthetized guinea‐pigs using a semi‐quantitative morphometric technique whereby the magnitude of discharge of stained intracellular mucus, expressed as a mucus score (MS), was related inversely to discharge. 2. Capsaicin (i.v.) induced goblet cell secretion: a decrease of 50% in MS below control (indicative of increased secretion) was maximal at 3.3 x 10(‐9) mol/kg. 3. Capsaicin‐induced secretion was unaffected either by prior vagus nerve section or by pre‐treatment with atropine, propranolol and phentolamine which suggests that local axon reflexes with release of sensory neuropeptides are involved in the response. 4. Intravenous substance P (SP), neurokinin A (NKA), neurokinin B (NKB), and calcitonin gene‐related peptide (CGRP) produced dose‐related increases in goblet cell secretion, with SP the most potent. Doses (mol/kg) causing a 50% decrease in MS from control were 3.5 x 10(‐12) for SP; 72 x 10(‐10) for NKA; 1.6 x 10(‐9) for NKB; and 1.2 x 10(‐8) for CGRP. The maximal increase in goblet cell secretion was 75% of control and occurred with SP at 10(‐10) mol/kg. 5. SP‐induced mucus discharge was not inhibited by atropine or the histamine receptor antagonists mepyramine or cimetidine. 6. We conclude that in guinea‐pig trachea, goblet cell secretion is under the control of capsaicin‐sensitive sensory nerves and release of neuropeptides from these nerves may induce mucus discharge via tachykinin receptors of the NK‐1 subtype (indicated by an order of potency of SP greater than NKA greater than NKB).
Mechanism of potassium efflux and action potential shortening during ischaemia in isolated mammalian cardiac muscle.
Authors: Gasser R N , Vaughan‐Jones R D
Published: December 2014

1. Ischaemia was simulated in the isolated sheep cardiac Purkinje fibre and guinea‐pig papillary muscle by immersing the preparations in paraffin oil. Ion‐selective microelectrodes recorded potassium (Ks+) and pH (pHs) in the thin film of Tyrode solution trapped at the fibre surface while other microelectrodes recorded intracellular pH (pHi), membrane potential and action potentials (AP) (evoked by field stimulation), or membrane current (two‐microelectrode voltage clamp in shortened Purkinje fibres). Twitch tension was also monitored. The paraffin oil model reproduced the salient characteristics of myocardial ischaemia, i.e. a decrease of twitch tension; a decrease of pHi and pHs; a rise in Ks+ (by 2‐3 mM); a depolarization of diastolic membrane potential; considerable shortening of the AP (up to 30% within 4 min). 2. The sulphonylurea compounds, glibenclamide (200 microM) and tolbutamide (1 mM), known inhibitors of the KATP channel, completely blocked the ischaemic rise of Ks+ and prevented AP shortening. Ischaemic tension decline was notably less pronounced in the presence of sulphonylureas. 3. The ischaemic increase of slope conductance (Purkinje fibre) was prevented by 1 mM‐tolbutamide and 200 microM‐glibenclamide. 4. Sulphonylureas did not affect resting membrane potential, the AP or the current‐voltage relationship under non‐ischaemic conditions (this also indicates that ischaemic Ks+ accumulation is not fuelled by the background K+ current [iK1] which was shown, as expected, to be Ba2+ sensitive). 5. In a normally perfused preparation, reducing intracellular ATP by inhibiting glycolysis with 2‐deoxyglucose (DOG) produced a similar AP shortening plus a membrane hyperpolarization, both of which were inhibited by tolbutamide or glibenclamide. The AP shortening was not related uniquely to the fall of pHi observed under these conditions since experimentally reducing pHi (by reducing pHo in the absence of DOG) lengthened rather than shortened the AP. 6. The possibility that the ischaemic rise in Ks+ might be the cause of AP shortening was excluded by the observation that, in a normally perfused Purkinje fibre, experimentally reducing pHi (by an amount similar to that seen during ischaemia) completely neutralized the AP‐shortening effect of an elevated Ko+ (from 4.5 to 6.5 mM). Furthermore, the sulphonylurea‐sensitive AP shortening seen during DOG treatment could not have been associated with a Ks+ rise since, in these particular experiments, the fibres were well perfused and diastolic membrane potential hyperpolarized.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of acidosis on the interval‐force relation and mechanical restitution in ferret papillary muscle.
Authors: McCall E , Orchard C H
Published: December 2014

1. The effect of a respiratory acidosis on the interval‐force relation and on mechanical restitution was investigated in ferret papillary muscles. 2. Acidosis (pH 6.85) decreased developed force over a range of stimulation frequencies (1.0.06 Hz); the percentage decrease was greatest at the lowest stimulation frequencies. Qualitatively similar effects of acidosis on developed force were observed in the presence of the sarcoplasmic reticulum (SR) inhibitor ryanodine. 3. Mechanical restitution curves were constructed by interpolating extra‐systoles at different test intervals following a train of steady‐state beats. Mechanical restitution in ferret papillary muscle was triphasic: an initial, rapid, exponential increase in force with test intervals to 2 s, a further increase with test intervals between 60 and 90 s and then a slow decline, with a plateau at about 30 min (0.33 Hz, 30 degrees C). 4. Acidosis slowed the initial phase of mechanical restitution. The degree of slowing depended on the steady‐state stimulation frequency, being greatest at low frequencies. 5. Inhibition of the SR abolished the initial phase of mechanical restitution, suggesting that this phase depends on Ca2+ release from the SR. 6. The strength of the first contraction after the extra‐systole varied inversely with the size of the extra‐systole under all conditions studied. 7. It is concluded that acidosis may inhibit the SR by altering the time required for Ca2+ recycling between contractions. This effect may alter Ca2+ release from the SR during acidosis, and may underlie the mechanical alternans (the alternation of small and large contractions) that can occur during acidosis.
A fast, transient K+ current in neurohypophysial nerve terminals of the rat.
Authors: Thorn P J , Wang X M , Lemos J R
Published: December 2014

1. Nerve terminals of the rat posterior pituitary were acutely dissociated and identified using a combination of morphological and immunohistochemical techniques. Macroscopic terminal membrane currents and voltages were studied using the whole‐cell patch clamp technique. 2. In physiological solutions, depolarizing voltage clamp steps, from a holding potential (‐80 mV) similar to the normal terminal resting potential, elicited a fast, inward followed by a fast, transient, outward current. 3. The threshold of activation for the outward current was ‐60 mV. The outward current quickly reached a peak and then decayed more slowly. The decay was fitted by two exponentials with time constants of 21 +/‐ 2.9 and 143 +/‐ 36 ms. These decay constants did not show a dependence on voltage. The time to peak of the outward current decreased and the amplitude increased with increasingly depolarized potential steps. 4. The outward current was blocked by the substitution of K+ with Cs+ and its reversal potential was consistent with a potassium current. 5. The transient outward current showed steady‐state inactivation at more depolarized (than ‐80 mV) holding potentials with 50% inactivation occurring at ‐47.9 mV. The time course of recovery from inactivation was complex with full recovery taking greater than 16 s. 6. 4‐Aminopyridine (4‐AP) blocked the transient outward current in a dose‐dependent manner (approximately IC50 = 3 mM), while charybdotoxin (4 micrograms/ml) and tetraethylammonium (100 mM) had no effect on the current amplitude. 7. Lowering external [Ca2+] had no effect on the fast, transient outward current nor did the calcium channel blocker Cd2+ (2 mM). 8. The neurohypophysial outward current reported here corresponds most closely to IA, and not to the delayed rectifier or Ca2(+)‐activated K+ currents. Neurohypophysial IA, however, appears to be different from the outward currents found in the cell bodies in the hypothalamus which project their axons to the posterior pituitary. 9. Under current clamp, evoked action potential duration increased (122%) upon application of 5 mM‐4‐AP, indicating that IA is involved in neurohypophysial spike repolarization. 10. The existence of this current could help explain why maximal peptide release only occurs in response to bursts of electrical activity invading the nerve terminals.
Autoreceptor‐mediated purinergic and cholinergic inhibition of motor nerve terminal calcium currents in the rat.
Authors: Hamilton B R , Smith D O
Published: December 2014

1. After blocking K+ currents with 10 mM‐tetraethylammonium (TEA) or TEA plus 250 microM‐3,4‐diaminopyridine (3,4‐DAP). motor nerve terminal Ca2+ currents were recorded using focal extracellular electrodes. Two transmitters released from the terminal. ATP and acetylcholine (ACh), were then applied, and the effects on the nerve terminal Ca2+ current were measured. 2. ATP (50 microM) reduced the Ca2+ current by 34%, but this action is prevented when hydrolysis to adenosine is blocked by alpha,beta‐methyladenosine 5'‐diphosphate (200 microM). Thus, inhibition by ATP presumably occurs subsequent to ATP hydrolysis to adenosine. 3. Adenosine (50 microM) inhibited the terminal Ca2+ current by 29%. This was mimicked by the adenosine analogue L‐phenylisopropyl adenosine (L‐PIA) and blocked by theophylline (100 microM), which antagonizes adenosine receptors at micromolar concentrations. 4. ACh (100 microM) or the anticholinesterase methane sulphonyl fluoride (MSF; 1 mM) also depressed the terminal Ca2+ current. This response was mimicked by muscarine (100 microM) and antagonized by atropine (100 microM) or pirenzipine (4 microM), which is generally specific for M1 receptors. 5. Addition of Ba2+, which blocks adenosine‐mediated K+ currents, had no effect on the inhibitory effects of either adenosine or ACh; similarly, neither adenosine nor ACh in the bath affected K+ current records obtained after blocking all inward currents with 10 mM‐Co2+ and focal application of tetrodotoxin. 6. Incubation of the muscle for 4 h in pertussis toxin (10(‐5) g ml‐1) eliminated both adenosine‐ and ACh‐induced inhibition of the terminal Ca2+ current. This result indicates the possible involvement of a G protein in the transduction of the feedback pathway. 7. Neither cyclic AMP analogues, the adenylate cyclase activator forskolin (10 microM), the phorbol ester phorbol 12‐myristate 13‐acetate (PMA; 3 microM) nor the diacylglycerol analogue 1,2‐oleoylacetylglycerol (OAG; 3 microM) had any effect on adenosine‐ or ACh‐induced depression of the terminal Ca2+ current. Therefore, pathways involving these particular second messengers are most probably not involved. 8. The effects of adenosine and ACh are non‐additive. 9. These results indicate that ATP and ACh, which are released during exocytosis, may inhibit their own release through attenuation of the terminal Ca2+ current via autoreceptors coupled to a G protein.
Chloride secretion stimulated by prostaglandin E1 and by forskolin in a canine renal epithelial cell line.
Authors: Simmons N L
Published: December 2014

1. The actions of prostaglandins upon ion transport in a renal‐derived cultured epithelium (MDCK) have been investigated. 2. Prostaglandin E1 (PGE1) stimulates an inwards short‐circuit current (SCC) in voltage‐clamped epithelial layers mounted in Ussing chambers. Measurements of transepithelial Cl‐ fluxes, cation and anion replacement of the bathing media and the use of the Cl‐ channel blocker 3‐nitro‐2(3‐phenylpropylamino)‐benzoic acid (NPPB) are consistent with the PGE1‐stimulated inward SCC resulting predominantly from basal to apical Cl‐ secretion. 3. The response of MDCK epithelia is relatively specific for prostaglandins of the E series. PGE1 is most effective when applied to the basal bathing solutions, though near‐maximal stimulation of SCC was possible with 1 microM‐PGE1 added to the apical bathing solution. 4. Forskolin addition (10 microM) stimulates an inwards SCC in MDCK epithelia which displays similar characteristics and is of a similar magnitude to that observed with PGE1. In the presence of isobutylmethylzanthine, PGE1 and forskolin are capable of elevating intracellular cyclic AMP accumulation, suggesting that stimulation of inward SCC is mediated via a cyclic AMP‐dependent mechanism.
Inhibition of atrial receptor‐induced renal responses by stimulation of carotid baroreceptors in anaesthetized dogs.
Authors: Karim F , Majid D S
Published: December 2014

1. Dogs were anaesthetized with chloralose and artificially ventilated. The receptors at three pulmonary vein‐atrial junctions and in the left atrial appendage were stimulated by distension of small balloons. The carotid sinuses were vascularly isolated and perfused with arterial blood. A volume reservoir was connected to the aorta via the common carotid and femoral arteries to keep the mean aortic pressure constant (78.8 +/‐ 2.9 mmHg at low and 87.1 +/‐ 4.3 mmHg at high carotid sinus pressure, CSP). Propranolol and atropine were infused (i.v.) at 17 and 13 micrograms kg‐1 min‐1 respectively in order to block beta‐adrenergic and cholinergic receptor activities. The renal blood flow was measured by an electromagnetic flow meter (wrap‐round probe), glomerular filtration rate by creatinine clearance, urinary sodium excretion by flame photometry and osmolar excretion by osmometry. 2. In twelve tests in eight dogs, stimulation of the left atrial receptors for 13 min, at a mean CSP of 68.6 +/‐ 2.3 mmHg, resulted in significant increases in renal blood flow from 216 +/‐ 20.0 to 230 +/‐ 22.1 ml min‐1 (100 g renal mass)‐1 (P less than 0.005), glomerular filtration rate from 33.9 +/‐ 3.2 to 42.1 +/‐ 4.1 ml min‐1 100 g‐1 (P less than 0.005), filtration fraction from 0.23 +/‐ 0.02 to 0.26 +/‐ 0.02 (P less than 0.005), urine flow rate from 0.21 +/‐ 0.03 to 0.26 +/‐ 0.03 ml min‐1 100 g‐1 (P less than 0.001), sodium excretion from 12.9 +/‐ 4.0 to 16.4 +/‐ 4.8 mumol min‐1 100 g‐1 (P less than 0.01), osmolar excretion from 196 +/‐ 27.8 to 246 +/‐ 32.9 muosmol min‐1 100 g‐1 (P less than 0.005), whilst free water clearance decreased from ‐0.39 +/‐ 0.07 to ‐0.50 +/‐ 0.09 ml min‐1 100 g‐1 (P less than 0.005). However, the fractional excretion of sodium did not change. 3. In nine tests in seven dogs, stimulation of the left atrial receptors at a constantly high CSP (161 +/‐ 11.3 mmHg) did not produce significant change in any of the renal variables. 4. The results show that high level excitation of carotid baroreceptors can completely inhibit the reflex renal haemodynamic and functional responses to atrial receptor stimulation.
Mean circulatory filling pressure during splanchnic nerve stimulation and whole‐body hypoxia in the anaesthetized cat.
Authors: Bower E A , O'Donnell C P
Published: December 2014

1. Mean circulatory filling pressure (MCFP) was measured in cats under chloralose anaesthesia by obstruction of blood flow in the pulmonary artery. Pressures in the aorta, hepatic portal vein and right atrium were recorded, and MCFP was estimated from the value at which all three pressures became equal when blood was pumped from aorta to vena cava during circulatory arrest. Simultaneous equality was not attained at MCFP values below 5 mmHg. 2. In cats ventilated by positive pressure after administration of gallamine, MCFP was 9.7 +/‐ 0.3 mmHg (n = 14). The values of MCFP measured in six cats before and after administration of gallamine did not differ significantly. Change of blood volume altered MCFP linearly over the range 5‐21 mmHg. Noradrenaline (7.5 micrograms kg‐1 min‐1) increased MCFP from 9.3 +/‐ 0.9 to 16.5 +/‐ 0.6 mmHg (n = 4), and phentolamine (2 mg kg‐1) reduced it to 5.6 +/‐ 0.3 mmHg (n = 5). 3. Changes in MCFP were evoked at different circulating blood volumes by stimulation of the splanchnic sympathetic nerves and by whole‐body hypoxia. Ablation of all splanchnic nerves reduced MCFP from 9.4 +/‐ 0.5 to 7.1 +/‐ 0.3 mmHg (n = 5) and stimulation of their distal ends at 10 Hz increased it by 4.1 +/‐ 0.4 mmHg (n = 4); similar increments were obtained at different blood volumes and initial values of MCFP. 4. Hypoxia increased MCFP by 0.23 mmHg per 1 mmHg fall in arterial oxygen tension below Pa,O2 56 mmHg (r = ‐0.86; n = 24). Similar increments were obtained at different blood volumes and initial values of MCFP. Ablation of all splanchnic nerves reduced the increments by 60%, and administration of phentolamine abolished them.
Salivary secretion and grooming behaviour during heat exposure in freely moving rats.
Authors: Yanase M , Kanosue K , Yasuda H , Tanaka H
Published: December 2014

1. At neutral (24 degrees C) and at hot (40 degrees C) ambient temperatures (Ta) salivary secretion from the submandibular gland of freely moving rats was recorded, together with simultaneous observation of saliva‐spreading behaviour (grooming). 2. At a Ta of 24 degrees C, basal salivary flow was less than 2 microliters/min. When rats were first placed in the experimental chamber, brief grooming bouts often occurred. Transient secretion at more than 10 microliters/min was associated with this grooming, and the rate of salivary flow was positively correlated with the duration of grooming activity. 3. At a Ta of 40 degrees C, grooming appeared frequently and salivary secretion at more than 20 microliters/min continued even between grooming bouts. Threshold rectal temperatures (Tre) for thermally induced grooming (38.2 +/‐ 0.2 degrees C) and for salivary secretion (38.2 +/‐ 0.1 degrees C) were similar, and for eleven of sixteen rats the two thresholds coincided. 4. At the threshold Tre both the rate of salivary secretion and the duration of grooming increased in a stepwise fashion. Above the threshold, there was no correlation between the duration of grooming and the rate of salivary flow. 5. Thermally induced salivary secretion and grooming behaviour appear to be controlled by independent mechanisms.