bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of histamine, high potassium and carbachol on 42K efflux from longitudinal muscle of guinea‐pig intestine
Authors: Bolton T. B. , Clark J. P. 
Published: December 2014

1. Shortening and rate of loss of 42K were studied in strips of longitudinal muscle taken from guinea‐pig ileum.2. Carbachol, histamine and raising the external potassium concentration, [K+]o, to 120 m
m in the presence of atropine caused equal maximal shortenings of the muscle, but unequal maximal increases in 42K efflux: maximal 42K effluxes obtainable in response to raised [K+]o and histamine were about ⅔ and ⅓ respectively of the maximal efflux in response to carbachol. In the absence of atropine the increase in 42K efflux produced by 120 m
m‐[K+]o was about 50% larger, probably because of the release of acetylcholine from nerve endings in the tissue.3. If inhibitors of histamine metabolism were applied, or a H2‐receptor blocker (cimetidine), the maximum 42K efflux produced by histamine was not increased. An analogue of histamine reputed to resist metabolic degradation did not produce a larger increase in 42K efflux than histamine. The smaller maximal effect of histamine on 42K efflux than carbachol may be because it can open fewer ion channels in the smooth muscle membrane.4. The ratio of the concentrations producing 50% maximal shortening and 50% maximal 42K efflux was about 1:1.3 for raised [K+]o but about 1:20 for histamine and carbachol. Depolarization by raising [K+]o appears to be less effective in causing tension development than similar depolarizations produced by carbachol or histamine.5. The relative effects of carbachol, histamine and raised [K+]o were discussed in the light of their similar depolarizing actions. Increases in 42K efflux did not appear to be caused primarily either by contraction or by depolarization of the muscle. Access of the stimulant to cells and receptors other than those which are superficially situated was suggested as being an important factor in deciding the smaller increase in 42K efflux seen with some stimulants. Histamine receptors may be fewer in number than muscarinic receptors and less able in their activated form to open channels through which potassium ions can escape.
Effect of Escherichia coli heat‐stable enterotoxin, cholera toxin and theophylline on ion transport in porcine colon
Authors: Argenzio R. A. , Whipp S. C. 
Published: December 2014

1. The effect of heat‐stable enterotoxin (ST) of Escherichia coli, cholera toxin (CT), and theophylline (a phosphodiesterase inhibitor) on ion and water transport was studied with an in vivo isolated loop system of the pig colon.2. All three agents abolished net Na absorption as a result of a decrease in the lumen to blood Na flux alone. With all three agents, net Cl absorption was reduced, but not abolished, and net HCO3 secretion was elicited. Luminal pCO2 was reduced with CT and theophylline from that observed in normal Ringer alone.3. Theophylline resulted in a prompt and sustained increase in both cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP) levels in colonic mucosa studied in vitro. ST selectively elevated cyclic GMP, whereas CT selectively elevated cyclic AMP. These responses paralleled the time course and magnitude of response of the transepithelial electrical potential difference (ψLB) measured in vivo.4. Ion replacement studies in the presence or absence of theophylline showed that in the absence of Na, Cl absorption was slightly reduced and HCO3 secretion was elicited; no further additive effects of theophylline in the absence of luminal Na were observed. In the absence of luminal Cl, net Na absorption was abolished and HCO3 was absorbed; theophylline resulted in significant net Na and HCO3 secretion. Theophylline also increased ψLB in the absence of either luminal Na or Cl.5. Results suggest that in the presence of theophylline or enterotoxin, the coupled Na—H and Cl—HCO3 exchange processes that are normally responsible for at least half of the net NaCl absorption by this tissue are interrupted. Active HCO3 secretion is observed and Cl absorption under these conditions can be entirely explained as a consequence of ψLB. Thus, these studies indicate that the colon may participate in the production of diarrhoea of enterotoxigenic origin. They also suggest an important functional role of cyclic nucleotides in controlling the acidity and volume of colonic contents.
The activity of cerebellar neurones of an elasmobranch fish (Scyliorhinus canicula) during a reflex movement of a fin
Authors: Paul D. H. , Roberts B. L. 
Published: December 2014

1. Response of neurones in the corpus cerebelli of Scyliorhinus canicula (Elasmobranchii) have been recorded in decerebrate unanaesthetized fish during the performance of pectoral fin reflexes (p.f.r.) evoked by electrical stimulation of the fins.2. Of 421 single units recorded in the posterior dorsal quadrant of the corpus, 111 (26%) had their discharges modulated when the reflex was evoked; fifty nine were Purkinje (P) cells discharging single spikes, thirteen were P cells discharging complex responses, thirty‐six were stellate (S) cells and three were not positively identified.3. The responses of fifty‐one units (thirty‐seven P cells and fourteen S cells) were analysed in detail. In thirty‐one of the P cells and all the S cells the initial response was excitatory, six P cells gave an inhibitory response only and a further three were inhibited after the initial excitation. Only one S cell had an inhibitory component in its response.4. The discharges of the S cells completely overlapped the inhibitory responses of the P cells.5. Only one cell (a P cell) was evoked at a latency shorter than that of the p.f.r. In one other P cell discharging single spikes spontaneously, the evoked response was a long latency (146 msec) complex response. Four other P cells discharged only complex responses but the pattern of their response to the p.f.r. was similar to that of P cells discharging single spikes only.6. No cerebellar responses were evoked if the fin stimulus was below the threshold necessary to evoke a p.f.r. In curarized fish, unit responses were recorded that were qualitatively similar to those recorded in unparalysed fish.7. These results suggest that (i) because of the long latency of the responses, the cerebellum is unlikely to have a role in the initiation of the p.f.r.; (ii) the responses during the p.f.r. were evoked via a mossy fibre‐parallel fibre pathway; (iii) the responses were correlated with motor activity rather than sensory input.
High‐energy phosphate metabolism and energy liberation associated with rapid shortening in frog skeletal muscle
Authors: Homsher E. , Irving M. , Wallner A. 
Published: December 2014

1. High‐energy phosphate metabolism and energy liberated as heat and work were measured in 3 sec tetani of frog sartorius muscles at 0 °C.2. Three contraction periods were studied: (a) shortening at near‐maximum velocity for 0.3 sec from sarcomere length 2.6 to 1.8 μm, beginning after 2 sec of isometric stimulation, (b) the 0.7 sec isometric period immediately following such rapid shortening, (c) the period from 2 to 3 sec in an isometric tetanus at sarcomere length 1.8 μm.3. There were no significant changes in levels of ATP, ADP or AMP in any contraction period. The observed changes in inorganic phosphate and creatine levels indicated that the only significant reaction occurring was phosphocreatine splitting.4. The mean rate of high‐energy phosphate splitting during rapid shortening, 0.48 ± 0.24 μmole/g.sec (mean ±
s.e. of mean, n = 29; ‘g’ refers to blotted muscle weight), was not significantly different from that in the 1 sec period in the isometric tetanus, 0.32 ± 0.11 μmole/g.sec (n = 17). The mean rate in the post‐shortening period, 0.71 ± 0.10 μmole/g.sec (n = 22), was greater than that in the 1 sec period in the isometric tetanus, and this difference is significant (P < 0.02, t test).5. A large quantity of heat plus work was produced during the rapid shortening period, but less than half of this could be accounted for by simultaneous chemical reactions. The unexplained enthalpy production was 6.5 ± 2.6 mJ/g (mean ±
s.e. of mean). No significant unexplained enthalpy was produced in the 1 sec period in the isometric tetanus.6. In the post‐shortening period the observed enthalpy was less, by 6.2 ± 2.6 mJ/g, than that expected from the simultaneous chemical reactions.7. The results are interpreted in terms of an exothermic shift in the population of cross‐bridge states during rapid shortening. It is suggested that a relatively slow subsequent step prevents many of these cross‐bridges from completing the cycle and splitting ATP until after the end of shortening.
The effect of extracellular calcium deprivation on amylase secretion and 45Ca efflux from rat pancreas
Authors: Argent B. E. , Case R. M. , Hirst Frances C. 
Published: December 2014

1. The role of extracellular Ca2+ in pancreatic enzyme secretion and 45Ca efflux evoked by acetylcholine (ACh) and caerulein has been assessed in the incubated, uncinate pancreas of young rats.2. In a medium containing 2·5 × 10−3
m‐Ca2+, the maximal rates of amylase secretion evoked by optimal doses of each secretagogue were similar. However, the time courses of amylase release during prolonged stimulation of the gland were different.3. The time course of amylase secretion in response to an optimal dose of ACh (10−5
m) was characterized by an initial rapid increase followed by a slow sustained rise. For caerulein (10−8
m), an initial rapid rise was followed either by a plateau or slight decline in the rate of amylase secretion.4. Both secretagogues produced similar increases in the rate coefficient of 45Ca efflux from the gland.5. With supra‐optimal doses of the secretagogues, amylase secretion, but not the rate coefficient of 45Ca efflux, was depressed.6. Reducing the extracellular Ca2+ concentration did not have a marked effect on basal amylase secretion but inhibited the action of both secretagogues. When the Ca2+ concentration was 10−6
m or lower, these inhibitory effects were irreversible. Amylase secretion stimulated by ACh was more sensitive to extracellular Ca2+ deprivation than that stimulated by caerulein, the concentration required for half‐maximal secretion being about 9‐fold greater for ACh.7. Decreasing the extracellular Ca2+ concentration increased both the basal and stimulated rate coefficients of 45Ca efflux.8. Our results support the hypothesis that pancreatic enzyme secretagogues act by releasing bound Ca2+ from sites within the acinar cell. Furthermore, they suggest that the site utilized by ACh is more amenable to depletion, via changes in extracellular Ca2+ concentration, than that employed by caerulein.
Uptake of adenosine and release of adenine derivatives in mammalian non‐myelinated nerve fibres at rest and during activity
Authors: Maire J. C. , Medilanski J. , Straub R. W. 
Published: December 2014

1. Influx of adenosine into rabbit non‐myelinated nerve fibres was measured using [2‐3H]adenosine. The uptake of radioactivity increased linearly with duration of incubation for up to 60 min and adenosine concentration up to 200 μ
m. The uptake at different adenosine concentrations showed a saturable component with a half‐maximal activation at 17·1 μ
m and a linear part.2. The radioactivity taken up was rapidly incorporated into AMP, ADP and ATP. Isotopic equilibrium between the nucleotides was achieved within 15 min.3. The uptake of 3H from 0·2 μ
m‐adenosine was almost completely inhibited by addition of 200 μ
m‐adenosine and to a similar extent by 200 μ
m‐tubercidin and AMP; a 70% inhibition was found with ATP and ADP; α, β methylene‐ADP had no effect.4. ATP, ADP and AMP added to the extracellular medium of a desheathed vagus were slowly hydrolysed.5. In preparations loaded with [2‐3H]adenosine and then washed with adenosine and label‐free solution there was a steady efflux of radioactivity amounting to 0·18 × 10−3/min. Addition of adenosine or tubercidin transiently increased the efflux.6. Electrical stimulation caused an extra release of radioactivity. The extra fractional loss was 21·8 × 10−6/impulse in preparations that had rested for several hours; it decreased to 2·3 × 10−6/impulse when stimulation was applied after a 30 min rest.7. The radioactivity of the resting efflux and of the extra efflux after stimulation was found mostly in inosine and hypoxanthine; adenosine and adenine accounted for only 3%, and the nucleotides for less than 1% of the efflux.8. Adenosine added to the external medium of a desheathed nerve was slowly deaminated.9. It is concluded that inosine and hypoxanthine found in the effluent from desheathed vagus nerve trunk result from release of these compounds from nerve fibres and not from extracellular breakdown of released ATP or adenosine.10. Electrical activity in non‐myelinated nerve fibres of the nerve trunk thus causes the release of metabolites (inosine and hypoxanthine) together with small amounts of adenosine and adenine, while release of ATP and other nucleotides is almost completely absent.
Effects of cholinergic drugs on receptive field properties of rabbit retinal ganglion cells
Authors: Ariel M. , Daw N. W. 
Published: December 2014

1. Retinal ganglion cells were recorded extracellularly from the rabbit's eye in situ to study the effects of cholinergic drugs on receptive field properties. Physostigmine, an acetylcholinesterase inhibitor, and nicotine increased the spontaneous activity of nearly all retinal ganglion cell types. The effectiveness of physostigmine was roughly correlated with the neurone's inherent level of spontaneous activity. Brisk cells, having high rates of spontaneous firing, showed large increases in their maintained discharge, whereas sluggish cells, with few or no spontaneous spikes, showed small and sometimes transient increases in spontaneous activity during physostigmine.2. The sensitivity of ganglion cells to spots of optimal size and position did not change substantially during the infusion of physostigmine. However, the responsiveness to light (number of spikes per stimulus above the spontaneous level) increased. This effect occurred with sluggish and more complex cells, rarely with brisk cells.3. Another effect of physostigmine on sluggish and more complex cells was to make these cells ‘on—off’. The additional response to the inappropriate change in contrast had a long latency and lacked an initial transient burst.4. Complex receptive field properties such as orientation sensitivity, radial grating inhibition, speed tuning and size specificity were also examined. These inhibitory properties were still present during infusion of physostigmine and, in most cases, the trigger feature of each cell type remained.5. These results are consistent with pharmacological results on ACh release from the retina. There appear to be two types of release of ACh, having their most powerful influences on separate classes of cells. One release (transient), occurs at light onset and offset and acts primarily on sluggish and more complex ganglion cells; the other release (tonic) is not light‐modulated and acts primarily on brisk cells. A wiring diagram for the ACh cells is suggested.
Eye position signals in the flocculus of the monkey during smooth‐pursuit eye movements
Authors: Noda Hiroharu , Warabi Tateo 
Published: December 2014

1. Discharges of Purkinje cells and mossy fibres were recorded from the flocculus of monkeys trained to fixate a small visual target and to track the target when it moved slowly.2. Discharges of Purkinje cells changed tonically with shifts of gaze. Firing rates were linearly related to eye positions for either the entire or more than half the eye‐position range in 12·6% of Purkinje cells tested (76/603 units).3. The eye position‐related activity (position component) was observable in these cells also during smooth‐pursuit eye movements. It was typically seen during slow eye movements (velocities less than 10 deg/s) but became undetectable during high velocity movements (faster than 50 deg/s).4. The position component became prominent when smooth pursuit was executed at the preferred loci of the individual cells. In the majority of the cells tested at their preferred loci, the position component was observable to a relatively high frequency, such as 0·5 Hz (± 10 deg; peak velocity 31 deg/s).5. Forty‐five mossy fibre units showed saccade‐related bursts and position‐related intersaccadic tonic activity during steady eye position. In each unit, the position component was found only during fixations within a specific range of eye positions. During fixations outside these regions, all position‐related mossy fibres were completely silent.6. During sinusoidal smooth‐pursuit eye movements, the mossy fibres also displayed cyclic modulations in activity. All fibres discharged with eye movements in one direction and were silent during eye movements in the other direction.7. Saccade‐related bursts from mossy fibres led the onset of saccades, ranging from 0 to 19 ms with a mean lead‐time of 6·9 ms. This observation negates the possibility that the position‐related signals might represent proprioceptive impulses from the stretch receptors of the extraocular muscle.
Activation and inactivation characteristics of the sodium permeability in muscle fibres from Rana temporaria
Authors: Collins Carol A. , Rojas E. , Suarez‐Isla B. A. 
Published: December 2014

1. The steady‐state and kinetic characteristics of the processes of activation and inactivation of the Na+ permeability, PNa, were measured in cut skeletal muscle fibres from Rana temporaria under voltage‐clamp conditions.2. The specific resistance, rss, in series with the surface sarcolemma, was estimated as 6 Ω cm2 by measuring the initial value of the membrane potential transient in response to current pulses under current‐clamp conditions. To reduce the error in the potential across the sarcolemma introduced by rss, Na+ currents were recorded using positive feed‐back compensation, in the presence of tetrodotoxin (2·4‐5 n
m).3. PNa(t) was fitted with m3h kinetics assuming a voltage‐dependent delay, δt, to the start of the activation process.4. The PNa—Vp curve exhibited saturation at potentials more positive than 30 mV. m∞, calculated as (PNa, ∞/P̄Na)⅓ as a function of Vp, was a sigmoid curve with a mid point at ‐35 mV. The slope, dm∞/dVp, at this point was 0·032 mV−1.5. Using a double‐pulse protocol a non‐exponential time course for the development of fast inactivation at small depolarizations was observed.6. The time constant for activation, τm, as a function of Vp, and τh as a function of Vp, could be fitted with an approximately bell‐shaped function, maximum of 430 μs at ‐43 mV and 925 μs at ‐78 mV respectively, at 15 °C.7. The mid‐point potential of the h∞—Vl curve occurred at ‐58 mV, and h∞ approached 1 for V1 values more negative than ‐103 mV.8. Using a double‐pulse procedure the development of a slow inactivation of the Na+ current was demonstrated. Its time course could be described in terms of a single exponential function, time constant equal to 0·58 s. The recovery from slow inactivation could be described by a similar exponential for recovery times smaller than 1 s.
Adrenergic mechanisms and chemoreception in the carotid body of the cat and rabbit
Authors: Folgering H. , Ponte J. , Sadig T. 
Published: December 2014

1. The effect of β‐adrenergic and dopaminergic agonists and antagonists on the chemoreceptor response to graded hypoxia and hypercapnia was tested in nineteen cats and ten rabbits anaesthetized either with chloralose—urethane or pentobarbitone sodium, paralysed with pancuronium bromide and artificially ventilated.2. The inhibitory action of dopamine was confirmed. The inhibition following intra‐arterial bolus injection was blocked by haloperidol; dopamine then excited and this excitation was blocked with propranolol. Adrenaline or noradrenaline caused a transient inhibition followed by a marked excitation. The inhibition was blocked with haloperidol and the excitation blocked with propranolol or metoprolol. Isoprenaline excited without inhibition and this was blocked with propranolol or metoprolol.3. A novel finding was that the chemoreceptor response to hypoxia was markedly reduced or even abolished with propranolol or metoprolol. The response was enhanced with a constant infusion of isoprenaline, adrenaline or noradrenaline in proportion to the degree of hypoxia, an effect mimicked by raising CO2. The chemoreceptor response to hypoxia was similarly enhanced by haloperidol and depressed by a constant infusion of dopamine in proportion to the degree of hypoxia.4. The effect of these drugs on the chemoreceptor response to hypercapnia was less constant. In the majority of tests the aminergic agonists and antagonists caused a parallel shift of the CO2 response curves in the same direction as the O2 response curves and by amounts proportional to the degree of hypoxia. In some tests these drugs caused a change in the slope of the CO2 response curves but only if Pa, O2 was less than 60 mmHg.5. One interpretation of these results is that hypoxia exerts a presynaptic action, causing the release of noradrenaline and dopamine from Type I cells, and that these substances act upon aminergic receptors on the sensory fibre, causing a change in potential and discharge frequency proportional to the rates of dopamine and noradrenaline release.6. An additional or alternative interpretation is that O2 and CO2 (the latter most probably acting on intracellular pH) alter the sensitivity of the aminergic receptors to their agonists.
Calcium efflux from the rat neurohypophysis
Authors: Nordmann Jean J. , Zyzek Evelyne 
Published: December 2014

1. Calcium efflux from isolated rat neurophypophyses has been studied. Curve fitting of the wash‐out curves suggests three phases with t½ of ca. 3, 15 and 130 min.2. The slow component of the 45Ca efflux is attributed to efflux of intracellular Ca. On the basis of the temperature sensitivity of the Ca efflux, the activation energy has been calculated to be approximately 12,000 cal/mole, corresponding to a Q10 of ca. 2·0.3. Ca efflux decreased by approximately 32% when external Na was replaced by choline. Lio, in the presence or absence of Cao, was as effective as Nao in stimulating the Ca efflux.4. The curve relating Ca efflux to [Na]o or [Li]o is sigmoid and suggests that at least two Na (or Li) ions are necessary to activate the efflux of each Ca ion. Cao does not modify the absolute Na‐dependent Ca efflux but decreases the affinity for Na of the site involved in Ca extrusion.5. Removal of Cao decreased the Ca efflux by ca. 44% in Na‐free media. The apparent affinity for Cao of the Cao‐activated Ca efflux (KmCao = 20 μM) is greatly decreased by the presence of 150 mM‐Na (KmCao = 0·8 mM).6. Lanthanum decreased the total Ca efflux by ca. 60% and totally abolished the Nao‐activated and Cao‐activated Ca efflux.7. Vanadate reduced the Ca efflux remaining in Na‐, Ca‐free saline by 73%.8. Elevation of Nai with ouabain did not modify the rate of loss of 45Ca.9. Increased concentration of Ko stimulated transiently the 45Ca loss. The time course of this increase depends on the Cao concentration ([Ca]o).10. Cyanide or CCCP (carbonyl cyanide m‐chlorophenylhydrazone) increased transiently the Ca efflux. The increase induced by cyanide could only be observed when the neural lobes had been over‐loaded with 45Ca.11. Membrane destruction induced by high temperature eliminated the effect of [Na]o and [Ca]o on 45Ca efflux.12. In 150 mM‐Na‐containing saline, half‐maximum activation of 45Ca uptake occurs in the 0·2‐0·4 mM [Ca]o range.13. The Ca efflux from isolated pituicytes was not affected by removal of Nao.14. In conclusion we show that Ca efflux from neurosecretory nerve terminals can be subdivided into three components of approximately the same magnitude, one which is activated by Nao, another by Cao and a third component which is independent of Nao and Cao.