bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical energetics in repeated contractions of frog sartorius muscle at 0° C
Authors: Kushmerick M. J. , Paul R. J. 
Published: December 2014

1. Recovery oxygen consumption (ΔO2) was measured in aerobic, unpoisoned frog sartorius muscles at 0° C following a series of repeated tetani.2. For a series of tetani having nearly identical tension—time integrals, ΔO2 was dependent on the interval between tetani and reached a maximal value for intervals equal to or greater than 200 sec.3. For a series of tetani at short (5 sec) intervals, ΔO2 was not distinguishable from ΔO2 following a single long tetanus having a tension‐time integral similar to that of the sum of the series.4. A model is proposed to account for these observations in terms of the initial chemical reactions (Δ ∼ P) including a saturable non‐steady state reaction which utilizes about 1 μmole Δ ∼ P/g and which is superimposed on an energy utilization proportional to the tension—time integral. Measurements of ΔO2 and Δ ∼ P as functions of tetanic duration and interval between tetani are consistent with such a model.5. These experiments show that, in addition to parameters usually considered, the previous contractile history of a muscle plays a significant role in determining the chemical energy cost of an isometric contraction.
The functional significance of sodium channels in pancreatic beta‐cell membranes
Authors: Donatsch P. , Lowe D. A. , Richardson B. P. , Taylor Pamela 
Published: December 2014

1. The existence and functional significance of Na channels in pancreatic β‐cell membranes were investigated by studying the effects of the plant alkaloid veratridine on the temporal release of insulin from perfused isolated rat islets of Langerhans.2. 100 μ
M veratridine evoked a sustained threefold increase in insulin release which was almost completely inhibited by 3 μ
M tetrodotoxin (TTX). This action of TTX was rapidly reversible.3. The simultaneous presence of 100 μ
M propranolol, 100 μ
M phenoxy‐benzamine and 10 μ
M atropine did not alter the magnitude of the response to 100 μ
M veratridine, indicating that the action of veratridine on the β‐cells was direct and was not mediated via the release of neurotrans‐mitters from nerve endings within the islets.4. 45Ca uptake by isolated islets in static incubation was increased almost threefold by 100 μ
M veratridine. This increase was completely inhibited by the simultaneous presence of 3 μ
M TTX.5. Replacement of Nao by choline caused a transient fourfold increase in insulin release which was associated with an increase in the uptake of 45Ca from the extracellular space of similar magnitude. Subsequent exposure of islets to 100 μ
M veratridine still evoked some insulin release but this only achieved 32% of that secreted by islets exposed to veratridine in medium of normal [Na]o.6. The addition of 2·5 m
M CoCl2 to the medium caused a 62·5% inhibition of veratridine‐mediated insulin release.7. In Ca‐free medium supplemented with 1 m
M EGTA, 100 μ
M veratridine evoked insulin release of equal magnitude and of similar temporal relationship to that obtained in the presence of normal [Ca]o.8. A twofold increase in insulin release that occurred in the 15 min period immediately following exposure to 1 m
M ouabain was completely independent of [Ca]o. Subsequent ouabain‐evoked release became increasingly dependent on [Ca]o.9. Tetrodotoxin (3 μ
M) inhibited the first phase of insulin release evoked by 16·7 m
M
d‐glucose by 37% and the second phase by 20%.10. Both Na and Ca appear capable of entering through Na channels opened in the β‐cell membrane by veratridine. The increase in [Na]i, resulting from the veratridine mediated increase in PNa+, causes depolarization of the β‐cell membrane with a consequent opening of voltage‐sensitive, Co2+‐blockable channels for additional Ca entry. An increase in [Na]i also increases [Ca]i by altering the equilibria of intracellular Ca‐sequestering mechanisms. The small but significant reduction of glucose‐mediated insulin release by TTX indicates that glucose has a rather weak action on the Na channel and a more pronounced effect on the voltage‐dependent Co2+‐blockable Ca channel.
Interacting effects of temperature and extracellular calcium on the spontaneous release of transmitter at the frog neuromuscular junction
Authors: Duncan C. J. , Statham Helen E. 
Published: December 2014

1. Temperature has a characteristic effect on the frequency of m.e.p.p.s at the frog neuromuscular junction; the spontaneous release of transmitter is not affected by temperature changes below 10° C whereas the system is highly temperature‐sensitive above 20° C.2. A very similar result is obtained when the experiment is repeated in saline containing Ca2+ buffered at 5 × 10−7
M, suggesting that it is unlikely that the major action of temperature is to cause an increase in Ca2+ influx.3. It is suggested that the main effect of temperature at the presynaptic terminals is a modification of [Ca2+]i by an action on intracellular Ca2+ stores.4. The interacting effects of theophylline and the divalent cation ionophore A23187 on m.e.p.p. frequency suggest that intracellular Ca2+ stores, in addition to the mitochondria, may well be of importance in controlling [Ca2+]i.5. Changes in [Ca2+]o produce a modification of m.e.p.p. frequency, but the details of the response are dependent on temperature. The spontaneous release of transmitter is most sensitive to an increase in [Ca2+]o at 23° C, whereas the greater effect is found at 13° C when [Ca2+]o is lowered.6. It is suggested (i) that m.e.p.p. frequency is primarily determined by [Ca2+]i at the presynaptic terminals, (ii) that the presynaptic terminals are normally able to maintain [Ca2+]i almost constant in spite of increases in Ca influx associated with ionophore treatment or with a rise in [Ca2+]o. However, if the steady‐state position of [Ca2+]i is previously raised by an increased efflux from intracellular stores (produced by elevated temperature or theophylline pre‐treatment), increased influx causes a rise in both [Ca2+]i and in m.e.p.p. frequency.
Self‐facilitation of ganglion cells in the retina of the turtle
Authors: Marchiafava P. L. , Torre V. 
Published: December 2014

1. Ganglion cells responses to illumination and to optic nerve stimulation were recorded intracellularly from the retina of the turtle. All ganglion cells were identified by their antidromic responses to optic nerve stimulation.2. When solitary spikes are produced following antidromic, orthodromic or intracellular stimulation, about 20% of the recorded ganglion cells show an additional depolarization along the falling phase of the action potential (post‐spike depolarization, PSD).3. The PSD following the antidromic action potential disappears upon collision with a direct spike or when the antidromic spike is prevented from invading the cell soma.4. By pairing two optic nerve stimuli the PSD is depressed with brief interstimulus intervals, but gradually recovers to the control amplitude 600‐800 msec after the conditioning shock.5. The PSD is tentatively interpreted as an e.p.s.p. transmitted by ganglion cell collaterals originating at the level of the soma dendritic complex of the recorded cell.6. The interspike interval histogram of ganglion cells showing PSD is characterized by a peak at about 10 msec, as opposed to a peak between 12 and 100 msec observed in cells without PSD. It is suggested that the occurrence of PSD facilitate the onset of additional action potentials at brief interspikes intervals, thus potentiating ganglion cell discharges.
Release of adenosine triphosphate from isolated adult heart cells in response to hypoxia
Authors: Forrester T. , Williams Carole A. 
Published: December 2014

1. Adult rat heart cells were isolated enzymically and ATP was identified in the cell suspension using the firefly luminescence technique. Adenosine 5′‐triphosphate (ATP) was not detected from cell suspensions obtained from hearts which had been left asystolic for 10 min.2. It was found that ATP 0·34 ± 0·22 μ
M/mg protein was released by cells kept in an oxygenated condition, while ATP 1·28 ± 0·41 μ
M/mg protein was initially released by cells made hypoxic.3. Addition of Ca2+ in a concentration of 2 m
M caused cells to initially extrude ATP 0·40 ± 0·14 μ
M/mg protein. This was attributed to an inotropic effect.4. Extracellular ATPase activity in the fluid suspension was partially characterized, giving a Km of 13 μ
M and a V/2 of hydrolysed ATP 18·3 μ
M/min at 37° C. Q10 was found to be 4 between 25 and 37° C. Enzyme activity remained unaffected by either hypoxic conditions or ouabain.5. If these amounts of ATP are released from myocardial cells rendered hypoxic in vivo, then it must be concluded that ATP plays a principal role in the local control of myocardial blood flow.6. It is proposed that release of ATP occurs through the sarcolemma from an intracellular pool, and that alteration of the configuration of structural membrane protein controls the amounts of ATP extruded.
The effects of breathing of alternate breaths of air and a carbon dioxide rich gas mixture in anaesthetized cats
Authors: Wolff C. B. 
Published: December 2014

1. An in vivo pH electrode was used to assess the effect in anaesthetized cats of the administration of 5% CO2 (21% O2, balance N2) and air as alternate inspirates upon the time course of the carotid arterial pH, and by inference, the PCO2.2. This method of administration of CO2 and air resulted in a lowering of the recorded pH with the production of oscillations of twice the duration seen on air alone. These larger oscillations had a period of two respiratory cycles and their amplitude was approximately twice that of normal oscillations.3. The respiratory response consisted in all cases of an increase in mean tidal volume and ventilation, and in 50‐60% of recorded runs, of a highly specific sequence of tidal volume changes. The specific sequence was composed of alternately larger and smaller breaths which persisted while the larger oscillations continued.4. The use of the in vivo pH electrode made it possible to determine whether or not the tidal volume alternation was a result of sensitivity to carotid arterial PCO2 oscillations. By diverting the carotid arterial blood through a mixing chamber the amplitude of the double (respiratory) period oscillations was, in some cases, reduced but not eliminated. In these cases the specific pattern of tidal volume changes was still present in 60% of trials. In the cases where the pH fluctuations were completely eliminated the specific respiratory pattern was never present.5. Average breath to breath differences in tidal volume seen during control runs with large oscillations present ranged in size from 3·6 to 8·6% of the mean tidal volume. When the oscillations were completely eliminated by means of the mixing chamber the breath by breath differences only ranged from 0·2 to 2·7% of mean tidal volume. The change was highly significant.6. Mean tidal volume and ventilation were not altered by eliminating the large (double period) oscillations.7. It has been shown that the tidal volume is made to change from breath to breath in a persistent manner when there are recurrent changes in carotid arterial blood chemistry. The effects on respiration involve vascular receptors above the mid carotid arterial region. It is argued that the effects involve the sensitivity of the carotid bodies to rapid (within breath) changes in Pa, CO2. There appears to be no significant effect on mean ventilation of the dynamic component of the arterial PCO2 changes produced in these experiments.
Development of neuromuscular transmission in a larval tunicate
Authors: Ohmori Harunori , Sasaki Shigeto 
Published: December 2014

1. The time sequence of the development of acetylcholinesterase (AChE), acetylcholine (ACh) receptors and functional synapses on the embryonic muscle membrane in a tunicate larva (Halocynthia roretzi) was investigated in vivo.2. The fertilized tunicate egg was incubated in natural sea water at 9° C. Sixty‐eight hr after fertilization the free‐swimming larva was hatched, which had six striated muscle fibres in the tail. The developmental stage of the embryo was indicated by the developmental hours after fertilization.3. The transmitter at the neuromuscular junction in the hatched larva is ACh. (i) Neuromuscular transmission was completely blocked by
D‐tubocurarine (1‐5 × 10−5
M). (ii) Eserine (5‐10 × 10−7
M) approximately doubled the time constant of the falling phase of miniature excitatory junctional currents (e.j.c.s). (iii) The reversal potential of the membrane response to iontophoretically applied ACh was ‐10 mV and similar to that of e.j.c.s. (iv) AChE was present on the muscle membrane surface.4. AChE activity became visible histochemically on the embryonic cell membrane in the presumptive muscle region as early as the late gastrula stage (27 hr after fertilization, 12 hr before the ACh response appeared).5. The response to iontophoretically applied ACh was present at 39 hr after fertilization but could not be evoked at 38 hr.6. Between 39 and 41 hr after fertilization, the ACh responses increased rapidly, then remained relatively unchanged until larval hatching.7. The stage of the initial appearance of the ACh response corresponded to the stage when the Ca current abruptly increased in the muscle membrane.8. The first sign of neuromuscular transmission was appearance of a giant excitatory junctional potential (e.j.p.) with uniform amplitude (about 15‐20 mV) and slow time course (time constant of the falling phase of a giant e.j.c. was 23·4 ± 6·9 msec, mean and
S.D., at ‐60 mV and 11° C).9. Within a few hours, these giant e.j.p.s disappeared and were successively replaced by medium‐sized e.j.p.s and then e.j.p.s similar to those seen in hatched larvae (time constant of the falling phase of a miniature e.j.c. was 8·5 ± 1·8 msec at ‐60 mV and 11° C).
Cone signals in the cat's retina
Authors: Enroth-Cugell Christina , Hertz B. Gevene , Lennie P. 
Published: December 2014

1. The discharges of ganglion cells in the cat's retina were recorded under conditions intended to isolate the cone system.2. Stiles' two‐colour threshold technique permitted the photopic system to be studied when at its highest sensitivity. The absolute sensitivity of a ganglion cell, expressed in equivalent photons of λmax at the cornea per impulse discharged, was about 2500 times less when driven by cones than when driven by rods. This ratio improves to around 200 when allowance is made for the much smaller fraction absorbed by cones of photons incident on the cornea.3. The number of extra impulses discharged in response to a brief flash was approximately proportional to the number of photons in the flash, up to a limit.4. There was a region in the middle of the receptive field within which the area of a test spot and its illumination for threshold varied inversely. A flash extending over the peripheral part of the receptive field raised threshold above its minimum, presumably as a result of surround antagonism. Assessed from area—threshold curves, the balance of centre‐surround antagonism in the photopic receptive field did not seem to depend upon background illumination.5. The threshold for a small (0·2°) flash confined to the middle of the receptive field was independent of background illumination until the background exceeded a particular level, the ‘dark light’ (Io). In different units this ranged about a mean of 7·89 log photons (560 nm equivalent) deg−2 sec−1. For backgrounds that exceeded Io, threshold followed approximately Weber's law up to the highest illuminations that could be produced.6. With test flashes that filled the centre of the receptive field, the Weber fraction (test flash illumination/background illumination) in some units fell below 1%.7. Changes in the time course and latency of response accompanied the changes in sensitivity caused by alterations in background illumination. Responses of both X‐ and Y‐cells became more transient and faster.8. The loss of sensitivity to a test flash brought about by a steady background light depended upon the size of that light. Sensitivity varied inversely with background area within a central region that matched closely the summing area for test flashes.
Calcium movements during the release of catecholamines from the adrenal medulla: effects of methoxyverapamil and external cations
Authors: Aguirre J. , Pinto J. E. B. , Trifaró J. M. 
Published: December 2014

1. Cortex‐free adrenal glands previously labelled with the isotope 45Ca have been perfused with Locke or modified Locke solution to assess Ca2+ movements under different conditions.2. Substitution of Na+ by either sucrose or choline during perfusion with Ca2+‐free Locke solution induced a significant and sustained decrease in the 45Ca efflux. Concomitant with this effect there was an increase in the output of catecholamines from the perfused gland.3. In the presence of Ca2+ (2·2 m
M) in the perfusion fluid, Na+ omission induced an increase in the 45Ca efflux. This increase was significantly reduced if 3 × 10−4
M methoxyverapamil (D‐600) was present in the perfusion fluid. However, the increased catecholamine output in response to Na+ deprivation remained unchanged.4. Excess of Mg2+ (20 m
M) in the extracellular medium blocked the increase in catecholamine output in response to Na+ omission. However, the decrease in the 45Ca efflux produced by Na+ deprivation in the presence of this high concentration of Mg2+ was similar to that observed in the presence of 1·2 m
M‐Mg2+.5. In the absence of Mg2+ in the extracellular medium, substitution of Na+ by either sucrose or choline induced a sharp and transient increase in the 45Ca efflux rate coefficient. This increased 45Ca efflux, which has similar time course as the enhanced catecholamine output, was not affected by the presence of 3 × 10−4
M methoxyverapamil.6. In the absence of Mg2+, the graded substitution of Na+ in the perfusion medium by sucrose enhanced the efflux of 45Ca. This increase in the 45Ca outward movement was linearly related to the logarithm of the extracellular Na+ concentration.7. After perfusion of glands with Ca2+‐free Locke solution, the reintroduction of Ca2+ (2·2 m
M) into the perfusion fluid produced an increase in the 45Ca efflux. This was accompanied by a discharge of catecholamines.8. Although Mg2+ (20 m
M) was effective in blocking catecholamine release, this divalent cation did not modify the increase in the 45Ca efflux produced by Ca2+ reintroduction.9. In contrast to these later observations, methoxyverapamil (3 × 10−4
M) was effective in inhibiting both increases in catecholamine output and 45Ca efflux in response to Ca2+ reintroduction.10. It is concluded from these experiments that (a) Ca2+ movements in the adrenal medulla may involve both Na+‐Ca2+ and Ca2+‐Ca2+ exchange mechanisms; (b) the omission of Na+ from the extracellular environment produces not only an increase in the output of catecholamines but it may increase the intracellular levels of Ca2+ and that this may result in an increased Ca2+ efflux when Mg2+ is omitted from the perfusion fluids, and that (c) the competition between Ca2+ and Mg2+ during the secretory process may involve an intracellular site.
Regulation of compensatory kidney hypertrophy by its own products
Authors: Dicker S. E. , Morris Christine A. , Shipolini R. 
Published: December 2014

1. The ligation of blood vessels of one kidney of adult rats resulted in the compensatory hypertrophy of the other kidney. In most animals the rate of hypertrophy was indistinguishable from that observed after unilateral nephrectomy, but in a few cases the onset was retarded when the renal artery alone had been ligated and the collateral circulation increased.2. When the blood vessels of one kidney of adult rats were ligated and the cortex was excised, the rate of compensatory renal hypertrophy was similar to that observed after unilateral nephrectomy.3. In animals operated for simultaneous partial hepatectomy and unilateral nephrectomy, there was no sign of compensatory renal hypertrophy while the liver was undergoing regeneration. Renal hypertrophy started after 7 days, when about 98% of the amount of liver removed had been regenerated.4. Neither aseptic autolysis of one kidney following suppression of its blood supply, nor unilateral nephrectomy affected the rate of liver regeneration after simultaneous partial hepatectomy.5. Total splenectomy did not affect the rate of compensatory renal hypertrophy following unilateral nephrectomy.6. The heterotopic graft of renal cortical, but not of medullary, cells inhibited compensatory renal hypertrophy in adult rats. The removal of the graft after 14 days was followed by the resumption of compensatory hypertrophy.7. The inhibiting action of fractions of renal cortical extracts fractionated on Sephadex G100 resin and DEAE‐52 cellulose were assayed on the ‘growth’ of renal explants reared in vitro. The final material, though only partially purified, proved to have an inhibiting activity between 250 and 500 times greater than that of the initial extract.8. When injected into unilaterally nephrectomized rats, the partially purified extract from the renal cortex had an inhibiting effect on compensatory renal hypertrophy.9. Immunofluorescence technique showed that the partially purified cortical extract affected the proximal convoluted tubes specifically, irrespective of animal species.
The effect of prolonged inactivity upon the contraction characteristics of fast and slow mammalian twitch muscle (cat)
Authors: Davis C. J. F. , Montgomery A. 
Published: December 2014

1. Prolonged inactivity of soleus (slow twitch) and medial head of flexor digitorum longus (fast twitch: previously commonly known as flexor hallucis longus and hereafter referred to as FDL) muscles of the cat was produced by sodium pentobarbitone anaesthesia or spinal isolation. Isometric contraction characteristics were examined after 4‐22 days and 8‐49 days respectively.2. Sleep of up to 3 weeks' duration was associated with progressive changes in the weight, maximum tetanic tension, speed of contraction and absolute refractory period of fast twitch muscle. The slow muscle showed corresponding changes which were not so pronounced. Cord isolation resulted in similar changes which tended to be reversed after longer periods of disuse.3. Fast muscle frequently exhibited an after‐contraction with corresponding electromyographic activity following two weeks or more of disuse.4. The time to peak of FDL was prolonged, becoming approximately one and a half times normal. In contrast to other reports of disuse, that of soleus was normal or slightly prolonged.5. The ratio of twitch to tetanic tension of FDL increased to twice the normal value or greater and remained high. The soleus muscle showed a smaller increase with evidence of a return towards normal after longer periods of inactivity.6. Absolute refractory period of FDL was considerably prolonged (more than 50%) following barbiturate sleep and this also occurred, but to a lesser degree, with soleus after 4‐7 weeks of cord isolation.7. The observation that inactivity produced slowing rather than an increased speed of switch contraction indicates that aggregate activity is not the controlling factor. Changes seen in the contraction characteristics of FDL are noted to show a general similarity to those occurring following denervation.