bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cerebral glucose transport and oxygen consumption in sheep and rabbits
Authors: Pappenheimer J. R. , Setchell B. P. 
Published: December 2014

1. Mechanisms underlying the ability of ruminants to tolerate severe hypoglycaemia have been investigated. Anaesthetized sheep and rabbits were compared with respect to cerebral glucose transport and oxygen consumption as a function of glucose concentration in cerebral extracellular fluids.2. Glucose in plasma was decreased by insulin or increased by
I.V. infusion. Measurements were made of cerebral blood flow, arteriovenous concentration differences of glucose and oxygen and the concentration of glucose in c.s.f.3. Equations for carrier‐mediated transport accurately described steady‐state glucose flux across the blood—brain barrier as plasma concentration was varied from 0·2 to 30 m
M. In sheep, the affinity constant (Km) was 6 m
M and the maximum transport capacity (Ṫm) was 260 μmole min−1. 100 g1 brain. In rabbits, Km = 5·5 m
M and Ṫm = 280 μmole min−1. 100 g1. Transport of glucose across the blood—brain barrier of rabbits is at least as efficient as that in sheep and in both species Ṫm is 10–15 times greater than normal rates of glucose utilization.4. During hypoglycaemia the concentration of glucose in c.s.f. is less in sheep than in rabbits (Fig. 5). Steady‐state utilization of glucose by sheep brain decreased to 50% of normal when steady‐state concentration of glucose in c.s.f. (interstitial fluid) falls to 0·1 μmole ml.−1; in rabbits the corresponding concentration is 0·7 μmole ml.−1 (Fig. 6). We suggest that transport capacity of membranes separating cerebral interstitial fluid from the site of glucose phosphorylation is greater in sheep than in rabbits; this may be the principal adaptation which enables ruminants to withstand severe hypoglycaemia (Discussion II).5. Approximately 30 min were required to reach a steady state of glucose transport following a sudden increment of glucose concentration in plasma (Fig. 1). 80–100 min were required to reach a new steady‐state concentration of glucose in c.s.f.6. The molar ratio of steady‐state cerebral glucose utilization to oxygen consumption (6Ġ:Ȯ2) is normally 0·93 (
S.E. ± 0·05) but is decreased to the range 0·1–0·5 during sustained hypoglycaemia in both sheep and rabbits (Figs. 2, 3). Continued low glucose: oxygen ratios could be explained by (a) utilization of non‐carbohydrate substrates derived from blood or (b) utilization of stored lipid in brain. Only 0·1 g lipid/100 g brain would suffice to account for the observed rate of non‐glucose oxidative metabolism during 3 hr of severe hypoglycaemia (Discussion IV).
Matching of facilitation at the neuromuscular junction of the lobster: a possible case for influence of muscle on nerve
Authors: Frank Eric 
Published: December 2014

1. The facilitation of neuromuscular transmission, which occurs during repetitive activation, was examined in the proximal accessory flexor muscle in walking legs of the lobster using electrophysiological techniques.2. Post‐synaptic potentials (p.s.p.s) in different muscle fibres facilitated to markedly different degrees. P.s.p.s in some fibres did not facilitate at all, while in others they increased in size by 20–30 times during stimulation at 20 Hz even though all the excitatory neuromuscular synapses are made by a single axon.3. Stimulation of widely separated groups of synapses on any single muscle fibre evoked p.s.p.s with closely matched facilitation properties. Extracellular p.s.p.s recorded from single synaptic spots showed the same characteristics of facilitation as those of intracellular p.s.p.s in the same muscle fibre, suggesting that individual synaptic contacts on any single fibre are similar to each other.4. Facilitation can be accounted for by an increase in the number of quanta released from the nerve terminals. There is no evidence for an increase in post‐synaptic membrane sensitivity.5. Low Ca solutions reduce transmitter release with comparatively little change in facilitation, while Cs solutions increase the size of p.s.p.s without increasing the amplitude of spontaneous miniature potentials. Thus, at poorly facilitating synapses it is unlikely that the absence of facilitation is caused by the saturation of some post‐synaptic process.6. It is concluded that the excitatory presynaptic nerve terminals on a single muscle fibre have matching facilitation characteristics. Some interaction between individual muscle fibres and their associated nerve endings may be required to establish or maintain this matching.
Binding of catecholamines to connective tissue and the effect upon the responses of blood vessels to noradrenaline and to nerve stimulation
Authors: Powis Garth 
Published: December 2014

1. Quantitative estimates have been made of the binding of catecholamines to purified collagen and elastin, and the factors influencing this binding have been investigated.2. Collagen shows no specificity towards the binding of either the (−)‐ or (+)‐isomer of adrenaline or noradrenaline, at low concentrations. Elastin binds the (−)‐isomer of adrenaline and noradrenaline to twice the extent of the (+)‐isomer.3. Tetracyclines inhibit the binding of catecholamines to collagen and elastin. Oxytetracycline 10−4
M produces a maximum inhibition of the binding of (−)‐noradrenaline to collagen of 68·4%.4. The responses of perfused blood vessels to the administration of pulses of catecholamines or to adrenergic nerve stimulation have been measured.5. Oxytetracycline (10−4
M) potentiates the amplitude of the response of the rabbit ear artery to noradrenaline and to nerve stimulation, ten‐ and sixfold respectively.6. Those preparations with a high content of collagen and elastic tissue, the rabbit ear artery and the rat tail, are more susceptible to the potentiating effects of oxytetracycline than one with a low content, the rat anococcygeus.7. The results of the study suggest that in tissues with a high content of collagen and elastin, binding to extracellular sites is the major mechanism for terminating the response to noradrenaline or to adrenergic nerve stimulation.
Differential effects of glycerol treatment on membrane capacity and excitation—contraction coupling in toad sartorius fibres. With an Appendix
Authors: Dulhunty Angela F. , Gage Peter W. , Barry Peter H. 
Published: December 2014

Changes in membrane capacity and excitation—contraction coupling caused by glycerol movements have been investigated in toad sartorius fibres using a standard glycerol—Ringer solution containing 400 m
M glycerol.1. The rates of glycerol movement, in and out of fibres, were determined by measuring diameter changes in single fibres. Glycerol equilibrated across the surface membrane within 20‐25 min after changes in extracellular glycerol concentration.2. The reduction in membrane capacity, which occurs when glycerol‐loaded fibres are returned to Ringer solution, was slower than, and not dependent on, changes in fibre volume.3. To obtain the maximum reduction in membrane capacity, it was necessary to expose fibres to glycerol—Ringer for 50‐60 min and then to return them to Ringer for at least 60 min. If preparations were not kept in Ringer for the full 50‐60 min, the reduction in membrane capacity could be partially or completely reversed by returning the fibres to glycerol—Ringer.4. When fibres were exposed to glycerol—Ringer there was an initial transient contracture: twitches and K contractures were rapidly inhibited, and then slowly recovered over the next 40‐50 min. In some preparations, eventual potentiation of twitches was seen.5. When returned to Ringer solution after 60 min in glycerol—Ringer, preparations lost twitches and K contractures within 5‐10 min. The time course of this effect was very similar to the time course of the recovery of the normal volume after the initial swelling.6. The briefer the exposure to the glycerol—Ringer, the slower the loss of twitches and K contractures on return to Ringer. In contrast to the loss of membrane capacity, the lesion of excitation—contraction coupling was essentially irreversible. Exposure times as brief as 5 min were eventually effective in producing paralysed fibres which, however, still responded to caffeine.7. The differences in the glycerol load‐times required to produce decoupling of excitation and contraction, and disconnexion of the transverse tubules, show that the two effects are separable and that the first does not depend on the second.8. It is proposed that the two lesions obtained in glycerol‐treated fibres may be related to distension of the transverse tubular system. It is shown in an Appendix that the outward movement of glycerol from sarcoplasm to transverse tubules would be expected to produce some early swelling of the tubules and this is related to the loss of contraction. Furthermore, much greater swelling would occur if a slow‐loading compartment (presumed to be the sarcoplasmic reticulum) dumped glycerol into the transverse tubules: it is thought that this is related to the disconnexion of the transverse tubules.
Pancreatic acinar cells: acetylcholine‐induced membrane depolarization, calcium efflux and amylase release
Authors: Matthews E. K. , Petersen O. H. , Williams J. A. 
Published: December 2014

1. The effects of acetylcholine upon the output of amylase, Ca2+ efflux and membrane potential of pancreatic acinar cells have been measured in segments of mouse pancreas superfused in vitro.2. Amylase output was measured continuously using an on‐line automated fluorimetric method; Ca2+ efflux was monitored by measuring the release of 45Ca2+ from pre‐labelled tissue; and intracellular recordings of acinar transmembrane potentials were obtained with glass micro‐electrodes. In some experiments membrane potentials, and in others 45Ca2+ efflux, were measured concomitantly with amylase release.3. Acetylcholine depolarized the acinar cells, increased tissue 45Ca2+ efflux and raised amylase output, each with a similar dose‐dependence, i.e. a maximal response at 10−5
M, threshold ⋜ 10−8
M, and ED50 values of 0·7 × 10−7
M, 0·5 × 10−7
M, and 2 × 10−7
M for depolarization, amylase release, and 45Ca2+ efflux, respectively.4. In response to acetylcholine both depolarization and 45Ca2+ efflux preceded or coincided with the increase in amylase output.5. Acetylcholine 10−5
M and [K]0 47 m
M were without effect on 45Ca2+ efflux in the presence of atropine (3 × 10−6
M) but pancreozymin (0·3 u./ml.) still elicited a marked increase in 45Ca2+ release.6. These results suggest that the stimulatory action of acetylcholine on the pancreatic acinar cell involves, sequentially, a specific receptor‐activated increase in membrane permeability, depolarization, Ca2+ mobilization and amylase release. These events are discussed in relation to the integrated mechanism of stimulus‐secretion coupling.
The relationship between calcium exchange and enzyme secretion in the isolated rat pancreas
Authors: Case R. M. , Clausen T. 
Published: December 2014

1. The role of extracellular and intracellular Ca2+ in pancreatic enzyme secretion has been assessed by correlating the exchange of 45Ca with amylase secretion in the isolated uncinate pancreas of baby rats.2. The rate coefficient of 45Ca efflux from pre‐loaded glands declined continually (indicating that 45Ca is retained in several different pools) and probably reflects changes in the concentration of cytoplasmic free 45Ca, which is determined by the rate at which 45Ca is released from intracellular organelles into the cytoplasm.3. The rate coefficient of 45Ca release was not influenced by extracellular Ca2+ or Mg2+ concentrations.4. Cholecystokinin‐pancreozymin (CCK‐PZ) and acetylcholine accelerated the release of both 45Ca and amylase in a dose‐dependent fashion, even when extracellular Ca2+ was reduced to 0·1 m
M, but did not affect the initial rate of 45Ca uptake by the tissue.5. In Ca2+‐free media (containing 0·5 m
M‐EGTA) basal amylase secretion slowly declined and stimulated secretion was virtually abolished, but the accelerated release of 45Ca was maintained.6. These observations indicate that natural stimuli of pancreatic enzyme secretion alter 45Ca distribution in the cell by a process which is independent of extracellular Ca2+ and which is associated with amylase secretion provided that the plasma membrane has not been depleted of Ca2+.7. Secretin, glucagon and insulin did not influence 45Ca release. Secretin slightly increased amylase secretion, but this may have been a washout effect.8. Replacement of extracellular Na+ by Li+ increased the release of 45Ca and amylase, but only in the presence of extracellular Ca2+. Li+‐substitution also increased 45Ca uptake. Thus, under special conditions, secretion may be stimulated when increased amounts of Ca2+ are made available from extracellular sources.9. Hyperosmolarity (known to increase 45Ca release in muscle) also accelerated 45Ca release and amylase secretion.10. 2,4‐Dinitrophenol markedly accelerated 45Ca efflux but did not stimulate amylase secretion, indicating that a rise in cytoplasmic Ca2+ will not initiate secretion if energy metabolism is impaired.11. CCK‐PZ slightly increased the rate coefficient of 42K release, indicating a changed membrane permeability.12. The stimulatory effects of CCK‐PZ and acetylcholine were suppressed during Na+‐substitution by Li+, suggesting that the Na+ concentration gradient across the membrane is important in secretion.13. It is concluded that the primary action of CCK‐PZ and acetylcholine may be to increase the influx of Na+ into the cell by changing membrane permeability. This in turn is responsible for the release of Ca2+ from intracellular stores (probably endoplasmic reticulum), leading to a rise in Ca2+ concentration close to the structures involved in enzyme secretion. Secretion then follows provided that ATP is available and the plasma membrane is not depleted of Ca2+.
Reconstruction of the action potential of frog sartorius muscle
Authors: Adrian R. H. , Peachey L. D. 
Published: December 2014

1. Propagated action potentials of striated muscle are calculated using an equivalent circuit that represents the transverse tubular system as a radial cable of sixteen elements. The membrane of the transverse tubules is assumed to have activatable ionic currents similar to those in the fibre surface.2. The configuration of the after‐potential and the conduction velocity are best accounted for by postulating a resistance of about 150Ω cm2 separating the extracellular fluid from the lumen of the transverse tubules at the edge of the fibre, and a density of sodium channels in the tubular wall about a twentieth of that in the fibre surface.3. Calculations with imposed voltage steps at the fibre surface suggest that the potential across the tubular membrane at the centre of the fibre is very far from clamped.4. Currents providing charge for the tubular capacity can give rise to substantial errors in estimating the zero‐current potential of the ionic currents.
Changes in the adenine nucleotide content of preparations of the rat small intestine in vitro
Authors: Bronk J. R. , Leese H. J. 
Published: December 2014

1. The adenine nucleotide content of rat jejunal mucosa has been measured. For fresh tissue the concentrations of the three nucleotides in the total water are approximately: ATP, 1·4 m
M; ADP, 1·0 m
M; and AMP, 0·5 m
M.2. The adenine nucleotide content of mucosal slices prepared from rat jejunum was about 80% of that of fresh tissue, but the slices rapidly lost nucleotides when they were incubated in vitro. After a 4 min incubation the mucosal tissue contained about 1 μmole/g dry wt. of each of the three nucleotides. This represented only 14% of the ATP, 20% of the ADP and 36% of the AMP originally present. Further incubation had little effect on the ATP and ADP content, but some additional AMP was lost.3. Additions of glucose, amino acids, phosphate, pyruvate, butyrate or glucose‐6‐phosphate did not prevent the loss of nucleotides from the mucosal slices. The addition of ADP (1 m
M) did restore the ATP content of slices to a value close to that of fresh tissue within 2 min, but the nucleotide content declined again on further incubation.4. The respiration rate of mucosal slices falls progressively during incubation in vitro. This decline was largely prevented by the addition of ADP.5. Although nucleotide loss occurred most rapidly from mucosal slices, it was also observed with rings of whole intestinal wall and, less rapidly, with everted sacs.6. ATP added to incubations of mucosal slices disappeared at a rate of about 30 μmole/min. g dry wt.7. These results suggest that the adenine nucleotide content of preparations of rat small intestine studied in vitro is likely to be severely reduced. The addition of nucleotides to the incubation medium produces only a temporary increase in the nucleotide content of the tissue.
Synaptic connexions of two symmetrically placed giant serotonin‐containing neurones
Authors: Cottrell G. A. , Macon J. B. 
Published: December 2014

1. Each giant serotonin cell in Helix pomatia makes synaptic connexions with three non‐amine‐containing neurones: the anterior, middle and posterior buccal cells.2. Individual e.p.s.p.s, of 500–600 msec duration, were observed in both left and right middle cells following each evoked giant serotonin cell action potential. They were facilitated with repetitive stimulation of the giant serotonin cells and summed to give rise to an action potential. The membrane resistance of the middle cells was reduced when the giant serotonin cells were stimulated to fire rapidly. Evidence is presented which suggests that the link between each giant serotonin cell and each middle cell is monosynaptic.3. Iontophoretically applied serotonin produced a depolarizing potential change in the middle cell perikaryon; the response rapidly desensitized on repetitive application.4. Morphine abolished reversibly the middle cell serotonin potential and antagonized transmission from the giant serotonin cells to the middle cells. Lowering the Na concentration of the medium reversibly diminished the size of the serotonin potential and the giant serotonin cell elicited e.p.s.p.s in the middle cells.5. Reserpine, which depletes serotonin in the giant serotonin cell, impaired transmission from these cells to the middle cells.6. The results suggest that serotonin is the synaptic transmitter released from the giant serotonin cells on to the middle cells and that this system is a suitable model for further analysis of the neuronal role of serotonin.
Capillary permeability to protein as a factor in the control of plasma volume
Authors: Wraight E. P. 
Published: December 2014

1. Measurements of plasma volume, blood volume, extracellular fluid volume and capillary permeability to albumin were made in rats before and after plasmapheresis extending over 2 days.2. In spite of a mean reduction of albumin concentration of nearly 40%, plasma volume showed a significant increase of 12%. There was a slight increase in blood volume and a slight decrease in extracellular fluid volume but these changes were not statistically significant.3. The mean capillary permeability to albumin was significantly lower after plasmapheresis than before and changes in permeability showed a strong negative correlation with changes in plasma volume. The possibility of a causal relationship is discussed.
Whole kidney and cortical blood flow in rats on high and low sodium diets
Authors: Mercer P. F. , Zusko E. A. 
Published: December 2014

1. A method to measure total and cortical blood flow in the rat kidney has been described.2. Using this method it was found that total renal blood flow increased when rats were placed on both high and low sodium diets.3. Outer cortical blood flow in rats on a normal diet was found to be higher than the blood flow in the inner cortical region.4. The blood flow to the inner cortical region increased in rats on a low sodium diet and outer cortical blood flow did not change from normal values.5. When rats were placed on a diet high in sodium the blood flow to the outer region increased over normal values but inner cortical blood flow was not different from control values.
Electrical excitability in the egg cell membrane of the tunicate
Authors: Miyazaki Shun‐Ichi , Takahashi Kunitaro , Tsuda Kazuko 
Published: December 2014

1. With the purpose of studying the differentiation of an excitable membrane, the electrical properties of the tunicate egg, a mosaic egg, was examined by intracellular recording techniques. The species used were Halocynthia aurantium Pallas and H. roretzi Drashe.2. The membrane in the matured but unfertilized egg, the fertilized but uncleaved egg, and the cleaved egg showed the resting potential of +5 to −15 mV.3. Hyperpolarization beyond −60 mV elicited a regenerative response in the form of an ‘off response’ with a critical membrane potential of about −40 mV and with an over‐shoot of 10–20 mV above the original resting potential.4. The removal of Na from standard artificial sea water and the enhancement of Ca in Na‐free ASW revealed both Na and Ca components in the ‘off response’.5. In both std ASW and Na‐free ASW the I—V relation of the egg cell membrane showed marked non‐linearity, forming an S‐shaped curve. In the range of positive membrane potential, the embryonic membrane showed a moderate outward‐going rectification; in the potential range below −60 mV there was a considerable inward‐going rectification. So far as examined, the shape of the I—V relation was affected only by changes of K concentration in the ASW, but not by those of other cations.6. Specific capacity of the egg cell membrane was 1·0 μF/cm2. The specific slope resistance below −70 mV was 130 kΩ cm2 for the unicellular egg and 50 kΩ cm2 for the two cell embryo.
Intracellular pH of snail neurones measured with a new pH‐sensitive glass micro‐electrode
Authors: Thomas R. C. 
Published: December 2014

1. The construction and properties of a new design of pH‐sensitive micro‐electrode are described. The electrodes are very durable, and have a recessed configuration so that only the extreme tip, which can be as small as 1 μm in diameter, needs to enter the cell.2. The average intracellular pH in thirty‐two snail neurones was 7·4. This was not in accord with a passive distribution of H+ ions across the cell membrane.3. Changing membrane potential or external pH had only slow effects on internal pH.4. Removing external K had no effect, and removing external Na had only slow and variable effects on intracellular pH.5. Anoxia, azide and DNP all caused a slow fall in internal pH.6. External CO2 caused large and rapid decreases in internal pH, which external bicarbonate appeared to offset slowly. Injected bicarbonate increased internal pH.7. The size of the pH changes caused by CO2 suggested a minimum intracellular buffering power of 25 m‐equiv H+/unit pH per l., equivalent to that of 150 m
M Tris maleate, pH 7·4.8. External ammonia caused a large and rapid increase in internal pH, while the injection of ammonium ions had the opposite effect.
Complementary lowering of the behavioural and physiological thermoregulatory set‐points by tetrodotoxin and saxitoxin in the cat
Authors: Clark Wesley G. , Lipton J. M. 
Published: December 2014

1. Injections of tetrodotoxin or saxitoxin (25 ng in 0·10 ml.) into a lateral cerebral ventricle caused deep body temperature of cats to fall approximately the same amount (2° C) whether the animals were resting in the cold (4° C) or were responding to escape heat.2. Continuous exposure to heat either prevented the hypothermic response or enhanced the level of tachypnoea required to lower body temperature. Tetrodotoxin also caused hypothermia when an animal was lever pressing to obtain heat in the cold environment.3. These results provide evidence that agents which alter the set‐point for physiological thermoregulatory activity produce a complementary shift in the behavioural set‐point as well.