bluuebunny/crossref_metadata_2025_split huggingface dataset:
A preparation of perfused small intestine for the study of absorption in amphibia
Authors: Parsons D. S. , Prichard J. S. 
Published: December 2014

1. A preparation of amphibian small intestine perfused through its vascular system is described. Vascular perfusion with a bicarbonate Ringer solution containing a colloid is used to control the composition of the environment of the submucosal faces of the absorbing cells and to carry away for collection any material extruded from these cells. Oxygenation of the mucosal cells is derived primarily from fluid circulated through the intestinal lumen. The preparation exhibits physiological properties of transport for periods of up to 5 hr. After 5 hr perfusion the epithelial cells show no signs of gross cellular damage when examined either by light or by electron microscopy.2. The relationship between the hydrostatic pressure at the mesenteric artery and the rate of perfusion through the vascular bed is substantially linear. The pressure—flow relationships in the mesenteric bed, including an apparent ‘critical closing pressure’, are primarily determined by the hydrostatic pressure in the intestinal lumen. Alterations in the hydrostatic pressure in the intestinal lumen also change the relative proportions of the vascular infusate which appear in the portal venous effluent and in the fluid exuded from the serosal surface of the preparation (‘sweat’). Hydrostatic distension pressures above about 10 cm H2O reduce the rate of collection of fluid from the portal vein and increase the rate of collection of ‘sweat’.3. An increase in the rate of vascular perfusion increases the total rate of glucose appearance although the glucose concentrations in both the portal effluent and the ‘sweat’ are reduced.4. The glucose translocation rate is related in an alinear saturable fashion to the luminal concentration of glucose. By making a correction for metabolic loss of glucose during its passage through the intestinal cell, the relationship existing between the lumen concentration and the uptake of the sugar by the mucosal cells has been calculated. This relationship is found to fit Michaelis—Menten type kinetics. The Km of the intestinal translocation process for glucose in Rana pipiens was 0·45 ± 0·13 (4) μ
M. The mean Vmax was 137·5 ± 35·3 (4) μ
M/hr/g fat‐free dry wt.5. When phlorrhizin (10−5
M) is added to the vascular perfusate, no inhibition of glucose transport is seen for at least 60 min. When strophanthin is added to the vascular perfusate (5 × 10−5
M), a markedly greater inhibition of glucose transport is observed than when it is introduced to the luminal circulation.6. Earlier studies of the vascular perfusion of isolated small intestine are tabulated. The experimental findings are discussed in relation to a model of the mode of action of the epithelial cell for glucose transport.
Absorption of histamine from the gastrointestinal tract of dogs in vivo
Authors: Duncan Jessie G. C. , Waton N. G. 
Published: December 2014

1. In anaesthetized dogs, various amounts of [14C]histamine were introduced into the lumen of a ligated intestinal loop or of the ligated stomach and the absorption of this histamine was studied by determining the radioactive histamine in the venous blood coming from the ligated part.2. After the introduction of 5‐5000 μg [14C]histamine, into a loop of jejunum, or of 50 μg into a loop of duodenum, ileum or colon, radioactive histamine was detected in all eight successive 15 min samples of venous blood collected during 2 hr. The percentage recovery of the [14C]histamine in the blood during this period varied between 0·04 and 3·7.3. After the introduction of 10 mg [14C]histamine into the stomach, radioactive histamine was detected in all samples of gastric venous blood collected at various times during the following 4 hr.4. After the introduction of 50‐5000 μg [14C]histamine into a loop of jejunum, radioactive histamine was also detected in the general arterial blood.5. When a jejunal loop was perfused through its artery with a dextransaline solution, the absorption of [14C]histamine from the lumen into the venous effluent was much greater than when the blood supply was kept intact.6. A large part of the [14C]histamine introduced into an intestinal loop was inactivated or destroyed either in the lumen or the wall since only a part was recovered in the venous blood, contents and wall of the loop at the end of 2 hr. When different amounts of [14C]histamine were introduced into a jejunal loop the recovery was shown to be dependent on the dose. With 5 μg it amounted to about 1% whereas with 5000 μg to 29‐42%. The recovery of the [14C]histamine introduced into a perfused jejunal loop was greater.7. In dogs and cats large amounts of free histamine were found in the contents of the stomach 2 hr after a meat meal, and much smaller amounts in the contents of loops from the small intestine. The amounts found in the contents of loops from the colon varied greatly.8. In eighteen commercial dog and cat foods the free histamine contents were found to vary over fiftyfold, from 0·06 to 3·5 mg/100 g.9. The significance of the results is discussed in relation to the role of histamine as a humoral agent in the ‘gastric’ and ‘intestinal phases’ of gastric secretion.
Visual adaptation of the rhodopsin rods in the frog's retina
Authors: Donner K. O. , Reuter Tom 
Published: December 2014

1. The threshold of the discharge from single ganglion cells in the excised and opened frog's eye has been measured with on/off stimuli and test parameters that make it possible to activate the rhodopsin rods only. The test stimuli have been restricted to the central part of the receptive field, where no nervous reorganization can be observed with changes in the state of adaptation.2. When such thresholds and the intensities of the background lights are expressed in terms of the number of quanta absorbed per unit time, it is found that three factors can be correlated with the thresholds measured in various states of light‐ and dark‐adaptation: (i) the intensity of a steady background, (ii) the rate of regeneration of rhodopsin, and (iii) the amount of metarhodopsin II present in the rods.3. The threshold is found to be proportional both to the intensity of a background and to the rate of regeneration, whereas there is a linear relationship between the logarithm of the threshold and the amount of metarhodopsin II.4. The presence of metarhodopsin elevates all thresholds, the absolute threshold, increment thresholds and the thresholds elevated by regenerating rhodopsin in the same way.5. The saturation of the rods at high background intensities is found to be correlated with the accumulation of significant amounts of metarhodopsin in the rods, caused by the bleaching effect of the background.6. The effect of metarhodopsin on the threshold is independent of the amount of rhodopsin present in the rods.7. The combined effect of all three factors can be expressed in a general formula, given as eqn. (7) on p. 74.8. A background not only reduces the signals from the rods illuminated, but also those from neighbouring unilluminated rods. This effect is rapidly decreased with increasing distance from rods covered by the background. This kind of lateral spread in the retina probably occurs also when the rate of regeneration affects the threshold. The effect of metarhodopsin, on the other hand, appears restricted to those receptors that contain this substance.
Miniature synaptic potentials at frog spinal neurones in the presence of tetrodotoxin
Authors: Colomo F. , Erulkar S. D. 
Published: December 2014

1. Spontaneous subthreshold potentials have been recorded with an intracellular electrode from neurones of the isolated spinal cord of the frog.2. Records of both depolarizing and hyperpolarizing potentials were obtained from cells in normal Ringer solution and also when impulse conduction in the cord had been abolished by tetrodotoxin (TTX).3. Comparisons of results before and after TTX show that the majority of the spontaneous potentials are analogous to miniature end‐plate potentials.
Multiple sensitivity of chorda tympani fibres of the rat and hamster to gustatory and thermal stimuli
Authors: Ogawa H. , Sato M. , Yamashita S. 
Published: December 2014

1. Impulse discharges in single chorda tympani fibres of rats and hamsters in response to gustatory stimuli representing the four basic qualities of taste as well as to cooling and warming of the tongue were recorded.2. In both rats and hamsters many fibres responded to more than one kind of gustatory stimulus as well as to thermal ones. The thermal sensitivity of these fibres was found to be about ‐0·5 impulses/sec. °C for cooling and 0·5 impulses/sec. °C for warming.3. Statistical calculations of the frequency of responses of chorda tympani fibres to single gustatory stimuli or combinations of stimuli were made, assuming that responsiveness to any one stimulus is independent of that to other stimuli. Evidence for relatively specific sensitivity to a particular stimulus or a particular combination of stimuli was obtained in the rat and the hamster.4. Across‐fibre correlation coefficients between the amounts of responses to a pair of stimuli were calculated. In both the rat and the hamster, significant positive correlations were obtained with HCl, quinine and cooling. In addition, a positive correlation between sucrose and warming and a negative correlation between sucrose and NaCl were obtained in the hamster. The results are discussed in relation to the interaction of gustatory and thermal sensations of the human tongue.
Sodium and calcium components of action potentials in Aplysia giant neurone
Authors: Geduldig D. , Junge D. 
Published: December 2014

1. Action potentials resulting from direct stimulation can be recorded from the soma of the Aplysia giant neurone (located in the visceral ganglion) in sodium‐free and in calcium‐free external solutions. The neurones were impaled by internal micro‐electrodes throughout the change of external solutions.2. Complete replacement of either sodium or calcium in the bathing medium with Tris results in only a partial reduction of spike overshoot. Simultaneous replacement of both sodium and calcium reversibly and quickly abolishes the spike.3. The sodium component of the spike in a calcium‐free medium is blocked by tetrodotoxin; the drug has no effect on the calcium‐dependent spike in sodium‐free medium. Externally applied cobalt chloride blocks only the calcium‐dependent component.4. In calcium‐free media, the overshoot value varies with sodium concentration in the manner predicted for a sodium electrode. In sodium‐free media, the membrane behaves like a calcium electrode.5. These results suggest that, during the normal action potential, both sodium and calcium act as carriers of the inward‐directed current.
The calcium content of human erythrocytes
Authors: Harrison D. G. , Long C. 
Published: December 2014

1. The calcium content of human erythrocytes, after removal of the buffy coat and washing free from plasma with isotonic sodium chloride, has been determined by atomic absorption spectrophotometry. The mean value found for normal subjects was 0·634 μg/ml. of packed erythrocytes (0·0158 μg‐atom/ml.). The corresponding values for magnesium and zinc were 79·7 and 20·1 μg/ml., respectively.2. The calcium is considered to be mostly and perhaps exclusively located in the erythrocyte membrane, since, after osmotic haemolysis, the same amount was found in the ghost cells as was present in the erythrocytes from which they were prepared. By contrast, magnesium and zinc, which are essentially intracellular, were lost to the extent of about 96 and 92%, respectively.3. About 90% of the calcium was removed from erythrocytes by washing with isotonic sodium chloride containing 5 m
M ethylenediaminetetraacetate (EDTA), or other complexing agents of high stability constant for calcium. A small fraction of the magnesium but none of the zinc was removed by this treatment.4. Other complexing agents of lower stability constant removed somewhat less calcium from the erythrocytes. Citrate was totally ineffective.5. The buffy coat had a high calcium content, but this could not be removed by washing with EDTA.6. Calcium was also determined in trichloroacetic acid extracts of ghost cells after ashing and treatment with bis‐(o‐hydroxyphenylimino)‐ethane and measuring the red complex spectrophotometrically. The values obtained confirmed the atomic absorption measurements.
post‐synaptic excitation and inhibition from primary afferents in neurones of the spinocervical tract
Authors: Hongo T. , Jankowska Elżbieta , Lundberg A. 
Published: December 2014

1. Intra‐ and extracellular recordings were made from cells of the spinocervical tract in the lumbosacral spinal cord. A convergence of monosynaptic excitatory post‐synaptic potentials (EPSPs) and disynaptic inhibitory post‐synaptic potentials (IPSPs) was a general pattern of effects from the low threshold cutaneous fibres. Unitary IPSPs, probably mediated via the same disynaptic path, were evoked by light touch of hairs, which was also the adequate stimulus for exciting the cells. The receptive field for unitary IPSPs was closely related to the excitatory receptive field but was eccentric, not of a surround type.2. EPSPs, IPSPs, or both, were evoked from the flexor reflex afferents in the great majority of neurones. Disynaptic IPSPs may be evoked from the interosseous nerve. No effects were produced by volleys in group I muscle afferents.3. It is suggested, on the basis of the spatial organization of the excitatory and inhibitory receptive skin fields, that the spinocervical tract may give information regarding the direction of tactile stimuli.
The effect of cyanide on the efflux of calcium from squid axons
Authors: Blaustein M. P. , Hodgkin A. L. 
Published: December 2014

1. The average rate constant for loss of 45Ca from an unpoisoned squid axon was 1·8 × 10−3 min−1, corresponding to an efflux of 0·2 p‐mole/cm2 sec.2. The Ca efflux from unpoisoned axons was reduced if external calcium was replaced with magnesium, or external sodium with lithium, choline or dextrose. Replacing both sodium and calcium reduced the efflux to about 40%.3. Cyanide caused little immediate change in Ca efflux but after 1½‐2½ hr the efflux increased to 5‐15 times its normal value. The effect was rapidly reversed when cyanide was removed.4. The large Ca efflux into cyanide was reduced by a factor of three when external calcium was replaced with magnesium and by a further factor of about six when external sodium was replaced with lithium.5. The Ca efflux from both poisoned and unpoisoned axons had a Q10 of 2‐3, was not affected by ouabain and was greatly reduced by injecting ethyleneglycol bis (aminoethylether)‐N,N′‐tetra‐acetic acid (EGTA).6. After injecting 45Ca along the axis, the efflux of calcium reached its maximum much more rapidly in a cyanide‐treated axon than in an unpoisoned axon.7. Pre‐treatment with cyanide greatly increased the rate at which calcium was lost from axoplasm extruded into flattened dialysis bags. A similar effect was observed when cyanide was applied after extrusion.8. Replacing external sodium glutamate with potassium glutamate greatly reduced the loss of 45Ca from intact axons poisoned with cyanide but had little effect on the loss from extruded axoplasm.9. The rate constant for loss of the Ca EGTA complex was about 3 × 10−5 min−1 for intact axons and 2 × 10−2 min−1 for extruded axoplasm.10. A possible explanation of the cyanide effect is that, after poisoning, calcium ions are released from a store and can then exchange at a higher rate with external sodium or calcium.11. The experiments suggest that part of the calcium efflux may be coupled to sodium entry.12. Theoretical equations for ‘diffusion and chemical reaction in a cylinder’ are described in the Appendix.
A study of the mechanism of water transfer across frog skin by a comparison of the permeability of the skin to deuterated and tritiated water
Authors: King Venetia 
Published: December 2014

1. Frog abdominal skins were placed between the two half‐cells of a modified version of Ussing's frog skin apparatus.2. The rate of equilibration of deuterated and tritiated water across the skin was followed at pH 5·0, 6·9, and 8·0 with Ringer solution bathing both surfaces of the skin; and at pH 7·0 with sulphate Ringer solution bathing both surfaces of the skin.3. The ratio of the permeability coefficients for the influx of deuterated and tritiated water had a mean value over all the experiments of 0·9954 ± 0·0207, n = 27, indicating that no isotope effect was observable within the limits of accuracy of the experimental method.4. The thickness of the unstirred layers associated with the frog skin was measured, and, from the data obtained, values of the true permeability coefficients for each isotope were calculated.
The sensitivity of muscle spindle afferents to small sinusoidal changes of length
Authors: Matthews P. B. C. , Stein R. B. 
Published: December 2014

1. Nerve impulses were recorded from spindle afferents of the soleus muscle during sinusoidal changes in muscle length at frequencies from 0·03 to 300 c/s. This was done in the decerebrate cat with intact motor outflow and ‘spontaneous’ fusimotor activity. Computer averaging over a number of cycles was used to measure the response, in impulses/sec, at different phases of the cycle.2. A linear range was described in which the discharges of the endings were approximately sinusoidally modulated, and in which increasing the amplitude of the stretching produced a proportional increase in the response. At 1 c/s the linear range extended up to only about 0·1 mm for primary endings, but was greater than 1 mm for secondary endings.3. The sensitivity of an ending in its linear range was defined as the amplitude of its response divided by the amplitude of the length change. The sensitivity of both primary and secondary endings increased progressively on increasing the frequency of stretching above 1 c/s. The experimental observations relating the sensitivity to the sinusoidal frequency were fitted over much of the range by a curve given by the vector sum of components proportional to the length and to the velocity of stretching. This curve has two parameters, a sensitivity at low frequencies (S), and a corner frequency (F) at which the length and velocity contributions are equal. The value of F was about 1·5 c/s for both primary and secondary muscle spindle endings. The value of S was very much greater for primary endings (median value 95 impulses/sec/mm) than for secondary endings (median value 7 impulses/sec/mm). The increasing sensitivity of the endings at higher frequencies caused a progressive reduction in the linear range when it was expressed as an amplitude of stretching, but it remained approximately constant when it was expressed as a modulation of the frequency of discharge.4. The primary endings were also extremely sensitive to maintained changes in length provided they were of sufficiently small amplitude.5. In the presence of fusimotor activity a high sensitivity of small changes was found over a wide range of muscle lengths. De‐efferented endings had a comparable high sensitivity when the muscle was at or beyond physiological full extension, but not when the muscle was shorter.6. The results are contrasted with those obtained previously using stretches of large amplitude, and the physiological significance of the high sensitivity of primary endings to small stretches is discussed in relation to the reflex control of movement.
The site of action of calcium in producing contraction in striated muscle
Authors: Gillis J. M. 
Published: December 2014

1. Contraction of glycerinated crab myofibrils, suspended in a relaxing medium containing Mg‐ATP and EGTA, was induced by iontophoretic application of Ca ions through a micropipette. Contraction was observed by phase‐contrast microscopy.2. The large size of the sarcomere (10‐15 μ) in the crab Cancer allowed applications of Ca ions at several discrete points along a single sarcomere.3. The threshold iontophoretic current needed to produce just visible contraction was measured for each position of the micropipette along the sarcomere. It was always lowest at the A—I junction.4. When Ca was delivered to the I band, the threshold current increased with the distance of the pipette from the A—I junction. Along the A band, the results depended on the sarcomere length: for short sarcomere lengths, the threshold current remained roughly constant over a large part of the A band; for long sarcomeres, it increased with the distance from the A—I junction in the same manner as in the case of the I band.5. As Ca reached the fibril by diffusion from the micropipette, the influence of the diffusion path on the threshold current was investigated.6. The length of the region of overlap of the thick and thin filaments in the A band was estimated by electron microscopy.7. The results demonstrate that, in order to produce contraction, Ca has to reach the region of overlap of the myofilaments.
The relation between the 5‐hydroxytryptamine content and aggregation of rabbit platelets
Authors: Baumgartner H. R. , Born G. V. R. 
Published: December 2014

1. Blood platelets containing different amounts of 5‐hydroxytryptamine (5–HT) were produced in vivo by the injection of 5‐hydroxytryptamine or of reserpine into normal rabbits and of 5‐hydroxytryptamine into reserpinized rabbits. Before and after these injections the aggregation of platelets was measured in vitro.2. Platelets of untreated rabbits were aggregated by adenosine diphosphate (ADP) and by 5‐hydroxytryptamine; (—)‐adrenaline alone did not produce aggregation but markedly increased aggregation by 5‐hydroxytryptamine.3. Platelets saturated with 5‐hydroxytryptamine in vivo were no longer aggregated in vitro by 5‐hydroxytryptamine or by 5‐hydroxytryptamine plus adrenaline, but their aggregation by ADP was unchanged.4. Platelets from reserpinized rabbits lost about 99% of their 5‐hydroxytryptamine; the aggregation of these platelets did not differ significantly from that of platelets from control rabbits.5. Platelets from reserpinized rabbits injected with 5‐hydroxytryptamine were aggregated neither by the amine alone nor by 5‐hydroxytryptamine plus adrenaline, although these platelets contained much less 5‐hydroxytryptamine than saturated platelets and only about one tenth as much as platelets from untreated rabbits.6. The findings support the hypothesis that the inhibitory effect of 5‐hydroxytryptamine administered in vivo on platelet aggregation in vitro is due to the association of the amine with the platelet membrane.