bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in plasma volume and protein content during exposures of working men to various temperatures before and after acclimitization to heat: separation of the roles of cutaneous and skeletal muscle circulation
Authors: Senay L. C. 
Published: December 2014

1. Ten male subjects were trained in stair stepping for 2 weeks. Group A (six subjects) was thereupon sequentially exposed for 45 min to dry bulb temperatures of 20, 40 and 30° C, a vapour pressure of 10–11 mm Hg and a wind speed of 1 m/sec in a climate tunnel. While temperature changes were being effected the subjects rested in an antechamber. Group B (four subjects) was exposed to a sequence of 40, 20 and 30° C. Work rate was the same for all subjects, i.e. 216 kg m/min (≃ to an oxygen consumption of 0·9 l./min). Duplicate experiments were run on both groups of subjects before and after acclimatization to heat.2. Throughout, periodic samples of venous blood, water and protein movement into or out of the extravascular compartment was assessed during exercise periods wherein blood flow was increased to exercising muscles (Group A, 20° C) or to both exercising muscles and skin (Group B, 40° C; Groups A and B, 30° C.)3. Mild exercise in a cool environment before and after acclimatization to heat was accompanied by expansion of the vascular volume and an increase in the amount of circulating protein.4. Mild exercise in a warm environment for 45 min was accompanied by haemoconcentration and loss of protein from the vascular volume before subjects were heat acclimatized. The results were reversed following heat acclimatization; i.e. exposure of Group B to 40° C and of Groups A and B to 30° C was accompanied by haemodilution and addition to (or maintenance of) plasma protein concentration.5. Effects of heat acclimatization on exposure of Group A to 40° C were also noted.6. The effects of heat acclimatization were ascribed to:(a) a change in permeability of cutaneous capillaries to large molecules,(b) an increased availability of translocatable protein within cutaneous interstitial spaces, and(c) a combination of both a and b.7. Further, the results supported a previous suggestion that addition or loss of water and protein from the vascular volume is dependent on the ratio of cutaneous to muscle blood flow.
Studies on the mechanism of action of angiotensin on ion transport by kidney cortex slices
Authors: Munday K. A. , Parsons B. J. , Poat Judith A. 
Published: December 2014

1. A study has been made of the effects of cyclic AMP, phosphodiesterase inhibitors and protein synthesis inhibitors on the response of rat kidney cortex slices to physiological doses of angiotensin.2. The additions of cyclic AMP, dibutyryl cyclic AMP and/or phosphodiesterase inhibitors to the incubation medium (conditions which would be expected to increase intracellular cyclic AMP levels) were without effect on sodium or potassium transport by kidney slices.3. Actinomycin D (an inhibitor of the transcription stage of protein synthesis), at concentrations which inhibit RNA synthesis by 75%, has no effect on either control or angiotensin stimulated sodium transport.4. Cycloheximide or puromycin (inhibitors of the translation stage of protein synthesis), at concentrations which inhibit protein synthesis by 70–80%, have no effect on control sodium and potassium transport by kidney slices, but completely block the angiotensin stimulation of these processes.5. These findings are discussed in relation to the possible involvement of cyclic AMP and protein synthesis in the mechanism of action of angiotensin on kidney sodium and potassium transport.
The temperature sensitivity of the Type I slowly adapting mechanoreceptors in cats and monkeys
Authors: Duclaux Roland , Kenshalo Dan R. 
Published: December 2014

1. The sensitivity of Type I slowly adapting mechanoreceptors in cat and monkey skin to temperature and changes in temperature was investigated.2. Multiple receptors innervated by a single axon appeared to be more frequent in the monkey than in the cat skin.3. The responses of these receptors to thermal stimulation at static skin temperatures from 27 to 40° C were similar in cats and monkeys. At 43° C the monkey receptors showed a higher steady‐state activity than the cat receptors.4. A maximum steady‐state frequency of 5·5 impulses/sec occurred in both the cat and monkey receptors at a static skin temperature of 37° C.5. The maximum dynamic response to cooling occurred at a skin temperature of 40° C. The response was near its maximum at 2° C cooling and increased but little with further increases in the intensity of cooling.6. Dynamic responses to cooling disappeared after the skin had been heated to 51° C for 35 sec and to mechanical stimulation after heating to 53° C for 35 sec. Excitation by either mechanical or thermal stimulation did not reappear within 1–2 hr.7. The response characteristics of the Type I slowly adapting mechanoreceptors to temperature and temperature changes differ from those of specific cold receptors.
The statistical nature of the acetylcholine potential and its molecular components
Authors: Katz B. , Miledi R. 
Published: December 2014

1. When a steady dose of acetylcholine (ACh) is applied to an end‐plate, the resulting depolarization is accompanied by a significant increase in voltage noise.2. The characteristic properties of this ACh noise (amplitude and time course) are examined under various experimental conditions. The voltage noise is analysed on the assumption that it arises from statistical fluctuations in reaction rate, and in the frequency of the elementary current pulses (‘shot effects’) produced by the action of ACh molecules.3. The elementary ACh current pulse (amplitude approximately 10−11 A), arises from a conductance change of the order of 10−10 Ω−1 which lasts for approximately 1 ms (at 20° C), and produces a minute depolarization, of the order of 0·3 μV. It is associated with a net charge transfer of nearly 10−14 C, equivalent to approximately 5 × 104 univalent ions.4. At low temperature, and during chronic denervation, the duration of the elementary current pulse increases, and the elementary voltage change becomes correspondingly larger.5. Curare has little or no effect on the characteristics of the elementary event.6. A comparative study of ACh and carbachol actions shows that carbachol produces considerably briefer, and therefore less effective, current pulses than ACh.
Pancreatic acinar cells: measurement of membrane potential and miniature depolarization potentials
Authors: Dean P. M. , Matthews E. K. 
Published: December 2014

1. Intracellular recordings of membrane potentials have been made in vitro from the exocrine acinar cells of the mouse pancreas using glass micro‐electrodes.2. The mean membrane potential of the acinar cells was −41·2 mV. Spontaneous miniature depolarization potentials of 0·5–5·0 mV amplitude and occurring at random intervals were often observed superimposed upon the resting membrane potential. Atropine 2·8 × 10−6
M decreased, and physostigmine 1·23 × 10−5
M increased, the frequency and amplitude of the miniature potentials.3. Electrical stimulation of the pancreatic nerves depolarized the acinar cells. Acetyl β‐methylcholine 10−6
M produced a sustained depolarization. Atropine 1·4 × 10−6
M blocked the depolarization to both electrical stimulation and acetyl β‐methylcholine.4. Pancreozymin depolarized the exocrine acinar cells but secretin did not.5. These results suggest that the miniature depolarization potentials are of cholinergic origin and that depolarization of the pancreatic exocrine cells by nerve stimulation or pancreozymin may trigger secretion.
Oxygen consumption by the component layers of the cornea
Authors: Freeman Ralph D. 
Published: December 2014

1. The structural integrity of the cornea is maintained by an active fluid transport system which depends on metabolism. Experiments were designed to establish the respiratory activity of each corneal layer.2. A rapid micropolarographic technique was used to determine the oxygen consumptions of the individual layers of the rabbit cornea.3. Inherent problems of the determinations have been made minimal by the use of both denuded and whole corneal tissue preparations. Four independent measures were obtained for each limiting layer (epithelium and endothelium).4. Results show that the endothelium, epithelium and stroma use 21, 40 and 39% respectively of the total oxygen consumption of the cornea. On the basis of volumes of oxygen per unit volume tissue, epithelial oxygen utilization is about ten times that of the stroma and approximately 0·2 that of the endothelium.5. The endothelium has a larger oxygen uptake than previously reported.6. The present results, in conjunction with other studies, indicate that the ratio of glycolytic to oxidative activity in the rabbit cornea is 0·87:0·13.
The decline of potassium permeability during extreme hyperpolarization in frog skeletal muscle
Authors: Almers W. 
Published: December 2014

1. The voltage‐clamp technique was used to separate the effects of K depletion in the T‐system from the decline in K permeability during hyperpolarization, and to characterize the time‐ and voltage‐dependence of the latter.2. K permeability due to the inward rectifier can be described as being proportional to a parameter which diminishes when the membrane is hyperpolarized beyond −120 mV. The parameter obeys first‐order kinetics. At 24° C, it can change with a time constant of 49 msec at −150 mV and 25 msec at −65 mV. At −200 mV the fall in membrane conductance due to the permeability change is to 30% of its initial value. The Q10 for the rate of conductance change at that potential is about 2·8.3. It is estimated that K inward current can lower the average K concentration in the T‐system by more than 50%, and that, on the average, the space enclosed by the T‐system should be less than 0·8% of the fibre volume. Assuming the T‐system space to be 0·3% of the fibre volume, it is calculated that on the average, and during hyperpolarization to about −150 mV, no more than 20% of the initial current should flow across the surface membrane.
Tension changes during and after stretch in frog muscle fibres
Authors: Sugi H. 
Published: December 2014

1. Small fibre bundles from the semitendinosus muscles of the frog were stretched during tetanic stimulation, and the resulting tension changes were studied over a wide range of stretch velocities from 0·1 to 150 cm/sec (0·1–100 length/sec). The experiments were performed within the range of fibre lengths where the resting tension was negligible.2. With stretch velocities of more than 30 cm/sec (20 length/sec), the tension rose abruptly at first, and then started to fall while the stretch still continued, indicating the ‘slip’ of the contractile component. When the fibres were stretched at 80–150 cm/sec (70–100 length/sec), the tension fell quickly below the initial isometric level at the end of the stretch, and then began to rise again to the initial isometric value.3. Following stretches of 30–60 cm/sec (20–50 length/sec), the tension showed a delayed transient rise. The delayed rise of tension became more marked as the amount of stretch was increased.4. In some preparations, oscillatory tension changes were observed following stretches of 50–100 cm/sec (40–70 length/sec).5. The tension developed above the isometric level during moderate‐velocity stretches of less than 15 cm/sec (10 length/sec) increased by lowering temperature, and showed a tendency to decay when the stretch velocity was suddenly reduced during a stretch.6. These results are discussed in relation to the sliding filament hypothesis, which provides an explanation for the findings of the present work.
Injections of calcium ions into spinal motoneurones
Authors: Krnjević K. , Lisiewicz A. 
Published: December 2014

1. In cats under Dial anaesthesia, Ca2+ was injected inside lumbosacral motoneurones, by passing currents between CaCl2‐ and KCl‐containing barrels of compound micropipettes.2. There was a reduction in excitability and a fall in membrane resistance, both rapid in onset and quickly reversible.3. The minimum effective injection current was ≈ 10 nA, and the effect reached a maximum with currents of ≈ 30 nA. The mean slope of resistance change against injection current was −1·7%/nA (
S.E. 0·35).4. The most common change in membrane potential was a hyperpolarization; but in nearly half the cases, there was no clear change or a small depolarization. A reversal level for the effect of Ca2+ could be measured in five cells: on the average, it was 10 mV more negative than the resting potential.5. Observations on i.p.s.p.s showed that Ca2+ probably does not alter gCl: it was concluded that the fall in membrane resistance caused by intracellular Ca2+ is mainly due to an increase in gK.6. These results confirm previous suggestions that a steep transmembrane gradient of Ca2+ is essential for the maintenance of a low membrane conductivity, and that a rise in internal free Ca2+ — whether due to influx or release from internal stores — may play an important role in regulating neuronal activity.
Evidence for disparity detecting neurones in the human visual system
Authors: Blakemore Colin , Hague Brian 
Published: December 2014

1. It is known that adaptation to a grating pattern causes a rise in the contrast threshold for test gratings of similar spatial frequency and orientation.2. We find this after‐effect also to be disparity‐specific. Adaptation to a grating at zero horizontal disparity (at the same distance as the fixation point) causes a greater elevation of threshold for patterns at the same disparity than for those at nearby disparities, closer or more distant than the fixation point.3. Adaptation to a grating at some disparity other than zero causes a disparity‐specific elevation of threshold centred on the adapting disparity.4. This finding also applies if the observer adapts to a grating but single bright bars are used as the test stimuli.5. The disparity‐specific ‘tuning curves’ revealed by these techniques are quite broad, having a half‐width at half‐amplitude of several min of disparity.6. Adaptation to a grating at one disparity causes an apparent change in the distance of test gratings at nearby disparities.7. We compare these psychophysical experiments with the properties of disparity‐selective binocular neurones in the visual cortex of cats and monkeys.
Cardiovascular and respiratory responses to changes in central command during isometric exercise at constant muscle tension
Authors: Goodwin G. M. , McCloskey D. I. , Mitchell J. H. 
Published: December 2014

1. Experiments were designed to show whether elements of the command descending from higher centres to exercising muscles provide an input for cardiovascular and respiratory control. Vibration, known to be a powerful stimulus to the primary afferents from muscle spindles, was applied to the biceps tendon of human subjects performing sustained isometric contractions with the biceps or the triceps muscle. When the biceps was contracting this activation of muscle spindle primary afferents in it provided an element of reflex excitation, so that less central command was required to achieve a given tension. When triceps was contracting, the activation of muscle spindle primary afferents in its antagonist, biceps, contributed an element of reflex inhibition, so that more central command than normally was required to achieve a given tension. The cardiovascular and respiratory responses to an isometric effort could thus be investigated at any tension when the central command was normal, decreased, or increased.2. Blood pressure, heart rate, and pulmonary ventilation all increase in an isometric effort. The increase in each is less when the central command is reduced. The increase in each is greater when the central command is increased.3. It is concluded that there is irradiation of cardiovascular and respiratory control centres by the descending central command during voluntary muscular contractions in man.
Metabolism and transfer of choline in hamster small intestine
Authors: Flower R. J. , Pollitt R. J. , Sanford P. A. , Smyth D. H. 
Published: December 2014

1. The transfer and metabolism of choline was studied with sacs of everted intestine of hamster.2. Approximately half the choline transferred from the mucosal fluid may be metabolized. High voltage electrophoresis, paper chromatography and ion exchange chromatography have been used to identify this meta bolite as betaine.3. The concentration of choline and betaine together accumulating in the gut wall and serosal fluid are greater than that of choline present initially in the mucosal fluid indicating some kind of specific mechanism for choline transport.4. A detailed analysis of choline transfer suggests that the movement of choline cannot be accounted for by simple diffusion. The concentration of choline accumulating in the gut wall and serosal fluid, the inhibitory effects of hemicholinium‐3 and α‐methylglucoside on choline transfer, and the insensitivity of betaine transfer to hemicholinium‐3 suggest a specific active transport process for choline independent of active betaine transport.
The relation of Rushton's ‘liminal length’ for excitation to the resting and active conductances of excitable cells
Authors: Noble D. 
Published: December 2014

1. The minimum (or liminal) length of an excitable cable that must lie above the inward current threshold in order to initiate propagation is derived using a simple polynomial representation of the ionic current—voltage relation.2. This model is then used to obtain an approximate equation for the liminal length that may easily be applied to excitable cells using experimental measurements of the ionic current.3. The equations are used to show that the liminal length in cardiac Purkinje fibres is expected to be much smaller than in squid nerve. The values calculated are similar to those obtained by Fozzard & Schoenberg (1972) from strength—duration curves.4. It is shown that the strength—duration curve for non‐uniform excitation is virtually independent of the resting membrane resistance. The strength—duration time constant may not, therefore, be related to the membrane time constant.
Strength—duration curves in cardiac Purkinje fibres: effects of liminal length and charge distribution
Authors: Fozzard H. A. , Schoenberg Mark 
Published: December 2014

1. Strength—duration curves for excitation in long point‐stimulated sheep cardiac Purkinje fibres, where the charge distribution varies along the length of the fibre, are characterized by (a) a time constant which is short relative to the membrane time constant, (b) an apparent fall in charge threshold for short duration stimuli, (c) an apparent rise in voltage threshold as measured by an electrode at the point of current passage (see Dominguez & Fozzard, 1970).2. Strength—duration curves obtained from shortened segments of Purkinje fibres, where the charge distribution along the segment is fairly uniform after 2–3 msec, have much larger time constants.3. For stimulus durations longer than the 2–3 msec necessary to establish charge uniformity, strength—duration curves obtained from shortened segments of Purkinje fibres were well fitted by the Lapicque—Hill equation, I/Irh = [1 — exp (—t/τ)]−1.4. The differences in the time constants and apparent voltage thresholds for point‐stimulated long fibres and uniformly charged short fibre segments could be explained by the liminal length concept of Rushton (1937). The liminal length concept, in its simplest form, states that a liminal length of fibre must be raised above a given voltage threshold in order for a propagated action potential to be generated.5. This concept predicts that the shorter the liminal length, the shorter the time constant of strength—duration curves in point‐stimulated long fibres.6. Another conclusion of the model is that only those point‐stimulated long fibres with longer liminal lengths would have a constant charge threshold for stimuli of the order of 0·2 τ.7. Liminal length was found by experiment and calculation to be about 0·1–0·2 λm in cardiac Purkinje fibres.8. The differences in behaviour with regards to excitation between the point‐stimulated theoretical squid axon and the point‐stimulated Purkinje fibre may be explained by assuming that the liminal length of the theoretical squid axon is several times larger than that of the Purkinje fibre.
Further evidence for a potassium‐like action of lithium ions on sodium efflux in frog skeletal muscle
Authors: Beaugé L. A. , Ortiz Olga 
Published: December 2014

1. The efflux of labelled sodium as well as net sodium and lithium changes were studied in aged high sodium sartorius muscles of the South American frog Leptodactilus ocelatus.2. In the presence of 2·5 m
M potassium in the media, the replacement of external sodium with lithium or magnesium resulted in an increase in sodium efflux. The magnitude of such increase was always larger in lithium.3. With the absence of potassium in the media, the response of sodium efflux to replacement of external sodium varied with the cation used as a substitute. In lithium Ringer there was always a noticeable increase, whereas in magnesium there was always a marked reduction. The same results were observed when calcium was substituted for magnesium.4. The replacement of 60 m
M external sodium with sucrose did not prevent the stimulating effect of 5 m
M potassium on sodium efflux, nor the inhibitory action of 10−4
M ouabain. This indicates that neither sucrose by itself, nor the lowering of the ionic strength, modified to an appreciable extent the function of the sodium pump.5. Net sodium extrusion took place against an electrochemical gradient in potassium‐free — 50 m
M sodium — m
M lithium Ringer. About 75% of this efflux was ouabain sensitive.6. Muscles made both sodium and lithium rich and incubated in potassium‐free — 60 m
M sodium — 50 m
M lithium Ringer also showed net sodium extrusion against an electrochemical gradient, which was 85% ouabain sensitive. This extrusion took place even under conditions where the changes in free energy favouring lithium entry were always lower than the changes in free energy opposing sodium going out. This indicates that a sodium‐lithium exchange by a counter‐transport process is unlikely.7. External potassium reduced the ouabain sensitive lithium influx in muscles incubated in lithium Ringer. The values found were 5·90 ± 0·39 μ‐mole/g.hr and 2·66 ± 0·43 μmole/g.hr in potassium‐free and 15 m
M potassium respectively. At the same time potassium had no effect on the ouabain‐insensitive lithium uptake.8. Muscles incubated in potassium‐free‐magnesium Ringer had a residual sodium efflux which could not be accounted for by passive movement. About 40% of it was abolished by 10−4
M ouabain. This ouabain‐sensitive part could be a consequence of some stimulation of the sodium pump by potassium leaking out of the cells. If this is correct it should be inhibited by external sodium and should not contribute to the total sodium efflux in potassium‐free sodium media.9. Magnesium was used as the reference cation to study the sodium‐stimulated sodium efflux under potassium‐free conditions. The total sodium efflux amounted to 0·668 hr−1 (rate constant) and was 71% ouabain sensitive.10. The present experiments demonstrated that lithium ions have a direct stimulating effect on sodium efflux in high sodium skeletal muscle, and strongly support the notion that this effect is produced by an activation of the sodium pump through a potassium‐like action.