bluuebunny/crossref_metadata_2025_split huggingface dataset:
Passage of macromolecules between alveolar and interstitial spaces in foetal and newly ventilated lungs of the lamb
Authors: Normand I. C. S. , Reynolds E. O. R. , Strang L. B. 
Published: December 2014

1. Experiments were performed on exteriorized foetal lambs to measure transfer of macromolecules (proteins and [125I]PVP) between lung alveolar liquid (Al) and lung interstitial liquid as represented by lung lymph (Lly). Transfer was measured in the foetus and during a 2 hr period of positive pressure ventilation.2. In thirteen experiments [125I]PVP was introduced into Al and, after a control period, the lungs were ventilated for 2 hr. In six other experiments the [125I]PVP was injected intravenously; and in two of these the lungs were ventilated for 2 hr. Measurements were made of protein and of [125I]PVP concentration in plasma and Lly collected at intervals throughout the experiment, as well as in Al obtained before ventilation and at the end of ventilation after degassing the lung. [125I]PVP in the samples was separated into fractions of different Stokes—Einstein radius by gel filtration using Sephadex G‐200.3. Before ventilation there was evidence of a negligible transfer of protein from Lly to Al (mean protein Al/Lly = 0·014) or of [125I]PVP from Al to Lly (mean [125I]PVP Lly/Al = 0·00017). The effect of ventilation for 2 hr was to produce an increase in both ratios, but by a variable amount (after 2 hr ventilation mean protein Al/Lly = 0·70 ± 0·08 (
S.E. of mean) and mean [125I]PVP Lly/Al = 0·48 ± 0·09). By calculating Lly/Al ratios for [125I]PVP fractions obtained by gel filtration it was shown that in transfer from Al to Lly during ventilation molecular sieving could be detected, the degree of which was expressed by means of a Relative Sieving Index (RSI). Significant correlations were found between the minimum surface tension of lung extracts, and two other indicators of lung maturity on the one hand, and the protein and [125I]PVP ratios and RSI on the other; so that the more mature the lamb the less the transfer of macromolecules during ventilation and the greater the degree of molecular sieving.4. By comparing concentrations of [125I]PVP gel filtration fractions in lymph and plasma, when the [125I]PVP had been placed in Al, we demonstrated some sieving of molecules (in the range 34–15 Å) in their absorption from interstitial space to plasma.5. It was concluded that in the lungs of the foetal lamb there is an almost complete barrier to the transfer of macromolecules between alveolar and interstitial spaces; that positive pressure ventilation for 2 hr causes a very variable degree of break‐down in this barrier, and that the degree of break‐down is usually greater in immature than in mature lungs.
Effects of Ca removal on the smooth muscle of the guinea‐pig taenia coli
Authors: Bülbring Edith , Tomita T. 
Published: December 2014

1. The effects of removing the external Ca ions on the spontaneous and evoked activity of the smooth muscle of the guinea‐pig taenia coli were investigated with the double sucrose‐gap method.2. In Ca‐free Locke solution the membrane was depolarized, the membrane resistance became low, the spike amplitude became small and the mechanical response decreased. In most preparations the electrical and mechanical activity was abolished within 10 min, but in some preparations the electrical activity continued for more than 30 min.3. In Ca‐free solution containing 0·1 m
M‐EGTA, the membrane was depolarized and the electrical and mechanical activity was abolished within 5 min in every preparation. When NaCl was replaced with sucrose, the effects of Ca removal on the spike activity and contraction appeared very slowly and the membrane potential and membrane resistance remained unchanged.4. When Ca was replaced with Mg (2 m
M) the spike was blocked within 1 min without depolarization or reduction of the membrane resistance. In Na‐deficient (sucrose) solution, the presence of Mg accelerated the disappearance of the spike caused by Ca removal.5. In Ca‐free solution containing 0·5 m
M‐Mg, a spike‐like activity was observed without accompanying mechanical response. This activity was blocked by increasing the Mg concentration above 2 m
M. It was Na‐dependent, since it was abolished by removing Na from the external solution, but it was not influenced by tetrodotoxin (2 × 10−6 g/ml.).6. It was concluded that calcium has at least two functions, one as current carrier for the action potential and another as controller of the Na permeability of the membrane. It was also suggested that the Ca which is bound at the membrane may be utilized as a source of Ca ions to carry the current for the action potential.
Some metabolic responses of axotomized neurones to contact between their axons and denervated muscle
Authors: Watson W. E. 
Published: December 2014

1. The nucleolar and cell body dry mass and nucleic acid content of hypoglossal neurones were measured in adult rats using interference microscopy and ultra‐violet absorption microspectrography.2. The left hypoglossal nerve was transplanted into the ipsilateral sternomastoid. Seventy days later the sternomastoid was denervated by dividing the ipsilateral spinal accessory nerve. This was followed by metabolic changes in hypoglossal nerve cells.3. The changes induced in hypoglossal neurones by division of the ipsilateral accessory nerve did not occur if botulinum toxin was injected locally at the same time.4. In other rats the left hypoglossal nerve was anastomosed to the proximal stump of the ipsilateral median nerve simultaneously divided at the level of the wrist. Seventy days later this median nerve was divided in the axilla. This was followed by metabolic changes in hypoglossal nerve cells.5. These results are discussed in relation to the possible roles of reacting Schwann cells, degenerating axoplasm and denervated muscle in maintaining aspects of the metabolic response of nerve cells to injury.6. It is suggested that the synthesis of acetylcholine by an axonal ending, or its release, is dependent upon the presence of an adjacent membrane which can respond to it, and that the metabolic changes measured in the nerve cell body are secondary to this response of the axon terminal.
An estimate of the proportion of the resting membrane conductance of the smooth muscle of guinea‐pig taenia coli attributable to chloride
Authors: Ohashi H. 
Published: December 2014

1. The contribution of Cl and K to the steady‐state membrane conductance of the smooth muscle of the guinea‐pig taenia coli has been investigated by measuring the increase in membrane resistance in Cl‐deficient and K‐deficient solutions. A large external electrode was used for passing current and the voltage change was recorded with an intracellular electrode. The experiments were carried out in hypertonic solution in order to suppress spontaneous activity.2. When the tissue was exposed to K‐deficient solution, the amplitude and time course of the electrotonic potential was increased and the membrane was hyperpolarized.3. When the tissue was exposed to Cl‐deficient solutions in which Cl was replaced with an impermeant anion, benzene sulphonate, the size and time course of the electrotonic potential was increased whereas the membrane potential, after 20–30 min equilibration, was unchanged. The magnitude of the increase of the electrotonic potential depended on the substituted amount of Cl.4. When the tissue was exposed to low K the relation between the membrane conductance and the remaining external K concentration was the same in the presence of the normal Cl concentration and in Cl‐deficient solution (7 m
M‐Cl). It was therefore concluded that any effect of benzene sulphonate on the K conductance is negligible.5. The effects of Cl or K deficiency on the electrotonic potential indicate that Cl and K ions account for most of the membrane conductance and that the contribution by Cl is about 40%.6. The ratio of PCl/PK was calculated from the constant field theory on the assumption that the contribution of ions other than K and Cl to the membrane conductance is negligibly small. The mean value was 0·40.
Dependence of acetylcholine desensitization on the membrane potential of frog muscle fibre and on the ionic changes in the medium
Authors: Magazanik L. G. , Vyskočil F. 
Published: December 2014

1. The rate of desensitization of the post‐synaptic membrane to prolonged action of acetylcholine was investigated during (a) potassium depolarization of the frog muscle fibre, (b) artificial changes of the membrane potential and (c) in the presence of some multivalent cations and of caffeine.2. Depolarization of the muscle fibre by 15 m
M‐K+ led to a slowing down in the development of desensitization by 80%. This effect on desensitization produced by membrane potential changes could account for the previously described effect of increased K+ concentration.3. Electrotonically produced depolarization of the muscle fibre membrane resulted in a decrease, hyperpolarization in an increase of the rate of desensitization.4. Several multivalent cations can be, according to their ability to increase rate of desensitization, arranged in the following series: [Formula: see text]5. Caffeine in a concentration of 1·5 m
M does not affect the rate of desensitization.6. A hypothesis is presented suggesting that desensitization is not only restricted to the receptor level but that it also occurs, at least partly, at the terminal stages of the activation system.
Rubidium, sodium and ouabain interactions on the influx of rubidium in rat red blood cells
Authors: Beaugé L. A. , Ortíz Olga 
Published: December 2014

1. The activation curve of rubidium influx by external rubidium in rat red cells showed an inflexion at a concentration around 0·2 m
M. This inflexion point was displaced to the right by ouabain.2. The removal of sodium from the external solution changed the characteristics of the activation curve of rubidium influx. At external rubidium below 0·5 m
M the uptake increased whereas above that concentration there was marked reduction. Thus the sodium‐free effect on rubidium uptake is dependent on the external rubidium concentration.3. With 0·25 m
M rubidium, the relationship between increase of rubidium influx and reduction of external sodium followed a more or less exponential function. All the increment was ouabain‐sensitive.4. With a rubidium concentration above 0·5 m
M the reduction of the rubidium uptake, as sodium was removed, followed curves of complex shape. With 10 m
M rubidium, when sodium was reduced from 5 m
M to zero, there was an increase instead of a further reduction. These results suggest interactions of several effects.5. The ouabain sensitivity of the rubidium influx in rat red cells is smaller than in other systems studied up to now. The dose—response curve was shifted to the right as the rubidium concentration increased and a plateau was obtained with rubidium only below 1 m
M at 10−5
M ouabain. When plotted as a percentage of the maximal inhibition the points fell into the theoretical curve following a simple one reactant/one site reaction.6. Ouabain inhibition seems to be a complex function of at least three variables: the concentration of the glycoside, the concentration of sodium and the concentration of rubidium. When sodium was absent, 10 μ
M rubidium was able to prevent, to a great extent, the inhibition produced by 10−5 and 10−4
M ouabain.
The contribution by glial cells to surface recordings from the optic nerve of an amphibian
Authors: Cohen M. W. 
Published: December 2014

1. The contribution by glial cells to surface recordings has been examined in the optic nerve of the amphibian Necturus maculosus. The method of current injection was employed selectively to alter the membrane potential of glial cells without affecting that of the axons. The resulting changes in potential were recorded simultaneously from the surface of the nerve using the sucrose gap method and intracellularly from a glial cell near the gap.2. The sucrose gap method recorded 40% of the changes in glial membrane potential. This percentage was not affected when the current electrode was inserted into different glial cells while maintaining the recording conditions constant.3. Following axonal degeneration, produced by removing the eye 2‐3 months earlier, the percentage contribution by glia increased to 84%.4. By measuring sucrose gap responses to changes in Ko it was possible to estimate that the sucrose gap method recorded 31–60% of changes in axonal membrane potential. It was also determined that the axons, unlike glial cells, are relatively insensitive to reductions in Ko. Surface responses to decreases in external potassium thus reflect the magnitude of the glial contribution.5. It is concluded that changes in glial membrane potential contribute about as much to surface recordings from the optic nerve of Necturus as do equivalent changes in axonal membrane potential. The contributions by the glial cells and axons are related to the relative volumes of tissue they respectively occupy. The significance of these findings to the analysis of surface recordings from the mammalian brain is discussed. Since mammalian glial cells, like those in Amphibia and the leech, become depolarized during neuronal activity and on the basis of electron microscopic evidence appear to be electrically coupled, it is likely that they contribute to the electroencephalogram.
Centrifugal inhibitory processes affecting neurones in the cat cochlear nucleus
Authors: Comis S. D. 
Published: December 2014

1. Stimulation of the lateral part of the olivary S‐segment in the cat inhibited neurones in the ipsilateral cochlear nucleus. A smaller number of neurones located in the ventral division of the cochlear nucleus were excited.2. It is suggested that inhibition in the ipsilateral cochlear nucleus may be mediated directly by fibres making synaptic connexions on the cochlear nucleus neurones, or indirectly by inhibitory fibres acting at the cochlea.3. The direct inhibitory process at the cochlear nucleus is unaffected by strychnine, whereas the inhibitory process at the cochlea is abolished by strychnine.4. A cochlear nucleus neurone can be influenced simultaneously by excitatory and inhibitory processes.
Effects of cholinergic and adrenergic blocking agents on the activity of the eccrine sweat glands
Authors: Foster K. G. , Weiner J. S. 
Published: December 2014

1. The effects of blocking agents on the responsiveness of the cast' pad and human forearm sweat glands have been studied.2. Of the anti‐adrenergic substances examined (dibenamine, phenoxybenzamine, bretylium, guanethidine and phentolamine) only high doses of guanethidine and phentolamine produced any consistent and significant measure of blockade, and small doses of atropine were as effective as these large doses of guanethidine or phentolamine.3. It is concluded from the blockade of chemical stimulation as well as transmission by these substances that (1) there are only cholinergic fibres innervating eccrine sweat glands, and (2) any inhibitory action by anti‐adrenergic substances is due to interaction with cholinergic receptors in the glands.
Estimates of probability of transmitter release at the mammalian neuromuscular junction
Authors: Christensen B. N. , Martin A. R. 
Published: December 2014

1. Intracellular records of end‐plate potentials (e.p.p.s) were obtained from curarized neuromuscular junctions in the rat diaphragm.2. Statistical estimates of the quantal release probability (p) were made at individual junctions from measurements of the means and variances of e.p.p. amplitudes at two different levels of Ca concentration. It was assumed that the release process was binomial and that the number of quanta available for release (n) was independent of external Ca.3. These estimates of p were compared with those obtained by measuring depression of e.p.p. amplitudes after single conditioning shocks and assuming that the depression was due to depletion of n. The statistical estimates were consistently smaller.4. This disparity, plus the additional observation that depression was not linearly related to the number of quanta released by one or more conditioning shocks, suggested that depression was not due entirely to depletion and that the depletion assumption led to an over‐estimate of p.5. A third method of estimating p from measurements of the decline of e.p.p. amplitudes during rapid stimulation also appeared to result in an over‐estimate.
Effects of cations on prolactin and growth hormone secretion by rat adenohypophyses in vitro
Authors: Parsons J. A. 
Published: December 2014

1. Explants of rat adenohypophyses were incubated in medium 199, Earle's saline, or modified Earle's saline (K‐Earle's) with different calcium, magnesium, sodium and potassium concentrations for 4‐6 hr at 37° C in 5% CO2 in O2.2. The amount of prolactin and growth hormone in explants and in medium was estimated by disk electrophoresis and densitometry.3. Low calcium inhibited prolactin secretion by 40–60%. Low magnesium and slightly increased (5×) magnesium (4·1 m
M) did not influence prolactin secretion in either 1·8 m
M or low calcium, but 10 and 20 m
M magnesium inhibited secretion by 50 and 70%, respectively. Inhibition of prolactin secretion by high magnesium was reversible.4. Decreasing sodium by 80% had no effect on prolactin secretion, but low sodium inhibited the sustained, although not acute, secretion of this hormone.5. Low potassium did not affect the secretion of either prolactin or growth hormone. Increased potassium (32 or 54 m
M) slightly stimulated prolactin secretion by adenohypophyses of males but had no effect on the secretion of this hormone by female glands.6. In 1·8 m
M calcium, growth hormone secretion by pituitaries of males and females was markedly stimulated by increased potassium, but it was not appreciably affected by high potasium in low calcium. Increased potassium did not stimulate growth hormone secretion in medium containing low sodium with normal calcium.7. Secretion of prolactin and growth hormone by rat adenohypophyses is dependent upon calcium, but only growth hormone secretion is markedly stimulated by increased potassium. The difference in responsiveness to increased potassium, between the somatotrophs and lactotrophs, may be related to the predominant mode of hypothalamic control of these hormones.
The relation between calcium and contraction kinetics in skinned muscle fibres
Authors: Podolsky R. J. , Teichholz L. E. 
Published: December 2014

1. Segments of skinned frog muscle fibres were immersed in solutions in which the calcium ion concentration, and therefore the steady isometric force, was controlled with an EGTA buffer system. The contraction kinetics were measured when the load was quickly reduced to values less than the isometric force.2. The velocity of shortening following release from steady force was a hyperbolic function of relative load. The minimum quick displacement required to reduce the force from the steady isometric value to half this value was about 1% of the fibre segment length.3. The relative force—velocity relation was independent of pCa in the range 5·0–6·75. Thus calcium ions appear to control the number of sites at which cross‐bridges can be formed but have no significant effect on the kinetic properties of an individual bridge.4. Cross‐bridges along the length of a myofilament appear to act independently of each other.5. The force—velocity relations reported for intact muscle fibres during relaxation, when compared with those of skinned fibres at different calcium levels, indicate that the time course of the fall in force after a stimulus is essentially that of calcium removal from the myofilaments.
Consumption of kininogen in the submandibular salivary gland when activated by chorda stimulation
Authors: Gautvik K. M. , Hilton S. M. , Torres Sonia H. 
Published: December 2014

1. A method is described for determination of kininogen 1 (substrate mainly for plasma kallikrein) and kininogen 2 (substrate for glandular kallikrein) independently in cat plasma.2. In anaesthetized cats the arterial inflow to, and venous outflow from, the submandibular salivary gland were isolated: a roller pump giving constant volume inflow was interposed in the arterial circuit.3. Venous blood was collected at rest, during and after stimulation of the chorda tympani, and its content of kininogens 1 and 2 were estimated. Kininogen 2 was reduced up to 60% by chorda stimulation, whereas the level of kininogen 1 was unchanged.4. On close arterial infusion of bradykinin or histamine in amounts which produce large vascular effects, including increased capillary permeability, the venous blood levels of both kininogens 1 and 2 were unchanged.5. It is concluded that the selective loss of kininogen 2 on chorda stimulation results from the release of kallikrein into the tissue spaces and reflects the extent of kinin formation within the gland.
Effect of environmental temperature on the turnover of 5‐hydroxytryptamine in various areas of rat brain
Authors: Simmonds M. A. 
Published: December 2014

1. Rats were exposed to environmental temperatures of 9, 24 or 32° C and the turnover of 5‐hydroxytryptamine (5‐HT) was estimated in various areas of brain by two different methods in separate series of experiments. In the first method, small amounts of tritium labelled 5‐HT, [3H]5‐HT, were injected into the c.s.f. in order to label radioactively the endogenous 5‐HT in the brain. The rates of disappearance of [3H]5‐HT from discrete areas of brain were taken as indices of the rates of turnover of endogenous 5‐HT in these areas. In the second method, the rate of accumulation of endogenous 5‐HT after inhibition of monoamine oxidase by pargyline was taken as an estimate of 5‐HT turnover.2. The results obtained by each method were in agreement. The turnover of 5‐HT increased with increasing environmental temperature from 9 to 32° C in specific brain areas. During the first hour of exposure to 32° C, the turnover of 5‐HT increased in the preoptic area, hypothalamus and cortex + hippocampus, but not in striatum or midbrain. During the subsequent 2 hr at 32° C, however, the turnover of 5‐HT in the preoptic area and hypothalamus fell while that in the striatum showed a delayed rise.3. It is concluded that 5‐HT is involved in several different cerebral pathways which increase their activity upon exposure of the rat to heat. These pathways are not located exclusively in the preoptic area and hypothalamus.
Stimulus—response curves for the pulmonary vascular bed to hypoxia and hypercapnia
Authors: Barer Gwenda R. , Howard P. , Shaw J. W. 
Published: December 2014

1. In anaesthetized open‐chest cats and dogs, blood flow and gas tensions were measured in a circuit inserted into a pulmonary vein while ventilating the lobe which it drained with low O2 and high CO2 mixtures.2. Both hypoxic and hypercapnic mixtures caused a reduction in blood flow from the lobe.3. Stimulus—response curves relating blood flow to pulmonary venous PO2 and PCO2 were obtained. Those for hypoxia were usually asymptotic in shape; the curves became steep below 100 torr and flow sometimes fell to zero. The mean reduction in blood flow for every 20 torr fall in PO2 was 15·7% in cats and 11·8% in dogs. Those for hypercapnia were steep at first but levelled out at high PCO2 values; the maximum reduction in flow was 40–60% as vasoconstriction was only observed over a limited PCO2 range.4. Hypoventilation of the lobe led to a reduction in blood flow. This was mainly attributable to hypoxia though other factors such as hypercapnia may sometimes have contributed.5. Total occlusion of the bronchus of an O2‐filled lobe caused blood flow to fall in two phases. The first phase could be attributed to a rise in PCO2 and the second to a fall in PO2.6. The results confirm the hypothesis that hypoxia is an important factor regulating local blood flow in relation to local ventilation.