bluuebunny/crossref_metadata_2025_split huggingface dataset:
Binding of the cardiac glycoside ouabain to intact cells
Authors: Baker P. F. , Willis J. S. 
Published: December 2014

1. Measurements were made of the binding of [3H]ouabain to a variety of cell types.2. Two components of binding could usually be distinguished: a component that saturated at low glycoside concentrations and a component that increased up to the highest ouabain concentrations examined.3. Detailed studies with HeLa cells and kidney slices from guinea‐pigs showed that the saturable component is probably associated with inhibition of the Na pump. The main evidence for this is (a) at low concentrations of ouabain there is a close correspondence between the concentration of ouabain giving half‐maximum binding and the concentration giving half‐maximum inhibition of the Na pump; (b) at low glycoside concentrations, binding precedes inhibition of the Na pump; (c) the rate of binding is very sensitive to external K ions, being highest in the absence of K; (d) binding is reversible and the release of ouabain is associated with reactivation of the Na pump, (e) binding is reduced in the absence of Na ions and in the presence of metabolic inhibitors; (f) binding has a Q10 of about 4; and (g) in the presence of Na and ATP, lysed HeLa cells bind a similar amount of ouabain and the binding is sensitive to K ions.4. The linear component of binding does not seem to involve the Na pump and it may reflect uptake of ouabain into the cell interior. It has a Q10 of 2·5 and is unaffected by K concentrations which have a large effect on the saturable component.5. Bound ouabain could be removed from HeLa cells by low pH, trichloroacetic acid, urea, high temperatures and 100% ethanol. These agents did not distinguish between the two components of binding.6. Criteria are developed for estimating the number of Na pumping sites in cells and the data for ouabain‐binding to a number of cells is compared with the activity of the (Na + K)‐activated ATPase in the same tissues. Although the number of pumping sites varies from less than 1/μ2 to 1500/μ2 of membrane, the turnover at these sites seems to be fairly constant between 3,500 and 15,000 min−1 at 35° C.
Inhibition of the sodium pump in squid axons by cardiac glycosides: dependence on extracellular ions and metabolism
Authors: Baker P. F. , Willis J. S. 
Published: December 2014

1. The rate of inhibition of the Na pump by ouabain was examined both by direct measurement of the rate of decline of the Na efflux and by the binding of [3H]ouabain.2. The onset of inhibition of the Na efflux was concentration‐dependent; but did not follow simple first order kinetics. The time course of inhibition was roughly exponential although in about 30% of the axons inhibition was preceded by a transient stimulation of the Na efflux.3. Inhibition of the Na efflux by both ouabain and strophanthidin was apparently irreversible.4. The onset of inhibition was slowed markedly at low temperatures.5. Replacement of external Na by choline, dextrose or potassium slowed the rate of inhibition. Li behaved like Na and inhibition was faster in K‐ASW than in choline‐ASW.6. The rate of inhibition of Na‐Na exchange was similar to that of Na‐K exchange, but ouabain failed to bind securely to fully poisoned axons.7. Two components of [3H]ouabain‐binding could be distinguished. A linear component which probably reflects uptake into the cells and a saturable component which seems to reflect binding to Na‐pumping sites.8. The saturable component of binding followed a similar time course to the inhibition of the Na efflux and the rate of binding was reduced in choline‐ASW and in fully poisoned axons.9. Measurements of [3H]ouabain‐binding indicate that the number of Na pumping sites in the axon membrane is probably between 103 and 104/μ2.
The effect of adenosine on the release of the transmitter from the phrenic nerve of the rat
Authors: Ginsborg B. L. , Hirst G. D. S. 
Published: December 2014

1. The action of adenosine on neuromuscular transmission has been studied on the rat phrenic nerve—diaphragm preparation.2. Adenosine (0·025–10 m
M) reversibly reduced the quantum content of end‐plate potentials and the frequency of miniature end‐plate potentials to about half the control values in preparations in which transmission was blocked with high Mg2+ and/or low Ca2+ concentrations. Where transmission was blocked with tubocurarine, the amplitude of end‐plate potentials was reduced to about half the control values by adenosine.3. In solutions with very low Ca2+ concentrations (no added Ca2+ and 1 m
M‐EGTA) adenosine had a smaller effect on the frequency of miniature end‐plate potentials.4. The effect of adenosine (0·025 and 0·05 m
M) was abolished by theophylline (1·8 m
M).5. The results are discussed in relation to the increase in cyclic AMP in brain slices caused by adenosine and the abolition of this effect by theophylline (Sattin & Rall, 1970).
Potassium conductance changes in skeletal muscle and the potassium concentration in the transverse tubules
Authors: Almers W. 
Published: December 2014

1. When one hyperpolarizes a muscle fibre by passing electric current, the K conductance declines with time. Voltage‐clamp experiments on frog sartorius muscle fibres showed that two components contribute to this decline.2. A rapid component operates when the fibre is hyperpolarized to potentials more negative than −120 mV. Decline by this mechanism is reversed completely within 200 msec. The large effect of temperature on the kinetics of this process indicates that it represents a time‐dependent membrane permeability change.3. A slow component operates also at less negative potentials. Recovery at −65 mV takes place with half‐times of about 0·4 sec. The Q10 for the rate of recovery is 1·3, indicating that this process is diffusion limited.4. After prolonged hyperpolarization to potentials positive to −120 mV, membrane current at the resting potential is outward and persists for several seconds. At that time, the potential measured in the absence of membrane current is shifted in the negative direction by 3–5 mV.5. This shift and the time course of currents near the resting potential after hyperpolarization as well as the Q10 of 1·3 indicate that the slow process is due to changes in tubular K concentration and not to a time‐dependent membrane permeability change.6. At potentials less negative than −120 mV, tubular depletion can satisfactorily account for the decline of K conductance. At more negative potentials, the decline appears to be due to both depletion and a permeability change.
The effect of hyperventilation on maternal placental blood flow in pregnant rabbits
Authors: Leduc B. 
Published: December 2014

1. In anaesthetized pregnant rabbits near term, cardiac output and its distribution were measured by injection of isotope‐labelled microspheres. Hypocapnia (mean arterial PCO2 18 mm Hg), induced by intermittent positive pressure hyperventilation, caused a 43% reduction in maternal placental blood flow, attributed mainly to vasoconstriction. Myometrial flow was not significantly changed.2. Moderate hypercapnia (mean arterial PCO2 46 mm Hg) caused no change in placental flow, compared with observations made while breathing air spontaneously (PCO2 31 mm Hg).3. Intravenous infusions of adrenaline or noradrenaline 1 μg/kg. min caused maternal placental vasoconstriction.4. During the especially warm summer of 1969, there was a mean 46% reduction in maternal placental blood flow in pregnant rabbits near term, breathing room air spontaneously with normal blood gas values and rectal temperatures. This was associated with an increase in the number of runts and dead foetuses.
Rhodopsin bleaching signals in essential night blindness
Authors: Alpern M. , Holland M. G. , Ohba N. 
Published: December 2014

1. The dark‐adaptation curves of two subjects with essential night blindness revealed no evidence for functioning rod vision. Cone vision was normal.2. The photopupillomotor dark adaptation, and flash intensity response amplitude curves on one of these subjects confirmed the absence of rod function.3. However, there is the normal amount of rhodopsin in their rods with normal kinetics.4. Cone pigment kinetics are also nearly normal. After a full bleach, log threshold elevation of the foveal cones is linearly related to pigment regeneration. The constant of proportionality is about 3·0 as it is in the normal retina.5. After a full rhodopsin bleach, the contralateral pupil size recovered its full dark value along a curve which followed the regeneration of rhodopsin.6. The results in (5) are identical to those previously found on normal subjects.7. With the exception of a very small response attributed to the contribution of cones, no significant changes in pupil size were evoked by uniform ganzfeld steady backgrounds until the intensity of retinal illuminance was so high that appreciable rhodopsin was bleached. This contrast to the changes evoked by weak steady backgrounds in the normal eye.8. Therefore, rod bleaching signals are normal in such retinas but rod signals evoked by real lights are not functional. This supports Rushton's concept as to how bleaching signals influence retinal sensitivity as opposed to the view of Barlow.9. The defect in essential night blindness very probably involves the rod automatic gain control, but because of (4) the cone gain control must be normal.10. Therefore, rod and cone gain control mechanisms must be independent in these night blind retinas and, by analogy, in the normal retina as well.
The extent of the destruction, during passage through the lungs, of a substance secreted by the heart
Authors: Lockett Mary F. , Retallack R. W. , Sayers Linda 
Published: December 2014

1. In vitro, the lungs of male Wistar rats, 220–230 g, removed heart substance (HS) from saline perfusates. HS could not be recovered by subsequent perfusion with HS free solution.2. A maximum rate of HS‐uptake, 8·5 ng biological equivalents of 18‐monoacetate of
D‐aldosterone (18 MA)/min, was reached at a concentration of HS equivalent to 3·5 ng 18 MA/ml. at a flow of 6 ml./min.3. Uptake was not significantly affected by a fall in temperature from 38 to 18–20° C or by reduction in PCO2 to zero. Uptake was reduced by anoxia and was enhanced by decrease of pH from 7·4 to 6·6.4. 30% of the HS taken up by the lungs at 20° C was recoverable: none of the HS taken up at 38° C was recovered.5. Uptake of HS by binding is considered rate‐limiting to the destruction of HS in the lungs.6. The concentrations of HS found in the pulmonary and carotid arterial blood of cats under chloralose anaesthesia, during haemorrhage, were biologically equivalent to 1098 ± 38·7 and 169 ± 13·4 ng 18 MA/100 ml. (means ±
S.E.) respectively, in four experiments.
Cholinergic mechanisms in the rat somatosensory cerebral cortex
Authors: Stone T. W. 
Published: December 2014

1. The responses of identified cells in the rat cerebral cortex to cholinomimetic and anticholinergic substances has been investigated.2. Acetylcholine and muscarinic agonists have an excitatory action on 80% of pyramidal tract cells. This response is found especially on cells responding to specific thalamic stimulation and the burst of spikes evoked from this site can sometimes be blocked by the iontophoresis of atropine. This strongly suggests an excitatory transmitter function for acetylcholine in a specific thalamocortical pathway.3. Experiments on non‐pyramidal tract cells have detected a muscarinic depression of some cells, and a nicotinic excitation of some cells above a depth of 600 μ in the cortex.4. It is suggested that the increased release of acetylcholine from the cortex produced by atropine administration may be due to an excess of muscarinic inhibitory over excitatory synapses in the cortex.
Inhibition of compensatory renal growth in rats
Authors: Dicker S. E. 
Published: December 2014

1. Compensatory renal hypertrophy in unilaterally nephrectomized rats was measured by estimation of dry weight, protein content, RNA and DNA changes and rate of oxygen consumption. Inulin clearances (= GFR) and water and solute excretions were estimated in animals given by stomach tube either 5 ml. water or 5 ml. 0·6% NaCl solution/100 g body wt.2. Kidneys removed when animals were unilaterally nephrectomized were homogenized in 0·25
M sucrose and fractions containing mitochondria or microsomes were obtained by centrifugation. Renal cortex and medulla were similarly treated.3. Intraperitoneal injections of microsomes and/or supernatant fluid from a kidney homogenate or from the renal cortex usually inhibited compensatory growth of the contralateral kidney and prevented any increase of its protein content.4. Injections of microsomes and/or supernatant fluid from the renal medulla had no significant effect on the rate of compensatory hypertrophy.5. After
I.P. injection of microsomes and supernatant fluid from a homogenate from the renal cortex there was no rise of the RNA/DNA ratio in the contralateral kidney and the rate of oxygen uptake of its cortex decreased, while that of anaerobic glycolysis increased.6. Injections of microsomes and supernatant fluid from kidney homogenate did not affect glomerular filtration rate which increased as in control unilaterally nephrectomized rats.7. In unilaterally nephrectomized rats, injected with microsomes and supernatant fluid from a kidney homogenate, there was a decrease of osmolal clearance, in spite of the raised glomerular filtration rate. The decrease of osmolal clearance lasted for several days, and was most pronounced when the animals had been given by stomach tube 5 ml. 0·6% NaCl solution/100 g body wt.
A comparison of chemical and electrical synaptic transmission between single sensory cells and a motoneurone in the central nervous system of the leech
Authors: Nicholls J. G. , Purves D. 
Published: December 2014

In leech ganglia, three sensory cells of different modality converge on a motoneurone, where they form chemical and electrical synapses. Each of these synapses behaves in a characteristic manner and the nature of the transmission mechanism has significant functional consequences for the operation of the reflexes. An analysis has been made of the effects of trains of impulses on synaptic transmission through these pathways, using frequencies that correspond to natural firing.1. At the chemical synapse between the nociceptive sensory cell and the motoneurone, two opposing events occur: facilitation and depression. Thus, with trains of impulses, the synaptic potentials first increase in amplitude and then decrease. The two processes could be separated by altering the Mg and Ca content of the bathing fluid. In concentrations of Mg that reduced the amplitude of a single control chemical synaptic potential, pure facilitation occurred during a train. Depression predominated during brief trains in raised concentrations of Ca, although synaptic potentials were initially larger. These results suggest that changes in the amount of transmitter released by each presynaptic action potential can account for the changes observed in chemical synaptic transmission.2. In contrast, electrical transmission between the sensory cell responding to touch and the same motoneurone did not show facilitation or depression. The electrical coupling potential in the motoneurone was relatively constant when the touch cell fired at high or low frequencies in normal Ringer fluid, high Mg, or high Ca fluid.3. Further differences between chemical and electrical synapses were apparent when the preparation was cooled to 4° C. In the cold the latency of chemically evoked synaptic potentials in the motoneurone increased and their amplitude declined drastically with repetitive stimulation, while electrical coupling potentials were unaffected.4. A brief hyperpolarization of the presynaptic cell by injected current produced a marked and prolonged increase in chemically evoked synaptic potentials, but did not influence electrical synaptic transmission.5. The synapses of the sensory cell responding to pressure, which are both chemical and electrical, behaved as expected: the chemical synaptic potentials showed facilitation and depression while electrical transmission remained relatively constant.6. These experiments emphasize the different functional consequences of electrical or chemical synapses in reflex pathways for the transmission of signals that arise as a result of natural sensory stimuli.
Effects of noradrenaline on potassium efflux, membrane potential and electrolyte levels in tissue slices prepared from guinea‐pig liver
Authors: Haylett D. G. , Jenkinson D. H. 
Published: December 2014

1. Some effects of noradrenaline on potassium efflux, electrolyte levels, membrane potential and current distribution in guinea‐pig liver slices have been examined.2. The slices (thickness ca. 300 μm) were prepared from the median lobe of the liver and incubated at 38° C in a mammalian Ringer fluid containing 2 m
M pyruvate. After an initial recovery period, the ionic composition of the tissue remained stable for several hours.3. The steady‐state contents of sodium, potassium and chloride were 296, 266 and 272 m‐equiv/kg dry tissue respectively. The inulin space was 29 ml./100 g wet tissue.4. Most if not all of the tissue potassium was exchangeable. The rate constant for 42K efflux was 0·019 min−1.5. Noradrenaline (1 μ
M) markedly increased the efflux of 42K and within 2 min caused tissue potassium to fall by 8%. At the same time the sodium content rose.6. Traverses of the slices with micro‐electrodes showed many negative‐going deflexions of 30–40 mV in amplitude. The evidence suggests that these correspond to the membrane potentials of the parenchymal cells.7. Noradrenaline (1 μ
M) caused a reversible hyperpolarization of about 10 mV. The response became larger on replacing external chloride by isethionate or methylsulphate, but was little affected by a reduction in external potassium.8. After slices had been bathed in potassium and chloride‐free solutions for several min, restoration of external potassium caused the membrane potential to increase by up to 10 mV. This hyperpolarization, but not that caused by noradrenaline, was abolished by ouabain.9. Noradrenaline reduced the amplitude and quickened the time course of electrotonic potentials set up by current pulses from another microelectrode, suggesting that the membrane conductance had risen.10. Although certain mechanisms based on electrogenic active transport processes with unusual properties have not been excluded, the present findings are more simply explained by supposing that noradrenaline increases the potassium permeability of the parenchymal cell membrane.
Renin responses to water restriction and rehydration
Authors: Blair‐West J. R. , Brook A. H. , Simpson Pamela A. 
Published: December 2014

1. The effect of restricted water intake and rapid rehydration was studied in three conscious sheep with respect to plasma renin concentration (PRC), blood corticosteroid levels, plasma protein and electrolyte concentrations, and the renal and faecal excretion of sodium and potassium.2. During water restriction the plasma concentrations of renin, protein and sodium rose while aldosterone levels were low or undetectable. Plasma potassium levels were unchanged. External sodium and potassium balance appeared to be unaffected.3. During rehydration the sheep drank more than their estimated water deficit in 3–4 min with the following effects: PRC rose three‐ to fourfold during the ensuing 12 hr. Aldosterone levels too rose, while plasma protein, sodium and potassium concentrations fell. Urinary sodium excretion virtually ceased for 24 hr, and urine flow rate increased only little during this period.4. If there was a single stimulus to renin release during water restriction and rehydration, it was not an alteration in vascular or extravascular volume, total body sodium, systemic
B.P. or plasma sodium concentration.5. It is concluded that the rise in PRC in these experiments is compatible with the theory that altered sodium transport at the macula densa was the stimulus for renin release.
The vasomotor component of the carotid sinus baroreceptor reflex in the cat during stimulation of the hypothalamic defence area
Authors: Humphreys P. W. , Joels N. 
Published: December 2014

1. The effect of moderate intensities of stimulation of the hypothalamic defence area on the baroreceptor reflex has been investigated in the cat by comparing the responses of arterial blood pressure and perfusion pressure of the isolated hind‐limb muscle bed perfused at constant volume inflow, when the isolated carotid sinus was subjected to a series of non‐pulsatile pressures with and without simultaneous hypothalamic stimulation.2. In the absence of hypothalamic stimulation the characteristic sigmoid curves relating sinus pressure to blood pressure or muscle perfusion pressure were obtained.3. With simultaneous stimulation of the hypothalamus a similar sigmoid relationship was found. There was no evidence of any reduction in the over‐all power or maximum sensitivity of the baroreceptor reflex.4. However, in those cats which had been atropinized to abolish the cholinergically mediated muscle vasodilatation, the curves obtained during hypothalamic stimulation were displaced in such a manner as to suggest that, while baroreceptor modulation of vasoconstrictor tone continued during defence area stimulation, the blood pressure regulating mechanism had been ‘reset’ so that, within the physiological range of sinus pressures, any given level of sinus pressure was associated with a greater vasoconstrictor tone.5. In non‐atropinized cats there was little displacement of the curves relating sinus pressure to blood pressure, while the curves relating sinus pressure to muscle perfusion pressure were displaced in the opposite direction so that over‐all muscle vascular resistance was less than normal at each level of sinus pressure.