bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of manganese ions on the contraction of the frog's heart
Authors: Chapman R. A. , Ellis D. 
Published: December 2014

1. The effects of Mn2+ in particular but also of Ni2+, Co2+, Cd2+, verapamil and D600 on the contraction of isolated frog atrial trabeculae have been investigated. Contraction was initiated either by electrical stimulation, or by raising the [K]o or by lowering the [Na]o.2. Mn ions like Ca ions cause a hyperpolarization of the cell membrane and a rise in the threshold for the action potential and twitch. Mn ions, particularly at low concentrations, reduce the overshoot of the ventricular action potential.3. Mn ions reduce the strength of the regularly evoked heart beats. Prolonged exposure, in beating hearts, results in a rise in resting tension and often a small recovery of the heart beat.4. In normal Ringer solution and in Ringer free of Na ions, the addition of Mn causes the tension—depolarization curve to be displaced by an amount equivalent to an 18 mV hyperpolarization of the membrane potential for a tenfold increase in the divalent cation concentration.5. Mn, Co, Ni and Cd ions all cause a marked reduction in the tension generated by exclusion of Na ions from the bathing fluid. In the presence of these divalent cations the contracture divides into an initial phasic and a later tonic contraction. This inhibition is reversed by raising the [Ca]o, while the tension developed during the initial phasic contraction varies with the [Ca]o/[Mn]o quotient.6. A similar tonic contracture is initiated after exposure to Na‐free fluid containing a high [Mn]o by the addition of a small concentration of Na, Li, hydrazinium or hydroxylammonium ions.7. The organic ‘Ca antagonists’ verapamil and D600 have little effect on the contracture induced by lowering [Na]o even after prolonged exposure at relatively high concentrations but they do inhibit the twitch contraction and the K contractures.8. The effects of Mn on the Na‐withdrawal contracture of frog heart can be interpreted in terms of an exclusively extracellular effect where Mn ions resemble Na ions in their action, and both antagonize the movement of Ca across the cell membrane.9. The experimental evidence suggests that the K contracture in frog heart is initiated by a mechanism which is, in some ways different to that underlying the Na‐withdrawal contracture, and may involve two different sources of activator Ca.10. The several different effects of Mn on the frog heart probably reflects the ability of this cation to interfere with many processes involving Ca, and that there are a number of such processes involved in the results described in this work. The effects of Mn are more complex than might be generally supposed.
The variability of muscle nerve sympathetic activity in resting recumbent man
Authors: Sundlöf Göran , Wallin B. Gunnar 
Published: December 2014

1. Pulse synchronous bursts of multi‐unit sympathetic activity was recorded from median or peroneal muscle nerve fascicles in fourteen subjects resting in the recumbent position. The neural activity was quantitated in terms of burst incidence, i.e. the number of bursts in the mean voltage neurogram/100 heart beats, during successive rest periods of 2‐4 min.2. For each individual the burst incidence was fairly constant between different rest periods but the mean burst incidence varied widely between individuals, the range being from less than 10 to more than 90 bursts/100 heart beats.3. Simultaneous double nerve recordings were made on one subject from median and peroneal nerves and on eight subjects from the two peroneal nerves. There was always close similarity between the two records in such experiments regardless of which muscles the nerve fascicles innervated. When analysed separately the difference in burst incidence between the two sides ranged from 0·7 to 5·1 bursts/100 heart beats. The findings suggest that sympathetic neurones destined to skeletal muscles are subjected to a homogenous central drive and that contributions to the activity from ganglionic or segmental sources are of lesser importance.4. On seven subjects repeated recordings at rest were made with intervals of 3 weeks—21 months between recordings. In each subject mean burst incidences were similar in all recordings (range of differences 0·5‐11·2 bursts/100 heart beats) suggesting an individually constant level of sympathetic activity in muscle nerves.5. For each individual the variability of burst amplitudes in the mean voltage neurogram was described by burst amplitude spectra. Most subjects had a relatively larger proportion of small than high amplitude bursts, but there was a tendency for more even amplitude distributions in subjects with high burst incidence. The finding may be an indication of interindividual differences in the average number of impulses/burst.6. It is concluded that the multi‐unit recording technique can be used for comparisons of the level of muscle nerve ‘sympathetic tone’ between different subjects.
Human tactile detection thresholds: modification by inputs from specific tactile receptor classes
Authors: Ferrington D. G. , Nail B. S. , Rowe Mark 
Published: December 2014

1. Human detection thresholds for a vibratory stimulus applied to the volar surface of the index finger were examined under conditions where afferents from specific tactile receptor classes were simultaneously activated from the thenar eminence. The experiments were designed to test whether stimuli which have been shown previously to induce afferent inhibition of ‘tactile’ neurones in the cuneate nucleus of the cat could modify human subjective performance in a tactile detection task. Conditioning stimuli to the thenar eminence were usually of three forms; steady indentation to engage slowly adapting tactile receptors; 300 Hz vibration to engage Pacinian corpuscles; and 30 Hz vibration to engage the intradermal, rapidly adapting tactile receptors which are thought to be Meissner's corpuscles.2. In ten subjects the mean detection threshold for a 30 Hz test stimulus in the absence of conditioning stimulation was 8·6 ± 1·0 μm (
S.E.). Detection thresholds were increased substantially in the presence of a 300 Hz, 100 μm conditioning stimulus (mean increase 11·1 ± 2·0 μm), whereas minor or insignificant effects were seen with conditioning stimuli consisting of (a) 30 Hz, 100 μm (mean increase 1·4 ± 0·8 μm), (b) steady indentation, 1·5 mm in amplitude (mean increase 1·3 ± 0·7 μm) or (c) 300 Hz, 100 μm to the contralateral thenar eminence (mean increase 0·4 ± 0·5 μm).3. The 300 Hz conditioning stimulus to the ipsilateral thenar eminence caused a marked increase in detection thresholds at all test stimulus frequencies over the range 10‐450 Hz. The effects of the conditioning stimulation therefore operated on inputs from Pacinian corpuscles, which are responsible for vibration detection at 80‐450 Hz, and on inputs from the intradermal, rapidly adapting receptors which are responsible for vibration detection at 10‐80 Hz.4. The band width of conditioning vibratory frequencies which was effective at amplitudes of 100 μm in bringing about increases in detection threshold extended from 50‐80 Hz to 300 Hz, the maximum tested.5. Whereas amplitudes of 1‐2 μm produced clear increases in detection thresholds with conditioning stimuli of 300 Hz, amplitudes of > 200 μm were needed at 30 Hz.6. The observed elevations in detection threshold are consistent with an afferent‐induced inhibitory action exerted at synaptic relays of the sensory pathway by tactile inputs arising exclusively or predominantly from Pacinian corpuscles.
The effect of an increase in aortic pressure upon the inotropic state of eat and dog left ventricles
Authors: Elzinga G. , Noble M. I. M. , Stubbs J. 
Published: December 2014

1. The effect of increased aortic pressure on the inotropic state of the left ventricle was studied in isolated cat hearts, perfused with bovine red cells in Tyrode solution, ejecting into a hydraulic model with the same input impedance as that of the cat aorta.2. Inotropic state was assessed at a controlled left ventricular end‐diastolic pressure by interpolating single isovolumic beats by means of an occluder in the aortic cannula.3. When such isovolumic beats during periods of raised aortic pressure were compared with those during control periods, the difference in peak isovolumic pressure ranged from ‐0·3 to +0·5 kPa indicating differences in inotropic state which were small and inconsistent in direction.4. The maximum rate of rise of left ventricular pressure (dP/dtmax.) of ejecting beats was little affected by a rise of aortic pressure and the direction of changes was inconsistent.5. The effect of increased aortic pressure was studied in intact dogs after cardiac denervation; left ventricular end‐diastolic pressure was uncontrolled and therefore rose to a higher steady level.6. No consistent change of dP/dtmax. was found during the period of increased aortic pressure.7. All flow and pressure variables remained steady during the period of increased aortic pressure after the higher level of left ventricular end‐diastolic pressure had been established.8. These results demonstrate that neither the positive inotropic effect nor the negative inotropic effect of increased load dominates in these preparations. This may be the result of a balance between the two effects, or they may be of unimportant magnitude under physiological conditions.
Studies on the mechanism of renin release from isolated superfused rat glomeruli: effects of calcium, calcium ionophore and lanthanum
Authors: Baumbach L. , Leyssac P. P. 
Published: December 2014

1. The effects of external medium calcium concentration, the ionophore A23187 and lanthanum on the rate of renin release in vitro were studied with particular emphasis on results obtained from isolated superfused glomeruli of rat kidneys.2. The response to reduction in superfusate calcium concentration from 2 m
M was a graded and reversible increase in the rate of renin release. An increase in release was detectable at 0.2 m
M calcium; a threefold increase was found 36 min after a change from 2 m
M calcium to calcium‐free superfusate. A similar relative increase in release resulted from reductions from 0.1 m
M to zero calcium, but the absolute amounts of renin released were greater in this latter series. Renin release from kidney cortical slices similarly increased in response to calcium‐free incubation medium.3. The effects of A23187 on renin release were modest. Changing from 2 m
M calcium during control periods to calcium‐free Ringer with A23187 added caused an attenuated and more delayed increase in release than the change to calcium‐free Ringer without ionophore. This difference in response was abolished when glomeruli were superfused with 0.1 m
M calcium during the preceding 1 hr control period. There was no significant difference in renin release from glomeruli exposed to calcium‐free EGTA‐Ringer with and without A23187 in the 2 m
M calcium series; in the 0.1 m
M calcium series the increase in release following a shift to calcium‐free EGTA‐containing superfusate with A23187 added was significantly greater than in the absence of the ionophore.4. Addition of lanthanum (1 or 0.05 m
M) to calcium‐containing as well as calcium‐free superfusate resulted in a significant depression of renin release. Subsequent removal of the lanthanum did not restore the rate of release unless EGTA was added; in the latter case a massive increase in renin release occurred resulting in a marked depletion of the remaining renin content of the glomeruli.5. It is concluded that calcium influences renin release by a direct action on the juxtaglomerular cells. The data support the previous suggestion that basal renin release is a function of active, calcium‐dependent cell volume regulation — swelling causing an increase in the release; and further suggest that membrane‐bound calcium has a direct effect on the cell membrane permeability to renin.6. The results exclude that calcium‐stimulated exocytosis is responsible for basal renin release from the juxtaglomerular cells adhering to isolated glomeruli.
Effects of vascular perfusion on the accumulation, distribution and transfer of 3‐O‐methyl‐D‐glucose within and across the small intestine
Authors: Boyd C. A. R. , Parsons D. S. 
Published: December 2014

1. Factors affecting the transfer of the non‐metabolized, ‘actively transported’ sugar, 3‐O‐methyl‐
D‐glucose (3MG) across the small intestinal epithelium have been examined in vascularly perfused anuran intestine. Transfer has been studied during absorption in the steady state, and also during the period of transition from one steady state to another.2. During the steady state, the rate of absorption of 3MG from the intestinal lumen is equal to the rate of appearance in the portal venous effluent; this rate of transfer is to a small, but significant, extent directly related to the rate of arterial perfusion. With phlorizin in the intestinal lumen, transfer across the epithelium is reduced to very low rates which are independent of the rate of vascular perfusion.3. The apparent size of the tissue pool(s) of 3MG that have to be loaded to achieve the steady state rate of transfer are less than those that unload into the vascular bed after 3MG is removed from the intestinal lumen. This ‘up—down asymmetry’ is abolished when phlorizin is present in the intestinal lumen during the unloading phase.4. When 3MG is abruptly removed from the intestinal lumen after the tissue has been previously loaded with the sugar, the rate of washout into the vascular bed can be described by the sum of two exponential terms. The two terms differ in that the rate constant of the earlier ‘fast’ term is sensitive to the rate of vascular perfusion, while the later, ‘slow’, rate constant is insensitive to flow rate. The total quantity of 3MG that can be unloaded from the tissue into the portal venous effluent is decreased when phlorizin is present in the intestinal lumen during the unloading phase.5. Absorption from the lumen of the anuran intestine continues while the mesenteric circulation is interrupted. An estimate of the concentration of 3MG during the period of vascular stoppage can be made from the quantity recovered in the portal venous effluent when vascular perfusion is reinstituted (‘vascular stop‐flow’). The extent of the accumulation depends upon the duration of the vascular stoppage and the presence of Na ions in the intestinal lumen is essential for accumulation to occur.6. The findings are discussed in relation to the transfer of 3MG between various possible compartments in the tissue during absorption. Evidence is presented that a re‐uptake of previously absorbed 3MG may occur across the brush border membrane. Such a recycling of 3MG across the epithelium implies that the apparent unidirectional fluxes measured across the epithelium between the bulk phase of the lumen and the blood may underestimate the size of fluxes across the epithelium at the cellular level.
The effects of artificial lung inflation on reflexly induced bradycardia associated with apnoea in the dog
Authors: Angell‐James Jennifer E. , Daly M. De Burgh 
Published: December 2014

1. The cardiac effects of artificial inflation of the lungs were studied during reflexly induced apnoea and bradycardia in anaesthetized dogs.2. Reflex apnoea and bradycardia were induced (a) by stimulation of the larynx with water or by electrical stimulation of afferent fibres in the superior laryngeal nerve, or (b) by combined stimulation of the superior laryngeal nerve and carotid body chemoreceptors.3. During combined stimulation of the laryngeal and carotid body inputs, the activation of respiration normally evoked by chemoreceptor stimulation was inhibited whereas the chemoreceptor cardio‐inhibitory reflex was facilitated leading to periods of temporary cardiac arrest.4. In spontaneously breathing animals and in those artificially ventilated, lung inflation invariably caused tachycardia.5. Rhythmic artificial inflation of the lungs during the apnoeic period produced by the laryngeal input or by a combination of the laryngeal and chemoreceptor inputs wholly or partly reversed the bradycardia. This occurred using lung inflation volumes within the range of the normal tidal volume and inflation pressures of less than 12 mmHg; the response was independent of the composition of the gas used for inflating the lungs, and occurred at constant Pa, O2 and Pa, CO2. Lung inflation carried out during a reflexly induced arrest of the heart immediately restarted the heart and was accompanied by an exaggerated sinus arrhythmia.6. Evidence is presented that the observed effects of artificial lung inflation are reflex in origin with the vagus nerves as the main afferent and efferent pathways.7. Electrical stimulation of the central end of the cut pulmonary branches of the thoracic vagosympathetic nerves also caused tachycardia and had the same effects as lung inflation in modifying the reflexly induced bradycardia.8. Some clinical implications of these results are discussed.
Osmotic behaviour of human red blood cells: an interpretation in terms of negative intracellular fluid pressure
Authors: Hladky S. B. , Rink T. J. 
Published: December 2014

1. The observation that human red blood cells do not shrink in hypertonic media as much as expected for ideal osmometers has previously been explained in terms of either a marked increase in the osmotic coefficient of the cell contents or an increase in the chloride content of the cells.2. Changes in suspension pH and haematocrit have been observed when the concentration of the unbuffered NaCl medium was doubled. The small increases in external pH, and the size of the volume decreases, are inconsistent with variations in the Cl content as a significant factor in the non‐ideal osmotic responses.3. Membrane potentials of red cells in buffered media were followed using the fluorescent dye, diS‐C3‐(5). On shrinking at pH 7·4, the cells hyperpolarized ca. 5 mV as predicted if changes in the osmotic coefficient rather than in Cl content explained the osmotic behaviour.4. Regarding haemoglobin in concentrated solution as a solute with high osmotic coefficient is formally correct but is little help in understanding the properties of the solution. We have found it useful to consider separately haemoglobin and the rest of the contents of the cell. The haemoglobin then supports part of the total hydrostatic pressure on the cell leaving the crystalloid solution to experience a reduced fluid pressure. In greatly shrunken cells the contents act like a gel with the matrix of haemoglobin under compression and the fluid which fills the spaces within the matrix under tension.
Carbon dioxide and venous return and their interaction as stimuli to ventilation in the cat
Authors: Ponte J. , Purves M. J. 
Published: December 2014

1. Respiratory responses were measured in forty‐seven cats, made decerebrate or anaesthetized with pentobarbitone or chloralose‐urethane, to changes in the level of CO2 infused into the inferior vena cava via an external oxygenator circuit or to changes in the volume of venous return or to the inhalation of CO2.2. No consistent difference was found between the respiratory response to the increase in the level of CO2 infused or CO2 inhaled provided that the volume of venous return during both sets of tests was held constant at normal levels.3. If the volume of venous return was increased and the level of CO2 infused maintained at levels such that V̇CO2 did not increase, ventilation increased with a fall in Pa, CO2, a response lying approximately on the isometabolic curve.4. If the volume of venous return and the level of CO2 infusion were raised together, a spectrum of intermediate respiratory responses was obtained which reproduced all those seen in earlier papers, in muscular exercise or other hypermetabolic states.5. None of the steady‐state respiratory responses was significantly affected by bilateral vagotomy or section of the sinus nerves, though sinus nerve section slowed the responses to infused or inhaled CO2 and they were then less precisely controlled.6. Additional experiments indicated that where CO2 was infused or inhaled, the effective stimulus to respiration was an increase in mean Pa, CO2 in proportion to the CO2 added and that the respiratory response to CO2 was enhanced by reduced blood volume. How the changes in venous return were sensed and affected respiration, remains unclear.7. These results may explain why previous workers have obtained exaggerated respiratory responses to the infusion of CO2 and why respiration increases rapidly at the start of exercise and is then maintained at high levels without discernible change in the chemical stimulus in arterial blood.
Neurones in cat parastriate cortex sensitive to the direction of motion in three‐dimensional space
Authors: Cynader Max , Regan D. 
Published: December 2014

1. On psychophysical grounds, Beverley & Regan suggested that in man different neural mechanisms mediate the binocular perception of movement in depth and the binocular perception of positional (static) depth. They proposed that the human visual pathway contains several neural mechanisms, each sensitive to a different direction of motion in space. These mechanisms compute the direction of motion from the relative speeds and directions of movement of the left and right retinal images.2. We have recorded from 101 units in area 18 of cat visual cortex, searching for neurones tuned to the direction of motion in three dimensions, with properties that could account for the proposed directionally tuned binocular motion detectors in man. The cat's left eye viewed one bar, while its right eye simultaneously viewed a second bar. Single units were stimulated by independently oscillating the bars from side to side. The apparent direction of movement in three dimensions was altered by varying the relative speeds of the bars and their relative directions of motion. The mean (positional) disparity of the bars could also be varied.3. For one class of neurone (twenty cells), binocular stimulation inhibited firing for trajectories parallel to the frontoparallel plane over a large volume of space. Strong firing was produced by oppositely directed bar movements. Some of these neurones were especially narrowly tuned to the direction of movement in depth, responding only to a range of 2‐3°, i.e. to moving bodies that would hit or only narrowly miss the cat. These cells emphasized the direction of movement at the expense of positional information.3. These units occurred in clusters. On the perpendicular penetrations in which they were found, they comprised a substantial majority of all cells encountered.5. For a second class of neurone (nine cells), binocular facilitation produced selective responses to objects moving along trajectories that missed the head.6. The two classes of neurone provide a basis for four proposed directionally tuned binocular motion detectors.7. A third class of neurone (seventeen cells) was selectively sensitive to movements parallel to the frontoparallel plane. There was strong binocular facilitation when the bars moved at the same speeds in the same directions: oppositely directed movements might be more than 100 times less effective. These neurones may signal positional disparity.8. These three classes of neurone cut across established categories. Only when both eyes were stimulated simultaneously with targets moving in different speeds and directions was it possible to demonstrate the binocular interactions described here.