bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transport of potassium at the blood—brain barrier
Authors: Bradbury M. W. B. , Segal M. B. , Wilson Janet 
Published: December 2014

1. The pial surface of different regions of the central nervous system of the rabbit have been bathed with artificial cerebrospinal fluid (c.s.f.), containing different concentrations of potassium. The object has been to change the composition of the interstitial fluid with respect to this ion, where it is adjacent to subarachnoid c.s.f.2. Two techniques, subarachnoid perfusion from the supracallosal space between the hemispheres to the cisterna magna and barbotage from the cisterna magna, have been used. If the artificial c.s.f. contains Evans Blue, the former procedure results in maximum staining of the pia and underlying nervous tissue of the pons‐medulla and spinal cord. The latter procedure results in maximum staining of the medial and supero‐lateral surfaces of the cerebral hemispheres, particularly anteriorly.3. During subarachnoid perfusion at 0·06 ml./min with the potassium‐free fluid, most regions of the brain took up significantly greater amounts of 42K than was the case during perfusion with the fluids containing 3 and 10 m‐equiv/l. For blue cerebral cortex, the tissue subjected directly to the inflowing fluid and showing the biggest differences, the ratios, c.p.m. per g brain/c.p.m. per ml. plasma, were 1·71 ± 0·12 (+44%), 1·19 ± 0·05 and 1·07 ± 0·08 (−10%) during perfusion with the fluids containing, 0, 3 and 10 m‐equiv/l. respectively.4. During barbotage, the uptake of 42K into pons‐medulla and spinal cord from blood plasma, the concentration in the latter being effectively kept near constant, was, at the end of 2 hr, greater when the fluid contained potassium, 0 m=‐equiv/l. rather than 10 m‐equiv/l. Thus the ratio, c.p.m per g brain/c.p.m. per ml. plasma was (0·99 ± 0·04 (+36%) as against 0·73 ± 0·05 for pons‐medulla where the difference was greatest.5. Simultaneous measurements of the entry of [14C]urea from blood to different regions of the central nervous system revealed no significant differences due to the differing concentrations of potassium imposed by either barbotage or subarachnoid perfusion. This appears to exclude a non‐specific cause for the changes in 42K uptake, an example of which might be a changing blood flow.6. Reasons are given for supposing that the big increase in 42K uptake due to the potassium‐free fluid must be due to events occurring at the blood—brain barrier. This might be some form of interaction, possibly the single file effect, such that a low potassium concentration in the interstitial fluid potentiates 42K influx across the blood—brain barrier. Alternatively it might be due to a low potassium concentration in this fluid greatly reducing active potassium movement from interstitial fluid to blood. The former explanation would conform neatly with the present results; but the latter would additionally be compatible with other evidence concerning the homoeostasis of potassium concentration in c.s.f. and the interstitial fluid of brain.
The effects of calcium and magnesium on sodium fluxes through gills of Carassius auratus, L
Authors: Cuthbert A. W. , Maetz J. 
Published: December 2014

1. Removal of calcium from Carassius either with chelating agents or by adaptation to deionized water increased sodium influx through the gills twofold.2. Treatment of fish with chelating agents increased sodium outflux, whereas adaptation to deionized water reduced sodium outflux. The effects on outflux do not appear to result from calcium removal.3. Addition of calcium (2–20 m
M) reversed the effects on influx of chelating agents and of adaptation to deionized water.4. Magnesium (2–10 m
M) was without significant effect on sodium influx, but increased the outflow in fish adapted to deionized water.
The dependence of plateau currents in cardiac Purkinje fibres on the interval between action potentials
Authors: Hauswirth O. , Noble D. , Tsien R. W. 
Published: December 2014

1. The influence of diastolic interval on ionic currents that may determine the action potential duration in cardiac Purkinje fibres was investigated. As the diastolic interval is shortened from about 5 sec, the first effect on the action potential is to reduce and then abolish the notch at the beginning of the plateau.2. This effect corresponds to the influence of diastolic interval on the magnitude of a transient outward chloride current known as the ‘dynamic current’.3. Further shortening of the diastolic interval produces a slight shortening of the action potential until intervals less than about 500 msec are used. The action potential then becomes considerably shorter. The ‘time constant’ of decay of this major influence of one action potential on the duration of the subsequent action potential is about 200 msec.4. This effect corresponds to the time course of decay of an outward (mainly K) current known as ix1.5. It is shown that variations in the magnitude of ix1 may be responsible for the alternation in action potential duration at the beginning of a train of stimuli known as ‘electrical alternans’.6. The results in general are consistent with the view that ix1 is the main current involved in determining the interval—duration relation although they cannot exclude the possibility that an inward current with a reavailability time course similar to the decay time course of ix1 might also be involved.
The frequency response of frog muscle spindles under various conditions
Authors: Kirkwood P. A. 
Published: December 2014

1. Nerve impulses were recorded from afferents from non‐contracting spindles from the isolated extensor longus dig. IV muscle of the frog during small sinusoidal changes in muscle length at frequencies from 0·001 to 100 Hz. A computer of average transients was used to average the spike distribution during a number of cycles, and hence to determine the spindle response in impulses/sec at different phases of the cycle.2. At any one frequency the response could be described by a sinusoid, whose amplitude was approximately proportional to the amplitude of the stretch and whose phase was approximately constant, together with a non‐linearity dependent principally upon non‐linearities in the static response.3. The frequency response was estimated from the sinusoid responses. In conventional terms, it consisted of a straight line of positive slope below 2 Hz and a maximum between 7 and 16 Hz.4. The slope of the frequency response was dependent on the mean length of the preparation, typically varying from zero to about 0·5 (3 db/octave) over the physiological range of the passive muscle. The shape of the peak appeared to depend on the mean firing frequency.5. The responses to ramp stretches of one second duration and up to 2 mm in amplitude were also measured. Responses predicted from the sinusoid measurements were the same shape as the measured responses, but were larger by a factor of about 1·4.6. The shapes of both the frequency responses and the responses to ramps were hardly affected by an operation that removed most of the polar parts of the spindles.7. The results are discussed in terms of internal spindle mechanisms.
The slowing of gastric emptying by four strong acids and three weak acids
Authors: Hunt J. N. , Knox M. T. 
Published: December 2014

1. Test meals of 750 ml. water containing a range of concentrations of hydrochloric, nitric, sulphuric, cyclamic (cyclohexylsulphamic), tartaric,
L‐ascorbic and citric acids were instilled into the stomachs of sixteen healthy subjects.2. The greater the concentration of an acid in the instilled meal, the greater was the volume of meal recovered after a fixed interval.3. For the weak acids, tartaric, ascorbic and citric, the concentrations which gave a recovery of 450 ml., out of the 750 ml. instilled, increased with increase in the molecular weight of the acid.4. For the strong acids, hydrochloric, nitric, sulphuric and cyclamic, the concentrations which gave a recovery of 450 ml., out of the 750 ml. instilled, were approximately equal. These concentrations were less than those for weak acids.5. The strong acids with high molecular weights were slightly more effective in slowing gastric emptying than were those with low molecular weights.6. The approximate equality of effectiveness of nitric, sulphuric and cyclamic acids to hydrochloric acid is attributed to the presence of chloride ion in the duodenal contents. Thus all the strong acids instilled produce an environment of hydrochloric acid around the receptor.7. A model for a duodenal receptor responding to acids is proposed.
The visual evoked potential as a function of contrast of a grating pattern
Authors: Campbell F. W. , Kulikowski J. J. 
Published: December 2014

1. It was shown that the potentials evoked by using a grating pattern alternated in phase at 8 Hz is proportional to the logarithm of the supra‐threshold contrast. Other functions were considered, but they did not describe the data so parsimoniously.2. The same logarithmic function described the results when a grating was simply flashed on and off; therefore, the apparent movement accompanying the phase alternations is not necessary to evoke the potential.3. The contrast at which the evoked potential reached the theoretically zero voltage (C0) was compared with the psychophysical contrast threshold, determined by means of proportion‐of‐time seen measurements; the C0 contrast corresponded to 50% time seen.4. The potential, corrected for the proportion‐of‐time seen, was found linearly related to contrast.
Quantitative investigations of the adhesiveness of circulating polymorphonuclear leucocytes to blood vessel walls
Authors: Atherton Anne , Born G. V. R. 
Published: December 2014

1. A new simple method is described for quantitating the adhesiveness of circulating polymorphonuclear leucocytes, or granulocytes, to the walls of blood vessels. The cheek pouch of anaesthetized hamsters or a small part of the mesentery of anaesthetized mice were prepared for continuous microscopic observation of selected venules. Those granulocytes which moved sufficiently slowly to be individually visible were counted for 1 or 2 min periods as they rolled past a selected point on one side of a vessel. The velocity distribution of these cells was determined by analysing films. Films were used also to measure mean blood flow velocity in the venules by observing embolizing platelet thrombi induced by the iontophoretic application of adenosine diphosphate. Emigration of granulocytes into the tissues was quantitated by enumerating them in standard areas of stained histological sections.2. In control experiments with hamster cheek pouch venules, the rolling granulocyte count usually passed through a maximum shortly after the preparation was set up and then fell to a low constant value. In mouse mesentery venules the count remained at a low approximately constant value from the beginning for at least 3 hr.3. The mean velocity of blood flow in the venules was between 900 and 200 μ/sec. All rolling granulocytes moved much more slowly; in hamster cheek pouch venules the mean velocity was about 20 μ/sec and in mouse mesentery venules about 10 μ/sec. Around these means the velocity distribution of individual cells was narrow.4. Rolling of granulocytes was abolished by superfusing ethylenediamine tetra‐acetate (EDTA, 0·1
M) suggesting that the phenomenon depends on calcium or magnesium ions.5. Agents were applied locally to the observed venules. Human serum albumin, trypsin or histamine in high concentrations did not affect the rolling granulocyte count.6. The rolling granulocyte count was increased during the application of Hammarsten casein or Escherichia coli culture filtrate which are chemotactic to granulocytes in vitro. These agents did not cause alterations in mean blood flow velocity in the observed venules which might have accounted for the effect on the rolling granulocyte counts. When E. coli culture filtrate was perfused through mouse intestine the increase in rolling granulocyte count in the draining venous blood was proportional to the logarithm of the concentration of filtrate.7. The rolling granulocyte count was also increased by the local application of plasma globulin permeability factor or lymph node permeability factor.8. Granulocyte counts in standard histological sections showed no significant increases in control preparations but considerable increases following the application of Hammarsten casein.
An electrophysiological demonstration of the axonal projections of single spinal interneurones in the cat
Authors: Jankowska Elżbieta , Roberts W. J. 
Published: December 2014

1. Single interneurones excited from group Ia afferents and located in the ventral horn of the spinal cord in the cat were activated antidromically by stimulation of their axons with one micro‐electrode while recording extracellularly close to their somas with a second micro‐electrode. The interneurones studied were those which, according to previous indirect evidence, should mediate the reciprocal Ia inhibition of motoneurones.2. Two subgroups of these interneurones were studied: those excited from group Ia afferents in the quadriceps (Q) and posterior bicepssemitendinosus (PBSt) nerves. Most of them could be activated from a number of separate loci in the PBSt and Q motor nuclei respectively and from the ventral or lateral funiculi.3. The location of the axonal branches and the extent of their branching in the motor nuclei were reconstructed by comparing the latencies of the responses and the thresholds (0·1–5 μA) for antidromic activation of single interneurones from different electrode positions in a number of tracks, having previously established the relation between the threshold and the distance from the stimulated fibres. For the main branches in the white matter the conduction velocity was found to be about 70 m/sec.4. The axonal projections of the investigated interneurones were found to be fully consistent with the hypothesis that they mediate reciprocal inhibition of motoneurones.
Inotropic responses of the left ventricle to changes in aortic arch pressure in anaesthetized dogs
Authors: Hainsworth R. , Karim F. 
Published: December 2014

1. Inotropic changes in the left ventricle in chloralose anaesthetized dogs were determined in response to changes in non‐pulsatile pressure perfusing the vascularly isolated aortic arch.2. Inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dt max) in preparations in which heart rate, mean ascending aortic pressure and brachiocephalic (i.e. carotid sinus and cerebral) perfusion pressure were held constant.3. dP/dt max increased (average +43%) when aortic pressure was reduced from a level above that which produced maximum depression of the myocardium to a level below which no further responses could be obtained; responses occurred as aortic arch pressure was changed between 250 and 90 mm Hg.5. In the same preparations changes in the brachiocephalic artery perfusion pressure with aortic arch pressure held constant resulted in similar inotropic responses.6. It is suggested that aortic arch baroreceptors may be of importance in the control of the inotropic state of the heart.
Ionic fluxes and permeabilities of cell membranes in rat liver
Authors: Claret M. , Mazet J. L. 
Published: December 2014

1. Intracellular ion concentrations, measured in rat liver perfused with saline solutions were, at steady state:[K]1 = 113; [Na]1 = 16·4; [Cl]1 = 25·5 m‐mole l.−1 of cells.2. Intracellular Cl concentration was measured when both [Cl]o and membrane potential were changed. The experimental values were close to the predicted ones by the Nernst equation, indicating a passive distribution of this ion across the cell membrane.3. Fluxes were determined by means of radioactive tracers and had the following values:mK = 6·6; mNa = 12·4 and mCl = 8 × 10−12 mole cm−2 sec−1.4. When Na was replaced by Li in the perfusing solutions, the Na efflux was decreased by 3·3 × 10−12 mole cm−2 sec−1. This was attributed to a Na‐for‐Na exchange (exchange‐diffusion).5. A mathematical model was applied to the perfused liver. It allowed estimation of the actual fluxes across the membrane. Corrections resulting from the application of the model remain small.6. The permeability coefficients were calculated from the passive fluxes and were:PK = 7·6; PNa = 4·0; PCl = 12·3 × 10−8 cm sec−1, corresponding to relative permeabilities of PNa/PK = 0·52 and PCl/PK = 1·6.7. The membrane potential calculated from the Goldman equation was significantly different from the measured one. This may be accounted for by an electrogenic activity of the Na—K pump. Applying the Mullins & Noda equation, the ratio of active Na flux to active K flux becomes 3/2.
Effects of sugar and amino acid transport on transepithelial fluxes of sodium and chloride of short circuited rat jejunum
Authors: Munck B. G. 
Published: December 2014

1. Using the Ussing Zerahn (1951) technique the relation between short circuit current (Isc) and unidirectional ion fluxes across the short circuited rat jejunum has been examined.2. These parameters of jejunal function have been measured in absence of sugars and amino acids and at 10 m
M glucose, 28 m
M glucose, 28 m
M galactose and 20 m
M proline. Sulphate has been used as substituent for chloride on both sides of the gut wall and potassium has been used on the serosal side to substitute for sodium. With regard to the effects of proline on Isc and ion fluxes, investigations were made to see whether sulphate and potassium substitutions significantly affected proline transport.3. The purpose of the study was to examine the Isc seen in sugars and amino acid free conditions and the Δ Isc induced by these substances. Further, it was our purpose to examine the validity of extending to amino acids and sugars in general the suggestion that jejunal transport of these substances stimulates an electroneutral secretion of sodium chloride.4. In the absence of sugars and amino acids at least two‐thirds of an Isc of 50–70 μA/cm2 are accounted for by a process of chloride secretion located in the deep parts of the epithelium. The remaining one third or less of the Isc can be accounted for in terms of net flux of sodium. The results further indicate that a state of hypoxia in the deep part of the epithelium is the cause of the very low Isc, p.d. on electrical resistance usually found for sacs of everted rat jejunum.5. The increase in Isc induced by proline and glucose is best accounted for by the simultaneously induced increase in mucosa to serosa flux of sodium. There is no compelling evidence that proline should increase Isc by a stimulation of chloride secretion.6. Proline, glucose (and galactose) stimulate unidirectional fluxes of sodium and chloride. The effects on serosa to mucosa fluxes equal or exceed those on mucosa to serosa fluxes. The effect of proline on mucosa to serosa flux of thiourea exceeds by far that on serosa to mucosa flux. This and the effects of potassium and sulphate substitution lead to the conclusions in (7) and (8).7. Transport of sugars and amino acids induces or stimulates in rat jejunum in vitro an electroneutral secretion of sodium chloride.8. This effect suffices to explain why, in spite of marked increases in Isc, increments in net flux of sodium are not induced by transport of proline and glucose. It also explains why the effects of sugar and amino acid transport on water transport in vitro are much less than in vivo.
The uptake and hydrolysis of p‐nitrophenyl phosphate by red cells in relation to ATP hydrolysis by the sodium pump
Authors: Cotterrell D. , Whittam R. 
Published: December 2014

1. The hydrolysis of p‐nitrophenyl phosphate has been studied in human red cells, ghosts and haemoglobin‐free membranes to see whether hydrolysis was related to the functioning of the sodium pump.2. The cell membrane restricted p‐nitrophenyl phosphate entry into cells and was rate‐limiting for hydrolysis by the large amount of intracellular soluble phosphatase. The uptake was inversely proportional to the external chloride concentration, and inhibitors (phloretin and persantin) of inorganic phosphate uptake also reduced p‐nitrophenyl phosphate uptake and hydrolysis. The entry mechanism of p‐nitrophenyl phosphate appears to be similar to that of inorganic phosphate.3. p‐Nitrophenyl phosphate was hydrolysed in cells almost entirely by ouabain‐insensitive phosphatases, both soluble and membrane bound. In ghosts containing less soluble enzyme than cells there was still no component of p‐nitrophenyl phosphate hydrolysis that was related to the sodium pump in being sensitive to external potassium or ouabain.4. Haemoglobin‐free membranes lacking soluble p‐nitrophenyl phosphatase required potassium for optimum p‐nitrophenyl phosphate hydrolysis and this part was inhibited by ouabain as was also ATP hydrolysis by the sodium pump. The rates of potassium‐dependent and potassium‐independent hydrolysis were each increased about threefold on decreasing the electrolyte concentration from 150 to 25 m
M. The response was found whether the main electrolyte was potassium chloride, sodium chloride, choline chloride or Tris chloride. In contrast, the changes were not found when the osmotic pressure was varied to the same extent with non‐electrolytes. p‐Nitrophenyl phosphate hydrolysis was thus activated on lowering the ionic strength. The soluble enzyme was similarly affected and the effect was reversible.5. The membrane ATPase activity was unaffected by the changes in ionic strength which markedly altered p‐nitrophenyl phosphate hydrolysis.6. These results with red cell membranes show that the ionic strength under physiological conditions largely prevents the hydrolysis of p‐nitrophenyl phosphate, but not of ATP. A possible mechanism is discussed in terms of the effect of different structures of water in electrolyte and non‐electrolyte solutions on the enzymic activity of the sodium pump.
Mechanical response with reversed electrical response to noradrenaline by Ca‐deprived arterial smooth muscle
Authors: Keatinge W. R. 
Published: December 2014

1. When sheep carotid arteries had become electrically active after 30 min in Ca‐free saline, noradrenaline 0·1 m
M caused almost as much contraction as it did with Ca 1·25 m
M present; it also caused slight electrical depolarization, usually with increased spike frequency, followed by electrical quiescence.2. In Ca‐free saline with EDTA the arteries became profoundly depolarized, and their mechanical responses greatly reduced, within a few minutes. The mechanical responses to noradrenaline that remained were accompanied by electrical repolarization or, after longer periods in EDTA, by no electrical change.3. This residual mechanical responsiveness to noradrenaline, always tested at 36° C, declined on average 26 times as rapidly during exposure to EDTA at 36° C as at 5° C and was not reduced by increasing the concentration of EDTA from 1·25 to 12·5 m
M. This temperature‐sensitivity was significantly too high to be explained by a diffusion‐limited process.4. The results suggest that most of the tissue Ca responsible for contractility in simple Ca‐free saline was either free in the extracellular space or in cellular stores that were discharged within a few minutes when free extracellular Ca was removed. They also indicate a small resistant Ca store which did not communicate with the exterior by diffusion, and part of which noradrenaline could utilize for contraction by means not dependent on depolarization conducted from the cell membrane.