bluuebunny/crossref_metadata_2025 huggingface dataset:
Tension changes during and after stretch in frog muscle fibres
Authors: Sugi H.
Published: December 2014

1. Small fibre bundles from the semitendinosus muscles of the frog were stretched during tetanic stimulation, and the resulting tension changes were studied over a wide range of stretch velocities from 0·1 to 150 cm/sec (0·1–100 length/sec). The experiments were performed within the range of fibre lengths where the resting tension was negligible.

2. With stretch velocities of more than 30 cm/sec (20 length/sec), the tension rose abruptly at first, and then started to fall while the stretch still continued, indicating the ‘slip’ of the contractile component. When the fibres were stretched at 80–150 cm/sec (70–100 length/sec), the tension fell quickly below the initial isometric level at the end of the stretch, and then began to rise again to the initial isometric value.

3. Following stretches of 30–60 cm/sec (20–50 length/sec), the tension showed a delayed transient rise. The delayed rise of tension became more marked as the amount of stretch was increased.

4. In some preparations, oscillatory tension changes were observed following stretches of 50–100 cm/sec (40–70 length/sec).

5. The tension developed above the isometric level during moderate‐velocity stretches of less than 15 cm/sec (10 length/sec) increased by lowering temperature, and showed a tendency to decay when the stretch velocity was suddenly reduced during a stretch.

6. These results are discussed in relation to the sliding filament hypothesis, which provides an explanation for the findings of the present work.
Injections of calcium ions into spinal motoneurones
Authors: Krnjević K. , Lisiewicz A.
Published: December 2014

1. In cats under Dial anaesthesia, Ca2+ was injected inside lumbosacral motoneurones, by passing currents between CaCl2‐ and KCl‐containing barrels of compound micropipettes.

2. There was a reduction in excitability and a fall in membrane resistance, both rapid in onset and quickly reversible.

3. The minimum effective injection current was ≈ 10 nA, and the effect reached a maximum with currents of ≈ 30 nA. The mean slope of resistance change against injection current was −1·7%/nA (
S.E. 0·35).

4. The most common change in membrane potential was a hyperpolarization; but in nearly half the cases, there was no clear change or a small depolarization. A reversal level for the effect of Ca2+ could be measured in five cells: on the average, it was 10 mV more negative than the resting potential.

5. Observations on i.p.s.p.s showed that Ca2+ probably does not alter gCl: it was concluded that the fall in membrane resistance caused by intracellular Ca2+ is mainly due to an increase in gK.

6. These results confirm previous suggestions that a steep transmembrane gradient of Ca2+ is essential for the maintenance of a low membrane conductivity, and that a rise in internal free Ca2+ — whether due to influx or release from internal stores — may play an important role in regulating neuronal activity.
Evidence for disparity detecting neurones in the human visual system
Authors: Blakemore Colin , Hague Brian
Published: December 2014

1. It is known that adaptation to a grating pattern causes a rise in the contrast threshold for test gratings of similar spatial frequency and orientation.

2. We find this after‐effect also to be disparity‐specific. Adaptation to a grating at zero horizontal disparity (at the same distance as the fixation point) causes a greater elevation of threshold for patterns at the same disparity than for those at nearby disparities, closer or more distant than the fixation point.

3. Adaptation to a grating at some disparity other than zero causes a disparity‐specific elevation of threshold centred on the adapting disparity.

4. This finding also applies if the observer adapts to a grating but single bright bars are used as the test stimuli.

5. The disparity‐specific ‘tuning curves’ revealed by these techniques are quite broad, having a half‐width at half‐amplitude of several min of disparity.

6. Adaptation to a grating at one disparity causes an apparent change in the distance of test gratings at nearby disparities.

7. We compare these psychophysical experiments with the properties of disparity‐selective binocular neurones in the visual cortex of cats and monkeys.
Cardiovascular and respiratory responses to changes in central command during isometric exercise at constant muscle tension
Authors: Goodwin G. M. , McCloskey D. I. , Mitchell J. H.
Published: December 2014

1. Experiments were designed to show whether elements of the command descending from higher centres to exercising muscles provide an input for cardiovascular and respiratory control. Vibration, known to be a powerful stimulus to the primary afferents from muscle spindles, was applied to the biceps tendon of human subjects performing sustained isometric contractions with the biceps or the triceps muscle. When the biceps was contracting this activation of muscle spindle primary afferents in it provided an element of reflex excitation, so that less central command was required to achieve a given tension. When triceps was contracting, the activation of muscle spindle primary afferents in its antagonist, biceps, contributed an element of reflex inhibition, so that more central command than normally was required to achieve a given tension. The cardiovascular and respiratory responses to an isometric effort could thus be investigated at any tension when the central command was normal, decreased, or increased.

2. Blood pressure, heart rate, and pulmonary ventilation all increase in an isometric effort. The increase in each is less when the central command is reduced. The increase in each is greater when the central command is increased.

3. It is concluded that there is irradiation of cardiovascular and respiratory control centres by the descending central command during voluntary muscular contractions in man.
Metabolism and transfer of choline in hamster small intestine
Authors: Flower R. J. , Pollitt R. J. , Sanford P. A. , Smyth D. H.
Published: December 2014

1. The transfer and metabolism of choline was studied with sacs of everted intestine of hamster.

2. Approximately half the choline transferred from the mucosal fluid may be metabolized. High voltage electrophoresis, paper chromatography and ion exchange chromatography have been used to identify this meta bolite as betaine.

3. The concentration of choline and betaine together accumulating in the gut wall and serosal fluid are greater than that of choline present initially in the mucosal fluid indicating some kind of specific mechanism for choline transport.

4. A detailed analysis of choline transfer suggests that the movement of choline cannot be accounted for by simple diffusion. The concentration of choline accumulating in the gut wall and serosal fluid, the inhibitory effects of hemicholinium‐3 and α‐methylglucoside on choline transfer, and the insensitivity of betaine transfer to hemicholinium‐3 suggest a specific active transport process for choline independent of active betaine transport.
The relation of Rushton's ‘liminal length’ for excitation to the resting and active conductances of excitable cells
Authors: Noble D.
Published: December 2014

1. The minimum (or liminal) length of an excitable cable that must lie above the inward current threshold in order to initiate propagation is derived using a simple polynomial representation of the ionic current—voltage relation.

2. This model is then used to obtain an approximate equation for the liminal length that may easily be applied to excitable cells using experimental measurements of the ionic current.

3. The equations are used to show that the liminal length in cardiac Purkinje fibres is expected to be much smaller than in squid nerve. The values calculated are similar to those obtained by Fozzard & Schoenberg (1972) from strength—duration curves.

4. It is shown that the strength—duration curve for non‐uniform excitation is virtually independent of the resting membrane resistance. The strength—duration time constant may not, therefore, be related to the membrane time constant.
Strength—duration curves in cardiac Purkinje fibres: effects of liminal length and charge distribution
Authors: Fozzard H. A. , Schoenberg Mark
Published: December 2014

1. Strength—duration curves for excitation in long point‐stimulated sheep cardiac Purkinje fibres, where the charge distribution varies along the length of the fibre, are characterized by (a) a time constant which is short relative to the membrane time constant, (b) an apparent fall in charge threshold for short duration stimuli, (c) an apparent rise in voltage threshold as measured by an electrode at the point of current passage (see Dominguez & Fozzard, 1970).

2. Strength—duration curves obtained from shortened segments of Purkinje fibres, where the charge distribution along the segment is fairly uniform after 2–3 msec, have much larger time constants.

3. For stimulus durations longer than the 2–3 msec necessary to establish charge uniformity, strength—duration curves obtained from shortened segments of Purkinje fibres were well fitted by the Lapicque—Hill equation, I/Irh = [1 — exp (—t/τ)]−1.

4. The differences in the time constants and apparent voltage thresholds for point‐stimulated long fibres and uniformly charged short fibre segments could be explained by the liminal length concept of Rushton (1937). The liminal length concept, in its simplest form, states that a liminal length of fibre must be raised above a given voltage threshold in order for a propagated action potential to be generated.

5. This concept predicts that the shorter the liminal length, the shorter the time constant of strength—duration curves in point‐stimulated long fibres.

6. Another conclusion of the model is that only those point‐stimulated long fibres with longer liminal lengths would have a constant charge threshold for stimuli of the order of 0·2 τ.

7. Liminal length was found by experiment and calculation to be about 0·1–0·2 λm in cardiac Purkinje fibres.

8. The differences in behaviour with regards to excitation between the point‐stimulated theoretical squid axon and the point‐stimulated Purkinje fibre may be explained by assuming that the liminal length of the theoretical squid axon is several times larger than that of the Purkinje fibre.
Further evidence for a potassium‐like action of lithium ions on sodium efflux in frog skeletal muscle
Authors: Beaugé L. A. , Ortiz Olga
Published: December 2014

1. The efflux of labelled sodium as well as net sodium and lithium changes were studied in aged high sodium sartorius muscles of the South American frog Leptodactilus ocelatus.

2. In the presence of 2·5 m
M potassium in the media, the replacement of external sodium with lithium or magnesium resulted in an increase in sodium efflux. The magnitude of such increase was always larger in lithium.

3. With the absence of potassium in the media, the response of sodium efflux to replacement of external sodium varied with the cation used as a substitute. In lithium Ringer there was always a noticeable increase, whereas in magnesium there was always a marked reduction. The same results were observed when calcium was substituted for magnesium.

4. The replacement of 60 m
M external sodium with sucrose did not prevent the stimulating effect of 5 m
M potassium on sodium efflux, nor the inhibitory action of 10−4
M ouabain. This indicates that neither sucrose by itself, nor the lowering of the ionic strength, modified to an appreciable extent the function of the sodium pump.

5. Net sodium extrusion took place against an electrochemical gradient in potassium‐free — 50 m
M sodium — m
M lithium Ringer. About 75% of this efflux was ouabain sensitive.

6. Muscles made both sodium and lithium rich and incubated in potassium‐free — 60 m
M sodium — 50 m
M lithium Ringer also showed net sodium extrusion against an electrochemical gradient, which was 85% ouabain sensitive. This extrusion took place even under conditions where the changes in free energy favouring lithium entry were always lower than the changes in free energy opposing sodium going out. This indicates that a sodium‐lithium exchange by a counter‐transport process is unlikely.

7. External potassium reduced the ouabain sensitive lithium influx in muscles incubated in lithium Ringer. The values found were 5·90 ± 0·39 μ‐mole/g.hr and 2·66 ± 0·43 μmole/g.hr in potassium‐free and 15 m
M potassium respectively. At the same time potassium had no effect on the ouabain‐insensitive lithium uptake.

8. Muscles incubated in potassium‐free‐magnesium Ringer had a residual sodium efflux which could not be accounted for by passive movement. About 40% of it was abolished by 10−4
M ouabain. This ouabain‐sensitive part could be a consequence of some stimulation of the sodium pump by potassium leaking out of the cells. If this is correct it should be inhibited by external sodium and should not contribute to the total sodium efflux in potassium‐free sodium media.

9. Magnesium was used as the reference cation to study the sodium‐stimulated sodium efflux under potassium‐free conditions. The total sodium efflux amounted to 0·668 hr−1 (rate constant) and was 71% ouabain sensitive.

10. The present experiments demonstrated that lithium ions have a direct stimulating effect on sodium efflux in high sodium skeletal muscle, and strongly support the notion that this effect is produced by an activation of the sodium pump through a potassium‐like action.
A computer simulation of conduction in demyelinated nerve fibres
Authors: Koles Z. J. , Rasminsky M.
Published: December 2014

1. The theoretical effects of demyelination on conduction of a propagated impulse have been examined in a computer simulated myelinated nerve fibre. Demyelination was simulated by increasing the capacitance and conductance of the myelin sheath of individual internodes or parts of internodes.

2. Internodal conduction time increased as myelin thickness was decreased. The increase in internodal conduction time became more precipitous as the myelin became thinner. Propagation continued past a single demyelinated internode until myelin thickness was uniformly reduced to less than 2·7% of normal myelin thickness.

3. Paranodal demyelination was more effective in slowing impulse conduction than was uniform demyelination of an entire internode with an equivalent rise in overall internodal capacitance and conductance.

4. The effects on conduction of demyelination of two adjacent internodes or of two internodes separated by a normal internode were more than the sum of the effects of demyelination of each internode individually.

5. Propagation across a severely demyelinated internode was blocked with an increase in internal sodium concentration which had a trivial effect on conduction in a normal fibre.

6. Propagation across a severely demyelinated internode was blocked with increased temperature at a temperature at which propagation proceeds normally across normal internodes.

7. The similarity between the findings of the computer simulations and the experimental findings in demyelinated fibres is discussed.
Changes in regional blood flow and cardiodynamics evoked by electrical stimulation of the fastigial nucleus in the cat and their similarity to orthostatic reflexes
Authors: Doba Nobutaka , Reis Donald J.
Published: December 2014

1. Changes in regional blood flow and cardiodynamics were measured in anaesthetized paralysed cats during electrical stimulation of the rostral fastigial nucleus.

2. Fastigial stimulation results in a graded, highly reproducible and stereotyped cardiovascular response characterized by (a) increased systolic, diastolic and mean arterial pressures without changes in central venous or occluded vein pressure, (b) decreased blood flow and increased vascular resistance in the axillary, renal, femoral and mesenteric arteries, increased flow without any change in vascular resistance in the common carotid artery, and increase in total peripheral resistance, (c) a small increase in heart rate and myocardial contractile force, decrease in calculated stroke volume, and no change in the cardiac output.

3. Changes in regional arterial flow were abolished by transection of sympathetic nerves or blockade of α‐adrenergic receptors by systemic administration of phentolamine.

4. Changes in heart rate and myocardial contractility were abolished by stellate ganglionectomy or blockade of β‐adrenergic receptors by propranolol.

5. No changes in pupillary diameter or retraction of the nictitating membrane were seen during fastigial stimulation with stimuli producing substantial changes in blood pressure.

6. The fastigial pressor response represents a highly reproducible, stereotyped, graded, and differentiated pattern of activation of sympathetic preganglionic neurones.

7. The pattern of cardiovascular effects of fastigial stimulation simulates the compensatory (orthostatic) reflex response to maintenance of an upright posture.

8. Fastigial stimulation appears to excite the neural network subserving orthostatic reflexes.
Pyrogen fever and prostaglandin‐like activity in cerebrospinal fluid
Authors: Feldberg W. , Gupta K. P.
Published: December 2014

1. In the unanaesthetized cat, rectal temperature was recorded and c.s.f. was collected from a Collison cannula implanted into the third ventricle with its opening lying in close proximity to the anterior hypothalamus. Samples of c.s.f. were collected from the same cat, during normal temperature, during fever produced by Shigella dysenteriae injected into the third ventricle and during the fall in temperature which occurred when the antipyretic paracetamol was injected intraperitoneally during the pyrogen fever.

2. The samples of c.s.f., when tested on the rat stomach fundus preparation, caused contractions which were not due, or at most to a small degree only, to 5‐hydroxytryptamine, as they were resistant to BOL. They were therefore probably due to a prostaglandin‐like substance.

3. When assayed against PGE1, the activity of c.s.f. collected from cats when their body temperature was normal corresponded to between 1·3 and 10 ng/ml. The values, whether low or high, rose over 2·5‐4 times to between 4 and 35 ng/ml. in c.s.f. collected during pyrogen fever; they were again low, between 1·5 and 6 ng/ml., in samples collected when the fever had been brought down by paracetamol, but rose again with the return of fever.

4. The results provide direct evidence for the theory that fever produced by pyrogens results from their ability to increase synthesis and release of prostaglandins, and that antipyretics bring down the fever because they inhibit the increased synthesis.
Sodium uptake by frog skin and its modification by inhibitors of transepithelial sodium transport
Authors: Erlij D. , Smith M. W.
Published: December 2014

1. The suitability of inulin and mannitol as markers of the diffusional space that exists between the surface of frog skin and the outer barrier to sodium transport has been compared in experiments designed to measure the rapid uptake of sodium.

2. Inulin and mannitol both equilibrate finally with the same space at the outer surface of the frog skin, but the rate at which this equilibration occurs is considerably faster for mannitol.

3. The dependence of the rapid uptake of sodium on the concentration of sodium in the external medium, using mannitol to correct for extracellular sodium, can be described by simple saturation kinetics with an apparent Km for sodium entry of 24 mM and a maximal rate of uptake of 1·28 μequiv/cm2. hr.

4. The effect of amiloride is to inhibit sodium uptake, the degree of inhibition depending both on the concentration of sodium in the external medium and on the level of transepithelial transport normally maintained by the skin.

5. Ouabain inhibits sodium uptake when the tissue has been pre‐incubated in sodium containing medium. It has no effect on sodium uptake if the pre‐incubation takes place in sodium free medium.

6. A short‐circuit current and potential difference can be elicited across frog skin in the presence of ouabain, by increasing the concentration of sodium bathing the outside surface. This potential and short‐circuit current is abolished by the presence of amiloride.

7. These results provide direct evidence that amiloride acts to stop entry of sodium into the transport compartment and suggest that the ouabain inhibition of sodium uptake is mediated primarily through an increase of epithelial sodium concentration.
Sensory inputs to neurones in Clarke's column from muscle, cutaneous and joint receptors
Authors: Kuno M. , Muñoz‐Martinez E. J. , Randić Mirjana
Published: December 2014

1. Discharge of neurones at the region of Clarke's column of the cat was recorded intracellularly or extracellularly in response to electrical stimulation of various hind limb nerves or to adequate stimuli applied to a variety of sensory receptors.

2. According to the type of excitatory sensory input, the neurones were classified into four groups. Their relative proportions were: muscle group, 55–65%; cutaneous group, 15–25%; joint group, 5–15%; convergent group, 10–20%.

3. The location of the neurone cell bodies was examined by marking the site of extracellular recording with fast green. The neurones of the muscle or cutaneous group were found to be within Clarke's column. One out of four neurones tested for the joint group and two out of six cells examined for the convergent group were found to be located outside the column.

4. There was no difference in axonal conduction velocity among the neurones of different groups.

5. The neurones of different groups could be distinguished in terms of the pattern of discharges recorded under ‘resting’ conditions and during activation of sensory receptors. It is suggested that information carried by dorsal spinocerebellar tract neurones to the cerebellum has a lower signal‐to‐noise ratio for cutaneous inputs than for muscle or joint inputs.
Synaptic action on Clarke's column neurones in relation to afferent terminal size
Authors: Kuno M. , Muñoz‐Martinez E. J. , Randić Mirjana
Published: December 2014

1. Excitatory post‐synaptic potentials (e.p.s.p.s) were recorded intracellularly from Clarke's column neurones (DSCT neurones) of the cat in response to adequate stimuli applied to a variety of sensory receptors.

2. The amplitude of e.p.s.p.s so produced varied from less than 0·2 mV to more than 2–3 mV. The amplitude distribution of e.p.s.p.s suggested that the mean number of ‘quanta’ of transmitter released by one impulse varied widely from one fibre to another arising from a given type of sensory receptor.

3. The average amplitude of e.p.s.p.s evoked by single afferent impulses was significantly smaller for cutaneous inputs than for muscle or joint inputs. However, synaptic action on DSCT neurones produced by different sensory inputs was equally greater, on the average, than that on spinal motoneurones.

4. Both small and large e.p.s.p.s in DSCT neurones failed to increase in amplitude during post‐synaptic hyperpolarization applied through the cell body. This failure could not be attributed to possible anomalous rectification in the post‐synaptic membrane.

5. Small and large e.p.s.p.s were comparable in half‐decay time, but there was a positive correlation between amplitude and time‐to‐peak of e.p.s.p.s. It is suggested that the locations of synapses responsible for small and large e.p.s.p.s are intermingled on the dendrites and that large e.p.s.p.s are associated with a longer duration of transmitter action than small e.p.s.p.s.

6. Degenerating terminals of primary afferent fibres on DSCT neurones and motoneurones were examined with the electron microscope after chronic section of the dorsal roots.

7. Dendritic degenerating terminals showed no significant difference in size between motoneurones and DSCT neurones. Degenerating ‘giant’ terminals were found on DSCT neurones, but they were located only on or very close to the cell body.

8. It is concluded that the major factor responsible for a large number of ‘quanta’ of transmitter released at synapses on DSCT neurones is the number of multiple synaptic contacts formed by one afferent fibre rather than the size of individual synapses.
The calcium pump of cardiac sarcoplasmic reticulum. Functional alterations at different levels of thyroid state in rabbits
Authors: Suko J.
Published: December 2014

1. Cardiac sarcoplasmic reticulum (SR) was prepared by differential centrifugation from euthyroid, hyperthyroid, hypothyroid as well as 131I‐treated plus thyroxine‐substituted rabbits. The function of the isolated SR has been characterized by measuring the ATP‐dependent calcium uptake, the calcium storing capacity, the calcium concentrating ability and the calcium‐dependent ATP hydrolysis by the calcium‐activated ATPase in the presence of oxalate.

2. The rate of calcium uptake and the rate of the calcium‐dependent ATP hydrolysis (calcium‐activated ATPase) by the SR were significantly increased in hyperthyroidism, whilst both activities were markedly reduced in hypothyroidism. Thyroxine administration to 131I‐treated animals prevented a decrease in the rate of calcium uptake as well as in the rate of the calcium‐dependent ATP hydrolysis by the calcium‐activated ATPase.

3. The transport ratio (rate of calcium uptake divided by the rate of calcium‐dependent ATP hydrolysis) of SR preparations from euthyroid controls was 0·93, suggesting a stoicheiometry of calcium uptake and calcium‐activated ATP split of 1·0. The transport ratio was unchanged in one hyper‐ and hypothyroid group, whilst a small but significant decrease or increase was observed after an excessive thyroxine treatment of a prolonged state of hypothyroidism, respectively.

4. The saturation kinetics of calcium transport by the SR were described by Michaelis—Menten kinetics. The maximum rate of calcium uptake (V) was 0·193±0·004, 0·223±0·002 and 0·124±0·003 μmole Ca2+/mg protein. min (means ±S.E.) for euthyroid, hyperthyroid and hypothyroid SR, respectively. The Michaelis constants (Km) were (2·87±0·30) × 10−7
M (2·68±0·15) × 10−7
M and (4·00±0·48) × 10−7
M for the euthyroid, hyperthyroid and hypothyroid SR, respectively (means ±S.E.). The Km values for the hyper‐ and hypothyroid SR were not significantly different from controls.

5. The calcium storing capacity as well as the calcium concentrating ability of the SR was unaltered at different levels of thyroid activity.

6. The steady‐state level of calcium was the same for SR isolated from euthyroid, hyperthyroid and hypothyroid rabbits, indicating that calcium influx and calcium efflux are strongly coupled at steady‐state filling of the SR.

7. It is suggested that the increased or reduced rate of calcium transport by the SR in hyperthyroidism or hypothyroidism, respectively, found in vitro, might be at least partially responsible for the shortening of the relaxation time of cardiac muscle in the hyperthyroid state and the prolongation of the relaxation time in the hypothyroid state observed in vitro and in vivo.
Periodic vernier acuity
Authors: Tyler C. William
Published: December 2014

1. Sinusoidal curvature was produced in a vertical stimulus line generated on an oscilloscope screen. Sensitivity to sinusoidal curvature (periodic vernier acuity) was measured by the method of adjustment as a function of spatial frequency of the curvature.

2. Sensitivity was maximal at about 3 c/deg and reduced steeply for both higher and lower spatial frequencies of curvature.

3. Sensitivity at 10° in the periphery was greatly reduced but showed very little low frequency reduction.

4. The effect of number of cycles present was checked by reduction of the field size with spatial frequency such that a fixed number of cycles of the stimulus were visible. This procedure did not affect the decline in sensitivity at spatial frequencies below 0·3 c/deg but reduced sensitivity at higher spatial frequencies.

5. The results were interpreted in terms of cortical orientation detectors. It is suggested that the low frequency sensitivity is limited by a fixed value for the maximum difference in orientation in the stimulus (i.e. 20 and 30′ for the present subjects). The high frequency sensitivity was limited by grating acuity and required spatial integration of the stimulus information over about 2·5°.
An upper limit to the number of sodium channels in frog skin epithelium
Authors: Cuthbert A. W.
Published: December 2014

1. Binding of [14C]amiloride to the mucosal surface of frog skin epithelium has been measured in the presence and absence of an excess of unlabelled amiloride. Simultaneous records were obtained of the sodium transport through the skin as indicated by the short circuit current.

2. The number of binding sites with affinities for amiloride of 5 × 107 l./mole was around 400/μm2.

3. The relation between the binding sites and sodium channels is discussed.

4. Making certain assumptions it is concluded that when frog skin epithelium is bathed in Ringer solution each sodium channel can handle 8000 sodium ions/sec.
Effects of noradrenaline and isoprenaline, in combination with α‐ and β‐receptor blocking substances, on the action potential of cardiac Purkinje fibres
Authors: Giotti A. , Ledda F. , Mannaioni P. F.
Published: December 2014

1. The effects of noradrenaline and isoprenaline on the repolarization phase of the action potential have been studied in the Purkinje fibres of sheep heart, electrically driven at constant rates.

2. Isoprenaline (2, 5 and 8 × 10−8 g/ml.) increases the slope of phase 2 of repolarization and decreases the plateau length; the resulting decrease in action potential duration is concentration dependent, but not rate dependent.

3. The effect of isoprenaline on the action potential duration is entirely blocked by propranolol (10−7 g/ml.) and unaffected by phentolamine (5 × 10−7 g/ml.).

4. In phentolamine (5 × 10−7 g/ml.) pretreated preparations the response induced by noradrenaline (5 × 10−8, 1 and 5 × 10−7 g/ml.) is very similar to that induced by isoprenaline.

5. In propranolol (2·5 × 10−7 g/ml.) pretreated preparations noradrenaline causes a lengthening of the plateau phase and an increase in action potential duration.

6. The relationship of these results to the presence of both α‐ and β‐receptors in cardiac Purkinje fibres is discussed.
The measurement of dog gastric mucosal blood flow by radioactive aniline clearance compared with amidopyrine clearance
Authors: Curwain B. P. , Holton Pamela
Published: December 2014

1. Methods for the estimation of radioactive aniline in body fluids are described. The recovery of aniline added to blood, plasma and gastric juice was over 90% of the recovery from saline.

2. In the doses used aniline caused methaemoglobinaemia of 5–11% of total haemoglobin. No other effect was detected. Gastric secretion was also unaffected.

3. Aniline clearance increased in parallel with acid secretion from Heidenhain pouches in conscious dogs and in anaesthetized dogs. In conscious dogs the ratio of aniline clearance to acid secretion was significantly higher for histamine stimulation than for pentagastrin stimulation.

4. Aniline and amidopyrine clearances were compared simultaneously in the same dogs. Aniline clearance was about 80% of amidopyrine clearance.

5. The proportion of aniline bound to plasma proteins was measured by two methods and found to be 25%. When aniline clearance was corrected for plasma binding, aniline and amidopyrine clearances were equal.
An electrophysiological analysis of the storage and release of noradrenaline at sympathetic nerve terminals
Authors: Bennett M. R.
Published: December 2014

1. An electrophysiological analysis has been made of the storage and release of noradrenaline (NAd) in the sympathetic nerve terminals of the isolated vas deferens of the mouse. The amplitude of the excitatory junction potentials (e.j.p.s) recorded intracellularly in smooth muscle cells was taken as a measure of the NAd output per impulse from the terminals of sympathetic axons.

2. During short trains of impulses (< 100), the amplitude of the e.j.p. increased with successive impulses at the beginning of a train, and then either continued to increase until a steady‐state amplitude was reached (frequencies < 1 Hz), or decreased until a depressed steady amplitude was reached (frequencies > 1 Hz).

3. During trains of impulses lasting for several minutes, the amplitude of the e.j.p. continually declined (frequencies > 1 Hz) until a steady‐state amplitude was reached after 8 min of stimulation. This steady‐state amplitude is smaller, the higher the frequency of stimulation.

4. During short trains of impulses in the presence of high magnesium solutions, the amplitude of successive e.j.p.s increased until a steady state was reached, no matter what the frequency of stimulation. This growth of the e.j.p. amplitude during a train could be quantitatively predicted in terms of the linear summation of the individual facilitatory effects introduced by each impulse in the train.

5. During trains of impulses lasting for several minutes, in the presence of a NAd synthesis blocker, the amplitude of the e.j.p. continually declined along a curve which could be described as the sum of two exponential components: one with a time constant of 1 min and the other of 10 min.

6. These results suggest that NAd is released from a small pool of transmitter in sympathetic nerve terminals, which is replenished from two stores, which are in turn replenished by the synthesis of new NAd.
Metabolism and the electrical activity of anoxic ventricular muscle
Authors: McDonald Terence F. , MacLeod Don P.
Published: December 2014

1. The action potential duration of anoxic guinea‐pig ventricular muscle was related to ATP generated by glycolysis. In 50 mM glucose medium the action potential duration was maintained; in 5 mM glucose medium the action potential duration shortened, the glycolytic rate declined and the ATP content was reduced.

2. The action potential amplitude was related to the metabolic state of the muscle but not to the intracellular sodium concentration.

3. It is suggested that changes in the action potential duration and overshoot in anoxic muscle may be due to an influence of metabolism on the slow inward current.

4. Anoxic muscle incubated for 8 hr in 5 mM glucose medium had an Em of −77·1 mV compared to −81·1 mV in fresh muscle. The calculated Ek of anoxic muscle was −47·4 mV.

5. The resting potential of anoxic muscle was separated into two components, one dependent on potassium distribution and the other on the activity of an electrogenic sodium pump.

6. The electrogenic pump component was stimulated upon raising the glucose concentration of the medium or upon raising the external potassium concentration.

7. The electrogenic pump component was inhibited by ouabain or by reduction of the temperature from 35 to 8° C.
Ionic transport and membrane potential of rat liver cells in normal and low‐chloride solutions
Authors: Claret Brigitte , Claret M. , Mazet J. L.
Published: December 2014

1. The ouabain‐sensitive component of Na efflux and K influx amount to 58 and 72% respectively. Taking into account also (a) the diffusional passive fluxes of Na (5%) and K (13%), as estimated by Ussing's equation and (b) the ouabain‐insensitive Na‐Na exchange (28%), 85% (K) and 90% (Na) of the measured total fluxes can be accounted for.

2. Na efflux is diminished when K is partially or totally removed from the medium. This effect is reversible, indicating probably activation of the Na pump by external K.

3. The coupling ratio of Na and K ouabain‐sensitive fluxes is equal to 1·58, suggesting that three Na ions are removed from and two K ions are carried into the cell in one cycle of the pump. Hence, in liver cell membranes, the Na pump must be electrogenic.

4. A tenfold decrease in [Cl]o by substitution with an impermeant anion results in a membrane hyperpolarization and a decrease in [Cl]i. Cl loss from the liver is compensated by an equivalent loss of intracellular K to preserve electroneutrality.

5. The measurement of passive fluxes indicates that Cl removal from the perfusing solutions increases PK but does not alter PNa.

6. Addition of ouabain brings about a depolarization which is three times greater in low‐Cl solutions (21·9 mV) than in normal‐Cl solutions (6·8 mV).

7. It is concluded that hyperpolarization which develops when Cl ions are removed can be accounted for entirely by (a) the increase in PK, (b) the increase of the contribution of the electrogenic pump to membrane potential.
Luminance‐dependent changes in mesopic visual contrast sensitivity
Authors: Smith Robert A.
Published: December 2014

Spatial and temporal modulation transfer functions have been measured as a function of luminance at scotopic and mesopic levels. It is found that throughout the scotopic range the data can be accounted for by a two process visual system, with the processes having the following properties.

Simple excitatory process

This mechanism summates over somewhat less than 1 square degree of visual angle and over about 200 msec of time. These properties do not change with luminance, but the over‐all sensitivity of the mechanism follows the De Vries—Rose law. The temporal properties of this mechanism follows those of the scotopic b‐wave. At high luminances, the temporal, but not spatial, properties of this mechanism break down in a manner which had not been studied.

Low‐frequency inhibitory process

This process is manifest as a decrease in sensitivity from that of the simple excitatory process. Its effect is observed only when both spatial and temporal frequency are low, suggesting that it has a larger (perhaps 3 ×) summation area in both space and time. The inhibitory process is not observed below a certain threshold luminance, which is highly dependent upon the configuration of the stimulus. For a suitable stimulus, this threshold will be well into the scotopic luminance range.

It is suggested that these two processes represent psychophysical correlates of the centre and surround of retinal receptive fields.
The effect of citric acid and its sodium salts in test meals on the gastric outputs of acid and of chloride
Authors: Hunt J. N. , Knox M. T.
Published: December 2014

Five subjects were given 750 ml. test meals lasting 10–20 min, containing 0–300 m
N citric acid, monosodium dihydrogen citrate, disodium monohydrogen citrate or trisodium citrate.

1. Increase in concentration of sodium citrate in the range 0–125 m
N gave increasing outputs of acid and chloride.

2. The more acid the meal for any given citrate ion concentration, the less the output of acid and chloride.

3. The greater the concentration of an acid citrate salt, the less the output of acid.

4. There was evidence of loss of acid from the stomach by diffusion with the more acid meals.
Innate seasonal oscillations in the rate of milk secretion in goats
Authors: Linzell J. L.
Published: December 2014

1. When goats were kept in continuous milk production for 2–4 yr the rate of milk secretion oscillated in a sinusoidal fashion with a mean wavelength of 49·7 ± 1 weeks, being highest in summer and lowest in winter.

2. Milk [Cl] tended to be higher in summer and [protein] highest in winter but there were no seasonal changes in [fat], [lactose], [Na] or [K].

3. There were no seasonal oscillations in body weight but the udders were larger in summer than in winter although this did not solely account for the changes in milk yield.

4. Although the autumnal fall in yield and the rise in the spring coincided with the breeding season, seasonal variations also occurred in two ovariectomized animals.

5. Seasonal fluctuations were independent of diet, occurring equally in animals that had never eaten grass but were fed continuously on dry feed and hay ad libitum.

6. Annual oscillations in yield and udder size but not [protein] and [Cl] were also exhibited in two goats kept in a constant temperature chamber at 14 ± 2° C, fed every 2 hr and subjected continuously to 16 hr light and 8 hr dark. These observations have so far persisted for 2 yr in one goat and for 3 yr in the other. However, the wave‐length was reduced to 45 ± 1 weeks. Oestrus was suppressed for 2 years.
Efferent control of arterial chemoreceptors mediated by glossopharyngeal fibres and artifacts introduced by stimulation techniques
Authors: Goodman N. W.
Published: December 2014

1. In anaesthetized cats, stimulation of the cut carotid sinus nerve generally caused a reduction in discharge in afferent fibres peeled from the nerve distal to the stimulating electrodes, though this was somewhat variable. In four out of five fibres the inhibition was reduced or abolished by close intra‐arterial injection of atropine. Only single fibres were used.

2. There was a risk of adventitious excitation of the afferent fibre by stimulus escape. Some of the features of this excitation and the ease with which it occurred were investigated using an isolated length of vagus, baroreceptor fibres and chemoreceptor fibres. Low concentrations of local anaesthetic could raise the threshold for adventitious excitation whilst not affecting the normal passage of impulses.

3. During stimulation of the efferent components of the sinus nerve, a continuous check for adventitious excitation was kept, utilizing the fact that chemoreceptor fibres show a minimum inter‐spike interval of about 10 msec.

4. The true inhibition of discharge would seem to be vasomotor in origin.
The effect of glycerol treatment on crab muscle fibres
Authors: Papir Dalia
Published: December 2014

1. Membrane constants of the closer muscle of the ghost crab, Ocypoda cursor, were determined before and after treatment in hypertonic glycerol solution and return to an artificial sea‐water (
A.S.W.) solution.

2. Muscle contraction was abolished after return of the muscle to
A.S.W.

3. The membrane capacitance was reduced from 29·0 μF/cm2 to 10·5 μF/cm2.

4. Other passive properties of the muscle membrane, not dependent on capacitance, were not changed.

5. The presynaptic nerve, transmitter release, post‐synaptic sensitivity to transmitter and ionic mechanisms of synaptic action were unaffected by glycerol treatment.

6. More than 60% of the membrane capacitance/unit area is contributed by the complex tubular system.

7. The tubular system in crustacea is necessary for excitation‐contraction coupling.
The orderly recruitment of human motor units during voluntary isometric contractions
Authors: Milner‐Brown H. S. , Stein R. B. , Yemm R.
Published: December 2014

1. The contractile properties of human motor units from the first dorsal interosseus muscle of the hand were studied during voluntary isometric contractions using recently developed techniques.

2. The twitch tensions produced by motor units varied widely from about 0·1–10 g. The twitch tension of a motor unit varied nearly linearly as a function of the level of voluntary force at which it was recruited over the entire range of forces studied (0–2 kg).

3. The number of additional motor units recruited during a given increment in force declined sharply at high levels of voluntary force. This suggests that even though the high threshold units generate more tension, the contribution of recruitment to increases in voluntary force declines at higher force levels.

4. Contraction times for these motor units varied from 30 to 100 msec. Over 80% had contraction times less than 70 msec, and might be classed as fast twitch motor units. The larger motor units, which were recruited at higher threshold forces, tended to have shorter contraction times than the smaller units.
Reconstitution of the sodium pump from protein and phosphatidylserine: features of ouabain binding
Authors: Chipperfield A. R. , Whittam R.
Published: December 2014

1. A study has been made of ATP splitting and ouabain binding to the sodium pump reconstituted from protein and phosphatidylserine.

2. Ouabain was bound to protein alone, but when phosphatidylserine was added, binding was increased threefold. The stimulation resembled the course of activation of sodium‐dependent ATPase activity.

3. EGTA partly simulated the activation of ATPase by phosphatidylserine but did not enhance binding.

4. The dissociation constant for the enzyme‐ouabain complex was 3·5 × 10−8
M. The turnover number (2,000 molecules of ATP per minute) and the number of receptor sites (3·8 × 1013 per mg protein) were calculated.

5. The results provide further evidence of the involvement of phosphatidylserine in the action of the sodium pump.
The characteristics of ‘end‐plate noise’ produced by different depolarizing drugs
Authors: Katz B. , Miledi R.
Published: December 2014

1. End‐plate depolarization and associated ‘membrane noise’ due to decamethonium, acetylthiocholine and suberyldicholine have been examined and compared with the effects of acetylcholine and carbachol.

2. The transient ionic channels resulting from the action of decamethonium and acetylthiocholine are of much shorter duration than those produced by acetylcholine. They are, therefore, similarly to carbachol channels, less effective in causing membrane depolarization.

3. Suberyldicholine, on the other hand, produces ion channels whose duration exceeds that of acetylcholine.

4. Lowering the temperature causes an increase in amplitude of the elementary potential change produced by decamethonium and acetylthiocholine.

5. The relation between the characteristic features of drug‐induced membrane noise and the underlying molecular reaction rates is discussed.
Receptive fields of simple cells in the cat striate cortex
Authors: Bishop P. O. , Coombs J. S. , Henry G. H.
Published: December 2014

1. The excitatory and inhibitory components in the receptive fields of unimodal simple cells in the striate cortex of the cat anaesthetized with nitrous oxide have been described using slits of light and single light‐dark edges as stimuli.

2. There is a small excitatory region (excitatory complex) centrally located in the receptive field that is made up of various combinations and spatial arrangements of subliminal excitatory and discharge subregions or centres.

3. The subliminal excitatory centres were revealed by a binocular facilitation technique. The excitability of the cell was raised by repeated stimulation via one eye while the neurone was tested with single edges via the other eye.

4. The subliminal excitatory and discharge centres are each specifically activated by only one type of edge, light‐dark or dark‐light, and then only in one direction of motion. All the subregions in the excitatory complex have the same optimal stimulus orientation.

5. Inhibitory components in the receptive field were identified by stimulating the cell with bars of light and single edges against an artificial background discharge produced by repeated stimulation separately applied either to the same eye (monocular conditioning) or to the other eye (binocular conditioning). There are powerful inhibitory sidebands to either side of the excitatory complex and these inhibitory regions merge to include the excitatory complex when stimulus orientation is angled away from the optimal.

6. Excitation is highly stimulus specific whereas inhibition is non‐specific.

7. The organization of the two receptive fields of a binocularly discharged cell can be closely similar.

8. The attempt is made to translate the concept of subliminal excitatory and discharge centres into specific neural mechanisms involving both the geniculo‐cortical input and various intracortical circuits.

9. These new developments call for only minor modifications to the model we have proposed for the organization of the receptive field.