bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activation heat, activation metabolism and tension‐related heat in frog semitendinosus muscles
Authors: Homsher E. , Mommaerts W. F. H. M. , Ricchiuti N. V. , Wallner A. 
Published: December 2014

1. Frog semitendinosus muscles were stretched to various lengths beyond the rest length (l0) and their initial heat and isometric tension production were measured.2. As the overlap between the thick and thin filaments is reduced, the initial twitch heat and tension decline in a linear manner. At a point at which the twitch tension approaches zero, the initial heat is 30% of that seen at l0. It is concluded that this heat is the activation heat and reflects the energetics of calcium release and reaccumulation. The initial heat at shorter sarcomere lengths appears to be the sum of the activation heat plus a heat production associated with the interaction of the thick and thin filaments.3. A similar relationship between heat and tension production is seen in tetanic contractions.4. The time course of activation heat production in a twitch can be resolved into two phases: a temperature insensitive (Q10 < 1·3) ‘fast’ phase (with a time constant of 45 msec) and a temperature sensitive (Q10 = 2·8) ‘slow’ phase (with a time constant of 330 msec at 0° C).5. Measurements of the creatine phosphate (PC) hydrolysis by muscles contracting isometrically at various muscle lengths at and beyond l0, indicate an enthalpy change of −11·2 kcal/mole PC hydrolysed. The enthalpy change for the ATP hydrolysis by muscles stretched so that little or no tension was produced with stimulation was −9·9 kcal/mole ATP hydrolysed. It is concluded that the net activation heat is produced by the hydrolysis of PC or ATP.
Intracellular pH, H ion flux and H ion permeability coefficient in bullfrog toe muscle
Authors: Izutsu K. T. 
Published: December 2014

1. The dimethyloxazolidinedione (DMO) technique was used to estimate intracellular pH (pHi) in bullfrog toe muscles incubated in vitro. The control value of pHi was 7·16 + ± 0·01 (
S.D.).2. pHi was affected by changes in PCO2 and external bicarbonate ion concentration ([HCO3−]0). At a given PCO2, decreasing the external [HCO3−] was more effective in lowering pHi than increasing the external [HCO3−] was in increasing pHi.3. On the assumption that the changes in pHi were due to hydrogen ion [H+) movements across the membrane, a H+ flux of 10−13 mole/cm2. sec was calculated. The corresponding H+ permeability coefficient was 10−3 cm/sec.4. The variability of the tissue CO2 buffer value was examined.
Analysis of the membrane capacity in frog muscle
Authors: Hodgkin A. L. , Nakajima S. 
Published: December 2014

1. The membrane capacity (Cf) was determined from the conduction velocity and the time constant of the foot of the action potential in frog's skeletal muscle.2. In normal fibres Cf was 2·6 μF/cm2, and the value was almost constant over a range of diameter from 55 to 140 μ.3. In fibres, in which the transverse tubular system was disconnected from the surface by the glycerol treatment, Cf was 0·9 μF/cm2 and was fairly constant over a range of diameter from 60 to 130 μ. The low frequency capacity in glycerol‐treated fibres was 1·9 μF/cm2.4. These results as well as those obtained at low frequencies were consistent with the electrical model proposed by Adrian, Chandler & Hodgkin (1969).5. Analysis in terms of the model and of Peachey's (1965) data on tubular dimensions led to the following quantitative conclusions. The capacities of the surface membrane (CS) and of the tubular wall (CW) are both about 1 μF/cm2. The conductances of the surface membrane (GS) and tubular wall (GW) are ca. 0·11 and 0·03 mmho/cm2, respectively. The conductivity of the luminal fluid in the tubules is ca. 6 mmho/cm.
Modifications of dorsal horn cell activities in the spinal cord, after intra‐arterial injection of bradykinin
Authors: Besson J. M. , Conseiller C. , Hamann K.‐F. , Maillard Marie‐Claude 
Published: December 2014

1. A method is described to study the modification in the activity of the lamina IV and V cells of the dorsal horn under the intra‐arterial administration of bradykinin into the hind limb of the spinal cat.2. The modifications induced by intra‐arterial injection of bradykinin preferentially affected the lamina V cells (77% of the units) and produced few changes in the lamina IV cells (16% of the units showed variations).3. 52% of the lamina V cells were activated; the mean increase in the firing rate was 700%. The mean latency of the effect was 20 sec and the mean duration was 47 sec. However, there was large variance in the excitatory effect across cells. On the other hand, for the same cell, the observed effects were perfectly reproducible and injections of physiological fluid induced no response.4. 25% of the lamina V cells were inhibited. Generally, the activity of the cell was reduced to 13% of its initial value; in some cases, a total suppression of activity was observed. The mean latency of the inhibitory effect was 12 sec and its duration 28 sec. All these units had a very wide inhibitory field (activated by stimulations of low intensity) which asymmetrically surrounds the excitatory field.5. This study confirms the role played by the lamina V cells in the transmission of nociceptive messages. The existence of inhibitory phenomena is in favour of the gate control theory described by Melzack & Wall (1965) without deciding the pre‐ or post‐synaptic nature of these mechanisms.
The effects of vasopressin on the diuretic response to left atrial distension
Authors: Ledsome J. R. , Mason J. M. 
Published: December 2014

1. The diuretic response to left atrial distension was studied during infusion of saline or during infusion of vasopressin at four different dose rates.2. During infusion of saline left atrial distension caused an increase in free water clearance and an increase in osmolal clearance.3. During infusion of vasopressin at a rate of 0·025 m‐u./kg.min and 0·1 m‐u./kg.min there was no statistically significant increase in free water clearance during left atrial distension but there were variations in free water clearance in individual experiments.4. During infusion of vasopressin in doses of 0·4 m‐u./kg.min and 1·0 m‐u./kg.min changes in free water clearance were dependent upon changes in osmolal clearance indicating that these doses of vasopressin provided a maximum antidiuretic effect.5. Infusion of vasopressin had no effect on the increase in osmolal clearance which occurred in response to left atrial distension.6. The results allow the view that a part of the diuretic response to left atrial distension could depend upon a decrease in the concentration of antidiuretic hormone in the circulating blood.
Active secretion of thyroxine into bile: the role of tissue thyroxine‐binding sites
Authors: Hillier A. P. 
Published: December 2014

1. An investigation has been made into factors regulating the secretion of thyroid hormones into bile. The preparation employed was the isolated rat liver perfused with a modified Tyrode solution.2. Tracer amounts of radioactive thyroxine were injected into the Tyrode solution just before its entry into the liver. This allowed the thyroxine‐binding sites in the tissue to capture most of the injected hormone. It was found that this tissue‐bound hormone was then gradually secreted into the bile and that the process could be resolved into two components. There was a steady, continuous secretion of hormone, which maintained a fairly constant bile:liver ratio in thyroxine concentration of about 2·3. There was also, superimposed upon this, an extra transient secretion of thyroxine occurring just after the injection. This transient effect was abolished by injecting the hormone at 22° C and it was probably due to the sudden flood of free thyroxine into the tissue during the 15 sec injection period.3. Very similar results were obtained with tri‐iodothyronine except that the secretion process maintained a higher bile:liver ratio of about 3·7.4. The secretion mechanism was extremely sensitive to changes in temperature and it was able to generate very high concentrations of free thyroxine in the bile. It was concluded that the over‐all process was probably an active one.5. The presence of 30% bovine serum in the perfusion fluid did not reduce the bile:liver thyroxine ratio even though it caused a massive fall in the amount of thyroxine in the tissue.6. These results show that the rate of thyroxine secretion into bile is determined by the total amount of thyroxine trapped in the tissue. It is not directly related to the concentration of free thyroxine in the perfusing medium.7. It is suggested that the secretion mechanism works from a small intracellular pool of free thyroxine which is in rapid exchange with the large pool of tissue‐bound hormone, and that thyroxine exchange between this small intracellular pool and the free thyroxine pool in the plasma is relatively slow.
Autoregulation of thyroxine secretion into bile
Authors: Hillier A. P. 
Published: December 2014

1. An investigation has been made into the effect on thyroxine secretion into bile of suddenly raising the thyroxine concentration in the liver.2. Isolated rat livers, perfused with Tyrode solution, were injected with trace amounts of radioactive thyroxine. This injected hormone was captured by the binding sites in the tissue and then gradually secreted into the bile. A second injection of 100 μg stable (non‐radioactive) thyroxine caused an enormous increase in the secretion rate. At its peak, the concentration of thyroxine in the bile was about 24 × its concentration in the liver (this was 10 × higher than the concentration ratio at tracer thyroxine levels). The effect extended well into the physiological range and injections of only 0·1 μg stable thyroxine caused a transient doubling of the secretion rate. Tri‐iodothyronine also accelerated thyroxine secretion but it was 30 × less potent than thyroxine.3. In contrast, the secretion of tri‐iodothyronine into bile was only very slightly affected by injections of stable thyroxine or tri‐iodothyronine, the maximum response being a 20–30% increase in the secretion rate.4. This autoregulating mechanism would help to stabilize the concentration of thyroxine in the tissues but not the concentration of tri‐iodothyronine.
An electrophysiological analysis of the synthesis of acetylcholine in preganglionic nerve terminals
Authors: Bennett M. R. , McLachlan Elspeth M. 
Published: December 2014

1. An electrophysiological analysis has been made of the synthesis of acetylcholine (ACh) in the preganglionic nerve terminals of the isolated superior cervical ganglion of the guinea‐pig. The mean amplitude of excitatory post‐synaptic potentials recorded intracellularly was taken as a measure of the ACh output per impulse from the terminals of a preganglionic axon.2. Prolonged repetitive stimulation of the cervical sympathetic trunk at 10 and 20 Hz led to a decline in ACh output over the first 5‐15 min and then a maintained output for periods of up to an hour. The mean level of maintained output was 0·4 of the peak initial output.3. The maintained level of output was shown to be equal to the rate of synthesis of new transmitter and was not dependent on the addition of choline (3 × 10−5
M) to the fluid in the organ bath.4. The ACh output per minute was shown to be directly proportional to the frequency of stimulation.5. A model has been proposed of the storage and synthesis of ACh in preganglionic nerve terminals during prolonged stimulation, in which choline from the hydrolysis of released ACh is the main source of substrate for synthesis of new transmitter, and the rate at which synthesis proceeds is controlled by the rate at which transmitter is released.
Intestinal absorption rate of L‐methionine in man and the effect of glucose in the perfusing fluid
Authors: Cook G. C. 
Published: December 2014

1. Using a double‐lumen tube perfusion system the rates of absorption of
L‐methionine and glucose from a 30 cm segment of the jejunum were estimated in eight relatively normal Zambian African subjects. The effect of each substrate on the absorption of the other has also been investigated. The solutions perfused were given at 12·0 ml. min−1, and contained (A) 100 m‐mole l.−1
L‐methionine, (B) 100 m‐mole l.−1
L‐methionine and 150 m‐mole l.−1 glucose and (C) 150 m‐mole l.−1 glucose.2. The presence of glucose in the perfusing fluid did not significantly alter the mean absorption rate of methionine; in six subjects, the rate of methionine absorption from solution B was less than from solution A, but in two there was a marked difference in the opposite direction. This may indicate an individual difference in the effect of glucose on
L‐methionine absorption in man. The presence of methionine in the perfusing fluid did not significantly alter the mean absorption rate of glucose.3. Five subjects had a transitory psychiatric disturbance after the investigation. The cause of this is not clear, but was probably caused by the absorption of a break‐down product of methionine from the large intestine.
Reflex discharge patterns of cardiac vagal efferent fibres
Authors: Kunze Diana Lee 
Published: December 2014

1. Unit activity was recorded from single and few fibre preparations in a cardiac branch of the right vagus nerve of the cat.2. Increases in blood pressure mediated solely by the right carotid sinus nerve produced bradycardia when all other nerves to the heart had been cut. Myelinated fibres in the cardiac branch of the right vagus nerve were reflexly activated by the same procedure.3. The fibres were silent when blood pressure was below 140–150 mm Hg. As the pressure began to rise, they discharged phasically with the cardiac cycle. At pressures greater than 180 mm Hg, the discharge was continuous attaining maximum rates of 40/sec.4. Stimulation of carotid body chemoreceptors also reflexly excited these fibres, as did stimulation of baroreceptors in both the left carotid sinus and aortic arch. Afferent fibres in the left vagus discharging in response to changes in blood pressure reflexly excited the cardiac efferent fibres. Increases in phrenic motoneurone discharge coincided with inhibition of these fibres. Electrical stimulation of the glossopharyngeal nerve also produced inhibition.
The effect of denervation on the mechanical and electrical responses of fast and slow mammalian twitch muscle
Authors: Lewis D. M. 
Published: December 2014

1. The soleus (slow twitch), flexors digitorum and hallucis longus muscles (fast twitch) of the cat were denervated. Isometric contractions and electrical responses were examined 2–160 days after the operation.2. In the first week the time course of the twitch and the ratio of tetanus tension to twitch tension were normal in both muscles. The maximum rate of rise of tension in the tetanus was reduced in fast muscles.3. In the second week all the twitches showed a normal contraction phase but relaxations were interrupted by a repetitive after‐contraction. This became less marked after longer periods of denervation.4. During the third and subsequent weeks, the contraction and relaxation phases of the twitches in all muscles became slower than normal. These changes were greater in fast muscles which, nevertheless, remained quite distinct from soleus. The ratio of tetanus tension to twitch tension fell below normal. It is suggested that these changes are brought about by more complete activation of the contractile proteins in a twitch. In flexor hallucis longus the rate of rise of tension in isometric tetani was found to be further reduced. No change was found in soleus.5. In extracellular and intracellular records the initial response was a single action potential. An after‐discharge occurred in a proportion of fibres during the relaxation phase of the twitch.6. The intracellularly recorded action potential was smaller and had a longer duration than that of normal muscle. Refractory period increased. Conduction velocity decreased. These changes were greater in fast muscle and differences between fast and slow twitch muscle were less marked than in normal muscle. Fibrillation potentials occurred at the same rate in fast and slow muscle.7. The mechanisms of the mechanical changes are discussed and the possible relevance to the question of motor nerve influence on muscle is indicated.
Potentiation and depression of synaptic transmission in the olfactory cortex of the guinea‐pig
Authors: Richards C. D. 
Published: December 2014

1. The extracellular field potentials of the olfactory cortex evoked by stimulation of the lateral olfactory tract (l.o.t.) were studied in in vitro preparations from the olfactory cortex. The field potentials comprised an initial diphasic wave — the l.o.t. compound action potential — followed by a negative wave of about 10 msec duration which in turn was followed by a low amplitude positive wave of long duration (100 msec or more). In this paper, the size of the negative field potential (extracellularly recorded EPSP) has been studied during and after periods of repetitive stimulation of the l.o.t.2. If two identical volleys were delivered to the l.o.t. the second evoked EPSP was not the same size as the conditioning EPSP. At brief conditioning intervals (up to 10 msec) the second (test) EPSP was smaller than the control. For conditioning intervals between 10 and 200 msec, the test EPSP was potentiated over the control. For long conditioning intervals (300 msec up to 5 sec) the test EPSP was again slightly smaller than the control EPSP. After a brief conditioning train, the depression of a test EPSP (elicited 300 msec or more after the conditioning train) was more pronounced and lasted longer. These changes of test EPSP size were attributed to the presence of two opposing processes: an initial potentiation superimposed on a more prolonged but less pronounced depression.3. During prolonged repetitive stimulation the final steady amplitude of an EPSP varied with the frequency of stimulation. At low frequencies (0·5–2/sec) the steady EPSP amplitude was 90–95% of the initial control amplitude. At moderate frequencies (5–20/sec) the steady EPSP amplitude was greater than the initial control. At high frequencies (above 20/sec) the steady amplitude of the EPSPs declined with increasing frequency of stimulation. Potentiation of EPSPs was observed early in a train of impulses when the stimulation frequency was 5–70/sec.4. After a large number of stimuli at frequencies from 20 to 100/sec the amplitude of individual, infrequently evoked, EPSPs passed through a phase of depression that lasted about 30 sec. This depression was followed by a phase of potentiation (post‐tetanic potentiation). The amplitude and duration of post‐tetanic potentiation appeared to depend on the characteristics of the conditioning train.5. The discussion compares the results obtained with those obtained for other mammalian synapses. It is suggested that the transmitter in the presynaptic terminals could be in three parts, (a) immediately available transmitter (b) conditionally available transmitter requiring a single nerve impulse for its availability and (c) main depot transmitter which replenishes the other two stores. Potentiation and depression of evoked EPSPs were interpreted in terms of changes in the amount of transmitter released by the test volley. According to this analysis, a fixed proportion (about 10%) of the immediately available transmitter is released by each nerve impulse.
The importance of timing on the respiratory effects of intermittent carotid sinus nerve stimulation
Authors: Eldridge Frederic L. 
Published: December 2014

1. The respiratory response, measured directly as tidal volume or indirectly by using integrated peak phrenic activity, to intermittent electrical stimulation of the carotid sinus nerve was determined in anaesthetized cats.2. Stimulation at rates of 20–25 Hz for 0·5 sec had a rapid effect, increasing inspiratory airflow and phrenic discharge, but only if applied during inspiration. An increase in tidal volume or peak level of integrated phrenic discharge occurred only if the stimulus was exhibited during the second half of inspiration. Continuous stimulation had no greater effect on size or frequency of breathing than did intermittent inspiratory stimuli alone. Stimulation during expiration had no effect on the form or magnitude of subsequent breaths.3. Stimuli in expiration led to a prolongation of expiration. Stimuli in late inspiration caused a prolongation of both inspiration and expiration. Because of these effects, the respiratory rate could be changed by stimulation; in some instances entrainment of respiration by the intermittent carotid sinus nerve stimuli occurred.4. The findings are attributable to modulation of incoming carotid sinus nerve information by the central respiratory neurones, which use primarily that which arrives during inspiration. They show a possible mechanism by which oscillating signals may have a different effect than their mean level would indicate.
The passage of calcium and strontium across the gut of the anaesthetized goat
Authors: Gibbons R. A. , Sansom B. F. , Sellwood R. 
Published: December 2014

1. The translocation of calcium and strontium across the intestine of the anaesthetized goat has been studied. It has been found to be unaffected by ouabain, by the absence of sodium, by a severely hypertonic environment and by heparin and chondroitin sulphate. Thus it is unlikely that, in the intact goat, the trans‐mucosal sodium and calcium transport systems are interrelated.2. The effect of sodium alginate both on the rate of absorption and the calcium/strontium discrimination ratio has been confirmed.3. The movement of calcium ion in both directions across the intestinal mucosa has been studied and evidence for the active transport of calcium adduced.
Efflux of potassium from the isolated frog retina: a study of the photic effect
Authors: Cavaggioni A. , Sorbi R. T. , Turini S. 
Published: December 2014

1. Illumination of the isolated frog retina reduces the efflux of 42K (and 86Rb).2. Perfusion with a solution containing glutamate ions does not abolish the effect, although the electroretinogram is modified and the b‐wave absent in this condition.3. Perfusion with a solution with only 2·36 m
M sodium abolishes the effect of light on the efflux of potassium (and rubidium).4. The amplitude of the photic effect, measured in the first 2 min of illumination, is in linear proportion with the logarithm of the concentration of extracellular sodium ions.5. A steady rate of absorption of a few quanta per rod and per second yields a just detectable effect on the efflux of potassium (and rubidium).6. Strong illuminations followed by darkness reduce the efflux of rubidium for a period of time roughly comparable to the time of dark adaptation.7. The interpretation is proposed that the photoreceptor cells (and possibly other retinal cells too) cause the effect, and that the retention of potassium induced by light is secondary to the hyperpolarization of their membrane.