bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radial spread of contraction in frog muscle fibres
Authors: Adrian R. H. , Costantin L. L. , Peachey L. D. 
Published: December 2014

1. The membrane potential of isolated muscle fibres in solutions containing tetrodotoxin (TTX) was controlled with a two‐electrode voltage clamp. The striation pattern in the region of the electrodes was observed microscopically.2. With square steps of depolarization of increasing magnitude, contraction occurs first in the myofibrils just beneath the surface membrane, and then spreads inwards towards the axis of the fibre as the depolarization is increased.3. From the depolarizations which make the superficial and axial myofibrils contract it is possible to estimate a space constant (λT) for electrotonic spread in a transverse tubular network.4. λT was found to vary with fibre radius; for a 50 μ fibre it was about 60 μ. λT was not greatly affected by tetraethylammonium (TEA) chloride (111 m
M), or by sucrose substitution of most of the sodium chloride in the Ringer solution.5. The ratio of the depolarization threshold for contraction of surface myofibrils and of central myofibrils was smaller for short (3 msec) than for long depolarization.6. Action potentials, recorded from a sartorius fibre, were used as the command signal for the voltage‐clamped fibre in tetrodotoxin. The central myofibrils of this fibre did not appear to contract unless the imposed ‘action potentials’ were of normal size.7. The passive electrical characteristics of the transverse tubular system will just allow an action potential, at room temperature, to activate the myofibrils at the centre of a frog muscle fibre. An active potential change would be required to achieve a safety factor appreciably greater than one for this process.
The mechanical properties of cat soleus muscle during controlled lengthening and shortening movements
Authors: Joyce G. C. , Rack P. M. H. , Westbury D. R. 
Published: December 2014

1. By supplying pulses to different subdivisions of the ventral nerve roots in rotation, it was possible to obtain smooth contractions of cat soleus with low rates of stimulation.2. After contracting isometrically the muscle was subjected to constant velocity lengthening or shortening movements.3. During shortening the tension always fell below the isometric value. The fall in tension was usually greatest when low rates of stimulation were used.4. The effect of lengthening on tension depended on the rate of stimulation. At high rates of stimulation the tension during lengthening always rose above the isometric tension. At lower rates of stimulation (5–15 pulses/sec) the tension rose at the beginning of an extension, but decreased later in the movement to a level that was often less than the isometric tension corresponding to that muscle length. At these stimulus rates the tension during isometric contraction was usually higher than during a sustained movement in either direction.5. At low rates of stimulation longitudinal vibratory movements of more than 0·1 mm also reduced the tension far below the isometric value, whereas the reduction was quite slight when the rate of stimulation was high.6. The isometric tension during smooth contractions at low stimulus rates was remarkable in the following respects: it developed rather slowly, it was higher than the tension during or immediately after movements, and it was only slowly regained after movement had ceased.7. The results are discussed in relation to the sliding filament theory of muscle contraction, which, with certain assumptions, provides an explanation for many of the findings.
The clearance and antidiuretic potency of neurohypophysial hormones in man, and their plasma binding and stability
Authors: Fabian Miriam , Forsling Mary L. , Jones J. J. , Pryor J. S. 
Published: December 2014

1. Bio‐assay techniques have been used to measure plasma levels of neurohypophysial hormones in man, following either a single injection or a continuous infusion.2. The median half‐life of oxytocin after a single injection of 2 u. was 3·2 min (2·0–5·7, 95% confidence limits); this increased significantly (P < 0·01) to 4·8 min (4·4–6·1) when the hormone was infused at a rate of 500 m‐u./min. The vasopressins had appreciably longer half‐lives. After a single injection of 1 or 1·5 u. 8‐lysine vasopressin (LVP), the half‐life was 5·7 min (3·6–6·0). Continuous infusions of the hormones at a rate of 120 m‐u./min yielded half‐lives of 5·5 min (5·0–7·1) for LVP, and 5·6 min (3·9–9·5) for 8‐arginine vasopressin (AVP).3. The apparent volumes of distribution of the hormones were all of the order of two thirds the extracellular volume.4. In accordance with its shorter half‐life, the clearance of oxytocin was greater than that of the vasopressins (1·5 l./min, compared with 1·0 l./min).5. The antidiuretic potencies of the hormones were studied in over‐hydrated subjects, by measuring the rate of urine excretion following an
I.V. injection. Duration of antidiuretic action increased in the order: oxytocin, LVP, AVP. A 5:1 mixture of oxytocin and AVP was not as long‐lasting as AVP alone. 8·5% (4–22) of an administered dose of AVP was excreted in the urine, and this amount was significantly correlated with urine volume (r = +0·67, P < 0·05).6. Ultrafiltration of human plasma containing exogenous hormones showed that 30% (13–50) of AVP was bound, the degree of binding being independent of concentration over the range used (50–400 μ‐u./ml.) In contrast, oxytocin was completely unbound.7. Exogenous oxytocin was more stable than exogenous AVP in human plasma. At 4° C there was no significant loss of oxytocin until 7 days, whereas 20% of AVP was inactivated in 2 days. At 37° C a 20% loss of AVP occurred within 4 hr, and a 50% loss within 24 hr; corresponding times for oxytocin were 24 and 48 hr.
Nerve‐mediated excitation and inhibition of the smooth muscle cells of the avian gizzard
Authors: Bennett Terence 
Published: December 2014

1. The electrical events evoked in smooth muscle cells of the chick and pigeon gizzards by vagal, perivascular sympathetic and transmural stimulation were recorded with intracellular micro‐electrodes.2. Single stimulating pulses applied to the extrinsic nerves, or to intrinsic fibres, produced excitatory junction potentials (E.J.P.s) which were blocked by hyoscine. Repetitive stimulation caused facilitation of E.J.P.s and, at higher frequencies, summation. When the tissue was well oxygenated, maximal stimulation evoked action potentials and the tissue contracted. If the tissue was allowed to become anoxic, action potentials were blocked and thus junctional transmission could be observed uncomplicated by tissue contraction.3. Cholinergic E.J.P.s appeared to be due to stimulation of both post‐ganglionic neurones and the pre‐ganglionic input to post‐ganglionic neurones, since ganglion‐blocking drugs abolished the late phase of complex E.J.P.s while leaving unaffected their initial components.4. Repetitive perivascular sympathetic stimulation, after cholinergic E.J.P.s had been blocked by hyoscine, evoked a slow, long‐lasting depolarization of the muscle cells. This depolarization was blocked by guanethidine (5 × 10−6 g/ml.) and was mimicked by noradrenaline (10−7 g/ml.).5. Under non‐anoxic conditions, the tissue underwent rhythmical contractions which were associated with action potential firing. When the tissue was anoxic action potentials were not seen, but spontaneous membrane depolarizations resembling E.J.P.s were observed. Spontaneous miniature excitatory junction potentials (M.E.J.P.s) were observed only infrequently whether the tissue was well oxygenated or not.6. Single stimulating pulses applied to extrinsic or intrinsic nerves frequently evoked inhibitory junction potentials (I.J.P.s) in smooth muscle cells of the gizzards of both birds. I.J.P.s were blocked by tetrodotoxin (10−7 g/ml.). Repetitive stimulation of inhibitory nerves gave rise to a membrane hyperpolarization; when stimulation was stopped the membrane potential showed rebound depolarization.7. These results are discussed in terms of the autonomic innervation of the avian gizzard, and possible explanations of the various types of activity observed are considered.
Fat metabolism and heat production in young rabbits
Authors: Hardman M. J. , Hey E. N. , Hull D. 
Published: December 2014

1. The rates of oxygen consumption were measured in 6–8‐day‐old rabbits at 34 and 15° C after varying periods of starvation and cold exposure. At the start of the experiment the rabbits had been fasted for 24 hr. Eight rabbits were studied immediately, six after 24 and six after 48 hr in a cold environment (20° C), and twelve after a further 48 hr in a warm environment (34° C). All the animals had a similar increase in oxygen consumption during the final hour of cold exposure (15° C).2. The rabbits kept at 20° C lost 83% of the fat stored in their brown adipose tissue within 24 hr and a further 11% in the next 24 hr. The fat content of white adipose tissue had fallen by 75% at 48 hr. In contrast rabbits kept unfed at 34° C had lost 47% of the fat in brown adipose tissue and 44% of the fat in white adipose tissue after 48 hr.3. In six rabbits subcutaneous thermocouples demonstrated that local heat production continued in brown adipose tissue after 48 hr cold exposure.4. In the rabbits kept at 34° C the final cold exposure caused a large increase in the serum free fatty acid and glycerol concentrations. Much lower concentrations were found in rabbits kept at 20° C.5. The results show that the fat stored in the brown adipose tissue of young rabbits exposed to cold is preferentially used for heat production. When this store of fat is exhausted, brown adipose tissue still produces heat presumably by oxidizing fat and glucose taken from the circulation.
Calcium and potassium currents of the membrane of a barnacle muscle fibre in relation to the calcium spike
Authors: Hagiwara Susumu , Hayashi Hideo , Takahashi Kunitaro 
Published: December 2014

1. The behaviour of membrane currents in a giant muscle fibre of a certain barnacle Balanus nubilus, Darwin, was studied by using voltage clamp technique after treating fibres with a Ca‐chelating internal solution.2. Membrane currents can be classified into an early transient current and a late outward current.3. The early transient current can be considered a sum of an inward and an outward component of different properties.4. A conditioning depolarization suppresses the inward component but not the outward component.5. Procaine suppresses the outward component and Co ions suppress the inward component.6. Changes in the external Ca ion concentration alter the inward component but not the outward component.7. The inward component is considered to be carried by Ca ions and the outward component mainly by K ions.8. The outward component of the early current is similar to the current expected from the resting membrane conductance.9. It is concluded that the early conductance increase of the barnacle muscle fibre membrane occurs only to Ca ions but not to K ions, although the membrane potential at the peak of spike is determined by both ions.
The preferential release of newly synthesized transmitter by a sympathetic ganglion
Authors: Collier B. 
Published: December 2014

1. The acetylcholine (ACh) store of cat's superior cervical ganglia was replaced with radioactive ACh by perfusion, during stimulation, with [3H]choline—Locke solution. Perfusion was continued with Locke containing unlabelled choline (Ch) (in physiological concentration) and the release of labelled and unlabelled ACh was measured.2. Electrical stimulation of the preganglionic sympathetic nerve (20/sec or 5/sec), or stimulation by perfusing with raised K, released ACh that had a lower specific radioactivity than ganglionic ACh. The proportion of released ACh that was labelled was slightly higher when stimulation was at lower frequency or by K.3. Preganglionic nerve stimulation released, in the first few minutes, ACh that had a specific activity 70–80% of ganglionic ACh, but after 5 min the proportion of label in the released ACh fell to 35–45% of that in the ganglion.4. It is concluded that newly synthesized ACh is released before equilibration with preformed stores, and the significance of this to the mechanism of transmitter release is discussed.
The delayed pressor response to small doses of intravenous noradrenaline in conscious rabbits
Authors: de Swiet M. , Dickinson C. J. 
Published: December 2014

1. Noradrenaline, infused intravenously at low rates into conscious rabbits, can sustain a moderate elevation of blood pressure of 20–40 mm Hg. The most effective dose range is 0·1–0·5 μg.kg−1.min−1.2. Toxic manifestations and tachyphylaxis occur at higher infusion rates, but have also been seen at infusion rates within this range.3. The highest sustained rise of blood pressure was obtained after initially low infusion rates had been gradually increased over a period of 2‐4 weeks.
A study of chemoreceptor and baroreceptor A and C‐fibres in the cat carotid nerve
Authors: Fidone S. J. , Sato A. 
Published: December 2014

1. 149 A‐fibres and 52 C‐fibres from the cat carotid nerve were studied in vivo with single‐unit recording techniques. These units subserved chemoreceptor and baroreceptor modalities. In addition, half of the C‐fibres were determined to be efferent in origin. The estimated fibre diameter spectrum for chemoreceptor and baroreceptor A‐fibres is described.2. The discharge pattern of chemoreceptor A and C‐fibres was characteristically irregular both at rest and during activation. However, about 5% of the chemoreceptor A‐fibre population exhibited a very regular discharge pattern, even at low rates of firing.3. In comparing A and C‐fibres, it was found that chemoreceptor and baroreceptor A‐fibres had lower thresholds, shorter response latencies, more rapid acceleration of discharge and higher discharge frequencies than their C‐fibre counterparts.4. During strong chemoreceptor or baroreceptor stimulation, interaction of the ‘spontaneous’ whole nerve activity with the evoked A and C‐fibre compound action potentials provided a method of estimating the relative proportions of chemoreceptors and baroreceptors in the A and C‐fibre populations of the carotid nerve. The A‐fibre population was found to be comprised of approximately 2/3 chemoreceptors, 1/3 baroreceptors. The reverse was true for the C‐fibre population, i.e. 2/3 baroreceptors, 1/3 chemoreceptors.5. A stepwise C‐fibre response is described which may arise from the several C‐fibres within a single Schwann cell.
Enzymic properties of myosin in fast and slow twitch muscles of the cat following cross‐innervation
Authors: Buller A. J. , Mommaerts W. F. H. M. , Seraydarian Krikor 
Published: December 2014

1. Following cross‐innervation of the cat flexor digitorum longus muscle (
F.D.L., fast‐twitch) and soleus muscle (slow‐twitch) the isometric twitch speed of the
F.D.L. muscle decreases while the contraction time of soleus increases. The tetanus—twitch ratio of soleus is also increased.2. Myosin or myofibrils from normal or self‐reinnervated fast‐twitch muscles of the cat split adenosine triphosphate (ATP) more rapidly than myosin or myofibrils from slow twitch muscles.3. Following cross‐innervation the myosin and myofibrillar ATPase activity of flexor digitorum longus muscle falls, to become nearly equal to that of normal or self‐reinnervated soleus muscle. The ATPase activity of cross‐innervated soleus muscle increases only slightly.
Polymerizing equilibria in neurophysin
Authors: Burford G. D. , Ginsburg M. , Thomas P. J. 
Published: December 2014

1. Evidence for the occurrence of a rapidly polymerizing equilibrium system in freshly prepared aqueous solutions of porcine neurophysin has been obtained by frontal and zonal analysis of gel‐filtration elution patterns.2. Elution volumes increased with decreasing protein concentration and derivative analysis of fronts suggested the existence of different polymerizing forms varying in relative proportion with protein concentration.3. In the presence of lysine vasopressin, the results suggested a shift of the equilibrium in favour of higher polymerizing forms.4. In the presence of Ca2+ elution patterns became characteristic of a monodisperse system of relatively high molecular weight. The effect of Ca2+ did not survive removal of the ion and was not reproduced by Mg2+.5. Evidence for a slowly developing polymerization of neurophysin in aqueous solution has been obtained in experiments with solution prepared 24 hr before subjection to gel‐filtration.6. A model is proposed for the description of the binding of lysine vasopressin to porcine neurophysin.
Transmission from vasoconstrictor and vasodilator nerves to single smooth muscle cells of the guinea‐pig uterine artery
Authors: Bell Christopher 
Published: December 2014

1. Previous studies have shown that perivascular nerve stimulation of the uterine artery of the guinea‐pig evokes an adrenergic constrictor response and a dilator response with two components. The first of these, only present during pregnancy, is cholinergic. The second is non‐cholinergic and is present at all times. Intracellular recording from single smooth muscle cells in isolated arterial segments has now been used to investigate the transmission processes associated with these responses.2. The mean resting membrane potential of the muscle cells was 60·7 mV in arteries from both virgin animals (range 50–68 mV) and from animals in late pregnancy (range 48–76 mV).3. Low frequency perivascular stimulation evoked excitatory junction potentials (EJPs) which reached a maximum amplitude of about 5 mV, lasted about 900‐1000 msec, and showed facilitation at frequencies of stimulation of 0·1 Hz or above and summation at frequencies of stimulation of 1·2 Hz or above.4. These EJPs were abolished by exposure of the tissue to bretylium (2 × 10−6 g/ml.). It is therefore concluded that the EJPs were due to transmission from adrenergic nerves.5. Perivascular stimulation at frequencies above 10 Hz evoked a depolarizing response which was often surmounted by a small (5 mV) local spike potential. Such depolarizing responses were associated only with localized contractions of the arterial muscle.6. In the presence of low extracellular K+ concentrations, perivascular stimulation at frequencies above 10 Hz gave rise to a depolarizing response topped by an action potential of up to 50 mV amplitude, and more generalized contraction of the tissue than was seen in normal K+ solution.7. After blockade of the adrenergic vasoconstrictor fibres, no response to perivascular stimulation was observed normally. However, following moderate depolarization of the membrane with noradrenaline, stimulation evoked a hyperpolarization of up to 6 mV in amplitude.8. This response showed no discrete junction potentials, had a latency of up to 2000 msec and was only observed with stimulation at frequencies of 2 Hz or greater. The response was obtained in both pregnant and non‐pregnant animals, and was unaffected by hyoscine, but was abolished by cinchocaine.9. No changes in membrane potential attributable to transmission from cholinergic dilator nerves could be revealed in arteries from pregnant animals. Furthermore, high concentrations of acetylcholine had no polarizing effect on the muscle cells. It is suggested that the cholinergic dilator nerves may not act via changes in membrane potential.
A reconsideration of the Poisson hypothesis for transmitter release at the crayfish neuromuscular junction
Authors: Bittner G. D. , Harrison J. 
Published: December 2014

1. Transmitter release from excitor nerve terminals in the crayfish opener muscle was studied with both intra‐ and extracellular electrodes.2. The amplitude distribution of quanta recorded extracellularly from a single release site did not fit the compound Poisson hypothesis in two thirds of the data sets.3. Some data appeared to be non‐Poisson because specific quantal multiples were released; the non‐Poisson nature of release for other sets could be due to variable invasion of the axonal spike into the terminal region.4. In some muscle fibres, the number of quanta released at one ending to any given impulse in a stimulus train was correlated with the number of quanta released at other endings on the same fibre. This suggests that such endings may be supplied by nerve twigs arising from a common branch point with a very low safety factor for transmission.5. No consistent relationship was found between the amplitudes of the intra‐ and extracellular spontaneous potentials recorded from the same muscle fibre.
The difference in sensitivity to cardiac steriods of (Na+ + K+)‐stimulated ATPase and amino acid transport in the intestinal mucosa of the rat and other species
Authors: Robinson J. W. L. 
Published: December 2014

1. The effect of various cardioactive steroids on the activity of a microsomal (Na+ + K+)‐activated ATPase from rat intestinal mucosa has been studied and compared with their effects on
L‐phenylalanine and
D‐galactose transport by rings of rat intestine in vitro. A similar comparison between the sensitivities to ouabain of microsomal (Na+ + K+)‐ATPase and of phenylalanine transport in the intestines of the mouse, guinea‐pig and toad has been made.2. The rat intestinal enzyme is 50% inhibited by a concentration of 1 × 10−4
M ouabain, 1 × 10−5
M scillaren A and 4 × 10−6
M scilliroside. At concentrations which almost completely inhibit the (Na+ + K+)‐ATPase activity, these steroids have no effect on the transport of phenylalanine or galactose by the rat intestine. Only at concentrations of 1 × 10−3
M are scillaren A and scilliroside able to reduce phenylalanine accumulation significantly, the same concentration of ouabain being effective only in the absence of external potassium ions. Digitoxin, 1 × 10−4
M, a comparatively apolar glycoside, had no action on phenylalanine transport in the rat intestine.3. The effect of ouabain on the (Na+ + K+)‐ATPase and phenylalanine transport system in the mouse intestine is completely analogous to its effect on these parameters in the rat.4. A half‐maximal inhibition of guinea‐pig intestinal (Na+ + K+)‐ATPase by ouabain occurs at an inhibitor concentration of 2 × 10−6
M, but phenylalanine transport by this tissue is only half‐maximally reduced at a concentration of 3 × 10−5
M. Similarly, in the rabbit intestine, there appears to be a difference of an order of magnitude between the sensitivities of the two parameters.5. In the toad, 50% inhibition of the enzymic activity is observed at a concentration of 3 × 10−5
M ouabain, whereas a concentration of 8 × 10−4
M is required to reduce phenylalanine accumulation by one half.6. These findings are consistent with the suggestion that an (Na+ + K+)‐stimulated ATPase is not the only enzyme in the epithelial cells of the intestinal mucosa that is responsible for sodium extrusion (the mechanism for sodium extrusion being intimately coupled with the mechanism for active amino acid transport); therefore, a second, as yet unidentified, enzyme system must be postulated to account for bulk sodium flow through the intestine.