bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mechanical efficiency of treadmill running against a horizontal impeding force
Authors: Lloyd B. B. , Zacks R. M. 
Published: December 2014

1. A method for determining the apparent mechanical efficiency of running against a horizontal impeding force is described. The results of studies on three well trained athletes have been summarized.2. A linear relation was found between metabolic rate and external work rate. The apparent mechanical efficiency was calculated as the inverse of the slope of the linear regression line of metabolic rate on external work rate × 102 (percentage).3. The over‐all mean for apparent load‐running efficiency (LRE) was 36·1%. The differences in LRE between subjects were not statistically significant. No measurable change in LRE occurred with habituation.4. Values are given for Ek, the net energy cost of unloaded horizontal treadmill running per kilogram of bodyweight and per kilometre of distance covered. The over‐all mean for Ek was 0·83 kcal. kg−1. km−1.5. The efficiency values obtained are discussed and compared with other values of running efficiency obtained by different methods, and with studies on isolated muscle.
Changes in the activity of sarcoplasmic reticulum fragments and actomyosin isolated from skeletal muscle of thyroxine‐treated cats
Authors: Ash A. S. F. , Besch H. R. , Harigaya S. , Zaimis Eleanor 
Published: December 2014

1. Sarcoplasmic reticulum fragments (SRF) and actomyosin were isolated from skeletal muscle of cats treated either with thyroxine or with placebo tablets, for 5–16 months.2. Ca2+ uptake and binding by SRF, measured in the presence and absence of oxalate respectively, were reduced by thyroxine treatment.3. Actomyosin from the thyroxine‐treated animals underwent ATP‐induced syneresis at a faster rate than did that from the controls.4. Syneresis of the actomyosin preparations from controls and treated animals was inhibited to the same extent by EGTA when rates of syneresis were made the same by adjustment of the KCl concentration in the assay media. In contrast, at any given KCl concentration, syneresis of actomyosin from thyroxine‐treated animals was inhibited to a lesser extent by EGTA.5. At the end of the isolation procedure, the amount of Ca2+ remaining in the actomyosin suspension was similar for both treated and control animals.6. It was concluded that the effect of thyroxine on skeletal muscle may be the result of an action on both the sarcoplasmic reticulum and the contractile protein complex.
Magnesium exchange in rat ventricle
Authors: Page Ernest , Polimeni Philip I. 
Published: December 2014

1. The exchange of cellular Mg with external 28Mg in the rat left ventricle was measured in vivo and, under conditions approximating a steady state, in an isolated, working rat heart perfused and contracting at 36–38° C.2. About 98% of cellular Mg exchanged at a single rate.3. The rate of exchange in vivo was the same as that observed in independent in vitro measurements of the influx and efflux at the physiological external Mg2+ concentration of 0·56 m
M. The rate was 0·15 ± 0·02 m‐mole/(kg dry ventricle.min) or 0·21 ± 0·02 p‐mole/(cm2.sec).4. In the perfused heart the dependence of the influx on the external Mg concentration was hyperbolic with an apparent Vmax of 0·31 ± 0·04 m‐moles/(kg dry weight.min) and an apparent Km of 0·57 ± 0·08 m
M.5. The Mg efflux into a solution containing 2·8 m
M‐Mg was markedly faster than that into a Mg‐free solution.6. These results are interpreted as consistent with a carrier‐mediated transport of Mg across the plasma membrane.
Physiological and structural changes in the cat's soleus muscle due to immobilization at different lengths by plaster casts*
Authors: Tabary J. C. , Tabary C. , Tardieu C. , Tardieu G. , Goldspink G. 
Published: December 2014

1. Passive length—tension curves were established for cat soleus muscles that had been immobilized in different positions. Muscles that had been immobilized in the lengthened position showed no difference in their length—tension properties to those of normal muscles. However, those immobilized in the shortened position showed a considerable decrease in extensibility.2. Muscle fibre length, sarcomere length and the total number of sarcomeres along single teased fibres were also determined for muscles immobilized in different positions. Soleus muscles immobilized in the lengthened position were found to have 20% more sarcomeres in series than normal muscles whilst those immobilized in the shortened position had 40% less than normal muscles.3. When the plaster casts were removed from muscles that had been immobilized in the shortened position, the length—tension curves and sarcomere number returned to normal within 4 weeks. Muscles that were immobilized in a shortened position and then immobilized in a second position were found to rapidly adjust to the second position with respect to their passive length—tension properties and sarcomere number.4. A change in the number of sarcomere in series seems to be the way in which the sarcomere length of the muscle is adjusted to its new functional length. The change in the length—tension properties which accompanies a decrease in sarcomere number appears to be the mechanism which prevents the muscle from being overstretched.
Species difference in the choleretic response to bile salts
Authors: Klaassen Curtis D. 
Published: December 2014

1. Cholic, taurocholic and dehydrocholic acids were administered
I.V. to rats, rabbits and dogs (3·12–100 mg/kg). With the higher doses of cholic acid, the bile flow was increased sixfold in the dog and only 2 to 2½‐fold in the rat and rabbit. The choleretic response was also maintained for a longer time in the dog (90 min) than in the rat or rabbit (20–30 min).2. Similar species differences in the choleretic response to taurocholic acid and dehydrocholic acid were observed. However, the bile flow returned to control rates more rapidly for cholic acid (10–15 min for rat and rabbit, 45 min for dog) and more slowly for dehydrocholic acid (25–40 min for rat and rabbit, 120 min for dog).3. Cholic acid is conjugated more rapidly by the rabbit and rat than dog.4. An increase in the biliary bile acid concentration was observed in all three species after the
I.V. administration of the bile acid excreted by each species.5. Control bile flow was much higher in the rat (50 μl./min.kg) and the rabbit (70 μl./min.kg) than in the dog (5 μl./min.kg).6. Part of the difference in the choleretic response of the three species to the bile acids appears to be due to this difference in basal bile production.7. Administration of taurocholic acid to the rat increases the biliary bile acid concentration in the bile but the bile flow may either increase or decrease, questioning the mechanism by which bile acids increase bile flow.
The post‐natal changes in minimal metabolic rate in the pig
Authors: Studzinski T. 
Published: December 2014

1. Minimal metabolic rate was measured as oxygen consumption in new‐born pigs when environmental temperature was rising and passing through thermal neutrality.2. Three different periods were observed in 20 days after birth. The first period included the time from birth to 82 hr and was characterized by a continuous rise in minimal metabolic rate from 9·4 to 16·0 ml. O2/kg.min (70% increase). The second period extended from 82 hr to 9·5 days with values near to 16 ml. O2/kg.min. The third period beginning on the eleventh day lasted until observations ceased on the twentieth day and was characterized by a 25–30% fall in minimal metabolic rate when compared with the second period.3. Minimal metabolic rates from the second and third period were proportional to body weight and not to the surface area. Exponential factors for body weight were 0·93 and 0·96 for the second and third periods respectively.4. Rectal temperature rose from 38·6° C on the first day to 39·3° C on the second and 39·5° C on the fourth day after birth.5. Environmental temperature associated with minimal metabolic rate showed a general tendency to fall from 36·5 in the first 4 days to between 33 and 34° C in the following days.6. Age rather than body weight is the decisive factor influencing changes in minimal metabolic rate in the new‐born pig.
Axon‐schwann cell interaction in the squid nerve fibre
Authors: Villegas Jorge 
Published: December 2014

The electrical properties of Schwann cells and the effects of neuronal impulses on their membrane potential have been studied in the giant nerve fibre of the squid.1. The behaviour of the Schwann cell membrane to current injection into the cell was ohmic. No impulse‐like responses were observed with displacements of 35 mV in the membrane potential. The resistance of the Schwann cell membrane was found to be approximately 103 Ω cm2.2. A long‐lasting hyperpolarization is observed in the Schwann cells following the conduction of impulse trains by the axon. Whereas the propagation of a single impulse had little effect, prolonged stimulation of the fibre at 250 impulses/sec was followed by a hyperpolarization of the Schwann cell that gradually declined over a period of several minutes.3. The prolonged effects of nerve impulse trains on the Schwann cell were similar to those produced by depolarizing current pulses applied to the axon by the voltage‐clamp technique. Thus, a series of depolarizing pulses in the axon was followed by a long‐lasting hyperpolarization of the Schwann cells. In contrast, the application of a series of hyperpolarizing 100 mV pulses at a frequency of 1/sec had no apparent effects.4. Changes in the external potassium concentration did not reproduce the long‐lasting effects of nerve excitation.5. The hyperpolarizing effects of impulse trains were abolished by the incubation of the nerve fibre in a sea‐water solution containing trypsin.6. These findings are discussed in relation to the possible mechanisms that might be responsible for the long‐lasting hyperpolarizations of the Schwann cells.
Chromatic sensitivity and spatial organization of LGN neurone receptive fields in cat: cone‐rod interaction
Authors: Hammond P. 
Published: December 2014

1. The results described are for detailed analyses of fifty‐four isolated LGN units, in response to monochromatic stimuli presented against achromatic, mid‐mesopic backgrounds. Forty‐seven were positively identified cells from the A‐laminae; the remaining seven were fibres from the optic radiation.2. Cells are classified according to firing pattern. Phasic cells respond almost exclusively with a discharge transient. Tonic cells, by contrast, give a maintained component in addition. In general, tonic cells possess higher spontaneous firing frequencies than phasic cells and the antagonistic surrounds of their receptive fields are more potent. In other respects the two classes appear to be functionally similar.3. All cells within the A‐laminae receive input involving both rods and 556 nm cones.4. The spatial organization of geniculate receptive fields, unlike retinal fields, is little different for cone and rod vision. In the infrequent instances where a change is apparent, it is small and can go in either direction: rod fields are then on balance slightly larger than cone fields.5. The locus of maximum sensitivity for the receptive field surround is described by a circle, concentric with the field centre; it is invariant with respect to stimulus geometry, or changeover from cone to rod vision.6. This result implies that the receptive field surround mechanism does not extend through the field centre. It supports the notion that the centre and surround of each geniculate cell receptive field are mediated by discrete retinal inputs.
Conductance change during the inhibitory potential in the guinea‐pig taenia coli
Authors: Tomita T. 
Published: December 2014

1. Effects of membrane polarization and of reduction in external K and Cl concentration on the inhibitory potential were investigated in the guinea‐pig taenia coli.2. Depolarization of the membrane increased the inhibitory potential while hyperpolarization decreased it. The relationship between the degree of membrane polarization and the amplitude of inhibitory potential was linear. The inhibitory potential was abolished or slightly reversed in polarity, when the membrane was hyperpolarized by 25–40 mV in different preparations.3. Removal of external K ion depolarized the membrane for about 5 min and increased the inhibitory potential more than could be accounted for by the depolarization. Readmission of K transiently hyperpolarized the membrane, probably due to an activation of the Na‐K pump, and reduced the inhibitory potential, but no reversal of polarity in the inhibitory potential was observed during this hyperpolarizing phase.4. The membrane was transiently depolarized when the external Cl concentration was reduced by substituting with isethionate. Hyperpolarization was produced by restoring the external Cl concentration to normal. Changes in the amplitude of inhibitory potentials during alterations in Cl concentration occurred as expected from the shift of the membrane potential.5. From the results, it is concluded that the membrane conductance is increased during the inhibitory potential, and that an increase in the K permeability is the main factor for hyperpolarization of the membrane.
The receptors concerned in the actions of catecholamines on glucose release, membrane potential and ion movements in guinea‐pig liver
Authors: Haylett D. G. , Jenkinson D. H. 
Published: December 2014

1. Experiments have been made to identify the kinds of receptors concerned in the actions of catecholamines in increasing potassium efflux, membrane potential and glucose release in tissue slices prepared from guinea‐pig liver.2. Glucose release could be accelerated by activation of either of two distinct receptors, one of which resembles the α receptor of Ahlquist's classification, the other being β‐like. Thus both amidephrine and isoprenaline (sympathomimetic amines which selectively activate α and β receptors respectively) elicited the response.3. The effect of isoprenaline on glucose release was inhibited by the β blocking agent propranolol (1 μ
M) but not by the α blocker phentolamine (10 μ
M), whereas the converse held for amidephrine. However, the degree of antagonism observed with phentolamine was less than found in smooth muscle, suggesting that the α‐like receptor in the liver may differ somewhat from that in other tissues, or be less accessible to the antagonist.4. Amidephrine, like noradrenaline, increased the efflux of 42K from the slices and caused hyperpolarization, suggesting that the increase in potassium permeability underlying these responses is α‐mediated. This conclusion was supported by the finding that the effect of amidephrine on membrane potential was inhibited by phentolamine but not propranolol (1 μ
M).5. In keeping with this interpretation, low concentrations (20–50 n
M) of isoprenaline, although sufficient to activate the β receptors (as judged by the effect on glucose release) had little effect on the ionic composition of the tissue, and caused only a small increase in 42K efflux. Thus the ‘ion movement’ and ‘glucose’ responses could be largely dissociated.6. Larger concentrations (1–6 μ
M) of isoprenaline increased 42K efflux to a greater extent, although the effect was always less than with the same concentration of noradrenaline.7. Activation of the β‐receptors caused a small and inconsistent hyperpolarization which became more pronounced and also more reproducible on replacing the chloride content of the bathing fluid by the larger anion isethionate.8. Although these results show that activation of either of two distinct adrenergic receptors in guinea‐pig liver can cause the same end‐response (e.g. an increase in glucose release, or, under some circumstances, hyperpolarization of the cell membrane), the underlying mechanisms cannot be assumed to be identical. This is discussed.
Cholinergic and non‐cholinergic transmission in the medial geniculate nucleus of the cat
Authors: Tebēcis Andris K. 
Published: December 2014

1. Studies involving the electrophoretic administration of antagonists of ACh (atropine, DHβE) and cholinesterase inhibitors (neostigmine, physostigmine) to MGN neurones indicate that ACh is an excitatory transmitter in the feline MGN, most probably released from fibres which originate in or traverse the mesencephalon.2. Auditory afferents to the MGN, cortico‐geniculate fibres and the excitatory fibres which mediate ‘spontaneous’ firing of MGN neurones are unlikely to be cholinergic.3. Almost all geniculo‐cortical relay cells are excited by ACh, this excitation being mediated by receptors which have both muscarinic and nicotinic properties. The excitation of relay cells by ACh is sometimes preceded or followed by a depression of firing which is resistant to atropine and DHβE, but the significance of this depression is unknown.4. The firing of many unidentified MGN neurones is depressed by ACh in the absence of any excitation, and this depression is blocked by both atropine and DHβE, and potentiated by anticholinesterases. This type of depression by ACh may be related to cholinergic inhibition, but this possibility has yet to be investigated.
Prostaglandin action on pancreatic blood flow and on electrolyte and enzyme secretion by exocrine pancreas in vivo and in vitro
Authors: Case R. M. , Scratcherd T. 
Published: December 2014

1. Intra‐arterial injection or infusion of prostaglandins E1 and E2 into anaesthetized cats caused a fall in arterial blood pressure, a reduction in pancreatic blood flow and an inhibition of secretin‐stimulated pancreatic electrolyte secretion. In some experiments these effects were preceded by a transient increase in blood flow and secretion.2. The fall in blood pressure and reduction in blood flow, but not the inhibition of secretion, were much less marked following administration of the α‐adrenergic blocking agent phenoxybenzamine.3. Prostaglandins F1α and F2α caused only a slight reduction in blood pressure and had very little effect on pancreatic blood flow or electrolyte secretion.4. Addition of prostaglandins to the perfusate of the saline‐perfused cat pancreas stimulated electrolyte secretion, with E1 = E2 ≫ F1α = F2α. This stimulatory action was markedly potentiated by theophylline.5. Enzyme secretion was not stimulated by any of the prostaglandins, even in the presence of theophylline.6. It is concluded that prostaglandins can stimulate electrolyte transport by exocrine pancreas, perhaps through a mechanism involving adenylate cyclase, but that in vivo this action is masked by a secondary inhibition resulting either from vasoconstriction, or from the libration of an antisecretory agent, or both.
The kinetics of transmitter release at the frog neuromuscular junction
Authors: Barrett Ellen F. , Stevens C. F. 
Published: December 2014

1. Fluctuations in the latency of focally recorded end‐plate currents were analysed to determine the time course of the probabilistic presynaptic process underlying quantal release evoked after single nerve stimuli at the frog neuromuscular junction.2. The early falling phase of the presynaptic probability function can be fitted by a single exponential over two orders of magnitude of quantal release rate. The time constant of the early falling phase is about 0·5 msec at 11° C, and increases with decreasing temperature with a Q10 of at least 4 over the range 1–12° C.3. After this early exponential fall, quantal release probability returns to control levels with a much slower time course.4. Conditioning nerve stimuli increase the magnitude and slightly prolong the early time course of release evoked by a test stimulus. When facilitation is calculated for matched time intervals following the conditioning and testing stimuli, it is found that the magnitude of the small, late residual tail of release is facilitated by a greater percentage than the magnitude of larger, early portions of release.5. These results are discussed in terms of the hypothesis (Katz & Miledi, 1968) that evoked release and facilitation are mediated by a common presynaptic factor which activates release in a non‐linear manner.
Synaptic frequency response: the influence of sinusoidal changes in stimulation frequency on the amplitude of the end‐plate potential
Authors: Landau E. M. , Lass Y. 
Published: December 2014

1. The synaptic response to frequency modulated trains of stimuli was investigated at the neuromuscular junction of the frog. The frequency of stimulation was usually varied sinusoidally about a carrier frequency of ca. 25 impulses per sec (Hz).2. The post‐synaptic response to sinusoidally modulated trains of nerve stimuli was found to grow almost linearly when the variations in input frequency were increased up to 60% of the carrier frequency.3. The synaptic frequency response (gain and phase) was reminiscent of that of a low‐pass filter, best transmitting slow variations in input frequency.4. The synaptic filter characteristics could not be explained by the post‐synaptic cable properties, but were attributed to presynaptic facilitation processes.
The rate equation and activation energies for the uptake of α‐aminoisobutyric acid by mouse brain slices
Authors: Cohen Stephen R. 
Published: December 2014

1. The initial influx of the amino acid analogue AIB at medium concentrations of 0·05–20 mM into mouse cerebrum slices incubated at temperatures from 20 to 45° C follows the rate law v = Vmax/(1 + Kt/S)+kuS. The linear term kuS arises from an unsaturable process of concentrative uptake.2. At 37° C the kinetic constants are Kt = 1·12 mM; Vmax = 0·39 μmole AIB/g final wet wt. of slices. min; and ku = 0·054 μmole AIB/g final wet wt. of slices. mM‐AIB. min.3. At infinitesmal substrate concentrations 13% of influx is via the unsaturable process. This rises to 73% for 20 mM substrate.4. Kt is independent of temperature. The other constants increase rapidly with temperature. Arrhenius activation energies are 14·1 kcal/mole for Vmax and 17·4 kcal/mole for ku.
Transmitter release by mammalian motor nerve terminals in response to focal polarization
Authors: Cooke J. D. , Quastel D. M. J. 
Published: December 2014

1. A method is described by which mammalian motor nerve terminals may be uniformly polarized by focally applied current, and the extra‐cellular potential in the synaptic cleft, corresponding to any current, estimated.2. The relationship between log m.e.p.p. frequency and local extra‐cellular field is flat for hyperpolarization and ascends linearly with depolarization. With depolarization, m.e.p.p. frequency is multiplied about tenfold for every — 18 mV. This characteristic becomes steeper the closer the polarizing electrode to the nerve terminal with a limiting value of ten‐fold per — 15 mV.3. There exists a population of small m.e.p.p.s which are generated at the same end‐plate as normal m.e.p.p.s.4. Following a prolonged depolarizing pulse there is an increase of m.e.p.p. frequency which continues for periods of up to several minutes.5. With hyperpolarizing pulses m.e.p.p. frequency may increase in a characteristic ‘bursty’ manner. Similar bursts of m.e.p.p.s also occur spontaneously, but far less frequently, without polarization.6. During a depolarizing pulse, m.e.p.p. frequency becomes maximal or near maximal within 2 sec. There is little subsequent alteration of m.e.p.p. frequency. Numbers of m.e.p.p.s occurring during depolarizing pulses follow the Poisson distribution.7. Following a depolarizing pulse, numbers of m.e.p.p.s released by a subsequent pulse may be either increased or diminished.8. Comparison of the response of m.e.p.p. frequency to raised [K] and to extrinsic presynaptic polarization leads to the conclusion that the presynaptic transmembrane potential change corresponding to any focal current pulse is about two thirds of the local extracellular potential field. Hence the slope of the linear portion of the presynaptic transfer function is about tenfold per 10 mV presynaptic depolarization.