bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of previous dietary history of calcium intake on the skeleton and calcium absorption in the rat
Authors: Kemm J. R. 
Published: December 2014

1. Rats were fed either a high or a low calcium diet for 6 weeks. Thereafter all were given the low calcium diet, and the time during which differences persisted between the two groups in apparent absorption of calcium and urinary excretion of calcium has been studied. The apparent absorption of calcium is the same in the two groups after 15 days but the differences in urinary excretion of calcium persist longer.2. Faecal endogenous calcium and true absorption of calcium have been measured by an isotope dilution technique. The fall in apparent absorption of calcium seen in rats fed a high calcium diet is in part due to a fall in true absorption. Faecal endogenous calcium is also increased in these animals.3. The amount of calcium and phosphate in the bones is increased by feeding a high calcium diet and decreased by feeding a very low phosphate diet. Femur, humerus, caudal vertebrae and calvaria are equally affected by the different diets.4. There are strong inverse correlations between absorption of calcium and the percentage of calcium in the bones. This suggests that absorption of calcium may be regulated by the degree of bone mineralization.5. Rats were fed diets with different calcium phosphate ratios for 6 weeks. Thereafter all were given a low calcium diet with a calcium: phosphorous ratio of 1 and absorption and urinary excretion of calcium were studied. The effects of the different diets may be explained by their effect on calcium status and bone mineralization.
The spinal origin of the motor and inhibitory innervation of the rat anococcygeus muscles
Authors: Gillespie J. S. , McGrath J. C. 
Published: December 2014

1. A preparation is described whereby the responses of the two anococcygeus muscles can be recorded in vivo in the pithed rat and the autonomic outflows to the muscle selectively stimulated in the spinal canal.2. Motor responses are obtained from stimulation at two levels; an upper extending from T 11 to L 3 and a lower from L 6 to S 2. Stimulation between these levels, i.e. between L 3 and L 6, produces no response. The response to stimulation at both upper and lower levels is abolished by phentolamine. The response to stimulation in the upper region is abolished by hexamethonium and is, therefore, presumably preganglionic; the response to stimulation at the lower level is resistant to hexamethonium and presumably post‐ganglionic. Stimulation at levels above T 11 causes contraction after a delay, by liberating catecholamines from the adrenal medulla. This effect is blocked by both phentolamine and hexamethonium.3. If the adrenergic motor nerves are blocked and the muscle tone raised by a combination of guanethidine and tyramine, stimulation between L 5 and S 2 produces inhibition. The inhibitory outflow, therefore, overlaps the motor outflow but extends one segment more rostral (L 5). Stimulation restricted to this L 5 segment even in the presence of a normal unblocked motor innervation causes inhibition. The inhibitory response is blocked by hexamethonium or mecamylamine but desensitization and ‘escape’ occurs. This desensitization is less than that observed in the vas deferens when its motor nerves are similarly stimulated in the spinal cord.4. It is concluded that inhibitory fibres to the anococcygeus arise in the spinal cord and are organized in the pattern of the autonomic nervous system with a peripheral synapse. The site of origin of these inhibitory fibres is different from the motor adrenergic fibres to the muscle.
Maintenance of normal corneal thickness in the cold in vivo (hibernation) as opposed to in vitro
Authors: Bito L. Z. , Roberts Jane C. , Saraf S. 
Published: December 2014

1. Corneal thickness was measured in vivo in normothermic and hibernating (body temperature = 7–10° C) woodchucks and the [Na+], [K+], [Mg2+] and water content of woodchuck and rabbit corneas were determined on freshly isolated tissues.2. Woodchuck eyes from both normothermic and hibernating animals were incubated in moist chambers at 5 or 11° C and the corneal thickness was measured periodically.3. Woodchuck corneas undergo continuous swelling when kept in vitro in a moist chamber at either 5 or 11° C. The rate of this swelling was the same for eyes from active and hibernating animals; it was almost completely reversible upon rewarming at 35° C.4. In the hibernating woodchuck the corneal thickness did not increase measurably, even after several days of hibernation, although the mean corneal temperature was 9·4° C.5. At 7° C, the lactate production of corneas from both hibernating and normothermic woodchucks was reduced to about one fifth its levels measured at 37° C. Oxygen consumption was also greatly reduced in the cold although the endothelial O2 consumption of corneas from hibernating woodchucks appears to be relatively insensitive to cold.6. It is concluded that removal of the eye and/or the in vitro conditions per se render the cornea more vulnerable to the effects of cold, possibly as a result of the elimination of the influences of orbital tissues and/or secretions or as a result of changes in some intrinsic properties of the cornea due to the elimination of neurohumoural factors or the release of autocoids.7. The finding that normal corneal thickness can be maintained under conditions where the environment is maintained essentially constant for days strongly argues against the validity of the recently proposed nonsteady‐state theory of corneal thickness control.
Isometric contractions of motor units in a fast twitch muscle of the cat
Authors: Bagust J. , Knott Sarah , Lewis D. M. , Luck J. C. , Westerman R. A. 
Published: December 2014

1. Isosmetric contractions of cat flexor digitorum longus whole muscles and of functionally isolated motor units have been measured under conditions similar to those used by Buller & Lewis (1965a).2. Motor unit twitch time to peak was inversely related to axonal conduction velocity. The logarithm of tetanic tension was directly related to conduction velocity. These relationships suggest that each motoneurone has an influence on the muscle fibres which it innervates.3. The ratio of twitch to tetanic tension was directly related to the time to peak of the motor unit. This fact might be explained by variation between motor units of the duration of ‘active state’.4. The muscle length at which tension was maximal varied between motor units and the optima were found over the range of muscle lengths which could occur in the body. Slow motor units had longer optimal lengths.5. The sample of motor units was considered to be unbiased because the distribution of axon conduction velocities was compatible with reported motor fibre diameter spectra of the muscle nerve. The mean motor unit tetanic tension gave a reasonable estimate of the number of α‐motor axons in the muscle nerve. Twitch tensions gave a value that was 40% higher.6. Motor unit and whole muscle data were in good agreement for length‐tetanus tension curves, for times to peak and for twitch‐tetanus ratios at long muscle lengths.
The asymmetry of the facilitated transfer system for hexoses in human red cells and the simple kinetics of a two component model
Authors: Baker G. F. , Widdas W. F. 
Published: December 2014

1. 4, 6‐O‐Ethylidene‐α‐
D‐glucopyranose (ethylidene glucose) has been used to study the competitive inhibition of glucose exchange fluxes when the reagent was (i) inside the cells and (ii) on the outside.2. 50% inhibition of glucose exchange at 20 m
M and 16° C required 200 m
M ethylidene glucose when on the inside in contrast to 25–30 m
M when on the outside.3. The inhibitions at different inhibitor/glucose concentration ratios were measured and analysis of the data suggested that the half‐saturation constant for ethylidene glucose was 6 times that for glucose inside the cell as against 1·5 outside. The analysis, however, suggested an asymmetry in respect to the affinities for glucose of approximately ten‐fold and this would make the asymmetry towards ethylidene glucose forty‐fold.4. Such asymmetries make it necessary to consider a transfer mechanism for sugars with different components on the outer and inner membrane interfaces and simple kinetics for a two component system have been developed and used for analysing the experimental data quantitatively.5. The kinetic similarities to and difference from the kinetics of a simple mobile carrier and those of some more recent models are briefly discussed.
The effects of temperature and metabolic inhibitors on the spontaneous relaxation of the potassium contracture of the heart of the frog Rana pipiens
Authors: Chapman R. A. 
Published: December 2014

1. The spontaneous relaxation of the potassium contracture and the relaxation induced by the removal of extracellular calcium or the restoration of the original potassium concentration, in the frog heart, show a strong dependence on temperature.2. The energy of activation of the later exponential phase of the spontaneous relaxation is 10·43 kcal mole−1, a value close to that reported for the binding of calcium ions by isolated sarcoplasmic reticulum, but larger than that for the calcium efflux from mammalian heart.3. The use of metabolic inhibitors shows that relaxation can be sustained when glycolysis is poisoned, but the disruption of oxidative phosphorylation slows relaxation.4. Poisoning of both glycolysis and oxidative phosphorylation blocks all but the small initial part of the spontaneous relaxation of the potassium contracture and also interferes with relaxation induced by other means.5. The results are considered to favour the existence, in frog heart, of an active intracellular relaxing system which uses ATP as its substrate to lower the sarcoplasmic calcium concentration. This system is likely to be the sarcoplasmic reticulum but the mitochondria could also be involved.
Pancreatic acinar cells: ionic dependence of the membrane potential and acetylcholine‐induced depolarization
Authors: Matthews E. K. , Petersen O. H. 
Published: December 2014

1. Intracellular recordings of membrane potentials have been made in vitro from the exocrine acinar cells of the mouse pancreas using glass micro‐electrodes.2. The mean membrane potential of the acinar cells during superfusion with Krebs‐Henseleit solution was −39·2 mV. Increasing [K]o tenfold decreased the membrane potential by 28 mV when [K]o was above 10 m
M. This depolarization was not affected by atropine (1·4 × 10−6
M). Strophanthin‐G (10−3
M) slowly depolarized the cells at about 10 mV hr−1.3. Brief exposure to acetylcholine (ACh), 5·5 × 10−5
M, or pancreozymin resulted in a short lasting depolarization of the acinar cells. Atropine (1·4 × 10−6
M) blocked the depolarizing action of ACh but not that of pancreozymin. Adrenaline (5·5 × 10−5
M) or cyclic AMP (10−3‐10−4
M) did not influence the membrane potential.4. The amplitude of the ACh‐induced depolarization was not dependent on the presence of CO2/HCO3 in the bathing fluid, but it was closely dependent on the extracellular Na concentration. However, ACh was still able to evoke a small depolarization even after prolonged exposure of the tissue to a Na‐free solution.5. During exposure of the tissue to a Ca‐free solution the resting membrane potential was decreased and the ACh‐induced depolarization was significantly reduced. Some substances which are known in other tissues to inhibit membrane Ca2+ currents, i.e. La3+, D‐600 and tetracaine, were able to reduce, but never abolish, the ACh‐induced depolarization.6. These results suggest that the effect of ACh on the pancreatic acinar cell is to increase the permeability of the membrane to commonly occurring ions with a consequent Na‐influx and a small Ca‐influx.
Effects of membrane depolarization on light scattering by cerebral cortical slices
Authors: Lipton Peter 
Published: December 2014

1. A system is described for simultaneously measuring the respiration and the reflectance of a tissue slice and is applied to a study of guinea‐pig cerebral cortical slices.2. Reducing bathing medium osmolarity led to a reversible decrease in reflectance of these slices (as well as slices from liver and kidney cortex). In half isotonic solutions reflectance was reduced by 31%.3. Anoxia led to a decreased reflectance which was eliminated if all the Cl was substituted by the larger glucuronate anion.4. It is concluded that slice reflectance is lowered when cellular volumes are increased by water or isotonic solution influx.5. Membrane depolarization effected by ouabain, high (60 m
M) K bathing medium, veratridine or repeated electrical pulses led to rapid decreases in reflectance of 25, 27, 31 and 7·5% respectively. Turning off the electrical pulses caused reflectance to return to control values. Reversibility of the chemical effectors was not tested.6. Substitution of Cl by glucuronate abolished the reflectance changes, although it did not inhibit the increased respiration induced by the depolarizing stimuli.7. Tetrodotoxin abolished both the respiratory and reflectance effects of veratridine and electrical pulses but had no effect upon those of high K or ouabain.8. The decrease in reflectance began about 1 sec after initiation of the pulses and was half maximal by 8 sec.9. Titrating reflectance against [K] showed that an increase of 5 m
M‐K led to a 4% decrease in reflectance and that reflectance became minimal between 60 and 80 m
M‐K+.10. It is concluded that membrane depolarization in excitable cells of the cerebral cortex (and also, possibly, in the glia) causes rapid increases in cell volume due to influx of isotonic solution.11. The results indicate, more specifically, that changes in intercellular K concentrations of size and duration thought to occur following nervous activity in the
C.N.S. cause cell volume changes large enough to drastically reduce the intercellular volumes and so, transiently, increase extracellular molecular and ionic concentrations. Increases of extracellular [K] and [Ca] have significant effects upon synaptic transmission and upon spontaneous nervous activity. It is suggested that nervous activity in one cell (or portion of it) might, in this way, strongly influence function in neighbouring elements.
Effects of potassium cyanide, strophanthin or sodium‐free perfusion fluid on the electrical potential difference across the guinea‐pig placenta perfused in situ
Authors: Štulc J. , Švihovec J. 
Published: December 2014

1. The possible role of active transport of Na in generating the transplacental potential difference (p.d.) was studied in the guinea‐pig placenta perfused in situ by testing the effects of strophanthin or KCN added to the perfusate or of Na‐free perfusion fluid.2. The p.d. across the perfused placenta was about −20 mV, and was relatively steady during perfusion.3. Strophanthin (10−5
M) slightly increased the p.d. In a concentration of 2 × 10−6
M strophanthin was without significant effect.4. KCN (10−3
M) decreased the p.d. When KCN was removed after a 30 min treatment the p.d. increased significantly exceeding the initial level. KCN (10−4
M) slightly increased the p.d.5. Perfusion with Na‐free fluid decreased the p.d. to a steady level of about 50–60% of the control values.6. Perfusion with Na‐free fluid containing KCN (10−3
M) for 30 min decreased the p.d. However, the effect did not seem different from the effect of KCN (10−3
M) or Na‐free fluid alone. When KCN was removed the p.d. significantly increased in spite of continued perfusion with Na‐free fluid.7. Excepting the effect of KCN (10−4
M), which could not be explained, the observations were found to be consistent with active transport of Na from foetal to maternal side of the placenta as a source of the p.d. The Na transport could account for about 40–50% of the p.d.
Intracellular recording from the myenteric plexus of the guinea‐pig ileum
Authors: Nishi S. , North R. A. 
Published: December 2014

1. Ganglion cells of the myenteric plexus of the guinea‐pig ileum have been studied with intracellular micro‐electrodes.2. Three types of cell were distinguished. Type 1 cells had a high resistance (58 MΩ) and had properties similar to guinea‐pig sympathetic ganglion cells. Type 2 cells were also excitable but had a lower resistance (21 MΩ) and showed accommodation to depolarizing current pulses. Type 3 cells were inexcitable.3. Point stimulation within 150 μm excited neurones either antidromically or orthodromically, sometimes both.4. Antidromic responses had a small all‐or‐nothing component which was subthreshold for the soma spike. Two or more such components sometimes occurred, and were probably due to stimulation of two or more cell processes.5. Excitatory post‐synaptic potentials (e.p.s.p.s) were blocked by hexamethonium (400 μ
M). They progressively declined in amplitude when elicited at frequencies of 0·05 Hz or more, and this is discussed in relation to studies on acetylcholine (ACh) output.6. Many cells often showed a slow after‐hyperpolarization following a direct or antidromic spike. Its mechanism and significance are discussed.7. Spontaneous e.p.s.p.s and spikes were occasionally seen.8. Intracellular injection of a fluorescent dye reveals that the neurones have one to seven processes, which usually arise from the poles of the oval soma.
Effect of insulin upon the sodium pump in frog skeletal muscle
Authors: Moore Richard D. 
Published: December 2014

1. Insulin increased the rate of net Na extrusion from Na‐loaded frog skeletal muscle into glucose‐free Na‐Ringer. After a 90 min period of efflux, the insulin‐treated muscles contained approximately 11% less intracellular water than did their controls. This decrease in intracellular water resulted in an increase in the concentration of intracellular K, [K+]i, even though there was no definite effect upon net K flux. In spite of the decrease in intracellular water, [Na+]i was lower in those muscles treated with 500 m‐u. insulin/ml. than in the controls.2. Insulin consistently increased 22Na efflux into Na‐Ringer containing either 10 or 2·5 m
M‐K+. This effect was reversible and was not produced by other proteins.3. Acetylstrophanthidin (5 × 10−6
M) blocked all or nearly all net Na efflux even in the presence of insulin. The presence of this concentration of acetylstrophanthidin or of K‐free Na‐Ringer inhibited the effect of insulin upon 22Na efflux from Na‐loaded muscles.4. All of the above results indicate that insulin in some way increases the activity of the Na pump. The inhibition by K‐free Na‐Ringer also suggests that this is not due to production of additional pump sites.5. Insulin also increased 22Na efflux and net sodium efflux into Li‐Ringer. When the new steady‐state was reached after addition of insulin, the 22Na kinetics still obeyed a power relation to intracellular 22Na. However, in every single case, insulin resulted in a decrease of approximately 18% in the exponent, n.6. Curve‐fitting of the kinetic data to equations based upon a three‐site model of the Na pump suggests that insulin increases the affinity of the sites toward Na+. In terms of Eisenman's theory of ion selectivity, this would indicate an increase in the anionic field strength of the Na‐carrying sites and also predict that the increase in affinity for H+ would be greater than that for Na+. This latter prediction is entirely consistent with the observed decrease in n.7. The results suggest that insulin may be increasing H+ efflux as well as Na+ efflux and thereby may be increasing intracellular pH. It is suggested that some of the intracellular effects of insulin might be mediated by such an effect.
Effects of tubocurarine and eserine on the axon‐Schwann cell relationship in the squid nerve fibre
Authors: Villegas Jorge 
Published: December 2014

The effects of eserine and
D‐tubocurarine on the axon and Schwann cell membrane potentials have been studied in the giant nerve fibre of the squid.1. The addition of eserine at concentrations of up to 10−4
M to the external sea‐water medium has no appreciable effects on either the Schwann cell electrical potential of unstimulated nerve fibres or on the resting and action potentials of the axon.2. However, eserine at a concentration of 10−9
M prolongs the long‐lasting Schwann cell hyperpolarizations which follow the conduction of impulse trains by the axon.3. Higher concentrations of eserine (10−7, 10−4
M) decrease and block the long‐lasting effects of nerve impulse train conduction.4.
D‐tubocurarine at concentrations of up to 10−5
M has no appreciable effect on the resting and action potentials of the axon.5. However,
D‐tubocurarine at a concentration of 10−9
M blocks completely the hyperpolarizing effects of nerve impulse trains on the Schwann cell electrical potential.6. In addition to its blocking action,
D‐tubocurarine induces transient hyperpolarizations in the Schwann cells of unstimulated nerve fibres both in intact fibres and in slitted preparations.7. These findings suggest that a cholinergic system, which may be located at the axon‐Schwann cell boundary, is involved in the genesis of the long‐lasting Schwann cell hyperpolarization caused by the conduction of nerve impulse trains by the axon.
The role of the liver in non‐shivering thermogenesis in the rat
Authors: Stoner H. B. 
Published: December 2014

1. The temperatures of the liver and afferent aortic and portal blood were measured in 20° C acclimated rats at different environmental temperatures (Ta) between 20 and 37° C. The heated‐thermocouple technique was used to measure the metabolic heat production of the liver, its blood flow, and to correct the temperature difference between it and the reference junction for blood flow.2. The temperature of the liver was higher than that of the afferent blood. On raising Ta from 20 to 30° C the liver temperature fell and the temperature difference between the liver and the aortic blood was reduced despite the decrease in the thermal gradient between the liver and the exterior and a small reduction in hepatic blood flow. A further rise in Ta to 37° C led to an increase in the liver and blood temperatures. The same pattern was seen when the temperature differences were corrected for blood flow.3. Metabolic heat production in the liver decreased when Ta was raised from 20 to 30° C.4. In a 20° C environment inhibition of non‐shivering thermogenesis with propranolol HCl (10 mg/kg body wt.
I.V.) led to a fall in the temperature of the liver and its metabolic heat production towards levels found in untreated rats at Ta = 30° C. Consequently, in treated rats the change in metabolic heat production on raising Ta to 30° C was less than in untreated ones.5. These results are interpreted as evidence for the participation of the liver in thermoregulatory non‐shivering thermogenesis.