bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Role of Phosphoinositide Metabolism in Signal Transduction in Secretory Cells
Authors: Putney James W. 
Published: April 2021

ABSTRACT
Activation of a variety of cell surface receptors results in a biphasic increase in the cytoplasmic Ca2+ concentration, due to the release, or mobilization, of intracellular Ca2+ stores and to the entry of Ca2+ from the extracellular space. Stimulation of these same receptors also results in the phospholipase-C-catalysed hydrolysis of the minor plasma membrane phospholipid, phosphatidylinositol 4,5-bisphosphate, with the concomitant formation of inositol 1,4,5-trisphosphate [Ins(l,4,5)P3] and diacylglycerol. Analogous to the adenylyl cyclase signalling system, receptor-mediated stimulation of phospholipase C also appears to occur through one or more intermediary guanine nucleotide-dependent regulatory proteins. It is well established that phosphatidylinositol 4,5-bisphosphate hydrolysis is responsible for the changes in Ca2+ homeostasis. There is strong evidence that Ins(l,4,5)P3 stimulates Ca2+ release from intracellular stores. The Camreleasing actions of Ins(l,4,5)P3 are terminated by its metabolism through two distinct pathways. Ins(l,4,5)P3 is dephosphorylated by a 5-phosphatase to Ins(l,4)P2; alternatively, Ins(l,4,5)P3 can also be phosphorylated to Ins(l,3,4,5)P4 by a 3-kinase. Whereas the mechanism of Ca2+ mobilization is understood, the precise mechanisms involved in Ca2+ entry are not known; a recent proposal that Ins(l,4,5)P3, by emptying an intracellular Ca2+ pool, secondarily elicits Ca2+ entry will be considered. This review summarizes our current understanding of the mechanisms by which inositol phosphates regulate cytoplasmic Ca2+ concentrations.
Optimizing Release From Peptide Hormone Secretory Nerve Terminals
Authors: Bicknell R. J. 
Published: April 2021

ABSTRACT
Secretion of the peptide neurohormones oxytocin and vasopressin from terminals of magnocellular neurones in the mammalian neurohypophysis is elicited by conduction of depolarizing action potentials into terminal membranes, inducing opening of voltage-sensitive Ca2+ channels, entry of Ca2+ from the extracellular space and a rise in cytoplasmic Ca2+ concentration. The amount of peptide released per action potential is not immutable. In particular, the patterns in which action potentials are generated at the cell somata of the two types of neurone each appear exquisitely suited to optimize the release process at the terminal by utilizing a frequency-facilitation mechanism and by minimizing a mechanism of fatigue in the release process. The different properties of oxytocin and vasopressin neurones are of important physiological significance. The secretory terminals are also a site of receptor-mediated influences of neuromodulators which can greatly alter release efficiency. The mechanisms underlying facilitation and fatigue are not clearly understood. The evidence suggests that processes both prior to depolarization of the terminals (propagation and form of the action potentials) and directly at the terminals (frequency/pattern-dependent Ca2+ entry and channel openings) are involved. Transient activity-related increases in extracellular K+ concentration may be involved at both sites. Two types of neuromodulation have been partly characterized. K-Opioid receptors in secretory terminal membranes directly modulate depolarization-evoked peptide release probably via interactions with Ca2+ channels. β-Adrenergic receptors localized on neurohypophyseal astroglial cells mediate more subtle effects of noradrenaline. In the more chronic situation the neurohypophyseal astroglia alter their morphological relationships with neurosecretory elements and the basal lamina at release sites, changes which may also serve to optimize the secretory process.
The Humidity Reactions of the Wood-Louse,Porcellio Scaber(Latreille)
Authors: Gunn D. L. 
Published: April 2021

ABSTRACTPorcellio scaber exhibits hygrokinesis, being very active in dry air and almost motionless in nearly saturated air. With rising humidity a steadily increasing proportion of a batch of specimens is found to be inactive at any one moment. P. scaber also shows hygrophobotactic behaviour. The effect of both reactions is to collect the animals into moist air. In a humidity gradient of given steepness the intensity of the humidity preference varies at different parts of the humidity range. There is no reaction at all if the gradient does not include a region below 65 per cent R.H. There is definite reaction to a difference of 6 per cent R.H. in approximately half-saturated air. The humidity receptors, if they are confined to one area, apparently do not lie on the abdomen or on the head region.
The Determination of the Auditory Placode in the Chick
Authors: Waddington C. H. 
Published: April 2021

ABSTRACTThe presumptive ear ectoderm, removed from its normal site and transplanted to the amnio-cardiac vesicle, does not develop into an otic placode unless it comes from an embryo with more than nine pairs of somites. The ectoderm which grows over the place from which the presumptive ear ectoderm is removed is induced to form an otic placode, the size of the placode being smaller the older the embryo at the time of operation. If the wall of the neural tube, including the neural crest, is removed from the region of the ear in embryos younger than the nine-somite stage, an ear may nevertheless be formed. Since the ear ectoderm at this stage is not capable of differentiating when isolated, this result shows that inducing agencies other than the neural material are active at this stage. In some of the operated embryos, the acoustico-facialis ganglion was completely lacking, so this structure cannot be the sole organizer of the ear, as Szepsenwol suggested. If both the wall of the neural tube and the presumptive ear ectoderm are removed, no ear is formed even in stages younger than the nine-somite stage, so that it appears that the non-neural inducing agents are more effective when working on presumptive ectoderm of this age than when working on non-presumptive ectoderm. This suggests that the ear ectoderm is beginning to be determined some time before it acquires the capacity for independent differentiation. The wall of the neural tube, from the ear region, can induce a small ear when grafted under the ectoderm of the anterior part of the head. The evidence suggests that the induction of the ear in normal development is due to the combined action of several structures, of which the wall of the neural tube, and the tissues derived from it (ganglia), is one but not the only one.
On the Structure and Function of the Wandering Cells in the Wall of the Alimentary Canal of Nudibranchiate Mollusca
Authors: Millott Norman 
Published: April 2021

ABSTRACTThe lining epithelium and subjacent tissues of the gut of nudibranch molluscs contain characteristic wandering cells. Although probably amoeboid when alive, the wandering cells after fixation are seen to possess a very definite rounded form. They have a distinct nucleus. The cytoplasm contains a variety of inclusions, and, characteristically, a well-marked eosinophile area. The reaction of the cells to stains is described. The wandering cells were found to take up iron saccharate, which had been injected into the haemocoele. The wandering cells are regarded as a special type of blood cell. Evidence indicates that the wandering cells of nudibranchs are excretory, taking up effete matter from the haemocoele and discharging it into the lumen of the gut.
On Phosphorus Metabolism in Embryonic Life
Authors: Lehmann Hermann , Needham Joseph 
Published: April 2021

ABSTRACTThe chick embryo possesses the power of synthesizing creatinephosphate from phosphopyruvic acid and creatine with adenylic acid as phosphate transporter. This reaction has been followed back into the early stages of development. At the 43 rd hour (approximately the beginning of cardiac activity) it is present in an unweakened state. At the 23rd hour (during the closure of the neural folds), although phosphopyruvic acid is dephosphorylated by adenylic acid, phosphagen synthesis is exceedingly weak. At no age does the synthesis of argininephosphate occur in the chick embryo. The significance of this and the above facts is discussed in the text.
Muscular Mechanisms of Snake Locomotion: an Electromyographic Study of the Sidewinding and Concertina Modes of Crotalus Cerastes, Nerodia Fasciata and Elaphe Obsoleta
Authors: Jayne Bruce C. 
Published: April 2021

ABSTRACT
Synchronized electromyography and cinematography were used to determine the muscle activity of colubroid snakes during sidewinding and concertina locomotion. The primary muscles studied were the three largest, most superficial epaxial muscles: the Mm. semispinalis-spinalis, longissimus dorsi and iliocostalis. Sidewinding locomotion of Nerodia fasciata and Crotalus cerastes was the result of continuous posterior propagation of contractile blocks consisting of several adjacent muscle segments. During sidewinding, the activity of the M. longissimus dorsi and M. iliocostalis was primarily unilateral, beginning when a body region was convex and ending when it was maximally concave on the side of the active muscle. Unilateral activity of the M. semispinalis-spinalis correlated with lateral flexion in addition to bilateral activity that correlated with dorsiflexion of the vertebral column. During concertina locomotion of N. fasciata and Elaphe obsoleta, muscle activity also involved blocks of several simultaneously active adjacent muscle segments, but all major activity was unilateral and was not propagated posteriorly in a simple continuous fashion. Muscle activity during concertina locomotion correlated either with lateral flexion towards the side of the active muscle or with the maintenance of static contact with the sides of a tunnel. The number of simultaneously active adjacent muscle segments and the maximum duration of continuous muscle activity varied significantly between Nerodia and Elaphe and among the different widths of tunnels. Theoretical considerations combined with observed differences suggest that the more elongate body of Elaphe is advantageous for performing concertina locomotion. There was no consistent evidence that nonhomologous muscles with tendinous interconnections functioned as single units during either of these two locomotor modes. Although individual segments of the studied epaxial muscles span several vertebrae, via long, tendinous connections, consistent kinematic correlations with muscle activity were observed only between the contractile portion of a muscle segment and the vertebrae adjacent to that contractile portion.
Power Output and Force-Velocity Relationship of Live Fibres From White Myotomal Muscle of the Dogfish, Scyliorhinus Canicula
Authors: Curtin N. A. , Woledge R. C. 
Published: April 2021

ABSTRACT
The relationship between force and velocity of shortening and between power and velocity were examined for myotomal muscle fibre bundles from the dogfish. The maximum velocity of shortening, mean value 4·8 ± 0·2 μms−1 half sarco-mere−1 (±S.E.M., N = 13), was determined by the ‘slack steP′ method (Edman, 1979) and was found to be independent of fish length. The force-velocity relationship was hyperbolic, except at the high-force end where the observations were below the hyperbola fitted to the rest of the data. The maximum power output was 91 ± 14 W kg−1 wet mass (±S.E.M., N = 7) at a velocity of shortening of 1·3 ± 0·3 jams−1 half sarcomere−1 (±S.E.M., N = 7). This power output is considerably higher than that previously reported for skinned fibres (Bone et al. 1986). Correspondingly the force-velocity relationship is less curved for intact fibres than for skinned fibres. The maximum swimming speed (normalized for fish length) predicted from the observed power output of the muscle fibres decreased with increasing fish size; it ranged from 12·9 to 7·8 fish lengths s−1 for fish 0 155-0·645m in length.
Hypocalcaemic Activity of Trout Hypocalcin and Bovine Parathyroid Hormone in Stanniectomized Eels
Authors: Lafeber Floris P. J. G. , Hanssen R. G. J. M. , Bonga S. E. Wendelaar 
Published: April 2021

ABSTRACT
Hypocalcin isolated from trout corpuscles of Stannius (CS) and bovine parathyroid hormone (bPTH) induce hypocalcaemia when injected intra-arterially in hypercalcaemic, stanniectomized (STX) eels. On a molar basis, both hormones have almost the same potency. Upon injection of hypocalcin we observed a decrease in blood ionic calcium level which fully accounts for the decrease in total calcium. Injections of bPTH also resulted in a decrease of total and ionic calcium concentrations in the blood. The decrease in ionic calcium level upon injection of bPTH, however, did not fully account for the decrease in total calcium concentration of the blood. Nevertheless, hypocalcin and bPTH showed striking similarity in bioactivity in stanniectomized eels. Some similarity in three-dimensional structure of both hormones may underlie this phenomenon.
In Vivo and In Vitro Effects of Adrenergic Stimulation on Chloride/Bicarbonate Exchange in Rainbow Trout Erythrocytes
Authors: Tufts B. L. , Ferguson R. A. , Boutilier R. G. 
Published: April 2021

ABSTRACT
In vitro and in vivo experiments were carried out to determine the effect of catecholamines on erythrocytic chloride/bicarbonate exchange in the rainbow trout. A further modified boat assay is described and was used to measure bicarbonate flux through intact erythrocytes. Catecholamines had no significant effect on the bicarbonate flux in vitro. The erythrocytes were sensitive to adrenergic stimulation, however, since the agonists used caused a decrease in the pH gradient across the erythrocyte membrane. Exhaustive exercise was associated with an increase in bicarbonate flux through the intact erythrocytes. The mechanism for this increase is not clear, but it is evidently not adrenergic in origin.
Activation of Multiply Innervated Fast and Slow Myotomal Muscle Fibres of the Teleost Myoxocephalus Scorpius
Authors: Altringham J. D. , Johnston I. A. 
Published: April 2021

ABSTRACT
A nerve-muscle preparation from the sculpin Myoxocephalus scorpius was used to study the membrane response of fast and slow muscle fibres to stimulation of the spinal nerves. There was no significant difference between resting potential in fast (−81·9mV) and slow fibres (−80·8mV). Fast fibres responded to a supra-threshold stimulus in the spinal nerve with an action potential. Overshoots of up to +32 mV were recorded. Both junction potentials and overshooting action potentials were observed in the slow fibres.
The twitch/tetanus characteristics of myotomal muscle were investigated using isolated bundles of ‘live’ fast and slow fibres. Both fibre types responded to a single stimulus with a mechanical twitch. Fused tetani were obtained at around 50Hz in fast fibres and 20 Hz in slow fibres. In the slow fibres, tetanic tension increased with frequency up to around 50 Hz. At frequencies giving maximum tetanic tension, the twitch/tetanus ratio was 0·70 for fast fibres and 0·29 for slow ones.
These results are discussed with reference to the polyneuronal/multiterminal innervation pattern of the myotomal muscle in teleost fish and its role in locomotion.
Responses of Intermediary Metabolism to Acute Handling Stress and Recovery in Untrained and Trained Leuciscus Cephalus (Cyprinidae, Teleostei)
Authors: Lackner R. , Wieser W. , Huber M. , Via J. Dalla 
Published: April 2021

ABSTRACT
Juvenile Leuciscus cephalus L. were forced to swim against a current of 25cms−1 (3-5 body lengths s−1) intermittently for more than 2 months. Their metabolic responses to acute handling stress and recovery were compared to those of untrained L. cephalus. The concentrations of glycolytic intermediates, malate and phosphocreatine were determined in whole-body homogenates of different fish before and immediately after mechanical stimulation leading to exhaustion, as well as after 5, 15, 30, 60 and 120 min of recovery. The time course of recovery was described by fitting a bi-exponential equation. In untrained fish glycolytic metabolites, except pyruvate, showed maximum concentrations immediately after termination of the stress period, whereas in trained fish these maxima were delayed. In trained L. cephalus the concentrations of all metabolites investigated returned to pre-exercise levels much faster than in untrained fish. Most characteristically, lactate was removed about four times faster from the tissues of trained than from those of untrained L. cephalus. It is argued that anaerobic recovery, a well-known characteristic of exercise physiology in man and other vertebrates, is the driving force of accelerated recovery of trained L. cephalus.
Molecular Basis of the Difference in Oxygen Affinity Between Maternal and Foetal Red Blood Cells in the Viviparous Garter Snake Thamnophis Elegans
Authors: Berner Nancy J. , Ingermann Rolf L. 
Published: April 2021

ABSTRACT
Molecular mechanisms that may explain why oxygen affinity is higher in foetal than in maternal red blood cells were studied in the viviparous garter snake, Thamnophis elegans (Baird and Girard). Foetal and adult haemoglobins were structurally indistinguishable, as demonstrated by native polyacrylamide gel electrophoresis (PAGE), sodium dodecyl sulphate PAGE, low pH/urea PAGE, and gel filtration column chromatography. Oxygen-binding studies of haemoglobin in the absence of organic phosphates showed that adult and foetal haemoglobins had relatively high affinities for oxygen, low Bohr coefficients, and Hill coefficients of about 4·0 at pH 7·0. Adenosine triphosphate (ATP) lowered the oxygen affinity of the haemoglobins from about 3·6 to 9·6 mmHg (1 mmHg = 133·3 Pa) at pH6·8. Maternal red cells contained more nucleoside triphosphate (NTP) (primarily ATP) than did foetal cells by about 0·9molNTP mol−1 haemoglobin tetramer. No 2,3-diphosphoglycerate was detected in the cells. Combined levels of magnesium and calcium were comparable in maternal and foetal red cells. Mean corpuscular haemoglobin concentrations (MCHC) in foetal red cells were about 79% of maternal values. There were no significant differences in maternal and foetal methaemoglobin levels. It appears that a difference in maternal and foetal red cell organic phosphate concentrations, and possibly MCHC values, rather than a difference in haemoglobin structures, explain why oxygen affinity is higher in foetal than in maternal red blood cells in T. elegans.
Role of Midgut Electrogenic K+ Pump Potential Difference in Regulating Lumen K+ and Ph in Larval Lepidoptera
Authors: Dow Julian A. T. , Harvey William R. 
Published: April 2021

ABSTRACT
Larvae of Manduca sexta were fed on tobacco leaves or synthetic diets with differing potassium content. For all diets tested, midgut lumen K+ activity coefficients were low, and midgut lumen K+ activities, K+ concentrations and pH values were as closely regulated as in blood. The transmidgut electrochemical potential difference for potassium based on activities was lower than had previously been estimated from concentrations, but was dominated by the electrical gradient established by the electrogenic K+ ATPase. Midgut K+ activities and pH profiles were similar, as would be suggested by a model in which the generation of high pH was linked to electrogenic K+ transport.
Production of Single-Domain Magnetite Throughout Life by Sockeye Salmon, Oncorhynchus Nerka
Authors: Walker Michael M. , Quinn Thomas P. , Kirschvink Joseph L. , Groot Cornelis 
Published: April 2021

ABSTRACT
Although single-domain particles of biogenic magnetite have been found in different species of pelagic fishes, nothing is known about when it is synthesized, or about whether the time during life when it is produced is correlated with the development of responses to magnetic field stimuli. We have investigated production of biogenic magnetite suitable for use in magnetoreception in different life stages of the sockeye salmon, Oncorhynchus nerka (Walbaum). Sockeye salmon were chosen because responses in orientation arenas to magnetic field stimuli have been demonstrated in both fry and smolt stages of this species.
We found significant quantities of single-domain magnetite in connective tissue from the ethmoid region of the skull of adult (4-year-old) sockeye salmon. The ontogenetic study revealed an orderly increase in the amount of magnetic material in the same region of the skull but not in other tissues of sockeye salmon fry, yearlings and smolts. The physical properties of this material closely matched those of magnetite particles extracted from the ethmoid tissue of the adult fish. We suggest that single-domain magnetite particles suitable for use in magnetoreception are produced throughout life in the ethmoid region of the skull in sockeye salmon. Based on theoretical calculations, we conclude that there are enough particles present in the skulls of the fry to mediate their responses to magnetic field direction. By the smolt stage, the amount of magnetite present in the front of the skull is sufficient to provide the fish with a magnetoreceptor capable of detecting small changes in the intensity of the geomagnetic field.
Other tissues of the salmon, such as the eye and skin, often contained ferromagnetic material, although the magnetizations of these tissues were usually more variable than in the ethmoid tissue. These deposits of unidentified magnetic material, some of which may be magnetite, appear almost exclusively in adults and so would not be useful in magnetoreception by young fish. We suggest that tissue from within the ethmoid region of the skull in pelagic fishes is the only site yet identified where magnetite suitable for use in magnetoreception is concentrated.
An Acoustic Oxygen Telemetry Transmitter for the Study of Exposure of Fish to Variations in Environmental Dissolved Oxygen
Authors: Priede I. G. , Solbé J. F. DE L. G. , Nott J. E. 
Published: April 2021

ABSTRACT
In natural waters the dissolved oxygen concentration can vary considerably both spatially and temporally in rivers (Solbé, 1988), lakes (Gnaiger, 1983), coral reefs (Griffith et al. 1987) and the thermocline in the open ocean (Dizon et al. 1987). There are uncertainties in extrapolating laboratory studies on effects of hypoxia on fish performance (Jones, 1971) to field situations (Priede et al. 1988). This paper describes a transmitter which enables a continuous readout of fluctuations experienced by fish during normal activity in such conditions to be monitored by a remote receiving station on the shore or in a boat.