bluuebunny/crossref_metadata_2025_split huggingface dataset:
Latitudinal Variation in the Abundance and Oxidative Capacities of Muscle Mitochondria in Perciform Fishes
Authors: Johnston Ian A. , Calvo Jorge , Guderley Helga , Fernandez Daniel , Palmer Lisa 
Published: April 2021

ABSTRACT
The abundance, distribution and oxidative capacities of mitochondria have been investigated in the red pectoral fin adductor muscles of fish (Order Perciformes) that use a predominantly labriform style of swimming. Mediterranean Sea species from the families Labridae, Serranidae, Sparidae and Antarctic Nototheniidae and non-Antarctic Nototheniidae and Channichthyidae were studied. Sub-Antarctic species from the Beagle Channel, Tierra del Fuego, included the pelagic haemoglobin-less icefish (Champsocephalus esox) and the róbalo (Eleginops maclovinus), which occurs as far north as 35°S. In Champsocephalus esox, the mitochondrial volume density of red muscle was 0.51 and mitochondrial cristae surface density (43.9 μm2μm−3) was higher than reported for Antarctic icefishes. In the red-blooded, active pelagic or semi-pelagic species, mitochondrial volume density was within the range 0.27–0.33 regardless of habitat temperature. Amongst less active demersal species, mitochondrial volume density ranged from 0.29–0.33 in polar species to 0.08–0.13 in Mediterranean species. In Antarctic species and Champsocephalus esox, myofibrils occurred in ribbons or clusters one fibril thick entirely surrounded by mitochondria. The volume density of intracellular lipid droplets was not correlated with activity patterns or habitat temperature. In a comparison of Eleginops maclovinus caught in summer (approximately 10°C) and winter (approximately 4°C), mitochondrial volume density did not differ, whereas the surface density of mitochondrial clusters was higher in summer fish. The temperature-dependence of the state 3 respiration rate of isolated mitochondria with pyruvate as substrate was described by a single quadratic relationship for all species, indicating no significant up-regulation of the maximum rate of oxygen uptake per milligram mitochondrial protein in Antarctic species. Our results support the conclusion that increasing the volume and surface density of mitochondrial clusters is the primary mechanism for enhancing the aerobic capacity of muscle in cold-water fish.
Optimal Shortening Velocity (V/Vmax) Of Skeletal Muscle During Cyclical Contractions: Length–Force Effects And Velocity-Dependent Activation And Deactivation
Authors: Askew Graham N. , Marsh Richard L. 
Published: April 2021

ABSTRACT
The force–velocity relationship has frequently been used to predict the shortening velocity that muscles should use to generate maximal net power output. Such predictions ignore other well-characterized intrinsic properties of the muscle, such as the length–force relationship and the kinetics of activation and deactivation (relaxation). We examined the effects of relative shortening velocity on the maximum net power output (over the entire cycle) of mouse soleus muscle, using sawtooth strain trajectories over a range of cycle frequencies. The strain trajectory was varied such that the proportion of the cycle spent shortening was 25, 50 or 75 % of the total cycle duration.
A peak isotonic power output of 167 W kg−1 was obtained at a relative shortening velocity (V/Vmax) of 0.22. Over the range of cyclical contractions studied, the optimal V/Vmax for power production ranged almost fourfold from 0.075 to 0.30, with a maximum net power output of 94 W kg−1. The net power output increased as the proportion of the cycle spent shortening increased. Under conditions where the strain amplitude was high (i.e. low cycle frequencies and strain trajectories where the proportion of time spent shortening was greater than that spent lengthening), the effects of the length–force relationship reduced the optimal V/Vmax below that predicted from the force–velocity curve. At high cycle frequencies and also for strain trajectories with brief shortening periods, higher rates of activation and deactivation with increased strain rate shifted the optimal V/Vmax above that predicted from the force–velocity relationship. Thus, the force–velocity relationship alone does not accurately predict the optimal V/Vmax for maximum power production in muscles that operate over a wide range of conditions (e.g. red muscle of fish).
The change in the rates of activation and deactivation with increasing velocity of stretch and shortening, respectively, made it difficult to model force accurately on the basis of the force–velocity and length–force relationships and isometric activation and deactivation kinetics. The discrepancies between the modelled and measured forces were largest at high cycle frequencies.
Analyses of Cdna and Recombinant Protein for A Potent Vasoactive Protein In Saliva of A Blood-Feeding Black Fly, Simulium Vittatum
Authors: Cupp Mary S. , Ribeiro José M. C. , Champagne Donald E. , Cupp Eddie W. 
Published: April 2021

ABSTRACT
A cDNA was cloned from the salivary glands of a blood-feeding black fly Simulium vittatum. The encoded protein has been given the name Simulium vittatum erythema protein or SVEP, because of its ability to increase blood perfusion in skin capillaries, resulting in the well-characterized erythema of black fly bites. The full-length cDNA contains 548 base pairs which encode 152 amino acid residues of the nascent protein. Post-translational processing produces a mature, secreted protein of 133 residues with a molecular mass of 15.4 kDa. Recombinant SVEP (rSVEP) was produced in a baculovirus expression system and purified by a one-step reversed-phase HPLC procedure. Analyses of physical properties and biological potency demonstrated fidelity of rSVEP to the native protein. Recombinant SVEP relaxed rabbit aorta preparations when preconstricted with 2 μmol l−1 phenylephrine or 25 mmol l−1 K+ but not with 60 mmol l−1 K+. Further, the rSVEP-induced relaxation response of phenylephrine-constricted aorta was inhibited by glibenclamide (10 μmol l−1), suggesting that at least part of its action to relax smooth muscle may result from the opening of ATP-dependent K+ channels. SVEP is a novel salivary-gland-derived vasoactive protein that may be essential for blood feeding by black flies and could potentially enhance transmission of filarial parasites.
Innervation Pattern Of A Pool Of Nine Excitatory Motor Neurons In The Flexor Tibiae Muscle Of A Locust Hind Leg
Authors: Sasaki K. , Burrows M. 
Published: April 2021

ABSTRACT
The flexor tibiae muscle of a locust hind leg consists of 10–11 pairs of fibre bundles in the main body of the muscle and a distal pair of bundles that form the accessory flexor muscle, all of which insert onto a common tendon. It is much smaller than the antagonistic extensor tibiae muscle and yet it is innervated by nine excitatory motor neurons, compared with only two for the extensor. To determine the pattern of innervation within the muscle by individual motor neurons, branches of the nerve (N5B2) that supplies the different muscle bundles were backfilled to reveal somata in the metathoracic ganglion. This showed that different muscle bundles are innervated by different numbers of excitatory motor neurons. Physiological mapping of the innervation was then carried out by intracellular recordings from the somata of flexor motor neurons in the metathoracic ganglion using microelectrodes. Spikes were evoked in these neurons by the injection of current, and matching junctional potentials were sought in fibres throughout the muscle using a second intracellular electrode.
Each motor neuron innervates only a restricted array of muscle fibres and, although some innervate a larger array than others, none innervates fibres throughout the muscle. Some motor neurons innervate only proximal fibres and others only more distal fibres, so that the most proximal and most distal bundles of muscle fibres are innervated by non-overlapping sets of motor neurons. More motor neurons innervate proximal bundles than distal ones, and there are some asymmetries in the number of motor neurons innervating corresponding bundles on either side of the tendon.
Individual motor neurons cause slow, fast or intermediate movements of the tibia, but their patterns of innervation overlap in the different muscle bundles. Furthermore, individual muscle fibres may also be innervated by motor neurons with different properties.
A Genetic Deficiency That Spans the Flightin Gene of Drosophila Melanogaster affects the Ultrastructure and Function of the Flight Muscles
Authors: Vigoreaux Jim O. , Hernandez Carmen , Moore Jeff , Ayer Gretchen , Maughan David 
Published: April 2021

ABSTRACT
We have developed a reverse-genetic approach to study the function of flightin, a unique protein of the flight muscle myofibril of Drosophila melanogaster. We describe the generation and characterization of Df(3L)fln1, a lethal genetic deficiency in the 76BE region of the third chromosome which deletes several genes, including the gene for flightin. We show that heterozygous flies harboring the Df(3L)fln1 mutation exhibit both impaired flight and ultrastructural defects in their flight muscle myofibrils. We found that the mutation does not interfere with assembly of the myofibril but leads to disorganization of peripheral myofilaments in adult myofibrils. Most myofibrils, nevertheless, retain an intact core that represents approximately 80 % of the normal lattice diameter. Mechanical analysis of single skinned flight muscle fibers demonstrates that the mutation has no significant effect on net power output but increases the frequency at which maximum power is delivered to the wings, potentially reducing the overall performance of the flight system. The results suggest that flightin is an indispensable part of the flight muscle contractile mechanism.
Partitioning the Effects of Temperature and Kinematic Viscosity on the C-Start Performance of Adult Fishes
Authors: Johnson T. P. , Cullum A. J. , Bennett A. F. 
Published: April 2021

ABSTRACT
Temperature has been shown to have a significant effect on swimming performance in teleost fish. This thermal dependence has usually been attributed to correlated changes in muscle contractile physiology. However, the physical properties of all materials, including both water and living tissues, are profoundly affected by changes in temperature. In particular, both the kinematic viscosity of water and the flexible body dynamics of the fish (independent of muscle contractile activity) are substantially higher at lower temperatures. In this study, we investigated the extent to which the observed thermal dependence of locomotor performance of fish simply reflects changes in the biophysical properties of the aqueous medium independent of the changing physiology of the animals. C-starts (escape swimming) of adult goldfish (Carassius auratus, length approximately 8 cm) were video-taped (400 frames s−1) at 5 °C and 20 °C in fresh water and at 20 °C in fresh water containing 1.2 % dextran (kinematic viscosity equivalent to that of water at 5 °C). Temperature had a significant positive effect on maximum forward velocity (m s−1), angular velocity (degrees s−1) and total distance moved, but viscosity had no detectable effect on any kinematic parameters at 20 °C. Since viscous forces may have more pronounced effects on smaller fish, C-starts of adult guppies (Poecilia reticulata, length approximately 2 cm) were video-taped in fresh water and in fresh water containing 1.2 % and 3.6 % dextran at 20 °C. Viscosity had a significant effect on kinematic variables only at 3.6 % dextran; at 1.2 % dextran, the effects were marginal. It was concluded that most of the observed thermal dependence of C-starts at temperatures normally experienced by these fish was due to changes in physiological processes as opposed to physical changes in the environment.
The Characterization of Presynaptic Octopamine Receptors Modulating Octopamine Release From an Identified Neurone in the Locust
Authors: Howell Kim M. R. , Evans Peter D. 
Published: April 2021

ABSTRACT
Octopamine release has been demonstrated from the dorsal unpaired median neurone to the locust extensor-tibiae muscle (DUMETi) in response to high-[K+] saline. Here, we provide evidence for the existence of presynaptic inhibitory autoreceptors for octopamine on the DUMETi terminals and report on their pharmacological profile. Octopamine release was initiated by exposure to high-[K+] saline (0.1 mol l−1) and measured using a radioenzyme assay for octopamine. Octopamine receptor antagonists (10−4 mol l−1) potentiated the high-[K+]-mediated release of octopamine with the following rank order of potency: phentolamine = metoclopramide &gt; mianserin = chlorpromazine &gt; cyproheptadine &gt; yohimbine. Octopamine receptor agonists (10−4 mol l−1) inhibited the high-[K+]-mediated release of octopamine with the following rank order of potency: naphazoline &gt; tolazoline &gt; clonidine. Thus, the octopamine autoreceptors on the DUMETi terminals are much closer pharmacologically to the pre-and postsynaptic OCTOPAMINE2 receptors in the locust extensor-tibiae muscle preparation than to the OCTOPAMINE3 receptors from the locust central nervous system. The results suggest that there is likely to be more than one type of insect neuronal octopamine receptor. It is also likely that presynaptic modulation of octopamine release may be confined to octopamine receptors since a wide range of other putative modulatory substances did not produce this effect.
Epithelial Glucose Transport By Lobster Antennal Gland
Authors: Behnke Rachel D. , Busquets-Turner Liz , Ahearn Gregory A. 
Published: April 2021

ABSTRACT
Transport of D-[3H]glucose into lobster (Homarus americanus) brush-border membrane vesicles (BBMVs) prepared by Mg2+ precipitation from antennal gland labyrinth–coelomosac tissue was examined. Influx of D-glucose occurred primarily by a phlorizin-sensitive, Na+-dependent carrier similar to that found in vertebrate renal epithelium. An inwardly directed Na+ gradient drove concentrative D-glucose uptake, whereas similar gradients of Li+ and K+ did not. Stimulation by the Na+ gradient was further enhanced by the imposition of an inside-negative potential difference and also by increases in the pH of the vesicle and incubation media. An analysis of cis inhibition of D-glucose uptake by a number of sugars and sugar derivatives indicated that the transporter requires (a) that the sugar substrate be a D-pyranose in the C1 chair conformation and (b) that the hydroxyl groups at C2 and C3 of the ring be unmodified and equatorial. Apparent kinetic parameters for glucose uptake were determined under zero-trans, short-circuited conditions. Maximal influx of D-glucose into vesicles was estimated to be 96 pmol mg−1 protein s−1. Half-maximal influx was determined to occur at 0.20 mmol l−1 D-glucose. The relationship between external Na+ concentration and glucose influx was sigmoidal, and the stoichiometry of Na+-dependent glucose transport found to be 3 Na+:1 glucose using the static head method.
Intensity Responses of the Single Auditory Receptor of Notodontid Moths: A Test of the Peripheral Interaction Hypothesis in Moth Ears
Authors: Fullard James H. , Forrest Evelyn , Surlykke Annemarie 
Published: April 2021

ABSTRACT
It has been proposed that the most sensitive auditory receptor cell (A1) in the two-celled ears of certain noctuoid moths is inhibited by its partner, the A2 cell, at high stimulus intensities. We used the single-celled ears of notodontid moths, also noctuoids, to test this hypothesis. The A1 cells of all but one of the moths tested exhibited non-monotonic firing rates, with reduced firing rates at high stimulus intensities and showing no relationship to the firing rate of the only other receptor, the non-auditory B cell. These results challenge the peripheral interaction hypothesis for A1 firing patterns in two-celled moth ears. An examination of notodontid A1 adaptation rates and laser vibrometry results suggests that receptor adaptation and tympanal motion non-linearity are more likely explanations for the non-monotonic receptor firing observed in both single- and multi-celled moth ears.
Changes In the Ultrastructure Of Surviving Distal Segments Of Severed Axons Of The Rock Lobster
Authors: Parnas I. , Shahrabany-Baranes O. , Feinstein N. , Grant P. , Adelsberger H. , Dudel J. 
Published: April 2021

ABSTRACT
Peripheral axons of lobsters can survive for many months after axotomy. We have investigated the structural and ultrastructural changes seen after axotomy using confocal microscopy and electron microscopy. While the proximal stump had a normal appearance, the distal part of the cut axon became lobulated, and glial cells penetrated the original glial tube (axon tube) in which the axon normally runs. The changes proceeded from the cut end towards the muscle. As time elapsed, the axon tube seemed to be filled with glial cells, but interposed small profiles of the original axon could be identified by injection of a fluorescent dye into the axon. The glial cells send cytoplasmic projections deep into folds of the axolemma, and nuclei were found at the end of these long processes. Proliferation of glial cells was also seen.
Thermal Control of Metabolic Cold Defence In Pigeons Columba Livia
Authors: Østnes Jan Eivind , Bech Claus 
Published: April 2021

ABSTRACT
Metabolic rate (MR) and various body temperatures were recorded in pigeons Columba livia during gradual lowering of the ambient temperature (Ta) and during cold exposure (−10 °C) for an entire circadian cycle. The aim was to study how changes in MR accorded with the observed body temperature displacements and our knowledge of regional cold sensitivity. When Ta was lowered from 28 to −10 °C, the threefold increase in MR was accompanied by a significant increase in deep-body and spinal cord temperatures. Cold exposure also resulted in a distinct rise in breast skin temperature, whereas the skin temperatures of the neck, back and leg decreased significantly. Thus, during acute cold exposure of pigeons, peripheral thermosensors seem to have the primary effect in mediating metabolic cold defence, while internal thermosensors are apparently of minor importance. By using differential weightings of various skin areas, cold-sensitivity values of between −3.9 and −14.7 W kg−1 °C−1 were estimated. These values indicate a much higher skin thermosensitivity of birds than has been previously suggested. When cold-exposed for an entire circadian cycle, the pigeons usually maintained a low leg skin temperature. However, during these experiments, the pigeons showed regular distinct increases in leg skin temperature, obviously due to cold-induced vasodilatations (CIVDs). The flushing of cold peripheral blood through the body in connection with these CIVDs resulted in a decrease in deep-body temperature (Tb), to which the pigeons responded with a distinct increase in MR. From the concomitant changes in MR and Tb, a total body cold sensitivity of −8.0W kg−1 °C−1 was calculated, a value that is close to the previously published cold-sensitivity value of pigeons. This shows that, at least under some naturally occurring conditions, internal thermosensors will provide a significant error signal in the control of metabolic cold defence. Furthermore, the results of our study show that the relative importance of various thermosensitive sites in the control of metabolic cold defence is contextual.
Pulsatile Urea Excretion In Gulf Toadfish (Opsanus Beta): Evidence For Activation Of A Specific Facilitated Diffusion Transport System
Authors: Wood Chris M. , Gilmour K. M. , Perry S. F. , Part P. , Laurent P. , Walsh Patrick J. 
Published: April 2021

ABSTRACT
When toadfish are made ureotelic by a crowding/ confinement protocol, they excrete approximately 90 % of their urea nitrogen (urea-N) production in large, irregular pulses (1–2 pulses per day) from the gill region. We investigated three hypotheses as to the mechanism of pulsatile excretion: (i) the presence of an active reabsorptive ‘back-transport’ mechanism that is periodically inhibited to allow urea-N excretion to occur; (ii) the periodic occurrence of a generalized, non-specific increase in gill permeability; and (iii) the presence of a specific facilitated diffusion transport system that is periodically activated. Exposure of toadfish during non-pulse periods to treatments designed to block a ‘back-transport’ mechanism (Na+-free sea water or the urea analogues 30 mmol l−1 thiourea or 30 mmol l−1 acetamide in the external water) did not stimulate a leakage of urea-N, thereby opposing the first hypothesis. The second hypothesis was opposed by several results. Neither injection of the potent branchial vasodilator L-isoprenaline (10−5 mol l−1) nor infusion of NH4Cl, the latter at levels known to stimulate urea-N efflux in perfused gills, had any effect on urea-N excretion. Furthermore, during natural pulse events, when the normally very low gill permeability to urea (3×10−7 cm s−1) increased at least 35-fold, there was no accompanying increase in permeability to either 3H2O (1.5×10−5 cm s−1) or the paracellular marker [14C]PEG-4000 (10−8 cm s−1). However [14C]thiourea permeability (1.5×10−7 cm s−1) increased approximately fivefold, in support of the third hypothesis. Furthermore, when 30 mmol l−1 urea was placed in the external water, a concentration (60 000 μmol-N l−1) approximately three times that of blood (20 000 μmol-N l−1), each efflux pulse event (measured with [14C]urea) was accompanied by a net uptake, such that blood urea-N levels rose rather than fell. A proportional 1:1 relationship between influx per unit external concentration and efflux per unit internal (i.e. plasma) concentration indicated a fully bidirectional transport system. The simultaneous presence of 60 mmol l−1 thiourea in the external water inhibited the influx component by 73 %, further supporting this conclusion. These data, together with recent molecular, morphological and endocrinological evidence, strongly suggest that pulsatile urea-N excretion is caused by the periodic activation of a facilitated urea transporter in the gills, similar to the vasopressin-regulated urea transporter in the mammalian kidney.
Proliferation And Differentiation Properties Of Permanent Schwann Cell Lines Immortalized With A Temperature-Sensitive Oncogene
Authors: Thi Anh Do , Evrard Claudine , Rouget Pierre 
Published: April 2021

ABSTRACT
Permanent Schwann cells lines have been established in culture after stable transfection of newborn rat Schwann cells with the pJC-SVLTtsA vector, expressing a thermosensitive oncogene driven by the early promoter-enhancer region of the gliotropic GS/B variant of the papovavirus JC. The proliferation and differentiation of two clonal cell lines have been studied. The cells of these lines display the morphology of primary Schwann cells and express Schwann cell differentiation markers such as the S-100 protein, laminin, the low-affinity receptor to nerve growth factor and the glial fibrillary acidic protein. One of the lines is able to differentiate further. Indeed, in the presence of dorsal root ganglion neurones, the cells synthesize the myelin Po protein and are capable of some myelination, although to a lesser extent than secondary Schwann cells.