bluuebunny/crossref_metadata_2025_split huggingface dataset:
Urate deposits in the gecarcinid land crab Gecarcoidea natalis are synthesised de novo from Excess dietary nitrogen
Authors: Linton Stuart M. , Greenaway Peter 
Published: April 2021

ABSTRACT
The urate content of the gecarcinid land crab Gecarcoidea natalis was correlated to the amount of nitrogen assimilated. Crabs fed a high-nitrogen diet (ad libitum amounts of soy beans and fig leaves, Ficus macrophylla) for 6 weeks assimilated approximately 23 times more nitrogen (33.9±5.6 mmol kg−1 day−1) than animals fed a diet low in nitrogen (fig leaves alone) (1.5±0.7 mmol kg−1 day−1). Animals maintained on a high-nitrogen diet accumulated urate (67.1±29.4 mmol kg−1 dry mass), while animals fed the low-nitrogen diet did not accumulate significant amounts of urate compared with the control animals killed at the beginning of the dietary period. The urate deposits clearly originate from the excess dietary nitrogen ingested on the high-nitrogen diet. The intake of preformed dietary purine was low (0.028±0.005 mmol kg−1 dry mass) and at most could only account for 0.04 % of the urate accumulated by crabs fed the high-nitrogen diet. This indicates that the urate was synthesised de novo. When crabs were fed a high-nitrogen diet supplemented with [15N]glycine, the 15N heavy isotope was incorporated into urate. This provided direct evidence that the urate was synthesised de novo.
Actual and ‘optimum’ flight speeds: field data reassessed
Authors: Pennycuick C. J. 
Published: April 2021

ABSTRACT
Previously published field observations of the air speeds of 36 species of birds, all observed by the same method (ornithodolite), were compared with estimates of the corresponding minimum power speeds, calculated with a default body drag coefficient of 0.1. This value, which was derived from recent wind tunnel studies, represents a downward revision from default values previously used and leads, in turn, to an upward revision of estimated minimum power speeds. The mean observed air speeds are now distributed around the minimum power speed, rather than in between the speeds for minimum power and maximum range, as they were before. Although the field data do not represent migration, examination of the marginal effects of small changes of speed, on power and lift:drag ratio, indicates that flying at the maximum range speed on migration may not represent an ‘optimal’ or even a practical strategy and that cruising speeds may be limited by the muscle power available or by aerobic capacity. Caution in constructing ‘optimisation’ theories is indicated.
Anti-diuresis in the blood-feeding insect Rhodnius prolixus Stål: the peptide CAP2b and cyclic GMP inhibit Malpighian tubule fluid secretion
Authors: Quinlan Michael C. , Tublitz Nathan J. , O’Donnell Michael J. 
Published: April 2021

ABSTRACT
Rhodnius prolixus eliminates NaCl-rich urine at high rates following its infrequent but massive blood meals. This diuresis involves stimulation of Malpighian tubule fluid secretion by diuretic hormones released in response to distention of the abdomen during feeding. The precipitous decline in urine flow that occurs several hours after feeding has been thought until now to result from a decline in diuretic hormone release. We suggest here that insect cardioacceleratory peptide 2b (CAP2b) and cyclic GMP are part of a novel mechanism of anti-diuresis. Secretion rates of 5-hydroxytryptamine-stimulated Malpighian tubules are reduced by low doses of CAP2b or cyclic GMP. Maximal secretion rates are restored by exposing tubules to 1 mmol l-1 cyclic AMP. Levels of cyclic GMP in isolated tubules increase in response to CAP2b, consistent with a role for cyclic GMP as an intracellular second messenger. Levels of cyclic GMP in tubules also increase as urine output rates decline in vivo, suggesting a physiological role for this nucleotide in the termination of diuresis.
Nutritional Homeostasis in LocUsts: Is There a Mechanism for Increased Energy Expenditure During Carbohydrate Overfeeding?
Authors: Zanotto Flavia P. , Gouveia Scott M. , Simpson Stephen J. , Raubenheimer D. , Calder Phillip C. 
Published: April 2021

ABSTRACT
Maintenance of carbohydrate balance via changes in CO2 output volume was investigated in locusts using a flow-through respirometer. The effect of an imbalance in the dietary protein to digestible carbohydrate ratio on expired CO2 levels was measured in locusts fed one of two synthetic diets [7 % protein, 21 % digestible carbohydrate (7:21) and 21 % protein, 7 % digestible carbohydrate (21:7)]. Additionally, the effect of dietary dilution was investigated by feeding locusts one of two diets with a close-to-optimal ratio of protein to carbohydrate, one containing 7 % protein and 7 % digestible carbohydrate (7:7) and the other containing 21 % protein and 21 % digestible carbohydrate (21:21). For insects fed unbalanced diets, a higher CO2 output volume was measured during feeding on diet 7:21 when compared with insects fed on diet 21:7. Locusts also expired a greater volume of CO2 during the entire 2 h observation period. This response is consistent with specific metabolic control of carbohydrate balance via enhanced respiration. For insects fed balanced diets, the total volume of CO2 expired over the duration of a meal was greater for insects fed diet 7:7 than for those fed diet 21:21, although this was due entirely to meals lasting longer on the more dilute diet. However, the basal level of respiration rate was greater for insects fed diet 21:21 and, as a result, over the entire 2 h period, CO2 output volume did not differ between locusts fed diet 7:7 or 21:21. A possible mechanism for enhanced CO2 output volume on the nutritionally unbalanced diet was investigated, namely triglyceride/fatty-acid substrate cycling. There was no evidence for the presence of the thermogenic effect of this particular cycle on locusts as a means for dealing with excess ingested carbohydrate.
The Effects of Seasonal Hypertrophy and Atrophy on Fiber Morphology, Metabolic Substrate Concentration and Sound Characteristics of the Weakfish Sonic Muscle
Authors: Connaughton M. A. , Fine M. L. , Taylor M. H. 
Published: April 2021

ABSTRACT
Male weakfish Cynoscion regalis possess highly specialized, bilateral, striated sonic muscles used in sound production associated with courtship. Androgen-driven hypertrophy of the muscles during the late spring spawning period results in a tripling of sonic muscle mass followed by post-spawning atrophy. This study examined the morphological and biochemical changes underlying seasonal changes in sonic muscle mass and the functional effects of these on contraction as measured by sound production. Sonic muscle fiber cross-sectional area (CSA) increased significantly during the period of hypertrophy and then decreased by nearly 60 %. Both the CSA of the contractile cylinder and that of the peripheral sarcoplasm decreased significantly by late summer, with the peripheral ring of sarcoplasm virtually disappearing. Muscle protein content followed a similar trend, suggesting a major loss of structural elements during atrophy. Muscle glycogen and lipid content decreased precipitously in early June during the period of maximal sound production. Sound pressure level increased and sound pulse duration decreased with increasing sonic muscle mass, indicating that sonic muscle fibers contract with greater force and shorter duration during the spawning season. Neither the pulse repetition rate nor the number of pulses varied seasonally or with muscle mass, suggesting that the effects of steroids on the acoustic variables are more pronounced peripherally than in the central nervous system. Seasonal sonic muscle hypertrophy, therefore, functions as a secondary sexual characteristic that maximizes vocalization amplitude during the spawning period.
Changing Patterns of Vasculature in the Developing Amphibian Retina
Authors: Dunlop S. A. , Moore S. R. , Beazley L. D. 
Published: April 2021

ABSTRACT
Patterns of vascularisation were examined in whole-mounted retinae from tadpole stages to adulthood in the tree frog Litoria moorei using perfusion with Indian ink. Changing cell densities in the underlying ganglion cell layer were studied in a parallel Cresyl-stained series. Throughout development, the vasculature was pan-retinal and the hyaloid vessel was prominent. In early tadpole stages, capillaries were arranged as a honeycomb, and their number increased at a rate sufficient to maintain high densities in the face of increasing retinal area; major arteries and veins condensed within the capillary network. By early post-metamorphic life, the retinal vasculature was remodelled by the loss of four-fifths of the capillaries; the reduction in their density was far greater than could be accounted for by continuing retinal growth. This loss resulted in a change from the honeycomb appearance to one with largely parallel vessels linked by fewer connecting ones, an arrangement that became increasingly pronounced. In post-metamorphic life, the number of branch points increased such that their density decreased only slightly in the face of considerable increases in retinal area. The density of branch points varied across the retina and changed with age. Initially, the vasculature was most dense centrally, but by mid-larval life densities were highest in two patches located in the mid-temporal and mid-nasal retina. Thereafter, the vasculature increasingly assumed gradients resembling an area centralis and visual streak, a profile that survived the vascular remodelling. The development of density gradients in the vasculature preceded that of cells in the ganglion cell layer, the latter appearing only following metamorphosis. However, in post-metamorphic life, the topographies of the retinal vasculature and cells in the ganglion cell layer were closely related.
Locomotion On The Water Surface: Propulsive Mechanisms Of The Fisher Spider Dolomedes Triton
Authors: Suter Robert B. , Rosenberg Oren , Loeb Sandra , Wildman Horatio , Long John H. 
Published: April 2021

ABSTRACT
Using kinematic and mechanical experiments, we have shown how fisher spiders, Dolomedes triton (Araneae, Pisauridae), can generate horizontal propulsive forces using their legs. This horizontal thrust is provided primarily by the drag of the leg and its associated dimple as both move across the water surface. Less important sources of resistance are surface tension and bow waves. The relative contributions of drag, surface tension and bow waves were examined in several different ways. In one experiment, we measured the forces acting on a leg segment as water flowed past it in non-turbulent flow; the bow wave was not present at leg relative velocities below 0.2 m s−1 and thus cannot play a role in thrust production at low leg speeds. In a second experiment, we varied the surface tension by altering the concentration of ethanol from 0 % to 9 % in the experimental water tank. At a constant dimple depth, force varied little with changes in surface tension, a result consistent with the hypothesis that drag is the primary source of resistance. In addition, however, as surface tension decreased from 0.072 to 0.064 N m−1, the power exponent of the relationship between force and velocity (as measured by the exponent of the power function relating the two variables) increased; at lower surface tensions, down to 0.054 N m−1, the power exponent of the relationship between force and velocity decreased. These results suggest an influence of surface tension (albeit still secondary to drag) in generating horizontal resistance to leg movement. We also measured flow disturbance in the water downstream from a leg segment and confirmed that, even at velocities well below 0.2 m s−1, the leg-cum-dimple transferred momentum to the water, which is a clear indication that drag is a contributor to the resistance encountered by a spider’s leg. Finally, modeling the leg-cum-dimple as a circular cylinder generates values of drag that account for 75–98 % of the measured leg force when the dimple is 0 or 1 mm deep. These results not only elucidate the primary mechanism of propulsion for D. triton and other similar-sized arthropods, such as adult water striders (Gerridae), but also suggest that the formerly enigmatic locomotion of very small water-walking organisms (e.g. first-instar water striders) can be understood in the same way.
Intracellular Ca2+ Release Mediated by Metabotropic Glutamate Receptor Activation In The Leech Giant Glial Cell
Authors: Lohr Christian , Deitmer Joachim W. 
Published: April 2021

ABSTRACT
We have investigated the effects of glutamate and glutamate receptor ligands on the intracellular free Ca2+ concentration ([Ca2+]i) and the membrane potential (Em) of single, identified neuropile glial cells in the central nervous system of the leech Hirudo medicinalis. Exposed glial cells of isolated ganglia were filled iontophoretically with the Ca2+ indicator dye Fura-2. Application of glutamate (200–500 μmol l−1) caused biphasic membrane potential shifts and increases in [Ca2+]i, which were only partly reduced by either removing extracellular Ca2+ or blocking ionotropic glutamate receptors with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 50–100 μmol l−1). Metabotropic glutamate receptor (mGluR) ligands had the following rank of potency in inducing a rise in [Ca2+]i: quisqualate (QQ, 200 μmol l−1) &gt; glutamate (200 μmol l−1) &gt; L(+)2-amino-3-phosphonopropionic acid (L-AP3, 200 μmol l−1) &gt; trans-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD, 400 μmol l−1). The mGluR-selective antagonist (RS)-α-methyl-4-carboxyphenylglycine [(RS)-MCPG, 1 mmol l−1] significantly reduced glutamate-evoked increases in [Ca2+]i by 20 %. Incubation of the ganglia with the endoplasmic ATPase inhibitor cyclopiazonic acid (CPA, 10 μmol l−1) caused a significant (53 %) reduction of glutamate-induced [Ca2+]i transients, while incubation with lithium ions (2 mmol l−1) resulted in a 46 % reduction. The effects of depleting the Ca2+ stores with CPA and of CNQX were additive. We conclude that glutamate-induced [Ca2+]i transients were mediated by activation of both Ca2+-permeable ionotropic non-NMDA receptors and of metabotropic glutamate receptors leading to Ca2+ release from intracellular Ca2+ stores.
Molecular Genetic Analysis of V-ATPase Function in Drosophila Melanogaster
Authors: Dow Julian A. T. , Davies Shireen A. , Guo Yiquan , Graham Shirley , Finbow Malcolm E. , Kaiser Kim 
Published: April 2021

ABSTRACT
V-ATPases are phylogenetically widespread, highly conserved, multisubunit proton pumps. Originally characterised in endomembranes, they have been found to energise transport across plasma membranes in a range of animal cells and particularly in certain epithelia. While yeast is the model of choice for the rapid generation and identification of V-ATPase mutants, it does not allow their analysis in a plasma membrane context. For such purposes, Drosophila melanogaster is a uniquely suitable model. Accordingly, we have cloned and characterised genes encoding several V-ATPase subunits in D. melanogaster and, using P-element technology, we have succeeded in generating multiple new alleles. Reporter gene constructs reveal ubiquitous expression, but at particularly high levels in those epithelia thought to be energised by V-ATPases, and several of the alleles have lethal recessive phenotypes characterised by epithelial dysfunction. These results, while providing the first gene knockouts of V-ATPases in animals, also illustrate the general utility of D. melanogaster as a model for the genetic analysis of ion transport and its control in epithelia.
The Key Role of the H+ V-ATPase in Acid–Base Balance and Na+ Transport Processes in Frog Skin
Authors: Ehrenfeld Jordi , Klein Ulla 
Published: April 2021

ABSTRACT
Frogs are faced with various osmoregulatory problems, such as compensation of salt and water loss or metabolic acidification. Being exposed both to air and to pond water of low salinity in their natural habitat, the epithelium of the frog skin serves as one of the major organs for body fluid homeostasis. For years, the frog skin has been the guiding model for ion transport processes in animal cells energized by a Na+-motive force. Meanwhile, however, it was demonstrated that under natural conditions Na+ uptake is electrically coupled to active H+ secretion, mediated by an electrogenic H+ pump. A proton-motive force generated at the apical membrane of the mitochondria-rich cells (MR cells) energizes Na+ entry via apical Na+ channels. The basolateral Na+/K+ P-ATPase then pumps Na+ out of the cell into the body fluid. Thus, there are two pumps functioning in series, both involved in transepithelial Na+ transport.
Our recent investigations provided conclusive evidence that the H+ pump of the frog skin is an H+ V-ATPase. In transport studies, Na+ absorption and H+ secretion were blocked by micromolar concentrations of bafilomycin A1 or concanamycin A, two highly specific inhibitors of H+ V-ATPases. Using immunofluorescence microscopy, H+-V-ATPase-like immunoreactivity was found in MR cells in the region of their apical membrane foldings and intracellularly in the apical portion of the cell at so far unidentified locations. Besides the definition of its molecular nature, these results also confirmed the localization of the H+ pump in the apical membrane of the MR cells. These cells were already candidates for H+-V-ATPase localization mostly from correlations between their morphological features and their epithelial H+ secretion capacity. So far, there is evidence for only one type of MR cell serving both H+ and HCO3− secretion through an apical Cl−/HCO3− antiporter.
H+-V-ATPase-mediated H+ secretion and thus Na+ absorption can be modulated by complementary mechanisms. Changes in intracellular H+ concentration linked to the animal’s acid–base status will directly influence H+ V-ATPase activity. Acute acidification increases H+ current, probably as a result of the insertion of H+-V-ATPase-bearing vesicles by exocytotic processes, while alkalization causes the reverse effects. Chronic metabolic acidosis induces an increase in MR cell number in response to hormonal signals.
The Renal Electrogenic Na+:HCO3− Cotransporter
Authors: Boron Walter F. , Hediger Matthias A. , Boulpaep Emile L. , Romero Michael F. 
Published: April 2021

ABSTRACT
The electrogenic Na+:HCO3− cotransporter (symporter) is the major transporter for HCO3− reabsorption across the basolateral membrane of the renal proximal tubule and also contributes significantly to Na+ reabsorption. We expression-cloned the salamander renal electrogenic Na+:Bicarbonate Cotransporter (NBC) in Xenopus laevis oocytes. After injecting poly(A)+ RNA, fractionated poly(A)+ RNA or cRNA, we used microelectrodes to monitor membrane potential (Vm) and intracellular pH (pHi). All solutions contained ouabain to block the Na+/K+ pump (P-ATPase). After applying 1.5 % CO2/10 mmol l−1 HCO3− (pH 7.5) and allowing pHi to stabilize from the CO2-induced acidification, we removed Na+. In native oocytes or water-injected controls, removing Na+ hyperpolarized the cell by −5 mV and had no effect on pHi. In oocytes injected with poly(A)+ RNA, removing Na+ transiently depolarized the cell by −10 mV and caused pHi to decrease; both effects were blocked by 4,4′-diisothiocyano-2,2′-stilbenedisulfonate (DIDS) and required HCO3−. We enriched the signal by electrophoretic fractionation of the poly(A)+ RNA, and constructed a size-selected cDNA library in pSPORT1 using the optimal fraction. Screening the Ambystoma library yielded a single clone (aNBC). Expression was first obvious 3 days after injection of NBC cRNA. Adding CO2/HCO3− induced a large (&gt;50 mV) and rapid hyperpolarization, followed by a partial relaxation as pHi stabilized. Subsequent Na+ removal depolarized the cell by more than 40 mV and decreased pHi. aNBC is a full-length clone with a start Met and a poly(A)+ tail; it encodes a protein with 1025 amino acids and several putative membrane-spanning domains. aNBC is the first member of a new family of Na+-linked HCO3− transporters. We used aNBC to screen a rat kidney cDNA library, and identified a full-length cDNA clone (rNBC) that encodes a protein of 1035 amino acids. rNBC is 86 % identical to aNBC and can be functionally expressed in oocytes.
Elementary and Global Aspects of Calcium Signalling
Authors: Berridge Michael J. 
Published: April 2021

ABSTRACT
Calcium is a ubiquitous second messenger used to regulate a wide range of cellular processes. This role in signalling has to be conducted against the rigid homeostatic mechanisms that ensure that the resting level of Ca2+ is kept low (i.e. between 20 and 100 nmol l−1) in order to avoid the cytotoxic effects of a prolonged elevation of [Ca2+]. Cells have evolved a sophisticated signalling system based on the generation of brief pulses of Ca2+ which enables this ion to be used as a messenger, thus avoiding its toxic effects. Such Ca2+ spikes usually result from the coordinated release of Ca2+ from internal stores using either inositol 1,4,5-trisphosphate or ryanodine receptors. Using Ca2+ imaging techniques, the opening of individual channels has now been visualized and models have been proposed to explain how these elementary events are coordinated to generate the global Ca2+ signals that regulate cellular activity.
Homeostasis Of Energy Conduction, Neurotransmitters, Cytotoxic Compounds And Metal Ions
Authors: Nelson Nathan 
Published: April 2021

ABSTRACT
Communication among unconnected cells requires the release of extracellular messengers and specific receptor mechanisms on, or in, the target cells. Signalling substances include hormones, neurotransmitter substances, trophic factors and diffusible substances. In higher organisms, synaptic transmission is the principal method of communication between cells, especially in the nervous system. Nerve cells mediate fast signalling between sensory systems and the central nervous system (CNS) and between the CNS and effector systems. Within the CNS, nerve cells form complex circuits that serve the integration of inputs and the generation of specific activity patterns. Synaptic transmission is the most important means by which nerve cells communicate. There are two principal types of synaptic transmission; electrical and chemical. Electrical transmission involves ion fluxes across membranes. In many cases, synaptic transmission is chemical and involves the secretion of signalling substances. In most cases, the termination of chemical transmission is achieved by rapid uptake of the released neurotransmitter by specific high-affinity neurotransmitter transporters into the synaptic terminal or the surrounding glial cells (Kuhar, 1973; Iversen and Kelly, 1975; Kanner, 1983, 1989; Kanner and Schuldiner, 1987). It has been known for many years that neurones and glia can accumulate neurotransmitters by Na+-dependent transport processes. Neurotransmitters are cotransported with Na+ utilizing the energy stored in transmembrane electrochemical gradients generated by primary ion pumps (Kanner, 1983). Studies on neurotransmitter uptake have demonstrated the existence of multiple uptake systems, each relatively selective for a specific neurotransmitter. Neurotransmitters are transported across membranes by at least four distinct families of transporters: (1) vesicular transporters that function in the uptake of neurotransmitters into synaptic vesicles and granules (Schuldiner, 1994); (2) Na+- and Cl−-dependent (Na+/Cl−) transporters that operate on the plasma membrane of neuronal and glia cells (Uhl, 1992; Schloss et al. 1992; Amara and Kuhar, 1993); (3) Na+/K+-dependent transporters that function on the plasma membranes, especially in glutamate transport (Kanner, 1993); and (4) general amino acid transport systems that participate in controlling the availability of neurotransmitters outside the cells (McGivan and Pastor-Anglada, 1994).