bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chloride-Dependent Organic Phosphate Sensitivity of the Oxygenation Reaction in Crocodilian Hemoglobins
Authors: Weber Roy E. , White Fred N. 
Published: April 2021

ABSTRACT
We show that crocodilian hemoglobins (Hbs), which previously have been considered to be model pigments lacking allosteric interaction with organic phosphate esters, do exhibit oxylabile ATP and 2,3-diphosphoglycerate (DPG) binding that decreases O2 affinity and increases pH sensitivity (Bohr effect), in the absence of Cl−and at the low Cl−concentrations that may occur in crocodilian plasma during ‘post-ingestive alkaline tides’. Hbs from different species vary in their phosphate sensitivities. In Alligator mississippiensis Hb, O2 affinity shows greater ATP than DPG sensitivity at low [cofactor]/[Hb] ratios. In Paleosuchus palpebrosus Hb, where even a high Cl−concentration (0.1 mol l−1) does not completely suppress the phosphate effects, the opposite is true, whereas both ATP and DPG exert similar effects in Caiman crocodilus Hb. Lactate, at concentrations that may occur after intensive exercise, similarly depresses Hb O2-affinity, indicating an O2 demand/O2 supply feedback regulation. Curiously, inositol hexaphosphate (IHP), a potent allosteric effector in other vertebrate Hbs, has no effect on A. mississippiensis and P. palpebrosus Hb and only small effects on C. crocodilus Hb, presumably because of steric hindrance at the binding site. The molecular mechanisms underlying the observations (particularly the implication of β82-Lys, i.e. the lysine residue at position 82 of the β-chains that binds phosphate and Cl−) are considered. Their physiological significance requires further study.
The Effects of Hypoxia, Hyperoxia or Hypercapnia on the Acid–base Disequilibrium in the Arterial Blood of Rainbow Trout
Authors: Gilmour Kathleen M. , Perry Steve F. 
Published: April 2021

ABSTRACT
An extracorporeal circulation in combination with a stop–flow technique was used to characterize the acid–base disequilibrium in the arterial blood of rainbow trout Oncorhynchus mykiss during environmental hypoxia, hyperoxia or hypercapnia. Arterial blood was routed from the coeliac artery through an external circuit in which pH (pHa), partial pressure of oxygen and partial pressure of carbon dioxide were monitored continuously. The stop–flow condition was imposed by turning off the pump which drove the external loop. Water or was adjusted to give the experimental conditions by bubbling N2, O2 or CO2 through a water equilibration column supplying the fish.
During normoxia, the arterial blood exhibited a positive acid–base disequilibrium of approximately 0.04 pH units; that is, pH increased over the stop–flow period by 0.04 units. The extent of the imbalance was increased significantly by hypoxia (final =2.7–3.7 kPa; pH=0.05 units). In fish exposed to hyperoxia (final =47–67 kPa), the direction of the disequilibrium was reversed; pHa declined by 0.03 units. During hyperoxia, CO2 excretion was impaired by 63% and the of postbranchial blood was higher than that of prebranchial blood. It is therefore conceivable that a reversal of the normal, outwardly directed, diffusion gradient for CO2 accounted for the negative disequilibrium; CO2 uptake at the gills would drive plasma CO2/HCO3−/H+ reactions towards CO2 hydration and H+ formation. During hypercapnia, fish exhibited a twofold increase in the positive pH disequilibrium (ΔpH=0.06 units).
The results of this study confirmed the existence of an acid–base disequilibrium in the arterial blood of rainbow trout and clearly demonstrated that the extent and/or direction of the disequilibrium are influenced by the respiratory status of the fish.
Evidence for Hydration-Dependent Closing of Pore Structures in the Cuticle of Periplaneta Americana
Authors: Machin J. , Smith J. J. B. , Lampert G. J. 
Published: April 2021

ABSTRACT
Integumental electrical resistances were measured on the antenna, pronotum, forewing, second abdominal tergite, fifth abdominal sternite and the femur of the third leg in restrained male and female Periplaneta americana. The same measurements, excepting those on antenna and wing, were made on last-instar nymphs. Electrical contact was made through two externally applied glass tubes filled with cockroach Ringer with a combined contact area of about 2 mm2. Resistances corresponding to current flows through two thicknesses of integument were measured using a current-clamping amplifier. Calculated electrical conductances tended to be higher in the antennae, pronotum and abdominal tergites than in the legs and wings. Conductances of the pronotum and abdominal tergites were significantly higher (P&lt;0.001) in males than in females. The literature suggests that male abdominal tergites are the site of sex pheromone production. In nymphs as well as adults, the conductances of all areas, except the antennae of males, decreased following dehydration and a decline in animal water content. In most cases the magnitude of the decrease was tightly correlated with initial hydrated conductance. The data suggest that variations in regional conductances in hydrated animals are principally due to differences in dermal gland density. We argue that the decrease in conductance following dehydration is evidence of a mechanism closing dermal gland openings in times of water stress.
Physical Properties Of Gametes In Three Sea Urchin Species
Authors: Thomas Florence I. M. 
Published: April 2021

ABSTRACT
Physical properties (density in kg m-3, viscosity, sinking rates and dispersion rate) of the gametes and associated spawned materials were measured for three species of sea urchin, Tripneustes gratilla, Echinometra mathaei and Colobocentrotus atratus, from habitats that differ in wave exposure. The gametes of all three species are negatively buoyant, highly viscous and exhibit shear-thinning (a decrease in viscosity with increasing shear rate). Female gametes are more viscous than male gametes, and the viscosity of female gametes differs among the three species. The viscosity of female gametes is highest for C. atratus, the species from habitats most exposed to wave action. Within the species T. gratilla, viscosity of female gametes is higher in habitats exposed to wave action than in more protected habitats.
Evidence reported in this paper suggests that the shear-thinning of gametes may provide a performance advantage for these sea urchins. High viscosity of gametes at low shear rates may decrease gamete dispersal upon release and, under certain flow conditions, allow gametes to form strings and clumps on the surface of the urchin. Depending upon the morphology of the surface, these clumps or strings may be retained and fertilization may occur within these clumps or strings. Conversely, low viscosity of gametes at high shear rates decreases the power required to extrude gametes through the gonoduct during spawning.
Effect Of Mechanical Vibration On Active Tension In The Longitudinal Retractor Muscle Of A Sea Cucumber Stichopus Japonicus
Authors: Kobayashi T. , Ushitani H. , Wada H. , Inoue J. , Kawakami T. , Sugi H. 
Published: April 2021

ABSTRACT
The effect of mechanical vibration on active tension in an echinoderm somatic smooth muscle was studied using the longitudinal retractor muscle (LRM) of a sea cucumber Stichopus japonicus. VBThe steady contracture tension in LRM fibres maximally activated with 10−3 mol l−1 acetylcholine (ACh) was reduced by vibrations (peak-to-peak amplitude, 0.5–2.5% of l0, where l0 is the slack length of the muscle; frequency, 5–100 Hz). The extent of reduction of active contracture tension increased with increasing amplitude of vibration, but it did not change appreciably with increasing frequency of vibration. The steady contracture tension in LRM fibres submaximally activated with 10−5 mol l−1 ACh was more markedly reduced by vibrations than was that in maximally activated fibres. The vibration-induced reduction of active contracture tension disappeared when temperature was lowered from 20–23 to 0°C. The development of contracture tension in LRM fibres activated with ACh was not affected by mechanical vibration. These results are discussed in connection with the vibration-induced decrease in the rate of breakage of the actin–myosin linkages responsible for isometric force generation.
Extreme Drag Forces and the Survival of Wind-and Water-Swept Organisms
Authors: Denny Mark W. 
Published: April 2021

ABSTRACT
A stationary organism exposed to steady turbulent flow is subjected to a drag force that fluctuates about a mean, and when the drag on the organism is characterized, it is traditionally this mean force that is cited. Important information is lost, however, when the fluctuations in drag are ignored. This is particularly true when extreme drag forces are relevant; for instance, when predicting the survival of benthic animals on wave-swept shores and in torrential streams, or of plants in windblown terrestrial habitats.
This study reports on the probability distribution of drag fluctuations for five objects: a flat plate, large and small cylinders, a sphere and a limpet shell. Distributions vary substantially among different objects exposed to the same mainstream flow; the sphere and limpet exhibit larger fluctuations than the plate and cylinders. The distribution of extremes in drag is used to predict the likelihood that an organism will be dislodged. For organisms in which the applied fluid-dynamic stress is near the mean breaking stress (e.g. some corals, trees and mussels), calculations made using the extreme drag can yield a probability of dislodgment substantially higher than that calculated using the average.
Maintenance of Dynamic Strain Similarity and Environmental Stress Factor in Different Flow Habitats: Thallus Allometry and Material Properties of a Giant Kelp
Authors: Johnson A. S. , Koehl M. A. R. 
Published: April 2021

ABSTRACTWe have focused on the giant kelp Nereocystis luetkeana to examine the mechanical scaling of benthic marine organisms loaded in tension by hydrodynamic forces. If we consider simply the allometry of the kelp’s morphological characters, we conclude that their stipes are underscaled relative to the blade area they support (i.e. that the kelp do not maintain stress or elastic similarity as they grow). However, a closer look at the characteristics of these kelp in the field reveals (1) that they have different blade shapes (and hence drag coefficients) and stipe material properties in different hydrodynamic environments, and (2) that they show a decrease in drag coefficient as they become larger. One consequence of these adjustments of blade and stipe morphology is that the maximum stresses in N. luetkeana stipes, when the kelp are pulled by peak tidal currents in their respective habitats, are similar for kelp of different sizes and for kelp from different sites. Hence, sessile organisms such as these kelp can, via their growth responses in different mechanical environments, show a phenomenon analogous to dynamic strain similarity. In addition, N. luetkeana also maintain a constant environmental stress factor, the ratio of the stress required to break a component of an organism (in this case the stipe) at some stage in its life to the maximum stress normally encountered in the habitat by that component during that stage (in this case, stress due to the drag on a kelp exposed to the peak tidal currents typical of the site at which it lives), both between habitats and as they grow.
Renal and Small Intestinal Sodium-Dependent Symporters of Phosphate and Sulphate
Authors: Murer Heini , Markovich Daniel , Biber Jürg 
Published: April 2021

ABSTRACT
Homeostasis of inorganic phosphate (Pi) and sulphate (Si) is largely achieved by absorption in the mammalian small intestine and by reabsorption in the proximal tubule of the kidney. Under normal physiological conditions, the kidney appears to play the major role in maintaining the extracellular concentration of these anions. In both epithelia, reabsorption of Pi and to some extent also of Si underlie a variety of regulatory acute and chronic control mechanisms. Acute regulatory mechanisms are predominantly found in renal Pi reabsorption, whereas chronic regulation of transepithelial Pi transport is observed in both tissues. Also, in both epithelia, apically located sodium-dependent transport systems (Na+/Pi and Na+/Si symport) represent major targets for known regulatory factors.
By expression cloning using oocytes of Xenopus laevis, renal and small intestinal Na+-dependent phosphate and sulphate transport systems have been identified. Evidence has been obtained that cloned Na+/Pi and Na+/Si symporters are localized in the apical membrane of proximal tubular or small intestinal epithelial cells respectively. Furthermore, recent results indicate that one of the cloned Na+/Pi symporters is involved in the physiological and pathophysiological regulation of proximal tubular Pi reabsorption.
Biochemistry and Molecular Biology of the Vesicular Monoamine Transporter from Chromaffin Granules
Authors: Henry J.-P. , Botton D. , Sagne C. , Isambert M.-F. , Desnos C. , Blanchard V. , Raisman-Vozari R. , Krejci E. , Massoulie J. , Gasnier B. 
Published: April 2021

ABSTRACT
Prior to secretion, monoamines (catecholamines, serotonin, histamine) are concentrated from the cytoplasm into vesicles by vesicular monoamine transporters (VMAT). These transporters also carry non-physiological compounds, e.g. the neurotoxin methyl-4-phenylpyridinium. VMAT acts as an electrogenic antiporter (exchanger) of protons and monoamines, using a proton electrochemical gradient. Vesicular transport is inhibited by specific ligands, including tetrabenazine, ketanserin and reserpine. The mechanism of transport and the biochemistry of VMAT have been analyzed with the help of these tools, using mainly the chromaffin granules from bovine adrenal glands as a source of transporter.
Although biochemical studies did not suggest a multiplicity of VMATs, two homologous but distinct VMAT genes have recently been cloned from rat, bovine and human adrenal glands. The VMAT proteins are predicted to possess 12 transmembrane segments, with both extremities lying on the cytoplasmic side. They possess N-glycosylation sites in a putative luminal loop and phosphorylation sites in cytoplasmic domains.
In rat, VMAT1 is expressed in the adrenal gland whereas VMAT2 is expressed in the brain. In contrast, we found that the bovine adrenal gland expressed both VMAT1 and VMAT2. VMAT2 corresponds to the major transporter of chromaffin granules, as shown by partial peptidic sequences of the purified protein and by a pharmacological analysis of the transport obtained in transfected COS cells (COS cells are monkey kidney cells possessing the ability to replicate SV-40-origin-containing plasmids). We discuss the possibility that VMAT1 may be specifically addressed to large secretory granules vesicles, whereas VMAT2 may also be addressed to small synaptic vesicles; species differences would then reflect the distinct physiological roles of the small synaptic vesicles in the adrenal gland.
K+/H+ Antiport in the Tobacco Hornworm Midgut: the K+-Transporting Component of the K+ Pump
Authors: Lepier Alexandra , Azuma Masaaki , Harvey William R. , Wieczorek Helmut 
Published: April 2021

ABSTRACT
The midgut of the tobacco hornworm secretes K+ across the apical plasma membrane of its goblet cells. This secondary K+ transport results from K+/H+ antiport energized by the proton-motive force generated by a primary, H+-transporting plasma membrane V-ATPase. Thus, the lepidopteran midgut constitutes a well-established example of the emerging concept that the proton-motive force is an alternative to the classical sodium-motive force for the energization of animal plasma membranes.
K+/H+ antiport in the tobacco hornworm midgut is electrophoretic, exchanging 2H+ for 1K+. Under physiological conditions, it is energized by the voltage component of the proton-motive force. The strong coupling of electrophoretic K+/2H+ antiport with the electrogenic V-ATPase provides, in principle, the minimal device for the alkalization of the midgut lumen to pH values higher than 11.
K+/H+ antiport is insensitive to bafilomycin A1, but is inhibited by amiloride or Concanavalin A. Lectin staining of blots after SDS–PAGE revealed several glycosylated polypeptides in the goblet cell apical membrane which are not part of the V-ATPase and thus are candidates for the antiporter protein. Current efforts are focused on the isolation of the K+/H+ antiporter.
Respiratory Muscle Activity in Relation to Vocalization in Flying Bats
Authors: Lancaster Winston C. , Henson O. W. , Keating A. W. 
Published: April 2021

ABSTRACT
The structure of the thoracic and abdominal walls of Pteronotus parnellii (Microchiroptera: Mormoopidae) was described with respect to their function in respiration and vocalization. We monitored electromyographic activity of respiratory and flight muscles in relation to echolocative vocalization. In flight, signals were telemetered with a small FM transmitter modified to summate the low-frequency myopotentials with biosonar signals from a ceramic-crystal microphone. Recordings were also made from the same bats confined to a small cage. Vocalizations were used as the parameter by which all muscle activities were correlated. A discrete burst of activity in the lateral abdominal wall muscles accompanied each vocalization. Diaphragmatic myopotentials occurred between groups of calls and did not coincide with activity of the abdominal wall or with vocalizations. Flight muscles were not active in resting bats. During flight, vocalizations and the abdominal muscle activity that accompanied them coincided with myopotentials of the pectoralis and serratus ventralis muscles.
We propose that contractions of the lateral abdominal wall provide the primary power for the production of intense biosonar vocalization in flying and in stationary bats. In flight, synchronization of vocalization with activity of the pectoralis and serratus ventralis jointly contribute to the pressurization of the thoraco-abdominal cavity. This utilization of pressure that is normally generated in flight facilitates respiration and allows for the production of intense vocalizations with little additional energetic expenditure.
Peripheral Regeneration and Central Sprouting of Sensory Neurone Axons in Aplysia Californica Following Nerve Injury
Authors: Steffensen Isabella , Dulin Michael F. , Walters Edgar T. , Morris Catherine E. 
Published: April 2021

ABSTRACT
Morphological methods were used to examine injury-induced growth of peripheral and central axons of nociceptive mechanosensory neurones in the ventrocaudal (VC) clusters of the pleural ganglia of Aplysia californica. Pedal nerve crush transected all axons in the nerve while leaving the overlying sheath largely intact. Immunohistochemical staining was performed with an antibody to a sensory-neurone-specific peptide, sensorin-A. Following bilateral crush of pedal nerve p9, which innervates the tail, sensorin-A immunofluorescence was lost distal to the crush site within 2 days. Fine immunopositive fibres began to invade the crush region within 5 days. These fibres arborized in the crush region and gradually extended down the crushed nerve. Immunopositive fibres were found near the tail within 3 weeks. Similar results were obtained after injecting individual sensory neurone somata in the tail/p9 region of the VC cluster with biocytin. Biocytin injections and horseradish peroxidase injections 3 weeks after ipsilateral pedal nerve crush revealed new fibres projecting rostrally from the tail/p9 region of the VC cluster and entering the pleural–cerebral and pleural–abdominal connectives. Such projections were never observed in control, uncrushed preparations. These results demonstrate that nerve injury triggers extensive growth of both peripheral and central processes of the VC sensory neurones.
Plasma Ammonia Concentration in Brown Trout in Soft Acidic Water and its Relationship to Decreased Swimming Performance
Authors: Beaumont M. W. , Butler P. J. , Taylor E. W. 
Published: April 2021

ABSTRACT
Adult brown trout (300–600 g) were acclimated for 2 weeks to an artificial soft water (Ca2+, 50 μmol l−1) and maintained at either 5 °C (October to March) or 15 °C (May to August). Following insertion of a cannula into the dorsal aorta under MS-222 anaesthesia and a recovery period of 2 days, the fish were exposed to a 4 day episode of sub-lethal copper levels at pH 5 or kept at control conditions of pH 7 without copper. The copper concentrations had been predetermined by toxicity testing and were approximately 0.47 μmol l−1 at 5 °C and 0.08 μmol l−1 at 15 °C. At 5 °C, a group of fish was also exposed to approximately 0.08 μmol l−1 copper at pH 5.
Plasma total ammonia (Tamm) concentration was significantly elevated by exposure to copper and pH 5. In resting trout exposed to the appropriate sub-lethal copper concentration at pH 5, Tamm was six and 7.5 times greater at 5 and 15 °C, respectively, than those of control trout at the respective temperatures. Although unconfirmed, an elevation of ammonia production alone seems unlikely to account for such substantial increases. From previous studies, there is little evidence of impairment of respiratory gas exchange in trout exposed to these copper concentrations and yet, in the acidic test waters, the gradient of NH3 partial pressure between fish and water was 5.5–6 times greater than that under control conditions.
Swimming performance determined by the critical swimming speed (Ucrit) was reduced by copper and acid exposure, and a significant relationship existed between Ucrit and the plasma ammonia concentration of exercised trout. Ammonium ions influence several key enzymes involved in energy metabolism, and elevated ammonia levels might, therefore, reduce the capacity of muscle to exercise. Alternatively, ammonia may have affected the nervous coordination of exercise either centrally or by disrupting peripheral motor innervation.
Interactions of Cortisol and Nitrogen Metabolism in the Ureogenic Gulf Toadfish Opsanus Beta
Authors: Hopkins Todd E. , Wood Chris M. , Walsh Patrick J. 
Published: April 2021

ABSTRACT
We examined the relationship between plasma cortisol levels, hepatic glutamine synthetase (GNS) activity and the form of nitrogen excreted (e.g. urea, ammonia) in undisturbed versus confined/crowded (acutely stressed) gulf toadfish. Specifically, we tested the hypothesis that acute increases in plasma cortisol levels are required to trigger the increase in GNS activity induced by the confinement/crowding stress. Toadfish responded to the stress of confinement/crowding with an initial cortisol surge (approximately 37 ng ml-1 at 2 h), which was rapidly cleared and was indistinguishable from resting levels (approximately 10 ng ml-1 by 24 h). Treatment of fish with metyrapone (which inhibits cortisol synthesis) successfully blocked the acute 2 h confinement/crowding-induced surge in plasma cortisol levels. Additionally, GNS activity in confined fish 24 h after metyrapone injection also did not differ from that of control fish, indicating that acute GNS activation probably requires the earlier (2 h) cortisol peak.
In post-absorptive fish, a strong relationship between total nitrogen excretion rate and plasma cortisol levels was evident. The percentage of nitrogen excreted as ammonia was inversely related to liver GNS activity. However, GNS activity explained only part (at most 57 %) of the variability in the percentage of nitrogen excreted as ammonia/urea, suggesting that this is not the sole factor setting the degree of ureogenesis. When toadfish are fed, the relationships between total nitrogen excretion rate and cortisol levels, and between percentage nitrogen excreted as ammonia and GNS activity, are virtually absent. Taken together, our results indicate that a stress response may be only one of several mechanisms by which ureogenesis is activated in gulf toadfish.