bluuebunny/crossref_metadata_2025_split huggingface dataset:
EmrE, the Smallest Ion-Coupled Transporter, Provides a Unique Paradigm for Structure–Function Studies
Authors: Schuldiner Shimon , Lebendiker Mario , Yerushalmi Hagit 
Published: April 2021

ABSTRACT
EmrE is an Escherichia coli multidrug transporter which confers resistance to a wide variety of toxicants by actively removing them in exchange for hydrogen ions. EmrE is a highly hydrophobic 12 kDa protein which has been purified by taking advantage of its unique solubility in organic solvents. After solubilization and purification, the protein retains its ability to transport as judged from the fact that it can be reconstituted in a functional form. Hydrophobicity analysis of the sequence yielded four putative transmembrane domains of similar sizes. Results from transmission Fourier transform infrared measurements agree remarkably well with this hypothesis and yielded α-helical estimates of 78 % and 80 % for EmrE in CHCl3:MeOH and 1,2-dimyristoyl phosphocholine, respectively. Furthermore, the fact that most of the amide groups in the protein do not undergo amide–proton H/D exchange implies that most (approximately 80 %) of the residues are embedded in the bilayer. These observations are only consistent with four transmembrane helices. A domain lined by Cys41 and Cys95 accessible only to substrates such as the organic mercurial 4-(chloromercuri)benzoic acid has been identified. Both residues are asymmetric in their location with respect to the plane of the membrane, Cys95 being closer than Cys41 to the outside face of the membrane. In co-reconstitution experiments of wild-type protein with three different inactive mutants, negative dominance has been observed. This phenomenon suggests that EmrE is functional as a homo-oligomer.
Oxygen and Carbon Dioxide Transport in Vertebrate Erythrocytes: An Evolutionary Change in the Role of Membrane Transport
Authors: Nikinmaa Mikko 
Published: April 2021

ABSTRACT
Two major strategies are apparent for the regulation of gas transport by vertebrate blood except in the myxinoids, which seem to have little scope for such regulation. In lampreys and teleost fish, haemoglobins have low buffering capacities and large Bohr/Haldane effects. Na+/H+ exchange plays an important role in the control of haemoglobin oxygen-affinity in these vertebrate groups. The large Bohr/Haldane effect also facilitates carbon dioxide transport: the blood (or erythrocyte) pH increases upon deoxygenation, thus increasing the concentration of bicarbonate formed at a given carbon dioxide tension. In lampreys, the bicarbonate permeability of the erythrocyte membrane is low. As a consequence, extracellular acid loads cannot be buffered by haemoglobin. In contrast, teleost erythrocytes possess a functional anion exchange, allowing extracellular proton loads to be buffered by haemoglobin. However, because the buffering capacity of teleost haemoglobins is low, buffering of extracellular acid loads is less effective in teleost fish than in elasmobranch fish and in air-breathing vertebrates whose haemoglobins have a high buffering capacity. However, the high buffering capacity of the haemoglobins diminishes the possibility of regulating haemoglobin oxygen-affinity via secondarily active Na+/H+ exchange, because intracellular pH changes, caused by proton efflux, remain small.
Contrasting Strategies for Anoxic Brain Survival – Glycolysis Up or Down
Authors: Lutz Peter L. , Nilsson Göran E. 
Published: April 2021

ABSTRACT
Anoxia-tolerant turtles and carp (Carassius) exhibit contrasting strategies for anoxic brain survival. In the turtle brain, the energy consumption is deeply depressed to the extent of producing a comatose-like state. Brain metabolic depression is brought about by activating channel arrest to reduce ion flux and through the release of inhibitory γ-aminobutyric acid (GABA) and the up-regulation of GABAA receptors. Key glycolytic enzymes are down-regulated during prolonged anoxia. The result is a suppression of neurotransmission and a substantial depression in brain electrical activity.
By contrast, Carassius remain active during anoxia, though at a reduced level. As in the turtle, there is an adenosine-mediated increase in brain blood flow but, in contrast to the turtle, this increase is sustained throughout the anoxic period. Key glycolytic enzymes are up-regulated and anaerobic glycolysis is enhanced. There is no evidence of channel arrest in Carassius brain. The probable result is that electrical activity in the brain is not suppressed but instead maintained at a level sufficient to regulate and control the locomotory and sensory activities of the anoxic carp.
The key adaptations permitting the continued high level of glycolysis in Carassius are the production and excretion of ethanol as the glycolytic end-product, which avoids self-pollution by lactate produced during glycolysis that occurs in other vertebrates.
The Influence of Surface Atmospheric Conditions on the Range and Area Reached by Animal Vocalizations
Authors: Larom David , Garstang Michael , Payne Katharine , Raspet Richard , Lindeque Malan 
Published: April 2021

ABSTRACT
Low-level vertical changes in temperature and wind exert powerful and predictable influences on the area ensonified by animal vocalizations. Computer modelling of low-frequency sound propagation in measured atmospheric conditions predicts that the calls of the savanna elephant at these frequencies can have ranges exceeding 10 km and that the calls will be highly directional in the presence of wind shear. Calling area is maximized under temperature inversions with low wind speeds. Calling area changes substantially over 24 h periods; on any given day, the calling area undergoes an expansion and contraction which may be as large as one order of magnitude. This cycle is modulated by topography, regional weather patterns, seasonality and possibly by climate variation. Similar influences affect the somewhat higher-frequency calls of lions and may be a selective pressure towards their crepuscular and nocturnal calling behaviour. Coyotes and wolves, which also live in areas with strong and prevalent nocturnal temperature inversions, show similar calling patterns, maximizing their chances of being heard over the longest possible distances. The pronounced dawn and evening vocalization peaks in other animals including birds, frogs and insects may reflect the same influences in combination with other factors which selectively limit high-frequency sound propagation. Atmospheric conditions therefore need to be taken into account in many field studies of animal behaviour. A simplified method for estimating sound propagation during field studies is presented.
Ion Transport and Acid–Base Balance in Freshwater Bivalves
Authors: Byrne Roger A. , Dietz Thomas H. 
Published: April 2021

ABSTRACT
Blood acid–base and ionic balance in freshwater bivalves is affected by the relative activities of epithelial Na+ and Cl− transporters. In the unionid Carunculina texasensis, the Na+/H+ exchanger is the predominant epithelial transporter that affects acid–base state, while Cl−/HCO3− exchange is of lesser importance. In the corbiculid Corbicula fluminea, Cl− and Na+ transport are both significant components affecting acid–base state. Serotonin (5-hydroxytryptamine, 5-HT) stimulates Na+ and Cl− transport in both species. In C. texasensis, the effect of exogenous serotonin is four times greater on Na+/H+ exchange than on Cl−/HCO3− transport, resulting in an increase in acid secretion and a rise in blood pH. In a Na+-free environment, serotonin had no effect on blood acid–base state in C. texasensis. In C. fluminea, the acid–base consequences of serotonin stimulation of Na+/H+ exchange were offset by similar increases in Cl−/HCO3− exchange and by alterations in blood in medium containing Na+. In Na+-free medium, stimulation of the Cl− transporter with 5-HT resulted in a decrease in blood pH. The differences between these two species are related to the reliance of C. fluminea on Cl− as the major anion in the blood, requiring high levels of epithelial Cl− transport. In C. texasensis, the anionic component of the blood consists of both Cl− and HCO3− and these ions are interchangeable over a wide concentration range. Extracellular acid–base balance in freshwater bivalves is governed, in part, by epithelial ion transporters.
Possible Mechanisms of Control of Vascular Resistance in the Lobster Homarus Americanus
Authors: Wilkens Jerrel L. 
Published: April 2021

ABSTRACT
In Homarus americanus, the resistance to fluid flow through each of the arteries leaving the heart, including the complete hemocoelic return pathways, can be controlled. Each of the five arterial types (anterior median, paired anterior lateral, paired hepatic, sternal and dorsal abdominal) exhibits a unique spectrum of responses to a battery of neurotransmitters (acetylcholine, glutamic acid, γ-aminobutyric acid) and neurohormones (dopamine, octopamine, 5-hydroxytryptamine, crustacean cardioactive peptide, FLRFamide-related peptides F1 and F2, and proctolin). Acetylcholine causes increases in resistance in all arteries except the anterior median artery; in the dorsal abdominal artery, this increase is antagonized by γ-aminobutyric acid. All neurohormones that are effective in a particular artery cause increases in resistance to flow. The sites of action of these compounds in the dorsal abdominal artery are valves located at major branch points; the sites of control in the other arteries are not known. It is concluded that the control of arterial resistance is a mechanism which the animal can exploit to produce different flow patterns among the various arteries.
Cyclic-Amp-Induced Water Uptake in A Moth Ovary: Inhibition by Bafilomycin and Anthracene-9-Carboxylic Acid
Authors: Wang Yuren , Telfer William H. 
Published: April 2021

ABSTRACT
The ion physiology of osmotic swelling and a consequent loss of epithelial patency was examined in the ovaries of the moth Hyalophora cecropia. After 30 min in the presence of an activator of cyclic-AMP-dependent protein kinase (PKA), the membrane potentials of both oocyte and follicle cells had hyperpolarized by approximately 30 %, cytoplasmic pH had dropped from 7.26 to 7.06, a normally low Cl− conductance had increased and the follicle cells had begun to swell. Since ion distribution studies have indicated that conductance increases should depolarize membranes in this system, it is proposed that hyperpolarization may be effected by an azide-inhibitable component of the membrane potential. Nanomolar levels of bafilomycin, an inhibitor of H+ V-ATPase, blocked the active component and prevented osmotic swelling in response to PKA activation. Under a variety of circumstances, correlations were seen between membrane potential and cytoplasmic pH, suggesting that substrate availability to the proton pump may contribute to hyperpolarization. H+ V-ATPases are known to energize ion and water transport across many epithelia, but in this case they generate water absorption by the epithelium. The increase in Cl− conductance was also required for the swelling response: the Cl− channel blocker anthracene-9-carboxylic acid prevented both swelling and hyperpolarization, as did Cl− substitution in the medium. Differences in isotope loading rates between 36Cl− and 86Rb+ suggested that, after PKA activation, Cl− functions other than as a counterion for K+ uptake.
Proline Powers Pre-Flight Warm-Up In The African Fruit Beetle Pachnoda Sinuata (Cetoniinae)
Authors: Auerswald Lutz , Schneider Peter , Gäde Gerd 
Published: April 2021

ABSTRACT
We investigated thoracic temperatures (Tth) during different activities of the endothermic fruit beetle Pachnoda sinuata and analysed which energy substrates are used for the pre-flight warm-up of its flight muscles.
Pachnoda sinuata elevates its Tth prior to take-off either by basking in the sun or by warming endothermically to a narrow range around 34 °C. During lift-generating tethered flight at low ambient temperatures (Ta=25 °C), Tth of P. sinuata decreases steadily until it reaches 28 °C, which is not sufficiently high to sustain flight. Tth remains stable during lift-generating tethered flight at high Ta (31 °C). Wingbeat frequency (fw) is dependent on Tth: when Tth declines, fw decreases in a linear manner.
The proline concentrations in the haemolymph and flight muscles decrease during warm-up. In contrast, the carbohydrate levels in the haemolymph and flight muscles are not affected by the warm-up process, while the glycogen level of the flight muscles declines significantly during the first 10 s of lift-generating tethered flight. This suggests that the energy for endothermic warm-up is produced solely by the oxidation of proline.
Measurements of the respiratory quotient (RQ) confirmed that P. sinuata uses a combination of carbohydrates and proline to power its flight. At rest and during lift-generating tethered flight, the RQ is approximately 0.9. During warm-up, the RQ is significantly lower at 0.82, which is close to the theoretical value of 0.8 for the partial oxidation of proline. The rate of oxygen consumption during endothermic warm-up is 45 % of that during lift-generating tethered flight
Oxygen-Sensitive Flight Metabolism in the Dragonfly Erythemis Simplicicollis
Authors: Harrison Jon F. , Lighton John R. B. 
Published: April 2021

ABSTRACT
Insect flight metabolism is completely aerobic, and insect resting metabolism is quite insensitive to atmospheric oxygen level, suggesting a large safety margin in the capacity of the tracheal system to deliver oxygen during flight. We tested the sensitivity of flight initiation and metabolism to atmospheric oxygen level in the libellulid dragonfly Erythemis (Mesothemis) simplicicollis using flow-through res.pirometric measurements of the rate of CO2 emission . Flight initiations were unimpaired in atmospheric oxygen levels as low as 10 %. However, flight m. etabolic rate was affected by ambient oxygen level. Flight decreased in hypoxic mixtures (5 kPa or 10 kPa oxygen) and increased in hyperoxic atmospheres (30 kPa or 50 kPa oxygen), suggesting that ambient oxygen level influences flight muscle oxygen partial pressure and the vigour of flight. These are the first data to show oxygen-limitation of flight metabolism in a free-flying insect. A low safety margin for oxygen delivery during dragonfly flight is consistent with a previous hypothesis that atmospheric hyperoxia facilitated gigantism in Paleozoic protodonates. However, allometric studies of tracheal morphology, and mechanisms and capacity of gas exchange in extant insects are necessary in order to test the hypothesis that the oxygen-sensitivity of aerobic metabolism increases with body size in insects.
Development of Sensory Processes During Limb Regeneration in Adult Crayfish
Authors: Cooper Robin L. 
Published: April 2021

ABSTRACT
The capacity of the crayfish Procambarus clarkii to regenerate its walking legs provides a system for studying the mechanisms of neural regeneration and repair. A set number of excitatory and inhibitory motor neurons innervate all the limb musculature throughout the normal development and regeneration of a limb. The cell bodies of the motor neurons reside within the segmental ganglion and, upon loss of the limb, their axons regrow from their severed distal ends. The cell bodies of the sensory neurons, in contrast, are located close to their sensory endings within the limb, and they are therefore lost, along with the limb, upon autotomy, leaving the severed, distal axonal stumps of the sensory neurons within the ganglionic root. During the regeneration of a limb, new sensory neurons develop within the limb, and their axons must then grow into the ganglionic root to make the appropriate connections for the new limb to become functional. Evidence is presented in the present paper that the sensory axonal stumps do not degenerate before the new sensory neurons appear within the root as the limb regenerates. These results also indicate a progressive advance of growth cones, presumably sensory in origin, towards the neuropil within the ganglion over time.
Tail-Flip Mechanism and Size-Dependent Kinematics of Escape Swimming in the Brown Shrimp Crangon Crangon
Authors: Arnott Stephen A. , Neil Douglas M. , Ansell Alan D. 
Published: April 2021

ABSTRACT
Tail-flip escape swimming by the brown shrimp Crangon crangon has been investigated across a range of body lengths (11–69 mm) using high-speed video analysis. This has revealed several novel aspects of the tail-flip mechanism when compared with that of other decapod crustaceans that have been studied. (i) The pattern of body flexion in C. crangon produces movement of the cephalothorax as well as the abdomen about the centre of mass. (ii) Shrimps form a ‘head-fan’ with their antennal scales, in addition to the tail-fan formed by their uropods, apparently for generating thrust during tail-flips. (iii) Shrimps typically swim on their side rather than in an upright body position. It is suggested that these features may be interlinked and derive from habitat specialisation.
The kinematic properties of tail-flips were found to vary with shrimp size. As shrimp body length increased, the rate of body flexion and re-extension decreased whilst the duration of tail-flips increased. Mean (and maximum) velocity estimates ranged between 0.4 m s−1 (0.7 m s−1) and 1.1 m s−1 (1.8 m s−1) for shrimps of different sizes. The combined effects of escape behaviour and size-dependent variability in tail-flip kinematics will have important implications with regard to predation risk.
Natriuretic Peptide Binding Sites in the Gills of the Pouched Lamprey Geotria Australis
Authors: Toop T. , Grozdanovski D. , Potter I. C. 
Published: April 2021

ABSTRACT
Iodinated atrial natriuretic peptide (ANP) binding sites were examined in the gills and ventral aorta of the adult upstream-migrating lamprey Geotria australis using tissue section autoradiography, in vitro competition analysis and affinity cross-linking, while guanylate cyclase assays were performed on gill membranes of both adult and juvenile lampreys. A partial natriuretic peptide (NP) receptor sequence was amplified using reverse transcription/ polymerase chain reaction (RT-PCR). The results indicated that there was specific NP binding to the aortic endothelium and to pillar cell regions in the axial plate and secondary lamellae. In competition studies, 50 % of NP binding was abolished by 4 nmol l−1 rat ANP, 35 nmol l−1 porcine C-type NP (CNP) and 45 nmol l−1 C-ANF (a truncated ANP). Affinity cross-linking followed by SDS–PAGE demonstrated two binding sites at 205 and 65 kDa under non-reducing conditions and at 85 and 65 kDa under reducing conditions. Guanylate cyclase assays demonstrated that, while no NP-stimulated GC activity occurred in adult lampreys, NP-stimulated enhancement of cyclic GMP accumulation was found in juveniles in fresh water and more particularly in salt water. RT-PCR amplified a 471 base pair fragment with 68 % amino acid sequence homology to the eel natriuretic peptide receptor D (NPR-D). This study suggests that NP binding sites in the adult gill and aorta are of an NPR-C/D type, whereas an additional GC-coupled site exists in juveniles.
The Electric Image in Weakly Electric Fish: Physical Images of Resistive Objects in Gnathonemus Petersii
Authors: Caputi A. A. , Budelli R. , Grant K. , Bell C. C. 
Published: April 2021

ABSTRACT
The present study describes a measurement-based model of electric image generation in the weakly electric mormyrid fish Gnathonemus petersii. Measurements of skin impedance, internal resistivity and fish body dimensions have been used to generate an electrical-equivalent model of the fish and to calculate electrical images and equivalent dipole sources for elementary resistive objects. These calculations allow us to understand how exafferent and reafferent signals are sensed by electroreceptors. An object’s electric image consists of the modulation of the transcutaneous voltage profile generated by the fish’s own discharge. The results suggest a set of rules for electrolocation: (1) the side of the fish where modulation is larger indicates the side on which the object is situated; (2) the object’s position in the electroreceptive field is indicated by the point of maximum modulation of the transcutaneous voltage; (3) the degree of focus of the image indicates the distance to the object. In addition, center–surround opposition originating at pre-receptor level is proposed.
Both experimental measurements and modeling indicate that fish skin impedance is relatively low (400–11 000 Ω cm2) and mainly resistive. This low skin impedance appears to enhance the local electric organ discharge modulation, the center–surround effect, the signal-to-noise ratio for electrolocation and the active space for electrocommunication.
Cold Inhibition of Cell Volume Regulation During the Freezing of Insect Malpighian Tubules
Authors: Neufeld Douglas S. , Leader John P. 
Published: April 2021

ABSTRACT
Cells in freeze-tolerant tissues must survive substantial shrinkage during exposure to the hyperosmolarity that results as solutes are excluded from extracellular ice. We investigated the possibility that this hyperosmotic shock elicits an acute regulatory volume increase (RVI) by monitoring the response of epithelial cell volume in the Malpighian tubules of the New Zealand alpine weta (Hemideina maori) during exposure to low temperature/hyperosmolarity (mimicking freezing conditions) or during an actual freeze/thaw cycle. The cross-sectional area of cells in isolated Malpighian tubules was measured using differential interference contrast microscopy. At 20 °C, cells held in saline containing 400 mmol l−1 glucose exhibit an RVI in response to hyperosmotic shock. Cross-sectional area decreased by 30 % immediately after a change from iso-osmotic (0.7 osmol l−1) to hyper-osmotic saline (2.1 osmol l−1, equal to the osmotic shock encountered during freezing to −4 °C) and then returned to 21 % below the control value 30 min after the exposure. Although substantial cellular function of Malpighian tubules was retained at low temperature (the rate of fluid secretion by isolated tubules at 4 °C was 72 % of that measured at 20 °C), no RVI was observed at 0 °C; cross-sectional area was 39 % below the control value immediately after the hyperosmotic exposure and 36 % below the control value 30 min after hyperosmotic exposure. Dibutyryl cyclic AMP potentiated the RVI observed at 20 °C, but failed to elicit an RVI at 0 °C. A substantial RVI was also absent when the saline contained trehalose rather than glucose, regardless of whether the tubules were held at 20 °C or 0 °C. The cross-sectional area of cells in saline containing glucose remained at approximately 30 % below the control value during an entire 30 min period of actual freezing to −4 °C, suggesting that an acute volume regulatory response was in fact inhibited during mild freezing. The inhibition of an acute RVI during mild freezing may serve to avoid the energetic expenditure associated with volume regulation at a time when the normal defence of cell volume appears to be unnecessary.