bluuebunny/crossref_metadata_2025_split huggingface dataset:
Covariation in Regulation of Affinity for Branchial Zinc and Calcium Uptake in Freshwater Rainbow Trout
Authors: Hogstrand Christer , Webb Nathan , Wood Chris M. 
Published: April 2021

ABSTRACT
The possible coupling between regulation of the affinities for branchial Zn and Ca influx was investigated in juvenile rainbow trout Oncorhynchus mykiss acclimated to relatively hard fresh water ([Ca]=1.0 mmol l−1). The Km for branchial Ca influx was manipulated experimentally by exposing the fish to 2.3 μmol l−1 waterborne Zn for a total of 28 days. This procedure resulted in rapidly increased Km values for both Ca and Zn influx, an effect that remained through the experimental period. There was a significant linear correlation (r=0.88, P&lt;0.02) between Km values for Ca and Zn measured at the same time points. Zn exposure caused progressively increasing maximum rate of transport, Jmax, values for Zn relative to the control value, but there was little, if any, effect on Jmax for Ca. These results support the idea of a shared transport site for Zn and Ca at the apical membrane of the gill epithelium and suggest that there is a certain degree of coregulation of branchial Zn and Ca uptake in rainbow trout. Removal of Ca from the water resulted in a large (six-to 24-fold) increase in affinity (decreased Km) for Zn influx and a modest (1.1-to 1.8-fold) increase in Jmax for Zn. Thus, Ca is a competitive inhibitor of Zn influx. In water lacking Ca, the Km for Zn in Zn-acclimated fish was no different from that of the control fish, suggesting that the Ca2+/Zn2+ transporter was regulated to improve Ca uptake.
The Electroneutral Cation–Chloride Cotransporters
Authors: Mount David B. , Delpire Eric , Gamba Gerardo , Hall Amy E. , Poch Esteban , Hoover Robert S. , Hebert Steven C. 
Published: April 2021

ABSTRACT
Electroneutral cation–chloride cotransporters are widely expressed and perform a variety of physiological roles. A novel gene family of five members, encompassing a Na+–Cl− transporter, two Na+–K+–2Cl− transporters and two K+–Cl− cotransporters, encodes these membrane proteins; homologous genes have also been identified in a prokaryote and a number of lower eukaryotes. The cotransporter proteins share a common predicted membrane topology, with twelve putative transmembrane segments flanked by long hydrophilic N- and C-terminal cytoplasmic domains. The molecular identification of these transporters has had a significant impact on the study of their function, regulation and pathophysiology.
Relaxation and Activation of Graviresponses in Paramecium Caudatum
Authors: Bräucker Richard , Murakami Akira , Ikegaya Kazuko , Yoshimura Kenjiro , Takahashi Keiichi , Machemer-Röhnisch Sigrun , Machemer Hans 
Published: April 2021

ABSTRACT
The kinetics of gravitaxis and gravikinesis in Paramecium caudatum were investigated by employing (1) step transitions from normal gravity (1 g) to weightlessness (microgravity) and (2) turns of the experimental chambers from the horizontal to the vertical position at 1 g. The transition to microgravity left existing cell orientations unchanged. Relaxation of negative gravitaxis under microgravity took longer than 10 s and may be described by the time constant of the decay of orientation coefficients. Gravitaxis was started at 1 g by turning the experimental chamber from a horizontal to a vertical position. Gravitaxis activated rapidly during the turning procedure and relaxed to an intermediate level after the turning had stopped. Gravity-induced regulation of swimming speed (gravikinesis) at 1 g had reached a steady state after 1 min; at this point, gravikinesis counteracted the effects of sedimentation (negative gravikinesis). A step transition to microgravity initially reversed the sign of the gravikinesis (positive gravikinesis). The relaxation of this kinetic response was not completed during 10 s of microgravity. The data suggest that gravikinesis is functionally unrelated to gravitaxis and is strongly affected by the rate of change in acceleration. We present a model explaining why gravikinesis reverses sign upon the onset of a step from 1 g to microgravity.
The Role of Angiotensin in Arterial Blood Pressure Regulation in the Toad Bufo Marinus
Authors: West N. H. , Kimmel P. , Topor Z. L. , Evered M. D. 
Published: April 2021

ABSTRACT
Little is known about the role of the renin–angiotensin system in anuran amphibians, although they appear to possess the functional components of such a system. We investigated the role of angiotensin (ANG) in arterial blood pressure regulation in the conscious toad Bufo marinus using the angiotensin-converting enzyme blocker captopril. We found that conversion of endogenous ANG I to ANG II made a significant contribution to mean arterial pressure in undisturbed animals. The vascular tone contributed by ANG II was not mediated via alpha adrenergic mechanisms because increases in pressure in response to ANG infusion were unaffected by the presence of the alpha antagonist phentolamine. Angiotensin-induced vasoconstriction was shown to be an important mechanism in arterial blood pressure regulation in the face of an acute hypotensive perturbation of pressure brought about by sodium nitroprusside. Blockade of the conversion of ANG I to ANG II significantly delayed the recovery of mean arterial pressure after sodium nitroprusside-induced hypotension. This suggests that the renin–angiotensin system may play an important role in the initial responses to hypotension in anurans, whether brought about by haemorrhage or dehydration.
Retinal Location is the Key to Identifying Predators in Fiddler Crabs (Uca Pugilator)
Authors: Layne John E. 
Published: April 2021

ABSTRACT
Fiddler crabs (Uca pugilator Bosc; Crustacea, Decapoda) feed and court in open, flat spaces. Their visual system has several putative adaptations to their flat habitat, including the tendency to keep the vertical axis of their eyes perpendicular to the plane of the substratum. It is hypothesized that one of the functions of this behavior is to distinguish accurately predators from conspecifics by aligning the region of the eye sensitive to predators with the region in space in which predators occur. To test this hypothesis, a crab was placed in a glass dish, and a moving stimulus was presented between 20 ° above and below eye level (horizontal). Stimuli below the crab’s horizon hardly ever evoked escape responses, while identical stimuli above the horizon produced escape responses whose frequency varied with the angular size, not the absolute size, of the stimulus. Experiments with artificial horizons showed that it is the position of the stimulus relative to the eye that is important, rather than its position relative to external cues such as the visible horizon, the vertical light gradient or the gravitational horizon. It is concluded that a crab responds to stimuli according to their position relative to its retinal equator. This conclusion is discussed in light of the crabs’ natural behavior with respect to supra-horizontal stimuli.
Passive Body Movement and Gas Exchange in the Frilled Lizard (Chlamydosaurus Kingii) and Goanna (Varanus Gouldii)
Authors: Frappell Peter B. , Mortola Jacopo P. 
Published: April 2021

ABSTRACT
The saccular lung in lizards is large and highly compliant compared with mammalian lungs, and these properties led us to question to what extent body movements could affect pulmonary gas exchange and the partial pressure of arterial blood gases. Specimens of two species of lizards, the frilled lizard (Chlamydosaurus kingii, approximately 600 g body mass) and the goanna (Varanus gouldii, approximately 1400 mass), were anaesthetised, maintained at approximately 36 °C and mechanically hyperventilated to lower the arterial partial pressure of carbon dioxide to below apnoeic threshold. Respiratory system compliance (Crs) averaged 0.112 ml kg−1 Pa−1 (goanna) and 0.173 ml kg−1 Pa−1 (frilled lizard), which is approximately 7–11 times the predicted value for a mammal of similar body mass. Mechanical ventilation was interrupted, and the changes in and were monitored over the following 10 min as the animal was either left immobile or subjected to imposed lateral body movements. During the post-hyperventilation apnoea, increased whereas did not always fall, sometimes even increasing, suggesting a reduction in the importance of pulmonary shunts. No significant differences were detected in the time course of changes in arterial blood gas levels or heart rate between runs with or without body movement. We conclude that in these species of lizards, despite the high Crs, lateral chest wall movements neither hinder nor favour pulmonary gas exchange.
Entrainment by River Chub Nocomis Micropogon and Smallmouth Bass Micropterus Dolomieu on Cylinders
Authors: Webb Paul W. 
Published: April 2021

ABSTRACT
Sympatric stream-dwelling river chub (Nocomis micropogon) and smallmouth bass (Micropterus dolomieu) were video-taped swimming in the presence of single cylinders spanning a flume. Fish were acclimated and tested at 13, 18 and 23 °C swimming in an increasing-velocity test with single vertically or horizontally oriented cylinders 6.4, 13, 19 or 25 mm in diameter. Cylinder orientation had little effect on entrainment. Both species avoided cylinders at low speeds. At intermediate speeds, some fish entrained on the cylinders, but they were displaced at higher speeds. Entrained fish made no regular swimming motions, but the median and paired fins and the body moved continuously and irregularly. The periodicity of body perturbations decreased and the amplitude increased with current speed. These also increased with cylinder diameter, but the variability was high and differences were not significant. Chub entrained in larger numbers and for longer over a wider range of current speeds and temperatures than bass. Entrainment by chub increased with cylinder diameter up to 13–19 mm, but declined for 25 mm cylinders. Bass did not entrain on 6.4 mm and 25 mm cylinders and showed very little entrainment at 13 and 18 °C, but entrainment was similar to that of chub at 23 °C.
Effects of Prey Size and Mobility on Prey-Capture Kinematics in Leopard Sharks Triakis Semifasciata
Authors: Ferry-Graham Lara A. 
Published: April 2021

ABSTRACT
Recent work on teleosts suggests that attack behaviors or kinematics may be modified by a predator on the basis of the size of the prey or the ability of the prey to sense predators and escape capture (elusivity). Sharks are generally presumed to be highly visual predators; thus, it is reasonable to expect that they might also be capable of such behavioral modulation. In this study, I investigated the effect of prey item size and type on prey-capture behavior in leopard sharks (Triakis semifasciata) that had been acclimated to feeding in the laboratory. Using high-speed video, sharks were filmed feeding on two sizes of the same prey item (thawed shrimp pieces) and two potentially more elusive prey items (live earthworms and live mud shrimp). In leopard sharks, little effect of prey elusivity was found for kinematic variables during prey capture. However, the large proportion of successful captures of the live prey suggests that they did not prove to be truly elusive prey items for the leopard shark. There were significant size effects on prey-capture kinematics, with the larger non-elusive items inducing greater head expansion during prey capture. Ram–suction index values also indicated that strikes on large, non-elusive prey had a significantly larger suction component than strikes on similar small prey items. This finding is interesting given that the two sizes of non-elusive prey item offered no differential challenge in terms of a performance consequence (reduced capture success).
Neurogenesis in the thoracic neuromeres of two crustaceans with different types of metamorphic development
Authors: Harzsch S. , Miller J. , Benton J. , Dawirs R. R. , Beltz B. 
Published: April 2021

ABSTRACT
The mode of embryonic and larval development and the ethology of metamorphosis in the spider crab and the American lobster are very different, and we took advantage of this to compare neuronal development in the two species. The goals of this study were to discover whether the differences in the maturation of the neuromuscular system in the pereopods and the metamorphic changes of motor behavior between the two species are reflected at the level of the developing nervous system (‘neurometamorphosis’). Furthermore, we wanted to broaden our understanding of the mechanisms that govern neuronal development in arthropods. Proliferation of neuronal stem cells in thoracic neuromeres 4–8 of the lobster Homarus americanus and the crab Hyas araneus was monitored over the course of embryonic and larval development using the in vivo incorporation of bromodeoxyuridine (BrdU). Neuropil structure was visualized using an antibody against Drosophila synapsin. While proliferation of neuronal precursors has ceased when embryogenesis is 80 % complete (E80%) in the lobster thoracic neuromeres, proliferation of neuroblasts in the crab persists throughout embryonic development and into larval life. The divergent temporal patterns of neurogenesis in the two crustacean species can be correlated with differences in larval life style and in the degree of maturation of the thoracic legs during metamorphic development. Several unusual aspects of neurogenesis reported here distinguish these crustaceans from other arthropods. Lobsters apparently lack a postembryonic period of proliferation in the thoracic neuromeres despite the metamorphic remodeling that takes place in the larval stages. In contrast, an increase in mitotic activity towards the end of embryonic development is found in crabs, and neuroblast proliferation persists throughout the process of hatching into the larval stages. In both E20% lobster embryos and mid-embryonic crabs, expression of engrailed was found in a corresponding set of neurons and putative glial cells at the posterior neuromere border, suggesting that these cells have acquired similar specific identities and might, therefore, be homologous. None of the BrdU-labeled neuroblasts (typically 6–8 per hemineuromere over a long period of embryogenesis) was positive for engrailed at this and subsequent stages. Our findings are discussed in relation to the spatial and temporal patterns of neurogenesis in insects.
Hydrogen ion titrations of the anodic and cathodic haemoglobin components of the European eel Anguilla anguilla
Authors: Brauner Colin J. , Weber Roy E. 
Published: April 2021

ABSTRACT
H+ titrations were conducted on the separated haemoglobin components of eel Anguilla anguilla in both the oxygenated and deoxygenated states. In anodic haemoglobin, the addition of GTP, and to a lesser extent Cl−, increased the magnitude of the Haldane effect and shifted its maximum value into the in vivo pH range. Of the 22 histidine residues in the anodic component, only approximately seven were titratable, presumably the β-chain residues at positions 41, 97, 109 and 146 (helical positions C7, FG4, G11 and HC3, respectively).
In cathodic haemoglobin, a small negative Haldane effect was observed at pH values between 6.8 and 8.5 which disappeared in the presence of GTP (molar ratio 3:1 GTP:haemoglobin tetramer). GTP had virtually no effect on the buffer value at fixed oxygenation status, and the lowest buffer value was observed at in vivo pH values. No titratable histidine residues were observed in the cathodic component, indicating that all 14 histidines in this component are buried.
We conclude that the anodic component, which constitutes two-thirds of the haemoglobin in the eel, plays the predominant role in CO2 transport and pH homeostasis in vivo.
Nitrogen metabolism of two portunid crabs, Carcinus maenas and Necora puber, during prolonged air exposure and subsequent recovery: a comparative study
Authors: Durand Fabrice , Regnault Michèle 
Published: April 2021

ABSTRACT
Carcinus maenas and Necora puber were exposed to air for 72 h and 18 h, respectively, at 18 °C. Nitrogen excretion, blood and muscle ammonia content and blood urate and lactate content were recorded throughout the experimental emersion and following reimmersion (recovery period).
During emersion, the rate of ammonia excretion was strongly reduced in both species, while urea and amine excretion were not enhanced. Blood and muscle ammonia content increased steadily, reaching 1.3 and 10.4 mmol l−1, respectively, after an 18 h emersion in N. puber. In contrast, in C. maenas, blood ammonia levels increased slightly during the first 12 h and then remained at this level (approximately 0.12 mmol l−1) until the end of emersion. Muscle ammonia content showed a non-significant increase at 12 h, after which values returned to control values (3.3 mmol l−1) for the next 60 h.
Blood urate and lactate content increased in emersed N. puber, indicating strong internal hypoxia, but urate content did not increase in C. maenas until the third day of emersion.
Upon reimmersion, both species released large amounts of ammonia within a few minutes. Two different patterns of ammonia release then were observed: ammonia excretion was enhanced for a further 3 h in N. puber, whereas raised ammonia excretion rates were observed for a further 24 h in C. maenas. These patterns, the recovery of blood and muscle ammonia levels and the calculated nitrogen balance between emersed and control crabs indicated that specific processes were used to manage the nitrogen overload induced by air exposure.
Whereas N. puber shows little or no ability to limit ammonia accumulation in its body, C. maenas exhibits strong regulation of its nitrogen metabolism. The probability that amino acid synthesis is involved in this regulation and whether these species use metabolic depression as a survival strategy are discussed.
Distinguishing metabolic heat from condensation heat during muscle recovery
Authors: Lou F. , Curtin N. A. , Woledge R. C. 
Published: April 2021

ABSTRACT
When a thermopile is used to measure the heat production of isolated muscle, the muscle is surrounded by gas saturated with water vapour, initially in equilibrium with the muscle. After contraction, the osmolarity of the muscle is raised so that it is no longer in equilibrium with the gas around it, and condensation will occur. When artificial muscles of known osmolarity were placed on a thermopile surrounded by gas in equilibrium with a solution of lower osmolarity, their temperature was found to be raised (by 102.7 mK osmol−1 l). This temperature increase was greatly reduced by covering the artificial muscle with a Teflon film. Experiments on living muscle from the dogfish Scyliorhinus canicula showed that muscle temperature was higher 2 min after a series of 20 twitches at 3 Hz if the muscle was not covered by Teflon than if it was covered. The Teflon covering did not diminish the muscle’s contractile performance. We conclude that the condensation of water does contribute to the heat measured during the recovery period, but that when the muscle is covered by Teflon film condensation heat can largely be prevented so that only genuine metabolic recovery heat is produced.
Locomotion in Alligator mississippiensis: kinematic effects of speed and posture and their relevance to the sprawling-to-erect paradigm
Authors: Reilly Stephen M. , Elias Jason A. 
Published: April 2021

ABSTRACT
In terms of locomotory posture, amphibians and lizards are considered to be sprawlers, mammals and dinosaurs are considered to be erect, and extant crocodilians are considered to be intermediate because they use the ‘high walk’, a semi-erect posture where the body is held half-way between the sprawling and erect grades during locomotion. In addition, crocodilians occasionally use a sprawling posture. Extant crocodilians, therefore, provide an interesting model in which to investigate the sprawling-to-erect transition in vertebrate evolution. This study quantifies the sprawl and high walk kinematics of the alligator Alligator mississippiensis moving at different speeds on a treadmill and compares them with kinematic data available for other vertebrates. These data allow us to examine the effects of speed on crocodilian postures and to examine how crocodilian locomotion relates to the sprawling-to-erect paradigm in vertebrate locomotion.
Our results show that the crocodilian sprawl is not functionally equivalent to the primitive sprawling behaviors exhibited by salamanders and lizards. In fact, although the high walks and sprawls of alligators exhibit some kinematic differences, they are actually much more similar than expected and, essentially, the crocodilian sprawl is a lower version of a high walk and could be termed a ‘low walk’.
In terms of the sprawling-to-erect transition, the high walk has knee kinematics intermediate between those of birds and non-archosaurian tetrapods, but alligators increase speed in a way completely different from other terrestrial vertebrates (distal rather than proximal limb elements are used to increase speed). These kinematic data viewed in the light of the fossil and phylogenetic evidence that modern crocodilians evolved from erect ancestors suggest that modern crocodilians have secondarily evolved a variable semi-erect posture and that they are problematic as an intermediate model for the evolutionary transition from sprawling to erect postures in archosaurs.
Transepithelial transport of nicotine and vinblastine in isolated malpighian tubules of the tobacco hornworm (Manduca sexta) suggests a P-glycoprotein-like mechanism
Authors: Gaertner Lorin S. , Murray Christine L. , Morris Catherine E. 
Published: April 2021

ABSTRACT
We have examined the accumulative transport properties of the Malpighian (excretory) tubules of the tobacco hornworm Manduca sexta to test the hypothesis that a P-glycoprotein-like multidrug transporter is active and is responsible for the excretion of dietary nicotine in this tissue. Isolated tubules were cannulated and exposed to radiolabelled forms of either nicotine (5 min exposure) or the P-glycoprotein substrate vinblastine (60 min exposure) in the bathing (basal surface) fluid. The luminal (apical) contents were then flushed, and lumen-to-bath ratios were measured. Although these ratios provide conservative estimates of the physiological ability of Malpighian tubules to move compounds from blood to lumen, tubules concentrated nicotine 10-fold from an initial bath concentration of 0.5 mmol l−1 and vinblastine threefold (from an initial concentration of 1 μmol l−1).
Vectorial transport of vinblastine and nicotine was eliminated by 25 μmol l−1 verapamil (a P-glycoprotein inhibitor) and was not dependent on the presence of a transepithelial electrical potential. Nicotine transport was inhibited by atropine (3 mmol l−1), while nicotine (⩾50 μmol l−1) significantly reduced vinblastine transport. Verapamil was effective at reducing vinblastine transport when applied to the basal side alone, but not when applied to the apical side alone. Taken together, these results are consistent with the idea that the active excretion of nicotine and other alkaloids by the tobacco hornworm is mediated by a P-glycoprotein-like mechanism.