bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for the Role of a Na+/HCO3−Cotransporter in Trout Hepatocyte pHi Regulation
Authors: Furimsky M. , Moon T. W. , Perry S. F. 
Published: April 2021

ABSTRACT
The mechanisms of intracellular pH (pHi) regulation were examined in hepatocytes of the rainbow trout Oncorhynchus mykiss. pHi was monitored using the pH-sensitive fluorescent dye BCECF, and the effects of various media and pharmacological agents were examined for their influence on baseline pHi and recovery rates from acid and base loading. Rates of Na+ uptake were measured using 22Na, and changes in membrane potential were examined using the potentiometric fluorescent dye Oxonol VI. The rate of proton extrusion following acid loading was diminished by the blockade of either Na+/H+ exchange (using amiloride) or anion transport (using DIDS). The removal of external HCO3− and the abolition of outward K+ diffusion by the channel blocker Ba2+ also decreased the rate of proton extrusion following acid load. Depolarization of the cell membrane with 50 mmol l−1 K+, however, did not affect pHi. The rate of recovery from base loading was significantly diminished by the blockade of anion transport, removal of external HCO3− and, to a lesser extent, by blocking Na+/H+ exchange. The blockade of K+ conductance had no effect. The decrease in Na+ uptake rate observed in the presence of the anion transport blocker DIDS and the DIDS-sensitive hyperpolarization of membrane potential during recovery from acid loading suggest that a Na+-dependent electrogenic transport system is involved in the restoration of pHi after intracellular acidification. The effects on baseline pHi indicate that the different membrane exchangers are tonically active in the maintenance of steady-state pHi. This study confirms the roles of a Na+/H+ exchanger and a Cl−/HCO3− exchanger in the regulation of trout hepatocyte pHi and provides new evidence that a Na+/HCO3− cotransporter contributes to pHi regulation.
The Resting Membrane Potential of White Muscle from Brown Trout (Salmo Trutta) Exposed to Copper in Soft, Acidic Water
Authors: Beaumont M. W. , Taylor E. W. , Butler P. J. 
Published: April 2021

ABSTRACT
Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (EM) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study EM was directly measured in white muscle fibres of trout exposed to copper and low pH (EM=−52.2±4.9 mV) and compared with that of unexposed, control animals (EM=−86.5±2.9 mV) (means ± S.E.M., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH4+ in determining the distribution of ammonia in fish.
Locomotion in Scombrid Fishes: Morphology and Kinematics of the Finlets of the Chub Mackerel Scomber Japonicus
Authors: Nauen Jennifer C. , Lauder George V. 
Published: April 2021

ABSTRACT
Finlets are small non-retractable fins located on the dorsal and ventral margins of the body between the second dorsal and anal fins and the tail of scombrid fishes. The morphology of the finlets, and finlet kinematics during swimming in a flow tank at speeds of 0.8–3.0 fork lengths s−1, were examined in the chub mackerel Scomber japonicus. Functionally, S. japonicus has five dorsal and anal triangular finlets (the fifth finlet is a pair of finlets acting in concert). Slips of muscle that insert onto the base of each finlet indicate the potential for active movement. In animals of similar mass, finlet length and area increased posteriorly. Finlet length, height and area show positive allometry in animals from 45 to 279 g body mass. Summed finlet area was approximately 15 % of caudal fin area.
During steady swimming, the finlets typically oscillated symmetrically in the horizontal and vertical planes. Finlet excursions in the x, y and z directions ranged from 1 to 5 mm, increased posteriorly and were independent of speed. The timing of the maximum amplitude of oscillation was phased posteriorly; the phase lag of the maximum amplitude of oscillation was independent of speed. During some periods of gliding, a finlet occasionally moved independently of the body and the other finlets, which indicated active control of finlet movement.
The angle of attack of the finlets averaged approximately 0 ° over a tailbeat, indicating no net contribution to thrust production via classical lift-based mechanisms. However, the timing of finlet movement relative to that of the tail suggests that more posterior finlets may direct some flow longitudinally as the tail decelerates and thereby contribute flow to the developing caudal fin vortex.
Movies available on-line: http://www.biologists.com/JEB/movies/jeb2618.html
Immunolocalization of Ion-Transport Proteins to Branchial Epithelium Mitochondria-Rich Cells in the Mudskipper (Periophthalmodon Schlosseri)
Authors: Wilson Jonathan M. , Randall David J. , Donowitz Mark , Vogl A. Wayne , Ip Alex K.-Y. 
Published: April 2021

ABSTRACT
The branchial epithelium of the mudskipper Periophthalmodon schlosseri is densely packed with mitochondria-rich (MR) cells. This species of mudskipper is also able to eliminate ammonia against large inward gradients and to tolerate extremely high environmental ammonia concentrations. To test whether these branchial MR cells are the sites of active ammonia elimination, we used an immunological approach to localize ion-transport proteins that have been shown pharmacologically to be involved in the elimination of NH4+(Na+/NH4+exchanger and Na+/NH4+-ATPase). We also investigated the role of carbonic anhydrase and boundary-layer pH effects in ammonia elimination by using the carbonic anhydrase inhibitor acetazolamide and by buffering the bath water with Hepes, respectively. In the branchial epithelium, Na+/H+exchangers (both NHE2- and NHE3-like isoforms), a cystic fibrosis transmembrane regulator (CFTR)-like anion channel, a vacuolar-type H+-ATPase (V-ATPase) and carbonic anhydrase immunoreactivity are associated with the apical crypt region of MR cells. Associated with the MR cell basolateral membrane and tubular system are the Na+/K+-ATPase and a Na+/K+/2Cl−cotransporter. A proportion of the ammonia eliminated by P. schlosseri involves carbonic anhydrase activity and is not dependent on boundary-layer pH effects. The apical CFTR-like anion channel may be serving as a HCO3−channel accounting for the acid–base neutral effects observed with net ammonia efflux inhibition.
Heat-Shock Protein Expression is Absent in the Antarctic Fish Trematomus Bernacchii (Family Nototheniidae)
Authors: Hofmann Gretchen E. , Buckley Bradley A. , Airaksinen Susanna , Keen John E. , Somero George N. 
Published: April 2021

ABSTRACT
The heat-shock response, the enhanced expression of one or more classes of molecular chaperones termed heat-shock proteins (hsps) in response to stress induced by high temperatures, is commonly viewed as a ‘universal’ characteristic of organisms. We examined the occurrence of the heat-shock response in a highly cold-adapted, stenothermal Antarctic teleost fish, Trematomus bernacchii, to determine whether this response has persisted in a lineage that has encountered very low and stable temperatures for at least the past 14–25 million years. The patterns of protein synthesis observed in in vivo metabolic labelling experiments that involved injection of 35S-labelled methionine and cysteine into whole fish previously subjected to a heat stress of 10 °C yielded no evidence for synthesis of any size class of heat-shock protein. Parallel in vivo labelling experiments with isolated hepatocytes similarly showed significant amounts of protein synthesis, but no indication of enhanced expression of any class of hsp. The heavy metal cadmium, which is known to induce synthesis of hsps, also failed to alter the pattern of proteins synthesized in hepatocytes. Although stress-induced chaperones could not be detected under any of the experimental condition used, solid-phase antibody (western) analysis revealed that a constitutively expressed 70 kDa chaperone was present in this species, as predicted on the basis of requirements for chaperoning during protein synthesis. Amounts of the constitutively expressed 70 kDa chaperone increased in brain, but not in gill, during 22 days of acclimation to 5 °C. The apparent absence of a heat-shock response in this highly stenothermal species is interpreted as an indication that a physiological capacity observed in almost all other organisms has been lost as a result of the absence of positive selection during evolution at stable sub-zero temperatures. Whether the loss of the heat-shock response is due to dysfunctional genes for inducible hsps (loss of open reading frames or functional regulatory regions), unstable messenger RNAs, the absence of a functional heat-shock factor or some other lesion remains to be determined.
Cortisol Increases Na+/K+-ATPase Density in Plasma Membranes of Gill Chloride Cells in the Freshwater Tilapia Oreochromis Mossambicus
Authors: Dang Zhichao , Balm Paul H. M. , Flik Gert , Wendelaar Bonga Sjoerd E. , Lock Robert A. C. 
Published: April 2021

ABSTRACT
The effect of cortisol on Na+/K+-ATPase expression in the gill chloride cells of tilapia Oreochromis mossambicus was studied by immunocytochemistry at the light and electron microscope levels. One of three doses of cortisol (low, 125 mg kg−1food; middle, 375 mg kg−1food; high, 750 mg kg−1food) was administered via the food (at a ration of 1.5 % of body mass) and the fish were sampled after 5 days. Plasma osmolality and Na+levels were elevated in the middle- and high-dose groups, and plasma cortisol levels in the high-dose groups. Hematocrit values were not affected by the treatments. Opercular membrane chloride cell density increased by 94 % and 286 % in the middle- and high-dose fish, respectively, whereas the gill chloride cell frequency increased by up to 28 % maximally in the high-dose fish. Lamellar gill chloride cells were absent in the control and low-dose groups, but were observed in the middle- and high-dose groups. Cortisol increased the volume of the tubular membrane system in mature gill chloride cells. Quantification of immunogold-labelled Na+/K+-ATPase antigen (a 104 kDa protein species, as demonstrated by western blot) revealed that the high dose of cortisol increases the Na+/K+-ATPase density in the tubular system of chloride cells. This is the first direct evidence that cortisol not only increases chloride cell numbers but also Na+/K+-ATPase density in these cells.
Molecular Characterization of a Urea Transporter in the Gill of the Gulf Toadfish (Opsanus Beta)
Authors: Walsh Patrick J. , Heitz Molly J. , Campbell Catherine E. , Cooper Gordon J. , Medina Monica , Wang Yuxiang S. , Goss Greg G. , Vincek Vladimir , Wood Chris M. , Smith Craig P. 
Published: April 2021

ABSTRACT
Urea excretion by the gulf toadfish (Opsanus beta) has been shown in previous studies to be a highly pulsatile facilitated transport, with excretion probably occurring at the gill. The present study reports the isolation of an 1800 base pair (kb) cDNA from toadfish gill with one open reading frame putatively encoding a 475-residue protein, the toadfish urea transporter (tUT). tUT, the first teleostean urea transporter cloned, has high homology with UTs (facilitated urea transporters) cloned from mammals, an amphibian and a shark, and most closely resembles the UT-A subfamily. When expressed in Xenopus laevis oocytes, tUT increased urea permeability (as measured by [14C]urea uptake) five- to sevenfold, and this permeability increase was abolished by phloretin, a common inhibitor of other UTs. Northern analysis using the 1.8 kb clone was performed to determine the tissue distribution and dynamics of tUT mRNA expression. Of six tissues examined (gill, liver, red blood cells, kidney, skin and intestine), only gill showed expression of tUT mRNA, with a predominant band at 1.8 kb and a minor band at 3.5 kb. During several points in the urea pulse cycle of toadfish (0, 4, 6, 12 and 18 h post-pulse), measured by excretion of [14C]urea into the water, gill mRNA samples were obtained. Expression of tUT mRNA was found to be largely invariant relative to expression of β-actin mRNA over the pulse cycle. These results further confirm the gill localization of urea transport in the toadfish and suggest that tUT regulation (and the regulation of pulsatile urea excretion) is probably not at the level of mRNA control. The results are discussed in the context of the mechanisms of vasopressin-regulated UT-A in mammalian kidney and morphological data for the toadfish gill.
Mechanisms of Gastrointestinal Copper Absorption in the African Walking Catfish: Copper Dose-Effects and a Novel Anion-Dependent Pathway in the Intestine
Authors: Handy R. D. , Musonda M. M. , Phillips C. , Falla S. J. 
Published: April 2021

ABSTRACT
In mammals, copper (Cu) absorption occurs mostly in the small intestine, and some of the Cu transporters involved in its uptake have been characterised. In fish, however, the regions of the gut involved in Cu absorption and the membrane transport mechanisms responsible for gastrointestinal Cu uptake are unknown. Everted gut sacs and isolated perfused intestine of Clarias gariepinus were used to explore Cu absorption (at 22 °C). Gut sacs exposed to 100 μmol l−1mucosal solution Cu ([Cu]m) showed that Cu was mostly (70 %) absorbed in the middle and hind intestine. Most of the accumulated Cu was located in the mucosa. In perfused intestines, cumulative Cu absorption from the mucosal solution to the serosal perfusate was greatest at 10 μmol l−1[Cu]m and decreased at higher values of [Cu]m, while tissue accumulation of Cu showed a dose-dependent elevation. Absorption efficiency therefore declined with increasing Cu dose, and basolateral transport was the limiting factor in Cu uptake. Serosal applications of the P-type ATPase inhibitor vanadate (100 μmol l−1) or the anion transport inhibitor DIDS (100 μmol l−1) caused threefold increases in net Cu uptake (at [Cu]m=10 μmol l−1). The vanadate effect was explained by a reduction in transepithelial potential rather than inhibition of Cu-ATPase, but the DIDS effect was not. Transepithelial potential, water transport and tissue [Cu] were not affected by DIDS, but tissue [K+] was elevated. Removal of Cl−simultaneously from both the mucosal and serosal solutions caused a 10-fold reduction in the rate of Cu uptake, while removal of Cl−from the mucosal solution only completely abolished Cu absorption to the serosal perfusate. Transepithelial potential effects are discussed. We conclude that Cu absorption occurs mostly in the intestine and is normally driven by a basolateral Cu/anion symport that prefers Cl−.
A Hydrodynamic Analysis of Fish Swimming Speed: Wake Structure and Locomotor Force in Slow and Fast Labriform Swimmers
Authors: Drucker Eliot G. , Lauder George V. 
Published: April 2021

ABSTRACT
Past study of interspecific variation in the swimming speed of fishes has focused on internal physiological mechanisms that may limit the ability of locomotor muscle to generate power. In this paper, we approach the question of why some fishes are able to swim faster than others from a hydrodynamic perspective, using the technique of digital particle image velocimetry which allows measurement of fluid velocity and estimation of wake momentum and mechanical forces for locomotion. We investigate the structure and strength of the wake in three dimensions to determine how hydrodynamic force varies in two species that differ markedly in maximum swimming speed. Black surfperch (Embiotoca jacksoni) and bluegill sunfish (Lepomis macrochirus) swim at low speeds using their pectoral fins exclusively, and at higher speeds switch to combined pectoral and caudal fin locomotion. E. jacksoni can swim twice as fast as similarly sized L. macrochirus using the pectoral fins alone. The pectoral fin wake of black surfperch at all speeds consists of two distinct vortex rings linked ventrally. As speed increases from 1.0 to 3.0 L s−1, where L is total body length, the vortex ring formed on the fin downstroke reorients to direct force increasingly downstream, parallel to the direction of locomotion. The ratio of laterally to downstream-directed force declines from 0.93 to 0.07 as speed increases. In contrast, the sunfish pectoral fin generates a single vortex ring per fin beat at low swimming speeds and a pair of linked vortex rings (with one ring only partially complete and attached to the body) at maximal labriform speeds. Across a biologically relevant range of swimming speeds, bluegill sunfish generate relatively large lateral forces with the paired fins: the ratio of lateral to downstream force remains at or above 1.0 at all speeds. By increasing wake momentum and by orienting this momentum in a direction more favorable for thrust than for lateral force, black surfperch are able to swim at twice the speed of bluegill sunfish using the pectoral fins. In sunfish, without a reorientation of shed vortices, increases in power output of pectoral fin muscle would have little effect on maximum locomotor speed. We present two hypotheses relating locomotor stability, maneuverability and the structure of the vortex wake. First, at low speeds, the large lateral forces exhibited by both species may be necessary for stability. Second, we propose a potential hydrodynamic trade-off between speed and maneuverability that arises as a geometric consequence of the orientation of vortex rings shed by the pectoral fins. Bluegill sunfish may be more maneuverable because of their ability to generate large mediolateral force asymmetries between the left- and right-side fins.
Patterns of Cardiovascular and Ventilatory Response to Elevated Metabolic States in the Lizard Varanus Exanthematicus
Authors: Hicks James W. , Wang Tobias , Bennett Albert F. 
Published: April 2021

ABSTRACT
The principal function of the cardiopulmonary systemis the precise matching of O2 and CO2 transport to the metabolic requirements of different tissues. In som e ecothermic vertebrates (amphibians and reptiles), increases dramatically following feeding. Factorial increments in range from 1.7 to 44 times above resting rates, and in some cases approaches or even exceeds values measured during physical activity. There is virtually no information on the cardiopulmonary response during the postprandial period in these animals or how the pattern of cardiopulmonary support compares with that during activity. In our experiments, pulmonary ventilation , heart rate (fH), systemic blood flow (Q̇sys), rate of oxygen consu mption and rate of carbon dioxide production were measured at 35 °C in the lizard Varanus exanthematicus for 24 h prior to the ingestion of meals of various sizes and measured continuously for up to 72 h during the postprandial period. The results of this study were compared with previously published values for treadmill exercise in the same experimental animals. The change in fH and stroke volume (VS) for a given increment in did not differ during exercise and digestion. In contrast, the ventilatory response was very dependent on the nature of the elevated metabolic state. During digestion, an increase in resulted in a relative hypoventilation in comparison with resting values, whereas hyperventilation characterized the response during activity. During exercise, breathing frequency (f) increased 10-to 40-fold above resting values accompanied by large reductions in tidalvolume (VT). In contrast, postprandial increases in resulted in relatively minor changes in f and VT almost doubled. These results indicate that, in these lizards, the cardiac response to elevated is stereotyped, the response being predictable irrespective of the source of the metabolic increment. In contrast, the ventilatory response is flexible and state-dependent, not only in pattern but also in its frequency and volume components.
Broad Oxygen Tolerance in the Nematode Caenorhabditis Elegans
Authors: Voorhies Wayne A. Van , Ward Samuel 
Published: April 2021

ABSTRACT
This study examined the effects of oxygen tensions ranging from 0 to 90 kPa on the metabolic rate (rate of carbon dioxide production), movement and survivorship of the free-living soil nematode Caenorhabditis elegans. C. elegans requires oxygen to develop and survive. However, it can maintain a normal metabolic rate at oxygen levels of 3.6 kPa and has near-normal metabolic rates at oxygen levels as low as 2 kPa. The ability to withstand low ambient oxygen levels appears to be a consequence of the small body size of C. elegans, which allows diffusion to supply oxygen readily to the cells without requiring any specialized respiratory or metabolic adaptations. Thus, the small size of this organism pre-adapts C. elegans to living in soil environments that commonly become hypoxic. Movement in C. elegans appears to have a relatively minor metabolic cost. Several developmental stages of C. elegans were able to withstand up to 24 h of anoxia without major mortality. Longer periods of anoxia significantly increased mortality, particularly for eggs. Remarkably, long-term exposure to 100 % oxygen had no effect on the metabolic rate of C. elegans, and populations were able to survive for a least 50 generations in 100 % (90 kPa) oxygen. Such hyperoxic conditions are fatal to most organisms within a short period.
Direct Determination of the Kinetics of Oxygen Diffusion to the Photocytes of a Bioluminescent Elaterid Larva, Measurement of Gas- and Aqueous-Phase Diffusional Barriers and Modelling of Oxygen Supply
Authors: Timmins Graham S. , Bechara Etelvino J. H. , Swartz Harold M. 
Published: April 2021

ABSTRACT
We describe the development and use of a direct kinetic technique to determine the time taken for oxygen to diffuse from the external environment into the light-producing cells (photocytes) in the prothorax of bioluminescent larvae of Pyrearinus termitilluminans. This was achieved by measuring the time course of the pseudoflash induced through sequential anoxia followed by normoxia. We have also determined the separate times taken for this oxygen diffusion in gaseous and tissue (predominantly aqueous) phases by using helium and nitrogen as the carrier gas. Of the total time taken for diffusion, that in the gas phase required 613±136 ms (mean ± S.E.M., N=5) whilst that in the aqueous phase required 1313±187 ms. These values imply pathlengths of diffusion in the gaseous and aqueous phases of 4.80×10−3±0.53×10−3 and 8.89×10−5±0.61×10−5 m, respectively. In addition, the pathlength of gas-phase diffusion was used to derive a parameter relating to the tortuosity of the tracheal system. These values, together with those obtained upon bioluminescent oxygen consumption, have been used to model oxygen supply to the photocyte. From these studies, it would also appear that the modulation of tracheolar fluid levels might be a significant mechanism of control of tissue oxygen levels in at least some insects.