bluuebunny/crossref_metadata_2025_split huggingface dataset:
Retinoic Acid Modulates Retinal Development in the Juveniles of a Teleost Fish
Authors: Browman Howard I. , Hawryshyn Craig W. 
Published: April 2021

ABSTRACT
Small (&lt;30 g) juvenile rainbow trout (Oncorhynchus mykiss) possess retinal photoreceptor mechanisms sensitive to light in the near ultraviolet, short (blue), middle (green) and long (red) wavelengths. During normal development, the ultraviolet cone mechanism gradually disappears until, by approximately 60–80 g, individuals are no longer sensitive in the ultraviolet. This shift in spectral sensitivity is associated with the loss of a single class of photoreceptor cells – small accessory corner cones – from the retinal photoreceptor cell mosaic. Treating small (&lt;15 g) rainbow trout with 10−6 mol l−1 all-trans retinoic acid (20 min exposure by immersion) induced a precocial loss of ultraviolet photosensitivity and an associated change in the retinal photoreceptor cell mosaic only 2 weeks after treatment. These changes were indistinguishable from the events that occur during normal development. Six weeks after exposure to retinoic acid, large (&gt;90 g) rainbow trout, which had lost their ultraviolet cones during normal development, were once again ultraviolet-photosensitive and small accessory corner cones were found in their retinas. These results imply that the ultraviolet-sensitive cones, although lost at one point during development, can reappear at another time during the life history of the same individual. Retinoic acid is involved in these morphogenetic processes.
Influence of Hypoxia and Adrenaline Administration on Coronary Blood Flow and Cardiac Performance in Seawater Rainbow Trout (Oncorhynchus Mykiss)
Authors: Gamperl A. K. , Pinder A. W. , Grant R. R. , Boutilier R. G. 
Published: April 2021

ABSTRACT
To investigate the relationship between cardiac performance and coronary perfusion, cardiovascular variables (Q̇, VS, fH, PDA) and coronary blood flow (q̇cor) were measured in rainbow trout (Oncorhynchus mykiss) (1.2–1.6 kg) before and after adrenergic stimulation (1.0 μg kg−1 adrenaline) under conditions of (1) normoxia, (2) hypoxia (approximate 12 kPa) and (3) 2.5 h after returning to normoxia. q̇cor for resting fish under normoxic conditions was 0.14±0.02 ml min−1 kg−1 (approximately 0.85% of Q̇). When exposed to hypoxia, although both resting Q̇ and q̇cor increased, q̇cor increased to a greater degree (Q̇ by 17% and q̇cor by 36%). During hypoxia, maximum adrenaline-stimulated Q̇ was comparable to that observed for normoxic fish. However, because Q̇ was elevated in resting hypoxic fish, the capacity of hypoxic fish to increase Q̇ above resting levels was 50% lower than that measured in normoxic fish. Although maximum q̇cor in adrenaline-injected hypoxic trout was greater than that measured in normoxic trout, post-injection increases in q̇cor (above resting levels) were not different between the two groups. Two and a half hours after hypoxic exposure, resting Q̇ was still elevated (11%) above normoxic levels, and the ability to increase Q̇ when adrenergically stimulated was not fully restored. These results suggest (1) that resting q̇cor in salmonids is approximately 1% of Q̇, (2) that increases in q̇cor may be important in maintaining cardiovascular performance during hypoxic conditions, (3) that interactions between α-adrenergic constriction and metabolically related vasodilation of the coronary vasculature are important in determining q̇cor in fish, (4) that exposure of fish to moderate environmental hypoxia reduces the scope for adrenergically mediated increases in Q̇, and (5) that periods of recovery in excess of several hours are required before cardiovascular performance returns to pre-hypoxic levels.
When Does Motion Relative to Neighboring Surfaces Alter the Flow Through Arrays of Hairs
Authors: Loudon C. , Best B. A. , Koehl M. A. R. 
Published: April 2021

ABSTRACT
Many animals from different phyla use structures bearing arrays of hairs to perform a variety of important functions, such as olfaction, gas exchange, suspension feeding and locomotion. The performance of all these functions depends on the motion of water or air around and through these arrays of hairs. Because organisms often move such hair-bearing appendages with respect to their bodies or the substratum, we assessed the effects of such motion relative to walls on the fluid flow between neighboring hairs. We compared flow fields near dynamically scaled physical models of hairs moving near walls with those calculated for such hairs in an unbounded fluid. Our results suggest that the methods an organism can use to change the flow through a hair-bearing appendage differ with Reynolds number (based on hair diameter). When Re is 10−2 or below, changing speed does not alter the proportion of the fluid that moves through rather than around the array, whereas moving relative to a wall increases it. In contrast, when Re is between 10−2 and 1, changes in speed have a big effect on the proportion of fluid moving through the array, while moving near walls makes little difference.
Determinants for the Activity of the Neutral Amino Acid/K+ Symport in Lepidopteran Larval Midgut
Authors: Giordana Barbara , Parenti Paolo 
Published: April 2021

ABSTRACT
The columnar cells of lepidopteran larvae express, in their apical brush-border membrane, a class of symporters which in vivo couple the intracellularly directed amino acid and K+ fluxes. An analysis of the functional properties of the symporter for neutral amino acids along the anterior, middle and posterior regions of the larval midgut of Bombyx mori demonstrated the ability of a K+ gradient to drive leucine accumulation into brush-border membrane vesicles (BBMV) in all three preparations. However, marked differences are evident between the posterior (P) and the anterior–middle (AM) regions. In P-BBMV, much higher intravesicular accumulations were observed, Vmax was six-to eightfold higher than in AM-BBMV, a lowering of external pH (pHe) from 8.7 to 7.2 caused a tenfold increase of Km, and the absence of a potential difference (ΔΨ) caused a threefold decrease of Vmax. In contrast, leucine uptake in AM-BBMV was poorly sensitive to both pH and ΔΨ. The kinetics of leucine uptake as a function of cis K+ concentration were hyperbolic in P-BBMV and sigmoidal in AM-BBMV. More than 50 amino acids and analogues were used in inhibition experiments to characterize the amino acid binding site. Branched-chain amino acids modified on the carboxyl moiety were recognized only by the P-BBMV symporter. In AM-BBMV, substrate affinity was increased by the presence of a heterocyclic sidechain, even in the presence of a modified carboxyl-or α-amino group. Together, these results suggest that isoforms of the neutral amino acid/K+ symporter are present. A natural inhibitor of amino acid symport has not yet been identified. However, several lines of evidence suggest that strong interactions exist between the amino acid/K+ symporter and the receptor for the lepidopteran-specific Bacillus thuringiensis δ-endotoxins. CryIA(a) toxin, highly toxic for B. mori larvae, produced a dose-dependent inhibition of leucine uptake into both BBMV populations. The toxin was able to block the symporter in its ternary and leucine-only forms.
Cation Antiports of Animal Plasma Membranes
Authors: Grinstein Sergio , Wieczorek Helmut 
Published: April 2021

ABSTRACT
Both organic and inorganic solutes can be transported across biological membranes against their electrochemical gradient, by coupling to the downhill movement of another species. In animal cells, the underlying mechanism most often involves symport (cotransport) or antiport (countertransport) with either sodium or hydrogen ions. The energy invested in the uphill translocation of solutes is ultimately provided by hydrolysis of ATP by Na+-or H+-transporting ATPases and is transiently stored as potential energy in the form of an electrochemical gradient of these ions.
Ionic Circuit Analysis of K+/H+ Antiport and Amino Acid/k+ Symport Energized by a Proton-Motive Force in Manduca Sexta Larval Midgut Vesicles
Authors: Martin Francis G. , Harvey William R. 
Published: April 2021

ABSTRACT
Amino acid/K+ symport (cotransport) across a model epithelium, the lepidopteran midgut, is energized by an electrogenic H+ V-ATPase (H+ pump) in parallel with an electrophoretic K+/H+ antiporter (exchanger). Attempts to analyze this process using well-known equilibrium thermodynamic equations (Nernst, Gibbs), diffusion equations (Nernst, Planck, Einstein, Goldman, Hodgkin, Katz) and equations based on Ohm’s law (Hodgkin, Huxley) have all encountered major difficulties. Although they are useful for analyzing nerve/muscle action potentials, these state equations assume that brief perturbations in membrane conductance, gm, and membrane voltage, Vm, occur so rapidly that no other parameters are significantly disturbed. However, transport studies often extend for minutes, even for hours. Perturbation of one parameter in complex transport systems invariably results in a state change as all of the other elements adjust to the prolonged stress.
The development of a comprehensive mathematical treatment for transport systems that contain pumps and porters (transporters) has been hampered by the empirical nature of the concept of membrane permeability and conductance. The empirical definition of permeability was developed before pumps and porters were known. Thus, ‘permeability’ is a gross parameter that, in practice if not in theory, could describe all transport pathways including pumps, porters and channels. To surmount these difficulties, we have applied ionic circuit analysis to vesicular systems containing insect midgut transport proteins. In this analysis, pumps, porters and channels, as well as ionic concentration gradients and membrane capacitance, are components of ionic circuits that function to transform metabolic energy (e.g. from ATP hydrolysis) into useful metabolic work (e.g. amino acid uptake). Computer-generated time courses reproduce key aspects of the coupling of the proton-motive force generated by an H+ V-ATPase to K+/2H+ antiport and amino acid/K+ symport in the lepidopteran midgut.
Na+-Independent Transport (Uniport) of Amino Acids and Glucose in Mammalian Cells
Authors: Kakuda Donald K. , MacLeod Carol L. 
Published: April 2021

ABSTRACT
Recent advances have made possible the isolation of the genes and their cDNAs encoding Na+-independent amino acid transporters. Two classes of amino acid ‘uniporters’ have been isolated. One class contains the mCAT (murine cationic αmino acid transporter) gene family that encodes proteins predicted to span the membrane 12–14 times and exhibits structural properties similar to the GLUT (glucose transporter) family and to other well-known transporters. The other class consists of two known genes, rBAT (related to B system αmino acid transporters) and 4F2hc, that share amino acid sequence similarity with α-amylases and α-glucosidases. They are type II glycoproteins predicted to span the membrane only once, yet they mediate the Na+-independent transport of cationic and zwitterionic amino acids in Xenopus oocytes. Mutations in the human rBAT gene have been identified by Palacín and his co-workers in several families suffering from a heritable form of cystinuria. This important finding clearly establishes a key role for rBAT in cystine transport. The two classes of amino acid transporters are compared with the well-studied GLUT family of Na+-independent glucose transporters.
Contribution of the Pentose Phosphate Shunt to the Formation of Co2 in Swimbladder Tissue of the Eel
Authors: Pelster B. , Hicks J. , Driedzic W. R. 
Published: April 2021

ABSTRACT
The contribution of the pentose phosphate shunt to glucose metabolism in the swimbladder tissue of the American eel Anguilla rostrata has been evaluated by comparing the rate of 14CO2 and [14C]lactate production from [1-14C]glucose and [6-14C]glucose. In blood-perfused swimbladder preparations, 0.18±0.07 nmol min−1of [6-14C]glucose and 3.19±0.57 nmol min−1 of [1-14C]glucose were converted to CO2. The rate of [14C]glucose conversion to [14C]lactate was about the same in preparations perfused with [6-14C]glucose and with [1-14C]glucose. This may indicate that the C5 skeleton formed in the pentose phosphate shunt is not returned to glycolysis and converted to lactate.
Although gas deposition was usually not measurable in these blood-perfused swimbladder preparations, 14CO2 was detected in the eel swimbladder gas of preparations perfused with [1-14C]glucose, but not in preparations perfused with [6-14C]glucose.
The results confirm the hypothesis that, in the eel swimbladder epithelium, some of the glucose taken up from the blood is metabolized in the pentose phosphate shunt. This results in the formation of CO2, which is released into the swimbladder as well as into the bloodstream.
The Efficiency of Frog Ventricular Muscle
Authors: Syme Douglas A. 
Published: April 2021

ABSTRACT
Mechanical power and oxygen consumption were measured simultaneously from isolated segments of trabecular muscle from the frog (Rana pipiens) ventricle. Power was measured using the work-loop technique, in which bundles of trabeculae were subjected to cyclic, sinusoidal length change and phasic stimulation. was measured using a polarographic O2 electrode.
Both mechanical power and increased with increasing cycle frequency (0.4–0.9 Hz), with increasing muscle length and with increasing strain (=shortening, range 0–25% of resting length). Net efficiency, defined as the ratio of mechanical power output to the energy equivalent of the increase in above resting level, was independent of cycle frequency and increased from 8.1 to 13.0% with increasing muscle length, and from 0 to 13% with increasing strain, in the ranges examined. Delta efficiency, defined as the slope of the line relating mechanical power output to the energy equivalent of , was 24–43%, similar to that reported from studies using intact hearts.
The cost of increasing power output was greater if power was increased by increasing cycle frequency or muscle length than if it was increased by increasing strain. The results suggest that the observation that pressure-loading is more costly than volume-loading is inherent to these muscle fibres and that frog cardiac muscle is, if anything, less efficient than most skeletal muscles studied thus far.
Substrate Structure And Amino Acid/K+ Symport In Brush-Border Membrane Vesicles From Larval Manduca Sexta Midgut
Authors: Parthasarathy R. , Xie Tao , Wolfersberger Michael G. , Harvey William R. 
Published: April 2021

ABSTRACT
The effects of amino acid sidechain length, substituent position and chirality on amino acid/K+ symport have been examined in rapid filtration experiments on brush-border membrane vesicles prepared from larval Manduca sexta midgut. Cis-inhibition and trans-stimulation protocols were used to examine the effects of amino acid analogs on the uptake of alanine, phenylalanine, leucine and lysine, which are cotransported with K+ by a zwitterionic symporter at the high pH characteristic of the midgut in vivo. The symporter was found to translocate both L- and D-stereoisomers of alanine, leucine and lysine, but only the L-form of phenylalanine. Alterations to substrate structure that leave the charge distribution unchanged do not affect symport. Thus, moving the methyl group from C-3 to C-5 in the sequence isoleucine, leucine and norleucine has no effect on their ability to inhibit leucine symport. Increasing sidechain length among alanine homologs has little effect on their ability to inhibit alanine uptake, but increasing the sidechain length of lysine homologs from 1 to 3 methylene groups enhances cis-inhibition and trans-stimulation of lysine symport. The substantial difference in molecular charge distribution among aminobutanoic acid isomers has a large impact on alanine symport with only α-(or 2-) aminobutanoic acid functioning as an alanine analog. Only those changes in substrate structure that are coupled to the molecular charge distribution seem to affect symport. The tolerance of the symporter may reflect a balance mandated by the conflicting demands of selectivity and throughput.
in vitro Investigation of the Factors Contributing to the Unique CO2 Transport Properties of Blood in the Sea Lamprey (Petromyzon Marinus)
Authors: Cameron Bruce A. , Tufts Bruce L. 
Published: April 2021

ABSTRACT
In vitro experiments were conducted to determine the factors contributing to the unusual distribution of CO2 in the blood of the sea lamprey. When rainbow trout red blood cells (RBCs) were equilibrated with a 3% CO2:nitrogen mixture in either normal saline or sodium-free saline, the extracellular total carbon dioxide content was highly dependent upon the fraction of RBCs in the suspension. In contrast, when lamprey RBCs were equilibrated in normal saline, the decreased with increasing hematocrit. In the absence of extracellular sodium, however, the in the lamprey RBC suspension also became positively correlated with hematocrit. These results suggest that the membrane of sea lamprey RBCs may be somewhat permeable to bicarbonate, but that transmembrane bicarbonate movements may only be detectable in vitro when Na+/H+ exchange is inactivated. Also in contrast to the results for rainbow trout, the changes in that occurred in lamprey RBC suspensions following a step increase in were not associated with any change in RBC chloride concentration and were not markedly affected by the chloride/bicarbonate exchange inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS). When lamprey RBCs in sodium-free saline were treated with an ionophore for anions, tributyl tin chloride (TBTC), however, the distribution of anions across the RBC membrane came to resemble that of the trout. Furthermore, the relationship between and hematocrit in suspensions of TBTC-treated lamprey RBCs also resembled that of trout in normal saline. Thus, these results demonstrate that both the presence of Na+/H+ exchange and the absence of significant anion exchange contribute to the unique CO2 transport properties of sea lamprey blood.
The Relationship Between the Length of the Cupulae of Free Neuromasts and Feeding Ability in Larvae of the Willow Shiner Gnathopogon Elongatus Caerulescens (Teleostei, Cyprinidae)
Authors: Mukai Yukinori , Yoshikawa Hiromasa , Kobayashi Hiroshi 
Published: April 2021

ABSTRACT
Free mechanosensory neuromasts of larval fishes have been described as playing a complementary role to vision in feeding behaviour (Disler, 1971; Iwai, 1972a,b). In certain species or under limited conditions, free neuromasts play a major role in detecting prey. The larvae of mottled sculpin Cottus bairdi can feed on Artemia in the dark by using free neuromasts (Jones and Janssen, 1992). Artificially blinded surface-feeding Aplocheilus lineatus can detect insects on the water surface by means of free neuromasts (Müller and Schwarts, 1982; Tittel et al. 1984; Bleckmann, 1988; Bleckmann et al. 1989). Furthermore, vibrations produced by swimming crustaceans are known to be a potent natural stimulus for the lateral line system in the Antarctic fish Pagothenia borchgrevinki (Montgomery and Macdonald, 1987; Montgomery, 1989). We found that larvae of a plankton feeder, the willow shiner Gnathopogon elongatus caerulescens (Sauvage) (Cypriniformes, Cyprinidae), fed on nauplii of Artemia in complete darkness. Ototoxic compounds, such as streptomycin, have been shown to disturb the function of the lateral line organ or free neuromasts (Kaus, 1987; Blaxter and Fuiman, 1989; Janssen, 1990; Jones and Janssen, 1992). Willow shiner larvae treated with streptomycin sulphate no longer feed on Artemia in the dark (Y. Mukai, in preparation).
The modulatory effect of schistoFLRFamide on heart and skeletal muscle in the locust Schistocerca gregaria
Authors: Robb Sandra , Evans Peter D. 
Published: April 2021

ABSTRACT
SchistoFLRFamide (PDVDHVFLRFamide) is one of the endogenous FMRFamide-like neuropeptides found in the nervous system of the locust Schistocerca gregaria (Robb et al. 1989; Robb and Evans, 1990). FMRFamide-like neuropeptides modulate the actions of a wide variety of both skeletal and visceral muscles in insects (Evans and Myers, 1986a; Schoofs et al. 1993b) and have been suggested to act both as circulatory hormones and as locally released neurotransmitters (see discussion in Robb and Evans, 1990).
Mechanisms of Na+ and Cl− Regulation in Freshwater-Adapted Rainbow Trout (Oncorhynchus Mykiss) During Exercise and Stress
Authors: Postlethwaite Emma K. , McDonald D. G. 
Published: April 2021

ABSTRACT
This study examined the mechanisms by which Na+ and Cl−are regulated in freshwater rainbow trout during exercise and stress. Aerobic exercise (at approximately 2 body lengths s−1) caused a brief increase in diffusive Na+ efflux and a brief decline in plasma Na+ and Cl−concentrations. This disturbance was rapidly compensated by a threefold increase in Na+ and Cl−influx (over the first 10–12 h of exercise) and by a reduction in Na+ efflux to 40 % of the control value by 7 h of exercise. The compensation produced a significant increase in whole− body [Na+], whereas whole−body [Cl−] remained unchanged. In contrast, confinement stress (for 4 or 8 h) caused an eightfold increase in Na+ and Cl−efflux which was sustained for at least the first 5 h of stress and resulted in large decreases in whole−body [Na+] and [Cl−]. Compensation of the losses was not complete until 24 h post−stress and was achieved by increases in Na+ and Cl− influx (of similar magnitude and timing to those observed during exercise) as well as reductions in Na+ and Cl− efflux to nearly zero. We conclude that ion influx increased because of an activation of inactive transport sites in the gills, whereas efflux was reduced by a reduction in branchial ionic permeability; both responses are mediated hormonally. Although the hormonal control mechanisms are as yet poorly defined, we argue that growth hormone and prolactin are responsible for the regulation of influx and efflux, respectively, and rule out either cortisol or epinephrine as having any role, at least with respect to the rapid [NaCl] regulation evident during exercise.
External, Internal and Total Work in Human Locomotion
Authors: Willems P. A. , Cavagna G. A. , Heglund N. C. 
Published: April 2021

ABSTRACT
The muscle–tendon work performed during locomotion can, in principle, be measured from the mechanical energy of the centre of mass of the whole body and the kinetic energy due to the movements of the body segments relative to the centre of mass of the body. Problems arise when calculating the muscle–tendon work from increases in mechanical energy, largely in correctly attributing these increases either to energy transfer or to muscle–tendon work.
In this study, the kinetic and gravitational potential energy of the centre of mass of the whole human body was measured (using a force platform) simultaneously with calculation of the kinetic and potential energy of the body segments due to their movements relative to the body centre of mass (using cinematography) at different speeds of walking and running.
Upper and lower boundaries to the total work were determined by including or excluding possible energy transfers between the segments of each limb, between the limbs and between the centre of mass of the body and the limbs.
It appears that the muscle–tendon work of locomotion is most accurately measured when energy transfers are only included between segments of the same limb, but not among the limbs or between the limbs and the centre of mass of the whole body.