bluuebunny/crossref_metadata_2025 huggingface dataset:
Nearfield detection of dipole sources by the goldfish (Carassius auratus) and the mottled sculpin (Cottus bairdi)
Authors: Coombs Sheryl
Published: April 2021

Surprisingly few behavioral data exist on dipole source detection by fish, despite the fact that dipole sources more closely approximate biologically relevant signals than do more nearly monopole sources such as loudspeakers, the stimulus used in nearly all fish auditory studies. In this study, dipole source detection is investigated for two fish species that differ in both their auditory and lateral line systems, the two systems capable of detecting dipole sources. Conditioned suppression of respiration in the goldfish and an unconditioned orienting response in the mottled sculpin were used to measure detection of a 6 mm diameter, sinusoidally vibrating sphere as a function of vibration frequency and source distance.

Sound pressure thresholds for the goldfish were nearly independent of distance (15–60 mm) at 800 Hz, but increased with distance at 50 Hz, as they did for the mottled sculpin. The slopes of 50 Hz source level–distance functions, however, differed between the two species. Slopes for the goldfish were independent of distance, remaining at around 8 dB per distance doubling, which is near the 6 dB per distance doubling measured for sound pressure attenuation away from the source, but less than the 18 dB per distance doubling for incompressible flow, measured with an anemometer. Those for the mottled sculpin increased with increasing distance, approaching 18 dB per distance doubling. The nonlinear increase in source level necessary to reach threshold detection was quite similar to the nonlinear decrease in incompressible flow levels measured with the anemometer. Nonlinear increases with distance for 50 Hz sources near the trunk of the mottled sculpin were also similar to those near the head of the fish, where changes in source frequency had little effect on source level–distance functions.

These results indicate that sound pressure detection by the ear is important for dipole detection by the goldfish, but that incompressible flow detection by the lateral line is more important for the mottled sculpin. They also indicate that fish such as the goldfish, with a pressure-sensitive swimbladder, are capable of detecting dipole sources at greater distances than are fish without such structures.
Mobilization of shell calcium by the chick chorioallantoic membrane in vitro
Authors: Packard Mary J.
Published: April 2021

Two explants of shell were removed from each of several fertile eggs of domestic fowl at different times during incubation. The chorioallantoic membrane (CAM) was removed from one of the explants (SHELL ONLY) and was left in situ on the other (SHELL+CAM). Explants were cultured for 24, 48 or 96 h at 37 °C and 5 % CO2 in air in individual Petri dishes containing Dulbecco’s modified Eagle’s medium, bovine serum albumin, penicillin and streptomycin. Both SHELL+CAM and SHELL ONLY explants released calcium into the culture medium, but the former released considerably more calcium than the latter. More calcium was released by SHELL+CAM explants taken from older eggs than from younger ones, but the age of the donor eggs did not affect release of calcium by SHELL ONLY explants. In addition, release of calcium by SHELL+CAM explants exceeded that shown by SHELL ONLY explants for multiple 24 h intervals. However, the capacity for sustained release of calcium by SHELL+CAM explants declined with age and maturity of the CAM. Manipulations that lead to the death of the CAM abolish the capacity for SHELL+CAM explants to release more calcium than SHELL ONLY explants. Differential release of calcium by SHELL+CAM explants was not attributable to calcium present in the CAM at the onset of culture or to non-specific degradation of the shell by intracellular constituents released as a result of the death of the CAM. Taken in concert, these results indicate that the CAM mobilizes calcium from the eggshell during in vitro culture.
Diving energetics in lesser scaup (Aythyta affinis, Eyton)
Authors: Stephenson Richard
Published: April 2021

Mechanical and aerobic energy costs of diving were measured simultaneously by closed-circuit respirometry in six lesser scaup Aythya affinis Eyton (body mass=591±30 g) during bouts of voluntary feeding dives. Durations of dives (td=13.5±1.4 s) and surface intervals (ti=16.3±2.2 s) were within the normal range for ducks diving to 1.5 m depth. Mechanical power output (3.69±0.24 W kg−1) and aerobic power input (29.32±2.47 W kg−1) were both higher than previous estimates. Buoyancy was found to be the dominant factor determining dive costs, contributing 62 % of the mechanical cost of descent and 87 % of the cost of staying at the bottom while feeding. Drag forces, including the contribution from the forward-moving hindlimbs during the recovery stroke of the leg-beat cycle, contributed 27 % and 13 % of the mechanical costs of descent and feeding, respectively. Inertial forces created by net acceleration during descent contributed approximately 11 % during descent but not at all during the feeding phase. Buoyant force at the start of voluntary dives (6.2±0.35 N kg−1) was significantly greater than that measured in restrained ducks (4.9±0.2 N kg−1). Loss of air from the plumage layer and compression due to hydrostatic pressure decreased buoyancy by 32 %. Mechanical work and power output were 1.9 and 2.4 times greater during descent than during the feeding phase. Therefore, energetic costs are strongly affected by dive-phase durations. Estimates by unsteady and steady biomechanical models differ significantly during descent but not during the feeding phase.
Gas Exchange of Captive Freely Diving Grey Seals (Halichoerus Grypus)
Authors: Reed J. Z. , Chambers C. , Fedak M. A. , Butler P. J.
Published: April 2021

When at sea, phocids dive for long periods and spend a high percentage of their time submerged. This behaviour requires some combination of an increased oxygen storage capacity, rapid oxygen loading at the surface and reduced oxygen utilisation when submerged. To assess these adaptations, breath-by-breath ventilation was studied in four adult grey seals (two male, two female, 160–250 kg), freely diving in a large outdoor tank where surface access was restricted to one breathing hole. The dive patterns obtained were similar to those recorded from freely diving wild grey seals. Respiratory frequency during the surface periods was 40% higher than that estimated from allometric relationships (19.4±0.7 breaths min−1), and tidal volume (6.3±1.2 l) was approximately five times higher than that estimated from allometric relationships. These adaptations produce a high minute volume and enable gas exchange to occur at the surface.

Mean oxygen consumption rate (, measured for a dive+surface cycle) decreased with increasing dive duration. The aerobic dive limit was estimated as 9.6 min for a 150 kg grey seal (using the overall average of 5.2 ml O2 min−1 kg−1), which is consistent with results from freely diving wild grey seals (only 6% of dives exceeded 10 min). End-tidal oxygen values varied during a surface period, following a U-shaped curve, which suggests that there is limited oxygen uptake from the lung and/or blood oxygen stores during dives. This result was unexpected and indicates that these seals are utilising substantial physiological responses to conserve oxygen, even during shallow voluntary diving.
Effects of Confinement/Crowding on Ureogenesis in the Gulf Toadfish Opsanus Beta
Authors: Walsh Patrick J. , Tucker Bonnie C. , Hopkins Todd E.
Published: April 2021

In order to elucidate the cues for, and the biochemical mechanisms of, the transition to ureogenesis in the gulf toadfish Opsanus beta, experiments on the effects of confinement/crowding were carried out. Confinement of toadfish to small volumes of water initiated a switch to nearly complete reliance on ureogenesis for nitrogen excretion within 24–48 h. Further experiments suggested that this switch was probably due to the physical confinement per se, rather than to a measurable build-up of ammonia in the water. However, the possibility of the response being triggered by a very low concentration of a pheromone-like substance was not excluded by our experimental design. The activities of several enzymes of ureogenesis, ornithine–citrulline transcarbamoylase, aspartate amino transferase and glutamine synthetase, increased in the liver of toadfish during confinement. Notably, glutamine synthetase activity increased almost fourfold within 24 h, and this increase preceded increases in urea excretion. A number of plasma and liver amino acid concentrations changed during confinement: there were declines in plasma asparagine, glutamate and glycine levels and an increase in plasma valine, as well as a decline in liver alanine and an increase in liver arginine concentrations. Liver glutamine was not detectable. When the amino acid data are taken together with the enzyme activity changes, it appears that the switch to ureogenesis occurs primarily upstream of the ornithine–urea cycle, at the level of supply of nitrogen to the pathway. The results are discussed in the context of the habitat of toadfish.
Gravity and Light Influence the Countershading Reflexes of the Cuttlefish Sepia Officinalis
Authors: Ferguson Graham P. , Messenger John B. , Budelmann Bernd U.
Published: April 2021

Rotation (roll or pitch) of a cuttlefish away from its normal orientation produces countershading reflexes (CSRs) that consist of chromatophore expansion on the ventral body surface. When rotation is in the roll plane, the CSR has two components on each side of the body. The first (component A) consists of a unilateral expansion of chromatophores on the uppermost latero-ventral edge of the mantle, the underside of the upper fin and the uppermost side of the head; it occurs when the angle of rotation is less than 90°. Further rotation (from approximately 90° to approximately 180°) adds the second component (component B): a unilateral expansion of the chromatophores on the upper half of the ventral surface of the mantle, funnel, head and arms. When rotation is in the pitch plane, chromatophores expand on the posterior part of the ventral mantle and fins when the head is down; when the head is up, chromatophores expand on the ventral surface of the arms, head and funnel and on the anterior part of the ventral mantle and fins. The pitch CSR is always bilateral.

Destruction of the gravity or the angular acceleration receptor systems of the statocysts demonstrates that it is the gravity receptor systems that drive the CSRs. Unilateral destruction of the gravity receptor systems shows that the pitch CSR is driven bilaterally, whereas the roll CSR is driven unilaterally. Components A and B of the roll CSR are driven by input from the ipsilateral statocyst, but component A is additionally driven by light.

Brain lesions provide evidence that the pathways for the CSRs run through the lateral basal lobes in the supraoesophageal part of the brain.
A Quantitative, Three-Dimensional Method for Analyzing Rotational Movement From Single-View Movies
Authors: Van Den Berg Coen
Published: April 2021

The study of animal movement is an important aspect of functional morphological research. The three-dimensional movements of (parts of) animals are usually recorded on two-dimensional film frames. For a quantitative analysis, the real movements should be reconstructed from their projections. If movements occur in one plane, their projection is distorted only if this plane is not parallel to the film plane. Provided that the parallel orientation of the movement with respect to the film plane is checked accurately, a two-dimensional method of analysis (ignoring projection errors) can be justified for quantitative analysis of planar movements.
The Scaling of Song Frequency in Cicadas
Authors: Bennet-Clark H. C. , Young D.
Published: April 2021

In male cicadas, sound is generated by a pair of tymbals on the abdomen (Pringle, 1954). The tymbals buckle inwards causing pressure changes in the abdominal cavity, from which sound is radiated through the tympana (Young, 1990). A recent model of sound production in cicadas suggests that the abdominal cavity and tympana act as the components of a Helmholtz resonator that is excited by the drive from the tymbals (Bennet-Clark and Young, 1992). A Helmholtz resonator consists of a cavity open to the outside via a hole which has a real or notional neck, and the resonant frequency f0 is given by the general equation: where c is the speed of sound in the fluid, taken as 340 m s−1 for air, A is the area of the neck, L is the length of the neck and V is the volume of the cavity. Where the resonator has two holes, these terms should be somewhat modified: A is the combined area of the two holes, L is 16/3πr (≈1.7r) for a simple hole in a thin-walled vessel and r is the radius of one hole (Seto, 1971). These modifications to equation 1, which include corrections for the acoustic end-effect at either side of a simple hole in the wall of a vessel, are applicable to a model of the male cicada, in which there are two tympana close to the ventral surface of the abdomen.
The Ontogeny of Shivering Thermogenesis in the Red-Winged Blackbird (Agelaius Phoeniceus)
Authors: Olson John M.
Published: April 2021

The ontogeny of shivering thermogenesis was investigated in the altricial red-winged blackbird (Agelaius phoeniceus). Two indices of heat production – the rate of oxygen consumption of the bird and the electromyographic (EMG) activity of the pectoralis (PECT) and gastrocnemius (GAST) muscles – were measured simultaneously in adult and nestling red-winged blackbirds as they were subjected first to thermoneutral temperatures and subsequently to progressively colder ambient temperatures (Ta). The ontogenetic changes in both indices indicated that the capability for thermogenesis in nestling red-winged blackbirds improved markedly with age. The metabolic rates of 3-day-old nestlings decreased during exposure to gradually falling ambient temperatures; at best, these nestlings were only able to maintain mass-specific at levels similar to or slightly above the resting metabolic rate at thermoneutral temperatures (RMR) for a short time before metabolic rates decreased with further cooling. Shivering was detected only in the PECT muscles and was of a relatively low intensity (maximum of sevenfold increase in intensity over basal levels). The 5-day-old nestlings increased mass-specific modestly (approximately 1.4-fold) above RMR and attained slightly higher maximal factorial increases in the EMG activity of the PECT (maximum of 18-fold basal levels) when exposed to the same experimental conditions. Shivering was also detected in the GAST muscles of these birds. The most striking improvements in both measures observed during the nestling period occurred between day 5 and day 8. Eight-day-old nestlings increased metabolic rates by approximately 2-to 2.5-fold over basal levels and sustained these elevated rates for longer before becoming hypothermic. Both the PECT and GAST muscles contributed significantly to shivering thermogenesis, and these older nestlings attained much higher factorial increases in the intensity of shivering (up to 72-fold) during exposure to cold temperatures. In addition, both the range and magnitude of the dominant frequencies of muscle activity in the PECT increased during postnatal development.

The PECT muscles were a principal site of shivering thermogenesis in all nestling and adult red-winged blackbirds studied here. Shivering in these muscles was a ‘first line defense’ against cold; the threshold temperature for shivering in the PECT muscles coincided with the lower critical temperature for oxygen consumption (TLC), and the subsequent increases in EMG activity in this muscle with further cooling correlated well with the corresponding increases in mass-specific .
Power Output of Scallop Adductor Muscle During Contractions Replicating The In Vivo Mechanical Cycle
Authors: Marsh Richard L. , Olson John M.
Published: April 2021

Because measurements on isolated skeletal muscles are often made with limited knowledge of in vivo kinematics, predictions of mechanical performance during natural movements are subject to considerable uncertainties. We used information on the in vivo length cycle and phase of activation of the scallop adductor during swimming at 10°C to design an in vitro contractile regime that replicated the natural cycle. Replicating the in vivo length cycle and stimulation regime resulted in power output during cyclic contractions that matched in vivo performance both qualitatively and quantitatively. When sinusoidal length changes were used instead of the natural length trajectory, the adductor muscle produced a similar average power output (approximately 30 W kg−1 at 1.9 Hz), but the distribution of power throughout the cycles was quite different. We examined the instantaneous force–velocity properties during cyclic contractions and found that the muscle operated on or near its isotonic force–velocity curve for only 30–40% of the time required for shortening. During sinusoidal length cycles, the force–velocity trajectory was quite different. We conclude that during cyclic contractions the isotonic force–velocity curve of skeletal muscle sets an approximate boundary to the force–velocity trajectory, but the shape of this trajectory, and thus the distribution of power output, depends on the pattern of length change.
Retinoic Acid Modulates Retinal Development in the Juveniles of a Teleost Fish
Authors: Browman Howard I. , Hawryshyn Craig W.
Published: April 2021

Small (<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 (<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 (>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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Scaling the Feeding Mechanism of Largemouth Bass (Micropterus Salmoides): Kinematics of Prey Capture
Authors: Richard Barton A. , Wainwright Peter C.
Published: April 2021

We present the first analysis of scaling effects on prey capture kinematics of a feeding vertebrate. The scaling of feeding kinematics of largemouth bass (Micropterus salmoides) was investigated using high-speed video (200 fields s 1) to determine what functional changes occur in the feeding mechanism as a consequence of body size. A size series of ten bass ranging from 32 to 210mm standard length was used for the study and ten feeding sequences from each individual were analyzed to quantify movements of the feeding apparatus during prey capture. Maximal linear and angular displacements of the strike scaled isometrically. The time course of the strike was longer in larger fish. Maximal velocities of displacement were more rapid in larger fish, but their scaling exponents indicated that the intrinsic rate of muscle shortening decreased with fish size. Morphological measurements of the lever arms of the lower jaw and of the two major muscles that drive the feeding mechanism were made to relate possible biomechanical changes in the feeding mechanism to the observed kinematic relationships. The lever arms of the lower jaw and the muscles scaled isometrically; hence, the relative slowing of movements with increasing body size cannot be attributed to changes in mechanical advantage with change in body size. The scaling of feeding kinematics in the largemouth bass is in accord with the scaling of rates of muscle contraction found in other lower vertebrates. These findings demonstrate that body size can have major effects on feeding kinematics and that future comparative studies of feeding kinematics should use empirical data on size effects in kinematic comparisons between taxa.
Thermal Adaptation of Cytoplasmic Malate Dehydrogenases of Eastern Pacific Barracuda (Sphyraena spp): The Role of Differential Isoenzyme Expression
Authors: Lin Jen-Jen , Somero George N.
Published: April 2021

Kinetic properties, electrophoretic patterns and thermal stabilities of cytoplasmic malate dehydrogenases (cMDHs) were compared in Eastern Pacific barracuda (Sphyraena spp) from different latitudes. All tissues of the tropical species S. ensis contained only a single, thermostable form of cMDH. Subtropical (S. lucasana) as well as north (S. argentea) and south (S. idiastes) temperate barracuda contained both thermostable and thermolabile cMDHs, the pattern characteristic of most teleosts. Kinetic studies using unfractioned cMDHs showed that the apparent Michaelis–Menten constant (Km) of cofactor (NADH) increased with temperature, but at the physiological temperatures of the four species, Km of NADH was conserved within a narrow range (20–23 μmol l−1). Thermostable and thermolabile cMDHs were chromatographically separated and compared. Thermolabile cMDHs had higher Km values for NADH at all measurement temperatures than did thermostable cMDHs. Thermolabile cMDHs isolated from congeneric barracuda exhibited similar kinetic properties (Kmversus temperature, optimal pH, optimal substrate and cofactor concentrations). Thermostable cMDHs, likewise, were similar among the barracuda. Conservation of Km in the differently thermally adapted barracudas is, therefore, apparently due to adjustments in the ratio of expression of the thermostable and thermolabile isoforms, rather than to temperature-adaptive differences among orthologous homologues, as is commonly found for enzymes encoded by a single gene locus. The effects of temperature on the Km of NADH for isolated thermostable and thermolabile cMDHs of a eurythermal goby, Gillichthys mirabilis, however, were consistent with adaptive change in orthologous homologues of cMDH. The selective basis for the absence of thermolabile cMDH in warm-adapted ectotherms, mammals and birds is discussed.
Daily Variations in the Response of Wood Mice Apodemus Sylvaticus to Noradrenaline
Authors: Haim A. , McDevitt R. M. , Speakman J. R.
Published: April 2021

Non-shivering thermogenesis (NST) is an important mechanism for heat production in many small rodent species. Daily rhythms of body (rectal) temperature (Tb) reflect the relationship between heat production and heat dissipation. The roles of photoperiod and the time of day at which NST is measured were studied in wood mice Apodemus sylvaticus.

Mice of both sexes (N=18) were acclimated to two different photoperiod regimes (16 h:8 h L:D and 8 h:16 h L:D) at a constant ambient temperature (Ta) of 24 °C. Non-shivering thermogenesis was measured as the maximal response of oxygen consumption and body temperature (TbNA) to a noradrenaline (NA) injection (1.5 mgkg−1 subcutaneously) in unanaesthetized mice at three different times in the daily rhythm of Tb (N=6 in each group).

Mice acclimated to 8 h:16 h L:D had a greater response to noradrenaline at the three different times of the day compared with those acclimated to 16 h:8 h L:D. The extent of the response to noradrenaline within each group varied with time of day; the smallest response was recorded at 18:00±1.5 h, and the greatest was at 01:00 h. These results suggest that photoperiod is an important cue for seasonal acclimatization in this species and that the response to noradrenaline follows a daily rhythm.
Extracellular and Intracellular Acid–Base Status in the Freshwater Crayfish Austropotamobius Pallipes Between 1 and 12 °C
Authors: Whiteley N. M. , Naylor J. K. , Taylor E. W.
Published: April 2021

Freshwater crayfish, Austropotamobius pallipes, caught in the winter when water temperature was 5 °C, were acclimated in the laboratory to 5 °C for 1 week and to 1 and 12 °C for 1 month before haemolymph and tissue samples were taken for acid–base analysis. In vivo, haemolymph (extracellular) pH increased by 0.14 units between 5 and 1 °C but remained unchanged between 5 and 12 °C, giving an overall ΔpHe/Δt value of −0.009 pH units °C−1 and an [H+] value of +3.3 nmol l−1. Haemolymph withdrawn from crayfish acclimated to 1 °C and warmed anaerobically in vitro to 12 °C had a ΔpHe/Δt value of −0.010 pH units °C−1. This was depressed compared with the values of −0.015 and −0.016 pH units °C−1 obtained from haemolymph withdrawn from crayfish held at 5 and 12 °C, respectively, but changes in H+ concentration were similar in all three groups. There was little change in intracellular pH with rise in temperature in either claw muscle (ΔpHi/Δt= −0.003 pH units °C−1) or hepatopancreas (ΔpHi/Δt= −0.006 pH units °C−1). In the heart, ΔpHi/Δt paralleled that in the haemolymph (−0.010 pH units °C−1), but the largest change was found in the abdominal muscle (−0.025 pH units °C−1). In all tissues apart from claw muscle, there was a metabolic acidosis, with an increase in metabolic acid load as temperature rose from 1 to 12 °C. The depressed in vivo ΔpHe/Δt value and the differences in ΔpHi/Δt between the tissues were attributed to active regulation of pHi, possibly to control enzyme function in the intracellular compartments. Tissues that are functionally important in the winter months, such as abdominal muscle, followed alphastat regulation, whereas tissues that are less active in the winter, such as claw muscle and hepatopancreas, maintained pHi irrespective of temperature, resulting in a relatively acidotic pHi, which may serve to depress the activity of metabolic enzymes.