bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Na+ and Ca2+ Currents in Bag Cells of Sexually Immature Aplysia Californica
Authors: Fieber Lynne A.
Published: April 2021

The neurosecretory bag cells of sexually mature Aplysia californica release egg-laying hormones as part of the reproductive process after a train of action potentials termed afterdischarge. Whole-cell voltage-clamp experiments were performed in cultured cells from sexually immature A. californica to characterize the inward voltage-gated currents for Na+ and Ca2+. The goal of these experiments was to investigate the regulation of excitability during sexual maturation.

Na+ currents in bag cells of immature A. californica were similar in several ways to those of mature animals. The Na+ currents activated at voltages less negative than −30 mV and peaked at 10–20 mV in artificial sea water. The time course and pharmacology of bag cell Na+ currents were similar to those of bag cells from mature A. californica, although the Na+ current density was lower in immature A. californica. Na+ currents were inhibited by tetrodotoxin (50 nmol l−1). The Na+ current was relatively insensitive to depolarized holding potentials (Vh), maintaining approximately 50 % of peak current amplitude present at Vh=−70 mV throughout the activation range at Vh=−30 mV. In experiments using a 1 s depolarized Vh prior to a test pulse, the half-inactivation voltage (V1/2) was −27 mV. Recovery of immature Na+ current from steady-state inactivation at Vh=−30 mV had a time constant (τ) of 9.5 ms, significantly slower than in mature animals.

Ca2+ currents of immature A. californica activated at approximately −30 mV and peaked at approximately 20 mV with 11 mmol l−1 Ba2+ as the charge carrier. The principle differences from mature Ca2+ currents were the low density of the immature Ca2+ currents and their ‘run-down’ in whole-cell recordings. The pharmacology and V1/2 of bag cell Ca2+ currents were similar to those of L-type Ca2+ currents in mature cells. The Ca2+ currents were inhibited 61±10 % by nifedipine (10 μmol l−1) and were unaffected by ω-conotoxin GVIA (10 μmol l−1). The Ca2+ currents were relatively insensitive to depolarized Vh, activating maximally at Vh=−90, −70 and −50 mV, and maintaining 50 % of this peak current amplitude throughout the activation range at Vh=−30 mV. The V1/2 was −23 mV in experiments in which cells were subjected to a 1 s depolarized Vh prior to a test pulse.

Na+ current amplitudes were maintained or increased during 1 min of 4 Hz test pulses in bag cells at Vh=−70 mV and Vh=−30 mV. In contrast, Ca2+ current run-down occurred during 1 min of 4 Hz test pulses in seven of 10 cells at Vh=−70 mV and in 12 of 12 cells at Vh=−30 mV.

The observed scarcity of Na+ and Ca2+ currents in immature bag cells as well as the specific characteristics of immature bag cell Ca2+ currents make repetitive action potential firing and hormone release less likely than in mature bag cells.
Estimation of water turnover rates of captive West Indian manatees (Trichechus manatus) held in fresh and salt water
Authors: Ortiz Rudy M. , Worthy Graham A. J. , Byers Floyd M.
Published: April 2021

The ability of West Indian manatees (Trichechus manatus) to move between fresh and salt water raises the question of whether manatees drink salt water. Water turnover rates were estimated in captive West Indian manatees using the deuterium oxide dilution technique. Rates were quantified in animals using four experimental treatments: (1) held in fresh water and fed lettuce (N=4), (2) held in salt water and fed lettuce (N=2), (3) acutely exposed to salt water and fed lettuce (N=4), and (4) chronically exposed to salt water with limited access to fresh water and fed sea grass (N=5). Animals held in fresh water had the highest turnover rates (145±12 ml kg−1 day−1) (mean ± S.E.M.). Animals acutely exposed to salt water decreased their turnover rate significantly when moved into salt water (from 124±15 to 65±15 ml kg−1 day−1) and subsequently increased their turnover rate upon re-entry to fresh water (146±19 ml kg−1 day−1). Manatees chronically exposed to salt water had significantly lower turnover rates (21±3 ml kg−1 day−1) compared with animals held in salt water and fed lettuce (45±3 ml kg−1 day−1). Manatees chronically exposed to salt water and fed sea grass had very low turnover rates compared with manatees held in salt water and fed lettuce, which is consistent with a lack of mariposia. Manatees in fresh water drank large volumes of water, which may make them susceptible to hyponatremia if access to a source of Na+ is not provided.
On the aerodynamics of moult gaps in birds
Authors: Hedenström Anders , Sunada Shigeru
Published: April 2021

During the moult, birds sequentially replace their flight feathers and thus temporarily have gaps in their wings. These gaps will vary in size and position(s) during the course of the moult. We investigated the aerodynamic effects of having moult gaps in a rectangular wing by using a vortex-lattice (panel) approach, and we modelled the effect of moult gap size at the wing moult initiation position, of gap position in the primary tract and of two simultaneous gaps (as occurs during secondary feather moulting in many birds). Both gap size and gap position had a detrimental effect on aerodynamic performance as measured by lift curve slope, effective aspect ratio and the aerodynamic efficiency of the wing. The effect was largest when the moult gap was well inside the wing, because the circulation declines close to the wing tip. In fact, when the gap was at the wing tip, the performance was slightly increased because the lift distribution then became closer to the optimal elliptical distribution. The detrimental effect of moult gaps increased with increasing aspect ratio, which could help to explain why large birds have relatively slow rates of moult associated with small gaps.
OPtimum Take-Off Techniques and Muscle Design for Long Jump
Authors: Seyfarth A. , Blickhan R. , Leeuwen J. L. Van
Published: April 2021

A two-segment model based on Alexander (1990; Phil. Trans. R. Soc. Lond. B 329, 3–10) was used to investigate the action of knee extensor muscles during long jumps. A more realistic representation of the muscle and tendon properties than implemented previously was necessary to demonstrate the advantages of eccentric force enhancement and non-linear tendon properties.

During the take-off phase of the long jump, highly stretched leg extensor muscles are able to generate the required vertical momentum. Thereby, serially arranged elastic structures may increase the duration of muscle lengthening and dissipative operation, resulting in an enhanced force generation of the muscle–tendon complex. To obtain maximum performance, athletes run at maximum speed and have a net loss in mechanical energy during the take-off phase. The positive work done by the concentrically operating muscle is clearly less than the work done by the surrounding system on the muscle during the eccentric phase.

Jumping performance was insensitive to changes in tendon compliance and muscle speed, but was greatly influenced by muscle strength and eccentric force enhancement. In agreement with a variety of experimental jumping performances, the optimal jumping technique (angle of attack) was insensitive to the approach speed and to muscle properties (muscle mass, the ratio of muscle fibre to tendon cross-sectional area, relative length of fibres and tendon). The muscle properties also restrict the predicted range of the angle of the velocity vector at take-off.
Bistable Membrane Potential of the Ciliate Coleps Hirtus
Authors: Rudberg Pia , Sand Olav
Published: April 2021

In normal recording solution, the swimming pattern of the freshwater ciliate Coleps hirtus, belonging to the class Prostomatea, consists of alternating periods of nearly linear forward swimming and circular swimming within a small area. Current-clamp recordings were performed to elucidate the mechanism for this behaviour. No members of this class have previously been studied using electrophysiological techniques. The ciliates were maintained in culture and fed on the planctonic alga Rhodomonas minuta. The membrane potential showed spontaneous shifts between a more negative (deep) level of approximately −50 mV and a less negative (shallow) level of approximately −30 mV. The input resistance and capacitance at the more negative level were approximately 400 MΩ and 120 pF respectively. C. hirtus displayed a pronounced inward rectification, which was virtually insensitive to 1 mmol l−1 Cs+ and almost completely blocked by 1 mmol l−1 Ba2+. Depolarising current injections failed to evoke graded, regenerative Ca2+ spikes. However, current-induced depolarisations from the more negative potential level (−50 mV) showed a pronounced shoulder during the repolarising phase. Increased current injections prolonged the shoulder, which occasionally stabilised at the shallow membrane potential (−30 mV). The membrane potential could be shifted to the deep level by brief hyperpolarising current injections. Similar biphasic membrane properties have not been reported previously in any ciliate. The bistability of the membrane potential was abolished in Ca2+-free solution containing Co2+ or Mg2+. In Ca2+-free solution containing 1 mmol l−1 Ba2+, brief depolarising current injections at the deep potential level evoked all-or-nothing action potentials with a prolonged plateau coinciding with the shallow potential. We conclude that the deep membrane potential in C. hirtus corresponds to the traditional resting potential, whereas the shallow level is a Ca2+-dependent plateau potential. In normal solution, the direction of the ciliary beat was backwards at the deep potential level and forwards at the shallow membrane potential, probably reflecting the two main phases of the swimming pattern.
Urine as a Source of Conspecific Disturbance Signals in the Crayfish Procambarus Clarkii
Authors: Schneider Rebecca A. Zulandt , Moore Paul A.
Published: April 2021

Chemical signals are an important aspect of ecological interactions in crustacean systems. Repellent chemical signals can be classified into three context-specific categories: chemicals released directly from a repellent stimulus (avoidance chemicals), chemicals released from damaged conspecifics (alarm chemicals) and chemicals released from stressed but undamaged conspecifics (stress chemicals). Our study examines the existence and putative source of the stress signals in crayfish. We hypothesize that Procambarus clarkii can recognize stressed individuals through chemical signals and also that the source of the signal that provides P. clarkii with information on the behavioral state of the sender is the urine. We collected urine and gill water from stressed and non-stressed animals, and chemicals from damaged conspecifics. Chemical cues were introduced into a test arena while several behavior patterns of P. clarkii were recorded. Stressed crayfish produce significantly more urine than non-stressed crayfish, and this urine caused crayfish to walk significantly faster and farther and away from the source of the signal. These results demonstrate that predator-stressed crayfish release urine that causes other crayfish to move away from the source of the signal. Responses to stress chemical signals may allow receiving organisms to avoid the fate of the signal sender.
Prevalence of Cutaneous Evaporation in Merriam’S Kangaroo Rat and its Adaptive Variation at the Subspecific Level
Authors: Tracy Randall L. , Walsberg Glenn E.
Published: April 2021

Previous estimates suggested that ventilatory evaporation constitutes the major source of water loss in kangaroo rats (Dipodomys spp.). We quantified rates of water loss in Merriam’s kangaroo rat (Dipodomys merriami) and demonstrate the degree to which acclimation to a particular thermal and hydric environment plays a role in the intraspecific variation in water loss evident in this species. We draw the following conclusions: (1) that water loss varies intraspecifically in Merriam’s kangaroo rat, in association with habitats of contrasting aridity and temperature; (2) that animals from more xeric locations have lower water loss rates than those from more mesic sites; (3) that most water loss is cutaneous, with ventilatory evaporative water loss contributing, at most, only 44 % to total evaporative water loss; and (4) that intraspecific differences in rates of water loss are not acclimatory, but fixed. After acclimating under the same conditions, xericsite animals still show a 33 % lower rate of evaporative water loss than mesic-site animals.
Regulation of Compatible Solute Accumulation in Larvae of the Mosquito Culex Tarsalis: Osmolarity VERSUS SALINITY
Authors: Patrick Marjorie L. , Bradley Timothy J.
Published: April 2021

In this study, we demonstrate that two of the osmolytes utilized in the osmoconforming strategy of larval Culex tarsalis are regulated by two fundamentally different signals. When the external osmolality was increased using salinity (sea salts), hemolymph NaCl, proline and trehalose concentrations increased significantly. When sorbitol was used to increase the external osmolality without an elevation in salt concentration, hemolymph NaCl and proline concentrations decreased, whereas hemolymph trehalose concentration increased. The results suggest that proline accumulation was cued by increases in salinity, whereas trehalose levels followed increases in osmolality. Interestingly, we found that C. tarsalis larvae accumulated the exogenous sorbitol in the hemolymph in an osmoconforming manner. We conducted further studies in which changes in hemolymph NaCl concentrations were manipulated using changes in environmental salinity. The results suggested that hemolymph proline accumulation was cued by the proximal signal of hemolymph NaCl levels. Regardless of which solute (sea salts, sorbitol or mixtures thereof) was used to raise the external osmolality, trehalose accumulation tracked the increase in total osmolality of the medium. These findings indicate that the synthesis and accumulation of these two osmolytes are regulated by two independent signals.
How Do Inositol and Glucose Modulate Feeding in Manduca Sexta Caterpillars
Authors: Glendinning John I. , Nelson Nancy M. , Bernays Elizabeth A.
Published: April 2021

Many species of caterpillar possess taste cells that respond exceptionally vigorously to the sugar alcohol myo-inositol. We examined the functional significance of these inositol-sensitive taste cells in Manduca sexta caterpillars through an integrated series of electrophysiological and behavioral studies. Neural recordings from all the gustatory chemosensilla revealed that M. sexta have only two pairs of inositol-sensitive taste cells, which respond strongly and selectively to myo-inositol, and two pairs of sugar-sensitive taste cells, which respond relatively weakly to sugars (glucose and sucrose). Behavioral studies established that myo-inositol incites feeding and counteracts the inhibitory effects of aversive taste stimuli (e.g. caffeine) on feeding, but does not promote increased consumption once feeding has been initiated. In contrast, glucose and sucrose did not produce any robust effects on feeding. We failed to obtain any evidence of sensory inhibition between taste cells that responded to myo-inositol and caffeine, indicating that myo-inositol counteracts the inhibitory effects of caffeine on feeding through a central gustatory mechanism. We conclude that sensory input from the inositol-sensitive taste cells, but not the sugar-sensitive taste cells, plays an important role in regulating feeding in M. sexta.
Fatigue Quality of Mammalian Tendons
Authors: Ker Robert F. , Wang Xiao Tong , Pike Anna V. L.
Published: April 2021

When excised tendons are subjected to a prolonged load, whether constant or oscillatory, fatigue damage accumulates, leading eventually to rupture. ‘Fatigue quality’, assessed by the time-to-rupture under a given stress, was found to vary hugely among the tendons of a wallaby hind limb. This material property correlates with the varied stresses to which tendons from different anatomical sites are exposed in life. The correlation was demonstrated by subjecting each excised tendon to a load equal to the maximum isometric force that its muscle could have developed. The time-to-rupture was then approximately the same for each tendon, on average 4.2 h. A model is introduced in which damage is proposed as the trigger for adaptation of fatigue quality. The model aims, in particular, to explain why low-stressed tendons are not made of a ‘better’ material, although this clearly exists since it is used in high-stressed tendons. The principle of design to a minimum quality is viable in biology because of the availability of self-repair to balance routine damage. Clinical symptoms, to be included under the general heading of ‘overuse injuries’, will only arise when this balance fails.
Excitatory and Inhibitory Roles of Central Ganglia in Initiation of the Insect Ecdysis Behavioural Sequence
Authors: Žitňan Dušan , Adams Michael E.
Published: April 2021

Insects shed their old cuticle by performing the ecdysis behavioural sequence. To activate each subunit of this set of programmed behaviours in Manduca sexta, specific central ganglia are targeted by pre-ecdysis-triggering (PETH) and ecdysis-triggering (ETH) hormones secreted from Inka cells. PETH and ETH act on each abdominal ganglion to initiate, within a few minutes, pre-ecdysis I and II, respectively. Shortly thereafter, ETH targets the tritocerebrum and suboesophageal ganglion to activate the ecdysis neural network in abdominal ganglia through the elevation of cyclic GMP (cGMP) levels. However, the onset of ecdysis behaviour is delayed by inhibitory factor(s) from the cephalic and thoracic ganglia. The switch from pre-ecdysis to ecdysis is controlled by an independent clock in each abdominal ganglion and is considerably accelerated after removal of the head and thorax. Eclosion hormone (EH) appears to be one of the central signals inducing elevation of cGMP levels and ecdysis, but these actions are quite variable and usually restricted to anterior ganglia. EH treatment of desheathed ganglia also elicits strong production of cGMP in intact ganglia, suggesting that this induction occurs via the release of additional downstream factors. Our data suggest that the initiation of pre-ecdysis and the transition to ecdysis are regulated by stimulatory and inhibitory factors released within the central nervous system after the initial actions of PETH and ETH.
Active NaCl Absorption Across Split Lamellae of Posterior Gills of the Chinese Crab Eriocheir Sinensis: Stimulation by Eyestalk Extract
Authors: Onken Horst , Schöbel Andreas , Kraft Jan , Putzenlechner Max
Published: April 2021

Split lamellae of the posterior gills of freshwater-adapted Chinese crabs (Eriocheir sinensis) were mounted in a modified Ussing-type chamber, and active and electrogenic absorption of Na+ and Cl− were measured as positive (INa) or negative (ICl) short-circuit currents. Haemolymph-side addition of eyestalk extract stimulated ICl by increasing both the transcellular Cl− conductance and the electromotive force for Cl− absorption. The effect was dose-dependent. Boiling the eyestalk extract did not change its effectiveness. The stimulating factor passed through dialysis tubing, indicating that it has a molecular mass of less than 2 kDa. RpcAMPS, a blocker of protein kinase A, reduced the stimulated ICl. Eyestalk extract stimulated INa by increasing the transcellular Na+ conductance at constant electromotive force. Amiloride-induced current-noise analysis revealed that stimulation of INa was accompanied by an increase in the apparent number of open apical Na+ channels at a slightly reduced single-channel current. In addition to the electrophysiological experiments, whole gills were perfused in the presence and in the absence of putative transport stimulators, and the specific activities of the V-ATPase and the Na+/K+-ATPase were measured. Eyestalk extract, theophylline or dibutyryl-cyclic AMP stimulated the activity of the V-ATPase, whereas the activity of the Na+/K+-ATPase was unaffected. The simultaneous presence of RpcAMPS prevented the stimulation of V-ATPase by eyestalk extract or theophylline.
Haemolymph Mg2+ Regulation in Decapod Crustaceans: Physiological Correlates and Ecological Consequences in Polar Areas
Authors: Frederich Markus , Sartoris Franz Josef , Arntz Wolf E. , Pörtner Hans-Otto
Published: April 2021

Reptant decapod crustaceans are almost absent from the Southern Ocean south of the Antarctic Convergence. We tested the hypothesis that this may be due to the reduced ability of this group to regulate Mg2+ levels in the haemolymph ([Mg2+]HL). Mg2+ acts as an anaesthetic in marine invertebrates and its level is higher in Reptantia (crabs such as Cancer spp., Chionoecetes spp., Maja spp., 30–50 mmol l−1) than in Natantia (prawns such as Pandalus spp., Palaemon spp., Crangon spp., 5–12 mmol l−1).

We varied [Mg2+]HL in three species of reptant decapod crustaceans, Carcinus maenas, Hyas araneus and Eurypodius latreillei, and investigated heart rate, the rate of oxygen consumption and levels of spontaneous and forced activity at different temperatures. The rate of oxygen consumption and heart rate increased significantly with reduction in [Mg2+]HL over the entire temperature range investigated in E. latreillei. In H. araneus, an increase in metabolic and heart rates compared with control values was found only at temperatures below 2 °C. Forced and spontaneous activity levels increased significantly in the group of [Mg2+]HL-reduced animals below 0 °C, at which control animals were mostly inactive. At a reduced [Mg2+]HL of 5–12 mmol l−1, which is the [Mg2+]HL of caridean shrimps in the Southern Ocean, Q10 and activation energy were reduced for all these variables and extended the temperature range over which physiological functions were maintained.

We suggest that the high [Mg2+]HL in Reptantia causes relaxation of the animals and reduces their scope for activity, especially at temperatures below 0 °C. The hypothesis that the synergistic effects of high [Mg2+]HL and low temperature probably prevented the Reptantia from recolonizing the permanently cold water of polar areas is discussed.
Central Role Of the Apical Membrane H+-Atpase in Electrogenesis and Epithelial Transport in Malpighian Tubules
Authors: Beyenbach Klaus W. , Pannabecker Thomas L. , Nagel Wolfram
Published: April 2021

The effects of bafilomycin A1, a blocker of V-type H+-ATPases, were investigated in Malpighian tubules of Aedes aegypti. Bafilomycin A1 reduced rates of transepithelial fluid secretion and the virtual short-circuit current (vIsc) with an IC50 of approximately 5 μmol l−1. As vIsc decreased, the electrical resistance increased across the whole epithelium and across the apical membrane, indicating effects on electroconductive pathways. Bafilomycin A1 had no effect when applied from the tubule lumen, pointing to the relative impermeability of the apical membrane to bafilomycin A1. Thus, bafilomycin A1 must take a cytoplasmic route to its blocking site in the proton channel of the H+-ATPase located in the apical membrane of principal cells. The inhibitory effects of bafilomycin A1 were qualitatively similar to those of dinitrophenol in that voltages across the epithelium (Vt), the basolateral membrane (Vbl) and the apical membrane (Va) depolarized towards zero in parallel. Moreover, Vbl always tracked Va, indicating electrical coupling between the two membranes through the shunt. Electrical coupling allows the H+-ATPase to energize not only the apical membrane, but also the basolateral membrane. Furthermore, electrical coupling offers a balance between electroconductive entry of cations across the basolateral membrane and extrusion across the apical membrane to support steady-state conditions during transepithelial transport.
The Inhibitory Effects Of γ-Aminobutyric Acid (Gaba) On Growth Hormone Secretion in the Goldfish Are Modulated by SEx Steroids
Authors: Trudeau V. L. , Kah O. , Chang J. P. , Sloley B. D. , Dubourg P. , Fraser E. J. , Peter R. E.
Published: April 2021

Double-labelling studies at the electron microscopic level demonstrated that γ-aminobutyric acid (GABA)-immunoreactive nerve endings are associated with growth-hormone-secreting cells in the proximal pars distalis of the goldfish pituitary gland, suggesting that GABA may be important for the control of growth hormone release in this species. An in vitro assay for GABA-transaminase activity demonstrated that the pituitary is a site for the metabolism of GABA to succinic acid. In vitro, GABA or the GABA antagonists bicuculline and saclofen did not affect the rate of growth hormone release from dispersed pituitary cells in static incubation. In contrast, intracerebroventricular injection of GABA reduced serum growth hormone levels within 30 min. During the seasonal gonadal cycle, intraperitoneal injection of GABA was without effect in sexually regressed goldfish, but caused a significant decrease in serum growth hormone levels in sexually recrudescent animals. Intraperitoneal implantation of solid silastic pellets containing oestradiol increased serum GH levels fivefold in sexually regressed and recrudescent goldfish; in both groups, GABA suppressed the oestradiol-stimulated increase in circulating growth hormone levels. The effect of oestradiol on basal serum growth hormone levels was specific since progesterone and testosterone were without effect. However, in recrudescent animals treated with progesterone and testosterone, the inhibitory effects of GABA on serum growth hormone levels were absent, indicating a differential role for these steroids in growth hormone release. Taken together, these results demonstrate that GABA has an inhibitory effect on growth hormone release in goldfish.
Identification of a Sea Urchin Na+ /K+ /2Cl− Cotransporter (Nkcc): Microfilament-Dependent Surface Expression is Mediated by Hypotonic Shock and Cyclic Amp
Authors: D’andrea-Winslow Lisanne , Strohmeier Gregg R. , Rossi Bernard , Hofman Paul
Published: April 2021

We report the identification of an invertebrate Na+/K+/2Cl− cotransporter, NKCC. As a model system, we used the immune cells (coelomocytes) of the Mediterranean sea urchin Paracentrotus lividus. These cells are particularly interesting because they can be activated to undergo a rapid and dynamic change in cell shape. We demonstrate that forskolin, a cyclic AMP agonist known to regulate NKCC, induced coelomocyte transformation at doses of 10 µmol l−1 and greater. Using two distinct monoclonal antibodies (T4 and T9) raised against the human intestinal epithelial NKCC, we have identified a high-molecular-mass (195 kDa) protein in coelomocyte extracts. We propose a novel method for the isolation of NKCC in one step by using bumetanide–Sepharose affinity chromatography under low-[Cl−] conditions. This method was successful in isolating coelomocyte 195 kDa NKCC. The T4 monoclonal antibody was used in immunocytochemical experiments to localize NKCC in resting and activated coelomocytes. In petalloid coelomocytes, a punctate, cytoplasmic distribution was observed in close proximity to actin filament bundles; in transformed coelomocytes, the immunofluorescence was distributed along the length of the filopodia and uniformly throughout the perinuclear region. The change in subcellular distribution of NKCC between the resting and the activated state was further investigated by using cell surface biotinylation followed by immunoprecipitation. These studies revealed an upregulation of NKCC at the plasma membrane upon activation, a process that was blocked by the F-actin-stabilizing drug phalloidin. These studies identify a novel model system in which to investigate a newly identified invertebrate Na+/K+/2Cl− cotransporter.
Oxidative Stress, Dna Damage And P53 Expression In The Larvae Of Atlantic Cod (Gadus Morhua) Exposed To Ultraviolet (290–400 nm) Radiation
Authors: Lesser Michael P. , Farrell Julianne H. , Walker Charles W.
Published: April 2021

Decreases in stratospheric ozone levels from anthropogenic inputs of chlorinated fluorocarbons have resulted in an increased amount of harmful ultraviolet-B (UVB, 290–320 nm) radiation reaching the sea surface in temperate latitudes (30–50°N). In the Gulf of Maine, present-day irradiances of ultraviolet-A (UVA, 320–400 nm) radiation can penetrate to depths of 23 m and UVB radiation can penetrate to depths of 7–12 m, where the rapidly developing embryos and larvae of the Atlantic cod (Gadus morhua) are known to occur. Laboratory exposures of embryos and larvae of Atlantic cod to ultraviolet radiation (UVR) equivalent to a depth of approximately 10 m in the Gulf of Maine resulted in significant mortality of developing embryos and a decrease in standard length at hatching for yolk-sac larvae. Larvae at the end of the experimental period also had lower concentrations of UVR-absorbing compounds and exhibited significantly greater damage to their DNA, measured as cyclobutane pyrimidine dimer formation, after exposure to UVB radiation. Larvae exposed to UVB radiation also exhibited significantly higher activities and protein concentrations of the antioxidant enzyme superoxide dismutase and significantly higher concentrations of the transcriptional activator p53. p53 is expressed in response to DNA damage and can result in cellular growth arrest in the G1-to S-phase of the cell cycle or to programmed cell death (apoptosis). Cellular death caused by apoptosis is the most likely cause of mortality in embryos and larvae in these laboratory experiments, while the smaller size at hatching in those larvae that survived is caused by permanent cellular growth arrest in response to DNA damage. In addition, the sub-lethal energetic costs of repairing DNA damage or responding to oxidative stress may also contribute to poor individual performance in surviving larvae that could also lead to increases in mortality. The irradiances of UVB radiation that elicit these responses in cod larvae can occur in many temperate latitudes, where these ecologically and commercially important fish are known to spawn, and may contribute to the high mortality of cod embryos and larvae in their natural environment.
Acute and Chronic Influence of Temperature on Red Blood Cell Anion Exchange
Authors: Jensen Frank B. , Wang Tobias , Brahm Jesper
Published: April 2021

Unidirectional 36Cl− efflux via the red blood cell anion exchanger was measured under Cl− self-exchange conditions (i.e. no net flow of anions) in rainbow trout Oncorhynchus mykiss and red-eared freshwater turtle Trachemys scripta to examine the effects of acute temperature changes and acclimation temperature on this process. We also evaluated the possible adaptation of anion exchange to different temperature regimes by including our previously published data on other animals. An acute temperature increase caused a significant increase in the rate constant (k) for unidirectional Cl− efflux in rainbow trout and freshwater turtle. After 3 weeks of temperature acclimation, 5 °C-acclimated rainbow trout showed only marginally higher Cl− transport rates than 15 °C-acclimated trout when compared at the same temperature. Apparent activation energies for red blood cell Cl− exchange in trout and turtle were lower than values reported in endothermic animals. The Q10 for red blood cell anion exchange was 2.0 in trout and 2.3 in turtle, values close to those for CO2 excretion, suggesting that, in ectothermic animals, the temperature sensitivity of band-3-mediated anion exchange matches the temperature sensitivity of CO2 transport (where red blood cell Cl−/HCO3− exchange is a rate-limiting step). In endotherms, such as man and chicken, Q10 values for red blood cell anion exchange are considerably higher but are no obstacle to CO2 transport, because body temperature is normally kept constant at values at which anion exchange rates are high. When compared at constant temperature, red blood cell Cl− permeability shows large differences among species (trout, carp, eel, cod, turtle, alligator, chicken and man). Cl− permeabilities are, however, remarkable similar when compared at preferred body temperatures, suggesting an appropriate evolutionary adaptation of red blood cell anion exchange function to the different thermal niches occupied by animals.
Free Vertical Moments and Transverse Forces in Human Walking and Their Role in Relation to Arm-Swing
Authors: Li Yu , Wang Weijie , Crompton Robin H. , Gunther Michael M.
Published: April 2021

We present force plate data on vertical free moments (force couples in the horizontal plane between the foot and the ground) and on transverse force during unloaded walking in different modes and at different speeds (including running) by adults of both sexes and by children, and examine loaded walking by adult males and one boy. Free moments in slow and normal-speed walking are characterised by a lateral peak in the accelerative phase of stance, but the peak during running, and in some cases of fast walking, occurs in the deceleration phase. Free moments are strongly affected by arm fixation in males, but less so in females. The pattern, but not the scale, of free moments is affected by loading position and side, but load magnitude has little effect if the loaded weight is treated as part of the body. Transverse force is more variable than sagittal force. In males, the transverse force curve shows a marked trough at mid-stance, whereas in females this trough is rarely seen. The transverse force of males also differs from that of females in response to arm fixation, showing a local medial inflection at three-quarters of the stance phase that is not present in females. Adults differ from children younger than 9 years in the presence of a very short, medially directed peak following heel-strike. Analysis of the effects of arm fixation and the timing of forces suggests strongly that arm-swing and free moments tend to reinforce each other in balancing trunk torques induced by the lower limbs. Both are of reduced importance in slow walking.
Physical Factors Affecting the Cost and Efficiency of Sound Production in the Treefrog Hyla Versicolor
Authors: Mclister James D.
Published: April 2021

The metabolic cost, energy output and efficiency (i.e. the ratio of energy output to metabolic cost) of sound production were compared among male grey treefrogs (Hyla versicolor) as a function of body size and temperature. The effects of call length (in notes per call) and dominant frequency (in kHz) were also considered. Cost, determined from the amount of oxygen consumed, averaged 12.1 mJ per note and was dependent only upon body mass. Acoustic energy per note, determined from oscillograms of recorded calls, averaged 0.34 mJ and was dependent only upon temperature. Conventional theory suggests that the efficiency of sound production should be a function of the ratio of the linear size of the radiating structures to the wavelength of the sound generated (i.e. efficiency is assumed to be a function of the product of mass0.33 and frequency), but efficiency in H. versicolor was found to be a function of the product of temperature2.1 and mass−1.08. Adjusting for temperature and body mass, the efficiency of sound production in H. versicolor (average 2.4 %) is greater than the efficiency of other frog species for which data are available. Temperature may affect acoustic energy output because trunk muscle contraction speed increases with temperature, which increases the velocity of airflow across the vocal cords.
Transport of Bile Acids in Hepatic and Non-Hepatic Tissues
Authors: St-Pierre Marie V. , Kullak-Ublick Gerd A. , Hagenbuch Bruno , Meier Peter J.
Published: April 2021

Bile acids are steroidal amphipathic molecules derived from the catabolism of cholesterol. They modulate bile flow and lipid secretion, are essential for the absorption of dietary fats and vitamins, and have been implicated in the regulation of all the key enzymes involved in cholesterol homeostasis. Bile acids recirculate through the liver, bile ducts, small intestine and portal vein to form an enterohepatic circuit. They exist as anions at physiological pH and, consequently, require a carrier for transport across the membranes of the enterohepatic tissues. Individual bile acid carriers have now been cloned from several species. Na+-dependent transporters that mediate uptake into hepatocytes and reabsorption from the intestine and biliary epithelium and an ATP-dependent transporter that pumps bile acids into bile comprise the classes of transporter that are specific for bile acids. In addition, at least four human and five rat genes that code for Na+-independent organic anion carriers with broad multi-substrate specificities that include bile acids have been discovered. Studies concerning the regulation of these carriers have permitted identification of molecular signals that dictate eventual changes in the uptake or excretion of bile acids, which in turn have profound physiological implications. This overview summarizes and compares all known bile acid transporters and highlights findings that have identified diseases linked to molecular defects in these carriers. Recent advances that have fostered a more complete appreciation for the elaborate disposition of bile acids in humans are emphasized.
Lift-Based Paddling in Diving Grebe
Authors: Johansson L. Christoffer , Norberg Ulla M. Lindhe
Published: April 2021

To examine the hydrodynamic propulsion mechanism of a diving great crested grebe (Podiceps cristatus), the three-dimensional kinematics was determined by digital analysis of sequential video images of dorsal and lateral views. During the acceleration phase of this foot-propelled bird, the feet move through an arc in a plane nearly normal to the bird’s line of motion through the water, i.e. the toes move dorsally and medially but not caudally relative to the water. The kinematics of the grebe’s lobed feet is different from that in anseriforms, whose feet move in a plane mostly parallel to the bird’s line of progress through the water. Our results suggest that the foot-propelled locomotor mechanism of grebes is based primarily on a lift-producing leg and foot stroke, in contrast to the drag-based locomotion assumed previously. We suggest that the lift-based paddling of grebes considerably increases both maximum swimming speed and energetic efficiency over drag-based propulsion. Furthermore, the results implicate a new interpretation of the functional morphology of these birds, with the toes serving as a self-stabilizing multi-slotted hydrofoil during the power phase.
The Process of Cell Adhesion Among Dissociated Single Cells of Hydra: Morphological Observations
Authors: Takaku Yasuharu , Hariyama Takahiko , Tsukahara Yasuo
Published: April 2021

Ultrastructural observations were made on the initial adhesion process at the adherent region of Hydra endodermal cell pairs brought into contact (following dissociation) using a three-dimensional laser manipulator. Total contact length across the diameter of the adherent region decreased during the period 10–60 min after initial adhesion. However, the mean numbers of closest (<4 nm) and medium (5–25 nm) separation distances between membranes (thought to be important in total cell adhesion) were not significantly different. These data indicate that adherent cell pairs maintain a constant adhesiveness during the first 60 min of the adhesion process, despite membrane rearrangements. The relative length of each separation distance in adherent cell pairs approached that reported previously for intact Hydra. The sums of lengths in both the closest and medium categories (as a proportion of total contact length) increased because the length of cleavages (distances >25 nm) decreased significantly during the same time period. These results suggest that adherent cell pairs undergo rapid, active membrane changes in the adherent region, which might be associated with cell sorting. The possible significance of these changes for active rearrangement are discussed.
Juvenile Coho Salmon Locomotion and Mosaic Muscle are Modified by 3’,3’,5’-Tri-Iodo-L-Thyronine (T3)
Authors: Katzman Shana , Cech Joseph J.
Published: April 2021

Studies of maximum aerobic swimming performance in smolting juvenile salmonids indicate that these animals may be aerobically compromised during downstream migration. To test our hypothesis that hyperthyroid status contributes to decreased swimming performance through modification of muscle contractility in juvenile (112 mm mean total length) coho salmon (Oncorhynchus kisutch), we measured swimming performance and isolated muscle bundle contractility of fish implanted with 3’,3’,5’-tri-iodo-L-thyronine (T3) pellets, of fish implanted with sham pellets and of fish with no pellet implantation (control group). After 3 weeks (N=12–13), critical swimming speeds (maximum aerobic swimming speed or Ucrit) were measured. Muscle bundles (N=15–16) were dissected from the hypaxial musculature and stimulated to measure the force and velocity of an isometric twitch and tetani. T3-treated fish demonstrated visible morphological changes associated with smoltification. Mean values of Ucrit were significantly decreased and the prolonged contraction (tetani) and twitch rates of contraction, relaxation and maximum force were significantly increased by T3 treatment compared with both the sham and control fish. Hematocrit, body mass and body length were not significantly affected by T3 treatment. In conclusion, we suggest that the reported decrease in Ucrit during salmonid smoltification may be mediated by endogenous T3-induced contractile modification of mosaic muscle fibers.
Comparison of the Efficiency of Rat Papillary Muscles During Afterloaded Isotonic Contractions and Contractions With Sinusoidal Length Changes
Authors: Mellors L. J. , Gibbs C. L. , Barclay C. J.
Published: April 2021

The results of previous studies suggest that the maximum mechanical efficiency of rat papillary muscles is lower during a contraction protocol involving sinusoidal length changes than during one involving afterloaded isotonic contractions. The aim of this study was to compare directly the efficiency of isolated rat papillary muscle preparations in isotonic and sinusoidal contraction protocols. Experiments were performed in vitro (27 °C) using left ventricular papillary muscles from adult rats. Each preparation performed three contraction protocols: (i) low-frequency afterloaded isotonic contractions (10 twitches at 0.2 Hz), (ii) sinusoidal length change contractions with phasic stimulation (40 twitches at 2 Hz) and (iii) high-frequency afterloaded isotonic contractions (40 twitches at 2 Hz). The first two protocols resembled those used in previous studies and the third combined the characteristics of the first two. The parameters for each protocol were adjusted to those that gave maximum efficiency. For the afterloaded isotonic protocols, the afterload was set to 0.3 of the maximum developed force. The sinusoidal length change protocol incorporated a cycle amplitude of ±5 % resting length and a stimulus phase of −10 °. Measurements of force output, muscle length change and muscle temperature change were used to calculate the work and heat produced during and after each protocol.

Net mechanical efficiency was defined as the proportion of the energy (enthalpy) liberated by the muscle that appeared as work. The efficiency in the low-frequency, isotonic contraction protocol was 21.1±1.4 % (mean ± S.E.M., N=6) and that in the sinusoidal protocol was 13.2±0.7 %, consistent with previous results. This difference was not due to the higher frequency or greater number of twitches because efficiency in the high-frequency, isotonic protocol was 21.5±1.0 %.

Although these results apparently confirm that efficiency is protocol-dependent, additional experiments designed to measure work output unambiguously indicated that the method used to calculate work output in isotonic contractions overestimated actual work output. When network output, which excludes work done by parallel elastic elements, rather than total work output was used to determine efficiency in afterloaded isotonic contractions, efficiency was similar to that for sinusoidal contractions. The maximum net mechanical efficiency of rat papillary muscles performing afterloaded isotonic or sinusoidal length change contractions was between 10 and 15 %.
A Maxi Cl− Channel in Cultured Pavement Cells From the Gills of the Freshwater Rainbow Trout Oncorhynchus Mykiss
Authors: O’Donnell M. J. , Kelly S. P. , Nurse C. A. , Wood C. M.
Published: April 2021

Primary cultures of pavement cells from the gills of a freshwater fish, the rainbow trout Oncorhynchus mykiss, have been studied for the first time using the patch-clamp technique. Gigaohm seals were obtained in approximately 95 % of cells studied, and channel activity was evident in a high proportion (>90 %). A large-conductance Cl− channel was evident in 6 % of cell-attached and in 31 % of inside-out patches. Single-channel conductance in inside-out patches was 372 pS, and current/voltage relationships were linear over the range −60 to +60 mV. The channel was activated by patch excision, and activation was often associated with polarization of the patch. The mean number of channels per patch was 1.9, and there were several subconductance states. The relationship between channel activity (NPo) and voltage was in the form of an inverted U, and channel activity was highest between 0 and +20 mV. Large-conductance Cl− channels showed a progressive time-dependent reduction in current in response to sustained polarization to voltages outside the range −20 mV to +20 mV. Permeability ratios (P) of Cl− to other anions were and Pisethionate/PCl=0.53. The channel was blocked by Zn2+, SITS, DIDS and diphenylamine carboxylate. This is the first description of a large-conductance Cl− channel in gill cells from freshwater or marine species. Possible functions of the channel are discussed.
The Drosophila Melanogaster Homologue of an Insect Calcitonin-Like Diuretic Peptide Stimulates V-ATPase Activity in Fruit Fly Malpighian Tubules
Authors: Coast Geoffrey M. , Webster Simon G. , Schegg Kathleen M. , Tobe Stephen S. , Schooley David A.
Published: April 2021

The Drosophila melanogaster homologue of an insect calcitonin-like diuretic hormone was identified in a BLAST search of the Drosophila genome database. The predicted 31-residue amidated peptide (D. melanogaster DH31; Drome-DH31) was synthesised and tested for activity on fruit fly Malpighian tubules. It increases tubule secretion by approximately 35 % of the response obtained with a myokinin from the housefly Musca domestica (muscakinin; Musdo-K) and has an EC50 of 4.3 nmol l−1.

The diuretic activities of Drome-DH31 and Musdo-K were additive when tested at threshold and supra-maximal concentrations, which suggests that they target different transport processes. In support of this, Drome-DH31 increased the rate of secretion by tubules held in bathing fluid with a reduced Cl− concentration, whereas Musdo-K did so only in the presence of Drome-DH31. Stimulation with Drome-DH31 increased the lumen-positive transepithelial potential in the main secretory segment of the tubule. This was attributed to activation of an apical electrogenic proton-translocating V-ATPase in principal cells, since it was associated with hyperpolarisation of the apical membrane potential and acidification of secreted urine by 0.25 pH units.

Exogenous 8-bromo-cyclic AMP and cyclic GMP increased tubule secretion to the same extent as Drome-DH31 and, when tested together with the diuretic peptide, their activities were not additive. Stimulation with Drome-DH31 resulted in a dose-dependent increase in cyclic AMP production by tubules incubated in saline containing 0.5 mmol l−1 3-isobutyl-1-methylxanthine, whereas cyclic GMP production was unchanged. Taken together, the data are consistent with Drome-DH31 activating an apical membrane V-ATPase via cyclic AMP. Since the K+ concentration of the secreted urine was unchanged, it is likely that Drome-DH31 has an equal effect on K+ and Na+ entry across the basolateral membrane.