bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Na+ and Ca2+ Currents in Bag Cells of Sexually Immature Aplysia Californica
Authors: Fieber Lynne A. 
Published: April 2021

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.