bluuebunny/crossref_metadata_2025 huggingface dataset:
Na+/Ca2+ exchange current in ventricular myocytes of fish heart: contribution to sarcolemmal Ca2+ influx
Authors: Vornanen Matti
Published: April 2021

Influx of extracellular Ca2+ plays a major role in the activation of contraction in fish cardiac cells. The relative contributions of Na+/Ca2+ exchange and L-type Ca2+ channels to Ca2+ influx are, however, unknown. Using a physiological action potential as the command pulse in voltage-clamped heart cells, we examined sarcolemmal Ca2+ influx through Na+/Ca2+ exchange and L-type Ca2+ channels in crucian carp (Carassius carassius L.) ventricular myocytes. When other cation conductances were blocked, a Ni2+-sensitive current with the characteristic voltage- and time-dependent properties of the Na+/Ca2+ exchange current could be distinguished. At the maximum overshoot voltage of the ventricular action potential (+40 mV; [Na+]i=10 mmol l−1), the density of the Na+/Ca2+ exchange current was 2.99±0.27 pA pF−1 for warm-acclimated fish (23 °C) and 2.38±0.42 pA pF−1 for cold-acclimated fish (4 °C) (means ± S.E.M., N=5–6; not significantly different, P=0.26). The relative contributions of the Na+/Ca2+ exchanger and L-type Ca2+ channels to Ca2+ influx were estimated using two partly different methods. Integration of the Ni2+-sensitive Na+/Ca2+ exchange current and the verapamil- and Cd2+-sensitive L-type Ca2+ current suggests that, during the action potential, approximately one-third of the activating Ca2+ comes through Na+/Ca2+ exchange and approximately two-thirds through L-type Ca2+ channels. An alternative method of analysis, using the inward tail current as a measure of the total sarcolemmal Ca2+ flux from which the Ni2+-sensitive Na+/Ca2+ exchange current was subtracted to obtain the Ca2+ influx through the channels, suggests that L-type Ca2+ channels and Na+/Ca2+ exchange are almost equally important in the activation of contraction. Furthermore, the time course of cell shortening is not adequately explained by sarcolemmal Ca2+ influx through the channels alone, but is well approximated by the sum of Ca2+ influx through the channels and the exchanger. The present results indicate that reverse Na+/Ca2+ exchange in crucian carp ventricular myocytes has sufficient capacity to trigger contraction and suggest that the exchange current makes a significant contribution to contractile Ca2+ during the physiological action potential. The relative significance of channels and exchanger molecules in sarcolemmal Ca2+ entry into crucian carp ventricular myocytes was unaffected by thermal acclimation when determined at 22 °C.
Oscillatory dynamics and information processing in olfactory systems
Authors: Gelperin Alan
Published: April 2021

Oscillatory dynamics is a universal design feature of olfactory information-processing systems. Recent results in honeybees and terrestrial slugs suggest that oscillations underlie temporal patterns of olfactory interneuron responses critical for odor discrimination. Additional general design features in olfactory information-processing systems include (1) the use of central processing areas receiving direct olfactory input for odor memory storage and (2) modulation of circuit dynamics and olfactory memory function by nitric oxide. Recent results in the procerebral lobe of the terrestrial slug Limax maximus, an olfactory analyzer with oscillatory dynamics and propagating activity waves, suggest that Lucifer Yellow can be used to reveal a band-shaped group of procerebral neurons involved in the storage of an odor memory. A model has been constructed to relate wave propagation and odor memory bands in the procerebral lobe of L. maximus and to relate these findings to glomerular odor representations in arthropods and vertebrates.
Spatio-Temporal Learning by the ant Ectatomma Ruidum
Authors: Schatz Bertrand , Lachaud Jean-Paul , Beugnon Guy
Published: April 2021

We tested, under field and laboratory conditions, whether the neotropical ant Ectatomma ruidum Roger can learn several associations between temporal and spatial changes in the daily pattern of food availability. Honey was shuffled between two or three feeding sites following a fixed daily schedule. Foragers learnt to associate particular sites with the specific times at which food was available, individually marked ants being observed on the correct sites at the correct times. Some ants anticipated the time of food delivery by approximately 30 min, and it was not necessary for them to be rewarded at the first stage of the sequence of food collection to continue their search for honey according to the correct schedule of reward. Ants also followed the same schedule when no honey was supplied at each stage of the sequence, and they stayed at the expected unrewarded site for a period equivalent to the reward period of the corresponding training phase, indicating that they had learnt when and for how long the food was available. Thus, ants rely on their spatio-temporal memory rather than on local cues coming from the honey source to guide them.
Muscle growth and development in normal-sex-ratio and all-female diploid and triploid Atlantic salmon
Authors: Johnston Ian A. , Strugnell Gillian , McCracken Marti L. , Johnstone Ray
Published: April 2021

Muscle development and growth were investigated in diploid populations of normal-sex-ratio and all-female Atlantic salmon (Salmo salar L.) and their triploid counterparts produced by high-pressure treatment. Somites were formed at the rate of 6 h−1 in both diploids and triploids at 6 °C. The rostral-to-caudal development of myotubes, myofibrils and acetylcholinesterase staining at the myosepta was slightly more advanced in triploid than in diploid fish, although the differences were smaller than among individual families. The c-met receptor tyrosine kinase was used as a molecular marker for the satellite cells involved in postembryonic muscle growth. Satellite cell nuclei comprised 17.5 % of total myonuclei in smolts and they were 24 % more abundant in diploid than in triploid fish. Cells expressing the myogenic regulatory factor myf-6, a marker of satellite cells committed to differentiation, represented 14.8 % of total myonuclei in diploids and 12.5 % in triploids. At ambient temperatures, the number of white muscle fibres in normal-sex-ratio fish increased more than 30-fold between the alevin and smolt stages, and approximately 3.5-fold further during the first year of seawater growth. The rate of muscle fibre recruitment in seawater stages was significantly greater in diploid than in triploid fish, reaching 1162 fibres day−1 and 608 fibres day−1, respectively, in all-female groups 800 days post-hatching. For 42 cm fork-length fish, there were approximately one-third more muscle fibres per myotome in diploid than in triploid groups, 649 878 and 413 619, respectively, for all-female fish. The probability density function of muscle fibre diameters in each fish was estimated using non-parametric smoothing techniques, and the mean densities for diploids (fD) and triploids (fT) were calculated. The peak fibre diameter was approximately 20 μm in all age classes, irrespective of ploidy. Distinct bimodal distributions of muscle fibre diameter were evident in all groups 775 days and 839 days post-hatching, reflecting seasonal cycles of fibre recruitment. fD and fT were compared using a non-parametric bootstrap technique and the reference band representing the null-hypothesis indicated that there was no difference with ploidy. Reference bands for normal-sex-ratio fish at 315 days and 470 days indicated that diploids had a higher percentage of smaller-diameter fibres and that triploid distributions had a thicker right-hand tail. Similar differences in fD and fT of muscle fibre diameters were found for all-female fish, although the statistical evidence was less strong. Reference bands indicated differences in the middle range of the distributions of muscle fibre diameter in fish 620–775 days post-hatch, with triploids having a thicker right-hand tail. Thus, a lower density of satellite cells was associated with reduced rates of fibre recruitment but a compensatory increase in muscle fibre hypertrophy in triploid compared with diploid fish.
Energy metabolism during embryonic development and larval growth of an Antarctic sea urchin
Authors: Marsh Adam G. , Leong Patrick K. K. , Manahan Donal T.
Published: April 2021

Developmental energetics of an Antarctic sea urchin, Sterechinus neumayeri, were quantified to describe the physiological bases underlying ontogenetic changes in metabolic rate at extreme cold temperatures (−1.5 °C). Rates of development from a four-arm to a six-arm larval stage were not affected by food availability. The respiratory cost of development to the six-arm larval stage (day 60) was 14.0 mJ for fed larvae and 8.2 mJ for unfed larvae. We observed three phases of metabolic regulation during development. During embryogenesis (day 0–22), increasing metabolic rates were proportional to increases in cell numbers. During early larval development (day 22–47), the differences in respiratory rate between fed and unfed larvae were not accounted for by cell number, but by cell-specific metabolic rate (respiratory rate normalized to DNA content). Once an advanced larval stage had been reached (day 47–60), cell-specific respiratory rate and mitochondrial densities (citrate synthase activity normalized to DNA content) were more equivalent between fed and unfed larvae, suggesting that size-specific metabolic rates were determined at a level of physiological regulation that was independent of cell numbers or feeding history.
Na+/K+-ATPase activity during early development and growth of an antarctic sea urchin
Authors: Leong P. K. K. , Manahan D. T.
Published: April 2021

In Antarctic environments, the physiological bases for long larval life spans under natural conditions of limited food availability are not understood. The Na+ pump is likely to be involved with hypometabolic regulation in such cold environments. Changes in the activity and metabolic importance of Na+/K+-ATPase were measured in embryos of the Antarctic sea urchin Sterechinus neumayeri and in larvae reared under different feeding conditions. The rate of increase of total Na+/K+-ATPase activity was 3.9 times faster in fed than in unfed larvae. During development and growth, there was an increase in the percentage of total, potential Na+/K+-ATPase activity that was physiologically utilized. In early (10-day-old) gastrulae, 17 % was utilized in vivo, increasing to 77 % in six-arm pluteus (48-day-old) larvae. The metabolic importance of in vivo Na+/K+-ATPase activity also increased during development, accounting for 12 % of metabolic rate at day 10 and 84 % at day 48. When compared at the same enzyme assay temperature (15 °C), the protein-specific total Na+/K+-ATPase activities for late embryonic (prism) and early larval (pluteus) stages of S. neumayeri were 2.6 times lower than those for comparable developmental stages of two temperate sea urchin species (Strongylocentrotus purpuratus and Lytechinus pictus).
Diet-induced plasticity in the taste system of an insect: localization to a single transduction pathway in an identified taste cell
Authors: Glendinning John I. , Ensslen Sonya , Eisenberg Michal E. , Weiskopf Phoebe
Published: April 2021

We studied exposure-induced sensitivity changes in an identified taste cell from Manduca sexta, a herbivorous caterpillar. This taste cell occurs within the lateral styloconic sensillum and responds selectively to compounds that humans characterize as bitter (e.g. caffeine, salicin and aristolochic acid). We made extracellular recordings from several classes of identified taste cell within the lateral sensillum, both before and after dietary exposure (for 48 h) to a suprathreshold concentration of caffeine, salicin or aristolochic acid. Our results revealed (1) that dietary exposure to caffeine desensitized the bitter-sensitive taste cell to caffeine, whereas dietary exposure to salicin or aristolochic acid did not desensitize the same taste cell to salicin or to aristolochic acid; (2) that dietary exposure to caffeine failed to alter the responsiveness of the sugar-, salt- or inositol-sensitive taste cells within the same sensillum; that the caffeine-induced desensitization phenomenon generalized to salicin, a compound that stimulates the same transduction pathway as caffeine, but not to aristolochic acid, a compound that stimulates a different pathway; and that chronically stimulating the lateral sensillum with caffeine, in the absence of ingestion, was sufficient to induce desensitization. We conclude that caffeine causes desensitization through a direct effect on a single transduction pathway within the bitter-sensitive taste cell.
Effect of low ambient mineral concentrations on the accumulation of calcium, magnesium and phosphorus by early life stages of the air-breathing armoured catfish Megalechis personata (Siluriformes: Callichthyidae)
Authors: Mol Jan H. , Atsma Wim , Flik Gert , Bouwmeester Hans , Osse Jan W. M.
Published: April 2021

The accumulation of calcium, magnesium and phosphorus was measured during an 8-week period in the early life stages of the air-breathing armoured catfish Megalechis personata acclimated to low-mineral fresh water (0.073 mmol l−1 calcium, 0.015 mmol l−1 magnesium, <0.001 mmol l−1 phosphate) and high-mineral fresh water (0.59 mmol l−1 calcium, 1.94 mmol l−1 magnesium, <0.001 mmol l−1 phosphate). The fish accumulated calcium twice as fast and phosphorus 1.5 times as fast in low-mineral fresh water (LMF) as in high-mineral fresh water (HMF), while the rate of accumulation of magnesium did not differ in LMF and HMF. The difference in the rates of accumulation of calcium and phosphorus between LMF and HMF was independent of the growth performance (food intake) in LMF and HMF. The mineral content of young M. personata from natural swamps and rainforest creeks in Suriname followed the LMF accumulation curves. The transition from aquatic respiration to bimodal respiration in the third week after hatching did not affect rates of mineral accumulation. The high rates of accumulation of calcium and magnesium of M. personata in LMF of 654 and 58 μmol h−1 kg−1, respectively, exceed the rates of uptake of calcium and magnesium of teleosts reported in the literature. The high rates of mineral accumulation in the early life stages of M. personata reflect the exponential growth during the first 8 weeks after hatching and the requirements of the juveniles while building their dermal armour. M. personata is well-adapted to neotropical fresh waters with an extremely low mineral content. The accumulation of calcium and phosphorus is discussed in relation to the function of the bony armour of M. personata.
The roles of the sun and the landscape in pigeon homing
Authors: Wallraff Hans G. , Chappell Jackie , Guilford Tim
Published: April 2021

It seems reasonable to assume that pigeons use visual features in the landscape for orientation when they are homing over familiar terrain. Experimental evidence to prove or disprove this possibility is, however, difficult to obtain. Here, we link the problem with the observation that deflections of initial orientation caused by clock-shift are often smaller than predicted on a pure sun compass basis. We substantiate the hypothesis that consistently reduced deflections and increased angular scatter occur only when pigeons are released in familiar areas where a remembered pattern of landscape features can conflict with the position of the sun. Repeated releases of the same individuals under clock-shift, or elimination of non-visual navigational clues (odours), appear to strengthen the conflicting influence of familiar visual landmarks. Accelerated returns of birds allowed to preview the surrounding familiar scenery before release also support the conclusion that the visual environment is included in the homing system of pigeons. The landscape, however, not only helps home-finding, if it is familiar, but may also have a distracting influence that contributes to the great variability of initial orientation patterns.
Muscle dynamics in skipjack tuna: timing of red muscle shortening in relation to activation and body curvature during steady swimming
Authors: Shadwick Robert E. , Katz Stephen L. , Korsmeyer Keith E. , Knower Torre , Covell James W.
Published: April 2021

Cyclic length changes in the internal red muscle of skipjack tuna (Katsuwonus pelamis) were measured using sonomicrometry while the fish swam in a water tunnel at steady speeds of 1.1–2.3 L s−1, where L is fork length. These data were coupled with simultaneous electromyographic (EMG) recordings. The onset of EMG activity occurred at virtually the same phase of the strain cycle for muscle at axial locations between approximately 0.4L and 0.74L, where the majority of the internal red muscle is located. Furthermore, EMG activity always began during muscle lengthening, 40–50 ° prior to peak length, suggesting that force enhancement by stretching and net positive work probably occur in red muscle all along the body. Our results support the idea that positive contractile power is derived from all the aerobic swimming muscle in tunas, while force transmission is provided primarily by connective tissue structures, such as skin and tendons, rather than by muscles performing negative work.

We also compared measured muscle length changes with midline curvature (as a potential index of muscle strain) calculated from synchronised video image analysis. Unlike contraction of the superficial red muscle in other fish, the shortening of internal red muscle in skipjack tuna substantially lags behind changes in the local midline curvature. The temporal separation of red muscle shortening and local curvature is so pronounced that, in the mid-body region, muscle shortening at each location is synchronous with midline curvature at locations that are 7–8 cm (i.e. 8–10 vertebral segments) more posterior. These results suggest that contraction of the internal red muscle causes deformation of the body at more posterior locations, rather than locally. This situation represents a unique departure from the model of a homogeneous bending beam, which describes red muscle strain in other fish during steady swimming, but is consistent with the idea that tunas produce thrust by motion of the caudal fin rather than by undulation of segments along the body.
Effects of sustained swimming on hepatic glucose production of rainbow trout
Authors: Shanghavi Deena S. , Weber Jean-Michel
Published: April 2021

The rate of hepatic glucose production (Raglucose) was measured by continuous infusions of 6-[3H]glucose in live rainbow trout (Oncorhynchus mykiss) before, during and after swimming for 3 h at 1.5 body lengths s−1 in a swim tunnel. Contrary to expectation, we found that sustained swimming causes a 33 % decline in the Ra,glucose of trout (from 7.6±2.1 to 5.1±1.3 μmol kg−1 min−1, means ± S.E.M., N=7), even though exercise of the same intensity elicits a two-to fourfold increase in all the mammalian species investigated to date. Measurements of catecholamine levels show that circulating [epinephrine] decreases by 30 % during exercise (from 4.7±0.3 to 3.3±0.4 nmol l−1, N=8), suggesting that this hormone is partly responsible for controlling the decline in Raglucose. The inhibiting effect of swimming on hepatic glucose production persists for at least 1 h after the cessation of exercise. In addition, rainbow trout can maintain a steady blood glucose concentration throughout sustained exercise by closely matching hepatic glucose production with peripheral glucose utilization, even though this species is generally considered to be a poor glucoregulator. This study provides the first continuous measurements of glucose kinetics during the transition from rest to work in an ectotherm and it suggests that circulating glucose is not an important fuel for aerobic locomotion in trout.
The control of blood pressure during external hypercapnia in the rainbow trout (Oncorhynchus mykiss)
Authors: Perry S. F. , Fritsche R. , Hoagland T. M. , Duff D. W. , Olson K. R.
Published: April 2021

Adult freshwater rainbow trout (Oncorhynchus mykiss) were exposed acutely (approximately 20 min) in a stepwise manner to increasing levels of environmental carbon dioxide ranging between 1.7 and 9.0 mmHg (0.23–1.2 kPa). Experiments were performed to examine, for the first time, the influence of hypercapnic acidosis on aspects of cardiovascular physiology including blood pressure, cardiac output and vascular resistance. Fish displayed dose (water CO2 partial pressure) -dependent increases in ventral aortic (13–39 %) and dorsal aortic (17–54 %) blood pressures that reflected marked increases in systemic vascular resistance (16–78 %); branchial vascular resistance was unaffected by hypercapnia. At the highest level of hypercapnia (9.0 mmHg), central venous pressure was significantly elevated by 54 %. Although cardiac output remained constant, heart rate was significantly lowered by 4–7 beats min−1 at the two highest levels of hypercapnia. To determine whether the cardiovascular responses to hypercapnia were being blunted by the stepwise increase in external , a separate group of fish was exposed directly to a single step of hypercapnia (water 8.0 mmHg). The cardiovascular responses were similar to those exhibited by the more gradually exposed fish except that central venous pressure did not increase and the extent of the bradycardia was greater (13 beats min−1).

After confirming the effectiveness of yohimbine in blocking the vasoconstrictory α-adrenoreceptors of the systemic vasculature, this antagonist was used as a tool to assess the importance of α-adrenoreceptor stimulation in promoting the cardiovascular responses during hypercapnia. Prior treatment of fish with yohimbine prevented the increased blood pressures and systemic vascular resistance during hypercapnia but did not influence the CO2-induced bradycardia. Plasma levels of catecholamines did not change during hypercapnia, and therefore the stimulation of the systemic α-adrenoreceptors presumably reflected increased sympathetic nerve activity.

To determine whether the cardiovascular changes elicited by hypercapnia were related to acidosis-induced hypoxaemia, fish were exposed to hypoxia in a stepwise manner (water 65–151 mmHg). The cardiovascular responses to hypoxia were markedly different from those to hypercapnia and consisted of pronounced increases in systemic and branchial vascular resistance, but only at the most severe level of hypoxia; ventral and dorsal aortic pressures were unaffected. The differences between the responses to hypercapnia and hypoxia, coupled with the smaller reductions in blood oxygen content during hypercapnia, support the hypothesis that the cardiovascular responses to CO2 are direct and are unrelated to hypoxaemia.
Increases in tissue free amino acid levels in response to prolonged emersion in marine crabs: an ammonia-detoxifying process efficient in the intertidal Carcinus maenas but not in the subtidal Necora puber
Authors: Durand Fabrice , Chausson Fabienne , Regnault Michèle
Published: April 2021

Carcinus maenas and Necora puber were exposed to air for 72 h and 18 h, respectively, at 18 °C. Changes in the free amino acid (FAA) content of their muscle, hepatopancreas and haemolymph were recorded during air-exposure and subsequent reimmersion. Muscle and hepatopancreas urate contents and haemolymph serum protein levels were also measured during emersion.

In air-exposed C. maenas, the muscle FAA pool increased significantly within the first 24 h of emersion. This increase was due to an increase in the non-essential amino acid (NEAA) pool only; the essential amino acid (EAA) pool did not change. In haemolymph, the EAA pool decreased during the first 24 h of emersion, whereas the FAA and NEAA pools did not change. However, in this compartment, glutamine levels increased throughout the air-exposure period. No significant changes in FAA, NEAA and EAA contents of the hepatopancreas were observed during the 72 h emersion.

In air-exposed N. puber, the FAA pools of muscle and hepatopancreas did not change, although changes in the levels of some amino acids were observed during the 18 h emersion period. In this species, large increases in both the NEAA and EAA pools in the haemolymph were recorded. High levels of urate were observed in the muscle and hepatopancreas of immersed N. puber, but no significant changes occurred during emersion. In contrast, immersed C. maenas exhibited low levels of urate in both compartments, and hepatopancreas urate levels increased slightly during emersion. Haemolymph protein content did not change in air-exposed N. puber, whereas it increased in the haemolymph of 72 h emersed C. maenas.

The origin of newly formed NEAAs and their role in ammonia detoxification, particularly in C. maenas, which is able to regulate its internal ammonia levels during such a prolonged emersion, are discussed.
Expression of membrane transporters in cane toad Bufo marinus oocytes
Authors: Markovich Daniel , Regeer Ralf R.
Published: April 2021

Membrane transport proteins (transporters and ion channels) have been extensively expressed in amphibian oocytes. The aims of this study were to determine whether oocytes from the cane toad Bufo marinus could be used as an alternative expression system to the broadly used Xenopus laevis oocytes. mRNAs encoding plasma membrane transporters NaSi-1 and sat-1 (sulphate transporters), NaDC-1 (dicarboxylate transporter), SGLT-1 (Na+/glucose cotransporter) and rBAT and 4F2 hc (amino acid transporters) were injected into B. marinus oocytes. All led to significant induction of their respective transport activities. Uptake rates were comparable with those in X. laevis oocytes, with the exception of rBAT, which was able to induce amino acid uptake only in X. laevis oocytes, suggesting that rBAT may require an endogenous X. laevis oocyte protein that is absent from B. marinus oocytes. Transport kinetics were determined for the NaSi-1 cotransporter in B. marinus oocytes, with identical results to those obtained in X. laevis oocytes. NaSi-1 specificity for the Na+ cation was determined, and the anions selenate, molybdate, tungstate, oxalate and thiosulphate could all inhibit NaSi-1-induced sulphate transport. This study demonstrates that cane toad oocytes can be used successfully to express plasma membrane proteins, making this a viable heterologous system for the expression of proteins.
Ultrastructural observations of adherent cell pairs in Hydra vulgaris
Authors: Takaku Yasuharu , Hariyama Takahiko , Kurachi Masashi , Tsukahara Yasuo
Published: April 2021

Previous morphological studies of cell sorting in Hydra vulgaris have considered only clusters of cells. Here, we present ultrastructural observations on the adherent region of cell pairs brought into contact (following dissociation) using a three-dimensional laser manipulator. There was a much larger area of close membrane contact between endodermal cell pairs in comparison with ectodermal cell pairs. Separation distances between membranes were categorized into three classes: closest distance (<4 nm); medium distance (5–25 nm); and cleavage (>25 nm). The sum of distances in the closest and medium categories as a proportion of total contact length was significantly greater (P<0.01) for endodermal cells (49.0±6.5 %) than for ectodermal cells (26.7±4.4 %). In intact Hydra, this sum of distances was also significantly greater for endodermal cells, indicating that newly adherent cells, even after adhesion for only 10 min, display similar morphological characteristics to cells in intact Hydra. This suggests that close membrane contacts contribute to differential cell adhesion, which may form the basis of the cell sorting process.
Roots as a site of hydrogen sulfide uptake in the hydrocarbon seep vestimentiferan Lamellibrachia sp.
Authors: Julian David , Gaill Françoise , Wood Eric , Arp Alissa J. , Fisher Charles R.
Published: April 2021

Vestimentiferan tubeworms have no mouth or gut, and the majority of their nutritional requirements are provided by endosymbiotic bacteria that utilize hydrogen sulfide oxidation to fix CO2 into organic molecules. It has been assumed that all vestimentiferans obtain the sulfide, O2 and CO2 needed by the bacteria across the plume (gill) surface, but some live in locations where very little sulfide is available in the sea water surrounding the plume. We propose that at least some of these vestimentiferans can grow a posterior extension of their body and tube down into the sea-floor sediment, and that they can use this extension, which we call the ‘root’, to take up sulfide directly from the interstitial water. In this study of the vestimentiferan Lamellibrachia sp., found at hydrocarbon seeps in the Gulf of Mexico at depths of approximately 700 m, we measured seawater and interstitial sulfide concentrations in the hydrocarbon seep habitat, determined the structural characteristics of the root tube using transmission electron microscopy, characterized the biochemical composition of the tube wall, and measured the sulfide permeability of the root tube. We found that, while the sulfide concentration is less than 1 μmol l−1 in the sea water surrounding the gills, it can be over 1.5 mmol l−1 at a depth of 10–25 cm in sediment beneath tubeworm bushes. The root tube is composed primarily of giant β-chitin crystallites (12–30 % of total mass) embedded in a protein matrix (50 % of total mass). Root tubes have a mean diameter of 1.4 mm, a mean wall thickness of 70 μm and can be over 20 cm long. The tubeworm itself typically extends its body to the distal tip of the root tube. The root tube wall was quite permeable to sulfide, having a permeability coefficient at 20 °C of 0.41×10−3 cm s−1, with root tube being 2.5 times more permeable to sulfide than trunk tube of the same diameter. The characteristics of the root suggest that it reaches down to the higher sulfide levels present in the deeper sediment and that it functions to increase the surface area available for sulfide uptake in a manner analogous to a respiratory organ.
Cardiovascular responses to adenosine in the antarctic fish Pagothenia borchgrevinki
Authors: Sundin Lena , Axelsson Michael , Davison William , Forster Malcolm E.
Published: April 2021

We have investigated the effects of adenosine on the cardiovascular system of the Antarctic fish Pagothenia borchgrevinki. Continuous measurements of ventral and dorsal aortic blood pressures, heart rate (fH) and ventral aortic blood flow (cardiac output, Q̇) were made using standard cannulation techniques and a single-crystal Doppler flowmeter. On line measurements of arterial were made using an oxygen electrode connected to an extracorporeal loop.

Adenosine (10 nmol kg−1) and the specific A1-receptor agonist N6-cyclopentyladenosine (CPA) elicited biphasic changes in the branchial and systemic resistances. While there was an initial decrease in the branchial resistance followed by an increase, the opposite was true for the systemic response. The resistance changes were significantly attenuated by aminophylline (a P1-receptor antagonist) and 8-cyclopentyltheophylline (CPT; an A1-receptor antagonist). In addition, adenosine induced an aminophylline-sensitive decrease in the arterial . The reduction was attenuated when pre-injection arterial was low.

Adenosine and CPA also caused a marked reduction in fH, with CPA being more potent. The bradycardia was blocked by aminophylline and CPT, demonstrating an involvement of A1 receptors in this response.
The mechanics of sound production in the puff adder Bitis arietans (Serpentes: viperidae) and the information content of the snake hiss
Authors: Young Bruce A. , Nejman Nancy , Meltzer Karen , Marvin Jessica
Published: April 2021

Puff adders (Bitis arietans), like many other snakes, hiss as part of their defensive repertoire. In B. arietans, the hisses have a clear quadraphasic pattern consisting of an initial exhalatory hiss, a brief transitional pause, an inhalatory hiss and a rest or breath-holding phase. Simultaneous recordings of body diameter, electrical activity in the intrinsic laryngeal musculature, airflow through the nasal passageway and sound production revealed that the anterior respiratory tract plays a passive role in hissing and that the costal pump is responsible for generating the quadraphasic pattern. During hissing, B. arietans uses the same mechanics previously described for normal respiratory ventilation in snakes. Analyses of artificial hisses reveal that the anterior respiratory tract of B. arietans has little ability to modify an exhalant airstream acoustically. The combination of the simple ventilatory mechanics used during hissing and the lack of acoustic modification of the exhalant airstream results in the production of an acoustically simple hiss. Cross-correlation matrix analyses of a variety of snake hisses showed a high degree of acoustic similarity between the sounds, almost approaching the levels determined for white noise. This high level of acoustic similarity reflects the low level of acoustic specialization within the sounds produced by snakes and the low potential for encoded information content.
The relationship between mechanical work and energy expenditure of locomotion in horses
Authors: Minetti A. E. , Ardigò L. P. , Reinach E. , Saibene F.
Published: April 2021

Three-dimensional motion capture and metabolic assessment were performed on four standardbred horses while walking, trotting and galloping on a motorized treadmill at different speeds. The mechanical work was partitioned into the internal work (WINT), due to the speed changes of body segments with respect to the body centre of mass, and the external work (WEXT), due to the position and speed changes of the body centre of mass with respect to the environment. The estimated total mechanical work (WTOT=WINT+WEXT) increased with speed, while metabolic work (C) remained rather constant. As a consequence, the ‘apparent efficiency’ (effAPP=WTOT/C) increased from 10 % (walking) to over 100 % (galloping), setting the highest value to date for terrestrial locomotion. The contribution of elastic structures in the horse’s limbs was evaluated by calculating the elastic energy stored and released during a single bounce (WEL,BOUNCE), which was approximately 1.23 J kg−1 for trotting and up to 6 J kg−1 for galloping. When taking into account the elastic energy stored by the spine bending and released as WINT, as suggested in the literature for galloping, WEL,BOUNCE was reduced by 0.88 J kg−1. Indirect evidence indicates that force, in addition to mechanical work, is also a determinant of the metabolic energy expenditure in horse locomotion.
Fluid secretion by isolated malpighian tubules of Drosophila melanogaster Meig.: effects of organic anions, quinacrine and a diuretic factor found in the secreted fluid
Authors: Riegel J. A. , Farndale R. W. , Maddrell S. H. P.
Published: April 2021

Para-aminohippuric acid (PAH, 0.2 and 1 mmol l−1) had no effect on the basal fluid secretion rate (FSR) of isolated Malpighian tubules of Drosophila melanogaster Meig. and did not affect stimulation of the FSR induced by adenosine 3′,5′ -monophosphate (cAMP). Phenol Red (phenolsulphonphthalein, PSP; 0.5 and 1 mmol l−1) slowed the FSR and abolished stimulation of the FSR by cAMP. Diodrast (1 mmol l−1) slightly, but significantly, reduced the FSR and greatly reduced the stimulation of the FSR normally provoked by cAMP and by the 3′,5′-monophosphates of guanosine (cGMP), inosine (cIMP) and uridine (cUMP). However, stimulation of the FSR by the 3′,5′ -monophosphate of cytidine (cCMP) was little affected by diodrast. Probenecid (0.2 or 1 mmol l−1) consistently stimulated the FSR, on average by approximately 25 %, but did not markedly inhibit the subsequent stimulation of the FSR by cAMP, cGMP or cIMP. However, the FSR of tubules stimulated by cGMP was temporarily lowered by probenecid. Quinacrine (0.1 mmol l−1) slowed basal FSR by an average of approximately 30 %, but subsequent stimulation of the FSR by cAMP was not noticeably affected. Both 0.1 mmol l−1 cAMP and 1 mmol l−1 probenecid stimulated adenylate cyclase activity in extracts of Malpighian tubules, but cIMP, cGMP, cUMP and diodrast were without effect in this regard. Uptake of radioactivity from a solution containing 500 nmol l−1 [3H]cAMP and 9.5 μmol l−1 cAMP was reduced by more than 90 % by 1 mmol l−1 PSP, by approximately 40 % by 0.2 mmol l−1 probenecid, by 36 % by 1 mmol l−1 diodrast and by 30 % by 1 mmol l−1 PAH. Neither 0.01 mmol l−1 ouabain nor 0.1 mmol l−1 quinacrine affected the uptake of [3H]cAMP by the Malpighian tubules. Fluid secreted by isolated Malpighian tubules of Drosophila melanogaster contains a factor that stimulated the FSR on average by approximately 50 %. The presence in the secreted fluid of cGMP at a concentration of 8.3 μmol l−1 did not explain the stimulatory effect on FSR.

These results support the existence of a carrier-mediated uptake of cyclic nucleotides into the Malpighian tubules of Drosophila melanogaster, possibly involving a multispecific transporter.
Osmoregulation in Drosophila melanogaster selected for urea tolerance
Authors: Pierce Valerie A. , Mueller Laurence D. , Gibbs Allen G.
Published: April 2021

Animals may adapt to hyperosmolar environments by either osmoregulating or osmoconforming. Osmoconforming animals generally accumulate organic osmolytes including sugars, amino acids or, in a few cases, urea. In the latter case, they also accumulate ‘urea-counteracting’ solutes to mitigate the toxic effects of urea. We examined the osmoregulatory adaptation of Drosophila melanogaster larvae selected to live in 300 mmol l−1 urea. Larvae are strong osmoregulators in environments with high NaCl or sucrose levels, but have increased hemolymph osmolarity on urea food. The increase in osmolarity on urea food is smaller in the selected larvae relative to unselected control larvae, and their respective hemolymph urea concentrations can account for the observed increases in total osmolarity. No other hemolymph components appear to act as urea-counteractants. Urea is calculated to be in equilibrium across body compartments in both selected and control larvae, indicating that the selected larvae are not sequestering it to lower their hemolymph osmolarity. The major physiological adaptation to urea does not appear to involve increased tolerance or improved osmoregulation per se, but rather mechanisms (e.g. metabolism, decreased uptake or increased excretion) that reduce overall urea levels and the consequent toxicity.
Voltage-dependent ionic currents in the ventromedial eclosion hormone neurons of Manduca sexta
Authors: Hewes Randall S.
Published: April 2021

The ventromedial cells (VM cells) of the moth Manduca sexta belong to a peptide hormone signaling hierarchy that directs an episodic and stereotyped behavior pattern, ecdysis. The VM cells respond to declining ecdysteroid titers at the end of the final larval molt with a transcription-dependent decrease in spike threshold and the abrupt release of the previously stockpiled neuropeptide, eclosion hormone (EH). This report describes whole-cell patch-clamp recordings of acutely isolated VM cell somata made to identify membrane currents that may underlie the increase in VM cell excitability during EH release and that may contribute to abrupt peptide release. There were at least three voltage-and time-dependent conductances in the VM cells. The inward current was carried exclusively by a voltage-dependent inward Ca2+ current (ICa), and the outward currents were a combination of a Ca2+-dependent outward K+ current (IK(Ca)) and a transient, voltage-dependent outward K+ current, the A current (IA). In current-clamp recordings, the currents present in the acutely isolated somata were sufficient to generate membrane properties similar to those observed in the VM cells in situ. This study represents the first step toward characterization of the mechanisms underlying the abrupt release of EH stores from the VM cells preceding ecdysis.
Lipid restructuring does not contribute to elevated activities of Na+/K+-ATPase in basolateral membranes from the gill of seawater-acclimated eel (Anguilla rostrata)
Authors: Crockett Elizabeth L.
Published: April 2021

In teleost fishes, increases in gill Na+/K+-ATPase activity accompanying the transition from fresh water to sea water may be attributed to changes in either the numbers of enzyme molecules present or to turnover number (kcat). The sensitivity of Na+/K+-ATPase to its chemical/physical environment in the membrane makes it plausible that modulation of enzyme activity may be driven, in part, by changes in membrane properties. In the current study, I test the hypothesis that lipid compositional changes (restructuring) contribute to the modulation of gill Na+/K+-ATPase activity. An enriched preparation of basolateral membranes was prepared from the gills of freshwater- and seawater-acclimated American eel (Anguilla rostrata). Phospholipid class distribution, fatty acyl chain compositions and cholesterol contents were determined. Phosphatidylcholine, the most abundant phospholipid present in gill basolateral membranes, makes up more than 60 % of the total phospholipid content in both freshwater- and seawater-acclimated animals. The contents of other phospholipids and major fatty acyl chains are also similar for the two acclimation groups. Cholesterol/phospholipid molar ratios are 0.28 for freshwater and 0.29 for seawater animals. The similarity between lipid compositions in membranes from freshwater- and seawater-acclimated eels indicates that lipid restructuring is not a mechanism for modulation of gill Na+/K+-ATPase activity in Anguilla rostrata, at least during the acclimation time course used in the present study.
Antibody to H+ V-Atpase subunit E colocalizes with portasomes in alkaline larval midgut of a freshwater mosquito (Aedes aegypti L.)
Authors: Zhuang Zhengpeng , Linser Paul J. , Harvey William R.
Published: April 2021

The pH profile, gross structure, ultrastructure and immunolabeling of the mosquito (Aedes aegypti) larval midgut are described as a first step in analyzing the role of plasma membrane H+ V-ATPase in the alkalization of the gut, nutrient uptake and ionic regulation. Binding of an antibody to H+ V-ATPase subunit E colocalizes with ‘portasomes’ (approximately 10 nm in diameter), which are thought to correspond to the V1 part of the H+ V-ATPase. In gastric caeca (pH 8), both antibody-binding sites and portasomes are located apically; in the anterior midgut (pH 10–11), they are located basally; and in the posterior midgut (pH≈8) they are again located apically. The hypothesis that the energization of alkalization is mediated by an H+ V-ATPase is supported by the inability of larvae to maintain the high pH after 72 h in 10 μM bafilomycin B1. Confirming earlier reports, the two principal epithelial cell types are designated as ‘columnar’ and ‘cuboidal’ cells. The apical plasma membranes (microvilli) of epithelial cells in the gastric caeca and basal infoldings of anterior midgut are invaded by mitochondria that lie within approximately 20 nm of the portasome-studded plasma membranes.

The colocalization of V-ATPase-immunolabeling sites and portasomes to specific plasma membranes within so-called ‘mitochondria-rich’ cells of gastric caeca and anterior midgut suggests that midgut alkalization in mosquitoes is achieved by molecular mechanisms similar to those that have been described in caterpillars, even though the gross structure of the midgut and the localization of the V-ATPase are dissimilar in the two species. In caterpillars, the high alkalinity is thought to break down dietary tannins, which block nutrient absorption; it may play a similar role in plant-detritus-feeding mosquito larvae. The colocalization of immunolabeling sites and portasomes, together with the presence of long, ‘absorptive-type’ microvilli in the posterior midgut, suggest that the V-ATPase energizes nutrient uptake there.
Contraction parameters, myosin composition and metabolic enzymes of the skeletal muscles of the etruscan shrew Suncus etruscus and of the common european white-toothed shrew Crocidura russula (Insectivora: soricidae)
Authors: Peters Thomas , Kubis Hans Peter , Wetzel Petra , Sender Susanne , Asmussen Gerhard , Fons Roger , Jürgens Klaus D.
Published: April 2021

In the Etruscan shrew, the isometric twitch contraction times of extensor digitorum longus (EDL) and soleus muscles are shorter than in any other mammal, allowing these muscles to contract at outstandingly high contraction frequencies. This species has the highest mass-specific metabolic rate of all mammals and requires fast skeletal muscles not only for locomotion but also for effective heat production and for an extremely high ventilation rate. No differences could be detected in the fibre type pattern, the myosin heavy and light chain composition, or in the activity of the metabolic enzymes lactate dehydrogenase and citrate synthase of the two limb muscles, the EDL and the soleus, which in larger mammalian species exhibit distinct differences in contractile proteins and metabolic enzymes. All properties determined in EDL and soleus muscles of Suncus etruscus, as well as in the larger Crocidura russula, are typical for fast-oxidative fibres, and the same holds for several other skeletal muscles including the diaphragm muscle of S. etruscus. Nevertheless, the EDL and soleus muscles showed different mechanical properties in the two shrew species. Relaxation times and, in C. russula, time to peak force are shorter in the EDL than in the soleus muscle. This is in accordance with the time course of the Ca2+ transients in these muscles. Such a result could be due to different parvalbumin concentrations, to a different volume fraction of the sarcoplasmic reticulum in the two muscles or to different Ca2+-ATPase activities. Alternatively, the lower content of cytosolic creatine kinase (CK) in the soleus compared with the EDL muscle could indicate that the observed difference in contraction times between these shrew muscles is due to the CK-controlled activity of their sarcoplasmic reticulum Ca2+-ATPase.
Metamorphosis in the summer flounder Paralichthys dentatus: changes in gill mitochondria-rich cells
Authors: Schreiber Alex M. , Specker Jennifer L.
Published: April 2021

Salinity tolerance changes during larval development and metamorphosis in the summer flounder (Paralichthys dentatus) and other teleosts. The physiological mechanisms responsible for osmoregulation during these early stages of development are not well understood. This study characterized changes in ultrastructure, intracellular membranes and immunoreactive Na+/K+-ATPase of mitochondria-rich cells (MRCs) in the gills of summer flounder during metamorphosis. Gill ultrastructure at the start of metamorphosis revealed only one type of MRC, which had weak reactivity to osmium and lacked a well-defined apical pit. In juveniles, two types of MRCs were observed: light-staining MRCs (LMRCs) with weak reactivity to osmium, and dark-staining MRCs (DMRCs) with strong reactivity to osmium and positioned adjacent to LMRCs. Compared with MRCs at the start of metamorphosis, the mitochondria of juvenile MRCs appeared smaller, with more transverse cristae and electron-dense matrices. Changes in MRCs during metamorphosis were also accompanied by increased immunoreactive Na+/K+-ATPase. These findings suggest that gill MRCs develop during the metamorphosis of summer flounder as the gill takes on an increasingly important osmoregulatory role.