bluuebunny/crossref_metadata_2025 huggingface dataset:
Endosymbiotic Chloroplasts in Molluscan Cells Contain Proteins Synthesized After Plastid Capture
Authors: Pierce Sidney K. , Biron Rachel W. , Rumpho Mary E.
Published: April 2021

Endosymbiotic chloroplasts within the cells of the ascoglossan slug Elysia chlorotica synthesize a variety of proteins including the large subunit of ribulose-1,5-bisphosphate-carboxylase oxygenase (RuBisCO) and the photosystem II protein D1. In addition, the effects of protein synthesis inhibitors suggest that some chloroplast-associated proteins are synthesized in the animal cytosol and subsequently translocated into the chloroplasts. Thus, the plastids not only synthesize proteins during this long-lived association, but the host cell seems to play a role in plastid protein turnover.
Pre- and Postembryonic Development, Growth and Turnover of Olfactory Receptor Neurones in Crayfish Antennules
Authors: Sandeman R. E. , Sandeman D. C.
Published: April 2021

The antennules of the crayfish Cherax destructor can first be observed as antero-laterally located lobes in embryos that have reached the 50 % stage of development. Clusters of cells that are probably the olfactory receptor neurones (ORNs) appear at the distal end of these lobes, which later differentiate into the lateral flagella of the antennules. New clusters of ORNs and segments are added at the proximal end of the lateral flagellum throughout the postembryonic stages and well into the juvenile adult stage. From a comparison of the exuvia and the newly emerged flagella in animals over a wide range of sizes, we conclude that, once the animals reach a certain size (approximately 7 mm carapace length), the most distal, and oldest, segments of the antennule are shed. Growth occurs from the proximal end of the flagellum, and the addition of new ORNs is the result of a delayed differentiation of the flagellar segments that takes place at the proximal end of the chemoreceptor array, about halfway along the flagellum.
Caffeine and Micromolar Ca2+ Concentrations Can Release Ca2+ from Ryanodine-Sensitive Stores in Crab and Lobster Striated Muscle Fibres
Authors: Lea Trevor J.
Published: April 2021

Ca2+ release mechanisms were studied in striated muscle from the walking legs of crabs using isometric tension recordings from isolated myofibrillar bundles. Caffeine-induced phasic contractions had properties consistent with Ca2+ release from a sarcoplasmic store, which could be optimally loaded in the presence of ATP at pCa 6.4–6.1. Ryanodine (10 μmol l−1) abolished the caffeine-induced contractions and in solutions with low Ca2+ buffering (0.1 mmol l−1 EGTA) itself caused phasic contractions, indicative of Ca2+ release. Ca2+-induced Ca2+ release (CICR) was observed in a pCa 5.8 solution (buffered by 1 mmol l−1 EGTA) as a phasic contraction of variable nature, inhibited by ryanodine (10 μmol l−1), procaine (10 mmol l−1) or benzocaine (5 mmol l−1). Ca2+ release was measured as a function of releasing pCa by using the force–time integral of the caffeine-induced contraction as an estimate of the Ca2+ remaining in the store. After the Ca2+ store had been loaded for 2 min at pCa 6.6, CICR was measured in the presence of 1 mmol l−1 Mg2+, 1 mmol l−1 EGTA and 5 mmol l−1 ATP. The threshold pCa for CICR was 6.0–6.4 under these conditions and more than 90 % of stored Ca2+ was released in 1 min by pCa values in the range 3.5–5.3. Benzocaine totally inhibited the release and promoted extra Ca2+ loading. Preliminary experiments showed a similar caffeine-releasable store in lobster abdominal muscle, which was slightly less sensitive to free [Ca2+]. It is concluded that in crustacean muscle caffeine and micromolar [Ca2+] can release Ca2+ from a ryanodine-sensitive store, which in many respects is similar to the sarcoplasmic reticulum of vertebrate skeletal and cardiac muscle.
Gaba-Like Immunoreactivity of an Identified Nonspiking Local Interneurone in the Crayfish Terminal Abdominal Ganglion
Authors: Nagayama Toshiki , Aonuma Hitoshi , Miyata Hiroki
Published: April 2021

Using an antiserum directed against γ-aminobutyric acid (GABA) to label neurones with GABA-like immunoreactivity, approximately 70 central neurones (68±9; mean ± S.E.M., N=9) were labelled in the terminal abdominal ganglion of the crayfish Procambarus clarkii. This mean number of neurones with GABA-like immunoreactivity represents approximately 10 % of the total number of neurones in the terminal ganglion. A combination of intracellular staining using Lucifer Yellow and immunocytochemical staining revealed that an identified nonspiking local interneurone (the local directionally selective interneurone, LDS) showed GABA-like immunoreactivity.
Control of Catecholamine and Serotonin Release from the Chromaffin Tissue of the Atlantic Hagfish
Authors: Bernier Nicholas J. , Perry Steve F.
Published: April 2021

An in situ saline-perfused systemic heart/posterior cardinal vein preparation of the Atlantic hagfish (Myxine glutinosa) was used to assess (1) the ability of the chromaffin tissue to release catecholamines in response to adrenocorticotropic hormone (ACTH; 7.5 i.u. kg−1), serotonin (250 nmol kg−1), carbachol (100 μmol kg−1), [Asn1-Val5]angiotensin II (Ang II; 100 nmol kg−1), histamine (0.3–300 μmol l−1) and a high-[K+] saline (60 mmol l−1), (2) whether serotonin is co-released with the catecholamines of the chromaffin tissues, and (3) the potential modulatory effects of NECA, an adenosine receptor agonist, and DPSPX, an adenosine receptor antagonist, on catecholamine release.

Bolus injections of ACTH, serotonin or carbachol, or perfusion with high-[K+] saline, all elicited the release of both adrenaline and noradrenaline. Pre-treatment with the serotonergic receptor antagonist methysergide or the cholinergic receptor antagonist hexamethonium abolished the serotonin- and carbachol-mediated catecholamine releases, respectively. Neither receptor antagonist affected the ACTH-mediated catecholamine release. Bolus injections of Ang II or perfusion with a range of histamine concentrations, two potent secretagogues in other vertebrates, did not elicit catecholamine secretion in hagfish.

While injections of Ang II or perfusion with the high-[K+] saline both elicited the release of serotonin, treatments with ACTH, carbachol or histamine did not. Hence, co-release of catecholamines and serotonin was elicited by non-specific cell membrane depolarization using K+, but not by the specific secretagogues assessed in this study.

The adenosine receptor agonist NECA and antagonist DPSPX significantly modified the secretory responses elicited by ACTH, serotonin and carbachol. The results suggest that adenosine may inhibit catecholamine release induced by serotonin or carbachol, while stimulating ACTH-induced release.

Although the contribution of the different secretagogues identified in this study has yet to be explored in vivo, our results suggest that the control of catecholamine and serotonin release from the aneural chromaffin tissue of the Atlantic hagfish can be achieved through hormonal and/or paracrine means.
The Physiology Of Massive Zinc Accumulation In The Liver Of Female Squirrelfish And Its Relationship To Reproduction
Authors: Hogstrand Christer , Gassman Nancy J. , Popova Bilyana , Wood Chris M. , Walsh Patrick J.
Published: April 2021

It is well known that zinc is an essential micronutrient and, as a rule, organisms keep relatively constant low levels of zinc to maintain cellular functions. The squirrelfish family (Holocentridae) is the only known exception from this rule. Squirrelfish accumulate very high concentrations of zinc in the liver. In the present study, we demonstrate that, while female squirrelfish store large amounts of zinc in the liver and ovaries, the males show zinc levels that are typical for vertebrates. The zinc content of the diet is the same in males and females, and zinc is not lost from the liver during starvation. Thus, the difference between genders in zinc storage is not dependent upon the diet. Rather, there are at least two processes that contribute to the accumulation in females. First, females possess high levels of two major zinc-binding proteins: metallothionein (MT) and a novel female-specific zinc-binding protein (FZnBP). In females, but not in males, almost all MT is present in the hepatocyte nucleus. FZnBP is exclusively found in the hepatocyte cytosol of females. Second, hepatocytes of female squirrelfish have a high capacity to transport zinc across the plasma membrane. In addition to the liver, only the gonads of females showed unusually high concentrations of zinc. Administration of exogenous oestrogen to females decreases the hepatic zinc concentration while there is a matching increase in the zinc content of the ovaries. Thus, oestrogen may trigger a redistribution of zinc from liver to ovaries. Together, our findings suggest that female squirrelfish may be uniquely adapted to detoxify zinc and to utilize it as a macronutrient for processes related to reproduction.
Molecular Forces Involved in Force Generation During Skeletal Muscle Contraction
Authors: Murphy Kenneth P. , Zhao Yan , Kawai Masataka
Published: April 2021

Recent advances in protein chemistry and the kinetic analysis of tension transients in skeletal muscle fibres have enabled us to elucidate the molecular forces involved in force generation by cross-bridges. On the basis of the temperature effect, we conclude that the elementary step that generates force is an endothermic reaction (the enthalpy change ΔH°=124 kJ mol−1 at 15 °C), which accompanies a large entropy increase (ΔS°= 430J K−1mol−1) and a reduction in the heat capacity (ΔCp=—6.4 kJ K−1 mol−1). Thus, it can be concluded that the force-generating step is an entropy-driven reaction. The above results suggest that hydrophobic interactions are the primary cause of force generation, and that polar interactions (hydrogen bonding and charge interactions) are involved to a lesser degree. On the basis of the thermodynamic data, we estimate that during force generation approximately 50 nm2 of surface area is involved for hydrophobic interactions and another 30 nm2 for polar interactions. These data suggest that both the actomyosin interaction and the cleft closure of the myosin head are essential for force generation.
Ontogeny of Visual and Mechanosensory Structure and Function in Atlantic Menhaden Brevoortia Tyrannus
Authors: Higgs Dennis M. , Fuiman Lee A.
Published: April 2021

The importance of visual, mechanoreceptive and auditory inputs to escape responses was examined in larvae of the Atlantic menhaden (Brevoortia tyrannus) presented with a simulated predatory stimulus. Ontogenetic changes in the retina, superficial neuromasts and auditory bullae were examined in concert with behavioral trials in which sensory inputs were selectively blocked. Menhaden larvae showed a decrease in cone photoreceptor density and first developed rod photoreceptors when their total length (TL) reached 8–10 mm; they began summing photoreceptive inputs at 12–14 mm TL. Inflation of the auditory bullae was complete by 15 mm TL. The proliferation of superficial neuromasts varied depending on their location, with cephalic superficial neuromasts decreasing in number beginning at 19 mm TL and numbers of trunk neuromasts continuing to increase throughout the larval period. In behavioral trials, responsiveness and the reactive distance to the approaching probe increased with increasing larva total length when all sensory inputs were available (control larvae). When visual inputs were blocked, responsiveness was lower than in control larvae, but still increased ontogenetically, while reactive distance showed no difference between control larvae and those lacking visual information. When neuromasts were ablated, ontogenetic increases in responsiveness and reactive distance were absent. Inflation of the auditory bullae had no discernible effect on behavior. The anatomical and behavioral results suggest that both vision and mechanoreception are used to trigger a response to a looming predatory stimulus and that mechanoreception, but not vision, contributes to the timing of the response. Ontogenetic improvements in performance are attributed mainly to neuromast proliferation and not to ontogenetic changes in the retina.
An N-Terminal Partial Sequence of the 13 kDa Pycnopodia Helianthoides Sperm Chemoattractant ‘Startrak’ Possesses Sperm-Attracting Activity
Authors: Miller Richard L. , Vogt Richard
Published: April 2021

Freshwater extracts of starfish ovaries were used to purify the sperm-attracting peptide ‘startrak’ from Pycnopodia helianthoides using hydrophobic interaction chromatography and DEAE–high-pressure liquid chromatography. Partially purified attractant had a molecular mass of 13 kDa, estimated from gel filtration and polyacrylamide gel electrophoresis results. The purified attractant was subjected to amino acid analysis and direct sequencing, and was found to consist largely of a single peptide composed of an estimated 127 residues based on a molecular mass of 13 kDa. An N-terminal sequence of amino acids from positions 3 to 34 was obtained and synthesized as: NH 2-Ala-Glu-Leu-Gly-Leu-Cys-Ile-Ala-Arg-Val-Arg-Gln-Gln-Asn-Gln-Gly-Gln-Asp-Asp-Val-Ser-Ile-Tyr-Gln-Ala-Ile-Met-Ser-Gln-Cys-Gln-Ser-COOH. The synthetic peptide possessed sperm-attracting activity 130 times greater than the activity of partially purified startrak and showed a pattern of species-specificity of sperm chemotaxis similar to that of startrak. Antibody prepared against synthetic peptide removed the sperm-attracting activity from crude and partially purified preparations of startrak. The partial sequence of startrak was not homologous with that of any of the known echinoid sperm motility-activating peptides.
In Vitro Differentiation Of Isolated Stem Cells From The Midgut Of Manduca Sexta Larvae
Authors: Sadrud-Din Sakeena , Loeb Marcia J. , Hakim Raziel S.
Published: April 2021

Isolated spherical stem cells from midguts of pharate fourth-instar larvae of Manduca sexta proliferated in vitro in the presence of 1 ng ml-1 20-hydroxyecdysone and co-cultured fat body tissue or cell-free fat body extract from M. sexta, Lymantria dispar or Heliothis virescens. In this environment, the stem cells were able to undergo mitosis and increase in number. However, stem cells were only able to differentiate to mature goblet and columnar cells when cell-free conditioned medium, taken from midgut cell cultures containing mature cells as well as stem cells and differentiating forms, was introduced into the culture medium. The presence of early and mature goblet cells, lying randomly on their sides, suggested that cell polarity developed in vitro as an intrinsic property of individual cells rather than with reference to an external inductive material. The differentiation factor (or factors) from the conditioned medium appears to include a heat-stable, peptide-like molecule of 10 kDa or less.
Structural Correlates of Speed and Endurance in Skeletal Muscle: The Rattlesnake Tailshaker Muscle
Authors: Schaeffer Paul J. , Conley Kevin E. , Lindstedt Stan L.
Published: April 2021

The western diamondback rattlesnake Crotalus atrox can rattle its tail continuously for hours at frequencies approaching 90 Hz. We examined the basis of these fast sustainable contractions using electromyography, data on oxygen uptake and the quantitative ultrastructure of the tailshaker muscle complex. The tailshaker muscle has no apparent unique structures; rather, the relative proportions of the structures common to all skeletal muscles appear to be present (1) to minimize activation, contraction and relaxation times via an extremely high volume density of sarcoplasmic reticulum (26 %) as well as, (2) to maximize ATP resysnthesis via a high volume density of mitochondria (26 %). The high rate of ATP supply is reflected in the in vivo muscle mass-specific oxygen uptake of this group of muscles which, at 585 ml O2 kg−1 min−1 during rattling at 30 °C body temperature, exceeds that reported for other ectotherm and many endotherm muscles. Since the change in oxygen uptake paralleled that of the rattling frequency over the range of measured body temperatures, there was a nearly constant O2 cost per muscle contraction (0.139±0.016 μl O2 g−1). Electromyo-graphic analysis suggests that each of the six muscles that make up the shaker complex may be a single motor unit. Finally, the maximum rate of mitochondrial oxygen uptake is similar to that of various mammals, a hummingbird, a lizard, an anuran amphibian and of isolated mitochondria (at 10 000–40 000 molecules O2 s−1 μm2 of cristae surface area, when normalized to 30 °C), suggesting a shared principle of design of the inner mitochondrial membrane among the vertebrates.
Localization Of Bursicon In Ccap-Immunoreactive Cells In The Thoracic Ganglia Of The Cricket Gryllus Bimaculatus
Authors: Kostron Barbara , Kaltenhauser Ulrike , Seibel Birgit , Bräunig Peter , Honegger H. Willi
Published: April 2021

Bursicon is a neuropeptide that induces tanning of the cuticle in freshly moulted insects. In an earlier investigation, we demonstrated that bursicon activity can be detected throughout the ventral nerve cord of the cricket Gryllus bimaculatus. This study aims at identifying the neurosecretory cells within the thoracic ganglia that produce bursicon. When homogenates of anterior pieces of thoracic ganglia were separated using SDS gel electrophoresis, proteins with bursicon activity could be eluted only from a slice of the gel spanning the 28–33 kDa region. In the anterior lateral cortex of the thoracic ganglia, there are two bilaterally paired neurosecretory cells with large vacuoles that project contralaterally to neurohaemal release sites associated with segmental nerves N5 and N6. These cells and their processes in N5 and N6 were labelled using antisera against crustacean cardioactive peptide (CCAP). The cell projecting into N6 showed a Tyndall effect (i.e. appeared opaque under oblique illumination) in older adults, and single isolated somata contained bursicon activity. Homogenates of nerves N5 and N6 also showed bursicon activity, but neither bursicon activity nor CCAP-immunoreactive processes were found in segmental nerve N4. The thoracic connectives, which contain three major CCAP-immunoreactive processes, also showed bursicon activity. Homogenates of posterior pieces of the thoracic ganglia did not contain bursicon activity. Western blots demonstrated that the anti-CCAP serum does not recognize the 30 kDa bursicon-active protein fraction. These results suggest that a CCAP-like neuropeptide and a protein with bursicon activity are co-localized in the anterior lateral neurosecretory cells of the thoracic ganglia and in their segmental homologues in the other ganglia. Additionally, we have shown using western blots that a monoclonal antibody raised against a 56 kDa protein from the housefly Musca domestica, a protein thought to be bursicon, does not label the 30 kDa bursicon-active protein of crickets. However, this antibody does label an unidentified 56 kDa protein isolated from anterior as well as posterior pieces of thoracic ganglia.
Adjustment of K′ for the Creatine Kinase, Adenylate Kinase and Atp Hydrolysis Equilibria to Varying Temperature and Ionic Strength
Authors: Teague Walter E. , Golding Elke M. , Dobson Geoffrey P.
Published: April 2021

Comparative physiologists and biochemists working with tissues at varying temperatures and ionic strength are required to adjust apparent equilibrium constants (K′) of biochemical reactions to the experimental conditions prior to calculating cytosolic bioenergetic parameters (transformed Gibbs free energy of formation, fΔG′ATP; cytosolic phosphorylation ratio, [ATP]/[ADP][Pi]; [phosphocreatine]:[orthophosphate] ratio [PCr]/[Pi]) and kinetic parameters (free [ADP], [Pi] and [AMP]). The present study shows how to adjust both K′ and the equilibrium constants of reference reactions (Kref) of creatine kinase (ATP: creatine N-phosphotransferase; EC 2.7.3.2), adenylate kinase (ATP:AMP phosphotransferase; EC 2.7.4.3) and adenosinetriphosphatase (ATP phosphohydrolase; EC 3.6.1.3) to temperature and ionic strength. This information, together with our previous study showing how to adjust equilibria to varying pH and pMg, is vital for the quantification of organ and tissue bioenergetics of ectotherms and endotherms under physiological conditions.
Roles of Gastric Gata DNA-Binding Proteins
Authors: Maeda Masatomo , Kubo Kentaro , Nishi Tsuyoshi , Futai Masamitsu
Published: April 2021

The gastric H+/K+-ATPase is a P-type ATPase that is specifically expressed in gastric parietal cells and is responsible for acid secretion into the stomach. We have found one or more gastric mucosal nuclear proteins that recognize a sequence motif in the 5’-upstream regions of the H+/K+-ATPase α-and β-subunit genes. This gastric motif, (G/C)PuPu(G/C)NGAT(A/T)PuPy, may be a binding site for a positive transcriptional regulator that functions specifically in parietal cells. We further demonstrated using cDNA cloning and in situ hybridization that novel zinc-finger proteins (GATA-GT1 and GATA-GT2) are present in the gastric parietal cells and bind to this motif. The proteins activate the transcription of the reporter gene with the 5’-upstream region of the H+/K+-ATPase β-subunit gene. These results suggest that gastric GATA DNA-binding proteins have important roles in transcriptional activation of H+/K+-ATPase genes in the parietal cells.
Age-Related Variation in Body Temperature, Thermoregulation and Activity in A Thermally Polymorphic Dragonfly
Authors: Marden James H. , Kramer Melissa G. , Frisch John
Published: April 2021

Thoracic temperatures (Tth) of Libellula pulchella dragonflies during activity in the field were compared between age classes and with laboratory measures of optimal thoracic temperature for flight performance (Tth,opt; a trait that varies during adult maturation in this species). Newly emerged adults (tenerals) had mean Tth values during flight (34.5 °C; range 29–40 °C) that did not differ from their mean Tth,opt (34.6 °C; range 28.5–43.8 °C). Mature adults had higher and more precisely regulated thoracic temperatures (mean Tth 41.7 °C; range 37.5–45.2 °C), which were somewhat lower than their mean Tth,opt (43.6 °C; range 38.7–49.9 °C). Among matures, behaviors requiring the highest levels of flight exertion (aerial copulation; mate guarding; escalated territorial contests) caused an elevation of Tth above that of concurrently sampled individuals engaged in routine flight (mean Tth difference 1.3 °C), which raised mean Tth to a level that was not significantly different from Tth,opt (42.5 versus 43.5 °C). Compared with tenerals, matures spent more time flying, made longer-duration flights and showed a more restricted pattern of daily activity. Sympatric Anax junius dragonflies that regulate Tth endothermically had a uniform pattern of activity across the entire day, i.e. occupied a broader ecological niche than that of L. pulchella. These results support the hypotheses that optimal body temperature evolves to match the elevated body temperatures that occur during exercise and that the ecological benefits of an expanded niche are a secondary benefit rather than a primary selective force during the evolution of homeothermy and high body temperatures.
Modulation of Membrane Currents by Cyclic Amp in Cleavage-Arrested Drosophila Neurons
Authors: Alshuaib Waleed B. , Byerly Lou
Published: April 2021

A number of Drosophila learning mutants have defective intracellular second-messenger systems. In an effort to develop techniques that will allow direct measurement of the effects of these mutations on whole-cell neuronal membrane currents, the perforated-patch whole-cell (PPWC) technique has been applied to cleavage-arrested cultured embryonic Drosophila neurons. This technique permits the measurement of membrane currents without disturbing the intracellular environment. As a result of the maintenance of the intracellular environment, Drosophila neuron currents are found to be much more stable than when measured using the conventional whole-cell (CWC) patch-clamp technique. Ca2+ channel currents, which typically ‘wash out’ within a few minutes of the beginning of CWC recording, are stable for the duration of the seal (tens of minutes) when measured using the PPWC technique. Since the learning mutations dunce and rutabaga disrupt cyclic AMP signalling, the actions of externally applied dibutyryl cyclic AMP (db-cAMP) and theophylline on Ca2+ and K+ channel currents were studied. db-cAMP and theophylline enhanced the Ba2+ current, carried by Ca2+ channels, but had no effect on the K+ current in the cleavage-arrested neurons. However, the large variability and reduction in density of Ba2+ and K+ currents raise questions about the suitability of using these cleavage-arrested cells as models for Drosophila neurons.
Short-Term Emersion Affects Cardiac Function and Regional Haemolymph Distribution in the Crab Cancer Magister
Authors: Airriess Chris N. , Mcmahon Brian R.
Published: April 2021

Changes in cardiac function and arterial haemolymph flow associated with 6 h of emersion were investigated in the crab Cancer magister using an ultrasonic flowmeter. This species is usually found sublittorally but, owing to the large-scale horizontal water movements associated with extreme tides, C. magister may occasionally become stranded on the beach. Laboratory experiments were designed such that the emersion period was typical of those that might be experienced by this crab in its natural environment.

The frequency of the heart beat began to decline sharply almost immediately after the start of the experimental emersion period. Cardiac stroke volume fell more gradually. The combined reduction in these two variables led to a maximum decrease in cardiac output of more than 70 % from the control rate. Haemolymph flow through all the arteries originating at the heart, with the exception of the anterior aorta, also declined markedly during emersion. As the water level in the experimental chamber fell below the inhalant branchial openings, a stereotypical, dramatic increase in haemolymph flow through the anterior aorta began and this continued for the duration of the emersion period.

The rapid time course of the decline in heart-beat frequency and the increase in haemolymph flow through the anterior aorta suggest a neural mechanism responding to the absence of ventilatory water in the branchial chambers. These responses may be adaptations, respectively, to conserve energy by reducing the minute volume of haemolymph pumped by the heart and to protect the supply of haemolymph to cephalic elements of the central nervous system. The decline in cardiac stroke volume, which occurs more slowly over the emersion period, may be a passive result of the failure to supply sufficient O2 to meet the aerobic demands of the cardiac ganglion.
In Vivo Muscle Protein Synthesis Rates in the American Lobster Homarus Americanus During the Moult Cycle and in Response to 20-Hydroxyecdysone
Authors: Haj Alicia J. El , Clarke Susan R. , Harrison Paul , Chang Ernest S.
Published: April 2021

Simultaneous measurements of in vivo rates of protein synthesis (Ks) in claw, leg and abdominal muscles were made in the American lobster Homarus americanus at three stages of the moult cycle. Ks values are significantly elevated during the premoult (stage D2–D3) and fall during the intermoult (stage C4) periods in all three muscles. Postmoult (stage A/B) levels are not significantly elevated above intermoult levels. Intermoult levels are between 0.3 and 0.4 % protein synthesized per day. In the premoult animals, the ribosomal activity (milligrams protein synthesized per microgram RNA per day) of the claw, abdominal and leg muscles is elevated three-to fivefold. The claw muscle maintains an elevated ribosomal activity into the postmoult stage whereas, by this stage, that of the other muscle tissues has fallen to intermoult levels. The RNA/protein ratios of the three muscle groups from intermoult, premoult and postmoult animals do not show any significant differences. 18S ribosomal RNA levels fluctuate slightly, with no consistent pattern over the moult cycle. In vivo injection of premoult concentrations of 20-hydroxyecdysone (20-HE) into intermoult lobsters results in elevated Ks values and ribosomal activity for the muscles after 3 days. RNA/protein ratios remain constant in the muscles in response to injections of 20-HE in vivo. In vitro preparations of leg muscle treated with 20-HE did not show similar elevated rates of protein synthesis.
Power at the Expense of Efficiency in Contraction of White Muscle Fibres From Dogfish Scyliorhinus Canicula
Authors: Curtin N. A. , Woledge R. C.
Published: April 2021

Work and heat production of white myotomal muscle fibres from dogfish were measured during sinusoidal movement (0.71–5.0 Hz) at 12 ˚C. Stimulus phase (stimulus timing relative to movement) and duty cycle (stimulus duration as a fraction of movement cycle duration) were varied to determine the parameters optimal for power output and for efficiency (work/total energy output). Movements of 0.067 and 0.120L0 were used, where L0 is the muscle fibre length giving maximum force in an isometric tetanus. At each frequency of movement and duty cycle, the stimulus phase giving the highest power was the same as that giving the highest efficiency. In contrast, at each frequency and optimal stimulus phase, the dependence of power on duty cycle was very different from the dependence of efficiency on duty cycle. Power generally increased with increasing duty cycle, whereas efficiency decreased. Thus, high power can be achieved at the expense of efficiency by adjusting stimulus duty cycle. When stimulus phase and duty cycle were optimized, efficiency was always higher for the larger distance of movement. The efficiency of energy conversion can be maintained at a high level as the frequency of movement increases from 1.25 to 5.0 Hz.
Dipeptide Transport by Crustacean Hepatopancreatic Brush-Border Membrane Vesicles
Authors: Thamotharan M. , Ahearn G. A.
Published: April 2021

Epithelial brush-border membrane vesicles (BBMVs) of lobster (Homarus americanus) hepatopancreas were formed by a Mg2+ precipitation technique. In these BBMVs, [14C]glycylsarcosine ([14C]Gly-Sar) uptake was stimulated by a transmembrane proton gradient. transmembrane K+ diffusion potential (inside negative) stimulated [14C]Gly-Sar uptake above that observed with short-circuited vesicles, while an inwardly directed Na+ gradient had no stimulatory effect on peptide uptake. [14C]Gly-Sar influx (over 10 s) occurred by a low-affinity, saturable, proton-gradient-dependent carrier system (Kt=5.90±0.13 mmol l−1, Jmax=4662±487 pmol mg−1 protein 10 s−1; mean ± S.E.M., N=3). This carrier exhibited a high-affinity proton binding site (KH=235±25 nmol l−1; pK=6.6) and an apparent 1H+:1Gly-Sar transport stoichiometry. Influx of 0.1 mmol l−1 [14C]Gly-Sar into lobster hepatopancreatic BBMVs was significantly (P<0.01) cis-inhibited by 10 mmol l−1 diethylpyrocarbonate and by a variety of other dipeptides (10 mmol l−1), suggesting a broad transport specificity. These observations strongly suggest that transport of peptides into crustacean hepatopancreas is proton-gradient-dependent and electrogenic, qualitatively resembling the peptide transport paradigm proposed for fish and mammals.
Intestinal Na+ and Cl− Levels Control Drinking Behavior in the Seawater-Adapted Eel Anguilla Japonica
Authors: Ando Masaaki , Nagashima Kei
Published: April 2021

To analyze drinking mechanisms in seawater teleosts, seawater-adapted eels were used as a model system. When the intestine of the eel was perfused with iso-osmotic mannitol, the eels drank sea water. However, when the perfusion medium was switched to iso-osmotic NaCl, seawater drinking was depressed. This depression was observed even after blocking NaCl absorption across the intestine by replacement of the perfusate with choline chloride or by treatment with furosemide, an inhibitor of NaCl and water absorption across the eel intestine. Furthermore, depression of drinking rate preceded an increase in urine flow by over 1 h. These results indicate that this depression is not due to a recovery of blood volume and suggest that intestinal Cl− itself inhibits drinking. Direct action of luminal Cl− on drinking behavior was further supported by the observation that perfusion with iso-osmotic NMDG–HCl, Tris–HCl, choline chloride and RbCl all inhibited seawater drinking. When NaCl in the perfusion medium was replaced with sodium acetate, sodium butyrate, sodium methylsulfate or NaSCN, the drinking rate was enhanced threefold, suggesting that Na+ itself stimulates drinking in the absence of Cl−. In the present study, concentrations of Na+ and Cl− in the swallowed fluid were also measured simultaneously. As the drinking rate was enhanced, the Na+ and Cl− concentrations in the gastrointestinal fluid were increased. On the basis of these results, it seems possible that high concentrations of Cl− in the intestine reduce the drinking rate, thus lowering esophageal Cl− concentration due to desalination of the ingested sea water. When Cl− concentration in the intestine falls below a certain level, Na+ will stimulate seawater drinking again.
Shape oscillations of human neutrophil leukocytes: characterization and relationship to cell motility
Authors: Ehrengruber Markus U. , Deranleau David A. , Coates Thomas D.
Published: April 2021

When neutrophil leukocytes are stimulated by chemotactic factors or by substratum contact, they change their shape. Shape changes are a prerequisite for cellular migration and typically involve the extrusion of thin, veil-like lamellipods and the development of morphological polarity. Stimulation also leads to changes in the neutrophil content of filamentous actin (F-actin), which is the major cytoskeletal component. Suspensions of human neutrophils stimulated with chemoattractants exhibit sinusoidal light-scattering oscillations with a period of approximately 8 s at 37 °C. These oscillations arise from periodic fluctuations in the cell body size caused by lamellipod extension and retraction cycles. The light-scattering oscillations are paralleled by corresponding oscillations in F-actin content. This raises the interesting possibility that cyclic actin polymerization constitutes the driving force for shape oscillations of suspended neutrophils. Similar periodic shape changes are present in neutrophils crawling on a surface, suggesting that shape oscillations are important for neutrophil motion. This review summarizes our present knowledge about shape oscillations in suspended and crawling neutrophils and discusses a possible role for these oscillations in neutrophil motility.
Local Differences in Myotendinous Junctions in Axial Muscle Fibres of Carp (Cyprinus Carpio L.)
Authors: Spierts Igor L. Y. , Akster H. A. , Vos I. H. C. , Osse J. W. M.
Published: April 2021

We studied the myotendinous junctions of anterior and posterior red and white axial muscle fibres of carp using stereology. In posterior axial muscle fibres of swimming fish, stress (load on the myotendinous junction) must be higher than in anterior fibres as posterior fibres have a longer phase of eccentric activity. As we expected the magnitude of the load on the junction to be reflected in its structure, we compared the interfacial ratio, the ratio between the area of the junctional sarcolemma and the cross-sectional fibre area, of these muscle fibres. This ratio differed significantly between the investigated groups, with red fibres and posterior fibres having the larger ratios. The higher interfacial ratio of posterior myotendinous junctions is in accordance with the proposition mentioned above. The difference between myotendinous junctions of red and white fibres is probably related to a difference in the duration of the load on the junction.
The Mechanical Properties of Fin Whale Arteries are Explained by Novel Connective Tissue Designs
Authors: Gosline John M. , Shadwick Robert E.
Published: April 2021

The aortic arch and the descending aorta in the fin whale (Balaenoptera physalus) are structurally and mechanically very different from comparable vessels in other mammals. Although the external diameter of the whale’s descending thoracic aorta (approximately 12 cm) is similar to that predicted by scaling relationships for terrestrial mammals, the wall thickness:diameter ratio in the whale (0.015) is much smaller than the characteristic value for other mammals (0.05). In addition, the elastic modulus of the thoracic aorta (12 MPa at 13 kPa blood pressure) is about 30 times higher than in other mammals. In contrast, the whale’s aortic arch has a wall thickness/diameter ratio (0.055) and an elastic modulus (0.4 MPa) that are essentially identical to those for other mammals. However, the aortic arch is unusual in that it can be deformed biaxially to very large strains without entering a region of high stiffness caused by the recruitment of fully extended collagen fibres. Chemical composition studies indicate that the elastin:collagen ratio is high in the aortic arch (approximately 2:1) and that this ratio falls in the thoracic (approximately 1:2) and abdominal (approximately 1:3) aortas, but the magnitude of the change in composition does not account for the dramatic difference in mechanical properties. This suggests that there are differences in the elastin and collagen fibre architecture of these vessels. The descending aorta contains dense bands of tendon-like, wavy collagen fibres that run in the plane of the arterial wall, forming a fibre-lattice that runs in parallel to the elastin lamellae and reinforces the wall, making it very stiff. The aortic arch contains a very different collagen fibre-lattice in which fibres appear to have a component of orientation that runs through the thickness of the artery wall. This suggests that the collagen fibres may be arranged in series with elastin-containing elements, a difference in tissue architecture that could account for both the lower stiffness and the extreme extensibility of the whale’s aortic arch. Thus, both the structure and the mechanical behaviour of the lamellar units in the aortic arch and aorta of the whale have presumably been modified to produce the unusual mechanical and haemodynamic properties of the whale circulation.
Elevation of Plasma Somatolactin Concentrations During Acidosis in Rainbow Trout (Oncorhynchus Mykiss)
Authors: Kakizawa Sho , Kaneko Toyoji , Hirano Tetsuya
Published: April 2021

Somatolactin (SL) is a putative pituitary hormone of the growth hormone (GH)/prolactin (PRL) family in fish; its physiological function has yet to be determined. Acidosis was induced in rainbow trout (Oncorhynchus mykiss) by exposure to acidic water (pH 4.5) or by exhaustive exercise, and plasma concentrations of SL, PRL and GH as well as other plasma parameters were examined. A decrease in blood pH was observed in fish from 1 day after water acidification until the end of the experiment at day 7. Plasma SL levels in the acid-exposed fish increased, reached a peak on day 1 and then returned to the initial level by day 4. No change was seen in plasma concentrations of PRL throughout the experiment. Plasma levels of GH, in contrast, decreased in the acid-exposed fish on days 2 and 4. Plasma cortisol levels in the acid-exposed fish were higher than the control level on days 4 and 7, although plasma cortisol levels did not increase above the initial level in response to water acidification. There was no significant change in the expression of SL-, PRL-and GH-mRNA in the pituitary gland. Levels of plasma Na+ and lactate were reduced 12 h after water acidification and remained low throughout the experiment. Exhaustive exercise in shallow water at neutral pH (7.5) resulted in a transient but pronounced acidosis, associated with increases in plasma SL, cortisol, Cas2+, phosphate and lactate levels. Plasma SL levels returned to the initial level along with the recovery of blood acid–base status. In contrast, plasma cortisol levels stayed elevated even 24 h after exercise. There was no correlation between plasma PRL and GH levels and blood pH. Elevation of plasma SL levels during acidosis suggests the possible involvement of SL in acid–base regulation in rainbow trout.
Locust ION Transport Peptide (ITP): Primary Structure, cDNA and Expression in a Baculovirus System
Authors: Meredith J. , Ring M. , Macins A. , Marschall J. , Cheng N. N. , Theilmann D. , Brock H. W. , Phillips J. E.
Published: April 2021

Ion transport peptide (ITP) purified from locust nervous corpus cardiacum (CC) has previously been shown to stimulate salt and water reabsorption and inhibit acid secretion in the ileum of Schistocerca gregaria. We used the partial amino acid sequence of purified ITP to derive degenerate primers. These were used to amplify a cDNA from brain RNA using reverse transcription and the polymerase chain reaction (RtPCR). This sequence was extended using anchored PCR to yield a partial, 517 bp cDNA clone. This cDNA encodes a putative ITP prohormone which could be cleaved at two dibasic amino acid sites to yield a 72 residue active amidated peptide. The deduced amino acid sequence from the cDNA agrees completely with the amino acid sequence and molecular mass (8564 Da) derived from analysis of purified ITP. Relative to a family of crustacean hyperglycaemic hormones (CHH), all six cysteine residues and many other amino acid residues are conserved in ITP, establishing that ITP is a homologue. However, CHH, crab eyestalk and CC extracts from distantly related insects have no action, whereas CC extracts from closely related insects are active on the locust ITP assay, showing that the bioassay is selective. Insect Sf9 cells transfected with a baculovirus containing our partial cDNA secreted a potent stimulant of locust ileal transport, confirming that the peptide encoded by our ITP clone has biological activity. The mRNA for ITP is restricted to the brain and CC. Interestingly, a related mRNA is observed in other tissues which are not active on the ITP bioassay.
The Advantages of an Unsteady Panel Method in Modelling the Aerodynamic Forces on Rigid Flapping Wings
Authors: Smith Michael J. C. , Wilkin Peter J. , Williams Marc H.
Published: April 2021

This paper responds to research into the aerodynamics of flapping wings and to the problem of the lack of an adequate method which accommodates large-scale trailing vortices. A comparative review is provided of prevailing aerodynamic methods, highlighting their respective limitations as well as strengths. The main advantages of an unsteady aerodynamic panel method are then introduced and illustrated by modelling the flapping wings of a tethered sphingid moth and comparing the results with those generated using a quasi-steady method. The improved correlations of the aerodynamic forces and the resultant graphics clearly demonstrate the advantages of the unsteady panel method (namely, its ability to detail the trailing wake and to include dynamic effects in a distributed manner).
Water Loss And Morphological Changes During Desiccation Of The Anhydrobiotic Nematode Ditylenchus Dipsaci
Authors: Wharton David A.
Published: April 2021

Ditylenchus dipsaci is an anhydrobiotic nematode which can withstand direct exposure to extreme desiccation. Water loss has been determined gravimetrically and morphological changes quantified by light microscopy. Water loss occurs in two distinct phases, with a permeability slump 2 min after the onset of desiccation. The permeability slump remains after treatment with sodium azide or carbon dioxide but disappears after heat treatment. There is a marked decrease in body length during the first 2 min of desiccation but diameter decreases throughout the desiccation period, mainly as a result of a decrease in the thickness of the hyaline layer. These observations suggest that one mechanism by which the nematode controls water loss during desiccation is by narrowing the groove between annulations. They also provide measurements on living nematodes which can be compared with more detailed observations using electron microscope techniques.
Characterization of two Myotropic Neuropeptides in the Fmrfamide family from Segmental Ganglia of the moth Manduca Sexta: Candidate Neurohormones and Neuromodulators
Authors: Kingan Timothy G. , Shabanowitz Jeffrey , Hunt Donald F. , Witten Jane L.
Published: April 2021

We have characterized two new members of the FMRFamide family of neuropeptides from the segmental ganglia of the tobacco hornworm Manduca sexta. Levels of peptides in ganglia used for purification were enhanced by manipulating their exposure to the steroid molting hormones. Explants of ganglia were cultured in the low-level ecdysteroid environment of diapausing pupae shown previously to evoke accumulation of FMRFamide-like immunoreactivity (FLI). Sufficient material for sequencing was obtained from 180 explanted ganglia. Extracts of ganglia were fractionated using two reverse-phase liquid chromatography procedures, and the immunoreactive fractions were subjected to sequence analysis using electrospray mass spectrometry. The sequences of the two peptides were determined to be GNSFLRFamide and DPSFLRFamide. These peptides have been named MasFLRFamide II and MasFLRFamide III, respectively; the previously characterized M. sexta FLRFamide (pEDVVHSFLRFamide) has been renamed MasFLRFamide I. The three peptides show distinctive tissue and developmental distributions as determined from fractionated extracts of larval and adult central nervous system structures and neurohemal organs. In the retrocerebral corpora cardiaca/corpora allata, MasFLRFamide I was the predominant form, while in the segmental ganglia MasFLRFamides II and III predominated. Higher levels of MasFLRFamide I and II were found in the adult, whereas there was little apparent change in the level of MasFLRFamide III upon metamorphosis. Determinations of peptide levels in fractionated hemolymph of newly emerged moths revealed that levels of MasFLRFamide I and III could exceed 10 nmol l-1. The actions of the three peptides were tested on the moth ileum. MasFLRFamides II and III were found to be stimulatory. At 1 nmol l-1, these peptides induced robust increases in the rate of rhythmic longitudinal and peristaltic waves of contractions. In contrast, MasFLRFamide I was ineffective even at 20 nmol l-1. Thus, while all three peptides have the characteristics of neurohormones in M. sexta, the physiological findings show that the heptapeptide FLRFamides have properties distinct from those of the decapeptide.
Voltage- and Ca2+-Gated Currents in Zebrafish Olfactory Receptor Neurons
Authors: Corotto Frank S. , Piper David R. , Chen Nansheng , Michel William C.
Published: April 2021

Voltage-and Ca2+-gated currents were recorded from isolated olfactory receptor neurons (ORNs) of the zebrafish Danio rerio using the whole-cell voltage-clamp technique. Zebrafish ORNs had an average capacitance of 0.66 pF and an average apparent input resistance of 8.0 GΩ. Depolarizing steps elicited transient inward currents followed by outward currents with transient and sustained components. The transient inward current (INa) was sensitive to 1 μmol l-1 tetrodotoxin, activated between -74 mV and-64 mV, and reached half-maximal conductance at -28 mV. Its peak amplitude averaged-101 pA. Steady-state inactivation of INa was half-maximal at an average test potential of -78 mV and recovery from inactivation proceeded with two time constants averaging 23 ms and 532 ms. A sustained, Co2+-sensitive current (ICa) activated between -44 mV and -34 mV and reached a peak amplitude averaging -9 pA at -14 mV. Outward currents were carried by K+, based on the reversal potentials of tail currents, and consisted of a Ca2+-dependent K+ current, a delayed rectifier current (IDR) and a transient K+ current (IA). The Ca2+-dependent K+ current (IK(Ca)) activated between -44 mV and -34 mV, whereas IDR and IA activated between -34 mV and -24 mV. In summary, zebrafish ORNs possess a complement of gated currents similar but not identical to that of ORNs from other vertebrates and which appears well suited for encoding a graded receptor potential into a train of action potentials.