bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Temperature on Power Output of Scup Red Muscle During Cyclical Length Changes
Authors: Rome Lawrence C. , Swank Douglas
Published: April 2021

To gain insight into how temperature affects locomotory performance, we measured power output of scup red muscle during oscillatory length changes at 10°C and 20°C. When we optimized work loop parameters, we found that maximum power was 27.9 W kg−1 at 20°C and 12.8 W kg−1 at 10°C, giving a Q10 of 2.29. Maximum power was generated at a higher oscillation frequency at 20°C (5 Hz) than at 10°C (2.5 Hz), and the Q10 for power output at a given oscillation frequency ranged from about 1 at 1Hz to about 5 at 7.5 Hz. An analysis of the results in terms of crossbridge kinetics suggests that the higher power output at 20°C is associated with both a higher Vmax (i.e. more power per cycling crossbridge) and faster activation and relaxation (i.e. a greater number of cycling crossbridges).

To obtain a more realistic understanding of the functional importance of temperature effects on muscle, we imposed on isolated muscle in vivo length changes and oscillation frequencies (measured during previous experiments on swimming scup) and the in vivo stimulus duty cycle (measured from electromyograms in this study). At 20°C, muscle bundles tested under these in vivo conditions produced nearly maximal power, suggesting that the muscle works optimally during locomotion and, thus, important contractile parameters have been adjusted to produce maximum mechanical power at the oscillation frequencies and length changes needed during swimming. At 10°C, muscle bundles tested under in vivo conditions produced much less power than was obtained during the ‘optimized’ work loop experiments discussed above. Furthermore, although ‘optimized’ work loop experiments showed that maximum power output occurs at 2.5 Hz, scup do not appear to swim with such a low tailbeat frequency. Although the reason for these apparent discrepancies at 10°C are not known, it shows that simple extrapolation from isolated muscle to the whole animal, without knowledge of how the muscle is actually used in vivo, can be misleading.
Swimming Performance and Haematological Variables in Splenectomized Rainbow Trout, Oncorhynchus Mykiss
Authors: Gallaugher P. , Axelsson M. , Farrell A. P.
Published: April 2021

Haematological variables were measured during aerobic swimming (45–55% of Ucrit) and at critical swimming velocity (Ucrit) in acutely splenectomized and sham-operated rainbow trout. There was no correlation between haematocrit (Hct) and Ucrit in either group of fish. The control values for the haematological variables did not differ significantly between the two groups of fish. Some haematological variables changed during aerobic swimming and at Ucrit, but there were no significant differences between the two groups for any of the variables. Arterial blood oxygen tension was significantly reduced at Ucrit. Arterial blood oxygen content was maintained in sham-operated fish because the Hct increased significantly. However, in the splenectomized animals, decreased (compared to control values) during aerobic swimming and at Ucrit because the Hct did not change. Plasma concentrations of lactate and catecholamines were elevated only at Ucrit. We provide evidence of a graded spleen contraction during aerobic swimming.
Amino Acid Uptake and Metabolism by Embryos of the Blenny Zoarces Viviparus
Authors: Korsgaard Bodil
Published: April 2021

The ability of blenny Zoarces viviparus (L.) embryos in early and late development to assimilate and metabolize ambient L-alanine was investigated in vitro and in vivo by means of autoradiographic and radiochemical methods. Autoradiograms showed that after 24 h of exposure to L-[14C]alanine, label was distributed in the tissues of the embryos.

Uptake rates for l4C-labelled L-alanine in vitro were estimated by measuring the disappearance of radioactivity from the medium. Net uptake rates were measured by high performance liquid chromatography of samples taken simultaneously from the medium. Uptake rates, based on uptake of the tracer (0.60 μmol g−1 h−1), were similar to net uptake rates (0.54 μmol g−1 h−1) in embryos in late development in the in vitro incubations in 60 μmol l−1 alanine. In vivo, the injected tracer was completely cleared from the ovarian fluid over 24h. After intraovarian and in vitro incubation of the embryos with labelled alanine, there was evidence for both catabolic and anabolic metabolism of the amino acid by production of l4CO2 and by incorporation of radioactivity into molecules insoluble in trichloroacetic acid, respectively.

The data provide evidence for uptake and metabolism of amino acids by embryos in vitro and in vivo. An increase in the capacity for uptake and metabolism of L-alanine may occur during development of the embryos in the ovary.
Influence of Haemoglobin Conformation, Nitrite and Eicosanoids on K+ Transport Across the Carp Red Blood Cell Membrane
Authors: Jensen Frank B.
Published: April 2021

The regulation of K+ transport across the red blood cell (RBC) membrane by haemoglobin (Hb) conformation was studied in carp, and the K+ transport mechanisms were identified. When a large proportion of Hb in the R quaternary structure was secured by oxygenation of blood at pH 8.14, a net RBC K+ efflux was induced, which was accompanied by RBC shrinkage. This K+ efflux was resistant to ouabain and inhibited by furosemide and DIDS and by substitution of NO3− for Cl−, showing it to result from a K+/C1− cotransport mechanism. Deoxygenation of the RBCs (Hb in T structure) eliminated the Cl−-dependent K+ efflux and resulted in a net K+ uptake via the Na+/K+ pump. These changes were fully reversible. Nitrite-induced methaemoglobin formation in deoxygenated blood, which converts a large fraction of the T structure Hb into an R-like conformation, shifted the K+ uptake to a Cl−-dependent K+ efflux similar to that seen in oxygenated cells. When the allosteric equilibrium between the R and T structures of Hb was gradually shifted towards the T state by decreases in pH, the Cl−-dependent K+ efflux from oxygenated cells decreased. At pH 7.52, where the Root effect caused a potent stabilisation of the T state, the K+ efflux was reversed to a net K+ uptake. A similar change was induced in methaemoglobin-containing deoxygenated blood, since low pH also favours a T-like conformation of metHb. The variable K+ fluxes could not be related to changes in membrane potential or pH but were always directly related to the experimental modulation of the relative proportions of R-and T-structure Hb. It is proposed that Hb conformation governs K+ movements via a different binding of T and R structures to integral membrane proteins, and that a large fraction of R-structure Hb triggers the Cl−-dependent K+ efflux mechanism. Application of inhibitors and a substrate of prostaglandin and leukotriene synthesis did not influence the K+ efflux from oxygenated erythrocytes. However, a fraction of the K+ efflux from nitrite-treated deoxygenated cells was inhibited by nordihydroguaiaretic acid, suggesting that a slightly larger K+ efflux from these RBCs than from oxygenated RBCs was related to leukotriene production caused by nitrite entry. A much larger influx of nitrite to deoxygenated than to oxygenated RBCs was positively correlated with the distribution ratio of H+ and the membrane potential, supporting the view that nitrite primarily enters the cells via conductive transport. The physiological implications of the results are discussed.
Modulation of Aplysia Californica Siphon Sensory Neurons by Conopressin G
Authors: Martínez-Padrón Manuel , Edstrom John , Wickham Michael , Lukowiak Ken
Published: April 2021

Conopressin G, a molluscan vasopressin-like peptide, when superfused over the abdominal ganglion suppressed gill withdrawal reflex behavior patterns. The effects of conopressin G on Aplysia californica central sensory neurons and on the sensory neuron to motor neuron synapse were inconsistent with its behavioral effects. That is, superfusion of the peptide facilitated synaptic transmission at this synapse and reversed low-frequency homosynaptic depression. Further, conopressin G potentiated frequency-dependent spike broadening, reduced spike threshold and reduced accommodation. A voltage-dependent outward K+ current was suppressed by the peptide. This current was also suppressed by Co2+ and Ba2+ and was relatively resistant to tetraethylammonium and 4-aminopyridine. The effects produced by conopressin G on the sensory neurons were not observed when Ca2+ was removed from the saline, when a low-Ca2+, high-Mg2+ saline was used or when other procedures that impair synaptic transmission were used. These results suggest that the effects of conopressin G were mediated by a polysynaptic pathway acting on the sensory neurons.
Physiology of V-ATPases
Authors: Harvey William R.
Published: April 2021

Protons migrate much faster than other ions through water, ice and water-lined membrane channels because they participate in hydrogen bonding and H+H2O exchange. Similarly, hydrogen bonding enables protons with amino, carbonyl, phosphoryl and sulfonyl residues to influence critically the charge, conformation and stability of proteins. Therefore, it is not surprising that regulation of proton concentration, or pH, is an essential requirement in biological systems. It is no surprise either that enzymes which regulate proton concentration (i.e. proton pumps) should have evolved or that evolution should have used these enzymes further, for energization of biological membranes. At present there appear to be three classes of ATP-hydrolyzing proton pumps, or H+-ATPases, which were dubbed P-ATPases, F-ATPases and V-ATPases, by Pederson and Carafoli (1987). H+-translocating P-ATPases, as well as the Na+/K+-ATPase of plasma membranes and the Ca2+-ATPase of sarcoplasmic reticulum, form phosphoaspartyl intermediates and are inhibited by the phosphate analogue orthovanadate. F-ATPases are the proton-translocating ATP synthases of mitochondria, chloroplasts and bacterial plasma membranes and are inhibited by azide.
The plant vacuole
Authors: Taiz Lincoln
Published: April 2021

Plant cells are unique in containing large acidic vacuoles which occupy most of the cell volume. The vacuolar H+-ATPase (V-ATPase) is the enzyme responsible for acidifying the central vacuole, although it is also present on Golgi and coated vesicles. Many secondary transport processes are driven by the proton-motive force generated by the V-ATPase, including reactions required for osmoregulation, homeostasis, storage, plant defense and many other functions. However, a second proton pump, the V-PPase, serves as a potential back-up system and may, in addition, pump potassium. The plant V-ATPase is structurally similar to other eukaryotic V-ATPases and its subunits appear to be encoded by small multigene families. These multigene families may play important roles in the regulation of gene expression and in the sorting of V-ATPase isoforms to different organelles.
Vacuolar-type H+-translocating ATPases IN plant endomembranes: subunit organization and multigene families
Authors: Sze Heven , Ward John M. , Lai Shoupeng , Perera Imara
Published: April 2021

Acidification of endomembrane compartments by the vacuolar-type H+-translocating ATPase (V-ATPase) is vital to the growth and development of plants. The V-ATPase purified from oat roots is a large complex of 650×10Mr that contains 10 different subunits of 70, 60,44,42, 36, 32, 29, 16, 13 and 12 × 103Mr. This set of ten polypeptides is sufficient to couple ATP hydrolysis to proton pumping after reconstitution of the ATPase into liposomes. Unlike some animal V-ATPases, the purified and reconstituted V-ATPase from oat is directly stimulated by Cl−. The peripheral complex of the ATPase includes the nucleotide-binding subunits of 70 and 60 × 103Mr and polypeptides of 44, 42, 36 and 29 × 103Mr. Six copies of the 16 × 103Mr proteolipid together with three other polypeptides are thought to make up the integral sector that forms the H+-conducting pathway. Release of the peripheral complex from the native membrane completely inactivates the pump; however, the peripheral subunits can be reassembled with the membrane sector to form a functional H+ pump.

Comparison of V-ATPases from several plants indicates considerable variations in subunit composition. Hence, several forms of the V-ATPase may exist among, and probably within, plant species. At least four distinct cDNAs encode the 16 × 103Mr proteolipid subunit in oat. Multiple genes could encode different subtypes of the H+ pump that are regulated by the developmental stage and physiological function specific to the cell or tissue type.
Evolution and isoforms of V-ATPase subunits
Authors: Gogarten J. Peter , Starke Thomas , Kibak Henrik , Fishmann Jenny , Taiz Lincoln
Published: April 2021

The structure of V- and F-ATPases/ATP synthases is remarkably conserved throughout evolution. Sequence analyses show that the V- and F-ATPases evolved from the same enzyme that was already present in the last common ancestor of all known extant life forms. The catalytic and non-catalytic subunits found in the dissociable head groups of both V-ATPases and F-ATPases are paralogous subunits, i.e. these two types of subunits evolved from a common ancestral gene. The gene duplication giving rise to these two genes (i.e. those encoding the catalytic and non-catalytic subunits) pre-dates the time of the last common ancestor. Similarities between the V- and F-ATPase subunits and an ATPase-like protein that is implicated in flagellar assembly are evaluated with regard to the early evolution of ATPases. Mapping of gene duplication events that occurred in the evolution of the proteolipid, the non-catalytic and the catalytic subunits onto the tree of life leads to a prediction of the likely quaternary structure of the encoded ATPases. The phylogenetic implications of V-ATPases found in eubacteria are discussed.

Different V-ATPase isoforms have been detected in some higher eukaryotes, whereas others were shown to have only a single gene encoding the catalytic V-ATPase subunit. These data are analyzed with respect to the possible function of the different isoforms (tissue-specific, organelle-specific). The point in evolution at which the different isoforms arose is mapped by phylogenetic analysis.
Structure and function of V-ATPases in endocytic and secretory organelles
Authors: Nelson Nathan
Published: April 2021

Chromaffin granules and clathrin-coated vesicles are major sources for V-ATPases of mammalian cells. Studies of these organelles have helped us to understand the structure and function of the enzyme. It was shown that V-ATPases are composed of distinct catalytic and membrane sectors containing several subunits. The subunit stoichiometry was determined to be 3A, 3B, 1C, 1D, 1E, 6c (proteolipids), 1Acl 15 and ?Ac39. Additional subunits are likely to be discovered. Resolution and reconstitution of the enzyme revealed that the catalytic and membrane sectors are interdependent for their partial activity. The catalytic sector has no ATPase activity when detached from the membrane sector, and the membrane sector when depleted of the catalytic sector does not conduct protons. The mechanistic significance of these properties is discussed.
The vacuolar H+-ATPase – one of the most fundamental ion pumps in nature
Authors: Nelson Nathan
Published: April 2021

An electrochemical gradient of protons (PMF) is a universal high-energy intermediate in biological systems. Two related families of proton pumps, denoted F-and V-ATPases, are among the principal generators of a PMF from ATP and can form ATP at the expense of a PMF. The enzymes of these two families share a similar structure and subunit composition; some subunits in the two families evolved from common ancestors. Other subunits having no common ancestry were added independently to the various enzymes and defined the two separate families. The general mechanism for the proton pumping activity is similar in the two families. However, whereas F-ATPases can act in both proton pumping and ATP formation, the V-ATPases of eukaryotes function exclusively as ATP-dependent proton pumps. The catalytic and membrane sectors of F-ATPases and archaebacterial V-ATPases can separately catalyze their specific partial activities of ATPase and proton conduction. The catalytic and membrane sectors of the eukaryotic V-ATPases cannot act separately. This property is correlated with the presence of a large proteolipid that traverses the membrane four times. The gene duplication of the smaller proteolipid in the formation of the large proteolipid was one of the most important events in the evolution of the V-ATPases of eukaryotic cells.
V-ATPases of the plasma membrane
Authors: Gluck Stephen
Published: April 2021

V-ATPases reside in high densities on the plasma membrane in specialized types of insect and vertebrate cells. They provide unique biochemical and electrophysiological properties that allow them to function in energizing the plasma membrane in insects, and in cellular acid excretion in vertebrates.
Driving Forces and Pathways For H+ and K+ Transport in Insect Midgut Goblet Cells
Authors: Moffett David F. , Koch Alan
Published: April 2021

In the midgut of larval lepidopteran insects, goblet cells are believed to secrete K+; the proposed mechanism involves an electrogenic K+/nH+ (n>l) antiporter coupled to primary active transport of H+ by a vacuolar-type ATPase. Goblet cells have a prominent apical cavity isolated from the gut lumen by a valve-like structure.

Using H+- and K+-selective microelectrodes, we showed that electrochemical gradients of H+ and K+ across the apical membrane and valve are consistent with active secretion of both ions into the cavity and that the transapical H+ electrochemical gradient, but not the transapical pH gradient, is competent to drive K+ secretion by a K+/nH+ antiporter.

We used 10 mmol l−1 tétramethylammonium ion (TMA+) as a marker for the ability of small cations to pass from the gut lumen through the valve to the goblet cavity, exploiting the high TMA+ sensitivity of ‘K+-sensitive’ microelectrodes. These studies showed that more than half of the cavities were inaccessible to TMA+. For those cavities that were accessible to TMA+, both entry and exit rates were too slow to be consistent with direct entry through the valves. One or more mixing compartments appear to lie between the lumen bathing solution and the goblet cavity. The lateral intercellular spaces and goblet cell cytoplasm are the most likely compartments. The results are not consistent with free diffusion of ions in a macroscopic valve passage; mechanisms that would allow K+ secreted into the goblet cavity to exit to the gut lumen, while preventing H+ from exiting, remain unclear.
Halobacterial A-ATP synthase in relation to V-ATPase
Authors: Ihara Kunio , Abe Tadahiro , Sugimura Ken-Ichiro , Mukohata Yasuo
Published: April 2021

The head piece separated from the A-ATP synthase of Halobacterium halobium hydrolyses ATP. This A1-ATPase is inhibited by nitrate but not by other chaotropic anions. The nitrate inhibition is noncompetitive with respect to ATP, reversible, and partially protected by chloride. In contrast, ATP synthase in situ (A1Ao-ATPase) is not inhibited by nitrate but apparently is inhibited by stronger chaotropic reagents, such as thiocyanate and trichloroacetate, which make the vesicle membrane permeable to protons. The mode of action of nitrate and chaotropic anions seems to differentiate A-ATPases from V-ATPases.

Other strains of Halobacterium, Haloferax, Haloarcula, Halococcus and Natronobacterium, contain at least two polypeptides immunochemically similar to the two major subunits, a (86× 103Mr on SDS-PAGE) and β (64×103Mr), of the A-ATPase of Halobacterium halobium. When solubilized, membrane vesicles of these halobacteria hydrolyse ATP. Their ATPases are commonly sensitive to nitrate. They require high concentrations of the supporting salt but depend differently on chloride or sulfate/sulfite. The A-ATPases of Halobacteriaceae appear to diverge with respect to salt preference.
Molecular genetics of the yeast vacuolar H+-ATPase
Authors: Anraku Yasuhiro , Hirata Ryogo , Wada Yoh , Ohya Yoshikazu
Published: April 2021

The yeast vacuolar proton-translocating ATPase was discovered in 1981 as the first member of the V-ATPases, which are now known to be ubiquitously distributed in eukaryotic vacuo-lysosomal organelles and archaebacteria. Nine VMA genes that are indispensable for expression of vacuolar ATPase activity have been identified in the yeast Saccharomyces cerevisiae. VMA1, VMA2, VMA3, VMA5 and VMA6 were cloned and characterized on the basis of partial amino acid sequences determined with the purified subunits. Genetic and biochemical studies of the yeast Pet–cls mutants have demonstrated that they are related to vma defects. Based on this evidence, VMA11 (CLS9), VMA 12 (CLS10) and VMA 13 (CLS11) were isolated from a yeast genomic DNA library by complementation of the vmal 1, vma!2 and vma!3 mutations, respectively. This article summarizes currently available information on the VMA genes and the molecular biological functions of the VMA gene products.
Comparative Rheology of Human and Trout Red Blood Cells
Authors: Nash Gerard B. , Egginton Stuart
Published: April 2021

We have studied the comparative rheology of individual red blood cells from humans and rainbow trout (Oncorhynchus mykiss) at their natural body temperatures. Trout red blood cells were large ellipsoids (about 16 µmX11.5 µmX2.5 µm) with a mean volume of 250 fl, a surface area of approximately 350 µm2 and an elongated nucleus of about 9 µmX5 µm. Although much larger than human red cells (diameter 8 µm, V=92 fl, A= 136 µm2), both theoretical calculation and experimental aspiration into micropipettes indicated that the limiting size of a cylindrical vessel that both types of cell could enter was approximately 3 µm. Nevertheless, individual trout red cells had much longer transit times through 5 µm filter pores and were much slower to enter 3–4 µm diameter micropipettes. Interestingly, the relative deformability of the trout cells depended on the pore size and applied pressure, with entry times for trout and human cells converging as pipette diameter increased. The relatively poor overall cellular deformability of the trout cells reflected their membrane rigidity (shear elastic modulus 4–5 times higher than that of human membrane), as well as their large size and the presence of a prominent nucleus. Capillary diameters in trout muscle are similar to those in the human microcirculation (about 3 µm), while systemic driving pressures are much lower. Therefore, either red cell deformability is a less critical circulatory parameter than has previously been thought, or the apparently disadvantageous blood rheology of trout is adequate because of the lower demand for tissue perfusion.
Temperature, Muscle Power Output and Limitations on Burst Locomotor Performance of the Lizard Dipsosaurus Dorsalis
Authors: Swoap Steven J. , Johnson Timothy P. , Josephson Robert K. , Bennett Albert F.
Published: April 2021

The mechanical power output of fast-twitch fibres from the iliofibularis of the lizard Dipsosaurus dorsalis was measured over a broad body temperature range using the oscillatory work-loop technique. The optimal cycling frequency, that frequency at which mechanical power output is maximal, increases with temperature from 3.3Hz at 15°C to 20.1Hz at 42°C. Maximum power output increases with temperature, from 20 W kg-1 at 15°C to 154 W kg-1 at 42°C, the largest power output yet measured using the work-loop technique. At low temperatures (15°C and 22°C), stride frequency during burst running is nearly identical to the optimal cycling frequency for in vitro power output, suggesting that maximum power output may limit hindlimb cycle frequency in vivo. However, at higher temperatures (35°C and 42°C), the optimal cycling frequency of the isolated muscle is significantly higher than the burst stride frequency, demonstrating that contractile events no longer limit hindlimb cycle frequency. At higher temperatures, it is thus unlikely that the fast-twitch fibres of this muscle in vivo attain their potential for maximum power output.
Unsteady Aerodynamic Performance of Model Wings at Low Reynolds Numbers
Authors: Dickinson Michael H. , Götz Karl G.
Published: April 2021

The synthesis of a comprehensive theory of force production in insect flight is hindered in part by the lack of precise knowledge of unsteady forces produced by wings. Data are especially sparse in the intermediate Reynolds number regime (10<Re<1000) appropriate for the flight of small insects. This paper attempts to fill this deficit by quantifying the time-dependence of aerodynamic forces for a simple yet important motion, rapid acceleration from rest to a constant velocity at a fixed angle of attack. The study couples the measurement of lift and drag on a two-dimensional model with simultaneous flow visualization. The results of these experiments are summarized below. At angles of attack below 13.5°, there was virtually no evidence of a delay in the generation of lift, in contrast to similar studies made at higher Reynolds numbers.At angles of attack above 13.5°, impulsive movement resulted in the production of a leading edge vortex that stayed attached to the wing for the first 2 chord lengths of travel, resulting in an 80% increase in lift compared to the performance measured 5 chord lengths later. It is argued that this increase is due to the process of detached vortex lift, analogous to the method of force production in delta-wing aircraft.As the initial leading edge vortex is shed from the wing, a second vortex of opposite vorticity develops from the trailing edge of the wing, correlating with a decrease in lift production. This pattern of alternating leading and trailing edge vortices generates a von Karman street, which is stable for at least 7.5 chord lengths of travel.Throughout the first 7.5 chords of travel the model wing exhibits a broad lift plateau at angles of attack up to 54°, which is not significantly altered by the addition of wing camber or surface projections.Taken together, these results indicate how the unsteady process of vortex generation at large angles of attack might contribute to the production of aerodynamic forces in insect flight. Because the fly wing typically moves only 2–4 chord lengths each half-stroke, the complex dynamic behavior of impulsively started wing profiles is more appropriate for models of insect flight than are steady-state approximations.
Synergism of Hormones Controlling Epithelial Fluid Transport in an Insect
Authors: Maddrell S. H. P. , Herman W. S. , Farndale R. W. , Riegel J. A.
Published: April 2021

Forskolin stimulates rapid fluid secretion by the Malpighian tubules of Rhodnius prolixus at concentrations above 5X10−6 mol l−1. In the presence of a threshold concentration of forskolin, the tubules are 30–50 times more sensitive to 5-hydroxytryptamine (5-HT) than in its absence. Similar synergism is seen between 5-HT and extracts of the mesothoracic ganglionic mass (which is rich in the peptide diuretic hormone, DH) and between 5-HT and samples of haemolymph, also rich in peptide DH, from fed insects 1–2h after feeding. The dose–response curves for mixtures of forskolin and 5-HT and of peptide DH and 5-HT are all very steep, approximately five times steeper than for any one stimulant alone.

Forskolin, 5-HT and extracts of the ganglionic mass all stimulated adenylate cyclase from broken membrane preparations from the Malpighian tubules in a dose-dependent manner and at doses similar to those required to stimulate fluid secretion by intact tubules. Mixtures of ganglionic extract and 5-HT stimulated adenylate cyclase activity in a synergistic fashion.

Injections into fifth-instar Rhodnius, 24h before feeding, of 5,7-dihydroxytryptamine, which is known to block or reduce 5-HT release, caused delays in the onset of the consequent diuresis or prevented it altogether. This is consistent with the proposal that the rapid onset of diuresis after feeding is caused by the simultaneous release of 5-HT and peptide DH acting synergistically.
A Comparison of the Effects of two Putative Diuretic Hormones from Locusta Migratoria On Isolated Locust Malpighian Tubules
Authors: Coast G. M. , Rayne R. C. , Hayes T. K. , Mallet A. I. , Thompson K. S. J. , Bacon J. P.
Published: April 2021

Previous work has shown that a peptide related to arginine vasopressin is present in the suboesophageal ganglion of the locust, Locusta migratoria. This peptide was determined to be an anti-parallel dimer of the nonapeptide Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-Gly-NH2 and was reported to stimulate cyclic AMP production and fluid secretion in a combined Malpighian tubules and midgut preparation from locusts. For these reasons the peptide has been called the arginine-vasopressin-like insect diuretic hormone (AVP-like IDH). Recently, a second diuretic peptide (Locusta-DP), which is related to corticotropin releasing factor, has been identified: this is a potent stimulant of fluid secretion and cyclic AMP production by isolated locust tubules. Because water balance in insects is likely to be controlled by a cocktail of hormones acting on both Malpighian tubules and hindgut, this study directly compares the activity of these two peptides in fluid secretion and cyclic AMP production bioassays on one target organ, the isolated Malpighian tubule of Locusta migratoria. Locusta-DP was synthesised directly, whereas the dimeric AVP-like IDH was obtained by oxidation of a synthetic nonapeptide monomer. Products were separated by RP-HPLC and their structures unequivocally confirmed by enzymatic digestion, sequence analysis and electrospray mass spectrometry. We show that Locusta-DP causes strong stimulation of fluid secretion and cyclic AMP production, whereas the AVP-like IDH has no effect in either assay. These findings are discussed in the light of recent work on the anatomy and physiology of the vasopressin-like immunoreactive (VPLI) neurones in the suboesophageal ganglion of Locusta migratoria, the proposed source of the AVP-like peptide.
Water Compartments and Osmoregulation in the Parasitic Nematode Pseudoterranova Decipiens
Authors: Fusé M. , Davey K. G. , Sommerville R. I.
Published: April 2021

A study of the time course of penetration of 3H2O into whole worms suggests that worms immersed in a hypo-osmotic environment (15% artificial sea water) reach full exchange equilibrium more slowly than worms in an iso-osmotic environment (40 % artificial sea water). The apparent water content, determined by dry mass, matches that determined by 3H2O exchange when worms are immersed for 24h in 40% artificial sea water (ASW), but the water content measured by 3H2O exchange is lower when worms are kept in a hypo-osmotic environment for 24h. These differences disappear after 48h. No such differences are apparent when sacs, consisting of cylinders of body wall lacking their intestines and pseudocoelomic fluid and closed at both ends by ligatures, are immersed in either 40% or 15% ASW for 24h. The placing of ligatures at the head, but not at the tail, results in a failure of worms immersed in 40% ASW or 15% ASW containing 3H2O to achieve full exchange equilibrium within 24h. These results suggest that although worms immersed in an iso-osmotic environment drink, those immersed in a hypo-osmotic environment do not, a conclusion supported by studies involving the addition of [14C]inulin to the medium. The application of ligatures to the head and tail of worms immersed in 40% ASW results in a slower penetration of 3H2O into the pseudocoelomic fluid, whereas similar ligatures do not further retard the penetration in worms exposed to 15% ASW. The results are consistent with a model which sees the pseudocoelomic fluid as consisting of two compartments containing water, one of which exchanges more slowly than the other.
Ammonia and urea excretion in Lahontan cutthroat trout (Oncorhynchus clarki henshawi) adapted to the highly alkaline Pyramid Lake (pH 9.4)
Authors: Wright Patricia A. , Iwama George K. , Wood Chris M.
Published: April 2021

Earlier studies have reported that acute exposure to alkaline pH strongly inhibits ammonia excretion in freshwater rainbow trout, but the Lahontan cutthroat trout thrives in Pyramid Lake, Nevada, at pH9.4. We investigated the rates and mechanisms of ammonia and urea excretion in this species in Pyramid Lake water to determine whether special strategies are employed to excrete nitrogenous wastes in an environment unfavourable for ammonia excretion. The majority of nitrogen wastes (N-wastes) were excreted as ammonia (56% through the gills, 10% through the kidney), while urea excretion accounted for 34% (32% gills, 2% kidney). Ammonia excretion was dependent on the NH3 partial pressure gradient across the gills and independent of Na+ influx and acidification of the gill water boundary layer. Acute exposure to more alkaline water (pH10) decreased ammonia excretion by 52%, while exposure to neutral water (pH7.6) increased ammonia excretion by 200%. When fish were held in a ‘closed system’ for 8h, ammonia excretion decreased as water ammonia levels increased over the first 6h. However, after 6h a marked increase in ammonia excretion occurred which may have been associated with an increase in the gradient and/or activation of a carrier-mediated transporter. We conclude that Lahontan cutthroat trout, adapted to pH9.4 water, maintain N-waste excretion by modifying mechanisms common to other teleosts. These modifications include lower rates of ammonia excretion, a higher ratio of urea excretion to ammonia excretion, a higher rate of renal ammonia excretion, greater plasma pH and greater total ammonia level (increased plasma ), which facilitate the diffusive excretion of NH3 across the gills, and a lack of dependence of ammonia excretion on Na+ influx.
The physiological responses of the Lahontan cutthroat trout (Oncorhynchus clarki henshawi), a resident of highly alkaline Pyramid Lake (pH 9.4), to challenge at pH 10
Authors: Wilkie Michael P. , Wright Patricia A. , Iwama George K. , Wood Chris M.
Published: April 2021

Desiccation of Pyramid Lake, Nevada, has led to continued increases in the lake’s alkalinity (currently pH9.4) that may threaten the resident Lahontan cutthroat trout population. In this study, Lahontan cutthroat trout were challenged with more alkaline water (pH10). The objectives were to describe physiological responses which may permit survival or lead to death in future potential environmental conditions and to cast further light on the mechanisms of nitrogenous waste excretion, acid–base regulation and ionoregulation in this unusual salmonid. Ammonia excretion (Jamm) was reduced by 50 % in the first few hours, but had fully recovered by 24h and exceeded control values by 36–48h. A sustained, twofold elevation of plasma ammonia concentration may have facilitated the recovery of Jamm by increasing the blood-to-water ammonia partial pressure diffusion gradient and NH4+ electrochemical gradient. Urea excretion (Jurea) almost doubled at 24–48h of pH10 exposure. Activities of ornithine–urea cycle enzymes in the liver were very low and there was no induction at pH10. However, all three enzymes of the uricolytic pathway were present, and allantoicase activity increased significantly at pH10, a possible explanation for the elevated Jurea. Increased liver glutamine synthetase activity at pH10 is consistent with a possible ammonia detoxification mechanism. A combined respiratory (decreased ) and metabolic (gain of basic equivalents) alkalosis developed at pH10 and resulted in a 0.25 unit increase in arterial blood pH. Electrochemical gradients for CO32- and OH− entry and H+ efflux all increased, but the gradient for HCO3− entry decreased to zero. Blood lactate level increased without marked changes in arterial O2 tension, suggesting that increased lactic acid production contributed to acid–base control. Plasma Na+ and Cl− levels decreased and K+ level increased during pH10 exposure. Survival at pH10 was relatively poor: more than 50% of the fish died after 72h exposure. Greatly elevated plasma and depressed plasma Na+ and Cl− levels in non-surviving trout suggest that a combination of ammonia toxicity and ionoregulatory failure led to death in susceptible cutthroat trout.
Motor Neuron M3 Controls Pharyngeal Muscle Relaxation Timing in Caenorhabditis Elegans
Authors: Avery Leon
Published: April 2021

Previous work has shown that 12 of the 14 types of neurons in the Caenorhabditis elegans pharyngeal nervous system are collectively but not individually necessary for the trapping and transport of bacteria. The aim of these experiments was to determine the functions of individual neuron types by laser−killing combinations of neurons and looking at the effects on behavior.

The motor neuron M3 and the sensory neuron I5 are important in trapping bacteria, as shown by two observations. First, when M3 and I5 are both killed, trapping is inefficient in the isthmus (the middle section of the pharynx). Second, M3 is sufficient in the absence of the other 11 neuron types for normal trapping in the corpus (anterior pharynx).

M3 and I5 influence the timing of pharyngeal muscle motions. When M3 is killed, pump duration (the interval from the beginning of pharyngeal contraction to the end of relaxation) increases from 170to 196ms. This increase is at least partially due to a slower relaxation. Thus, M3 speeds up relaxation. Pump duration decreases to 159ms when I5 is killed. When I5 and M3 are both killed, pump durations are long (192ms), just as when M3 alone is killed. These observations, together with previous electron microscopic work showing synapses from I5 to M3, suggest that I5 slows down relaxation by inhibiting M3.

To explain these results, I propose that M3 and I5 promote bacterial trapping by regulating the relative timing of muscle relaxation in different regions of the pharynx.
Damping in the Hinge of the Scallop Placopecten Magellanicus
Authors: Bowie Michael A. , Layes Jonathan D. , Demont M. Edwin
Published: April 2021

The family Pectinaceae are the only bivalves that have been well documented as swimmers (DeMont, 1992), although Ensis minor has been observed to swim (McMahon and McMahon, 1983). The behaviour was once regarded only as an escape response (Gäde, 1981; McMahon and McMahon, 1983), but some studies suggest seasonal migrations are involved (Gruffydd, 1976; DeMont, 1990). DeMont (1990) suggests that they swim at the natural frequency of the shell-hinge system for more efficient use of energy.
Augmentation Of Bursting Pacemaker Activity By Serotonin In An Identified Achatina Fulica Neurone: An Increase In Sodium- And Calcium-Activated Negative Slope Resistance Via Cyclic-Amp-Dependent Protein Phosphorylation
Authors: Funase Kozo , Watanabe Kazuko , Onozuka Minoru
Published: April 2021

The mechanism of serotonin (5-HT) action on bursting activity was examined in a bursting pacemaker neurone of the snail Achatina fulica. 5-HT augmented both the depolarizing and post-burst-hyperpolarizing phases of the bursting cycle in a dose-dependent manner. This biogenic amine also enhanced the negative slope resistance (NSR), which was normally detectable at membrane potentials between -40 and -20mV, and produced another NSR at voltages between -20 and 0mV. The former NSR disappeared in Na+-free saline and the latter was abolished by replacement with Co2+-substituted Ca2+-free saline. Both isobutylmethylxanthine, extracellularly applied, and intracellularly applied cyclic AMP simulated a 5-HT effect on the current–voltage relationships. In contrast, the 5-HT effect was suppressed in a dose-dependent manner by prior treatment with a cyclic-AMP-dependent protein kinase inhibitor, isoquinoline sulphonamide. Similar suppression was observed after intracellular injection of a cyclic-AMP-dependent protein kinase inhibitor isolated from bovine muscle. These results suggest that 5-HT may augment the bursting pacemaker activity by its stimulatory effect on both the slow Na+ channels and the Ca2+ channels through cyclic-AMP-dependent protein phosphorylation.
Convergence in the Feeding Mechanics of Ecomorphologically Similar Species in the Centrarchidae and Cichlidae
Authors: Norton Stephen F. , Brainerd Elizabeth L.
Published: April 2021

We examined the hypothesis that fish species with similar ecomorphological patterns, but from different taxonomic groups, would use similar feeding modes. We contrasted the feeding behavior of Micropterus salmoides (Lacépède) (Centrarchidae) and Cichla ocellaris (Block and Schneider) (Cichlidae), both large-mouthed piscivores with a locomotor morphology designed for fast acceleration, with Lepomis spp. (Centrarchidae) and Cichlosoma severum (Heckel) (Cichlidae), both small-mouthed predators on benthic invertebrates with a locomotor morphology designed for maneuverability. Pressure profiles in the buccal and opercular cavities were more similar for species that shared ecomorphological patterns than for species that shared phylogenetic histories. For smallmouthed predators, minimum buccal pressures were significantly greater and occurred earlier than the corresponding opercular pressures. For both large-mouthed predators, minimum buccal and opercular pressures were similar in magnitude and in timing. We developed the ram–suction index (RSI) to identify the relative contributions of ram feeding (i.e. predator movement) and of suction feeding (i.e. prey movement) to shortening the predator–prey distance during the strike. The RSI values for smallmouthed predators fell closer to the suction end of the ram–suction continuum than did strikes by the large-mouthed predators. The RSI provides a bench mark for evaluating the hydrodynamic consequences of intraspecific, interspecific and interprey variation in strike mechanics.
Re-Evaluation of the Stretch Sensitivity Hypothesis of Crustacean Hearts: Hypoxia, not Lack of Stretch, Causes Reduction in Heart Rate of Isolated Hearts
Authors: Wilkens J. L.
Published: April 2021

Decapod crustacean hearts are suspended by a three-dimensional array of alary ligaments. These ligaments are stretched during systole; diastolic filling via the ostia occurs as the ventricle is stretched by ligamental elastic recoil. There is no direct venous return to the hearts in these animals. In the present study, an isolated heart preparation with intact ligaments, hereafter called in situ, was used to evaluate the effects of artificially induced stretch on heart rate. Strongly beating in situ neurogenic hearts of the crab Carcinus maenas responded to direct perfusion of the ventricle with oxygenated saline and the attendant augmentation of natural stretch with a small increase in heart rate (fH); however, fH was well maintained for up to 15min after eliminating stretch by cutting the alary ligaments. In contrast to crabs, high rates of artificial perfusion usually depressed fH in crayfish hearts. Crab heart rate falls during hypoxia and this is readily reversed by even low rates of perfusion with oxygenated saline. It is concluded that the gradual decline in fH of totally isolated in vitro hearts arises from the deepening intraventricular hypoxia experienced by the cardiac ganglion.
Total Ammonia Concentration and PH of Haemolymph, Pleon Fluid and Maxillary Urine in Porcellio Scaber Lattreille (Isopoda, Oniscidea): Relationships to Ambient Humidity and Water Vapour Uptake
Authors: Wright Jonathan C. , O’Donnell Michael J.
Published: April 2021

Ammonia levels and pH were studied in body fluids of Porcellio scaber with special reference to ambient humidity and the timing of pleon fluid secretion and pleopodal ventilation. In high humidity (approximately 96.7%), concentrations of total ammonia (NH3+NH4+) in haemolymph display pronounced episodic changes, ranging from less than 1mmol l−1 to more than 50mmol l−1. Elevated concentrations (>5mmol l−1) occur in discrete bouts lasting from 40min to more than 2h. Concomitant changes in total ammonia levels are seen in pleon fluid and maxillary urine. Overall, mean ammonia concentrations in pleon fluid, but not maxillary urine, are significantly higher than in the haemolymph, which may indicate active secretion of NH4+ in the pleon. Elevated ammonia concentrations are not observed in reduced ambient humidities (85% and 30%). Evidence supports a physiological coupling between pleon NH3 volatilization and active water vapour absorption. Pleon fluid and haemolymph pH values are similar, discounting a role of alkalization in NH3 volatilization. Published rates of ammonia excretion are compatible with intermittent volatilization from pleon fluid and with measured NH3 levels during elevations in ammonia concentration.
The Relationship Between Intracellular pH and Swimming Performance of Brown Trout Exposed to Neutral and Sublethal pH
Authors: Butler P. J. , Day N.
Published: April 2021

Adult brown trout were acclimated for 2–4 weeks to artificial soft water ([Ca2+] 25 μmol l−1) at neutral pH and at summer (15°C) temperature. During this period they swam against a current of approximately 0.25 ms −1. They then had their dorsal aorta cannulated and were exposed to neutral or sublethal pH (4.5) for 4 days in still water.

After 4 days of exposure to sublethal pH, critical swimming speed (Ucrit) was 35% lower than that for fish at neutral pH. There were significant increases in arterial and in blood lactate concentrations at Ucrit compared with the values in resting fish at neutral pH and these led to significant reductions in plasma pH. There were no such changes in fish at sublethal pH. There were no significant changes in intracellular pH (pHi) of red blood cells at Ucrit, probably as a result of increases in the levels of plasma catecholamines. There were significant reductions in pHi of red and white muscle fibres at Ucrit. It is argued that these values were not as low in the white fibres as those seen in previous studies after fish have been chased to exhaustion and, therefore, that the fish in the present study were not completely exhausted, although they would no longer swim at a steady speed. As pHi of the red muscle was the same at Ucrit for fish at neutral and at sublethal pH, it is suggested that Ucrit (fatigue) coincides with a particular pHi of the red muscles and possible mechanisms are discussed.