bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitric oxide stimulates the stress-activated protein kinase p38 in rat renal mesangial cells
Authors: Huwiler Andrea , Pfeilschifter Josef 
Published: April 2021

ABSTRACT
Nitric oxide (NO) has gained increased attention as a diffusible universal messenger that plays a crucial role in the pathogenesis of inflammatory and autoimmune diseases. Recently, we reported that exogenous NO is able to activate the stress-activated protein kinase (SAPK) cascade in mesangial cells. Here, we demonstrate that exposure of glomerular mesangial cells to compounds releasing NO, including spermine-NO and (Z)-1-
{N-methyl-N-[6-(N-methylammoniohexyl)amino]diazen}-1-ium-1,2-diolate (MAHMA-NO), results in an activation of the stress-activated p38-mitogen-activated protein kinase (p38-MAPK) cascade as measured by the phosphorylation of the activator of transcription factor-2 (ATF2) in an immunocomplex kinase assay. Activation of the p38-MAPK cascade by a short stimulation (10 min) with the NO donor MAHMA-NO causes a large increase in ATF2 phosphorylation that is several times greater than that observed after stimulation with interleukin-1β, a well-known activator of the p38-MAPK pathway. Time course studies reveal that MAHMA-NO causes rapid and maximal activation of p38-MAPK after 10 min of stimulation and that activation declines to basal levels within 60 min. The longer-lived NO donor spermine-NO causes a comparable rapid activation of the p38-MAPK pathway; however, the increased activation state of p38-MAPK was maintained for several hours before control values were reattained after 24 h of stimulation. Furthermore, the NO donors also activated the classical extracellular signal-regulated kinase (ERK) p44-MAPK cascade as shown by phosphorylation of the specific substrate cytosolic phospholipase A2 in an immunocomplex kinase reaction. Both MAHMA-NO and spermine-NO cause a rapid activation of p44-MAPK after 10 min of stimulation. Interestingly, there is a second delayed peak of p44-MAPK activation after 4–24 h of stimulation with NO donors.
These results suggest that there is a differential activation pattern for stress-activated and mitogen-activated protein kinases by NO and that the integration of these signals may lead to specific cell responses.
Body bending during fast-starts in fish can be explained in terms of muscle torque and hydrodynamic resistance
Authors: Wakeling James M. , Johnston Ian A. 
Published: April 2021

ABSTRACT
Fish fast-starts are rapid events caused by the simultaneous onset of muscle activity along one side of the body. Spine curvature and the strain and electromyographic activity in white muscle were measured for fast-starts in the common carp Cyprinus carpio. The first bend of the fast-start was powered by muscle on the concave side: muscle fibres on this side were activated and began shortening simultaneously between the length-specific longitudinal sites 0.3L and 0.56L, where L is total body length. However, there was an increasing delay in the timing of the first peak in body curvature and muscle strain along the length of the body. Modelling studies related the rate of body bending to the muscle torque and hydrodynamic resistance of the fish. The muscle torque produced on the spine was greatest in the central region of the trunk, and this acted against the moments of inertia of the fish mass and added mass of water. It was concluded that a wave of body bending can be generated as a result of the hydrodynamic resistance of the fish despite the initiation of that bending being simultaneous along the length of the body.
How polarization-sensitive interneurones of crickets see the polarization pattern of the sky: a field study with an opto-electronic model neurone
Authors: Labhart T. 
Published: April 2021

ABSTRACT
Many insects gain directional information from the polarization pattern of the sky. Polarization vision is mediated by the specialized ommatidia of the dorsal rim area of the compound eye, which contains highly polarization-sensitive photoreceptors. In crickets Gryllus campestris, polarized light information conveyed by the dorsal rim ommatidia was found to be processed by polarization-opponent interneurones (POL-neurones). In this study, a field-proof opto-electronic model of a POL-neurone was constructed that implements the physiological properties of cricket POL-neurones as measured by previous electrophysiological experiments in the laboratory. Using this model neurone, both the strength of the celestial polarization signal and the directional information available to POL-neurones were assessed under a variety of meteorological conditions. We show that the polarization signal as experienced by cricket POL-neurones is very robust, both because of the special filtering properties of these neurones (polarization-antagonism, spatial low-pass, monochromacy) and because of the relatively stable e-vector pattern of the sky.
Optimizing Force and Velocity: Mandible Muscle Fibre Attachments in Ants
Authors: Paul Jürgen , Gronenberg Wulfila 
Published: April 2021

ABSTRACT
To be able to perform swift and powerful movements, ant mandible closer muscles are composed of two subpopulations of muscle fibres: fast fibres for rapid actions and slow fibres for forceful biting. All these fibres attach to a sturdy and complex apodeme which conveys force into the mandible base. Fast muscle fibres attach directly to the apodeme. Slow fibres may attach directly or insert at individual thin filament processes of the apodeme which vary in length. Comparisons of different ant species suggest two basic principles underlying the design of mandible muscles. (1) Ants specialized for fast mandible movements generally feature long heads which contain long fast muscle fibres that attach to the apodeme at small angles. Their muscles comprise only a few filament-attached fibres and they maximize speed of action at the expense of force output. (2) Ants performing particularly forceful mandible movements, such as seed cracking, rely on many short parallel muscle fibres contained within a broad head capsule. Their slower muscles incorporate a large proportion of filament-attached fibres. Two simple models explain how the attachment angles are optimized with respect to force and velocity output and how filament-attached fibres help to generate the largest power output from the available head capsule volume.
Evolution of complexity in motor patterns and jaw musculature of tetraodontiform fishes
Authors: Friel John P. , Wainwright Peter C. 
Published: April 2021

ABSTRACT
The prey-processing behavior and jaw-adducting musculature of tetraodontiform fishes provide a novel system for studying the evolution of muscles and their function. The history of this clade has involved a pattern of repeated ‘duplications’ of jaw muscles by physical subdivision of pre-existing muscles. As a result, the number of adductor mandibulae muscles in different taxa varies from as few as two to as many as eight. We used electromyography (EMG) to quantify motor-pattern variation of adductor mandibulae muscles in four tetraodontiform species during feeding events on prey items that varied in durability and elusiveness. Statistical analyses of variation in EMG variables revealed significant differences in motor patterns between duplicated muscles derived from a common ancestral muscle in seven of nine cases examined. Overall individual EMG timing variables (e.g. relative onset or duration of bursts) were slightly less likely to diverge functionally than amplitude variables (e.g. relative intensity of bursts). Functional divergence was found in significant overall differences between muscles and twice as frequently in significant muscle-by-prey interaction terms. Such interactions represent an underappreciated way in which motor patterns can evolve and diversify. Regional variation was documented in undivided muscles in two species, indicating that it is possible for functional subdivision to precede anatomical subdivision. This study shows that phylogenetic increases in the number of tetraodontiform jaw adductor muscles have been associated with increases in the functional complexity of the jaws at the level of muscle activation patterns.
CO2 excretion and postcapillary pH equilibration in blood-perfused turtle lungs
Authors: Stabenau Erich K. , Heming Thomas A. 
Published: April 2021

ABSTRACT
Turtles possess a significant postcapillary CO2 partial pressure disequilibrium between arterial blood and alveolar gas. There are several possible explanations for this blood disequilibrium including a slow rate of erythrocyte physiological anion shift (Cl−/HCO3− exchange) or inaccessibility of plasma HCO3− to red blood cell or pulmonary carbonic anhydrase. The present study characterized the contribution of erythrocyte anion exchange and pulmonary and erythrocyte carbonic anhydrase to CO2 excretion and, hence, to postcapillary CO2–HCO3−–H+ equilibration in blood-perfused turtle (Pseudemys scripta) lungs. Turtle lungs perfused in situ with red cell suspensions containing inhibitors of erythrocyte anion exchange and/or pulmonary and red cell carbonic anhydrase produced significant postcapillary blood and pH disequilibria, while no disequilibria were measured when lungs were perfused with control red cell suspensions. Erythrocyte anion exchange and pulmonary intravascular carbonic anhydrase contributed 11 % and 9 %, respectively, to CO2 excretion during single-pass perfusion, whereas red cell and pulmonary carbonic anhydrase contributed 32 % to the measured CO2 excretion. The lack of a measurable disequilibrium during perfusion with control erythrocyte suspensions in this study suggests that alternative mechanisms may be responsible for the arterial–lung disequilibrium measured during breathing or diving episodes in turtles.
Heart rates and diving behavior of leatherback sea turtles in the eastern pacific ocean
Authors: Southwood Amanda L. , Andrews Russel D. , Lutcavage Molly E. , Paladino Frank V. , West Nigel H. , George Robert H. , Jones David R. 
Published: April 2021

ABSTRACT
Heart rates and diving behavior of leatherback sea turtles (Dermochelys coriacea) were monitored at sea during the internesting interval. Instruments that recorded the electrocardiogram and the depth and duration of dives were deployed on six female leatherback turtles as they laid eggs at Playa Grande, Costa Rica. Turtles dived continually for the majority of the internesting interval and spent 57–68 % of the time at sea submerged. Mean dive depth was 19±1 m (mean ± S.D.) and the mean dive duration was 7.4±0.6 min. Heart rate declined immediately upon submergence and continued to fall during descent. All turtles showed an increase in heart rate before surfacing. The mean heart rate during dives of 17.4±0.9 beats min−1 (mean ± S.D.) was significantly lower than the mean heart rate at the surface of 24.9±1.3 beats min−1 (P&lt;0.05). Instantaneous heart rates as low as 1.05 beats min−1 were recorded during a 34 min dive. The mean heart rate over the entire dive cycle (dive + succeeding surface interval; 19.4±1.3 beats min−1 ) was more similar to the heart rate during diving than to the heart rate at the surface. Although dive and surface heart rates were significantly different from each other, heart rates during diving were 70 % of heart rates at the surface, showing that leatherback turtles do not experience a dramatic bradycardia during routine diving.
Impulse conduction in a sponge
Authors: Leys S. P. , Mackie G. O. , Meech R. W. 
Published: April 2021

ABSTRACT
All-or-none propagated electrical impulses were recorded from the hexactinellid sponge Rhabdocalyptus dawsoni using suction electrodes attached to lumps of aggregated sponge tissue grafted onto the surface of pieces of the same sponge. Impulses were normally evoked by means of externally applied electrical shocks. Recorded externally using an a.c.-coupled amplifier, the electrical event was triphasic and lasted approximately 30 s; integration gave a diphasic waveform. A further integration to give the form of the membrane action potential produced a monophasic signal. Impulses propagated at 0.27±0.1 cm s−1 with an absolute refractory period of 29 s and a relative refractory period of approximately 150 s. Concurrent thermistor flow meter recordings confirmed that water flow through the sponge was arrested following the passage of an impulse, presumably as result of the cessation of beating of the flagella in the flagellated chambers. Tactile stimuli also evoked impulses, as did addition of particulate material to the incoming water stream. Impulses continued to propagate through the sponge during arrests, indicating that the conduction and effector systems were independent. Sponges lack nerves, and a variety of evidence indicates that the conducting tissues are the syncytial trabecular reticulum and pinacoderm layers. Na+ -deficient solutions had little effect on the action potential, but propagation was blocked by 10 mmol l−1 Co2+, 1 mmol l−1 Mn2+ or 24 μmol l−1 nimodipine. Tetraethylammonium ions at 1–5 mmol l−1 also blocked propagation without prolonging the action potential. Impulse conduction in the sponge is discussed in relation to excitability and conduction in the protozoa and in plants and to non-nervous conduction in more advanced animals.
Luminal Acidification of Diverse Organelles by V-ATPase in Animal Cells
Authors: Futai Masamitsu , Oka Toshihiko , Sun-Wada Ge-Hong , Moriyama Yoshinori , Kanazawa Hiroshi , Wada Yoh 
Published: April 2021

ABSTRACT
Eukaryotic cells contain organelles bounded by a single membrane in the cytoplasm. These organelles have differentiated to carry out various functions in the pathways of endocytosis and exocytosis. Their lumina are acidic, with pH ranging from 4.5 to 6.5. This article describes recent studies on these animal cell organelles focusing on (1) the primary proton pump (vacuolar-type H+-ATPase) and (2) the functions of the organelle luminal acidity. We also discuss similarities and differences between vacuolar-type H+-ATPase and F-type ATPase. Our own studies and interests are emphasized.
Structure and Regulation of Insect Plasma Membrane H+ V-ATPase
Authors: Wieczorek Helmut , Grüber Gerhard , Harvey William R. , Huss Markus , Merzendorfer Hans , Zeiske Wolfgang 
Published: April 2021

ABSTRACT
H+ V-ATPases (V-ATPases) are found in two principal locations, in endomembranes and in plasma membranes. The plasma membrane V-ATPase from the midgut of larval Manduca sexta is the sole energizer of all transepithelial secondary transport processes. At least two properties make the lepidopteran midgut a model tissue for studies of general aspects of V-ATPases. First, it is a rich source for purification of the enzyme and therefore for structural studies: 20 larvae provide up to 0.5 mg of holoenzyme, and soluble, cytosolic V1 complexes can be obtained in even greater amounts of up to 2 mg.
Second, midgut ion-tranport processes are strictly controlled by the regulation of the V-ATPase, which is the sole energizer of all ion transport in this epithelium. Recent advances in our understanding the structure of the V1 and Vo complexes and of the regulation of the enzyme’s biosynthesis and ion-transport activity will be discussed.
H+V-ATPase-Dependent Luminal Acidification in the Kidney Collecting Duct and the Epididymis/Vas Deferens: Vesicle Recycling and Transcytotic Pathways
Authors: Brown Dennis , Breton Sylvie 
Published: April 2021

ABSTRACT
Many vertebrate transporting epithelia contain characteristic ‘mitochondria-rich’ cells that express high levels of a vacuolar proton-pumping ATPase (H+V-ATPase) on their plasma membrane and on intracellular vesicles. In the kidney cortex, A-cells and B-cells are involved in proton secretion and bicarbonate secretion, respectively, in the distal nephron and collecting duct. A-cells have an H+V-ATPase on their apical plasma membrane and on intracellular vesicles, whereas the cellular location of the H+V-ATPase can be apical, basolateral, bipolar or diffuse in B-cells. The rat epididymis and vas deferens also contain a distinct population of H+V-ATPase-rich epithelial cells. These cells are involved in generating a low luminal pH, which is involved in sperm maturation and in maintaining sperm in an immotile state during their passage through the epididymis and vas deferens. In both kidney and reproductive tract, H+V-ATPase-rich cells have a high rate of apical membrane recycling. H+V-ATPase molecules are transported between the cell surface and the cytoplasm in vesicles that have a well-defined ‘coat’ structure formed of the peripheral V1 subunits of the H+V-ATPase. In addition, we propose that B-type intercalated cells have a transcytotic pathway that enables them to shuttle H+V-ATPase molecules from apical to basolateral plasma membrane domains. This hypothesis is supported by data showing that A-cells and B-cells have different intracellular trafficking pathways for LGP120, a lysosomal glycoprotein. LGP120 was found both on the basolateral plasma membrane and in lysosomes in B-cells, whereas no LGP120 was detectable in the plasma membrane of A-cells. We propose that the ‘polarity reversal’ of the H+V-ATPase in B-intercalated cells is mediated by a physiologically regulated transcytotic pathway that may be similar to that existing in some other cell types.
Structure and Function of the Fo Complex of the ATP Synthase from Escherichia Coli
Authors: Altendorf Karlheinz , Stalz Wolf-Dieter , Greie Jörg-Christian , Deckers-Hebestreit Gabriele 
Published: April 2021

ABSTRACT
The membrane-bound ATP synthase (F1Fo) from mitochondria, chloroplasts and bacteria plays a crucial role in energy-transducing reactions. In the case of Escherichia coli, the reversible, proton-translocating ATPase complex consists of two different entities, F1 and Fo. The water-soluble F1 part carries the catalytic sites for ATP synthesis and hydrolysis. It is associated with the membrane-embedded Fo complex, which functions as a proton channel and consists of subunits a, b and c present in a stoichiometry of 1:2:12.
Subunit b was isolated by preparative gel electrophoresis, acetone-precipitated and renatured in a cholate-containing buffer. Reconstituted subunit b together with purified ac subcomplex is active in proton translocation and F1 binding, thereby demonstrating that subunit b had recovered its native conformation. Circular dichroism spectroscopy of subunit b reconstituted into liposomes revealed a rather high degree of α -helical conformation of 80 %.
After addition of a His6-tag to the N terminus of subunit a, a stable ab2 subcomplex was purified instead of a single subunit a, arguing in favour of a direct interaction between these subunits. After addition of subunit c and reconstitution into phospholipid vesicles, an Fo complex was obtained exhibiting rates of proton translocation and F1 binding comparable with those of wild-type Fo.
The epitopes of monoclonal antibodies against subunit c are located in the hydrophilic loop region (cL31–Q42) as mapped by enzyme-linked immunosorbent assay using overlapping synthetic heptapeptides. Binding studies revealed that all monoclonal antibodies (mAbs) bind to everted membrane vesicles irrespective of the presence or absence of F1. Although the hydrophilic region of subunit c, and especially the highly conserved residues cA40, cR41, cQ42 and cP43, are known to interact with subunits γ and ε of the F1 part, the mAb molecules have no effect on the function of Fo, either in proton translocation or in F1 binding. However, the F1 part and the mAb molecule(s) are bound simultaneously to the Fo complex, suggesting that not all c subunits are involved in the interaction with F1.
Cross-Linking and Electron Microscopy Studies of the Structure and Functioning of the Escherichia Coli ATP Synthase
Authors: Capaldi Roderick A. , Schulenberg Birte , Murray James , Aggeler Robert 
Published: April 2021

ABSTRACT
ATP synthase, also called F1Fo-ATPase, catalyzes the synthesis of ATP during oxidative phosphorylation. The enzyme is reversible and is able to use ATP to drive a proton gradient for transport purposes. Our work has focused on the enzyme from Escherichia coli (ECF1Fo). We have used a combination of methods to study this enzyme, including electron microscopy and chemical cross-linking.
The utility of these two approaches in particular, and the important insights they give into the structure and mechanism of the ATP synthase, are reviewed.
Rate Acceleration of ATP Hydrolysis by F1Fo-ATP Synthase
Authors: Senior Alan E. , Nadanaciva Sashi , Weber Joachim 
Published: April 2021

ABSTRACT
The rate acceleration of ATP hydrolysis by F1Fo-ATP synthase is of the order of 1011-fold. We present a cyclic enzyme mechanism for the reaction, relate it to known F1 X-ray structure and speculate on the linkage between enzyme reaction intermediates and subunit rotation. Next, we describe five factors known to be important in the Escherichia coli enzyme for the rate acceleration. First, the provision of substrate binding energy by residues lining the catalytic site is substantial; β-Lys155 and β-Arg182 are specific examples, both of which differentially support substrate MgATP versus product MgADP binding. Second, octahedral coordination of the Mg2+ in MgATP is crucial for both catalysis and catalytic site asymmetry. The residues involved are β-Thr156, β-Glu185 and β-Asp242. Third, there is stabilization of a pentacoordinate phosphorus catalytic transition state by residues β-Lys155, β-Arg182 and α-Arg376. Fourth, residue β-Glu181 binds the substrate water and stabilizes the catalytic transition state. Fifth, there is strong positive catalytic cooperativity, with binding of MgATP at all three sites yielding the maximum rate (Vmax); the molecular basis of this factor remains to be elucidated.
Steady-State and Pre-Steady-State Kinetics of the Mitochondrial F1Fo ATPase: Is Atp Synthase a Reversible Molecular Machine?
Authors: Vinogradov Andrei D. 
Published: April 2021

ABSTRACT
H+-ATP synthase (F1Fo ATPase) catalyzes the synthesis and/or hydrolysis of ATP, and the reactions are strongly affected by all the substrates (products) in a way clearly distinct from that expected of a simple reversibly operating enzyme. Recent studies have revealed the structure of F1, which is ideally suited for the alternating binding change mechanism, with a rotating γ-subunit as the energy-driven coupling device. According to this mechanism ATP, ADP, inorganic phosphate (Pi) and Mg2+ participate in the forward and reverse overall reactions exclusively as the substrates and products. However, both F1 and F1Fo demonstrate non-trivial steady-state and pre-steady-state kinetics as a function of variable substrate (product) concentrations. Several effectors cause unidirectional inhibition or activation of the enzyme. When considered separately, the unidirectional effects of ADP, Pi, Mg2+ and energy supply on ATP synthesis or hydrolysis may possibly be explained by very complex kinetic schemes; taken together, the results suggest that different conformational states of the enzyme operate in the ATP hydrolase and ATP synthase reactions. A possible mechanism for an energy-dependent switch between the two states of F1Fo ATPase is proposed.