bluuebunny/crossref_metadata_2025_split huggingface dataset:
Implications of Gill Arch Movements for Filter-Feeding: An X-Ray Cinematographical Study of Filter-Feeding White Bream (Blicca Bjoerkna) and Common Bream (Abramis Brama)
Authors: Den Berg Coen Van , Van Den Boogaart Jos G. M. , Sibbing Ferdinand A. , Osse Jan W. M. 
Published: April 2021

ABSTRACT
Previous research shows that the reducible-channel model of filter-feeding can probably be applied to common bream, but not to white bream. According to this model, zooplankton are retained in the channels between the medial gill rakers; the mesh size of the sieve can be reduced by lowering the lateral rakers of the neighbouring gill arch into these channels. Gill arch movements may well disturb this mechanism; the depressed lateral gill rakers will move in and out of the medial channels and also shift out of their centre. We have quantified these disturbances by measuring the gill arch movements during filter-feeding in white bream and common bream, using dorsal X-ray films. In both species, the lateral rakers are long enough to bridge the gill slits. It was expected that common bream, which can reduce their channels, would have considerably less shift out of the channel centre than white bream, which cannot reduce their channels. However, the predicted shift is 40–50% of the channel width in white bream and 75% in common bream. A new, dynamic retention mechanism is proposed for common bream. According to this hypothesis, once a particle is trapped in a reduced channel, the channel walls release mucus and the particle becomes sticky. Hence, particles need to be retained mechanically only during part of the gulping cycle. According to the hypothesis, this is achieved by sideways rotation of the lateral rakers in combination with their tapering shape. Retention mechanisms with interdigitating rakers are expected chiefly in facultative filter-feeders, because such mechanisms are easily disturbed by gill arch movements.
Activation and Physiological Role of Na+/H+ Exchange in Lamprey (Lampetra Fluviatilis) Erythrocytes
Authors: Virkki Leila V. , Nikinmaa Mikko 
Published: April 2021

ABSTRACT
The effects of intracellular acidification, osmotic shrinkage and (3-adrenergic stimulation on sodium transport across the membrane of lamprey (Lampetra fluviatilis) erythrocytes were investigated. Unidirectional ouabain-insensitive sodium flux, measured using radioactive 22Na, was increased markedly by intracellular acidification, to a lesser extent by osmotic shrinkage and only modestly by β-adrenergic stimulation. Na+/H+ exchange was activated in all of these cases. However, net sodium influx (and cell swelling caused by the influx of osmotically obliged water) was seen only in cells subjected to intracellular acidification. In contrast, practically no changes in red cell pH or in water or ion (Na+, K+ and Cl−) contents were seen after osmotic shrinkage or (3-adrenergic stimulation. Calculations of the [Na+]0/[Na+]i and [H+]0/[H+]i ratios across the erythrocyte membrane suggest that the virtual lack of net sodium movements in osmotically shrunken erythrocytes is due to the absence of a driving force for net transport of these ions via the Na+/H+ exchange pathway. It also appears that, in physiological conditions, the increase in the activity of the Na+/H+ exchanger by β-adrenergic stimulation is too small to mediate detectable net sodium transport.
Energy Metabolism by Trout Red Blood Cells: Substrate Utilisation
Authors: Pesquero J. , Roig T. , Bermudez J. , Sanchez J. 
Published: April 2021

ABSTRACT
The present study investigates energy metabolism by trout red blood cells. It is shown that they are able to use pyruvate at physiological concentrations as an aerobic source of energy. Moreover, microcalorimetric data suggest that trout erythrocytes are also able to use internal substrates, at least when maintained in vitro. Although the actual nature of these substrates has not been elucidated, glycogen appears to be the most probable.
The relationship between heat dissipation and oxygen consumption suggests that most of the oxygen is used to oxidize substrates, and the inhibition of respiratory activity by antimycin A indicates that there is no substantial utilisation of non-respiratory oxygen. However, the oxygen uptake by these cells does not appear to be related to substrate utilisation, measured from transformation of labelled molecules (either pyruvate or glucose); this may be due to mixing of labelled compounds with non-labelled molecules in the intracellular pools, because of the low metabolic rate of these cells.
Metamorphic And Speed Effects On Hindlimb Kinematics During Terrestrial Locomotion In The Salamander Dicamptodon Tenebrosus
Authors: Ashley-Ross Miriam A. 
Published: April 2021

ABSTRACT
The kinematics of the hindlimb during terrestrial treadmill locomotion in Dicamptodon tenebrosus were compared between larval and metamorphosed individuals at different speeds. Coordinates of marker points on the salamander’s midline, pelvic girdle and left hindlimb were digitized from high-speed videos (200 fields s−1). These yielded kinematic variables describing trunk flexion, pelvic girdle rotation, femoral protraction/retraction and knee flexion/extension. A three-way analysis of variance tested for mean differences among individuals, speeds and metamorphic stages for each variable. No significant overall effects of metamorphosis were found, although several variables showed significant stage × individual effects. Multivariate analyses revealed that the variance in kinematics of the larvae was significantly greater than that of the metamorphosed salamanders. Several variables showed significant speed effects or strong trends, among them stride length (increases with speed), cycle duration (decreases), contact interval (decreases) and phase variables describing the relative timing between minimum/maximum angles and the beginning of stance/swing phase. Such changes with speed are consistent with those shown for diverse arthropods and tetrapods and suggest that changes in stride length and timing events during a stride represent a general mechanism for effecting an increase in locomotor speed.
Effects of Muscle Length on the Emg–Force Relationship of the Cat Soleus Muscle Studied Using Non-Periodic Stimulation of Ventral Root Filaments
Authors: Guimaraes A. C. , Herzog W. , Hulliger M. , Zhang Y. T. , Day S. 
Published: April 2021

ABSTRACT
The effects of changing the length of the cat soleus muscle on electromyographic (EMG) signals, muscle force and the corresponding EMG–force relationship were assessed using distributed stimulation of ten ventral root filaments and irregular interpulse intervals. EMG–force relationships were first determined for four muscle lengths using a protocol of simultaneous addition and rate modulation of ventral root filaments. In the second test, three submaximal levels of stimulation were applied at eight muscle lengths. EMG signals were obtained using surface and wire electrodes, and force was measured using a strain transducer. For most muscle lengths, the relationships between integrated EMG and mean force obtained using wire and surface electrodes were sigmoid with a linear intermediate region. The effects of muscle length on EMG signals were likely to be associated with movement of the recording electrodes relative to each other and to the active motor units. Mean forces increased with increasing muscle length and with increasing levels of stimulation. Mean force–length relationships obtained using submaximal stimulation were not simply scaled down versions of the force–length relationship obtained using supramaximal stimulation of the soleus nerve, but appeared to be shifted towards longer muscle lengths.
Na+/Ca2+ Antiport in the Mammalian Heart
Authors: Reeves John P. , Condrescu Madalina , Chernaya Galina , Gardner Jeffrey P. 
Published: April 2021

ABSTRACTThe cardiac Na+/Ca2+ antiporter moves 3 Na+ across the plasma membrane in exchange for a single Ca2+ moving in the opposite direction. It is the principal Ca2+ efflux mechanism in myocardial cells; however, it also contributes to Ca2+ influx under certain conditions. It is particularly abundant in the heart, but is also expressed in other tissues such as smooth and skeletal muscle, the kidney and the brain. The cardiac antiporter itself is a protein of 938 amino acids, with a cleaved NH2-terminal signal sequence, 11 putative transmembrane segments and a large hydrophilic domain of 520 amino acids between the fifth and sixth transmembrane segments. Alternative mRNA splicing mechanisms generate tissue-specific isoforms in a limited region within the hydrophilic domain. Most of the hydrophilic domain can be deleted without altering the kinetics of the transport reaction; the regulatory properties of the antiporter are markedly affected by this deletion however. Two different modes of regulation of antiport activity have been characterized and appear to involve two different inactive states of the carrier. The first is promoted by the presence of cytosolic Na+ in the absence of ATP and the second is promoted by the absence of cytosolic Ca2+. ATP-dependent regulation of antiport activity may involve interactions with the cellular cytoskeleton, since the effects of ATP depletion can be mimicked by cytochalasin D. Ca2+-dependent regulation of antiport activity appears to involve the interaction of cytosolic Ca2+ with two acidic amino acid sequences within a limited region of the hydrophilic domain.
Endosomal Accumulation of pH Indicator Dyes Delivered as Acetoxymethyl Esters
Authors: Slayman Clifford L. , Moussatos Vasiliana V. , Webb Watt W. 
Published: April 2021

ABSTRACT
Intracellular distributions of the putative cytosolic pH indicator dyes BCECF [2′,7′-bis-(2-carboxyethyl)-5(and 6)-carboxyfluorescein], C.SNARF [5(and 6)-carboxy-seminaphthorhodafluor-1], and C.SNARF-calcein have been examined in Neurospora crassa and in murine fibroblasts (NIH-3T3 cells) under conditions in which both kinds of cells produce visible microscopic vacuoles. All three dyes were administered in electroneutral forms, with the hydroxyl and carboxyl groups esterified (designated as -AM esters). As judged qualitatively from fluorescence levels, hydrolytic derivatives of the two heavily esterified dyes (BCECF-AM and C.SNARF-calcein-AM) accumulated in the vacuoles after exposures of approximately 15 min or more, while the simpler dye (C.SNARF-AM) and its derivatives were almost excluded from visible vacuoles. Fluorescence from this dye, alone among the three, also washed out of Neurospora rapidly upon removal of extracellular dye. There was no evidence for stable accumulation of any of the dyes in cytosol per se. For BCECF(-AM), comparison of the distribution of fluorescence with the size distribution of vacuoles in Neurospora strongly suggests that the dyes are also accumulated by endomembranal vesicles (EMVs) which lie below the limit of resolution in the light microscope, and the same inference can be drawn for the fibroblasts. Uptake of -AM dyes by EMVs, including frank vacuoles, probably results from the action of intravesicular esterases, following diffusional entry of lipophilic neutral molecules or partially de-esterified anions. Calculations of actual cytosolic pH values, or even changes of pH, based on intracellular fluorescence of these dyes, clearly depend upon quantitative knowledge of the subcellular dye distribution. Therefore, until the problem is reliably solved of how to visualize submicroscopic vesicles in living cells, the safest approach to the use of BCECF, C-SNARF and their congeners for cytosolic pH measurement would be to devise methods for coaxing uptake of the ionic forms of these dyes and to abandon use of the esterified forms.
Molecular Physiology of the Na+/H+ Antiporter in Escherichia Coli
Authors: Padan Etana , Schuldiner Shimon 
Published: April 2021

ABSTRACT
All living cells maintain an inwardly directed Na+ gradient and a constant intracellular pH. Na+/H+ antiporters have been assigned an essential role in these homeostatic mechanisms in all cells. In Escherichia coli, two Na+/H+ antiporter genes, nhaA and nhaB, have been cloned. Deletion of either one or both showed that NhaA is essential for adaptation to high salinity, for growth at alkaline pH in the presence of Na+ and for challenging Li+ toxicity. NhaB confers tolerance to low levels of Na+ and becomes essential when the activity of NhaA limits growth.
The adaptive response to Na+ is mediated by the positive regulator nhaR, which transduces the signal (intracellular Na+) to expression of the nhaA gene. We have identified Glu-134 of NhaR as part of the ‘Na+ sensor’ of NhaA.
In agreement with the role of NhaA in pH homeostasis, its Na+-dependent expression is enhanced at alkaline pH. Reconstitution of pure NhaA and NhaB in proteoliposomes demonstrates that, whereas both are electrogenic (the H+/Na+ stoichiometry of NhaA is 2), only NhaA is pH-dependent, increasing its activity 1000-fold between pH 7 and 8.5. Mutating all the histidines of NhaA shows that His-226 is part of the ‘pH sensor’ of NhaA.
Bacterial Anion Exchange: Reductionist and Integrative Approaches to Membrane Biology
Authors: Maloney Peter C. , Yan Run-Tao , Abe Keietsu 
Published: April 2021

ABSTRACT
Studies of two different bacterial anion exchange proteins (antiporters) led us to conclude that both reductionist and integrative approaches contribute to progress in understanding membrane biology. We have used a reductionist perspective in applying cysteine scanning mutagenesis to probe individual amino acid positions of UhpT (uptake of hexose phosphate transporter), the carrier responsible for transport of glucose 6-phosphate by Escherichia coli. This work has established experimental criteria that should allow one to identify and localize the translocation pathway in such membrane proteins. An integrative view is exemplified by work with OxlT (oxalate transporter), the carrier used by an anaerobe Oxalobacter formigenes to catalyze the antiport of divalent oxalate and monovalent formate. The activity of OxlT is functionally coordinated with that of a cytosolic oxalyl decarboxylase; together, these vectorial and scalar activities constitute a metabolic proton pump, allowing O. formigenes to display decarboxylative phosphorylation. The role played by OxlT argues that membrane carriers can assume unanticipated emergent properties when their biochemical functions are properly articulated in relation to other aspects of cell function.
Hexose/H+ Symporters in Lower and Higher Plants
Authors: Caspari Thomas , Will Andreas , Opekarová Miroslava , Sauer Norbert , Tanner Widmar 
Published: April 2021

ABSTRACT
A well-studied transporter of plant cells is the hexose/H+symporter of the unicellular alga Chlorella kessleri. Its properties, studied in vivo, are briefly summarized. In part, they are atypical and it has been suggested that this porter acts in an asymmetric way. Three genes coding for Chlorella hexose transport activity have been identified (HUP1, HUP2 and HUP3). HUP1 cDNA expressed in a mutant of Schizosaccharomyces pombe not transporting any D-glucose has been studied in detail. Several mutants with changed Km values for substrate were obtained, some by random polymerase chain reaction mutation and selection for decreased sensitivity towards the toxic sugar 2-deoxyglucose, some by site-directed mutagenesis. The amino acids affected clustered in the centre of the putative transmembrane helices V, VII and XI. Large families of hexose transporter genes are found in higher plants (Arabidopsis, Chenopodium, Ricinus). Their functional role is discussed. Finally, the progress made in studying plant transporters in a vesicle system energized by cytochrome c oxidase is summarized.
Thermodynamics of Symport and Antiport Catalyzed by Cloned or Native Transporters
Authors: Gerencser George A. , Stevens Bruce R. 
Published: April 2021

ABSTRACT
Thermodynamic measurements are required to confirm whether cloned transport-associated proteins in a membrane truly constitute a functional transport system. Symport or antiport, catalyzed by native systems or by cloned proteins in membranes, can lead to steady-state intracellular accumulation of solute when the electrochemical potentials of activator ion and solute are energetically coupled. Secondary active transport can occur if an appropriate physical coupling mechanism exists in the membrane. Driving forces for secondary active transport are ultimately established by primary active transport or respiration. Steep steady-state gradients of solute can be maintained when the ion:solute coupling ratio is greater than one and/or when coupling includes an electrical component. Although the steady-state accumulation of substrate is independent of the exact physical mechanism of transport, non-equilibrium and equilibrium transport kinetics aid in interpreting the rate, direction (symport versus antiport) and control of ion-coupled flux across a membrane. In some cases, the activator ion’s chemical gradient alone is energetically adequate to maintain steady-state intracellular accumulation of solute, as demonstrated in invertebrate epithelial cells. To interpret accumulation ratios accurately, it is necessary to measure the intracellular activity coeffients for ions. For example, liquid ion-exchange microelectrode measurements demonstrate that over 30% of intracellular Na+ can be sequestered in epithelial cells.
The Effect of ATP-Sensitive Potassium Channel Modulation on Heart Rate in Isolated Muskrat and Guinea Pig Hearts
Authors: Streeby Daniel R. , McKean Thomas A. 
Published: April 2021

ABSTRACT
Muskrats (Ondontra zibethicus) are common freshwater diving mammals exhibiting a bradycardia with both forced and voluntary diving. This bradycardia is mediated by vagal innervation; however, if hypoxia is present there may be local factors that also decrease heart rate. Some of these local factors may include ATP-sensitive potassium channel activation and extracellular accumulation of potassium ions, hydrogen ions and lactate. The purpose of this study was to investigate the role of these factors in the isolated perfused hearts of muskrats and of a non-diving mammal, the guinea pig. Although lactate and proton administration reduced heart rate in isolated muskrat and guinea pig hearts, there was no difference in the response to lactate and proton infusion between the two species. Muskrat hearts were more sensitive to the heart-rate-lowering effects of exogenously applied potassium than were guinea pig hearts. Early increases in extracellular potassium concentration during hypoxia are thought to be mediated by the ATP-sensitive potassium channel. Activation of these channels under normoxic conditions had a mildly negative chronotropic effect in both species; however, activation of these channels with Lemakalim under hypoxic conditions caused the guinea pig heart to respond with an augmented bradycardia similar to that seen in the hypoxic muskrat heart in the absence of drugs. Inhibition of these channels by glibenclamide during hypoxia was partially successful in blocking the bradycardia in guinea pig hearts, but inhibition of the same channels in hypoxic muskrat hearts had a damaging effect as two of five hearts went into contracture during the hypoxia. Thus, although ATP-sensitive potassium channels appear to have a major role in the bradycardia of hypoxia in guinea pigs, the failure to prevent the bradycardia by inhibition of these channels in muskrat hearts suggests that multiple factors are involved in the hypoxia-induced bradycardia in this species.
Spontaneous Swimming Activity of Atlantic Cod Gadus Morhua Exposed to Graded Hypoxia at Three Temperatures
Authors: Schurmann Henrik , Steffensen John Fleng 
Published: April 2021

ABSTRACT
The spontaneous swimming activity of Atlantic cod Gadus morhua was investigated at graded levels of hypoxia at three temperatures (5, 10 and 15°C) by using a computerized system monitoring animal activity. The fish were tested individually, and swimming distance was used as a measure of activity. No significant effect of temperature on swimming distance in normoxic water was found. At all temperatures, activity level decreased with decreasing oxygen saturation. Swimming behaviour at normoxia and 50% and 25% oxygen saturation is described. No apparent avoidance of hypoxic water was found based on the distribution of swimming speeds and turning angles. The possible benefits of a decreased activity level in a hypoxic environment are discussed.
Respiratory Rhythm In The Isolated Central Nervous System Of Newborn Opossum
Authors: Zou Dong-Jing 
Published: April 2021

ABSTRACT
Respiratory activity was recorded from spinal ventral roots in the isolated intact central nervous system (CNS) of newborn opossum, Monodelphis domestica. These signals occurred in synchrony with movements of the ribs and the electromyogram (EMG) recorded from the intercostal muscles during inspiration. Rhythmical activity could be recorded for more than 6 h in acute preparations. The rhythm-generating region was shown to be located in the lower brain stem by perfusing different CNS regions with medium containing 20 mmol l−1 Mg2+, which blocks synaptic transmission reversibly in the opossum CNS. The conclusion that respiration was generated by neurones in the lower brain stem was further confirmed by selective ablation of part of the CNS. Recordings were made from 128 neurones in the respiratory region of the lower brain stem with activity related to the respiratory rhythm. They consisted of two inspiratory groups and two expiratory groups. In the groups of inspiratory units, recordings were made from 69 early inspiratory and 38 inspiratory units. In the groups of expiratory units, recordings were made from 17 post-inspiratory and 4 expiratory units. The sites of 22 respiratory neurones were marked in 4-day-old animals by injecting Pontamine Sky Blue. These neurones were distributed from 175 μm anterior to 525 μm posterior to the obex, from 225 to 450 μm lateral to the midline and from 175 to 425 μm deep to the ventral surface of the brain stem. The respiratory rhythm recorded in the isolated CNS was influenced by pH and neurotransmitters. The respiratory rate decreased by about 26% at high pH (7.7) and increased by about 33% at low pH (7.1). Bath application of noradrenaline (30– 100 μmol l−1) decreased the respiratory rate and increased the amplitude of the rhythmic bursts significantly. All these effects were reversible. The results presented here indicate that the isolated intact CNS of newborn opossum offers advantages for exploring mechanisms responsible for generating the respiratory rhythm.