bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vasodilation of swimbladder vessels in the european eel (Anguilla anguilla) induced by vasoactive intestinal polypeptide, nitric oxide, adenosine and protons
Authors: Schwerte Thorsten , Holmgren Susanne , Pelster Bernd 
Published: April 2021

ABSTRACT
The effects of β-adrenergic stimulation, vasoactive intestinal polypeptide (VIP), adenosine, the nitric oxide (NO)-releasing agent sodium nitroprusside and of metabolic end-products of gas gland cell metabolism on swimbladder blood flow were investigated using saline- or blood-perfused swimbladder preparations of the freshwater European eel Anguilla anguilla. While β-adrenergic vasodilation was not detectable, a bolus injection of adenosine (100 μl, 10−7 mol l−1) and application of VIP (10−7 mol kg−1) caused a significant decrease in perfusion pressure in saline-perfused swimbladder preparations. Immunohistochemical analysis revealed the presence of VIP-immunoreactive nerve fibres in the swimbladder artery and in the swimbladder vein (seawater-adapted eels were used for immunohistochemical studies). Application of sodium nitroprusside also elicited a small, but significant, decrease in perfusion pressure in saline-perfused swimbladder preparations, while preincubation of swimbladder tissue with Nωnitro-L-arginine, a non-selective inhibitor of nitric oxide synthase, significantly enhanced the flow-induced increase in perfusion pressure. Lactate, the major metabolic end-product of gas gland cell metabolism, had no effect on perfusion pressure. In contrast, an increase in proton concentration in both saline- and blood-perfused preparations induced a vasodilation, as indicated by a significant decrease in perfusion pressure. The results demonstrate that VIP, NO, adenosine and protons may induce a vasodilation of swimbladder blood vessels. None of these effects, however, compares in time span with the previously described immediate, short-lasting vasodilation of swimbladder vessels elicited by pulse stimulation of the vagus nerve.
Secretion of primary urine by glomeruli of the hagfish kidney
Authors: Riegel J. A. 
Published: April 2021

ABSTRACT
Adrenaline and noradrenaline increased the perfusion pressure (Pperf) and single glomerulus filtration rate (SGFR) of perfused hagfish glomeruli. Small amounts (0.1 % or 0.5 %) of bovine serum albumin (BSA) in perfusion fluids containing Ficoll 70 did not diminish the loss of colloid from hagfish glomerular capillaries as has been reported for other perfused capillaries. However, replacement of Ficoll 70 with an osmotically equivalent amount (3 %) of BSA appreciably reduced colloid loss. It was concluded that adrenaline and colloids enhanced flow through the urine-forming capillaries. Whereas adrenaline elevated the SGFR, colloid lowered the SGFR probably by a direct effect on the fluid permeability of the capillary walls.
The flow-enhancing effect of adrenaline was used to ensure the exposure of urine-forming capillaries to two inhibitors of active fluid transport, ouabain and 2,4-dinitrophenol (DNP). Both substances lowered the single glomerulus filtration fraction (SGFF), probably by affecting a fluid secretion mechanism. In addition, DNP diminished the flow-enhancing effect of adrenaline. This study provides relatively unequivocal evidence that fluid secretion underlies the formation of primary urine by the hagfish.
In vivo locomotor strain in the hindlimb bones of Alligator mississippiensis and Iguana iguana: implications for the evolution of limb bone safety factor and non-sprawling limb posture
Authors: Blob Richard W. , Biewener Andrew A. 
Published: April 2021

ABSTRACT
Limb postures of terrestrial tetrapods span a continuum from sprawling to fully upright; however, most experimental investigations of locomotor mechanics have focused on mammals and ground-dwelling birds that employ parasagittal limb kinematics, leaving much of the diversity of tetrapod locomotor mechanics unexplored. This study reports measurements of in vivo locomotor strain from the limb bones of lizard (Iguana iguana) and crocodilian (Alligator mississippiensis) species, animals from previously unsampled phylogenetic lineages with non-parasagittal limb posture and kinematics. Principal strain orientations and shear strain magnitudes indicate that the limb bones of these species experience considerable torsion during locomotion. This contrasts with patterns commonly observed in mammals, but matches predictions from kinematic observations of axial rotation in lizard and crocodilian limbs. Comparisons of locomotor load magnitudes with the mechanical properties of limb bones in Alligator and Iguana indicate that limb bone safety factors in bending for these species range from 5.5 to 10.8, as much as twice as high as safety factors previously calculated for mammals and birds. Limb bone safety factors in shear (3.9–5.4) for Alligator and Iguana are also moderately higher than safety factors to yield in bending for birds and mammals. Finally, correlations between limb posture and strain magnitudes in Alligator show that at some recording locations limb bone strains can increase during upright locomotion, in contrast to expectations based on size-correlated changes in posture among mammals that limb bone strains should decrease with the use of an upright posture. These data suggest that, in some lineages, strain magnitudes may not have been maintained at constant levels through the evolution of a non-sprawling posture unless the postural change was accompanied by a shift to parasagittal kinematics or by an evolutionary decrease in body size.
Kinematics of intraoral transport and swallowing in the herbivorous lizard Uromastix acanthinurus
Authors: Herrel Anthony , Vree Frits de 
Published: April 2021

ABSTRACT
The kinematics of intraoral transport and swallowing in lizards of the species Uromastix acanthinurus (Chamaeleonidae, Leiolepidinae) were investigated using cineradiography (50 frames s−1 ). Additional recordings were also made using high-speed (500 frames s−1 ) and conventional video systems (25 frames s−1 ). Small metal markers were inserted into different parts of the upper and lower jaw and the tongue. Cineradiographic images were digitised, and displacements of the body, head, upper and lower jaw and the tongue were quantified. Twenty additional variables depicting displacements and the timing of events were calculated. Multivariate analyses of variance indicated significant differences between feeding stages. Remarkably, only very few food-type-dependent differences were observed during intraoral transport, and no such differences could be demonstrated during swallowing. Using previously published data for the closely related insectivorous lizard Plocederma stellio, the effect of dietary specialisation in U. acanthinurus on the kinematic variables while eating locusts was examined. Species differed in a number of gape- and tongue-related variables. These differences may be related to differences in tongue structure between the species. Clearly, U. acanthinurus possesses a specialised gut and dental structure that allows them efficiently to cut pieces from whole leaves. However, a decrease in modulatory capacity seems to be a consequence of dietary specialisation in Uromastix acanthinurus.
Cardiovascular and gill microcirculatory effects of endothelin-1 in atlantic cod: evidence for pillar cell contraction
Authors: Stensløkken Kåre-Olav , Sundin Lena , Nilsson Göran E. 
Published: April 2021

ABSTRACT
Endothelin-1 (ET-1) has been shown to cause a considerable increase in the vascular resistance of fish gills. In trout, recent evidence suggest that this is the result of pillar cell contraction in the gill lamellae. Using epi-illumination microscopy to observe the gill lamellae of anaesthetised Atlantic cod (Gadus morhua), we show that ET-1 (100 ng kg−1, injected into the ventral aorta) causes an increase in pillar cell diameter, consistent with pillar cell contraction, and a shift of intralamellar blood flow from the lamellar sheet to the outer marginal channels. Simultaneously, there was an increase in ventral aortic blood pressure, a reduction in cardiac output, an increase in gill vascular resistance and a reduction in the oxygen partial pressure of venous blood. All these effects were blocked by the ETA/ETB receptor antagonist bosentan (5 mg kg−1 ). Pillar cell contraction is likely to be a mechanism for matching the functional respiratory surface area with the instantaneous respiratory needs of the fish.
Crystallization, Structure and Dynamics of the Proton-Translocating P-Type ATPase
Authors: Scarborough Gene A. 
Published: April 2021

ABSTRACT
Large single three-dimensional crystals of the dodecylmaltoside complex of the Neurospora crassa plasma membrane H+-ATPase (H+P-ATPase) can be grown in polyethylene-glycol-containing solutions optimized for moderate supersaturation of both the protein surfaces and detergent micellar region. Large two-dimensional H+ P-ATPase crystals also grow on the surface of such mixtures and on carbon films located at such surfaces. Electron crystallographic analysis of the two-dimensional crystals grown on carbon films has recently elucidated the structure of the H+ P-ATPase at a resolution of 0.8 nm in the membrane plane. The two-dimensional crystals comprise two offset layers of ring-shaped ATPase hexamers with their exocytoplasmic surfaces face to face. Side-to-side interactions between the cytoplasmic regions of the hexamers in each layer can be seen, and an interaction between identical exocytoplasmic loops in opposing hexamer layers holds the two layers together. Detergent rings around the membrane-embedded region of the hexamers are clearly visible, and detergent–detergent interactions between the rings are also apparent. The crystal packing forces thus comprise both protein–protein and detergent–detergent interactions, supporting the validity of the original crystallization strategy. Ten transmembrane helices in each ATPase monomer are well-defined in the structure map. They are all relatively straight, closely packed, moderately tilted at various angles with respect to a plane normal to the membrane surface and average approximately 3.5 nm in length. The transmembrane helix region is connected in at least three places to the larger cytoplasmic region, which comprises several discrete domains separated by relatively wide, deep clefts. Previous work has shown that the H+ P-ATPase undergoes substantial conformational changes during its catalytic cycle that are not changes in secondary structure. Importantly, the results of hydrogen/deuterium exchange experiments indicate that these conformational changes are probably rigid-body interdomain movements that lead to cleft closure. When interpreted within the framework of established principles of enzyme catalysis, this information on the structure and dynamics of the H+ P-ATPase molecule provides the basis of a rational model for the sequence of events that occurs as the ATPase proceeds through its transport cycle. The forces that drive the sequence can also be clearly stipulated. However, an understanding of the molecular mechanism of ion transport catalyzed by the H+ P-ATPase awaits an atomic resolution structure.
Analysis of the Membrane Domain of the Gastric H+/K+-ATPase
Authors: Munson Keith , Lambrecht Nils , Shin Jai Moo , Sachs George 
Published: April 2021

ABSTRACT
A structure of the catalytic or alpha subunit of the H+/K+-ATPase, with ten transmembrane segments, and of the beta subunit, with a single such segment, was established using a combination of tryptic cleavage and peptide sequencing and in vitro translation. Sites at which covalent ligands bind to external surfaces were also defined by cleavage, separation and sequencing. Cys813 was found to be the common covalent binding site for all the substituted pyridyl methylsulfinyl benzimidazoles. The binding region of a K+-competitive reagent, the 1,2α-imidazo-pyridine SCH 28080, was defined by the kinetic effects of site-specific mutations. Amino acids substitutions in membrane-spanning segments M1, M3, M4 and M6 were found to influence the apparent inhibitor constant, Ki, to varying degrees, some having a large effect, some a moderate effect and some a slight effect, whereas some mutations had no effect. We interpret changes in Ki without effects on the apparent Michaelis constant, Km, as affecting SCH 28080 binding only. Mutation of Cys813 significantly affected the Ki for SCH 28080, explaining the prevention of benzimidazole inhibition by the imidazo-pyridine.
A model of the alpha subunit was constructed with a vestibule on the luminal surface of the pump bounded by M1–M6 and containing the SCH 28080 binding region. The cation binding site is suggested to be more towards the cytoplasmic face of the enzyme’s membrane domain. This model predicts the membrane peptide associations for the catalytic subunit. Biochemical and yeast two-hybrid methods place the beta subunit in association with M8, whereas similar methods place M5/6 in proximity to M9/10. These results, when combined with analysis of the two-dimensional crystals of the sarcoplasmic reticular Ca2+ and Neurospora crassa H+-ATPases, provide the basis for a tentative model of the arrangement of the six core segments of the gastric H+/K+-ATPase.
Composition and Assembly of the Yeast Vacuolar H+-ATPase Complex
Authors: Graham Laurie A. , Powell Ben , Stevens Tom H. 
Published: April 2021

ABSTRACT
The proton-translocating ATPase (H+-ATPase) found on the membrane of the yeast vacuole is the best characterized member of the V-type ATPase family. Biochemical and genetic screens have led to the identification of 14 genes, the majority designated VMA (for vacuolar membrane ATPase) encoding subunits of the enzyme complex. At least eight genes encode for proteins comprising the peripherally associated catalytic V1 subcomplex, and six genes code for proteins forming the proton-translocating membrane Vo subcomplex. Several additional genes have been identified that encode proteins that are not part of the final V-ATPase complex yet are required for its assembly. These non-subunit Vma proteins function as dedicated V-ATPase assembly factors since their absence appears to inhibit assembly of the V-ATPase only. The assembly factors designated Vma12p, Vma21p and Vma22p have been localized to the membrane of the endoplasmic reticulum and aid the association of newly synthesized V-ATPase subunits translocated into the endoplasmic reticulum membrane. Two of these proteins, Vma12p and Vma22p, function together in an assembly complex that interacts directly with nascent V-ATPase subunits.
Coupling H+ Transport to Rotary Catalysis in F-Type ATP Synthases: Structure and Organization of the Transmembrane Rotary Motor
Authors: Fillingame R. H. , Jiang W. , Dmitriev O. Y. 
Published: April 2021

ABSTRACT
H+-transporting F1Fo-type ATP synthases utilize a transmembrane H+ potential to drive ATP formation by a rotary catalytic mechanism. ATP is formed in alternating β subunits of the extramembranous F1 sector of the enzyme, synthesis being driven by rotation of the γ subunit in the center of the F1 molecule between the alternating catalytic sites. The H+ electrochemical potential is thought to drive γ subunit rotation by first coupling H+ transport to rotation of an oligomeric rotor of c subunits within the transmembrane Fo sector. The γ subunit is forced to turn with the c12 oligomeric rotor as a result of connections between subunit c and the γ and ε subunits of F1. In this essay, we will review recent studies on the Escherichia coli Fo sector. The monomeric structure of subunit c, determined by nuclear magnetic resonance (NMR), is discussed first and used as a basis for the rest of the review. A model for the structural organization of the c12 oligomer in Fo, deduced from extensive cross-linking studies and by molecular modeling, is then described. The interactions between the the a1b2 ‘stator’ subcomplex of Fo and the c12 oligomer are then considered. A functional interaction between transmembrane helix 4 of subunit a (aTMH-4) and transmembrane helix 2 of subunit c (cTMH-2) during the proton-release step from Asp61 on cTMH-2 is suggested. Current a–c cross-linking data can only be explained by helix–helix swiveling or rotation during the proton transfer steps. A model that mechanically links helix rotation within a single subunit c to the incremental 30 ° rotation of the c12 oligomer is proposed. In the final section, the structural interactions between the surface residues of the c12 oligomer and subunits ε and γ are considered. A molecular model for the binding of subunit ε between the exposed, polar surfaces of two subunits c in the oligomer is proposed on the basis of cross-linking data and the NMR structures of the individual subunits.
Cellular Role of the V-Atpase In Neurospora Crassa: Analysis of Mutants Resistant to Concanamycin or Lacking the Catalytic Subunit A
Authors: Bowman Emma Jean , Bowman Barry J. 
Published: April 2021

ABSTRACT
Vacuolar ATPases (V-ATPases) are large complex enzymes that are structural and mechanistic relatives of F1Fo-ATPases. They hydrolyze ATP and pump protons across membranes to hyperpolarize membranes and, often, to acidify cellular compartments. The proton gradients generated are used to drive the movement of various compounds across membranes. V-ATPases are found in membranes of archaebacteria and some eubacteria, in various components of the endomembrane system of all eukaryotes and in the plasma membranes of many specialized eukaryotic cells. They have been implicated in a wide variety of cellular processes and are associated with several diseases. Bafilomycin and concanamycin, specific inhibitors of V-ATPases, have been instrumental in implicating the V-ATPase in many of these roles. To understand further the mechanism of inhibition by these antibiotics and the physiological role of the enzyme in the cell, we have isolated mutants of the filamentous fungus Neurospora crassa that are resistant to concanamycin. Concanamycin has a dramatic effect on hyphal morphology at acid pH and is lethal at basic pH. In the resistant mutants, the cells can germinate and grow, although abnormally, in basic medium. Thus far, none of the mutants we have characterized is mutated in a gene encoding a subunit of the V-ATPase. Instead, the largest class of mutants is mutated in the gene encoding the plasma-membrane H+-ATPase. Mutations in at least four uncharacterized genes can also confer resistance. Inactivation of the V-ATPase by disruption of vma-1, which encodes the catalytic subunit (A) of the enzyme, causes a much more severe phenotype than inhibition by concanamycin. A strain lacking vma-1 is seriously impaired in rate of growth, differentiation and capacity to produce viable spores. It is also completely resistant to concanamycin, indicating that the inhibitory effects of concanamycin in vivo are due to inhibition of the V-ATPase. How the multiplicity of ATPases within a cell is regulated and how their activity is integrated with other metabolic reactions is poorly understood. Mutant analysis should help unravel this puzzle.
Transport Properties of Cultured Branchial Epithelia from Freshwater Rainbow Trout: A Novel Preparation with Mitochondria-Rich Cells
Authors: Fletcher Mary , Kelly Scott P. , Pärt Peter , O’Donnell Michael J. , Wood Chris M. 
Published: April 2021

ABSTRACT
A new double-seeded insert (DSI) technique is described for culture of branchial epithelial preparations from freshwater rainbow trout on filter supports. DSI epithelia contain both pavement cells and mitochondria-rich (MR) cells (15.7±2.5 % of total cell numbers). MR cells occur singly or in clusters, are voluminous, open apically to the ‘external environment’ and exhibit ultrastructural characteristics similar to those found in the ‘chloride cells’ of freshwater fish gills. After 6–9 days in culture with Leibovitz’s L-15 medium on both surfaces (symmetrical conditions), transepithelial resistance (TER) stabilized at values as high as 34 kΩ cm2, indicative of electrically ‘tight’ epithelia. The density of MR cells, the surface area of their clusters and transepithelial potential (TEP; up to +8 mV basolateral positive, mean +1.9±0.2 mV) were all positively correlated with TER. In contrast, preparations cultured using an earlier single-seeded insert (SSI) technique contained only pavement cells and exhibited a negligible TEP under symmetrical conditions. Na+/K+-ATPase activities of DSI preparations were comparable with those in gill filaments, but did not differ from those of SSI epithelia. Replacement of the apical medium with fresh water to mimic the in vivo situation (asymmetrical conditions) induced a negative TEP (−6 to −15 mV) and increased permeability to the paracellular marker PEG-4000. Under symmetrical conditions, unidirectional Na+ and Cl− fluxes were in balance, and there was no active transport by the Ussing flux ratio criterion. Under asymmetrical conditions, there were large effluxes, small influxes and evidence for active Cl− uptake and Na+ extrusion. Unidirectional Ca2+ fluxes were only 0.5–1.0 % of Na+ and Cl− fluxes; active net Ca2+ uptake occurred under symmetrical conditions and active net extrusion under asymmetrical conditions. Thus, DSI epithelia exhibit some of the features of the intact gill, but improvements in culture conditions are needed before the MR cells will function as true freshwater ‘chloride cells’.
Desensitisation of Chromaffin Cell Nicotinic Receptors Does Not Impede Catecholamine Secretion During Acute Hypoxia in Rainbow Trout (Oncorhynchus Mykiss)
Authors: Lapner Katherine N. , Montpetit Colin J. , Perry Steve F. 
Published: April 2021

ABSTRACT
Experiments were performed on adult rainbow trout (Oncorhynchus mykiss) in vivo using chronically cannulated fish and in situ using a perfused posterior cardinal vein preparation (i) to characterise the desensitisation of chromaffin cell nicotinic receptors and (ii) to assess the ability of fish to secrete catecholamines during acute hypoxia with or without functional nicotinic receptors. Intra-arterial injection of nicotine (6.0×10−7 mol kg−1) caused a rapid increase in plasma adrenaline and noradrenaline levels; the magnitude of this response was unaffected by an injection of nicotine given 60 min earlier. Evidence for nicotinic receptor desensitisation, however, was provided during continuous intravenous infusion of nicotine (1.3×10−5 mol kg−1 h−1) in which plasma catecholamine levels increased initially but then returned to baseline levels. To ensure that the decline in circulating catecholamine concentrations during continuous nicotine infusion was not related to changes in storage levels or altered rates of degradation/clearance, in situ posterior cardinal vein preparations were derived from fish previously experiencing 60 min of saline or nicotine infusion. Confirmation of nicotinic receptor desensitisation was provided by demonstrating that the preparations derived from nicotine-infused fish were unresponsive to nicotine (10−5 mol l−1), yet remained responsive to angiotensin II (500 pmol kg−1). The in situ experiments demonstrated that desensitisation of the nicotinic receptor occurred within 5 min of receptor stimulation and that resensitisation was established 40 min later.
The ability to elevate plasma catecholamine levels during acute hypoxia (40–45 mmHg; 5.3–6.0 kPa) was not impaired in fish experiencing nicotinic receptor desensitisation. Indeed, peak plasma adrenaline levels were significantly higher in the desensitised fish during hypoxia than in controls (263±86 versus 69±26 nmol l−1; means ± S.E.M., N=6–9). Thus, the results of the present study demonstrate that activation of preganglionic sympathetic cholinergic nerve fibres and the resultant stimulation of nicotinic receptors is not the sole mechanism for eliciting catecholamine secretion during hypoxia.