bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Compartmental Approach to the Mechanism of Calcification in Hermatypic Corals
Authors: Tambutté Éric , Allemand Denis , Mueller Erich , Jaubert Jean 
Published: April 2021

ABSTRACT
Ca2+ compartments, Ca2+ transport and the calcification process were studied by using 45Ca as a tracer. The biological model used was clones of Stylophora pistillata developed into microcolonies whose skeleton is entirely covered by tissues, thus avoiding direct radioisotope exchange between the sea water and the skeleton. The study of Ca2+ compartments was performed by measuring two complementary parameters: Ca2+ influx and Ca2+ efflux kinetics. Kinetic analysis of 45Ca uptake revealed three exchangeable and one non-exchangeable Ca2+ compartments in these microcolonies. The first compartment was saturable with a short half-time (4 min), correlated to external Ca2+ concentration and insensitive to metabolic or ion transport inhibitors. This compartment (72.88 nmol Ca2+ mg-1 protein) has been previously attributed to sea water present in the coelenteron. The second Ca2+ compartment (7.12 nmol Ca2+ mg-1 protein) was soluble in NaOH, saturable with a half-time of 20 min and displayed a combination of Michaelis–Menten kinetics and diffusional entry. It was insensitive to a variety of inhibitors but its loading was stimulated by Ca2+ channel inhibitors. On the basis of uptake experiments, the existence of a third compartment with a rapid turnover rate (about 2 min) and a very small size is predicted. It is suggested that this compartment corresponds to the calicoblastic epithelium. Ca2+ flux through this compartment was facilitated by voltage-dependent Ca2+ channels (with L-type characteristics) and Ca2+-ATPase and was coupled to an anion carrier. Transcellular Ca2+ movement was dependent on the cytoskeleton. The rate of Ca2+ flux across this epithelium was about 975 pmol mg-1 protein min-1. The fourth calcium compartment, corresponding to the skeleton, was soluble in HCl and non-exchangeable. After a short lag phase (about 2 min), the rate of Ca2+ deposition was linear over a period of at least 5 h. The calcification rate was 975 pmol mg-1 protein h-1 at an irradiance of 175 μmol photons m-2 s-1. It followed Michaelis–Menten kinetics and saturated at levels (9 mmol l-1) close to the Ca2+ concentration of sea water. Wash-out (efflux) experiments employing several different protocols allowed identification of six compartments. The first two compartments were extracellular (bulk extracolonial water and coelenteron). The third compartment may be part of the second Ca2+ compartment identified by influx experiments. A fourth compartment was sensitive to the Ca2+ channel inhibitor D600 and appeared to be associated with the NaOH-soluble (tissue) Ca2+ pool. Two compartments were identified during skeletal efflux, the first being small and due to either tissue carry-over or a labile skeletal compartment. The second compartment corresponded to bulk skeletal deposition. The various efflux protocols produced varying estimates of tissue Ca2+ levels and calcification rates and, thus, coral post-incubation processing has a profound impact on experimental interpretation.
Nadph Diaphorase Activity In The Antennae Of The Hawkmoth Manduca Sexta
Authors: Stengl Monika , Zintl Rita 
Published: April 2021

ABSTRACT
Biochemical and physiological studies suggested that increases in the levels of cyclic GMP in insect antennal receptor cells play a role in olfactory adaptation. As inositol-trisphosphate-dependent Ca2+ influx appears to precede the increase in intracellular cyclic GMP levels, it was hypothesized that a Ca2+-dependent mechanism might stimulate the guanylyl cyclase. The present study used histochemical staining for NADPH diaphorase to examine whether antennal receptor neurones of male Manduca sexta could contain nitric oxide synthase. This Ca2+/calmodulin-dependent enzyme is a prerequisite for nitric-oxide-dependent stimulation of guanylyl cyclase and possesses NADPH diaphorase activity. It was found that a subpopulation of olfactory receptor neurones as well as mechano-, thermo- and hygroreceptors on the moth antenna are NADPH-diaphorase-positive. Staining was also seen in non-neuronal cells. In the developing antenna, the NADPH-diaphorase-dependent staining was first observed at pupal stage 13–14, at approximately the same time as the antennal receptor neurones became physiologically active. The number and location of stained receptor cells was highly variable, and significantly more pheromone-sensitive sensilla were NADPH-diaphorase-positive in pheromone-stimulated antennae. This suggests that the enzyme is transiently activated by pheromone rather than being continuously active.
Strain-Rate-Dependent Mechanical Properties of the Equine Hoof Wall
Authors: Kasapi Mario A. , Gosline John M. 
Published: April 2021

ABSTRACT
The mechanical properties of fully hydrated equine hoof wall were examined at various loading rates in compact tension (CT) fracture, tensile and three-point bending dynamic tests to determine possible effects of hoof wall viscoelasticity on fracture toughness and tensile parameters. Four cross-head rates were used in CT tests: 1.7 × 10−5, 1.7 × 10−3, 1.7× 10−2 and 2.5 m s-1; four strain rates were used in tensile tests: 1.6 × 10−3, 3.2× 10−2, 0.33 and 70 s-1. Speeds for the highest test rates were achieved using a large, custom-built impact pendulum. Bending test frequencies ranged from 0.04 to 200 Hz.
In CT tests, both the initial modulus Ei and the stress intensity factor K rose with increasing strain rate (from 0.38 to 0.76 GPa for Ei and from 0.71 to 1.4 MN m-3/2 for K), whereas the fracture toughness parameter J remained constant at 12 kJ m-2. All tensile parameters except ultimate strain were sensitive to strain rate. Ei, total energy to breakage and maximum stress rose with increasing strain rate from 0.28 to 0.85 GPa, from 5.4 to 9.7 MJ m-3 and from 17 to 31 MPa, respectively. Data from low-amplitude dynamic tests agreed well with Ei trends from CT and tensile tests.
Direction of crack growth differed through the thickness of the wall, the pattern of which resembled a trilaminar ply. Although scanning electron microscopic examination of fracture surfaces revealed a decreasing pseudo-ductile behaviour with increasing strain rate, and ultimate tensile parameters are positively affected, equine hoof wall viscoelasticity does not appear to compromise fracture toughness at high strain rates.
Separate Control Of Anion And Cation Transport In Malpighian Tubules Of Drosophila Melanogaster
Authors: O’Donnell M. J. , Dow J. A. T. , Huesmann G. R. , Tublitz N. J. , Maddrell S. H. P. 
Published: April 2021

ABSTRACT
Microelectrode measurements of basal, apical and transepithelial potentials in the Malpighian tubules of Drosophila melanogaster were obtained under a range of conditions in order to investigate whether each of the three main second messenger systems known to act in the tubules (cyclic AMP, cyclic GMP and Ca2+) acted specifically on either cation or anion transport, or whether they activated both systems.
Ion-selective microelectrode determinations of K+ concentration and pH of secreted fluid allowed the role of each signalling system to be analysed further.
Stimulation with cyclic nucleotides markedly alters the potential profile across principal cells through the selective activation of an apical electrogenic V-ATPase. By contrast, manipulation of extracellular chloride levels, combined with stimulation with leucokinin, does not affect the potential profile across the principal cells, showing that chloride must pass through another route.
The cell-permeant Ca2+ chelator BAPTA-AM was shown to suppress the action of leucokinins (insect peptides that induce rapid fluid secretion), but not those of cyclic AMP, the neuronally derived insect peptide cardioacceleratory peptide 2b (CAP2b) or its intracellular messenger cyclic GMP. This shows that leucokinins act through Ca2+ and not through cyclic nucleotides and that the cyclic nucleotide pathways do not co-activate the intracellular Ca2+ pathway to exert their effects.
Taken together, these results show that leucokinin acts through intracellular Ca2+, independently of cyclic AMP or cyclic GMP, to raise the chloride permeability of the epithelium. By contrast, either cyclic AMP or cyclic GMP (upon CAP2b stimulation) acts on the electrogenic cation-transporting apical V-ATPase, with only a negligible effect on anion conductance and without perturbing intracellular [Ca2+].
There is thus a clear functional separation between the control pathways acting on cation and anion transport in the tubules. Given the evidence from D. melanogaster and other species that chloride does not pass through the principal cells, we speculate that these two pathways may also be physically separated within cell subtypes of the tubules.
Seasonal Variations of Pineal Involvement in the Circadian Organization of the Ruin Lizard Podarcis Sicula
Authors: Innocenti A. , Bertolucci C. , Minutini L. , Foà A. 
Published: April 2021

ABSTRACT
To establish whether the effects of pinealectomy on circadian locomotor rhythmicity vary with season, we examined, in constant temperature and darkness, the locomotor behaviour of ruin lizards Podarcis sicula collected and subjected to pinealectomy at different times of the year. Changes in the freerunning period in response to pinealectomy were found to be significantly greater in summer than in winter, spring and autumn. Circadian activity time changed significantly in response to pinealectomy only in spring and summer. Furthermore, while pinealectomy was effective in altering the locomotor rhythms of all individual lizards tested in summer, the same surgery was found to leave locomotor rhythmicity of many lizards tested in autumn and winter completely undisturbed. These results demonstrate for the first time in a non-mammalian vertebrate that the pineal gland is centrally involved in determining circadian organization in some seasons and is only marginally involved in others.
Muscular Basis of Buccal Pressure: Inflation Behavior in the Striped Burrfish Chilomycterus Schoepfi
Authors: Wainwright Peter C. , Turingan Ralph G. 
Published: April 2021

ABSTRACT
We examined the relationship between commonly measured features of cranial muscle activity and the magnitude of sub-and superambient pressure measured inside the buccal cavity of the striped burrfish Chilomycterus schoepfi during inflation behavior. Buccal pressure was recorded simultaneously with electromyographic (EMG) records of activity from three expansive-phase muscles (levator operculi, levator pectoralis and hyohyoideus abductor) and three compressive-phase muscles (adductor mandibulae, protractor hyoideus and protractor pectoralis) in eight individuals. We quantified EMG activity in approximately 30 inflation cycles per fish by measuring the burst duration, rectified integrated area, intensity of activity (area divided by duration) and onset time relative to the onset of subambient pressure at the beginning of the cycle. Multiple regressions were calculated separately for data from each fish to investigate the relationships between pressure and EMG variables. The percentage of variation in minimum buccal pressure or area under the subambient pressure curve explained by the multiple-regression models ranged among individuals from approximately 52 to 84 %. The regression models accounted for more variation in peak pressure and the integrated area of superambient pressure; r2 ranged from 76 % to 97 %. The strong relationship between EMG activity and superambient buccal pressure suggests that the latter is probably a direct function of the strength of compressive-muscle contraction. In contrast, the magnitude of subambient pressure is a complex function of the area of the oral opening and the rate of buccal expansion, factors that do not appear to be as directly indicated by the degree of muscle activity.
Size-Dependent Neural Integration Between Genetically Different Colonies of a Marine Bryozoan
Authors: Shapiro Daniel F. 
Published: April 2021

ABSTRACT
Although the formation of genetic chimeras is rare in the animal kingdom, it has long been known that colonial marine invertebrates fuse under natural conditions, forming genetic chimeras. I report here an example of selective, partial fusion. When small colonies of the encrusting marine bryozoan Membranipora membranacea grow into contact, they usually become behaviorally coordinated: if one colony is disturbed, both colonies will simultaneously retract their feeding structures (lophophores). As a first step towards understanding the fitness consequences of this type of apparent fusion, I examine its mechanistic basis. Using assays of zooid behavior, electrophysiological recordings and 14C-labeled metabolites, I demonstrate that physiological integration between M. membranacea colonies is both partial and temporary. Specifically, this study demonstrates (1) that behavioral coordination is the result of neural integration between colonies, (2) that coordinated colony pairs do not exchange metabolites, and (3) that neural integration is a temporary phenomenon that is terminated as colonies grow larger. Additionally, I show that only those zooids at the middle of the intercolony border mediate neural integration. Partial physiological integration between M. membranacea colonies could be a highly specific interaction that increases the potential benefits of fusion (i.e. neural integration) while minimizing the potential costs (i.e. resource parasitism).
Does the Avian Ophthalmic Nerve Carry Magnetic Navigational Information?
Authors: Beason Robert C. , Semm Peter 
Published: April 2021

ABSTRACT
The bobolink (Dolichonyx oryzivorus) uses the earth’s magnetic field as one source of directional information for its migratory orientation. However, the location and structure of the magnetoreceptors that transduce the magnetic information to the nervous system are unknown. Because treatment with a strong magnetic pulse results in a change in the direction of orientation, one of the receptors is thought to involve a magnetizable material such as magnetite. The effects of the magnetizing treatment can be abolished (i.e. the bird returns to its original orientation) by blocking the ophthalmic branch of the trigeminal nerve, but the ability of the bird to select and maintain a direction is not affected. These results are consistent with the hypothesis that a magnetizable material such as magnetite is part of the magnetoreceptors that are associated with the ophthalmic nerve.
Uptake, Excretion and Respiration of Sucrose and Amino Acids by the Pea Aphid Acyrthosiphon Pisum
Authors: Rhodes J. D. , Croghan P. C. , Dixon A. F. G. 
Published: April 2021

ABSTRACT
Ingestion, excretion and respiration in aphids were studied using artificial diets labelled with radioactive sucrose or amino acids. The rate of ingestion of a 25 % w/v sucrose diet was 12.4 nl mg–1 h–1 and the honeydew excretion rate was 5.3 nl mg–1 h–1, about 43 % of the volume ingested during the same period. The concentration of sugars in the honeydew was equivalent to 0.53 mol l–1 sucrose and 69 % of the sucrose ingested was assimilated. The amino acid concentration of honeydew was 24.6 mmol l–1 and 94 % of the ingested amino acids were assimilated. Respiration was measured by collecting respired 14CO2 using a chamber which allowed the aphids to feed during the experiments on 14C-labelled artificial diets. While feeding on a 25 % w/v sucrose diet, sucrose was respired at the rate of 1.32X10–6 mmol mg–1 h–1, equivalent to 0.354 μl O2 mg–1 h–1, which was 14.6 % of the rate of ingestion. There was no evidence that reducing the dietary sucrose concentration from 22 to 11 % w/v had any effect on the rate at which sucrose was respired. Amino acids were respired at a rate of 0.14X10–6 mmol mg–1 h–1, which was 6.4 % of the rate of ingestion. Dietary sucrose was oxidised in preference to amino acids.
Plasticity of Fish Muscle Mitochondria with Thermal Acclimation
Authors: Guderley Helga , Johnston Ian A. 
Published: April 2021

ABSTRACT
Short-horned sculpin Myoxocephalus scorpius were acclimated to 5 and 15 °C to evaluate the impact of thermal acclimation upon maximal rates of substrate oxidation by mitochondria and upon the thermal sensitivity of their ADP affinity. Cold acclimation virtually doubled maximal rates of pyruvate oxidation at all experimental temperatures (2.5, 7.5, 12.5 and 20 °C). Rates of palmitoyl carnitine oxidation were also enhanced by cold acclimation, but to a lesser degree. At their respective acclimation temperatures, the mitochondria attained similar rates of pyruvate oxidation. For warm-acclimated sculpin, the Q10 values for mitochondrial pyruvate and palmitoyl carnitine oxidation were higher between 2.5 and 7.5 °C than between 7.5 and 12.5 °C or between 12.5 and 20 °C. In contrast, for cold-acclimated fish, the Q10 values did not differ over these thermal ranges. The Arrhenius activation energy for pyruvate oxidation was reduced by cold acclimation (from 70 to 55 kJ mol–1), whereas that for palmitoyl carnitine oxidation was unchanged (approximately 75 kJ mol–1). Cold acclimation did not alter the ADP affinity of mitochondria at low temperatures but markedly increased the apparent Km for ADP (Km,app) at 12.5 and 20 °C. At the acclimation temperatures, mitochondrial ADP Km,app values did not differ. The loss of ADP affinity at higher temperatures may represent a cost of the enhanced maximal oxidative capacity achieved during cold acclimation.
The Effects of Cyanobacteria and the Cyanobacterial Toxin Microcystin-Lr on Ca2+ Transport and Na+/K+-ATPase in Tilapia Gills
Authors: Bury N. R. , Flik G. , Eddy F. B. , Codd G. A. 
Published: April 2021

ABSTRACT
The effects of cytotoxic substances from cyanobacteria on ionic transport processes in tilapia (Oreochromis mossambicus) were examined. Inhibitory effects on ionic transport including whole-body Ca2+ fluxes and P-type ATPases of the gill were found. The compounds tested were (1) purified microcystin-LR (MC-LR), a heptapeptide hepatotoxin produced by the cyanobacterium Microcystis aeruginosa, (2) extracts from M. aeruginosa strain PCC 7820, a strain producing MC-LR and other microcystin variants, and (3) extracts of M. aeruginosa CYA 43, a strain producing toxins including small quantities of MC-LR. Whole-body Ca2+ influx was inhibited by a 24 h exposure to extracts of M. aeruginosa CYA 43 and 7820, but not by exposure to an equivalent amount (90 mg l-1) of purified MC-LR. Shorter exposure times (4 h) were ineffective. Fish exposed to extracts from M. aeruginosa CYA 43 showed significant plasma hypocalcaemia. Both strains of M. aeruginosa inhibited Ca2+ uptake by basolateral plasma membrane vesicles (BLMVs), endoplasmic reticulum (ER) and mitochondria, as well as BLMV K+-dependent p-nitrophenol phosphatase (pNPPase) activity. The hydrophobic fractions of the cyanobacterial extracts were the most potent, inhibiting BLMV, ER and mitochondrial Ca2+ uptake by up to 99 %, but they were less inhibitory of BLMV K+-dependent pNPPase activity. Purified MC-LR was without effect on these preparations. In conclusion, cytotoxic substances from cyanobacteria have the potential to disrupt normal physiological processes dependent upon Ca2+ transport processes in tilapia gills.
A Primary Cation Transport by a V-Type Atpase of Low Specificity
Authors: Küppers J. , Bunse I. 
Published: April 2021

ABSTRACT
The enzyme involved in outward K+ transport in insect epithelia belongs to the family of V-ATPases. Evidence has been reported relating the generation of the K+ gradient to a primary electrogenic proton transport via a distinct electrophoretic nH+/K+ antiport.
The subject of this paper is the transport of K+ at a thread hair sensillum of the cockroach in situ. We recorded changes in the voltage and resistance of the ion-transporting membrane and of shifts in pH caused by inhibition of energy metabolism and by putative inhibitors of a proton/cation exchanger. The results are supplemented by previous determinations of the K+ activities in the same preparation. In cockroach hair sensilla, the ion transport generates a membrane voltage of 105 mV. We found that the transport rendered the positive output compartment alkaline with respect to the cytoplasm by 1.0 pH unit compared with the pH at equilibrium distribution, and we infer that proton transport cannot be the process that energizes the generation of the K+ gradient.The ion transport created an electrochemical potential difference for protons, Δ ηH, of approximately 4.5 kJ mol–1, while the potential difference for K+, Δ ηK, amounted to approximately 11 kJ mol–1. Both potential differences are directed to the cytosol. It follows from Δ ηK/ Δ ηH that an antiport would have to be electrophoretic to drive K+ by LTH and it should, therefore, contribute to the membrane conductance. Amiloride and harmaline did not significantly change the pH in the adjacent spaces and did not affect the voltage or the resistance of the transporting membrane. Previous determinations of the impedance have shown that the ATP-independent conductance of this membrane is small, supporting the conclusion that it lacks an electrophoretic antiport.
From these results, we deduce that K+ transport in cockroach sensilla is not secondary to a proton transport and an electrochemical proton gradient. The phenomena observed match the performance of a primary, electrogenic, cation-translocating ATPase of the type deduced from analyses of the short-circuit current at the midgut epithelium of lepidopteran larvae. The validity of the H+ transport/antiport hypothesis is discussed.
Inhibition of Voltage-Dependent Ca2+ Influx by Extracellular ATP in Salivary Cells of the Leech Haementeria Ghilianii
Authors: Wuttke Werner A. , Munsch Thomas , Deitmer Joachim W. 
Published: April 2021

ABSTRACT
The effects of extracellular ATP on intracellular free Ca2+ concentration ([Ca2+]i) and depolarization-induced elevations of [Ca2+]i were investigated in salivary cells of the leech Haementeria ghilianii using the fluorescent Ca2+ indicator Fura-2. Simultaneously, the membrane potential was monitored or controlled by voltage-clamp. The cell membrane was depolarized either by transient elevations of the extracellular K+ concentration ([K+]o) to 90 mmol l−1 or by depolarizing steps under voltage-clamp. The resulting transient elevations of [Ca2+]i (Ca2+ transients) could be repeatedly elicited with little variability in amplitude. Ca2+ transients were completely inhibited by 2 mmol l−1 Ni2+ or in Ca2+-free saline. The transients are, therefore, dependent on Ca2+ influx from the external medium through voltage-gated Ca2+ channels. The Ca2+ influx was rapidly and reversibly inhibited by extracellular application of ATP. The effect was dose-dependent with a threshold concentration below 10−7 mol l−1. A 50 % reduction in the amplitude of Ca2+ transients was obtained by application of 1–2 μmol l−1 ATP or ATP--y-S (apparent IC50, 1.6 μmol l−1 ATP) and Ca2+ transients were almost completely inhibited by 30–100 μmol l−1 ATP. Resting [Ca2+]i, the resting membrane potential and membrane potential changes induced by 90 mmol l−1 [K+]o were not affected by ATP. Adenosine (10 μmol l−1) did not affect resting [Ca2+]i, the resting membrane potential or membrane potential changes induced by 90 mmol l−1 [K+]o and had little effect on Ca2+ transients. Suramin, an antagonist of vertebrate P2 receptors, was without effect on the inhibitory actions of ATP. We conclude that activation of a suramin-insensitive purinoceptor by ATP inhibits Ca2+ influx through voltage-gated Ca2+ channels in the salivary cells of Haementeria ghilianii.