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At least 937 records · Page 52Linked to original sources
PubMed1981

Amino acid transport in Myxicola giant axon: stability of the amino acid pool, taurine efflux, and trans effect of sodium.

1. The giant axon of Myxicola infundibulum was assessed for its suitability as a model preparation for study of amino acid transport mechanisms.2. The amino acid composition of axoplasm was measured and compared with those of coelomic fluid, muscle and axon sheath. The axoplasmic composition is unique. Axoplasm/coelomic fluid concentration ratios are all much larger than 1. The axoplasmic amino acid concentrations are (mmol/kg plasm): cysteic acid (104), aspartic acid (75), glutamic acid (10), taurine (64), serine (5), glycine (191) and alanine (5). Other amino acids or primary amines, if present, must have concentrations of less than 1 mm.3. The size of the sheath amino acid pool is 12% or less of the axoplasmic pool.4. The amino acid pool of axons soaked in sea water for up to 24 h is stable. Removal of Na from sea water causes a large increase of net efflux and net production of amino acids.5. Net amino acid production can not be detected in sheath. Metabolic production occurs in axoplasm with little accumulation. Time scales for production and net efflux are therefore similar.6. The Myxicola axon has a vigorous amino acid metabolism and transport systems capable of relatively large fluxes. Homeostasis is strongly linked to Na and may involve Na-coupled co-transport. Conservation of transmembrane amino acid gradients could be promoted in part by trans inhibition of efflux by external Na.7. Taurine is a useful model substrate because it is not catabolized in Myxicola and its net efflux is sensitive to Na. [(3)H]taurine efflux was measured from injected axons. Fluxes and internally recorded action potentials are stable for up to 6 h.8. Axon sheaths take up [(3)H]taurine from 10 mm-taurine sea water with an apparent half-time of 5 h. [(3)H]taurine washout from the apparent extracellular space has a half-time of 5 min. Washout from sheath cells has a half-time of 2-3 h. Sheath is not an important parallel compartment for taurine fluxes in the axon.9. Taurine efflux has a Q(10) of 1.8.10. Taurine efflux is insensitive to external taurine concentrations up to 10 mm.11. Taurine efflux is sensitive to external Na, but only if internal Na is high.12. Taurine is transported by a low-affinity Na-dependent system in Myxicola axon. Results could be explained by a carrier which is more mobile in the empty state than in the substrate-loaded state. Trans inhibition of taurine efflux by external Na is an important property of the system, and contributes to conservation of axoplasmic taurine.

Action Potentials↗
PubMed1982

Gallamine triethiodide-induced modifications of sodium conductance in Myxicola giant axons.

1. Internal gallamine triethiodide (Flaxedil) modifies Na+ channel kinetics in Myxicola axons but does not alter K+ conductance. The drug has no effect externally. 2. Gallamine initially increases the leakage-conductance, but this effect completely reverses within 30 min despite the maintained presence of drug. 3. During step depolarizations to membrane potentials less than -10 mV, gallamine slows the rate of Na+ inactivation, but all channels which have opened can still inactivate. During depolarizations to more positive potentials, gallamine-modified Na+ currents show a biphasic decline, and at VM greater than -10 mV, Na+ inactivation is incomplete as evidenced by the large Na+ tail currents which follow pulses sufficiently long to have allowed complete inactivation of normal Na+ channels. The tail currents are slower than normal Na+ tails, and exhibit a pronounced hook. With gallamine, the fraction of Na+ channels which do not inactivate increases sigmoidally over the range 0 mV to +80 mV. 4. For VM greater than ENa, gallamine almost completely blocks outward Na+ currents. The block is determined by the direction of Na+ current, rather than the absolute membrane potential. 5. Gallamine has no effect upon the rate of Na+ channel activation, the maximum Na+ conductance, the steady-state Na+ inactivation curve, or the rate of development or removal of inactivation by prepulses. 6. Gallamine eliminated physiological immobilization of intramembrane charge movements (QOFF and QON) and does not itself induce immobilization. Thus, in the presence of gallamine, QOFF following long pulses is the same as QOFF following short pulses.

Animals↗
PubMed1983

Insensitivity of activation delays in potassium and sodium channels to heavy water in Myxicola giant axons.

Substitution of heavy water (D2O) for H2O slows the Na+ and K+ currents in Myxicola giant axons by 40-50% at 5 degrees C. In contrast, the delays in Na+ K+ activation which can be produced by hyperpolarizing pre-pulses are not affected by solvent substitution. We suggest that in the cascade of transitions leading to the opening of Na+ and K+ channels, D2O affects only the final step that establishes the aqueous pore across the membrane.

Animals↗
PubMed1983

Kinetics of inward rectifier gating in the eggs of the marine polychaete, Neanthes arenaceodentata.

Potassium current through the inward rectifier of Neanthes arenaceodentata eggs was studied using a voltage-clamp technique. The instantaneous conductance, steady-state conductance and the time constant of current relaxation were analysed as functions of the membrane potential and the external potassium concentration ([K]o). Both the instantaneous and the steady-state conductances increased sigmoidally with hyperpolarization, reaching saturation values at potentials 40 mV more negative than the potassium equilibrium potential (EK). The time-dependent change in conductance followed first-order kinetics throughout an 80 mV potential range centred at EK. The conductances increased with time during hyperpolarizations and decreased with time during depolarizations. The time constant decreased sigmoidally about EK as the membrane potential (Vm) was made more positive. The results are interpreted in terms of two models. The first model assumes single-channel rectification. Forcing the data to conform with this assumption necessitates that the single-channel conductance, the open-channel probability, and the time constant of current relaxation all be nearly identical functions of Vm--EK. This coincidence is considered implausible. The second model ascribes the apparent instantaneous rectification to a fast kinetic process. This model correctly predicts the steady-state conductance, the time-constant of current relaxation, and the unexpected proportionality between the ratio of the steady-state and 'instantaneous' conductances and the time constant of current relaxation. This agreement between data and model is obtained even though neither of the rate constants of the slow gating process has the flexibility of voltage or potassium dependence. The results are considered to imply the existence of a fast gating mechanism in the kinetics of inward rectification.

Animals↗
PubMed1984

Two calcium currents in Neanthes arenaceodentatus egg cell membranes.

Two distinct types of Ca currents, Ca(I) and Ca(II), were found in the eggs of the marine polychaete Neanthes arenaceodentatus and studied under voltage-clamp conditions. Ca(I) and Ca(II) channels differ in their selectivity sequences, show different sensitivities to blocking by Cd, and have different activation thresholds. These facts indicate that the channels responsible for Ca(I) and Ca(II) currents are unique and different. Both Ca(I) and Ca(II) currents decrease with time under a maintained depolarization. This relaxation exhibits different kinetics, with those for Ca(II) being an order of magnitude slower than for Ca(I). The Ca(I) current relaxation has been shown previously to be due to a voltage-dependent inactivation. The magnitude of relaxation of the Ca(II) current elicited by a test-voltage step immediately following a conditioning-voltage step paralleled the magnitude of the peak of the Ca(II) current flowing during the conditioning pulse. The kinetics of the current relaxation depended upon bath Ca concentration, the kinetics slowing down as the bath Ca was increased. These observations are consistent with an external depletion being the cause of the current relaxation for the Ca(II) channel.

Animals↗
PubMed1993

Calcium accumulation by organelles within Myxicola axoplasm.

1. 45Ca2+ accumulation into inulin-inaccessible compartments within cytoplasm from the giant axon of Myxicola infundibulum was measured as a function of free calcium, pH, and time. Accumulation reached a maximum after 1 h and remained stable for at least 3 h. 2. At 0.5, 5, and 50 microM [Ca2+], in the presence of 1 mM ATP or 5 mM succinate, steady-state calcium uptake had a bell-shaped dependence on pH with a maximum near pH 7. Uptake was abolished by the proton uncoupling reagent carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP, 4 micrograms ml-1). 3. Uptake of the membrane permeant cation, [14C]-tetraphenylphosphonium (TPP+), also had a bell-shaped dependence on pH with a maximum pH approximately 7, suggesting a pH dependence of the electrical potential of a membrane enclosed cytoplasmic compartment. Cyanide (2 mM) inhibited TPP+ uptake. 4. Inositol 1,4,5-trisphosphate (IP3, 10 microM), reduced steady-state calcium accumulation by 20-22% at 0.5 microM free calcium, pH 7 (P < 0.01, n = 16) and at 5 microM free calcium, pH 8 (P < 0.0005, n = 35). No effects of IP3 were found at other pH or calcium concentrations. 5. Neither guanosine 5'-triphosphate (GTP) nor inositol 1,3,4,5-tetrakisphosphate (IP4) had an effect on calcium uptake (5 microM [Ca2+], pH 8). 6. At 0.5 microM free calcium; vanadate (10 microM) inhibited 20-30%, of the 45Ca2+ accumulation, thapsigargin (33 nM) inhibited 20-30%, and cyanide (2 mM) plus oligomycin B (2 micrograms ml-1), or valinomycin (1 microM), inhibited 70-80%. The fraction of uptake sensitive to thapsigargin fell as the free calcium increased; however, the sensitivity of uptake to cyanide plus oligomycin B was approximately 80% for 0.5, 5.0, and 50 microM [Ca2+]. 7. Thapsigargin had no additional inhibiting effect in the presence of cyanide plus oligomycin B. IP3 had no effect in the presence of cyanide plus oligomycin B or other mitochondrial inhibitors. 8. Results suggest the presence of both mitochondrial (70-80%) and non-mitochondrial (20-30%) calcium pools in this system (at 0.5-5.0 microM Ca2+). The apparent non-mitochondrial uptake (sensitive to thapsigargin, or IP3) is not detectable in the presence of mitochondrial inhibitors. We interpret these results as evidence of functional communication between mitochondrial and non-mitochondrial calcium stores.

Animals↗
PubMed2002

High abrasion resistance with sparse mineralization: copper biomineral in worm jaws.

Biominerals are widely exploited to harden or stiffen tissues in living organisms, with calcium-, silicon-, and iron-based minerals being most common. In notable contrast, the jaws of the marine bloodworm Glycera dibranchiata contain the copper-based biomineral atacamite [Cu2(OH)3Cl]. Polycrystalline fibers are oriented with the outer contour of the jaw. Using nanoindentation, we show that the mineral has a structural role and enhances hardness and stiffness. Despite the low degree of mineralization, bloodworm jaws exhibit an extraordinary resistance to abrasion, significantly exceeding that of vertebrate dentin and approaching that of tooth enamel.

Animals↗
PubMed2004

Osedax: bone-eating marine worms with dwarf males.

We describe a new genus, Osedax, and two new species of annelids with females that consume the bones of dead whales via ramifying roots. Molecular and morphological evidence revealed that Osedax belongs to the Siboglinidae, which includes pogonophoran and vestimentiferan worms from deep-sea vents, seeps, and anoxic basins. Osedax has skewed sex ratios with numerous dwarf (paedomorphic) males that live in the tubes of females. DNA sequences reveal that the two Osedax species diverged about 42 million years ago and currently maintain large populations ranging from 10(5) to 10(6) adult females.

Animals↗
PubMed2004

Ciliary photoreceptors with a vertebrate-type opsin in an invertebrate brain.

For vision, insect and vertebrate eyes use rhabdomeric and ciliary photoreceptor cells, respectively. These cells show distinct architecture and transduce the light signal by different phototransductory cascades. In the marine rag-worm Platynereis, we find both cell types: rhabdomeric photoreceptor cells in the eyes and ciliary photoreceptor cells in the brain. The latter use a photopigment closely related to vertebrate rod and cone opsins. Comparative analysis indicates that both types of photoreceptors, with distinct opsins, coexisted in Urbilateria, the last common ancestor of insects and vertebrates, and sheds new light on vertebrate eye evolution.

Amino Acid Sequence↗
PubMed2004

The cryptic filtering house of an invertebrate larva.

Planktonic larvae of the annelid Pectinaria californiensis construct and inhabit cryptic houses through which they filter seawater to concentrate food. Although filtering houses may be unique to pectinariid larvae, other transparent and ephemeral structures are secreted by the larvae of many marine invertebrates and may be involved in the performance of a variety of critical larval functions.

Animals↗
PubMed2005

Vertebrate-type intron-rich genes in the marine annelid Platynereis dumerilii.

Previous genome comparisons have suggested that one important trend in vertebrate evolution has been a sharp rise in intron abundance. By using genomic data and expressed sequence tags from the marine annelid Platynereis dumerilii, we provide direct evidence that about two-thirds of human introns predate the bilaterian radiation but were lost from insect and nematode genomes to a large extent. A comparison of coding exon sequences confirms the ancestral nature of Platynereis and human genes. Thus, the urbilaterian ancestor had complex, intron-rich genes that have been retained in Platynereis and human.

Animals↗
PubMed2006

Thermal preference and tolerance of alvinellids.

The highest oceanic temperatures are found at hydrothermal vents, where the polychaete Paralvinella sulfincola lives on vent sulfides within steep and dynamic thermal gradients. To determine P. sulfincola thermotolerance and preference, we developed a high-pressure aquarium that mimics in situ thermal gradients and permits P. sulfincola to move within the gradient. These polychaetes were thermotaxic, preferring temperatures of 40 degrees to 50 degrees C. Some individuals remained at 50 degrees C for 7 hours (the duration of the experiment), whereas others endured exposure to 55 degrees C for over 15 minutes, demonstrating that alvinellids prefer high temperatures and are among the most thermotolerant of marine organisms.

Animals↗
PubMed2007

Physiological proteomics of the uncultured endosymbiont of Riftia pachyptila.

The bacterial endosymbiont of the deep-sea tube worm Riftia pachyptila has never been successfully cultivated outside its host. In the absence of cultivation data, we have taken a proteomic approach based on the metagenome sequence to study the metabolism of this peculiar microorganism in detail. As one result, we found that three major sulfide oxidation proteins constitute approximately 12% of the total cytosolic proteome, which highlights the essential role of these enzymes for the symbiont's energy metabolism. Unexpectedly, the symbiont uses the reductive tricarboxylic acid cycle in addition to the previously identified Calvin cycle for CO2 fixation.

Animals↗
PubMed2000

Influences of dietary uptake and reactive sulfides on metal bioavailability from aquatic sediments.

Understanding how animals are exposed to the large repository of metal pollutants in aquatic sediments is complicated and is important in regulatory decisions. Experiments with four types of invertebrates showed that feeding behavior and dietary uptake control bioaccumulation of cadmium, silver, nickel, and zinc. Metal concentrations in animal tissue correlated with metal concentrations extracted from sediments, but not with metal in porewater, across a range of reactive sulfide concentrations, from 0.5 to 30 micromoles per gram. These results contradict the notion that metal bioavailability in sediments is controlled by geochemical equilibration of metals between porewater and reactive sulfides, a proposed basis for regulatory criteria for metals.

Animals↗