1,305 research outputs found
Apparent self-accelerating alternating assembly of semiconductor nanoparticles and polymers
Compact Polyelectrolyte Complexes: âSaloplasticâ Candidates for Biomaterials
Precipitates of polyelectrolyte complexes were transformed into rugged shapes suitable for bioimplants by ultracentrifugation in the presence of high salt concentration. Salt ions dope the complex, creating a softer material with viscous fluid-like properties. Complexes that were compacted under the centrifugal field (CoPECs) were made from poly(diallyldimethyl ammonium), PDADMA, as polycation, and poly(styrene sulfonate), PSS, or poly(methacrylic acid), PMAA, as polyanion. Dynamic mechanical testing revealed a rubbery plateau at lower frequencies for PSS/PDADMA with moduli that decreased with increasing salt concentration, as internal ion pair cross-links were broken. CoPECs had significantly lower modulii compared to similar polyelectrolyte complexes prepared by the âmultilayering â method. The difference in mechanical properties was ascribed to higher water content (located in micropores) for the former and, more importantly, to their nonstoichiometric polymer composition. The modulus of PMAA/PDADMA CoPECs, under physiological conditions, demonstrated dynamic mechanical properties that were close to those of the nucleus pulposus in an intervertebral disk
Multiple Scale Reorganization of Electrostatic Complexes of PolyStyrene Sulfonate and Lysozyme
We report on a SANS investigation into the potential for these structural
reorganization of complexes composed of lysozyme and small PSS chains of
opposite charge if the physicochemical conditions of the solutions are changed
after their formation. Mixtures of solutions of lysozyme and PSS with high
matter content and with an introduced charge ratio [-]/[+]intro close to the
electrostatic stoichiometry, lead to suspensions that are macroscopically
stable. They are composed at local scale of dense globular primary complexes of
radius ~ 100 {\AA}; at a higher scale they are organized fractally with a
dimension 2.1. We first show that the dilution of the solution of complexes,
all other physicochemical parameters remaining constant, induces a macroscopic
destabilization of the solutions but does not modify the structure of the
complexes at submicronic scales. This suggests that the colloidal stability of
the complexes can be explained by the interlocking of the fractal aggregates in
a network at high concentration: dilution does not break the local aggregate
structure but it does destroy the network. We show, secondly, that the addition
of salt does not change the almost frozen inner structure of the cores of the
primary complexes, although it does encourage growth of the complexes; these
coalesce into larger complexes as salt has partially screened the electrostatic
repulsions between two primary complexes. These larger primary complexes remain
aggregated with a fractal dimension of 2.1. Thirdly, we show that the addition
of PSS chains up to [-]/[+]intro ~ 20, after the formation of the primary
complex with a [-]/[+]intro close to 1, only slightly changes the inner
structure of the primary complexes. Moreover, in contrast to the synthesis
achieved in the one-step mixing procedure where the proteins are unfolded for a
range of [-]/[+]intro, the native conformation of the proteins is preserved
inside the frozen core
The selectivity, voltage-dependence and acid sensitivity of the tandem pore potassium channel TASK-1 : contributions of the pore domains
We have investigated the contribution to ionic
selectivity of residues in the selectivity filter and pore
helices of the P1 and P2 domains in the acid sensitive
potassium channel TASK-1. We used site directed mutagenesis
and electrophysiological studies, assisted by structural
models built through computational methods. We have
measured selectivity in channels expressed in Xenopus
oocytes, using voltage clamp to measure shifts in reversal
potential and current amplitudes when Rb+ or Na+ replaced
extracellular K+. Both P1 and P2 contribute to selectivity,
and most mutations, including mutation of residues in the
triplets GYG and GFG in P1 and P2, made channels nonselective.
We interpret the effects of theseâand of other
mutationsâin terms of the way the pore is likely to be
stabilised structurally. We show also that residues in the
outer pore mouth contribute to selectivity in TASK-1.
Mutations resulting in loss of selectivity (e.g. I94S, G95A)
were associated with slowing of the response of channels to
depolarisation. More important physiologically, pH sensitivity
is also lost or altered by such mutations. Mutations
that retained selectivity (e.g. I94L, I94V) also retained their
response to acidification. It is likely that responses both to
voltage and pH changes involve gating at the selectivity filter
Enhanced firing of locus coeruleus neurons and SK channel dysfunction are conserved in distinct models of prodromal Parkinson's disease
Parkinsonâs disease (PD) is clinically defined by the presence of the cardinal motor symptoms, which are associated with a loss of dopaminergic nigrostriatal neurons in the substantia nigra pars compacta (SNpc). While SNpc neurons serve as the prototypical cell-type to study cellular vulnerability in PD, there is an unmet need to extent our efforts to other neurons at risk. The noradrenergic locus coeruleus (LC) represents one of the first brain structures affected in Parkinsonâs disease (PD) and plays not only a crucial role for the evolving non-motor symptomatology, but it is also believed to contribute to disease progression by efferent noradrenergic deficiency. Therefore, we sought to characterize the electrophysiological properties of LC neurons in two distinct PD models: (1) in an in vivo mouse model of focal α-synuclein overexpression; and (2) in an in vitro rotenone-induced PD model. Despite the fundamental differences of these two PD models, α-synuclein overexpression as well as rotenone exposure led to an accelerated autonomous pacemaker frequency of LC neurons, accompanied by severe alterations of the afterhyperpolarization amplitude. On the mechanistic side, we suggest that Ca(2+)-activated K(+) (SK) channels are mediators of the increased LC neuronal excitability, as pharmacological activation of these channels is sufficient to prevent increased LC pacemaking and subsequent neuronal loss in the LC following in vitro rotenone exposure. These findings suggest a role of SK channels in PD by linking α-synuclein- and rotenone-induced changes in LC firing rate to SK channel dysfunction
Electrostatic-Assembly-Driven Formation of Supramolecular Rhombus Microparticles and Their Application for Fluorescent Nucleic Acid Detection
In this paper, we report on the large-scale formation of supramolecular rhombus
microparticles (SRMs) driven by electrostatic assembly, carried out by direct
mixing of an aqueous HAuCl4 solution and an ethanol solution of
4,4âČ-bipyridine at room temperature. We further demonstrate their use as
an effective fluorescent sensing platform for nucleic acid detection with a high
selectivity down to single-base mismatch. The general concept used in this
approach is based on adsorption of the fluorescently labeled single-stranded DNA
(ssDNA) probe by SRM, which is accompanied by substantial fluorescence
quenching. In the following assay, specific hybridization with its target to
form double-stranded DNA (dsDNA) results in desorption of ssDNA from SRM surface
and subsequent fluorescence recovery
Distribution locale et estimation des densitĂ©s des primates dans la rĂ©serve transfrontaliĂšre du fleuve Mono, Togo (Afrique de lâOuest)
La rĂ©serve de biosphĂšre de Mono est situĂ©e dans le « Dahomey Gap » qui sĂ©pare la ceinture des forĂȘts denses humides ouest-africaines en deux blocs forestiers : guinĂ©en (occidental) et congolais (oriental). Cette discontinuitĂ© climatique dahomĂ©enne est caractĂ©risĂ©e par des mosaĂŻques de forĂȘts denses semi-dĂ©cidues, des savanes guinĂ©ennes, des prairies marĂ©cageuses, des marais, des mangroves et des plans dâeau, des mosaĂŻques dâagroforĂȘts, champs et jachĂšres. Dans cette rĂ©serve centrĂ©e sur la vallĂ©e du Mono entre le Togo et le BĂ©nin, dâune surperficie de 2042,18 km2, nous nous Ă©valuĂ© le statut des populations des espĂšces de primates. Au total, 9 espĂšces ont Ă©tĂ© recensĂ©es : Galago senegalensis, Galagoides demidoff, Perodicticus potto, Papio anubis, Colobus vellerosus, Cercopithecus erythrogaster erythrogaster, Cercopithecus mona, Erythrocebus patas et Chlorocebus tantalus. Les populations de ces espĂšces sont distribuĂ©es dans quatre unitĂ©s fondamentales de la rĂ©serve : la forĂȘt dâAsrama, le complexe dâaires protĂ©gĂ©es de Togodo, la forĂȘt sacrĂ©e de GodjĂ©-Godjin et la forĂȘt sacrĂ©e dâAkissa. Les travaux ont clairement Ă©tabli un dĂ©placement saisonnier et rĂ©gulier des populations de ces espĂšces de primates dans ces diffĂ©rentes unitĂ©s Ă©cologiques. Le complexe dâaires protĂ©gĂ©es de Togodo constitue le sanctuaire pour les populations de primates dans le Sud du Togo et du BĂ©nin et principalement celle du Hocheur Ă ventre roux (Cercopithecus erythrogaster erythrogaster) considĂ©rĂ© comme espĂšce en danger critique sur la liste rouge de lâUICN.The reserve of biosphere of Mono river is located in the Dahomey Gap, which is the relatively arid interruption in the West African forest belt that stretches from the Accra Plains in Ghana across the Volta River through Togo to the eastern border of Benin. This West African climate discontinuity is characterized by mosaics of dense semi-deciduous forests, Guinean savannahs, swampy meadows, marshes, mangroves and bodies of water, mosaics of agroforest, farms and fallow land. In this reserve, centered on the Mono valley between Togo and Benin, with 2042.18 km2 area, we assessed the status of populations of primate species. Overall, 9 species were recorded: Galago senegalensis, Galagoides demidoff, Perodicticus potto, Papio anubis, Colobus vellerosus, Cercopithecus erythrogaster erythrogaster, Cercopithecus mona, Erythrocebus patas and Chlorocebus tantalus. The populations of these species are distributed in four basic units of the reserve: the Asmara forest, the Togodo protected area complex, the GodjĂ©-Godjin sacred forest and the Akissa sacred forest. Our works clearly established a seasonal and regular displacement of primate species populations among different ecological units. The Togodo protected areas complex is the sanctuary for primate populations in southern Togo and Benin, and mainly for the Red-bellied Monkey (Cercopithecus erythrogaster erythrogaster), which is considered a Critically Endangered species on the IUCN Red List
The Search for Gravitational Waves
Experiments aimed at searching for gravitational waves from astrophysical
sources have been under development for the last 40 years, but only now are
sensitivities reaching the level where there is a real possibility of
detections being made within the next five years. In this article a history of
detector development will be followed by a description of current detectors
such as LIGO, VIRGO, GEO 600, TAMA 300, Nautilus and Auriga. Preliminary
results from these detectors will be discussed and related to predicted
detection rates for some types of sources. Experimental challenges for detector
design are introduced and discussed in the context of detector developments for
the future.Comment: 21 pages, 7 figures, accepted J. Phys. B: At. Mol. Opt. Phy
Volume Regulated Anion Channel Currents of Rat Hippocampal Neurons and Their Contribution to Oxygen-and-Glucose Deprivation Induced Neuronal Death
Volume-regulated anion channels (VRAC) are widely expressed chloride channels that are critical for the cell volume regulation. In the mammalian central nervous system, the physiological expression of neuronal VRAC and its role in cerebral ischemia are issues largely unknown. We show that hypoosmotic medium induce an outwardly rectifying chloride conductance in CA1 pyramidal neurons in rat hippocampal slices. The induced chloride conductance was sensitive to some of the VRAC inhibitors, namely, IAA-94 (300 ”M) and NPPB (100 ”M), but not to tamoxifen (10 ”M). Using oxygen-and-glucose deprivation (OGD) to simulate ischemic conditions in slices, VRAC activation appeared after OGD induced anoxic depolarization (AD) that showed a progressive increase in current amplitude over the period of post-OGD reperfusion. The OGD induced VRAC currents were significantly inhibited by inhibitors for glutamate AMPA (30 ”M NBQX) and NMDA (40 ”M AP-5) receptors in the OGD solution, supporting the view that induction of AD requires an excessive Na+-loading via these receptors that in turn to activate neuronal VRAC. In the presence of NPPB and DCPIB in the post-OGD reperfusion solution, the OGD induced CA1 pyramidal neuron death, as measured by TO-PRO-3-I staining, was significantly reduced, although DCPIB did not appear to be an effective neuronal VRAC blocker. Altogether, we show that rat hippocampal pyramidal neurons express functional VRAC, and ischemic conditions can initial neuronal VRAC activation that may contribute to ischemic neuronal damage
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