Electrical and synaptic properties of embryonic luteinizing hormone-releasing hormone neurons in explant cultures.

Voltage- and ligand-activated channels in embryonic neurons containing luteinizing hormone-releasing hormone (LHRH) were studied by patch-pipette, whole-cell current and voltage clamp techniques. LHRH neurons were maintained in explant cultures derived from olfactory pit regions of embryonic mice. Cells were marked intracellularly with Lucifer yellow following recording. Sixty-two cells were unequivocally identified as LHRH neurons by Lucifer yellow and LHRH immunocytochemistry. The cultured LHRH neurons had resting potentials around -50 mV, exhibited spontaneous discharges generated by intrinsic and/or synaptic activities and contained a time-dependent inward rectifier (Iir). Voltage clamp analysis of ionic currents in the LHRH neuron soma revealed a tetrodotoxin-sensitive Na+ current (INa) and two major types of K+ currents, a transient current (IA), a delayed rectifier current (IK) and low- and high-voltage-activated Ca2+ currents. Spontaneous depolarizing synaptic potentials and depolarizations induced by direct application of gamma-aminobutyrate were both inhibited by picrotoxin or bicuculline, demonstrating the presence of functional gamma-aminobutyrate type A synapses on these neurons. Responses to glutamate were found in LHRH neurons in older cultures. Thus, embryonic LHRH neurons not yet positioned in their postnatal environment in the forebrain contained a highly differentiated repertoire of voltage- and ligand-gated channels.

Calmodulin is a selective mediator of Ca(2+)-induced Ca2+ release via the ryanodine receptor-like Ca2+ channel triggered by cyclic ADP-ribose.

The ryanodine receptor-like Ca2+ channel (RyRLC) is responsible for Ca2+ wave propagation and Ca2+ oscillations in certain nonmuscle cells by a Ca(2+)-induced Ca2+ release (CICR) mechanism. Cyclic ADP-ribose (cADPR), an enzymatic product derived from NAD+, is the only known endogenous metabolite that acts as an agonist on the RyRLC. However, the mode of action of cADPR is not clear. We have identified calmodulin as a functional mediator of cADPR-triggered CICR through the RyRLC in sea urchin eggs. cADPR-induced Ca2+ release consisted of two phases, an initial rapid release phase and a subsequent slower release. The second phase was selectively potentiated by calmodulin which, in turn, was activated by Ca2+ released during the initial phase. Caffeine enhanced the action of calmodulin. Calmodulin did not play a role in inositol 1,4,5-trisphosphate-induced Ca2+ release. These findings offer insights into the multiple pathways that regulate intracellular Ca2+ signaling.

Modulation of Sarco/Endoplasmic Reticulum Ca2+-ATPase 2 (SERCA2) function by acetylation following the treatment with histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA)

Background: Acetylation and deacetylation at specific lysine (K) residues is mediated by histone acetylases (HATs) and deacetylases (HDACs), respectively. HATs and HDACs act on both histone and non-histone proteins, regulating various processes, including cardiac impulse propagation. Aim of the present work was to establish whether the function of the Ca2+ ATPase SERCA2, one of the major players in Ca2+ reuptake during excitation-contraction coupling in cardiac myocytes (CMs), could be modulated by direct K acetylation. Materials and methods: HL-1 atrial mouse cells (donated by Prof. Claycomb), zebrafish and Streptozotocin-induced diabetic rat CMs were treated with the pan-inhibitor of class I and II HDACs suberanilohydroxamic acid (SAHA) for 1.5 hour. Evaluation of SERCA2 acetylation was analyzed by co-immunoprecipitation. SERCA2 activity was measured on microsomes by pyruvate/NADH coupled reaction assay. SERCA2 mutants were obtained after cloning wild-type and mutated sequences into the pCDNA3 vector and transfected into HEK cells. Ca2+ transients in CMs (loading with Fluo3-AM, field stimulation, 0.5 Hz) and in transfected HEK cells (loading with FLUO-4, caffeine pulse) were recorded. Results: Co-Immunoprecipitation experiments performed on HL-1 cells demonstrated a significant increase in the acetylation of SERCA2 after SAHA-treatment (2.5 ��M, n=3). This was associated with an increase in SERCA2 activity in microsomes obtained from HL-1 cells, after SAHA exposure (n=5). Accordingly, SAHA-treatment significantly shortened the Ca2+ reuptake time of adult zebrafish CMs. Further, SAHA 2.5 nM restored to control values the recovery time of Ca2+ transients decay in diabetic rat CMs. HDAC inhibition also improved contraction parameters, such as fraction of shortening, and increased pump activity in microsomes isolated from diabetic CMs (n=4). Notably, the K464, identified by bioinformatic tools as the most probable acetylation site on human SERCA2a, was mutated into Glutamine (Q) or Arginine (R) mimicking acetylation and deacetylation respectively. Measurements of Ca2+ transients in HEK cells revealed that the substitution of K464 with R significantly delayed the transient recovery time, thus indicating that deacetylation has a negative impact on SERCA2 function. Conclusions: Our results indicate that SERCA2 function can be improved by pro-acetylation interventions and that this mechanism of regulation is conserved among species. Therefore, the present work provides the basis to open the search for novel pharmacological tools able to specifically improve SERCA2 activity in diseases where its expression and/or function is impaired, such as diabetic cardiomyopathy.

Evolution of conducting channels in metallic atomic contacts under elastic deformation

We investigate both experimentally and theoretically the evolution of conductance in metallic one-atom contacts under elastic deformation. While simple metals like Au exhibit almost constant conductance plateaus, Al and Pb show inclined plateaus with positive and negative slopes. It is shown how these behaviors can be understood in terms of the orbital structure of the atoms forming the contact. This analysis provides further insight into the issue of conductance quantization in metallic contacts revealing important aspects of their atomic and electronic structures.

Influence of characteristics of irrigation channels on the breeding bird community of a wetland zone in southeast of Spain

The ���El Hondo Nature Park��� is mainly composed of a series of irrigation channels and water reservoirs, subjected to various regimes of management as well as reed and vegetation control, thus creating a great variety of habitats and situations. To determine the influence of these habitats and management regimes on the local bird community, a set of characteristics of these channels and their surrounding area were analysed with a Correspondence Analysis (CA). The degree of reed development in channels and the presence in the surroundings of orchards and other reed formations were the most decisive factors to explain the probability of occurrence of reed birds and waterbirds, as well as bird species richness and abundance. Other bird species were not directly influenced by channel variables, but only by those of surrounding land uses.

Direct versus indirect channels: Differentiated loss aversion in a high���involvement, non���frequently purchased hedonic product

Purpose ��� This article aims to investigate whether intermediaries reduce loss aversion in the context of a high-involvement non-frequently purchased hedonic product (tourism packages). Design/methodology/approach ��� The study incorporates the reference-dependent model into a multinomial logit model with random parameters, which controls for heterogeneity and allows representation of different correlation patterns between non-independent alternatives. Findings ��� Differentiated loss aversion is found: consumers buying high-involvement non-frequently purchased hedonic products are less loss averse when using an intermediary than when dealing with each provider separately and booking their services independently. This result can be taken as identifying consumer-based added value provided by the intermediaries. Practical implications ��� Knowing the effect of an increase in their prices is crucial for tourism collective brands (e.g. ���sun and sea���, ���inland���, ���green destinations���, ���World Heritage destinations���). This is especially applicable nowadays on account of the fact that many destinations have lowered prices to attract tourists (although, in the future, they will have to put prices back up to their normal levels). The negative effect of raising prices can be absorbed more easily via indirect channels when compared to individual providers, as the influence of loss aversion is lower for the former than the latter. The key implication is that intermediaries can ��� and should ��� add value in competition with direct e-tailing. Originality/value ��� Research on loss aversion in retailing has been prolific, exclusively focused on low-involvement and frequently purchased products without distinguishing the direct or indirect character of the distribution channel. However, less is known about other types of products such as high-involvement non-frequently purchased hedonic products. This article focuses on the latter and analyzes different patterns of loss aversion in direct and indirect channels.

Expression and cellular localization of the voltage-gated calcium channel ��2��3 in the rodent retina

High-voltage-activated calcium channels are hetero-oligomeric protein complexes that mediate multiple cellular processes, including the influx of extracellular Ca2+, neurotransmitter release, gene transcription, and synaptic plasticity. These channels consist of a primary ��1 pore-forming subunit, which is associated with an extracellular ��2�� subunit and an intracellular �� auxiliary subunit, which alter the gating properties and trafficking of the calcium channel. The cellular localization of the ��2��3 subunit in the mouse and rat retina is unknown. In this study using RT-PCR, a single band at ���305 bp corresponding to the predicted size of the ��2��3 subunit fragment was found in mouse and rat retina and brain homogenates. Western blotting of rodent retina and brain homogenates showed a single 123-kDa band. Immunohistochemistry with an affinity-purified antibody to the ��2��3 subunit revealed immunoreactive cell bodies in the ganglion cell layer and inner nuclear layer and immunoreactive processes in the inner plexiform layer and the outer plexiform layer. ��2��3 immunoreactivity was localized to multiple cell types, including ganglion, amacrine, and bipolar cells and photoreceptors, but not horizontal cells. The expression of the ��2��3 calcium channel subunit to multiple cell types suggests that this subunit participates widely in Ca-channel-mediated signaling in the retina.

Surface growth for molten silicon infiltration into carbon millimeter-sized channels: Lattice���Boltzmann simulations, experiments and models

The process of liquid silicon infiltration is investigated for channels with radii from 0.25 to 0.75 [mm] drilled in compact carbon preforms. The advantage of this setup is that the study of the phenomenon results to be simplified. For comparison purposes, attempts are made in order to work out a framework for evaluating the accuracy of simulations. The approach relies on dimensionless numbers involving the properties of the surface reaction. It turns out that complex hydrodynamic behavior derived from second Newton law can be made consistent with Lattice-Boltzmann simulations. The experiments give clear evidence that the growth of silicon carbide proceeds in two different stages and basic mechanisms are highlighted. Lattice-Boltzmann simulations prove to be an effective tool for the description of the growing phase. Namely, essential experimental constraints can be implemented. As a result, the existing models are useful to gain more insight on the process of reactive infiltration into porous media in the first stage of penetration, i.e. up to pore closure because of surface growth. A way allowing to implement the resistance from chemical reaction in Darcy law is also proposed.

Effects of Bisphenol A on ion channels: Experimental evidence and molecular mechanisms

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) produced in huge quantities in the manufacture of polycarbonate plastics and epoxy resins. It is present in most humans in developed countries, acting as a xenoestrogen and it is considered an environmental risk factor associated to several diseases. Among the whole array of identified mechanisms by which BPA can interfere with physiological processes in living organisms, changes on ion channel activity is one of the most poorly understood. There is still little evidence about BPA regulation of ion channel expression and function. However, this information is key to understand how BPA disrupts excitable and non-excitable cells, including neurons, endocrine cells and muscle cells. This report is the result of a comprehensive literature review on the effects of BPA on ion channels. We conclude that there is evidence to say that these important molecules may be key end-points for EDCs acting as xenoestrogens. However, more research on channel-mediated BPA effects is needed. Particularly, mechanistic studies to unravel the pathophysiological actions of BPA on ion channels at environmentally relevant doses.

Plasmodium induces swelling-activated ClC-2 anion channels in the host erythrocyte

Intraerythrocytic growth of the human malaria parasite Plasmodium falciparum depends on delivery of nutrients. Moreover, infection challenges cell volume constancy of the host erythrocyte requiring enhanced activity of cell volume regulatory mechanisms. Patch clamp recording demonstrated inwardly and outwardly rectifying anion channels in infected but not in control erythrocytes. The molecular identity of those channels remained elusive. We show here for one channel type that voltage dependence, cell volume sensitivity, and activation by oxidation are identical to ClC-2. Moreover, Western blots and FACS analysis showed protein and functional ClC-2 expression in human erythrocytes and erythrocytes from wild type (Clcn2(+/+)) but not from Clcn2(-/-) mice. Finally, patch clamp recording revealed activation of volume-sensitive inwardly rectifying channels in Plasmodium berghei-infected Clcn2(+/+) but not Clcn2(-/-) erythrocytes. Erythrocytes from infected mice of both genotypes differed in cell volume and inhibition of ClC-2 by ZnCl(2) (1 mm) induced an increase of cell volume only in parasitized Clcn2(+/+) erythrocytes. Lack of ClC-2 did not inhibit P. berghei development in vivo nor substantially affect the mortality of infected mice. In conclusion, activation of host ClC-2 channels participates in the altered permeability of Plasmodium-infected erythrocytes but is not required for intraerythrocytic parasite survival.

Depth-averaged numerical modeling for curved channels /

Cover title.

HIVEL2D : a two-dimensional flow model for high-velocity channels /

At head of title: "Repair, Evaluation, Maintenance, and Rehabilitation Research Program."

Houston-Galveston Navigation Channels, Texas Project.

"July 1995."

Houston-Galveston Navigation Channels, Texas Project.

"September 1995."