Towards a predictive model of Ca��⁺ puffs

We investigate key characteristics of Ca��⁺ puffs in deterministic and stochastic frameworks that all incorporate the cellular morphology of IP[subscript]3 receptor channel clusters. In a first step, we numerically study Ca��⁺ liberation in a three dimensional representation of a cluster environment with reaction-diffusion dynamics in both the cytosol and the lumen. These simulations reveal that Ca��⁺ concentrations at a releasing cluster range from 80 µM to 170 µM and equilibrate almost instantaneously on the time scale of the release duration. These highly elevated Ca��⁺ concentrations eliminate Ca��⁺ oscillations in a deterministic model of an IP[subscript]3R channel cluster at physiological parameter values as revealed by a linear stability analysis. The reason lies in the saturation of all feedback processes in the IP[subscript]3R gating dynamics, so that only fluctuations can restore experimentally observed Ca��⁺ oscillations. In this spirit, we derive master equations that allow us to analytically quantify the onset of Ca��⁺ puffs and hence the stochastic time scale of intracellular Ca��⁺ dynamics. Moving up the spatial scale, we suggest to formulate cellular dynamics in terms of waiting time distribution functions. This approach prevents the state space explosion that is typical for the description of cellular dynamics based on channel states and still contains information on molecular fluctuations. We illustrate this method by studying global Ca��⁺ oscillations.

Conferencia sobre el ALCA, el TLC CA- EE.UU

Introducción ¿Por qué Centroamérica pone tanto empeño en la prosecución de un acuerdo que implica concesiones sustanciales a EE.UU. y que, además, exige a los países centroamericanos un elevado esfuerzo de adecuación y de reducciones arancelarias? Ante el nuevo TLC de Centroamérica con los EE.UU. se pueden anticipar negociaciones en agricultura, integración de servicios y en el contenido de las leyes salariales y de regulación ambiental, Asimismo, la apertura del mercado de seguros, las telecomunicaciones, aeropuertos, etc. En la agenda de EE.UU. no se excluye nada. Todos los bienes y servicios estarán incluidos, desde productos agrícolas fuertemente subsidiados en EE.UU., hasta el agua potable seguridad social, educación universitaria y ciertos servicios bancarios

La inversión y el trabajo en el TLC CA-EE.UU

Reflexiones introductorias Para comprender las implicaciones del Tratado de Libre Comercio entre Estados Unidos y Centroamérica es necesario ubicarlo dentro de las tendencias predominantes del capitalismo actual. Las que nos parecen centrales para los efectos de esta ponencia –sabiendo que no son las únicas– son: la sobreacumulación, sobreproducción y concentración del capital, la ubicación de altas proporciones de capital en esferas no productivas y la creciente competencia de países asiáticos que sólo en la segunda mitad del siglo XX adquieren un papel destacado en el mercado mundial y, en particular, en el estadounidense.

La propiedad intelectual en el TLC CA-EE.UU. con énfasis en la propiedad intelectual de seres vivos

Introducción El capítulo de propiedad intelectual (PI) es simultáneamente uno de los más desmentidos y mas imprecisos del Tratado. Ello deja abiertas posibilidades para que Estados Unidos presione a fin de conseguir eventualmente concesiones más allá de lo estipulado en el texto actual. Su lectura pone de manifiesto la agobiante tendencia –que ya se observa en el Acuerdo en Aspectos Relacionados con la Propiedad Intelectual (ADPIC o TRIPs), de la Organización Mundial del Comercio (OMC)– enel sentido de buscar imponer un régimen homogéneo de PI, concebido sin consideración alguna al grado de desarrollo de cada país y de la soberanía de cada nación para darse sus propias leyes y normativa en éste y otros campos…

El TLC CA-EE.UU. Repercusiones en el sector agropecuario de Costa Rica

Introducción El pecado inicial del Tratado y, en general, de toda su negociación, es haber aceptado un tratamiento desigual que, al contrario de los que sostienen sus negociadores y defensores, es desigual, pero no a favor de nuestros países, sino a favor de la gran potencia del norte…

Costa Rica en el marco del TLC CA-EE.UU. y sus consecuencias en el área de telecomunicaciones

Introducción Costa Rica ocupa, en América Latina, el primer lugar en cuanto a desarrollo en el campo de telecomunicaciones, con una densidad de 28.54 líneas por cada 100 habitantes, Ocupamos, además, el primer lugar en América Latina en completición de llamadas desde EE.UU., el indicador que más integrante podría reflejar la calidad de la red telefónica de un país, con un 71.47%. En relación con la productividad, Costa Rica exhibe una de las más altas del mundo, 5.35 empleados por cada 1000 líneas telefónicas. El promedio para el Continente Americano es de 5.49, para Europa 6.10 y para África 12.82.

El TLC CA-EE.UU. y el Instituto Nacional de Seguros costarricense

Introducción Nuestra seguridad social está definida por al Constitución Política y algunas leyes, e integrada por instituciones, empresas y monopolios estatales, a lo que se les dio una responsabilidad social para con todos los costarricenses y extranjeros que viven en el país.

El proyecto de Estados Unidos que determina el contenido del TLC CA-EE.UU

Introducción Negociar es, ante todo, tener un proyecto, y teniéndolo, construir su vialidad por medio de la negociación. En la experiencia de la negociación del TLC CA-EE.UU. nos encontramos que una contraparte, Estados Unidos –y cuando aludo a Estados Unidos, estoy pensando en su clase dirigente–,  si tiene su proyecto y le está construyendo vialidad. La otra contraparte, que expresa los intereses de las oligarquías centroamericanas, no tienen proyecto alternativo. Como se hizo evidente con la firma del acuerdo del TLC, ni siquiera voluntad de resistir el proyecto de su contraparte. Su proyecto es precisamente formar parte del proyecto de la otra parte…

Diálogo con Luis Paulino Vargas: “EL TLC CA-EE.UU. más que un Tratado comercial es un Tratado sobre inversiones”

Diálogo con Luis Paulino Vargas: “EL TLC CA-EE.UU. más que un Tratado comercial es un Tratado sobre inversiones”

Bone response to a Ca- and P-enriched titanium surface obtained by anodization

This study evaluated bone response to a Ca- and P- enriched titanium (Ti) surface treated by a multiphase anodic spark deposition coating (BSP-AK). Two mongrel dogs received bilateral implantation of 3 Ti cylinders (4.1 x 12 mm) in the humerus, being either BSP-AK treated or untreated (machined - control). At 8 weeks postimplantation, bone fragments containing the implants were harvested and processed for histologic and histomorphometric analyses. Bone formation was observed in cortical area and towards the medullary canal associated to approximately 1/3 of implant extension. In most cases, in the medullary area, collagen fiber bundles were detected adjacent and oriented parallel to Ti surfaces. Such connective tissue formation exhibited focal areas of mineralized matrix lined by active osteoblasts. The mean percentages of bone-to-implant contact were 2.3 (0.0-7.2 range) for BSP-AK and 0.4 (0.0-1.3 range) for control. Although the Mann-Whitney test did not detect statistically significant differences between groups, these results indicate a trend of BSP-AK treated surfaces to support contact osteogenesis in an experimental model that produces low bone-to-implant contact values.

Allosteric Control of Gating Mechanisms Revisited: The Large Conductance Ca(2+)-Activated K(+) Channel

Large-conductance Ca(2+)-activated K(+) channels (BK) play a fundamental role in modulating membrane potential in many cell types. The gating of BK channels and its modulation by Ca(2+) and voltage has been the subject of intensive research over almost three decades, yielding several of the most complicated kinetic mechanisms ever proposed. A large number of open and closed states disposed, respectively, in two planes, named tiers, characterize these mechanisms. Transitions between states in the same plane are cooperative and modulated by Ca(2+). Transitions across planes are highly concerted and voltage-dependent. Here we reexamine the validity of the two-tiered hypothesis by restricting attention to the modulation by Ca(2+). Large single channel data sets at five Ca(2+) concentrations were simultaneously analyzed from a Bayesian perspective by using hidden Markov models and Markov-chain Monte Carlo stochastic integration techniques. Our results support a dramatic reduction in model complexity, favoring a simple mechanism derived from the Monod-Wyman-Changeux allosteric model for homotetramers, able to explain the Ca(2+) modulation of the gating process. This model differs from the standard Monod-Wyman-Changeux scheme in that one distinguishes when two Ca(2+) ions are bound to adjacent or diagonal subunits of the tetramer.

Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca, and Ti

Context. The formation and evolution of the Galactic bulge and its relationship with the other Galactic populations is still poorly understood. Aims. To establish the chemical differences and similarities between the bulge and other stellar populations, we performed an elemental abundance analysis of alpha- (O, Mg, Si, Ca, and Ti) and Z-odd (Na and Al) elements of red giant stars in the bulge as well as of local thin disk, thick disk and halo giants. Methods. We use high-resolution optical spectra of 25 bulge giants in Baade's window and 55 comparison giants (4 halo, 29 thin disk and 22 thick disk giants) in the solar neighborhood. All stars have similar stellar parameters but cover a broad range in metallicity (-1.5 < [Fe/H] < +0.5). A standard 1D local thermodynamic equilibrium analysis using both Kurucz and MARCS models yielded the abundances of O, Na, Mg, Al, Si, Ca, Ti and Fe. Our homogeneous and differential analysis of the Galactic stellar populations ensured that systematic errors were minimized. Results. We confirm the well-established differences for [alpha/Fe] at a given metallicity between the local thin and thick disks. For all the elements investigated, we find no chemical distinction between the bulge and the local thick disk, in agreement with our previous study of C, N and O but in contrast to other groups relying on literature values for nearby disk dwarf stars. For -1.5 < [Fe/H] < -0.3 exactly the same trend is followed by both the bulge and thick disk stars, with a star-to-star scatter of only 0.03 dex. Furthermore, both populations share the location of the knee in the [alpha/Fe] vs. [Fe/H] diagram. It still remains to be confirmed that the local thick disk extends to super-solar metallicities as is the case for the bulge. These are the most stringent constraints to date on the chemical similarity of these stellar populations. Conclusions. Our findings suggest that the bulge and local thick disk stars experienced similar formation timescales, star formation rates and initial mass functions, confirming thus the main outcomes of our previous homogeneous analysis of [O/Fe] from infrared spectra for nearly the same sample. The identical a-enhancements of thick disk and bulge stars may reflect a rapid chemical evolution taking place before the bulge and thick disk structures we see today were formed, or it may reflect Galactic orbital migration of inner disk/bulge stars resulting in stars in the solar neighborhood with thick-disk kinematics.

Structural and optical properties of rare earth-doped (Ba(0.77)Ca(0.23))(1-x)(Sm, Nd, Pr, Yb)(x)TiO(3)

The structural, dielectric, and vibrational properties of pure and rare earth (RE)-doped Ba(0.77) Ca(0.23)TiO(3) (BCT23; RE = Nd, Sm, Pr, Yb) ceramics obtained via solid-state reaction were investigated. The pure and RE-doped BCT23 ceramics sintered at 1450 degrees C in air for 4 h showed a dense microstructure in all ceramics. The use of RE ions as dopants introduced lattice-parameter changes that manifested in the reduction of the volume of the unit cell. RE-doped BCT23 samples exhibit a more homogenous microstructure due to the absence of a Ti-rich phase in the grain boundaries as demonstrated by scanning electron microscopy imaging. The incorporation of REs led to perturbations of the local symmetry of TiO(6) octahedra and the creation of a new Raman mode. The results of Raman scattering measurements indicated that the Curie temperature of the ferroelectric phase transition depends on the RE ion and ion content, with the Curie temperature shifting toward lower values as the RE content increases, with the exception of Yb(3+) doping, which did not affect the ferroelectric phase transition temperature. The phase transition behavior is explained using the standard soft mode model. Electronic paramagnetic resonance measurements showed the existence of Ti vacancies in the structure of RE-doped BCT23. Defects are created via charge compensation mechanisms due to the incorporation of elements with a different valence state relative to the ions of the pure BCT23 host. It is concluded that the Ti vacancies are responsible for the activation of the Raman mode at 840 cm(-1), which is in agreement with lattice dynamics calculations. (c) 2011 American Institute of Physics. [doi:10.1063/1.3594710]

Polarization effects in molecular dynamics simulations of glass-formers Ca(NO(3))(2)center dot nH(2)O, n=4, 6, and 8

Thermodynamics, equilibrium structure, and dynamics of glass-forming liquids Ca(NO(3))(2)center dot nH(2)O, n=4, 6, and 8, have been investigated by molecular dynamics (MD) simulations. A polarizable model was considered for H(2)O and NO(3)- on the basis of previous fluctuating charge models for pure water and the molten salt 2Ca(NO(3))(2)center dot 3KNO(3). Similar thermodynamic properties have been obtained with nonpolarizable and polarizable models. The glass transition temperature, T(g), estimated from MD simulations was dependent on polarization, in particular the dependence of T(g) with electrolyte concentration. Significant polarization effects on equilibrium structure were observed in cation-cation, cation-anion, and water-water structures. Polarization increases the diffusion coefficient of H(2)O, but does not change significantly the diffusion coefficients of ions. Viscosity decreases upon inclusion of polarization, but the conductivity calculated with the polarizable model is smaller than the nonpolarizable model because polarization enhances anion-cation interactions.