Assembly of an adult type acetylcholine receptor in a mouse cell line transfected with rat muscle epsilon-subunit DNA.

AbstractThe mouse muscle cell line BC3H-1 expresses an acetylcholine receptor (AChR) composed of α-,β-, and δ-subunits [1]. The functional characteristics of this AChR are comparable to the non-synaptic AChR subtype in mouse muscle [2,3]. To investigate the role of the ϵ-subunit, which is believed to replace the γ-subunit in forming the adult AChR subtype [4], BC3H-1 cells were stably transfected with cDNA encoding the rat muscle AChR ϵ-subunit. Expression of this cDNA was under the control of a heat shock promoter, and the plasmid carried the neomycin resistance gene for selection. Several clones were isolated that had integrated the plasmid DNA in a stable form and produced ϵ-subunit specific RNA after heat induction. Single-channel current recording from cells which contained abundant ϵ-subunit mRNA identified a novel AChR channel having a larger conductance than the native AChR in these cells. These results suggest that the rat muscle ϵ-subunit may assemble with mouse muscle α-, β- and δ-subunits to form a mouse-rat hybrid AChR with properties similar to that of end-plate channels in the mature mammalian neuromuscular synapse. The novel AChR channel appears in the surface membrane within a few hours following the rise in ϵ-subunit mRNA. Thus, the notion that replacement of the γ-subunit by the ϵ-subunit during development is the result of the postnatal rise in the level of ϵ-subunit specific mRNA is further supported

Anti-phospholipid-antibodies in patients with relapsing polychondritis

Relapsing polychondritis (RP) is an extremly rare multisystemic disease thought to be of autoimmune origin. In order to assess if RP is associated with anti-phospholipid antibodies (aPL), clinical data and sera of 21 patients with RP were collected in a multicentre study. Concentration of anti-cardiolipin antibodies (aCL) (IgG-, IgM-and IgA-isotypes), anti-phosphatidylserine-antibodies (aPS) (IgG-and IgM-isotypes) and anti-β-2-glycoprotein I-antibodies (aβ2 GPI) were measured by ELISA. In eight patients aCL were found to be elevated. One patient had elevated aPS. No patient had elevated aβ2 GPI. No patient had clinical signs and symptoms of a aPL syndrome. Interestingly, the two RP patients with the highest aPL had concomitant systemic lupus erythematosus (SLE). Therefore the presence of elevated aPL in RP is probably more closely related to an associated SLE than to RP itself. There is no convincing evidence that aPL are associated with RP

Un nuevo anestésico intravenoso: propofol : evaluación clínica y experimental en el perro

El propofol es un anestésico intravenoso no relacionado químicamente con ningún otro anestésico conocido. La inducción anestésica con propofol es rápida y el mantenimiento puede realizarse, bien mediante infusión continua, bien con dosis de mantenimiento en «bolus», y no presenta efecto acumulativo como ocurre con el tiopental sódico, anestésico muy similar en cuanto a acción anestésica y que sirve de referencia. Puede complementarse con analgésicos opiáceos u óxido nitroso para proporcionar analgesia. Al ser la recuperación anestésica más rápida en comparación con otros agentes anestésicos intravenosos o intramusculares, se reduce la aparición de complicaciones.Propofol is a new intravenous anaesthetic agent chemically unrelated to any other anaesthetic. When propofol is used, anaesthetic induction is fast and maintenance can be achieved by continuous infusion or by incremental doses in «bolus», without the cumulative effect seen with thiopentone, a well known barbiturate with similar anaesthetic activity and used as a reference drug. Complementation with opioids or nitrous oxide can provide adequate analgesia. Compared to other intravenous or intramuscular anaesthetic agents, anaesthetic recovery is fast, reducing the complications associated with more prolonged recoveries

Inundaciones y cambio climático

Las inundaciones de los ríos han sucedido de forma tradicional en numerosos ríos de la Península Ibérica, aportando grandes beneficios en la agricultura y en la disponibilidad de recursos hídricos, pero en la historia más reciente han originado graves daños en personas y bienes haciendo que hoy día predomine una percepción de las inundaciones como “catástrofes”. En el origen del incremento de la frecuencia de las inundaciones hay que mencionar la intensificación del uso del territorio, sellando y compactando los suelos haciendo que aumenten las escorrentías rápidas, y la alteración hidromorfológica de los ríos, concentrando las aguas y favoreciendo la ocurrencia de avenidas y desbordamientos. En el incremento exponencial de las pérdidas que las inundaciones han originado en los últimos años hay que referirse a la intensa ocupación de las riberas de los ríos y sus llanuras de inundación por personas y actividades económicas, con un desarrollo en dichas zonas no compatible con la dinámica fluvial. El cambio climático es considerado un factor de riesgo adicional muy variable según las regiones, y la estimación de sus efectos sobre las inundaciones presenta todavía numerosas incertidumbres. Atendiendo a ello se revisan algunos estudios e informes relacionados con el fenómeno de las inundaciones y su posible relación con el cambio climático, y se propone la restauración de los sistemas fluviales y la restricción de usos en las zonas inundables como estrategias más acertadas para hacer frente a la mencionada problemática de las inundaciones y a la incertidumbre creada con el cambio climático. El análisis de los sucesivos paradigmas históricos planteados por el hombre frente a las inundaciones de los ríos pone en evidencia el interés de cambiar unas estrategias de “defensa” en contra de ellas, tratando de evitar que ocurran, por otras de “convivencia” con las mismas gestionando de la forma más apropiada el riesgo de los daños que pueden generar, atendiendo al espíritu de las Directivas europeas Marco del Agua y de evaluación y gestión del riesgo de la inundación

Low-frequency excitations in glassy selenium: A comparison of neutron-scattering and molecular-dynamics results

The microscopic low-frequency dynamics of glassy selenium is investigated by means of the concurrent use of neutron inelastic scattering and computer simulations. A separation of the dynamic response in terms of intra- and interchain processes is achieved from the analysis of the simulation results. The S(Q,E) dynamic structure factors are analyzed in terms of the frequency moments or from a model scattering law, and the wave-vector dependence of the relevant quantities is established. Finally, the anomalous behavior of the heat capacity at moderately low temperatures is shown to be originated by mostly interchain interactions.Dirección General de Investigación Científica y Técnica PB89-0037-C

Percolation properties of the 2D Heisenberg model

We analyze the percolation properties of certain clusters defined on configurations of the 2--dimensional Heisenberg model. We find that, given any direction \vec{n} in O(3) space, the spins almost perpendicular to \vec{n} form a percolating cluster. This result gives indications of how the model can avoid a previously conjectured Kosterlitz-Thouless phase transition at finite temperature T.Comment: 4 pages, 3 eps figures. Revised version (more clear abstract, some new references

Low-frequency excitations in glassy selenium: A comparison of neutron-scattering and molecular-dynamics results

12 págs.; 9 figs.; 1 tab.The microscopic low-frequency dynamics of glassy selenium is investigated by means of the concurrent use of neutron inelastic scattering and computer simulations. A separation of the dynamic response in terms of intra- and interchain processes is achieved from the analysis of the simulation results. The S(Q,E) dynamic structure factors are analyzed in terms of the frequency moments or from a model scattering law, and the wave-vector dependence of the relevant quantities is established. Finally, the anomalous behavior of the heat capacity at moderately low temperatures is shown to be originated by mostly interchain interactions. © 1993 The American Physical Society.This work has been supported in part by DGICYT Grant No. PB89-0037-C03.Peer Reviewe