Interaction and interrelation of P2X7 and P2X4 receptor complexes in mouse lung epithelial cells

P2X4 and P2X7 receptors are ATP-gated ion channels that are co-expressed in alveolar epithelial type I cells. Both receptors are localized to the plasma membrane and partly associated with lipid rafts. Here we report on our study in an alveolar epithelial cell line of the molecular organization of P2X7R and P2X4R receptors and the effect of their knockdown. Native gel electrophoresis reveals three P2X7R complexes of ~430, ~580 and ~760 kDa. The latter two correspond exactly in size to signals of Cav-1, the structural protein of caveolae. Interestingly knockdown of P2rx7 affects protein levels, the intracellular distribution and the supramolecular organization of Cav-1 as well as of P2X4R, which is mainly detected in a complex of ~430 kDa. Our data suggest upregulation of P2X4R as a compensatory mechanism of P2X7R depletion.     

Respiration in the open ocean

A key question when trying to understand the global carbon cycle is whether the oceans are net sources or sinks of carbon. This will depend on the production of organic matter relative to the decomposition due to biological respiration. Estimates of respiration are available for the top layers, the mesopelagic layer, and the abyssal waters and sediments of various ocean regions. Although the total open ocean respiration is uncertain, it is probably substantially greater than most current estimates of particulate organic matter production. Nevertheless, whether the biota act as a net source or sink of carbon remains an open question.     

Unstable genetic system inDrosophila melanogaster: I. Instability at theCinnabar locus

Summary A mutant strain containing acinnabar allele (cn ^rbr ,rojo brillante) is reported, that produces wild-type revertants at thecinnabar (cn) locus. Incn ^rbr /cn heterozygotes the rate of mutation is highly increased. The presence of a mutator agent acting premeiotically is indicated.D.L. Lindsley and E.H. Grell, Genetic variations ofDrosophila melanogaster. Carnegie Institution of Washington, Washington, 1968; Publication No. 627.     

Granular physics: creating a dry variety of quicksand

Sand can normally support a weight by relying on internal force chains. Here we weaken this force-chain structure in very fine sand by allowing air to flow through it: we find that the sand can then no longer support weight, even when the air is turned off and the bed has settled--a ball sinks into the sand to a depth of about five diameters. The final depth of the ball scales linearly with its mass and, above a threshold mass, a jet is formed that shoots sand violently into the air.     

Identification and characterization of rod-derived cone viability factor

Retinitis pigmentosa is an untreatable, inherited retinal disease that leads to blindness. The disease initiates with the loss of night vision due to rod photoreceptor degeneration, followed by irreversible, progressive loss of cone photoreceptor. Cone loss is responsible for the main visual handicap, as cones are essential for day and high-acuity vision. Their loss is indirect, as most genes associated with retinitis pigmentosa are not expressed by these cells. We previously showed that factors secreted from rods are essential for cone viability. Here we identified one such trophic factor by expression cloning and named it rod-derived cone viability factor (RdCVF). RdCVF is a truncated thioredoxin-like protein specifically expressed by photoreceptors. The identification of this protein offers new treatment possibilities for retinitis pigmentosa.     

A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way

Many galaxies are thought to have supermassive black holes at their centres-more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray emission have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 +/- 1.5) x 10(6) solar masses (M(*)). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.