Ecto-5′-nucleotidase and intestinal ion secretion by enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) triggers a large release of adenosine triphosphate (ATP) from host intestinal cells and the extracellular ATP is broken down to adenosine diphosphate (ADP), AMP, and adenosine. Adenosine is a potent secretagogue in the small and large intestine. We suspected that ecto-5′-nucleotidase (CD73, an intestinal enzyme) was a critical enzyme involved in the conversion of AMP to adenosine and in the pathogenesis of EPEC diarrhea. We developed a nonradioactive method for measuring ecto-5′-nucleotidase in cultured T84 cell monolayers based on the detection of phosphate release from 5′-AMP. EPEC infection triggered a release of ecto-5′-nucleotidase from the cell surface into the supernatant medium. EPEC-induced 5′-nucleotidase release was not correlated with host cell death but instead with activation of phosphatidylinositol-specific phospholipase C (PI-PLC). Ecto-5′-nucleotidase was susceptible to inhibition by zinc acetate and by α,β-methylene-adenosine diphosphate (α,β-methylene-ADP). In the Ussing chamber, these inhibitors could reverse the chloride secretory responses triggered by 5′-AMP. In addition, α,β-methylene-ADP and zinc blocked the ability of 5′-AMP to stimulate EPEC growth under nutrient-limited conditions in vitro. Ecto-5′-nucleotidase appears to be the major enzyme responsible for generation of adenosine from adenine nucleotides in the T84 cell line, and inhibitors of ecto-5′-nucleotidase, such as α,β-methylene-ADP and zinc, might be useful for treatment of the watery diarrhea produced by EPEC infection

Report from the ISSI team meeting "A Virtual Observatory for meteoroids''

The content and format of the Virtual Meteor Observatory (VMO) was discussed in a one-week team meeting at the International Space Science Institute (ISSI) in Bern, Switzerland, in 2008 November. The current status of the VMO (in 'beta' version) was presented and discussed. The visual and camera sections are ready to be populated with data; a fireball section will be created. The radio/radar section is still open. In the discussion, several points were addressed: The relation to the Planetary Science Archive, treatment of shower catalogues, how to best perform astrometry, how to compute and store orbital data. The meeting ended by producing a list of future work, which is given at the end of the paper

The antarctic regional GPS network densification : Status and results

We report on the activities related to the IAG Subcommission 1.3f “Regional Reference Frame for Antarctica”. Campaign-style GPS observations have been carried out since 1995. Based on the Bernese GNSS Software the latest analysis yields results for about 30 stations aligned to the terrestrial reference frame solution IGS08. The obtained station motions are discussed in the context of plate kinematics and glacial-isostatic adjustment. It is demonstrated that the activities are a valuable contribution both to the ITRF densification in Antarctica and to geodynamic research.</p