Hepatic glutamine synthetase controls N5-methylglutamine in homeostasis and cancer

Glutamine synthetase (GS) activity is conserved from prokaryotes to humans, where the ATP-dependent production of glutamine from glutamate and ammonia is essential for neurotransmission and ammonia detoxification. Here, we show that mammalian GS uses glutamate and methylamine to produce a methylated glutamine analog, N5-methylglutamine. Untargeted metabolomics revealed that liver-specific GS deletion and its pharmacological inhibition in mice suppress hepatic and circulating levels of N5-methylglutamine. This alternative activity of GS was confirmed in human recombinant enzyme and cells, where a pathogenic mutation in the active site (R324C) promoted the synthesis of N5-methylglutamine over glutamine. N5-Methylglutamine is detected in the circulation, and its levels are sustained by the microbiome, as demonstrated by using germ-free mice. Finally, we show that urine levels of N5-methylglutamine correlate with tumor burden and GS expression in a β-catenin-driven model of liver cancer, highlighting the translational potential of this uncharacterized metabolite

Aprendizagem social: uma nova perspectiva sobre a aprendizagem em sistemas participados

Em muitas situações a aprendizagem experiencial é tida como um processo desenvolvido pelos indivíduos. Por vezes, também se defende que a aprendizagem experiencial pode ocorrer nos grupos ou nos sistemas sociais. Porém, poucos esforços têm sido empreendidos no sentido de conceptualizar os processos de «aprendizagem social». Neste texto, os autores destacam a importância da aprendizagem social no cenário de constantes mudanças que caracterizam os nossos tempos de modernização reflexiva. Partindo de alguns trabalhos de investigação, os autores constróem um quadro conceptual para a aprendizagem social baseado em quatro eixos: a acção, a reflexão, a cooperação e a comunicação. Argumentam que a aprendizagem social resulta do equilíbrio entre diferentes tensões que influenciam as decisões e as orientações dos sistemas de aprendizagem. Enfatizam, também, a forma pela qual neste contexto o poder, a responsabilidade e a criatividade desenvolvem um papel a considerar. Por fim, os autores apresentam algumas reflexões sobre o modo como estes processos de aprendizagem social podem ser influenciados por padrões externos e internos aos sistemas participados

Extracellular Ca2+ regulates the stimulation of Na+ transport in A6 renal epithelia

1968 — Ein Blick auf die Protestbewegungen 40 Jahre danach aus globaler Perspektive Ein Bericht von der 44. Konferenz der International Conference of Labour and Social History (ITH) in Linz, 11.-14. September 2008 Knapp 100 TeilnehmerInnen waren der Einladung zur 44. Linzer Konferenz gefolgt, die von der Internationalen Tagung der HistorikerInnen der Arbeiterbewegung und anderer sozialer Bewegungen (ITH) und der Kammer für Arbeiter und Angestellte Oberösterreich veranstaltet wurde. Marcel van..

Extracellular recordings from rat olfactory epithelium slices using micro electrode arrays

In complex organisms chemical sensation at the olfactory epithelium in the nose is translated into electrical signals that propagate toward the brain for odor identification. In this study the olfactory epithelium was coupled to an 8 × 8 multi-electrode array (MEA) for spatial odor detection. Sagittal slices of rat olfactory epithelium with intact connections to the olfactory bulb were analyzed for their electrical responses to odorants and stimulants. In the absence of odorants or stimulants, spontaneous spiking activity could be observed at multiple sites (on average 15 out of 59) with a mean frequency of 22 ± 5 Hz. When perfusing the slices with 0.1 mM isoamyl acetate or l-carvone, the mean spike frequency increased to 41 ± 6 Hz and 44 ± 7 Hz respectively. Spike frequency was a function of isoamyl acetate concentration and increased from 38 ±6 Hz at 0.05 mM to 49 ±7 Hz at 0.5 mM. In the presence of FSK + IBMX the mean spike frequency increased to 94 ± 10 Hz. In addition, while FSK + IBMX increased the spike frequency at all sites displaying spontaneous activity, the induced responses to isoamyl acetate and l-carvone displayed a different but partially overlapping spatial distribution pattern. In conclusion, parallel multi-site extracellular recordings by MEA in olfactory slices potentially provide a powerful tool for odorant identification and quantification. © 2013 Elsevier B.V.status: publishe

Primary culture of embryonic rat olfactory receptor neurons

Embryonic cells are very robust in surviving dissection and culturing protocols and easily adapt to their in vitro environment. Despite these advantages, research in the olfactory field on cultured embryonic olfactory neurons is sparse. In this study, two primary rat olfactory explant cultures of different embryonic d (E17 and E20) were established, comprising epithelium and bulb. The functionality of these neurons was tested by measuring intracellular calcium responses to cAMP-inducing agents forskolin (FSK) and 3-isobutyl-1-methylxanthine (IBMX) with fluorescence microscopy. For E17, the responsive cell fraction increased over time, from an initial 3% at the 1 d in vitro (DIV) to a maximum of 19% at 11 DIV. The response of E20 neurons fluctuated over time around a more or less stable 13%. A logistic regression analysis indicated a significant difference between both embryonic d in the response to FSK + IBMX. In addition, of these functional neurons, 23.3% of E17 and 54.3% of E20 cultures were responsive to the odorant isoamyl acetate.status: publishe

Hypotonic treatment evokes biphasic ATP release across the basolateral membrane of cultured renal epithelia (A6)

In renal A6 epithelia, an acute hypotonic shock evokes a transient increase in the intracellular Ca2+ concentration ([Ca2+]i) through a mechanism that is sensitive to the P2 receptor antagonist suramin, applied to the basolateral border only. This finding has been further characterized by examining ATP release across the basolateral membrane with luciferin-luciferase (LL) luminescence. Polarized epithelial monolayers, cultured on permeable supports were mounted in an Ussing-type chamber. We developed a LL pulse protocol to determine the rate of ATP release (RATP) in the basolateral compartment. Therefore, the perfusion at the basolateral border was repetitively interrupted during brief periods (90 s) to measure RATP as the slope of the initial rise in ATP content detected by LL luminescence. Under isosmotic conditions, 1 μl of A6 cells released ATP at a rate of 66 ± 8 fmol min−1. A sudden reduction of the basolateral osmolality from 260 to 140 mosmol (kg H2O)−1 elevated RATP rapidly to a peak value of 1.89 ± 0.11 pmol min−1 (RATPPeak) followed by a plateau phase reaching 0.51 ± 0.07 pmol min−1 (RATPPlat). Both RATPPeak and RATPPlat values increased with the degree of dilution. The magnitude of RATPPlat remained constant as long as the hyposmolality was maintained. Similarly, a steady ATP release of 0.78 ± 0.08 pmol min−1 was recorded after gradual dilution of the basolateral osmolality to 140 mosmol (kg H2O)−1. This RATP value, induced in the absence of cell swelling, is comparable to RATPPlat. Therefore, the steady ATP release is unrelated to membrane stretching, but possibly caused by the reduction of intracellular ionic strength during cell volume regulation. Independent determinations of dose-response curves for peak [Ca2+]i increase in response to exogenous ATP and basolateral hyposmolality demonstrated that the exogenous ATP concentration, required to mimic the osmotic reduction, was linearly correlated with RATPPeak. The link between the ATP release and the fast [Ca2+]i transient was also demonstrated by the depression of both phenomena by Cl− removal from the basolateral perfusate. The data are consistent with the notion that during hypotonicity, basolateral ATP release activates purinergic receptors, which underlies the suramin-sensitive rise of [Ca2+]i during the hyposmotic shock