24 research outputs found
Effect of hypoosmotic or isoosmotic low [NaCl] medium on amino acid levels measured in the rat cortex <i>in vivo</i>.
<p>(aâc) Microdialysis probes, implanted in the rat frontoparietal cortex, were perfused with hypoosmotic medium (â95 mM NaCl, â65% osmolarity) or isoosmotic low NaCl medium (â95 mM NaCl +167 mM mannitol) for one hour. In these experiments, the rat brain was perfused with both the hypoosmotic and isoosmotic medium on opposite sides of the cortex. The data represent average dialysate levels of glutamate (a), aspartate (b), and taurine (c) ±SEM from 5 rats. ** p<0.01, hypoosmotic vs. isoosmotic low [NaCl], repeated measures ANOVA. (dâe) In several experiments dialysate levels of glutamine (d, Nâ=â5), and asparagine (e, nâ=â3) were additionally measured on the âhypoosmoticâ side of the brain.</p
Effect of DNDS on swelling-activated D-[<sup>3</sup>H]aspartate release from cultured astrocytes and swelling-activated [<sup>3</sup>H]taurine uptake in cortical synaptosomes.
<p>(a) Cultured astrocytes preloaded with D-[<sup>3</sup>H]aspartate were superfused with hypoosmotic medium in the presence or absence of 2 mM DNDS. The data are the mean values of five experiments for each group ±SEM. *** p<0.001 hypo, vs. DNDS. (b) Release of preloaded [<sup>3</sup>H]taurine from cortical synaptosomes was measured under isoosmotic (BASAL) and hypoosmotic (HYPO) conditions in the presence or absence of 2 mM DNDS. The data are the mean values of integral 10-min [<sup>3</sup>H]taurine release ±SEM of three experiments performed in quadruplicate. ***p<0.001 vs. isoosmotic control (BASAL), <sup>###</sup>p<0.001 vs. hypoosmotic control (HYPO).</p
Effect of H<sub>2</sub>O<sub>2</sub> on hypoosmotic medium induced amino acid release in the cortex.
<p>(aâc) Two microdialysis probes implanted on opposite sides of the cortex were perfused with hypoosmotic medium in the presence or absence of 1 mM H<sub>2</sub>O<sub>2</sub> given 20 minutes prior to and during one-hour hypoosmotic medium perfusion. The data represent the average dialysate levels ±SEM of glutamate (a), aspartate (b) and taurine (c) from 9 rats. ** p<0.01 HYPO vs. HYPO+H<sub>2</sub>O<sub>2</sub>. In separate experiments, rats were perfused with 1 mM H<sub>2</sub>O<sub>2</sub> alone (Nâ=â5).</p
Dependence of taurine and glutamate uptake on extracellular [Na<sup>+</sup>] in cultured astrocytes.
<p>Taurine and glutamate transport rates were measured in primary astrocyte cultures using [<sup>3</sup>H]taurine and d-[<sup>3</sup>H]aspartate. Extracellular concentrations of amino acids were adjusted to 10 ”M using unlabeled taurine or l-glutamate. To compare glutamate versus taurine uptake, the values were normalized to uptake levels under basal conditions ([Na<sup>+</sup>]<sub>o</sub>â=â135 mM). Note that under basal conditions absolute d-[<sup>3</sup>H]aspartate uptake rate (nmols/mg protein) was âŒ5-fold higher compared to taurine. Data are the mean values ±SEM of three experiments from each group.</p
Effect of the glutamate transporter inhibitor dl-TBOA on hypoosmotic medium induced amino acid release in the cortex and glutamate transporter reversal in cultured astrocytes.
<p>(aâb) Microdialysis probes implanted on opposite sides of the cortex were perfused with hypoosmotic medium in the presence or absence of 500 ”M dl-TBOA, given 20 minutes prior to and during one hour hypoosmotic medium perfusion. The data represent average dialysate levels of glutamate (a), aspartate (b) ±SEM from 4 rats. ** p<0.01 HYPO vs. HYPO+TBOA. (c) DL-TBOA effectively prevented reversal of glutamate transporter in cultured astrocytes. Cultured astrocytes were superfused for one hour with 1 mM ouabain and additionally for 20 min high [KCl] (100 mM) plus ouabain to induce glutamate transporter reversal. 300 ”M dl-TBOA was given 10 minutes prior to and during the high [KCl] perfusion in the presence of ouabain. The data are the average values ±SEM for three experiments in each group. ** p<0.01 KCl vs. KCl+TBOA.</p
Effect of H<sub>2</sub>O<sub>2</sub> on swelling-activated taurine release from cultured astrocytes and cortical synaptosomes.
<p>(a) The effect of H<sub>2</sub>O<sub>2</sub> on swelling-activated [<sup>14</sup>C]taurine release from cultured astrocytes. Astrocytes were preloaded overnight with [<sup>14</sup>C]taurine and D-[<sup>3</sup>H]aspartate. 300 ”M H<sub>2</sub>O<sub>2</sub> was added to the media 10 min before and during exposure to hypoosmotic medium. For clarity, only [<sup>14</sup>C]taurine release is shown. The data are the mean values ±SEM of three experiments. **p<0.01 vs. hypotonic control. (b) The effect of H<sub>2</sub>O<sub>2</sub> on swelling activated [<sup>3</sup>H]taurine release from rat cortical synaptosomes. Integral [<sup>3</sup>H]taurine release was measured for 5 minutes as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003543#s2" target="_blank">Material and methods</a>. 300 ”M H<sub>2</sub>O<sub>2</sub> was present in media 10 min before and during measurements of taurine release. Data are the mean values ±SEM of three independent experiments performed in quadruplicate. ***p<0.001 vs. basal release.</p
Effect of the Ca<sup>2+</sup> channel blocker Cd<sup>2+</sup> on hypoosmotic medium-induced amino acid release in the cortex.
<p>(aâc) Microdialysis probes were perfused with hypoosmotic medium (HYPO) in the presence or absence of 300 ”M Cd<sup>2+</sup> given 20 minutes prior to and during one-hour hypoosmotic medium perfusion. Each rat had two microdialysis probes implanted on opposite sides of the cortex (one perfused with HYPO alone and the other with HYPO+Cd<sup>2+</sup>). The data represent the average dialysate levels ±SEM of glutamate (a), aspartate (b), and taurine (c) from 5 rats.</p
Hypothetical explanation of the experimental data showing differences in taurine and glutamate release <i>in vivo</i>.
<p>A reduction in medium osmolarity (â[osm]<sub>e</sub>) in the rat cortex causes an increase in the extracellular levels of the excitatory amino acids glutamate and aspartate and the sulfonic acid taurine via a mechanism sensitive to the anion channel blocker DNDS. Despite these similarities, the excitatory amino acid and taurine release demonstrate different kinetics and are likely mediated by different transport pathways (1 and 2) and/or originate from different cellular sources. The taurine pathway (1) but not the excitatory amino acid pathway (2) is activated by isoosmotic lowering of [NaCl]<sub>e</sub>. Conversely, the swelling-activated excitatory amino acid release pathway (2) but not the taurine pathway (1) is potentiated by H<sub>2</sub>O<sub>2</sub>. Alternative transport pathways that were considered in this study include: [Na<sup>+</sup>]<sub>e</sub>-dependent taurine transporters (3), [Na<sup>+</sup>]<sub>e</sub>/[K<sup>+</sup>]<sub>i</sub>-dependent glutamate transporters in neurons (4), and in astrocytes (5), which are sensitive to TBOA; and vesicular glutamate release (6), which is sensitive to the voltage-gated Ca<sup>2+</sup> channel blocker Cd<sup>2+</sup>. Based on the similarities of excitatory amino acid release <i>in vivo</i> and in cultured astrocytes, we speculate that glutamate release <i>in vivo</i> largely originates from glial cells. Similarities between taurine release <i>in vivo</i> and in synaptosomes suggest that taurine release may be of a neuronal origin.</p
Effect of the anion channel blocker DNDS on hypoosmotic medium-induced amino acid release in the rat cortex.
<p>(aâc) Microdialysis probes were perfused on opposite sides of the cortex with hypoosmotic medium (HYPO, â65% osmolarity) in the presence or absence of 10 mM DNDS, given one hour prior to and during one-hour hypoosmotic medium perfusion. The data represent average dialysate levels of glutamate (a), aspartate (b) and taurine (c) +/âSEM from 5 rats. * p<0.05, HYPO vs. HYPO+DNDS (glutamate); ** p<0.01, HYPO vs. HYPO+DNDS (aspartate); *** p<0.001 HYPO vs. HYPO+DNDS (taurine). Significance was determined by repeated measures ANOVA.</p
Sensitivity and Specificity of PW-Doppler parameters t<sub>s</sub>/t<sub>T</sub> and v<sub>max</sub> as predictors of plaque formation.
<p>Sensitivity and Specificity of PW-Doppler parameters t<sub>s</sub>/t<sub>T</sub> and v<sub>max</sub> as predictors of plaque formation.</p