No abstract

No abstract

Application of 4-(aminomethyl)cyclohexanecarboxylic acid (tranexamic acid; TAMCA) to the central nervous system (CNS) has been shown to result in hyperexcitability and convulsions. However, the mechanisms underlying this action are unknown. In the present study, we demonstrate that TAMCA binds to the ␥-aminobutyric acid (GABA) binding site of GABA A receptors in membranes from rat cerebral cortex and does not interfere with N-methyl-D-aspartate receptors. Patch-clamp studies using human embryonic kidney cells transiently transfected with recombinant GABA A receptors composed of ␣1␤2␥2 subunits showed that TAMCA did not activate these receptors but dose dependently blocked GABA-induced chloride ion flux with an IC 50 of 7.1 Ϯ 3.1 mM. Application of TAMCA to the lumbar spinal cord of rats resulted in dose-dependent hyperexcitability, which was completely blocked by coapplication of the GABA A receptor agonist muscimol. These results indicate that TAMCA may induce hyperexcitability by blocking GABA-driven inhibition of the CNS.

No abstract

Abstract. The eddy covariance method was applied for the first time to estimate fluxes of OH and HO 2 together with fluxes of isoprene, the sum of methyl vinyl ketone (MVK) and methacrolein (MACR) and the sum of monoterpenes above a mixed deciduous forest. Highly sensitive measurements of OH and HO 2 were performed by laser induced fluorescence (LIF), and biogenic volatile organic compounds (BVOCs) were measured by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) at a time resolution of 5 s, each. Wind speed was measured by a sonic anemometer at 10 Hz. The one-day feasibility study was conducted at a total height of 37 m, about 7 m above forest canopy, during the ECHO (Emission and CHemical transformation of biogenic volatile Organic compounds) intensive field study in July 2003. The daytime measurements yielded statistically significant OH fluxes directed downward into the direction of the canopy and HO 2 fluxes mainly upward out of the canopy. This hints towards a significant local chemical sink of OH by reactions with BVOCs, other organic and inorganic compounds and conversion of OH to HO 2 above the canopy. For OH the measured flux is locally balanced by chemical sources and sinks and direct transport of OH plays no important role for the local chemical OH budget at the measurement height, as expected from the short OH lifetime (<1 s). For HO 2 the chemical lifetime (20 s) is in the range of the turbulent transport time for transfer between the top of the canopy and the Correspondence to: R. Dlugi (rdlugi@gmx.de) measuring point. In this case, the radical balance is significantly influenced by both chemistry and transport processes. In addition, the highly time-resolved trace gas measurements were used to calculate the intensity of segregation of OH and BVOCs, demonstrating that the effective reaction rate of isoprene and OH was slowed down as much as 15% due to inhomogeneous mixing of the reactants. The paper describes the results, the applied methods and provides a detailed analysis of possible systematic errors of the covariance products.

[1] In the framework of the European project STACCATO, combined measurements of 10 Be and 7 Be were carried out regularly during a full year at the high-altitude stations, Jungfraujoch (JUN), Switzerland and Zugspitze (ZUG), Germany. Inspection of the variability of the ratio 10 Be/ 7 Be in relation to 10 Be, 7 Be, and relative humidity (RH) reveals that the ratio is independent from processes that have a clear effect on both radionuclides, such as wet scavenging. High ratio values are generally met under cyclonic or northerly advective conditions, which are the synoptic situations mostly related to stratosphere-to-troposphere transport (STT) events over central Europe, while the 10-day back trajectories indicate a stratospheric source for the majority of the cases within the upper 10% quantile of 10 Be/ 7 Be ratios. The monthly 10 Be/ 7 Be ratios show a clear May and June peak at JUN and a much weaker seasonality at ZUG. A simple mixing model is used for an independent estimate of the strength of STT throughout the year based on the 7 Be and 10 Be measurements. In spite of the various uncertainties, the results indicate a seasonal cycle of stratospheric ozone percentage contribution with an early spring maximum (3-11%) and autumn minimum (1-2%) at ZUG, while at JUN, a primary maximum in May and June (6-18%), a secondary maximum in March (4-13%), and a minimum again in autumn (1-4%) are revealed. Although the simple method applied here provides an independent estimate for the impact of STT to the lower troposphere, it nevertheless shows relatively good agreement with Lagrangian model calculations, especially for ZUG.

No abstract

No abstract