Glutamate Uptake Triggers Transporter-Mediated GABA Release from Astrocytes

Background: Glutamate (Glu) and c-aminobutyric acid (GABA) transporters play important roles in regulating neuronal activity. Glu is removed from the extracellular space dominantly by glial transporters. In contrast, GABA is mainly taken up by neurons. However, the glial GABA transporter subtypes share their localization with the Glu transporters and their expression is confined to the same subpopulation of astrocytes, raising the possibility of cooperation between Glu and GABA transport processes. Methodology/Principal Findings: Here we used diverse biological models both in vitro and in vivo to explore the interplay between these processes. We found that removal of Glu by astrocytic transporters triggers an elevation in the extracellular level of GABA. This coupling between excitatory and inhibitory signaling was found to be independent of Glu receptor-mediated depolarization, external presence of Ca2+ and glutamate decarboxylase activity. It was abolished in the presence of non-transportable blockers of glial Glu or GABA transporters, suggesting that the concerted action of these transporters underlies the process. Conclusions/Significance: Our results suggest that activation of Glu transporters results in GABA release through reversal of glial GABA transporters. This transporter-mediated interplay represents a direct link between inhibitory and excitatory neurotransmission and may function as a negative feedback combating intense excitation in pathological conditions such as epilepsy or ischemia

MULTIMODAL SIZE SPECTRA OF SUBMICROMETER PARTICLES BEARING VARIOUS ELEMENTS IN RURAL AIR

Samples of size-segregated submicrometer aerosol particles were collected with a microorifice impactor near Deep Creek Lake, a recreational area in rural western Maryland, and analyzed for up to 44 elements by instrumental neutron activation and X-ray fluorescence analyses. Differential concentration vs particle size spectra revealed as many as four distinct submicrometer aerosol modes with diameters between 0.09 and 1.0-mu-m in a single sample. The spectra of many elements, including Al, Zn, Na, K, Br, Ca, Ga, Fe, La, Sb, Ce, Ti, and I contained two or more modes. Modal diameters and S/Se ratios for samples influenced by northeasterly winds were smaller than those influenced by westerly winds, suggesting a greater age for the latter, despite the close proximity of several large coal-fired power plants to the west of the site. Large peaks in the spectra of S, As, Se, Sb, and V occurred at mass median aerodynamic diameters ranging from 0.3 to 0.6-mu-m in both day and nighttime samples. Simple dispersion estimates suggest that large peaks observed in daytime samples must include material from multiple sources, whereas mass in those observed in nighttime samples could be accounted for by single sources