| 10980012 |
Liu QY, Schaffner AE, Chang YH, Maric D, Barker JL: Persistent activation of GABA (A) receptor/Cl (-) channels by astrocyte-derived GABA in cultured embryonic rat hippocampal neurons. J Neurophysiol. 2000 Sep;84(3):1392-403.
Whole cell patch-clamp recordings using Cl (-)-filled pipettes revealed more negative levels of baseline current and associated current variance in embryonic rat hippocampal neurons co-cultured on a monolayer of astrocytes than those cultured on poly-D-lysine. These effects were mimicked by culturing neurons on poly-D-lysine in astrocyte-conditioned medium (ACM). The baseline current and variance decreased immediately in all cells after either local perfusion with saline or exposure to bicuculline, an antagonist of GABA at GABA (A) receptor/Cl (-) channels. Baseline current and variance in all cells reached a nadir at approximately 0 mV, the calculated equilibrium potential for Cl (-). Perfusion of ACM rapidly induced a sustained current in neurons, which also reversed polarity at approximately 0 mV. Bicuculline attenuated or eliminated the ACM-induced current at a concentration that completely blocked micromolar GABA-induced current. Quantitative analyses of spontaneously occurring fluctuations superimposed on the ACM-induced current revealed estimated unitary properties of the underlying channel activity similar to those calculated for GABA's activation of GABA (A) receptor/Cl (-) channels. Bicuculline-sensitive synaptic-like transients, which reversed at approximately 0 mV, were also detected in neurons cultured in ACM, and these were immediately eliminated along with the negative baseline current and superimposed current fluctuations by perfusion. Furthermore bicuculline-sensitive synaptic-like transients were rapidly and reversibly triggered when ACM was acutely applied. ACM induced an increase in cytoplasmic Ca (2+) in cultured embryonic hippocampal neurons that was completely blocked by bicuculline and strychnine. We conclude that astrocytes release diffusible substances, most likely GABA, that persistently activate GABA (A) receptor/Cl (-) channels in co-cultured neurons. |
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