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The Journal of Neurophysiology Vol. 84 No. 3 September 2000, pp. 1392-1403
Copyright ©2000 by the American Physiological Society
Channels by Astrocyte-Derived GABA in
Cultured Embryonic Rat Hippocampal Neurons
Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4066
Liu, Qi-Ying,
Anne E. Schaffner,
Yoong H. Chang,
Dragan Maric, and
Jeffery L. Barker.
Persistent Activation of GABAA
Receptor/Cl Channels by Astrocyte-Derived GABA in
Cultured Embryonic Rat Hippocampal Neurons. J. Neurophysiol. 84: 1392-1403, 2000. 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 GABAA
receptor/Cl channels. Baseline current and
variance in all cells reached a nadir at ~0 mV, the calculated
equilibrium potential for Cl. Perfusion of ACM
rapidly induced a sustained current in neurons, which also reversed
polarity at ~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
GABAA receptor/Cl
channels. Bicuculline-sensitive synaptic-like transients, which reversed at ~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 Ca2+ 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
GABAA receptor/Cl
channels in co-cultured neurons.
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