GABA induces a unique rise of [Ca]i in cultured rat hippocampal neurons.

GABA evoked a reversible rise of free intracellular calcium concentration ([Ca]i) in cultured rat hippocampal neurons, detected with Fluo-3 fluorescence in a confocal laser scanning microscope. The GABA-evoked change of [Ca]i was mimicked by muscimol and not by baclofen, but was only minimally affected by picrotoxin or bicuculline, indicating that this effect of GABA is not likely to be mediated by activation of GABAB receptor or by a conventional chloride-linked GABAA receptor. GABA-evoked rise of [Ca]i expressed a marked desensitization; only 10-20 minutes after a previous exposure to GABA was the response to a subsequent application fully expressed. This desensitization was not seen in electrophysiological responses to GABA or in [Ca]i changes evoked by NMDA in the same neurons. The GABA response appeared to be developmentally regulated and was seen in 1-7-day-old more than in 21-28-day-old cells. It is suggested that GABA evokes a unique change of [Ca]i in young hippocampal neurons.