GLUTAMATE RECEPTOR-MEDIATED CALCIUM RESPONSES IN ACUTELY ISOLATED HIPPOCAMPAL ASTROCYTES

GFAP(+) cells were acutely isolated from the hippocampi of 1-10 day ol d rats, and the intracellular calcium responses to L-glutamate, ATP, a nd 5-HT were studied in single cells, Eighty-two percent of such cells responded to glutamate, 20% of them responded to ATP, and none respon ded to 5-HT. The same cells that failed to respond to ATP and 5-HT oft en responded to glutamate. These proportions of cells responding to gl utamate and ATP are very similar to those reported for GFAP(+) astrocy tes in hippocampal slices (Porter and McCarthy, 1995a,b). After cultur ing for 1-2 days in serum-containing medium, 608 of such acutely isola ted cells responded to either glutamate or ATP, and 5% to 5-HT. After I week in culture, the percentage of cells responding to glutamate rem ained essentially the same (62%) but the percentages of cells respondi ng to ATP and 5-HT increased to 92% and 62%, respectively. These perce ntages were very close to the results obtained fi om primary hippocamp al astrocyte cultures prepared from 1 day old rats and cultured for 1- 2 weeks in vitro. Pharmacological characterization showed that the Ca2 + responses of acutely isolated hippocampal astrocytes from P1-10 rats was due to activation of a group I metabotropic glutamate receptor. T he calcium responses to ATP and 5-HT in acutely isolated cells that we re then cultured were mediated by P-2y and 5-HT2A receptors, respectiv ely. These data show that, like cortical astrocytes (Kimelberg et al., 1997), GFAP(+) astrocytes cultured from the hippocampi of young rats showed marked differences in receptor expression compared to their acu tely isolated counterparts. Also, since the astrocytes acutely isolate d from these 2 different brain regions showed qualitatively the same r esponses for the 3 receptors selected, it indicates a degree of homoge neity of receptor expression for astrocytes from these 2 brain regions . (C) 1997 Wiley-Liss, Inc.