Glutamate receptor‐mediated calcium responses in acutely isolated hippocampal astrocytes

GFAP(+) cells were acutely isolated from the hippocampi of 1–10 day old rats, and the intracellular calcium responses to L‐glutamate, ATP, and 5‐HT were studied in single cells. Eighty‐two percent of such cells responded to glutamate, 20% of them responded to ATP, and none responded to 5‐HT. The same cells that failed to respond to ATP and 5‐HT often responded to glutamate. These proportions of cells responding to glutamate and ATP are very similar to those reported for GFAP(+) astrocytes in hippocampal slices (Porter and McCarthy, 1995a,b). After culturing for 1–2 days in serum‐containing medium, 60% of such acutely isolated cells responded to either glutamate or ATP, and 5% to 5‐HT. After 1 week in culture, the percentage of cells responding to glutamate remained essentially the same (62%) but the percentages of cells responding to ATP and 5‐HT increased to 92% and 62%, respectively. These percentages were very close to the results obtained from primary hippocampal astrocyte cultures prepared from 1 day old rats and cultured for 1–2 weeks in vitro. Pharmacological characterization showed that the Ca 2+ responses of acutely isolated hippocampal astrocytes from P1–10 rats was due to activation of a group I metabotropic glutamate receptor. The calcium responses to ATP and 5‐HT in acutely isolated cells that were then cultured were mediated by P 2y and 5‐HT 2A receptors, respectively. 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 acutely isolated counterparts. Also, since the astrocytes acutely isolated from these 2 different brain regions showed qualitatively the same responses for the 3 receptors selected, it indicates a degree of homogeneity of receptor expression for astrocytes from these 2 brain regions. GLIA 21:380–389, 1997. © 1997 Wiley‐Liss, Inc.