TRANSMITTER-INDUCED CALCIUM RESPONSES DIFFER IN ASTROCYTES ACUTELY ISOLATED FROM RAT-BRAIN AND IN CULTURE

Glial fibrillary acid protein (GFAP)-positive astrocytes isolated from the cerebral cortices of 3-10-day-old rats frequently showed increase d intracellular Ca2+ concentration responses to L-glutamate and glutam ate analogues. However, few of the acutely isolated cells responded to ATP, and no such cells responded to serotonin [5-hydroxytryptamine (5 -HT)]. The same cell that failed to respond to ATP or 5-HT often respo nded to glutamate. Culturing acutely isolated cells in media containin g horse serum decreased Ca2+ responses to glutamate but increased the responses to ATP and induced responses to 5-HT. In primary cultures pr epared from the cerebral cortices of 1-day-old rats and cultured in ho rse serum, fewer of the cells responded to glutamate, but almost all c ells responded to ATP and 5-HT. The lack of, or limited response to, 5 -HT or ATP in the acutely isolated cells seems unlikely to be due to s elective damage to the respective receptors because acutely isolated G FAP-negative cells showed responses to ATP, several different protease s and mechanical dissociation yielded cells that also responded to glu tamate but not to ATP, and exposure of primary cultures to papain did not abolish Ca2+ responses to several transmitters. The responses of t he acutely isolated cells to glutamate but limited or lack of response s to ATP and 5-HT also correspond to what has been seen so far for ast rocytes in situ. Thus, the present studies provide direct evidence tha t some of the receptors seen in primary astrocyte cultures may reflect a response to culture conditions and that, in the context of the rele vant information so far available, acutely isolated astrocytes seem to reflect better the in vivo state.