ADENOSINE RECEPTORS MODULATE [CA2-SITU(](I) IN HIPPOCAMPAL ASTROCYTESIN)

Cultured astroglia express both adenosine and AIP purinergic receptors that are coupled to increases in intracellular calcium concentration ([Ca2+]i). Currently, there is little evidence that such purinergic re ceptors exist on astrocytes in vivo. To address this issue, calcium-se nsitive fluorescent dyes were used in conjunction with cenfocal micros copy and immunocytochemistry to examine the responsiveness of astrocyt es in acutely isolated hippocampal slices to purinergic neuroligands. Both ATP and adenosine induced dynamic increases in astrocytic [Ca2+]i that were blocked by the adenosine receptor antagonist 8-(p-sulfophen yl)theophylline. The responses to adenosine were not blocked by tetrod otoxin, 8-cyclopentyltheophylline, 8-(3-chlorostyryl)caffeine, dipyrid amole, or removal of extracellular calcium, The P-2y-selective agonist 2-methylthioadenosine triphosphate was unable to induce increases in astrocytic [Ca2+]i, whereas the P-2 agonist adenosine 5'-O-(2-thiodiph osphate) induced astrocytic responses in a low percentage of astrocyte s. These results indicate that the majority of hippocampal astrocytes in situ contain P-1 purinergic receptors coupled to increases in [Ca2]i, whereas a small minority appear to contain P-2 purinergic receptor s. Furthermore, individual hippocampal astrocytes responded to adenosi ne, glutamate, and depolarization with increases in [Ca2+]i. The exist ence of both purinergic and glutamatergic receptors on individual astr ocytes in situ suggests that astrocytes in vivo are able to integrate information derived from glutamate and adenosine receptor stimulation.