POTENTIATION OF ADENOSINE 5'-TRIPHOSPHATE CALCIUM RESPONSES BY DIADENOSINE PENTAPHOSPHATE IN INDIVIDUAL RAT CEREBELLAR ASTROCYTES

The calcium responses induced by adenosine 5'-triphosphate (ATP) were examined in single cerebellar type 1 astrocytes by fura-2 microfluorom etry. ATP elicited fast and transient increases of intracellular calci um concentration ([Ca2+](i)) even in the absence of extracellular calc ium, indicating the involvement of metabotropic purinoceptors. The co- stimulation with (PP5)-P-1-di(a- denosine-5')pentaphosphate (Ap(5)A; 0 .1 1 mu M) potentiated ATP-metabotropic calcium responses. After this preincubation ineffective concentrations of ATP triggered 40% of maxim al response. Co-stimulation with Ap(5)A and ATP was mandatory. The pot entiated response to ATP was also independent of extracellular Ca2+ an d was maintained for long periods of time (h). These results show a re levant interaction of purinoceptors that may imply a novel mechanism o f action for diadenosine polyphosphates. (C) 1998 Elsevier Science Ire land Ltd.