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 microfluorometry. ATP elicited fast and transient increases of intracellular calcium concentration ([Ca2+]i) even in the absence of extracellular calcium, indicating the involvement of metabotropic purinoceptors. The co-stimulation with P1P5-di(adenosine-5')pentaphosphate (Ap5A; 0.1 microM) potentiated ATP-metabotropic calcium responses. After this preincubation ineffective concentrations of ATP triggered 40% of maximal response. Co-stimulation with Ap5A and ATP was mandatory. The potentiated response to ATP was also independent of extracellular Ca2+ and was maintained for long periods of time (h). These results show a relevant interaction of purinoceptors that may imply a novel mechanism of action for diadenosine polyphosphates.