P2X7 and P2Y13 purinergic receptors mediate intracellular calcium responses to BzATP in rat cerebellar astrocytes

Previous work has established the presence of functional P2X(7) subunits in rat cerebellar astrocytes, which after stimulation with 3'-O-(4-benzoyl)benzoyl ATP (BzATP) evoked morphological changes that were not reproduced by any other nucleotide. To further characterize the receptor(s) and signaling mechanisms involved in the action of BzATP, we have employed fura-2 microfluorometry and the patch-clamp technique. BzATP elicited intracellular calcium responses that typically exhibited two components: the first one was transient and metabotropic in nature - sensitive to phospholipase C inhibition and pertussis toxin treatment -, whereas the second one was sustained and depended on the presence of extracellular calcium. The ionotropic nature of this latter component was corroborated by measurements of Mn2+ entry and macroscopic non-selective cation currents evoked by either BzATP (100 mu M) or ATP (1 mM). The two components of the calcium response to BzATP differed in their pharmacological sensitivity. The metabotropic component was partially sensitive to pyridoxalphosphate-5'-phosphate-6-azo-(-2-chloro-5-nitrophenyl)-2,4-disulfonate, a selective antagonist of P2Y(13) receptors, while the ionotropic component was modulated by external magnesium and markedly reduced by brilliant blue G and 3-(5-(2,3-dichlorophenyl)-1H-tetrazol-1-yl)methyl pyridine (A438079), thus implying the involvement of P2X(7) purinergic receptors. It is concluded that P2Y(13) and P2X(7) purinergic receptors are functionally expressed in rat cerebellar astrocytes and mediate the increase in intracellular calcium elicited by BzATP in these cells.