Different patterns of Ca(2+) signals are induced by low compared to high concentrations of P2Y agonists in microglia

Brain-resident macrophages (microglia) are key cellular elements in the preservation of tissue integrity. On the other hand, they can also contribute to the development of pathological events by causing an extensive and inappropriate inflammatory response. A growing number of reports indicate the involvement of nucleotides in the control of microglial functions. With this study on P2Y receptors in rat microglia, we want to contribute to the definition of their expression profile and to the characterisation of their signalling mechanisms leading to Ca(2+) movements. Endogenous nucleotides, when applied at a concentration of 100 μM, elicited robust Ca(2+) transients, thanks to a panel of metabotropic receptors comprising mainly P2Y(2), P2Y(6) and P2Y(12) subtypes. The involvement of P2Y(12) receptors in Ca(2+) responses induced by adenine nucleotides was confirmed by the pharmacological and pertussis toxin sensitivity of the response induced by adenosine diphosphate (ADP). Beside the G protein involved, Gi and Gq respectively, adenine and uracil nucleotides differed also for induction by the latter of a capacitative Ca(2+) plateau. Moreover, when applied at low (sub-micromolar) concentrations with a long-lasting challenge, uracil nucleotides elicited oscillatory Ca(2+) changes with low frequency of occurrence (≤ 1 min(−)), sometimes superimposed to an extracellular Ca(2+)-dependent sustained Ca(2+) rise. We conclude that different patterns of Ca(2+) transients are induced by low (i.e., oscillatory Ca(2+) activity) compared to high (i.e., fast release followed by sustained raise) concentrations of nucleotides, which can suggest different roles played by receptor stimulation depending not only on the type but also on the concentration of nucleotides.