MOUSE MICROGLIAL CELLS EXPRESS A PLASMA-MEMBRANE PORE GATED BY EXTRACELLULAR ATP

We have investigated responses to extracellular ATP (ATP(e)) in the mi croglial cell lines N9 and N13 and in freshly isolated mouse microglia l cells. Upon stimulation with this nucleotide, N9 and N13 cells under went an increase in the cytoplasmic free Ca2+ concentration ([Ca2+](i) ), a sustained depolarization of the plasma membrane, and an uptake of extracellular markers such as ethidium bromide and lucifer yellow; in creases in plasma membrane permeability were paralleled by striking mo rphologic changes, ATP(e), as well as other nucleotides, activated a s piking Ca2+ release from intracellular stores; however, only ATP(e) wa s also able to cause a massive transmembrane Ca2+ influx. The ATP anal ogue 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) triggered a sustained Ca2+ influx accompanied by little release from stores. The ATP deriva tive oxidized ATP (oATP) strongly inhibited Ca2+ influx, minimally aff ecting Ca2+ release. From ATP(e)-sensitive microglial cell lines, we s elected several ATP(e)-resistant clones that showed complete lack of A TP(e)-mediated plasma membrane permeability changes, although they ret ained the Ca2+ mobilization response from intracellular stores. ATP(e) -dependent plasma membrane permeability changes were also greatly redu ced in growth-arrested microglial cells. Finally, ATP(e) triggered IL- 1 beta release from wild-type but not ATP(e)-resistant microglial cell s. These results show that microglial cells express at least two purin ergic receptor subtypes, metabotropic (P2Y) and ionotropic (P2Z), and that the latter is modulated during cell cycle and coupled to IL-1 bet a release.