We investigated the action of ATP on the secretion of plasminogen, TNF-α, and IL-6 from microglia. ATP (10-100 μM) stimulated the release of plasminogen from rat cultured microglia in a concentration-dependent manner with a peak response at 5-10 min after the stimulation. The release was dependent on extracellular Ca2+ and was blocked by pretreatment with oxidized ATP, a blocker of P2X7. UTP, an agonist of P2Y2, also stimulated the release of plasminogen from a subpopulation (about 20% of total cells) of cultured microglia. The release was also dependent on extracellular Ca2+, suggesting a role of stocker-operated calcium entry (SOC). ATP potently stimulated TNF-α release from 2 h after the stimulation with TNF-α mRNA expression in primary cultures of rat brain microglia. The TNF-α release was maximally elicited by 1 mM ATP and 2′- and 3′-O-(4-benzoylbenzoyl)-adenosine 5′-triphosphate (BzATP), a P2X7 selective agonist, suggesting the involvement of P2X7. This TNF-α release was correlated with a sustained Ca2+ influx. The release was inhibited by PD98059, an inhibitor of MEK1 which activates extracellular signal-regulated protein kinase (ERK), and SB203580, an inhibitor of p38 MAP kinase. However, both ERK and p38 were rapidly activated by ATP even in the absence of extracellular Ca2+. These results indicate that extracellular ATP triggers TNF-α release in rat microglia via P2X7 in a manner dependent on the sustained Ca2+ influx and via the ERK/p38 cascade independently of Ca2+ influx. ATP caused the mRNA expression and release of IL-6 in a concentration-dependent manner in MG-5. The physiological meaning of these independent release mechanisms is also discussed.
All Science Journal Classification (ASJC) codes
- Drug Discovery