ATP stimulation of Ca 2+ ‐dependent plasminogen release from cultured microglia

ATP (10–100 μ m ), but not glutamate (100 μ m ), stimulated the release of plasminogen from microglia in a concentration‐dependent manner during a 10 min stimulation. However, neither ATP (100 μ m ) nor glutamate (100 μ m ) stimulated the release of NO. A one hour pretreatment with BAPTA‐AM (200 μ m ), which is metabolized in the cytosol to BAPTA (an intracellular Ca 2+ chelator), completely inhibited the plasminogen release evoked by ATP (100 μ m ). The Ca 2+ ionophore A23187 induced plasminogen release in a concentration‐dependent manner (0.3 μ m to 10 μ m ). ATP induced a transient increase in the intracellular calcium concentration ([Ca 2+ ] i ) in a concentration‐dependent manner which was very similar to the ATP‐evoked plasminogen release, whereas glutamate (100 μ m ) had no effect on [Ca 2+ ] i (70 out of 70 cells) in microglial cells. A second application of ATP (100 μ m ) stimulated an increase in [Ca 2+ ] i similar to that of the first application (21 out of 21 cells). The ATP‐evoked increase in [Ca 2+ ] i was totally dependent on extracellular Ca 2+ , 2‐Methylthio ATP was active (7 out of 7 cells), but α,β‐methylene ATP was inactive (7 out of 7 cells) at inducing an increase in [Ca 2+ ] i . Suramin (100 μ m ) was shown not to inhibit the ATP‐evoked increase in [Ca 2+ ] i (20 out of 20 cells). 2′‐ and 3′‐ O ‐(4‐Benzoylbenzoyl)‐adenosine 5′‐triphosphate (BzATP), a selective agonist of P2X 7 receptors, evoked a long‐lasting increase in [Ca 2+ ] i even at 1 μ m , a concentration at which ATP did not evoke the increase. One hour pretreatment with adenosine 5′‐triphosphate‐2′, 3′‐dialdehyde (oxidized ATP, 100 μ m ), a selective antagonist of P2X 7 receptors, blocked the increase in [Ca 2+ ] i induced by ATP (10 and 100 μ m ). These data suggest that ATP may transit information from neurones to microglia, resulting in an increase in [Ca 2+ ] i via the ionotropic P2X 7 receptor which stimulates the release of plasminogen from the microglia.British Journal of Pharmacology (1998) 123 , 1304–1310; doi: 10.1038/sj.bjp.0701732