ATP stimulation of Ca2+-dependent plasminogen release from cultured microglia

1 ATP (10-100 mu M), but not glutamate (100 mu M), stimulated the release of plasminogen from microglia in a concentration-dependent manner during a 10 min stimulation. However, neither ATP (100 mu M) nor glutamate (100 mu M) stimulated the release of NO. A one hour pretreatment with BAPTA-AM (200 mu M), which is metabolized in the cytosol to BAPTA (an intracellular Ca2+ chelator), completely inhibited the plasminogen release evoked by ATP (100 mu M). The Ca2+ ionophore A23187 induced plasminogen release in a concentration-dependent manner (0.3 mu M to 10 mu M). 2 ATP induced a transient increase in the intracellular calcium concentration ([Ca2+](i)) in a concentration-dependent manner which was very similar to the ATP-evoked plasminogen release, whereas glutamate (100 mu M) had no effect on [Ca2+](i) (70 out of 70 cells) in microglial cells. A second application of ATP (100 mu M) stimulated an increase in [Ca2+](i) similar to that of the first application (21 out of 21 cells). 3 The ATP-evoked increase in [Ca2+](i) was totally dependent on extracellular Ca2+ 2-Methylthio ATP I was active (7 out of 7 cells), but alpha,beta-methylene ATP was inactive (7 out of 7 cells) at Inducing an increase in [Ca2+](i). Suramin (100 mu M) was shown not to inhibit the ATP-evoked increase in [Ca2+](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 [Ca2+](i) even at 1 mu M, a concentration at which ATP did not evoke the increase. One hour pretreatment with adenosine 5'-triphosphate-2', 3'-dialdehyde (oxidized ATP, 100 mu M), a selective antagonist of P2X(7) receptors, blocked the increase in [Ca2+](i) induced by ATP (10 and 100 mu M). 4 These data suggest that ATP may transit information from neurones to microglia, resulting in an increase in [Ca2+](i) via the ionotropic P2X(7) receptor which stimulates the release of plasminogen from the microglia.