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ATP stimulation of Ca2+ -dependent plasminogen release from cultured microglia
K Inoue1, K Nakajima, T Morimoto
1Division of Pharmacology, National Institute of Health Sciences, Setagaya, Tokyo, Japan.
Abstract:
1. ATP (10-100 microM), but not glutamate (100 microM), stimulated the release of plasminogen from microglia in a concentration-dependent manner during a 10 min stimulation. However, neither ATP (100 microM) nor glutamate (100 microM) stimulated the release of NO. A one hour pretreatment with BAPTA-AM (200 microM), which is metabolized in the cytosol to BAPTA (an intracellular Ca2+ chelator), completely inhibited the plasminogen release evoked by ATP (100 microM). The Ca2+ ionophore A23187 induced plasminogen release in a concentration-dependent manner (0.3 microM to 10 microM). 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 microM) had no effect on [Ca2+]i (70 out of 70 cells) in microglial cells. A second application of ATP (100 microM) 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 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 microM) 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 P2X7 receptors, evoked a long-lasting increase in [Ca2+]i even at 1 microM, a concentration at which ATP did not evoke the increase. One hour pretreatment with adenosine 5'-triphosphate-2', 3'-dialdehyde (oxidized ATP, 100 microM), a selective antagonist of P2X7 receptors, blocked the increase in [Ca2+]i induced by ATP (10 and 100 microM). 4. These data suggest that ATP may transit information from neurones to microglia, resulting in an increase in [Ca2+]i via the ionotropic P2X7 receptor which stimulates the release of plasminogen from the microglia.
Insights
Adenosine triphosphate (ATP) stimulates plasminogen release from microglia by increasing intracellular calcium via P2X7 receptors. This mechanism highlights ATP
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia play crucial roles in the central nervous system.
- Extracellular ATP is a key signaling molecule released by neurons.
- The precise mechanisms by which neuronal signals influence microglial function are under investigation.
Purpose of the Study:
- To investigate the role of adenosine triphosphate (ATP) in modulating microglial function.
- To determine the signaling pathways involved in ATP-mediated microglial responses.
- To explore the potential release of plasminogen from microglia.
Main Methods:
- Primary microglial cultures were used.
- ATP and glutamate were applied to stimulate microglia.
- Plasminogen release, intracellular calcium concentration ([Ca2+]i) changes, and receptor activity were measured.
- Pharmacological agents like BAPTA-AM, A23187, and P2X7 receptor modulators were employed.
Main Results:
- ATP, but not glutamate, concentration-dependently stimulated plasminogen release from microglia.
- ATP induced a transient, concentration-dependent increase in [Ca2+]i, dependent on extracellular calcium.
- The P2X7 receptor was identified as the primary mediator of ATP-evoked calcium influx and plasminogen release.
- Inhibition of intracellular calcium increase with BAPTA-AM blocked ATP-stimulated plasminogen release.
Conclusions:
- Neuronal ATP signaling can modulate microglial activity.
- The P2X7 receptor is critical for mediating ATP's effects on microglia.
- ATP-induced calcium signaling via P2X7 receptors stimulates plasminogen release from microglia.
- This pathway may represent a mechanism for neuronal-microglial communication.