P2X7 receptor stimulation in primary cultures of rat spinal microglia induces downregulation of the activity for glutamate transport

Abstract

It has been shown that spinal microglia expressing certain types of glutamate transporters function in the modulation of neuropathogenesis. In this study, the effect of ATP, potentially able to mediate the communication between neurons and glial cells in the spinal cord on the transport of glutamate in cultured spinal microglia, was investigated. Both GLAST and GLT-1 were detected in the cells. Preincubation with ATP or 2′-3′-O-(4-benzoyl-benzoyl) ATP (BzATP), a selective agonist for the P2X₇ receptor, significantly blocked the uptake of glutamate. The effect of BzATP was reversed by pretreatment with brilliant blue G or oxidized ATP, each a selective antagonist for P2X₇. The inhibitory effect of P2X₇ receptor activation also occurred in the absence of extracellular Na⁺ or Ca²⁺, suggesting that the receptor regulates glutamate transport by a metabotropic pathway. Furthermore, pretreatment with inhibitors of mitogen-activated protein kinase kinase, or antioxidants, significantly reversed the inhibitory effect of BzATP on the uptake of glutamate. Incubation with BzATP led to a marked decrease in the V_max, but not the K_m, of glutamate transport. However, treatment with BzATP did not induce the trafficking of glutamate transporters. These results suggest that the activation of P2X₇ receptors in spinal microglia is important in the regulation of glutamate transport via activation of the extracellular signal-regulated kinase cascade and production of oxidants.