Physiological mechanisms of lysophosphatidylcholine-induced de-ramification of murine microglia

摘要

Activation of microglial cells, the resident macrophages of the brain, occurs rapidly following brain injury. De-ramification, i.e. transformation from ramified into amoeboid morphology is one of the earliest manifestations of microglial activation. In the present study, we identified the physiological mechanisms underlying microglial de-ramification induced by lysophosphatidylcholine (LPC). Patch-clamp experiments revealed activation of non-selective cation currents and Ca²⁺-dependent K⁺ currents by extracellular LPC. LPC-activated non-selective cation channels were permeable for monovalent and divalent cations. They were inhibited by Gd³⁺, La³⁺, Zn²⁺ and Grammostola spatulata venom, but were unaffected by diltiazem, LOE908MS, amiloride and DIDS. Ca²⁺ influx through non-selective cation channels caused sustained increases in intracellular Ca²⁺ concentration. These Ca²⁺ increases were sufficient to elicit charybdotoxin-sensitive Ca²⁺-dependent K⁺ currents. However, increased [Ca²⁺]i was not required for LPC-induced morphological changes. In LPC-stimulated microglial cells, non-selective cation currents caused transient membrane depolarization, which was followed by sustained membrane hyperpolarization induced by Ca²⁺-dependent K⁺ currents. Furthermore, LPC elicited K⁺ efflux by stimulating electroneutral K⁺–Cl⁻ cotransporters, which were inhibited by furosemide and DIOA. LPC-induced microglial de-ramification was prevented by simultaneous inhibition of non-selective cation channels and K⁺–Cl⁻ cotransporters, suggesting their functional importance for microglial activation.