Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA287

Poster Communications

Characterization of P2X4- and P2X7-receptors in microglia

M. Trang1, F. Markwardt1

1. Julius-Bernstein Institut for Physiology, ML University Halle-Wittenberg, Halle (Saale), Germany.

Microglia cells are immune-effector cells of the CNS. They are involved in inflammatory processes and nociception. Under pathological conditions, ATP is secreted into the extracellular space or released by damaged cells and activates purinergic receptors expressed on the microglia cells. Of the purinergic receptors, especially P2X4 and P2X7 receptors (P2X4R and P2X7R), ATP-activated cation channels, have been described to be involved in chronic nociceptive states such as neuropathic pain. We have investigated the activation of P2X4R- and P2X7R-mediated currents in microglia BV-2 cells by means of the whole cell voltage clamp technique. P2X4Rs were activated at low ATP concentrations ([ATP] = 10 µM) and are characterized by desensitizing currents. P2X7Rs were dominantly activated at high [ATP] (0.3 mM) or by Benzoyl-ATP and displayed a slowly increasing current component. The P2X4-receptor-blocker PSB 15417 inhibited the inactivating currents evoked by low [ATP] but was without significant effect at high [ATP]. In addition, the slow activating current component at high [ATP] was inhibited by PSB 15417, which might be explained by the existence of P2X4R/P2X7R heteromers or an additional blocking effect of PSB 15417 on P2X7R. A438079, a P2X7R blocker, especially inhibited the currents evoked at high [ATP]. But A438079 inhibited currents which were activated by low [ATP], too. This either suggests a P2X7R component evocable by low [ATP] or, again, the existence of P2X4R/P2X7R heteromers. We found an increase of the P2X4R-, but not P2X7R-dependent ion currents after simultaneous incubation with interferon-γ (IFN-γ) and lipopolysaccharide (LPS), whereas the exclusive incubation with IFN-γ, LPS, dexamethasone or interleukine-4 (IL-4) did not affect the currents significantly. Furthermore, the duration of cultivation significantly influenced the P2X7- and even more the P2X4-receptor-expression, i.e. the ATP-induced currents increased with longer lasting cultivation. In conclusion, the electrophysiological characteristics of ATP-induced currents did not indicate the existence of P2X4/P2X7 heteromers with a distinct phenotype different from P2X4 or P2X7 homotrimers. The pharmacological characteristics, however, leave open the formation of P2X4/P2X7 heteromers in microglia cells.

Where applicable, experiments conform with Society ethical requirements