Identification of the large-conductance background K⁺ channel in mouse B cells as TREK-2

Mouse B cells and their cell line (WEHI-231) express large-conductance background K⁺ channels (LK_bg) that are activated by arachidonic acids, characteristics similar to TREK-2. However, there is no evidence to identify the molecular nature of LK_bg; some properties of LK_bg were partly different from the reported results of TREK type channels. In this study, we compared the properties of cloned TREK-2 and LK _bg in terms of their sensitivities to ATP, phosphatidylinositol 4,5-bisphosphate (PIP₂), intracellular pH (pH_i), and membrane stretch. Similar to the previous findings of LK_bg, TREK-2 showed spontaneous activation after membrane excision (i-o patch) and were inhibited by MgATP or by PIP₂. The inhibition by MgATP was prevented by wortmannin, suggesting membrane-delimited regulation of TREKs by phosphoinositide (PI) kinase. The same was observed with the property of LK _bg; the activation of TREK-2 by membrane stretch was suppressed by U73122 (PLC inhibitor). As with the known properties of TREK-2, LK_bg were activated by acidic pH_i and inhibited by PKC activator. Finally, we confirmed the expression of TREK-2 in WEHI-231 by using RT-PCR and immunoblot analyses. The amplitude of background K⁺ current and the TREK-2 expression in WEHI-231 were commonly decreased by genetic knockdown of TREK-2 using small interfering RNA. The downregulation of TREK-2 attenuated Ca²⁺-influx induced by arachidonic acid in WEHI-231. As a whole, these results strongly indicate that TREK-2 encodes LK_bg in mouse B cells. We also newly suggest that the low activity of TREK-2 in intact cells is due to the inhibition by intrinsic PIP₂.