The GPR55 agonist lysophosphatidylinositol directly activates intermediate-conductance Ca2+-activated K+ channels

Lysophosphatidylinositol (LPI) was recently shown to act both as an extracellular mediator binding to G protein-coupled receptor 55 (GPR55) and as an intracellular messenger directly affecting a number of ion channels including large-conductance Ca2+ and voltage-gated potassium (BKCa) channels. Here, we explored the effect of LPI on intermediate-conductance Ca2+-activated K+ (IKCa) channels using excised inside-out patches from endothelial cells. The functional expression of IKCa was confirmed by the charybdotoxin-and TRAM-34-sensitive hyperpolarization to histamine and ATP. Moreover, the presence of single IKCa channels with a slope conductance of 39 pS in symmetric K+ gradient was directly confirmed in inside-out patches. When cytosolically applied in the range of concentrations of 0.3-10 mu M, which are well below the herein determined critical micelle concentration of approximately 30 mu M, LPI potentiated the IKCa single-channel activity in a concentration-dependent manner, while single-channel current amplitude was not affected. In the whole-cell configuration, LPI in the pipette was found to facilitate membrane hyperpolarization in response to low (0.5 mu M) histamine concentrations in a TRAM-34-sensitive manner. These results demonstrate a so far not-described receptor-independent effect of LPI on the IKCa single-channel activity of endothelial cells, thus, highlighting LPI as a potent intracellular messenger capable of modulating electrical responses in the vasculature.