The GPR55 agonist lysophosphatidylinositol directly activates intermediate-conductance Ca 2+-activated K + channels

Abstract

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 Ca 2+ and voltage-gated potassium (BK Ca) channels. Here, we explored the effect of LPI on intermediate-conductance Ca 2+-activated K + (IK Ca) channels using excised inside-out patches from endothelial cells. The functional expression of IK Ca was confirmed by the charybdotoxin- and TRAM-34-sensitive hyperpolarization to histamine and ATP. Moreover, the presence of single IK Ca 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 μM, which are well below the herein determined critical micelle concentration of approximately 30 μM, LPI potentiated the IK Ca 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 μM) histamine concentrations in a TRAM-34-sensitive manner. These results demonstrate a so far not-described receptor-independent effect of LPI on the IK Ca single-channel activity of endothelial cells, thus, highlighting LPI as a potent intracellular messenger capable of modulating electrical responses in the vasculature. © 2011 The Author(s).