318 GPR55-(in)dependent ion signalling of LPI A Bondarenko et al Figure 8 The LPI-evoked electrical responses depend on extracellular Na+ and LPI-triggered, slow cytosolic Na+ accumulation. Representative membrane potential recording showing LPI-evoked depolarization (n = 6) in the absence of Na+ and Ca2+ in the bath (left panel) and the corresponding statistical evaluation of LPI (5 mM)-evoked depolarization under control conditions (Control) and in the absence of Na+ and Ca2+ (right panel) (A). Representative recording of the inhibitory effect of Na+ withdrawal on LPI-evoked inward current (left panel) measured at a holding potential of -40 mV (n = 3). Endothelial cells were dialyzed with a Cs+- containing pipette solution and superfused with a Ca2+- and K+-free solution. Corresponding current-voltage relationship obtained from current responses to voltage ramps before and after the application of 5 mM LPI at time points indicated (left panel) (B). The effect of 5 mM LPI on intracellular Na+ was recorded in CoroNa™ Green-loaded cells that were transiently transfected with either siRNA control (Control: n = 17) or siRNA against GPR55 (n = 10) (C). Concentration-response correlation of LPI on the accumulation of cytosolic Na+ in a conventional buffer (EB#1) (left; n = 15–30) or in the absence of extracellular Na+ (right; n = 8–15) (D). *P < 0.005 versus control. cells. Because endothelial functions critically depend on Ca2+ entry and membrane potential ﬂuctuations, modulation of these parameters by LPI points to a unique messenger func- tion of LPI in the vasculature. Acknowledgements Dr M. Frieden (University of Geneva, Geneva, Switzerland) for critically reviewing this manuscript. This work was sup- ported by the Austrian Funds (F3010-B05, P20181-B05 and P21857-B18). Shamim Naghdi is funded by the FWF P20181-B05 within the PhD programme Molecular Medicine of the Medical Uni- versity of Graz. The authors thank Mrs Anna Schreilechner, BS, for her excel- lent technical assistance, Dr C.J.S. Edgell (University of North Carolina, Chapel Hill, NC, UCA) for the EA.hy926 cells and Conﬂicts of interest None to declare. British Journal of Pharmacology (2010) 161 308–320