Promiscuous Activation of Transient Receptor Potential Vanilloid 1 (TRPV1) Channels by Negatively Charged Intracellular Lipids THE KEY ROLE OF ENDOGENOUS PHOSPHOINOSITIDES IN MAINTAINING CHANNEL ACTIVITY

Background: Regulation of TRPV1 by phosphoinositides is controversial. Results: ATP reactivates TRPV1 after run-down in excised inside-out patches by generating phosphoinositides; many other negatively charged lipids may also support TRPV1 activity. Conclusion: Despite its promiscuous activation, phosphoinositides are the key endogenous cofactors for TRPV1 activity. Significance: Our data may reconcile discordant data obtained in different experimental settings. The regulation of the heat- and capsaicin-activated transient receptor potential vanilloid 1 (TRPV1) channels by phosphoinositides is controversial. Data in cellular systems support the dependence of TRPV1 activity on phosphoinositides. The purified TRPV1, however, was recently shown to be fully functional in artificial liposomes in the absence of phosphoinositides. Here, we show that several other negatively charged phospholipids, including phosphatidylglycerol, can also support TRPV1 activity in excised patches at high concentrations. When we incorporated TRPV1 into planar lipid bilayers consisting of neutral lipids, capsaicin-induced activity depended on phosphatidylinositol 4,5-bisphosphate. We also found that TRPV1 activity in excised patches ran down and that MgATP reactivated the channel. Inhibition of phosphatidylinositol 4-kinases or enzymatic removal of phosphatidylinositol abolished this effect of MgATP, suggesting that it activated TRPV1 by generating endogenous phosphoinositides. We conclude that endogenous phosphoinositides are positive cofactors for TRPV1 activity. Our data highlight the importance of specificity in lipid regulation of ion channels and may reconcile discordant data obtained in various experimental settings.