title: Complex functions of phosphatidylinositol 4,5-bisphosphate in regulation of TRPC5 cation channels.
abstract: The canonical transient receptor potential (TRPC) proteins have been recognized as key players in calcium entry pathways activated through phospholipase-C-coupled receptors. While it is clearly demonstrated that members of the TRPC3/6/7 subfamily are activated by diacylglycerol, the mechanism by which phospholipase C activates members of the TRPC1/4/5 subfamily remains a mystery. In this paper, we provide evidence for both negative and positive modulatory roles for membrane polyphosphoinositides in the regulation of TRPC5 channels. Depletion of polyphosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate (PIP2) through inhibition of phosphatidylinositol 4-kinase activates calcium entry and membrane currents in TRPC5-expressing but not in TRPC3- or TRPC7-expressing cells. Inclusion of polyphosphatidylinositol 4-phosphate or PIP2, but not phosphatidylinositol 3,4,5-trisphosphate, in the patch pipette inhibited TRPC5 currents. Paradoxically, depletion of PIP2 with a directed 5-phosphatase strategy inhibited TRPC5. Furthermore, when the activity of single TRPC5 channels was examined in excised patches, the channels were robustly activated by PIP2. These findings indicate complex functions for regulation of TRPC5 by PIP2, and we propose that membrane polyphosphoinositides may have at least two distinct functions in regulating TRPC5 channel activity.
authors.affiliation: Department of Health and Human Services, Laboratory of Signal Transduction, NIEHS/NIH, P.O.Box 12233, Research Triangle Park, NC 27709, USA. trebakm@mail.amc.edu
authors.forename: Mohamed
authors.initials: M
authors.lastname: Trebak
authors.forename: Loic
authors.initials: L
authors.lastname: Lemonnier
authors.forename: Wayne I
authors.initials: WI
authors.lastname: DeHaven
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Wedel
authors.forename: Gary S
authors.initials: GS
authors.lastname: Bird
authors.forename: James W
authors.initials: JW
authors.lastname: Putney
mesh_terms: D000730:Androstadienes / Q000378:metabolism; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002217:Carbachol / Q000378:metabolism; D002460:Cell Line; D018679:Cholinergic Agonists / Q000378:metabolism; D002867:Chromones / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D016210:Methacholine Chloride / Q000378:metabolism; D009025:Morpholines / Q000378:metabolism; D018408:Patch-Clamp Techniques; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism; D020123:Sirolimus / Q000378:metabolism; D050052:TRPC Cation Channels / Q000235:genetics / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D000903:Antibiotics, Antineoplastic; D018679:Cholinergic Agonists; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D019269:Phosphatidylinositol 4,5-Diphosphate; D010726:Phosphodiesterase Inhibitors; D050052:TRPC Cation Channels; C491780:TRPC5 protein, human; D016210:Methacholine Chloride; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D002217:Carbachol; D010738:Type C Phospholipases; D002118:Calcium; D020123:Sirolimus; D000077191:Wortmannin