title: Transient receptor potential melastatin 3 is a phosphoinositide-dependent ion channel.
abstract: Phosphoinositides are emerging as general regulators of the functionally diverse transient receptor potential (TRP) ion channel family. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) has been reported to positively regulate many TRP channels, but in several cases phosphoinositide regulation is controversial. TRP melastatin 3 (TRPM3) is a heat-activated ion channel that is also stimulated by chemical agonists, such as pregnenolone sulfate. Here, we used a wide array of approaches to determine the effects of phosphoinositides on TRPM3. We found that channel activity in excised inside-out patches decreased over time (rundown), an attribute of PI(4,5)P2-dependent ion channels. Channel activity could be restored by application of either synthetic dioctanoyl (diC8) or natural arachidonyl stearyl (AASt) PI(4,5)P2. The PI(4,5)P2 precursor phosphatidylinositol 4-phosphate (PI(4)P) was less effective at restoring channel activity. TRPM3 currents were also restored by MgATP, an effect which was inhibited by two different phosphatidylinositol 4-kinase inhibitors, or by pretreatment with a phosphatidylinositol-specific phospholipase C (PI-PLC) enzyme, indicating that MgATP acted by generating phosphoinositides. In intact cells, reduction of PI(4,5)P2 levels by chemically inducible phosphoinositide phosphatases or a voltage-sensitive 5'-phosphatase inhibited channel activity. Activation of PLC via muscarinic receptors also inhibited TRPM3 channel activity. Overall, our data indicate that TRPM3 is a phosphoinositide-dependent ion channel and that decreasing PI(4,5)P2 abundance limits its activity. As all other members of the TRPM family have also been shown to require PI(4,5)P2 for activity, our data establish PI(4,5)P2 as a general positive cofactor of this ion channel subfamily.
authors.affiliation: Department of Pharmacology and Physiology, Rutgers New Jersey Medical School, Newark, NJ 07103.
authors.forename: Doreen
authors.initials: D
authors.lastname: Badheka
authors.affiliation: Department of Pharmacology and Physiology, Rutgers New Jersey Medical School, Newark, NJ 07103.
authors.forename: Istvan
authors.initials: I
authors.lastname: Borbiro
authors.affiliation: Department of Pharmacology and Physiology, Rutgers New Jersey Medical School, Newark, NJ 07103 rohacsti@njms.rutgers.edu.
authors.forename: Tibor
authors.initials: T
authors.lastname: Rohacs
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D057809:HEK293 Cells; D006801:Humans; D009865:Oocytes / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D054801:Phosphoinositide Phospholipase C / Q000378:metabolism; D050053:TRPM Cation Channels / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000378:metabolism*; D014981:Xenopus / Q000378:metabolism
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D050053:TRPM Cation Channels; C475667:TRPM3 protein, human; D050916:TRPV Cation Channels; C037178:phosphatidylinositol 4-phosphate; D000255:Adenosine Triphosphate; D054801:Phosphoinositide Phospholipase C