title: Arachidonic acid can function as a signaling modulator by activating the TRPM5 cation channel in taste receptor cells.
abstract: Vertebrate sensory cells such as vomeronasal neurons and Drosophila photoreceptor cells use TRP channels to respond to exogenous stimuli. In mammalian taste cells, bitter and sweet substances as well as some amino acids are received by G protein-coupled receptors (T2Rs or T1Rs). As a result of activation of G protein and phospholipase Cbeta2, the TRPM5 channel is activated. Intracellular Ca(2+) is known to be a TRPM5 activator, but the participation of lipid activators remains unreported. To clarify the effect of arachidonic acid on TRPM5 in taste cells, we investigated the expression profile of a series of enzymes involved in controlling the intracellular free arachidonic acid level, with the result that in a subset of taste bud cells, monoglyceride lipase (MGL) and cyclooxygenase-2 (COX-2) are expressed as well as the previously reported group IIA phospholipase A(2) (PLA(2)-IIA). Double-labeling analysis revealed that MGL, COX-2 and PLA(2)-IIA are co-expressed in some cells that express TRPM5. We then investigated whether arachidonic acid activates TRPM5 via a heterologous expression system in HEK293 cells, and found that its activation occurred at 10 microM arachidonic acid. These results strongly suggest the possibility that arachidonic acid acts as a modulator of TRPM5 in taste signaling pathways.
authors.affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Oike
authors.forename: Minoru
authors.initials: M
authors.lastname: Wakamori
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Mori
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nakanishi
authors.forename: Ryo
authors.initials: R
authors.lastname: Taguchi
authors.forename: Takumi
authors.initials: T
authors.lastname: Misaka
authors.forename: Ichiro
authors.initials: I
authors.lastname: Matsumoto
authors.forename: Keiko
authors.initials: K
authors.lastname: Abe
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology / Q000502:physiology*; D002460:Cell Line; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D051546:Cyclooxygenase 2 / Q000378:metabolism; D054501:Group II Phospholipases A2; D006801:Humans; D015640:Ion Channel Gating; D037102:Lectins; D037181:Lectins, C-Type / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011956:Receptors, Cell Surface; D015398:Signal Transduction; D050053:TRPM Cation Channels / Q000187:drug effects / Q000502:physiology*; D013649:Taste
chemical_list: C023339:Clec10a protein, rat; D037102:Lectins; D037181:Lectins, C-Type; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D050053:TRPM Cation Channels; D016718:Arachidonic Acid; D051546:Cyclooxygenase 2; D010741:Phospholipases A; D054501:Group II Phospholipases A2