title: TRPM5 is a transient Ca2+-activated cation channel responding to rapid changes in [Ca2+]i.
abstract: Transient receptor potential (TRP) proteins are a diverse family of proteins with structural features typical of ion channels. TRPM5, a member of the TRPM subfamily, plays an important role in taste receptors, although its activation mechanism remains controversial and its function in signal transduction is unknown. Here we characterize the functional properties of heterologously expressed human TRPM5 in HEK-293 cells. TRPM5 displays characteristics of a calcium-activated, nonselective cation channel with a unitary conductance of 25 pS. TRPM5 is a monovalent-specific, nonselective cation channel that carries Na+, K+, and Cs+ ions equally well, but not Ca2+ ions. It is directly activated by [Ca2+]i at concentrations of 0.3-1 microM, whereas higher concentrations are inhibitory, resulting in a bell-shaped dose-response curve. It activates and deactivates rapidly even during sustained elevations in [Ca2+]i, thereby inducing a transient membrane depolarization. TRPM5 does not simply mirror levels of [Ca2+]i, but instead responds to the rate of change in [Ca2+]i in that it requires rapid changes in [Ca2+]i to generate significant whole-cell currents, whereas slow elevations in [Ca2+]i to equivalent levels are ineffective. Moreover, we demonstrate that TRPM5 is not limited to taste signal transduction, because we detect the presence of TRPM5 in a variety of tissues and we identify endogenous TRPM5-like currents in a pancreatic beta cell line. TRPM5 can be activated physiologically by inositol 1,4,5-trisphosphate-producing receptor agonists, and it may therefore couple intracellular Ca2+ release to electrical activity and subsequent cellular responses.
authors.affiliation: Children's Hospital, University of Mainz, Langenbeckstrasse 1, D-55101 Mainz, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Prawitt
authors.forename: Mahealani K
authors.initials: MK
authors.lastname: Monteilh-Zoller
authors.forename: Lili
authors.initials: L
authors.lastname: Brixel
authors.forename: Christian
authors.initials: C
authors.lastname: Spangenberg
authors.forename: Bernhard
authors.initials: B
authors.lastname: Zabel
authors.forename: Andrea
authors.initials: A
authors.lastname: Fleig
authors.forename: Reinhold
authors.initials: R
authors.lastname: Penner
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D002412:Cations; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006801:Humans; D007473:Ion Channels / Q000378:metabolism; D007515:Islets of Langerhans / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D050053:TRPM Cation Channels; D013649:Taste; D013650:Taste Buds / Q000378:metabolism; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D002412:Cations; D018076:DNA, Complementary; D007473:Ion Channels; D008565:Membrane Proteins; D050053:TRPM Cation Channels; C404409:TRPM5 protein, human; D002118:Calcium