title: Transient receptor potential melastatin 1 (TRPM1) is an ion-conducting plasma membrane channel inhibited by zinc ions.
abstract: TRPM1 is the founding member of the melastatin subgroup of transient receptor potential (TRP) proteins, but it has not yet been firmly established that TRPM1 proteins form ion channels. Consequently, the biophysical and pharmacological properties of these proteins are largely unknown. Here we show that heterologous expression of TRPM1 proteins induces ionic conductances that can be activated by extracellular steroid application. However the current amplitudes observed were too small to enable a reliable biophysical characterization. We overcame this limitation by modifying TRPM1 channels in several independent ways that increased the similarity to the closely related TRPM3 channels. The resulting constructs produced considerably larger currents after overexpression. We also demonstrate that unmodified TRPM1 and TRPM3 proteins form functional heteromultimeric channels. With these approaches, we measured the divalent permeability profile and found that channels containing the pore of TRPM1 are inhibited by extracellular zinc ions at physiological concentrations, in contrast to channels containing only the pore of TRPM3. Applying these findings to pancreatic β cells, we found that TRPM1 proteins do not play a major role in steroid-activated currents of these cells. The inhibition of TRPM1 by zinc ions is primarily due to a short stretch of seven amino acids present only in the pore region of TRPM1 but not of TRPM3. Combined, our data demonstrate that TRPM1 proteins are bona fide ion-conducting plasma membrane channels. Their distinct biophysical properties allow a reliable identification of endogenous TRPM1-mediated currents.
authors.affiliation: Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany.
authors.forename: Sachar
authors.initials: S
authors.lastname: Lambert
authors.forename: Anna
authors.initials: A
authors.lastname: Drews
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Rizun
authors.forename: Thomas F J
authors.initials: TF
authors.lastname: Wagner
authors.forename: Annette
authors.initials: A
authors.lastname: Lis
authors.forename: Stefanie
authors.initials: S
authors.lastname: Mannebach
authors.forename: Sandra
authors.initials: S
authors.lastname: Plant
authors.forename: Melanie
authors.initials: M
authors.lastname: Portz
authors.forename: Marcel
authors.initials: M
authors.lastname: Meissner
authors.forename: Stephan E
authors.initials: SE
authors.lastname: Philipp
authors.forename: Johannes
authors.initials: J
authors.lastname: Oberwinkler
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D004594:Electrophysiology; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D047468:Immunoprecipitation; D009154:Mutation; D050053:TRPM Cation Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology*
chemical_list: D050053:TRPM Cation Channels; C492059:TRPM1 protein, human; C475667:TRPM3 protein, human; D015032:Zinc