title: A cytosolic residue mediates Mg2+ block and regulates inward current amplitude of a transient receptor potential channel.
abstract: Members of the transient receptor potential (TRP) cation channel family control a wide variety of cellular functions by regulating calcium influx. In neurons, TRP channels may also modulate cell excitability. TRPC5 is a neuronal TRP channel that plays a role in controlling neurite extension in the hippocampus. Transiently expressed TRPC5 exhibits a doubly rectifying current-voltage relationship characterized by relatively large inward currents and a unique outwardly rectifying current with a "flat" segment between +10 and +40 mV that may be attributable to Mg2+ block. We find that intracellular Mg2+ blocks the outward current through TRPC5 with an IC50 of 457 microM. The block is mediated by a cytosolic aspartate residue, D633, situated between the termination of the sixth transmembrane domain and the "TRP box." The substitution of noncharged or positively charged residues for the negatively charged D633 resulted in a channel with markedly reduced inward currents, in addition to decreased Mg2+ block. This suggests that electrostatic attraction of cations by D633 may contribute to inward current amplitude in TRPC5. We propose that cytosolic negatively charged residues can modulate the conductivity of TRP cation channels.
authors.affiliation: Department of Pharmacology and Physiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103, USA. oboukhal@umdnj.edu
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Obukhov
authors.forename: Martha C
authors.initials: MC
authors.lastname: Nowycky
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001224:Aspartic Acid; D015220:Calcium Channels / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002460:Cell Line / Q000187:drug effects / Q000378:metabolism; D019281:Dimerization; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D008274:Magnesium / Q000494:pharmacology*; D051379:Mice; D008956:Models, Chemical; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D055503:Protein Multimerization; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000502:physiology; D013329:Structure-Activity Relationship; D050052:TRPC Cation Channels; D014162:Transfection
chemical_list: D015220:Calcium Channels; D027682:Cation Transport Proteins; D011993:Recombinant Fusion Proteins; D050052:TRPC Cation Channels; C112021:Trpc5 protein, mouse; C503500:Trpc5 protein, rat; D001224:Aspartic Acid; D006632:Histamine; D008274:Magnesium