title: Intracellular calcium strongly potentiates agonist-activated TRPC5 channels.
abstract: TRPC5 is a calcium (Ca(2+))-permeable nonselective cation channel expressed in several brain regions, including the hippocampus, cerebellum, and amygdala. Although TRPC5 is activated by receptors coupled to phospholipase C, the precise signaling pathway and modulatory signals remain poorly defined. We find that during continuous agonist activation, heterologously expressed TRPC5 currents are potentiated in a voltage-dependent manner ( approximately 5-fold at positive potentials and approximately 25-fold at negative potentials). The reversal potential, doubly rectifying current-voltage relation, and permeability to large cations such as N-methyl-d-glucamine remain unchanged during this potentiation. The TRPC5 current potentiation depends on extracellular Ca(2+): replacement by Ba(2+) or Mg(2+) abolishes it, whereas the addition of 10 mM Ca(2+) accelerates it. The site of action for Ca(2+) is intracellular, as simultaneous fura-2 imaging and patch clamp recordings indicate that potentiation is triggered at approximately 1 microM [Ca(2+)]. This potentiation is prevented when intracellular Ca(2+) is tightly buffered, but it is promoted when recording with internal solutions containing elevated [Ca(2+)]. In cell-attached and excised inside-out single-channel recordings, increases in internal [Ca(2+)] led to an approximately 10-20-fold increase in channel open probability, whereas single-channel conductance was unchanged. Ca(2+)-dependent potentiation should result in TRPC5 channel activation preferentially during periods of repetitive firing or coincident neurotransmitter receptor activation.
authors.affiliation: Howard Hughes Medical Institute, Department of Cardiology and Manton Center for Orphan Disease, Children's Hospital Boston, and Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Nathaniel T
authors.initials: NT
authors.lastname: Blair
authors.forename: J Stefan
authors.initials: JS
authors.lastname: Kaczmarek
authors.forename: David E
authors.initials: DE
authors.lastname: Clapham
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D002463:Cell Membrane Permeability; D018679:Cholinergic Agonists / Q000494:pharmacology; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials; D051379:Mice; D008856:Microscopy, Fluorescence; D018408:Patch-Clamp Techniques; D043643:Receptor, Muscarinic M1 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D050052:TRPC Cation Channels / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D002147:Calmodulin; D018679:Cholinergic Agonists; D043643:Receptor, Muscarinic M1; D050052:TRPC Cation Channels; C489571:TRPC4 ion channel; C112021:Trpc5 protein, mouse; D002217:Carbachol; D002118:Calcium