title: Regulated calcium channel in apical membranes renal proximal tubule cells.
abstract: Using the single-channel patch-clamp technique, we identified a Ca2+ channel in the apical membranes rabbit cultured proximal tubule cells. The channel is permeable to both Ca2+ and Ba2+ but not to monovalent cations. In on-cell patches, the channel opened infrequently and had a conductance of 4.6 +/- 0.9 pS (n = 5) with 105 mM CaCl2 in the pipette. Although addition of forskolin (12.5 microM) Cl2 is without effect, addition of phorbol 12-myristate 13-acetate (PMA, 1 microM) activated the channel. At 0 mV pipette voltage (resting state) in the on-cell patches, PMA increased open probability (P0) from 0 to 6.9 +/- 2.3% (n = 5) within 1-3 min of PMA application. Likewise, stretching the membrane patch (-10 to -30 mmHg) activated this channel (P0 increased to 5.3 +/- 2.1%, n = 3, at 0 mV applied pipette potential), with results consistent with a mechanosensitive channel. The channel displayed only modest voltage sensitivity, with mild activation on membrane hyperpolarization but with inactivation on strong depolarization. The addition of the L-type Ca2+ channel blocker (antagonist), nifedipine (10 microM), completely blocked this channel in both on-cell and inside-out patches, whereas the agonist, BAY K 8644 (5 microM) was without effect. It is concluded that this channel is a nifedipine-sensitive, protein kinase C-regulated Ca2+ channel and that it may play a role in Ca2+ signaling in the proximal tubule cells, particularly during periods of mechanical stress.
authors.affiliation: Department of Integrative Biology, University of Texas-Houston Health Science Center 77030, USA.
authors.forename: M I
authors.initials: MI
authors.lastname: Zhang
authors.forename: R G
authors.initials: RG
authors.lastname: O'Neil
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002414:Cations, Monovalent / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011817:Rabbits; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D002414:Cations, Monovalent; D005576:Colforsin; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium