title: Requirement of the TRPC1 cation channel in the generation of transient Ca2+ oscillations by the calcium-sensing receptor.
abstract: The calcium-sensing receptor (CaR) is an allosteric protein that responds to extracellular Ca(2+) ([Ca(2+)](o)) and aromatic amino acids with the production of different patterns of oscillations in intracellular Ca(2+) concentration ([Ca(2+)](i)). An increase in [Ca(2+)](o) stimulates phospholipase C-mediated production of inositol 1,4,5-trisphosphate and causes sinusoidal oscillations in [Ca(2+)](i). Conversely, aromatic amino acid-induced CaR activation does not stimulate phospholipase C but engages an unidentified signaling mechanism that promotes transient oscillations in [Ca(2+)](i). We show here that the [Ca(2+)](i) oscillations stimulated by aromatic amino acids were selectively abolished by TRPC1 down-regulation using either a pool of small inhibitory RNAs (siRNAs) or two different individual siRNAs that targeted different coding regions of TRPC1. Furthermore, [Ca(2+)](i) oscillations stimulated by aromatic amino acids were also abolished by inhibition of TRPC1 function with an antibody that binds the pore region of the channel. We also show that aromatic amino acid-stimulated [Ca(2+)](i) oscillations can be prevented by protein kinase C (PKC) inhibitors or siRNA-mediated PKCalpha down-regulation and impaired by either calmodulin antagonists or by the expression of a dominant-negative calmodulin mutant. We propose a model for the generation of CaR-mediated transient [Ca(2+)](i) oscillations that integrates its stimulation by aromatic amino acids with TRPC1 regulation by PKC and calmodulin.
authors.affiliation: Unit of Signal Transduction and Gastrointestinal Cancer, Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, University of California at Los Angeles, 900 Veteran Avenue, Los Angeles, CA 90095, USA. orey@mednet.ucla.edu
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Rey
authors.forename: Steven H
authors.initials: SH
authors.lastname: Young
authors.forename: Romeo
authors.initials: R
authors.lastname: Papazyan
authors.forename: Mark S
authors.initials: MS
authors.lastname: Shapiro
authors.forename: Enrique
authors.initials: E
authors.lastname: Rozengurt
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D018076:DNA, Complementary; D006801:Humans; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034741:RNA, Small Interfering; D044169:Receptors, Calcium-Sensing / Q000502:physiology*; D050052:TRPC Cation Channels / Q000378:metabolism / Q000502:physiology*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; D044169:Receptors, Calcium-Sensing; D050052:TRPC Cation Channels; C096351:transient receptor potential cation channel, subfamily C, member 1; D011493:Protein Kinase C; D010738:Type C Phospholipases; D002118:Calcium