title: Expression level of the canonical transient receptor potential 3 (TRPC3) channel determines its mechanism of activation.
abstract: Studies on the mechanism of activation of canonical transient receptor potential (TRPC) channels have often yielded conflicting results. In the current study, we have investigated the influence of expression level on the mode of regulation of TRPC3 channels. At relatively low levels of expression in DT40 chicken B-lymphocytes, TRPC3 was activated by the depletion of Ca2+ stores. Expression was increased by either transfecting with a 10-fold greater concentration of plasmid or transfecting with TRPC3 under control of a more efficient avian beta-actin promoter. At higher levels of expression, TRPC3 was no longer store-operated but could be activated through receptor-coupled phospholipase C. Under these expression conditions, TRPC3 was efficiently activated in DT40 cells lacking inositol 1,4,5-trisphosphate receptors. The Ca2+ store-operated channels formed upon expression of TRPC3 at limited levels were blocked by gadolinium; the receptor-activated channels formed upon expression of higher levels of TRPC3 were insensitive to gadolinium. These findings indicate that a single ion channel protein can form or contribute to the formation of channels regulated in two very distinct ways, i.e. either by phospholipase C-derived messengers or Ca2+ store-depletion. The mechanism of regulation of the channels depends on their level of expression.
authors.affiliation: Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health/DHHS, Research Triangle Park, NC 27709, USA.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Vazquez
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Wedel
authors.forename: Mohamed
authors.initials: M
authors.lastname: Trebak
authors.forename: Gary
authors.initials: G
authors.lastname: St  John Bird
authors.forename: James W
authors.initials: JW
authors.lastname: Putney
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002460:Cell Line; D002645:Chickens; D004396:Coloring Agents / Q000494:pharmacology; D016257:Fura-2 / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007473:Ion Channels / Q000096:biosynthesis* / Q000378:metabolism*; D018613:Microscopy, Confocal; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D043642:Receptor, Muscarinic M5; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism; D050052:TRPC Cation Channels; D013997:Time Factors; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D004396:Coloring Agents; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007473:Ion Channels; D043642:Receptor, Muscarinic M5; D018160:Receptors, Cytoplasmic and Nuclear; D011976:Receptors, Muscarinic; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; D010738:Type C Phospholipases; D002118:Calcium; D016257:Fura-2