title: Na+ entry via TRPC6 causes Ca2+ entry via NCX reversal in ATP stimulated smooth muscle cells.
abstract: Reversal of the Na+/Ca2+ -exchanger (NCX) has been shown to mediate Ca2+ influx during activation of G-protein linked receptors. Functional coupling between the reverse-mode NCX and the canonical transient receptor potential channels (TRPCs) has been proposed to mediate Ca2+ influx in HEK-293 cells overexpressing TRPC3. In this communication we present evidence for similar functional coupling of NCX to endogenously expressed TRPC6 in rat aorta smooth muscle cells. Selective inhibition of reverse-mode NCX with KB-R7943 and of non-selective cation-channels with SKF-96365 abolished Ca2+ influx in response to agonist stimulation (ATP). Expression of a dominant negative TRPC6 mutant also reduced the Ca2+ influx in proportion to its transfection efficiency. Calyculin A, which is known to disrupt the junctions of the plasma membrane and sarco/endoplasmic reticulum, increased global Na+ elevations and reduced stimulated Ca2+ influx. Together our data provide evidence that localized Na+ elevations are generated by TRPC6 and drive reversal of NCX to mediate Ca2+ influx.
authors.affiliation: Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada V6T 1Z1.
authors.forename: Virginia S
authors.initials: VS
authors.lastname: Lemos
authors.forename: Damon
authors.initials: D
authors.lastname: Poburko
authors.forename: Chiu-Hsiang
authors.initials: CH
authors.lastname: Liao
authors.forename: William C
authors.initials: WC
authors.lastname: Cole
authors.forename: Cornelis
authors.initials: C
authors.lastname: van Breemen
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D008387:Marine Toxins; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism*; D010080:Oxazoles / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D050052:TRPC Cation Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D008387:Marine Toxins; D010080:Oxazoles; D019831:Sodium-Calcium Exchanger; D050052:TRPC Cation Channels; C492145:Trpc6 protein, rat; C059041:calyculin A; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium