title: Sodium entry through endothelial store-operated calcium entry channels: regulation by Orai1.
abstract: Orai1 interacts with transient receptor potential protein of the canonical subfamily (TRPC4) and contributes to calcium selectivity of the endothelial cell store-operated calcium entry current (ISOC). Orai1 silencing increases sodium permeability and decreases membrane-associated calcium, although it is not known whether Orai1 is an important determinant of cytosolic sodium transitions. We test the hypothesis that, upon activation of store-operated calcium entry channels, Orai1 is a critical determinant of cytosolic sodium transitions. Activation of store-operated calcium entry channels transiently increased cytosolic calcium and sodium, characteristic of release from an intracellular store. The sodium response occurred more abruptly and returned to baseline more rapidly than did the transient calcium rise. Extracellular choline substitution for sodium did not inhibit the response, although 2-aminoethoxydiphenyl borate and YM-58483 reduced it by ∼50%. After this transient response, cytosolic sodium continued to increase due to influx through activated store-operated calcium entry channels. The magnitude of this sustained increase in cytosolic sodium was greater when experiments were conducted in low extracellular calcium and when Orai1 expression was silenced; these two interventions were not additive, suggesting a common mechanism. 2-Aminoethoxydiphenyl borate and YM-58483 inhibited the sustained increase in cytosolic sodium, only in the presence of Orai1. These studies demonstrate that sodium permeates activated store-operated calcium entry channels, resulting in an increase in cytosolic sodium; the magnitude of this response is determined by Orai1.
authors.affiliation: Department of Pharmacology, University of South Alabama, Mobile, Alabama; Center for Lung Biology, University of South Alabama, Mobile, Alabama.
authors.forename: Ningyong
authors.initials: N
authors.lastname: Xu
authors.affiliation: Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, Alabama; Center for Lung Biology, University of South Alabama, Mobile, Alabama.
authors.forename: Donna L
authors.initials: DL
authors.lastname: Cioffi
authors.affiliation: Department of Cell Biology and Neuroscience, University of South Alabama, Mobile, Alabama; Center for Lung Biology, University of South Alabama, Mobile, Alabama.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Alexeyev
authors.affiliation: Department of Pharmacology, University of South Alabama, Mobile, Alabama; Center for Lung Biology, University of South Alabama, Mobile, Alabama.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Rich
authors.affiliation: Department of Pharmacology, University of South Alabama, Mobile, Alabama; Department of Medicine, University of South Alabama, Mobile, Alabama; and Center for Lung Biology, University of South Alabama, Mobile, Alabama tstevens@southalabama.edu.
authors.forename: Troy
authors.initials: T
authors.lastname: Stevens
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D000071740:ORAI1 Protein; D034622:RNA Interference; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D050052:TRPC Cation Channels / Q000187:drug effects / Q000378:metabolism*; D014162:Transfection
chemical_list: D015220:Calcium Channels; D000071740:ORAI1 Protein; C532493:Orai1 protein, rat; D050052:TRPC Cation Channels; C489571:TRPC4 ion channel; C096351:transient receptor potential cation channel, subfamily C, member 1; D012964:Sodium; D002118:Calcium
keywords: calcium release; calcium release-activated calcium current; endoplasmic reticulum; permeability; transient receptor potential protein of the canonical subfamily