title: Complex role of STIM1 in the activation of store-independent Orai1/3 channels.
abstract: Orai proteins contribute to Ca(2+) entry into cells through both store-dependent, Ca(2+) release-activated Ca(2+) (CRAC) channels (Orai1) and store-independent, arachidonic acid (AA)-regulated Ca(2+) (ARC) and leukotriene C4 (LTC4)-regulated Ca(2+) (LRC) channels (Orai1/3 heteromultimers). Although activated by fundamentally different mechanisms, CRAC channels, like ARC and LRC channels, require stromal interacting molecule 1 (STIM1). The role of endoplasmic reticulum-resident STIM1 (ER-STIM1) in CRAC channel activation is widely accepted. Although ER-STIM1 is necessary and sufficient for LRC channel activation in vascular smooth muscle cells (VSMCs), the minor pool of STIM1 located at the plasma membrane (PM-STIM1) is necessary for ARC channel activation in HEK293 cells. To determine whether ARC and LRC conductances are mediated by the same or different populations of STIM1, Orai1, and Orai3 proteins, we used whole-cell and perforated patch-clamp recording to compare AA- and LTC4-activated currents in VSMCs and HEK293 cells. We found that both cell types show indistinguishable nonadditive LTC4- and AA-activated currents that require both Orai1 and Orai3, suggesting that both conductances are mediated by the same channel. Experiments using a nonmetabolizable form of AA or an inhibitor of 5-lipooxygenase suggested that ARC and LRC currents in both cell types could be activated by either LTC4 or AA, with LTC4 being more potent. Although PM-STIM1 was required for current activation by LTC4 and AA under whole-cell patch-clamp recordings in both cell types, ER-STIM1 was sufficient with perforated patch recordings. These results demonstrate that ARC and LRC currents are mediated by the same cellular populations of STIM1, Orai1, and Orai3, and suggest a complex role for both ER-STIM1 and PM-STIM1 in regulating these store-independent Orai1/3 channels.
authors.affiliation: Nanobioscience Constellation, State University of New York College of Nanoscale Science and Engineering, Albany, NY 12203.
authors.forename: Xuexin
authors.initials: X
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: José C
authors.initials: JC
authors.lastname: González-Cobos
authors.forename: Isaac
authors.initials: I
authors.lastname: Jardin
authors.forename: Christoph
authors.initials: C
authors.lastname: Romanin
authors.forename: Khalid
authors.initials: K
authors.lastname: Matrougui
authors.forename: Mohamed
authors.initials: M
authors.lastname: Trebak
mesh_terms: D000200:Action Potentials; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D017997:Leukotriene C4 / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D000071740:ORAI1 Protein; D051381:Rats; D000071737:Stromal Interaction Molecule 1
chemical_list: D015220:Calcium Channels; D008562:Membrane Glycoproteins; D000071740:ORAI1 Protein; C532493:Orai1 protein, rat; C573659:Orai3 protein, rat; C518857:Stim1 protein, rat; D000071737:Stromal Interaction Molecule 1; D016718:Arachidonic Acid; D017997:Leukotriene C4; D002118:Calcium