Calcium inhibition and calcium potentiation of Orai1, Orai2, and Orai3 calcium release-activated calcium channels

J Biol Chem. 2007 Jun 15;282(24):17548-56. doi: 10.1074/jbc.M611374200. Epub 2007 Apr 23.

Abstract

The recent discoveries of Stim1 and Orai proteins have shed light on the molecular makeup of both the endoplasmic reticulum Ca(2+) sensor and the calcium release-activated calcium (CRAC) channel, respectively. In this study, we investigated the regulation of CRAC channel function by extracellular Ca(2+) for channels composed primarily of Orai1, Orai2, and Orai3, by co-expressing these proteins together with Stim1, as well as the endogenous channels in HEK293 cells. As reported previously, Orai1 or Orai2 resulted in a substantial increase in CRAC current (I(crac)), but Orai3 failed to produce any detectable Ca(2+)-selective currents. However, sodium currents measured in the Orai3-expressing HEK293 cells were significantly larger in current density than Stim1-expressing cells. Moreover, upon switching to divalent free external solutions, Orai3 currents were considerably more stable than Orai1 or Orai2, indicating that Orai3 channels undergo a lesser degree of depotentiation. Additionally, the difference between depotentiation from Ca(2+) and Ba(2+) or Mg(2+) solutions was significantly less for Orai3 than for Orai1 or -2. Nonetheless, the Na(+) currents through Orai1, Orai2, and Orai3, as well as the endogenous store-operated Na(+) currents in HEK293 cells, were all inhibited by extracellular Ca(2+) with a half-maximal concentration of approximately 20 mum. We conclude that Orai1, -2, and -3 channels are similarly inhibited by extracellular Ca(2+), indicating similar affinities for Ca(2+) within the selectivity filter. Orai3 channels appeared to differ from Orai1 and -2 in being somewhat resistant to the process of Ca(2+) depotentiation.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Calcium / metabolism*
  • Calcium Channels / genetics
  • Calcium Channels / metabolism*
  • Cations, Divalent / metabolism
  • Cell Line
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism*
  • ORAI1 Protein
  • ORAI2 Protein
  • Patch-Clamp Techniques
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Stromal Interaction Molecule 1

Substances

  • Calcium Channels
  • Cations, Divalent
  • Membrane Proteins
  • Neoplasm Proteins
  • ORAI1 Protein
  • ORAI1 protein, human
  • ORAI2 Protein
  • ORAI2 protein, human
  • Orai3 protein, human
  • RNA, Small Interfering
  • STIM1 protein, human
  • Stromal Interaction Molecule 1
  • Calcium