Calcium Signaling Is Dispensable for Receptor Regulation of Endothelial Barrier Function

J Biol Chem. 2016 Oct 28;291(44):22894-22912. doi: 10.1074/jbc.M116.756114. Epub 2016 Sep 13.


Endothelial barrier function is tightly regulated by plasma membrane receptors and is crucial for tissue fluid homeostasis; its dysfunction causes disease, including sepsis and inflammation. The ubiquitous activation of Ca2+ signaling upon phospholipase C-coupled receptor ligation leads quite naturally to the assumption that Ca2+ signaling is required for receptor-regulated endothelial barrier function. This widespread hypothesis draws analogy from smooth muscle and proposes the requirement of G protein-coupled receptor (GPCR)-generated Ca2+ signaling in activating the endothelial contractile apparatus and generating interendothelial gaps. Notwithstanding endothelia being non-excitable in nature, the hypothesis of Ca2+-induced endothelial contraction has been invoked to explain actions of GPCR agonists that either disrupt or stabilize endothelial barrier function. Here, we challenge this correlative hypothesis by showing a lack of causal link between GPCR-generated Ca2+ signaling and changes in human microvascular endothelial barrier function. We used three endogenous GPCR agonists: thrombin and histamine, which disrupt endothelial barrier function, and sphingosine-1-phosphate, which stabilizes barrier function. The qualitatively different effects of these three agonists on endothelial barrier function occur independently of Ca2+ entry through the ubiquitous store-operated Ca2+ entry channel Orai1, global Ca2+ entry across the plasma membrane, and Ca2+ release from internal stores. However, disruption of endothelial barrier function by thrombin and histamine requires the Ca2+ sensor stromal interacting molecule-1 (STIM1), whereas sphingosine-1-phosphate-mediated enhancement of endothelial barrier function occurs independently of STIM1. We conclude that although STIM1 is required for GPCR-mediated disruption of barrier function, a causal link between GPCR-induced cytoplasmic Ca2+ increases and acute changes in barrier function is missing. Thus, the cytosolic Ca2+-induced endothelial contraction is a cum hoc fallacy that should be abandoned.

Keywords: G protein-coupled receptor (GPCR); calcium release-activated calcium channel protein 1 (ORAI1); calcium signaling; endothelial cell; endothelial dysfunction; stromal interaction molecule 1 (STIM1).

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Calcium / metabolism
  • Calcium Signaling*
  • Cell Membrane / genetics
  • Cell Membrane / metabolism
  • Cells, Cultured
  • Endothelial Cells / metabolism*
  • Humans
  • Lysophospholipids / metabolism
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism
  • ORAI1 Protein / genetics
  • ORAI1 Protein / metabolism
  • Sphingosine / analogs & derivatives
  • Sphingosine / metabolism
  • Stromal Interaction Molecule 1 / genetics
  • Stromal Interaction Molecule 1 / metabolism
  • Thrombin / genetics
  • Thrombin / metabolism


  • Lysophospholipids
  • Neoplasm Proteins
  • ORAI1 Protein
  • STIM1 protein, human
  • Stromal Interaction Molecule 1
  • sphingosine 1-phosphate
  • Thrombin
  • Sphingosine
  • Calcium