Increased Activation of Stromal Interaction Molecule-1/Orai-1 in Aorta From Hypertensive Rats

Abstract

Disturbances in the regulation of cytosolic calcium (Ca 2+ ) concentration play a key role in the vascular dysfunction associated with arterial hypertension. Stromal interaction molecules (STIMs) and Orai proteins represent a novel mechanism to control store-operated Ca 2+ entry. Although STIMs act as Ca 2+ sensors for the intracellular Ca 2+ stores, Orai is the putative pore-forming component of Ca 2+ release–activated Ca 2+ channels at the plasma membrane. We hypothesized that augmented activation of Ca 2+ release–activated Ca 2+ /Orai-1, through enhanced activity of STIM-1, plays a role in increased basal tonus and vascular reactivity in hypertensive animals. Endothelium-denuded aortic rings from Wistar-Kyoto and stroke-prone spontaneously hypertensive rats were used to evaluate contractions because of Ca 2+ influx. Depletion of intracellular Ca 2+ stores, which induces Ca 2+ release–activated Ca 2+ activation, was performed by placing arteries in Ca 2+ free-EGTA buffer. The addition of the Ca 2+ regular buffer produced greater contractions in aortas from stroke-prone spontaneously hypertensive rats versus Wistar-Kyoto rats. Thapsigargin (10 μmol/L), an inhibitor of the sarcoplasmic reticulum Ca 2+ ATPase, further increased these contractions, especially in stroke-prone spontaneously hypertensive rat aorta. Addition of the Ca 2+ release–activated Ca 2+ channel inhibitors 2-aminoethoxydiphenyl borate (100 μmol/L) or gadolinium (100 μmol/L), as well as neutralizing antibodies to STIM-1 or Orai-1, abolished thapsigargin-increased contraction and the differences in spontaneous tone between the groups. Expression of Orai-1 and STIM-1 proteins was increased in aorta from stroke-prone spontaneously hypertensive rats when compared with Wistar-Kyoto rats. These results support the hypothesis that both Orai-1 and STIM-1 contribute to abnormal vascular function in hypertension. Augmented activation of STIM-1/Orai-1 may represent the mechanism that leads to impaired control of intracellular Ca 2+ levels in hypertension.