Aims: The initiation of hypoxic pulmonary vasoconstriction (HPV) involves an increase in cytosolic calcium ([Ca2+]i) in pulmonary artery (PA) smooth muscle cells (PASMCs). Both the processes depend on extracellular Ca2+. Extracellular Ca2+ can be sensed by extracellular calcium-sensing receptor (CaSR). This study aims at determining whether CaSR is pivotal in the initiation of HPV. Results: Experiments were performed in cultured PASMCs, isolated PAs, and rats including CaSR knockdown preparations. Both hypoxia and H2O2 equivalent to the level achieved by hypoxia increased [Ca2+]i in an extracellular Ca2+-dependent manner in PASMCs, and this was inhibited by CaSR knockdown or its negative allosteric modulator, Calhex231. Hypoxia-increased H2O2 generation was diminished by mitochondria depletion. Mitochondria depletion abolished hypoxia-induced [Ca2+]i increase (HICI), which was reversed by H2O2 repletion. CaSR knockdown or Calhex231, however, prevented the reversible effect of H2O2. HICI was abolished by catalase-polyethylene glycol (PEG-Catalase), not superoxide dismutase-polyethylene glycol (PEG-SOD) pretreatment, attenuated by ryanodine receptor3-knockdown or inhibition of store-operated Ca2+ entry. HPV in vitro and in vivo was inhibited by Calhex231 and by CaSR knockdown. Innovation: A novel mechanism underlying HPV is revealed by the role of CaSR in orchestrating reactive oxygen species and [Ca2+]i signaling. Conclusions: The activation of mitochondrial H2O2-sensitized CaSR by extracellular Ca2+ mediates HICI in PASMCs and, thus, initiates HPV. Antioxid. Redox Signal. 17, 471–484.
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