Mobilization of sarcoplasmic reticulum stores by hypoxia leads to consequent activation of capacitative Ca2+ entry in isolated canine pulmonary arterial smooth muscle cells

摘要

Capacitative Ca²⁺ entry (CCE) has been speculated to contribute to Ca²⁺ influx during hypoxic pulmonary vasoconstriction (HPV). The aim of the present study was to directly test if acute hypoxia causes intracellular Ca²⁺ concentration ([Ca²⁺]i) rises through CCE in canine pulmonary artery smooth muscle cells (PASMCs). In PASMCs loaded with fura-2, hypoxia produced a transient rise in [Ca²⁺]i in Ca²⁺-free solution, indicating Ca²⁺ release from the intracellular Ca²⁺ stores. Subsequent addition of 2 mm Ca²⁺ in hypoxia elicited a sustained rise in [Ca²⁺]i, which was partially inhibited by 10 μm nisoldipine. The dihydropyridine-insensitive rise in [Ca²⁺]i was due to increased Ca²⁺ influx, because it was abolished in Ca²⁺-free solution and hypoxia was shown to significantly enhance the rate of Mn²⁺ quench of fura-2 fluorescence. The dihyropyridine-insensitive rise in [Ca²⁺]i and the increased rate of Mn²⁺ quench of fura-2 fluorescence were inhibited by 50 μm SKF 96365 and 500 μm Ni²⁺, but not by 100 μm La³⁺ or 100 μm Gd³⁺, exhibiting pharmacological properties characteristic of CCE. In addition, predepletion of the intracellular Ca²⁺ stores inhibited the rise in [Ca²⁺]i induced by hypoxia. These results provide the first direct evidence that acute hypoxia, by causing Ca²⁺ release from the intracellular stores, activates CCE in isolated canine PASMCs, which may contribute to HPV.