Mobilization of sarcoplasmic reticulum stores by hypoxia leads to consequent activation of capacitative Ca 2+ entry in isolated canine pulmonary arterial smooth muscle cells

Capacitative Ca 2+ entry (CCE) has been speculated to contribute to Ca 2+ influx during hypoxic pulmonary vasoconstriction (HPV). The aim of the present study was to directly test if acute hypoxia causes intracellular Ca 2+ concentration ([Ca 2+ ] i ) rises through CCE in canine pulmonary artery smooth muscle cells (PASMCs). In PASMCs loaded with fura‐2, hypoxia produced a transient rise in [Ca 2+ ] i in Ca 2+ ‐free solution, indicating Ca 2+ release from the intracellular Ca 2+ stores. Subsequent addition of 2 m m Ca 2+ in hypoxia elicited a sustained rise in [Ca 2+ ] i , which was partially inhibited by 10 μ m nisoldipine. The dihydropyridine‐insensitive rise in [Ca 2+ ] i was due to increased Ca 2+ influx, because it was abolished in Ca 2+ ‐free solution and hypoxia was shown to significantly enhance the rate of Mn 2+ quench of fura‐2 fluorescence. The dihyropyridine‐insensitive rise in [Ca 2+ ] i and the increased rate of Mn 2+ quench of fura‐2 fluorescence were inhibited by 50 μ m SKF 96365 and 500 μ m Ni 2+ , but not by 100 μ m La 3+ or 100 μ m Gd 3+ , exhibiting pharmacological properties characteristic of CCE. In addition, predepletion of the intracellular Ca 2+ stores inhibited the rise in [Ca 2+ ] i induced by hypoxia. These results provide the first direct evidence that acute hypoxia, by causing Ca 2+ release from the intracellular stores, activates CCE in isolated canine PASMCs, which may contribute to HPV.