Role of intracellular free Ca~(2+) concentration in the regulation of calcium-activated chloride channels in rat pulmonary artery smooth muscle cells

AIM: To investigate the role of intracellular free Ca2+ concentration ([Ca2+]i) in the regulation of calcium-activated chloride (ClCa) channels in pulmonary artery smooth muscle cells (PASMCs) of rats under normoxic, acute and chronic hypoxic conditions. METHODS: Acute hypoxia-induced contraction was observed in rat pulmonary artery by using routine blood vascular perfusion in vitro. The fluorescence Ca2+ indicator Fura-2/AM was used to observe [Ca2+]i of rat PASMCs in normal and chronic hypoxic condition. The influences of ClCa channels on PASMCs proliferation were assessed by MTT assay. RESULTS: (1) The ClCa channel blockers niflumic acid (NFA) and indaryloxyacetic acid (IAA-94) produced inhibitory effects on acute hypoxia-evoked contractions in pulmonary artery. (2) Under chronic hypoxic condition, [Ca2+]i was increased. In normoxic condition, [Ca2+]i was (123.63±18.98) nmol/L, and in hypoxic condition, [Ca2+]i was (281.75±16.48)nmol/L (P0.01). (3) In normoxic condition, [Ca2+]i had no significant change and no effect on ClCa channels was observed (P0.05). (4) Chronic hypoxic increased [Ca2+]i which opened ClCa channels. The NFA and IAA-94 blocked them and decreased [Ca2+]i from (281.75±16.48)nmol/L to (117.66±15.36)nmol/L (P0.01). (5) MTT assay showed that in chronic hypoxic condition NFA and IAA-94 decreased the value of absorbing light degree (A value) from 0.459±0.058 to 0.224±0.025 (P0.01). CONCLUSION: Hypoxia increased [Ca2+]i which opened ClCa channels and had a positive-feedback to [Ca2+]i. This may play an important role in hypoxic pulmonary hypertension. In chronic hypoxic condition, ClCa channel may play a role in the regulation of PASMCs proliferation.