Relationship of intracellular free Ca2+ concentration and calcium-activated chloride channels of pulmonary artery smooth muscle cells in rats under hypoxic conditions.

To investigate the relationship between intracellular free Ca2+ concentration ([Ca2+]i) and calcium-activated chloride (Clca) channels of pulmonary artery smooth muscle cells (PASMCs) in rats under acute and chronic hypoxic conditions, 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 under normal and chronic hypoxic condition. The effect of Clca channels on PASMCs proliferation was assessed by MTT assay. The Clca channel blockers niflumic acid (NFA) and indanyloxyacetic acid (IAA-94) exerted inhibitory effects on acute hypoxia-evoked contractions in the pulmonary artery. Under chronic hypoxic condition, [Ca2+]i was increased. Under normoxic condition, [Ca2+]i was (123.63 +/- 18.98) nmol/L, and in hypoxic condition, [Ca2+]i was (281.75 +/- 16.48) nmol/L (P<0.01). Under normoxic condition, [Ca2+]i showed no significant change and no effect on Clca channels was observed (P> 0.05). Chronic hypoxia increased [Ca2+]i which opened Clca channels. The NFA and IAA-94 blocked the channels and decreased [Ca2+]i from (281.75 +/- 16.48) nmol/L to (117.66 +/- 15.36) nmol/L (P<0.01). MTT assay showed that under chronic hypoxic condition NFA and IAA-94 decreased the value of absorbency (A value) from 0.459 +/- 0.058 to 0.224 +/- 0.025 (P<0.01). Hypoxia increased [Ca2+]i which opened Clca channels and had a positive-feedback in [Ca2+]i. This may play an important role in hypoxic pulmonary hypertension. Under chronic hypoxic condition, Clca channel may play a part in the regulation of proliferation of PASMCs.