Pulmonary arterial smooth muscle cell (PASMC) migration is a key component of the
vascular remodeling that occurs during the development of hypoxic
pulmonary hypertension, although the mechanisms governing this phenomenon remain poorly understood. Aquaporin-1 (AQP1), an integral membrane
water channel protein, has recently been shown to aid in migration of endothelial cells. Since AQP1 is expressed in certain types of vascular smooth muscle, we hypothesized that AQP1 would be expressed in PASMCs and would be required for migration in response to
hypoxia. Using PCR and immunoblot techniques, we determined the expression of AQPs in pulmonary vascular smooth muscle and the effect of
hypoxia on AQP levels, and we examined the role of AQP1 in
hypoxia-induced migration in rat PASMCs using Transwell filter assays. Moreover, since the cytoplasmic tail of AQP1 contains a putative
calcium binding site and an increase in intracellular
calcium concentration ([Ca(2+)](i)) is a hallmark of hypoxic exposure in PASMCs, we also determined whether the responses were Ca(2+) dependent. Results were compared with those obtained in aortic smooth muscle cells (AoSMCs). We found that although AQP1 was abundant in both PASMCs and AoSMCs,
hypoxia selectively increased
AQP1 protein levels, [Ca(2+)](i), and migration in PASMCs. Blockade of Ca(2+) entry through voltage-dependent Ca(2+) or nonselective
cation channels prevented the
hypoxia-induced increase in PASMC [Ca(2+)](i), AQP1 levels, and migration. Silencing AQP1 via
siRNA also prevented
hypoxia-induced migration of PASMCs. Our results suggest that
hypoxia induces a PASMC-specific increase in [Ca(2+)](i) that results in increased
AQP1 protein levels and cell migration.