Ca(2+) is a pivotal signal in human pulmonary artery smooth muscle cells (PASMCs) proliferation. Capacitative Ca(2+) entry (CCE) via the store-operated channel (SOC), which encoded by the transient receptor potential (TRP) gene, is an important mechanism for regulating intracellular Ca(2+) concentration ([Ca(2+)](i)) in PASMCs. Sildenafil, a potent type 5 nucleotide-dependent phosphodiesterase (PDE) inhibitor, has been proposed as a therapeutic tool to treat or prevent pulmonary arterial hypertension (PAH); however, the mechanism of its antiproliferative effect on PASMCs remains unclear. This study was designed to investigate the possible antiproliferative mechanism of sildenafil on human PASMCs, namely, its effect on the Ca(2+)-signal pathway. Cultured normal PASMCs were treated with endothelin-1 (ET-1) or ET-1 plus sildenafil separately. Cell number and viability were determined with a hemocytometer or MTT assay. [Ca(2+)](i) was measured by loading PASMCs with fura 2-AM. Expression of the TRPC1 gene and protein was detected by RT-PCR and Western blot, respectively. The results show that sildenafil dose-dependently inhibited the proliferation of PASMCs, the enhancement of basal [Ca(2+)](i) level, increase of CCE, and upregulation of TRPC expression induced by ET-1. These results suggest that sildenafil potently inhibits ET-1-induced PASMCs proliferation and downregulation of CCE and TRPC expression may be responsible for its antiproliferative effect.