Decreased p53 in human pulmonary arterial smooth muscle cells (PASMCs) is associated with the decreased Bax/Bcl-2 ratio, while increased p53 in human pulmonary arterial endothelial cells (PAECs) is associated with increased Bax/Bcl-2, in patients with idiopathic pulmonary arterial hypertension (IPAH), compared with normal controls. A: Western blot analysis of p53, Bax, and Bcl-2 in normal and IPAH PASMCs (left). Summarized data (means ± SE, n = 5; right) showing the protein level of p53 and the ratio of Bax/Bcl-2 in normal and IPAH PASMCs. B: Western blot analysis of p53, Bax, and Bcl-2 in normal and IPAH PAECs (left). Summarized data (means ± SE; right) showing the protein levels of p53 and the ratio of Bax/Bcl-2 in normal and IPAH PAECs. For these studies, all cells used were between 5 and 8 passages. We compare the same passage number of cells for each experiment. **P < 0.01 and ***P < 0.001 vs. Normal.