Ultrastructure of control and PAH pulmonary arterial endothelial cells and PAH lung tissue. Electromicroscopy of culture control (A, D) and PAH pulmonary arterial endothelial cells (B, E) and PAH lung tissue (C, F). Ultrastructure detail of endothelial cells in vitro (A, B, D, E) and in vivo (C, F) (scale bar: 1 μm). Weibel-Palade bodies in cultured endothelial cell (E) and endothelial cell of lung tissue (F) (arrows) (scale bar: 250 nm). M = mitochondria; N = nucleus; RBC = red blood cells.