A pulmonary artery endothelial factor causes unidirectional alignment of smooth muscle cells

Pulmonary artery and aorta endothelial and smooth muscle cells harvested from near term Rambouillet lambs were cultured. To determine whether cultured endothelial cells produce a factor which alters the shape and alignment of smooth muscle cells, rhodamine phalloidin staining of F-actin filaments was carried out, as well as time-lapse cinematography. We were able to demonstrate, with pulmonary artery but not with aortic cells in culture, an endothelial-derived factor which causes the smooth muscle cells to migrate and align in uniform direction. The effect could not be enhanced by making the endothelial cells hypoxic and was similar to that produced by exposing smooth muscle cells to KCl or directly to hypoxia.