In vitro expression of benzylamine oxidase activity in cultured porcine smooth muscle cells

Benzylamine oxidase (BzAO) activity was measured in cultured smooth muscle and endothelial cells derived from thoracic aorta of adult swine, and in homogenates of dissected aortic medial and intimal layers. BzAO appeared to be localized in aortic medial homogenates. Cultured smooth muscle cells (which were verified by electron microscopic characteristics and positive staining with antimyosin) showed high BzAO activity, with optimal activity at pH 7.0; no activity was detected in endothelial cells. Prolonged serial passage of smooth muscle cells resulted in increased BzAO activity, with the increase most marked by the 12th population doubling. Also, BzAO was found predominantly in the soluble portion of the culture medium of smooth muscle cells by their 12th population doubling. These findings support the concept that vascular BzAO is localized within medial smooth muscle cells, and suggest that smooth muscle cells may be capable of secreting BzAO.