Fine morphological aspects of the secretory process in arterial smooth muscle cells. II. Role of microtubules.

Preliminary results are presented regarding the role of the microtubular system in the secretory process in the rabbit aorta and pulmonary trunk smooth muscle cells. The results are based on electron microscopic findings of the effect of colchicine in vivo. On colchicine treatment an accumulation of secretory granules versus a vacuolar type of dilatation of the rough endoplasmic reticulum cisternae distinguishes two groups of smooth muscle cells. It is suggested that two secretory pathways operate in these cells, and that the cell microtubular status plays a key role in triggering one or the other pathway.