Electron Microscopic study on the Cellular Interrela-tionships in the Smooth Muscle

Abstract

In the smooth muscle cells of the rabbit colon and of the guinea pig urinary bladder, pinocytotic vesicles were frequently observed occurring on both sides of 2 opposing smooth muscle cell membranes. This specialized structure was named paired pinocytosis. The regular appearance of this paired pinocytosis with zonula adherens (intermediate junction) or with macula adherens (desmosome) along the contact surface of the smooth muscle cells was characteristically found in these tissues. The arrangements of the intermediate junctions or the desmosomes in these tissues sometimes structurally resemble the intercalated disc of the heart muscle. The possible significance of this structure is discussed in relation to the problems of the intercellular conduction of excitation in the smooth muscle tissue.