Cytoplasmic organization and quantitation of microtubules in bovine mammary epithelial cells during lactation and involution.

Ultrastructural examination of milk secretory cells from lactating bovine mammary gland revealed presence of numerous microtubules in the apical and paranuclear cytoplasm, particularly in the vicinity of Golgi components. Most microtubules were oriented perpendicular to the apical plasma membrane and appeared to form a framework around Golgi dictyosomal elements and secretory vesicles. In comparison, non-secretory cells obtained from involuting glands displayed few microtubules and these were randomly located throughout the cytoplasm with no particular orientation.