STRIATED ANCHORING FIBRILS-ANCHORING PLAQUE COMPLEXES AND THEIR RELATION TO HEMIDESMOSOMES OF MYOEPITHELIAL AND SECRETORY-CELLS IN MAMMARY-GLANDS OF LACTATING RATS

Striated anchoring fibrils (SAF) are associated with the basement memb rane underlying myoepithelial and acinar cells of mammary glands. Thei r proximal extremities are inserted in electron-dense areas of the lam ina densa, the anchoring plaques seen facing the hemidesmosomes of bot h myoepithelial and acinar cells. In the case of myoepithelial cells, the hemidesmosomes show a thick cytoplasmic plaque applied to the basa l plasma membrane in which cytoplasmic filaments are inserted. Facing this plaque but on the extracellular aspect and at a short distance of 5-10 nm, there is a thin layer of electron-dense nodular material cal led the subcell membrane plate, which is connected to the plasma membr ane by short filamentous bridges. Between this subcell membrane plate and the anchoring plaque, there is an abundance of fine anchoring fila ments crossing the lamina lucida. Such anchoring filaments are less ab undant in the lamina lucida outside the hemidesmosomal areas. In the c ase of acinar cells, the cytoplasmic plaques of the hemidesmosomes are thin and the associated cytoplasmic filaments less conspicuous. No di stinct subeell membrane plate is seen on the extracellular aspect of t he plasma membrane facing the cytoplasmic plaque of the hemidesmosomes . However, in this area numerous anchoring filaments cross the lamina lucida between the plasma membrane and the SAF-anchoring plaque comple x. The abundance, in these cells, of hemidesmosomes and their associat ion with SAF-anchoring plaque complexes seen in the basement membrane must constitute a strong attachment for both myoepithelial and acinar cells and bind them to the underlying collagen fibrils, thus preventin g their detachment from the connective tissue during the contractions of myoepithelial cells during milk ejection. (c) 1993 Wiley-Liss, Inc.