Freeze-fracture study of rat ventral prostate: secretory mechanisms in the epithelial cell

Membrane events during apocrine and merocrine secretion of rat ventral prostate epithelial cells were analyzed by freeze-fracture. Early morphological manifestation of both secretory modes involves focal clearance of microvilli characterized by their progressive inclination and attenuation over the apical membrane. Merocrine secretion includes invasion of the apical microfilament web by the secretory vesicle and clearance of membrane particles at the site of its interaction with the apical plasmalemma. During apocrine secretion, a portion of the plasma membrane cleared of microvilli projects into the lumen. Growth of this projection is accompanied by a progressive, but partial, clearing of membrane particles and results in the formation of a large bleb containing dilated endoplasmic reticulum cisternae. Completion of the process involves "degeneration" of the bleb and its release by constriction of a neck, and possibly, fusion of vesicular or tubular structures. Swelling and blebbing of microvilli are shown to be preparation artifacts.