The distribution of filipin-cholesterol complexes in secretory ameloblasts of rat incisor

The number of filipin-sterol complexes, visualised as 25-35 nm protuberances on freeze-fracture replicas of secretory ameloblasts of rat incisor, was small on the plasma membrane and nil on internal membranes of the cell body. Distal infoldings and vesicles inside Tomes process presented a higher number of protuberances. Such membrane-induced deformations were especially abundant on membrane remnants left inside the forming enamel and in holes at the dentine-enamel junction. This reflects regional variations of cholesterol or accessibility of cholesterol. Increased rigidity of membranous remnants may play a role in the induction of local defects during rat enamel formation. These observations clarify the origin of phospholipids and cholesterol detected biochemically.