A freeze-fracture cytochemical study of filipin-sterol complexes in pulp fibroblasts of the rat incisor.

The sterols in microdomains of the cell membrane of pulp fibroblasts react with the polyene antibiotic, filipin, to form filipin-sterol complexes (FSC). The FSC appear in ultra-thin sections as minute corrugations or deformations of the membrane. In freeze-fracture replicas, individual FSC were 20-30 nm elevations and were abundant on filopodial cell processes. They were not found in the membrane of cell-to-matrix attachment plaques or in cell-to-cell adherens junctions. The findings suggest that stabilization of the membrane at these sites may interfere with FSC formation and conversely that the absence of FSC may be an indication of membrane stabilization.