Inhomogeneous distribution of filipin-sterol complexes in the ciliary membrane of rat tracheal epithelium.

Pieces of rat trachea fixed in a glutaraldehyde solution containing 300 muM filipin, a sterol-specific polyene antibiotic (Elias et al., '78), were freeze-fractured in order to study the distribution of cholesterol within the ciliary membrane. Filipin-sterol complexes, recognizable as 25-30-nm protrusions on fracture faces, appeared densely and uniformly distributed over most of the ciliary membrane, but were absent from the region of the ciliary necklace. It is possible, therefore, that the ciliary necklace represents a cholesterol-poor area of membrane.