Sterol Distribution in Plasma Membranes

Freeze-Fracture Cytochemistry by Using a Sterol-Probe, Filipin

Abstract

It has been widely accepted that biological membranes consist of the planar, biochemically and functionally specialized mosaics. One of the most important components to exert these planar domains in membranes is sterol, which can be visualized by using sterolprobes such as filipin and saponins.
Filipin interacts with 3-β-hydroxysterols to produce 15-25nm protrusions or pits in membranes.These filipin-induced deformations of membranes can be detectable by electron microscopy of thin sections and freeze-fracture replicas, revealing the existence and topology of heterogenous sterol distribution in the membrane plane.
In this article, the freeze-fracture method to detect the geometrical distribution of sterols in membranes using filipin for a sterol-probe, namely freeze-fracture cytochemistry or intramembranous cytochemistry, is reviewed from view points of method, interpletation and application. The possibility of “false-negative” in filipin-labeling is also described. Finally, some interesting cases in sterol-topology in membranes are presented, including dynamic functional mosaics in mast cells and myoblasts, and multiple domains in sperm, fungus and epidermis.