Metal sandwich method to quick-freeze monolayer cultured cells for freeze-fracture

We describe a simple quick-freezing method to obtain a large fractured plane of the plasma membrane from monolayer cultured cells. Cells were grown on thin gold foil, inverted on a thin layer of gelatin on thin copper foil, and frozen by a quick press between two gold-plated copper blocks precooled in liquid nitrogen. The frozen cell sandwich was mounted on the cold stage of a freeze-fracture device with the gold side up and was fractured by separating the sandwich with a cold fracture knife. When this technique was applied to confluent monolayer cells, large replicas of the E-face of the upper plasma membrane and the P-face of the lower plasma membrane were obtained. The present metal sandwich method is simple, does not require any expensive equipment, and provides a large fracture plane of the plasma membrane for subsequent histochemical manipulation.