VISUALIZATION OF EXOCYTOSIS BY QUICK-FREEZING AND FREEZE-FRACTURE

This chapter discusses the visualization of exocytosis by quick freezing and freeze-fracture. Exocytosis occurs extremely rapidly. Quick freezing in combination with freeze-fracture offers advantages for visualizing exocytosis in that it captures events occurring within milliseconds after stimulation and reveals panoramic views of membranes. Cells frozen ultrarapidly—that is, by removing heat so fast that ice crystals are undetectable by electron microscopy (EM), can yield superbly preserved ultrastructure without membrane fusion-mimicking artifacts resulting from slow, selective chemical fixatives and membrane-disrupting cryoprotectants. The aluminum planchet to which specimens are frozen is designed to fit directly onto the Balzers (Nashua, NH) 301 specimen table and is secured with a screw cap. Alternatively, tables fitted with a pair of flange clamps can be custom designed for many freeze-fracture units, including the Balzers 400 model. © 1993, Elsevier Inc. All rights reserved.