Freeze-fracture study of the chromaffin cell during exocytosis: evidence for connections between the plasma membrane and secretory granules and for movements of plasma membrane-associated particles.
Exocytosis was studied in acetylcholine-stimulated bovine adrenal medulla. During a pre-exocytotic stage, chromaffin granules are found in juxtaposition to the plasma membrane and separated from it by an electron dense space 25--27 A in width. Freeze-fracture studies show this stage to be characterized by connections between the granules and the plasma membrane. These connections are apparently cytoplasmic but bridge both membranes; they are presumably proteinaceous, but their exact nature remains to be elucidated. Later stages of exocytosis were also studied by the freeze-fracture technique; a typical feature is the lack of intramembrane particles around the fusion site. Both connections and membrane particle movement are discussed in terms of recent biochemical findings.
D000109:Acetylcholine / Q000494:pharmacology; D000313:Adrenal Medulla / Q000648:ultrastructure*; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000648:ultrastructure; D002837:Chromaffin Granules / Q000648:ultrastructure*; D002838:Chromaffin System / Q000648:ultrastructure*; D005089:Exocytosis / Q000187:drug effects*; D005614:Freeze Fracturing; D007425:Intracellular Membranes / Q000648:ultrastructure*; D008854:Microscopy, Electron
D000109:Acetylcholine