Ultrastructural changes in contents of membrane-coating granules after extrusion from epithelial cells of hamster cheek pouch.

Membrane-coating granules of the epithelium of the hamster cheek pouch displayed a lamellated internal structure consisting of alternating thick and thin electron dense bands separated by translucent bands of equal width. The repeat distance of the contents was 8.5 nm +/- sd. 0.7 nm and the thickness of the major electron dense band was 3 nm +/- sd 0.4 nm. After exocytosis from the cells the lamellated material became organised into extensive sheets and the dimensions changed so that the repeat distance was 10.9 nm +/- sd 0.6 nm but the major electron dense band was virtually unchanged at 3.33 nm +/- sd 1.1 nm. The narrower or intermediate dense band became progressively less easy to see and was virtually invisible at the surface of the epithelium. It is suggested that the changes observed may be due to an increase in hydration of a phospholipid/protein complex in the granules by permeaton of water along the intermediate dense band.