The origin and distribution of membrane-bound vesicles associated with the brush border of chick intestinal mucosa.

The chick was used to investigate the incidence of vesicles, 60-75 nm in diameter, previously observed (Chandler et al. 1975) associated with the intestinal brush border of various animals. Samples were taken from 3 positions in the small intestine, from the duodenum, 20 nm proximal to the yolk stalk and 100 mm proximal to the ileocaecal junction, and vesicles were found mainly in the duodenum. They were evident in both germ-free and conventionally reared birds and their presence was unaffected by the addition of fibre to the diet. The vesicles arise from the microvillus membrane by budding or pinching off and associated with this is a spiral contraction of the microvillus. A possible mechanism controlling this process, involving the contractile microfilament core of the microvillus, is discussed, together with the likely significance of the production of vesicles.