Microvillous membrane vesicle accumulation in media during culture of intestine of chick embryo.

Explanting chick embryo duodenal tissue elicits an increase in the activities of alkaline phosphatase and maltase, an effect which is greatly enhanced by the addition of thyroxine. A large part of the elevated enzyme activity is released into the culture medium, from which it can be sedimented by centrifugation at 200 000 X g. The resulting pellet contains 87% or more of the alkaline phosphatase and maltase activity present in the medium at the end of 72 h of culture, but only about 25% of the protein. Negative staining of the pellet reveals the presence of microvesicles, the surfaces of which bear tiny protrusions resembling the knobs that have been seen on isolated microvilli and in preparations of purified microvillous membrane. The microvesicles appear to be derived from fragmentation of microvilli. Microvesicles with similar properties can be washed out of the duodenal lumen of embryos near hatching, suggesting that vesiculation may be a normal process that plays a useful role in intestinal function.