MARTIN, G.G.; SIMCOX, B.; OLSON, S.; AMIRIAN, E.; RUBIN, N.; Occidental College, Los Angeles; Occidental College, Los Angeles; Occidental College, Los Angeles; Occidental College, Los Angeles; Occidental College, Los Angeles: Formation, composition, and permeability of the peritrophic membrane in two decapod crustaceans; the ridgeback prawn Sicyonia ingentis and the American lobster Homarus americanus

In decapod crustaceans, ingested material is sorted within the foregut and sent to either the digestive gland for digestion and absorption, or to the midgut trunk (MGT), prior to elimination. The function of the MGT, which extends the length of the abdomen, is not clear, but it is not involved with digestion. Material entering the MGT is encased within a peritrophic membrane (PM) which separates it from the simple epithelium. Epithelial cells are elongate and the apical cytoplasm beneath the brush border is filled with electron-dense granules. Hydration of the granules leads to compound exocytosis and the release of material producing a thin PM lying along the tips of the microvilli. High magnification views of the PM show a weave of fibers that stain with the lectin wheat germ agglutinin (WGA), indicating chitin. The PM dissolves in solutions containing chitinase, but not in solutions containing protease or collagenase. In addition to encapsulating ingested food and debris, the PM may also prevent ingested pathogens from contacting and penetrating the epithelium. The permeability of the PM was examined by following the fate of tracers including lanthanum nitrate (<2 nm), ferritin (20 nm), and latex beads (50 and 1100 nm). The relative ease by which particles the sizes of viruses and bacteria can penetrate the PM will be discussed. Further studies will examine the permeability of the epithelium and basal lamina and begin to look at ways that pathogens evade these physical barriers.