Intestinal Fluid Transport: Studies with the Gut of Ascaris lumbricoides

Abstract

Sacs from the one-cell-thick intestinal wall of the pig round worm, Ascaris lumbricoides, were used to study fluid movement. Techniques were developed for making everted and noneverted sacs of this delicate tissue, and fluid movement was followed by the change in weight of the sacs. Fluid moved freely in response to an osmotic gradient but under isosmotic conditions it moved from the mucosal to the pseudocelomic side. With noneverted sacs the fluid movement, small under N2:CO2, 95:5, was inhibited by oxygen. There was a net inward movement of Na+ (pseudocelomic to mucosal side) which was unaffected by the gas phase. With everted sacs large fluid intakes were observed and these increased under aerobic conditions. Glucose increased fluid movement and was itself transported across the gut against a concentration gradient although at no time was a difference in osmosity detected. With the everted sacs there was a net movement of Na+ from the mucosal side to the inside of the sacs. Despite the large influx in fluid caused by glucose, the net movement of Na+ was unaffected by the presence of the sugar. Ouabain (10−2 mM) increased fluid movement provided the medium was not low in Na+. Photomicrographs showed that the intercellular spaces dilate during fluid transport.