EVIDENCE FOR A NONINTESTINAL NUTRITIONAL MECHANISM IN THE RHYNCHOCOELAN,LINEUS RUBER

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Abstract
1. Lineus ruber rapidly accumulates glucose from sea water into free pools within the worm concentrating the hexose to 17 times the original external concentration (10-4 M) in one hour. 2. Accumulated glucose, alanine and leucine are incorporated into protein, and additional glucose is incorporated into polysaccharide. No free glucose, alanine or leucine is effluxed during two minutes; however, succinate, derived from glucose, is detectable in the external medium when the incubation time is extended. 3. The demonstration of saturation kinetics for both glucose and galactose, the partial inhibition of glucose entry by galactose and inhibition of glucose accumulation by phlorizin, quercetin and ouabain is consistent with specific sites of glucose transport. 4. Similar kinetics for both alanine and leucine accumulation, their mutual competition for entry and the inability of carbohydrates, organic acid, and fatty acids to influence the uptake of alanine and leucine is consistent with specific transport sites for neutral amino acids. 5. Comparison of glucose accumulation by whole ligatured and unligatured worms, as well as along the length of unligatured worms, indicates that a majority of the sites of entry available to glucose in the worm's environment is through its epidermis. 6. Ultrastructural examination of free epidermal and gut luminal surfaces reveal that each is bounded by a plasmalemma with a surface area expanded by microvilli. The surface area of epidermis is greatly increased by numerous microvilli arranged in the form of a brush border and is greater than the analogous surface region of the gut. Presence of a brush border is characteristic of tissues with high rates of transport function.