Sugar transport in the gut of a limpet (Megathura crenulata)

The movement of four monosaccharides (D-glucose, D-galactose, 3-0-methyl-D-glucopyranose, and D-fructose) across the gut of the marine gastropod Megathura crenulata was studied using the everted sac technique of Crane and Wilson (1958). Positive S/M ratios (evidence for active transport) were obtained for D-glucose and 3-0-methyl-D-glucopyranose, but not for D-galactose and D-fructose in the posterior esophagus. No evidence was obtained for active transport of any of the four tested monosaccharides by either the anterior intestine or the posterior intestine. The net accumulation of D-glucose against an apparent concentration gradient by the posterior esophagus was dependent upon metabolic energy from glycolysis but not the tricarboxylic acid cycle. Thus, it is concluded that D-glucose and 3-0-methyl-D-glucopyranose are actively transported by the posterior esophagus. There appears to be no measurable water movement in the posterior esophagus during active transport of D-glucose or 3-0-methyl-D-glycopyranose. D-Glucose and D-galactose appear to be metabolized by all regions of the gut tested. D-fructose and 3-0-methyl-D-glucopyranose did not appear to undergo any significant amount of metabolism. Observed transmural potentials indicate active ion transport is present in all regions of the gut studied. Transmural potentials were significantly larger in the posterior esophagus than in the anterior or posterior intestine. The serosal surface was negative to the mucosal surface in all regions tested. The transmural potentials observed in the posterior esophagus were altered by the removal of oxygen and the presence of the glycolytic inhibitor, NaF.