Transepithelial D‐glucose and D‐fructose transport across lobster intestine

Abstract

The mechanisms of transepithelial absorption of dietary D-glucose and D-fructose were examined in the lobster, Homarus americanus, intestine using 3H-D-glucose and 3H-D-fructose. Lobster intestines were mounted in a perfusion chamber to determine transepithelial mucosal to serosal (MS) and serosal to mucosal (SM) transport mechanisms of glucose and fructose. Both MS glucose and fructose transports, as functions of luminal [sugar], increased in a hyperbolic manner, suggesting the presence of mucosal transport proteins. Phloridzin inhibited MS flux of glucose, but not that of fructose, suggesting the presence of an SGLT1-like transporter. Immunohistochemistry analysis, using a goat anti-rabbit GLUT5 polyclonal antibody, revealed the localization of a brush border GLUT5-like fructose transport protein. MS fructose transport was decreased in the presence of mucosal phloretin, but the same effect was not observed in the MS transport of glucose. Both SM glucose and fructose transports were decreased in the presence of increasing concentrations of serosal phloretin, suggesting the presence of a shared serosal GLUT2 transport protein for both sugars. D-glucose and D-fructose transports across lobster intestine are similar to those for sugar uptake in mammalian intestine, suggesting evolutionarily conserved absorption processes for these solutes.