Year

2010

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science in Biology (MS)

Department

Biology

First Advisor

Dr. Gregory Ahearn

Second Advisor

Dr. Judith Ochrietor

Third Advisor

Dr. John Hatle

Abstract

The mechanisms of transepithelial absorption of dietary D-glucose and D-fructose in the American lobster, Homarus americanus, were investigated in this study in order to determine whether sugar transport proteins have been conserved throughout evolution. Whole lobster intestine was isolated and mounted in a perfusion chamber to determine transepithelial mucosal to serosal (MS) and serosal to mucosal (SM) mechanisms of 3H-D-glucose and 3H-D-fructose transport across the intestine. Unidirectional MS and SM fluxes were measured by adding variable concentrations of 3H-D-glucose and 3H-D-fructose (2.5 to 50uM) to either the perfusate or the bath respectively and sampling the amount of radioactivity that exited the opposite side of the intestine. Both the transepithelial MS and SM transports of 3H-D-glucose and 3H-D-fructose were hyperbolic functions of sugar concentration. The net flux of both sugars indicated a net absorption of D-glucose and D-fructose into the serosal compartment. Inhibitory analysis showed that while phloridzin decreased MS 3H-D-glucose transport via a sodium glucose transport (SGLT 1-like) protein located on the mucosal membrane, 3H-D-fructose transport was not affected by the drug. Mucosal phloretin decreased MS D-fructose transport but not MS D-glucose transport. Immunohistochemistry analysis revealed the presence of a mucosal GLUT 5 transport protein on the mucosal membrane. Increasing serosal concentrations of phloretin decreased both SM D-glucose and D-fructose transport suggesting the presence of a serosal GLUT 2 used by both sugars. The results of this study support the concept of conserved mechanisms of sugar transport in multicellular animals.

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