Differential expression of the glucose transporters in mouse gustatory papillae

Taste receptors and their downstream signaling molecules are activated by sugars and sweeteners in the gut and participate in the regulation of glucose transport into enterocytes. The glucose transporter families GLUT and SGLT are responsible for the absorption of glucose, GLUT4 and SGLT1 being expressed preferentially in T1R3-positive taste cells. However, the expression patterns of the other glucose transporters in mouse gustatory tissues have not yet been elucidated. Therefore, we have examined the expression patterns of the glucose transporters (GLUT1-4 and SGLT1-3) in mouse gustatory tissues. Reverse transcription/polymerase chain reaction assays have revealed that GLUT1, 3, and 4 and SGLT1 mRNAs are expressed in the circumvallate papillae. Immunohistochemical analysis has shown that SGLT1 is expressed in a subset of the epithelial cells: from the basal cell layer to the prickle cell layer and in intragemmal and extragemmal epithelium cells in the circumvallate, foliate, and fungiform papillae. GLUT1, GLUT3, and GLUT4 are expressed in the prickle cell layers and/or basal cell layers in these papillae. Moreover, GLUT1, but not GLUT3 or GLUT4, is expressed in a subset of intragemmal and extragemmal epithelium cells in these papillae. Double-labeling experiments have demonstrated that GLUT1-positive taste bud cells coexpress gustducin and inositol 1,4,5-triphosphate receptor type III. These results suggest that SGLT1 and GLUT1 play a role in glucose-sensing and/or transport in mouse taste buds.