TRANSPORT PATHWAYS IN CANINE LINGUAL EPITHELIUM INVOLVED IN SWEET TASTE

The responses of canine lingual epithelium to D-glucose were measured in an Ussing chamber to determine the possible contribution of the osmotic changes of taste cells to the response of saccharides. With the mucosal solution containing 50 mM NaCl, 2 mM HEPES, pH 7.4 (solution A) and the serosal solution containing Krebs-Henseleit (KH) buffer the addition of up to 0.5 M D-glucose in the mucosal solution increased the short circuit current (Isc) in a sigmoidal manner. The D-glucose-stimulated Isc was inhibited by 0.1 mM amiloride or 1 mM ouabain added to either the mucosal or the serosal solution, and partially inhibited by 5 mM BaCl2 added to the serosal solution. The inhibition by these three compounds was also observed in the presence of 0.5 M NaCl. Ouabain also inhibited transport when added to solution A. These experiments suggest that in canine lingual epithelium the paracellular pathway permits molecules as large as ouabain (mol. wt 586) to diffuse from the mucosal to the serosal solution and vice versa under all osmotic conditions. These results may explain the phenomenon of intravascular taste. Such is not the case in rat tongue where ouabain only inhibited transport when added to the serosal solution. Increasing the osmolality of the serosal KH buffer by addition of relatively membrane-impermeable saccharides such as sucrose or L-glucose did not significantly alter the Isc, whereas making the serosal KH solution hypo-osmotic resulted in a transient decrease in Isc. These data suggest that the increase in Isc induced by saccharides, such as D-glucose, is not simply an osmotic response of the epithelium but more likely the consequence of saccharides binding weakly to receptors. That the response to both salts by themselves and in the presence of saccharides exhibits the same cation selectivity, and that both are inhibited by amiloride, ouabain, BaCl2 and LaCl3 suggest that in canine lingual epithelia, in contrast to rat epithelium, the responses to hyperosmotic concentrations of salts and saccharides might occur via the same transcellular pathways. © 1990 Oxford University Press.