Salt and acid studies on canine lingual epithelium
A section of dog tongue just anterior to the circumvallate papillae was placed in an Ussing chamber and characterized with respect to monovalent cation transport pathways, response to HCl, and the interaction between salt and acid for the purposes of determining whether ion transport through the tongue is related to the transduction process. The primary findings of this work follow. The stimulation of the short-circuit current (I(sc)) with decreasing pH on the dorsal surface results from a net Cl - efflux through an amiloride- and ouabain-insensitive pathway that changed its selectivity from cationic at neutral pH to anionic at lower pH values. The stimulation is abolished at isotonic NaCl concentrations. This behavior would not be predicted from the proton-binding model to a 'sour receptor' as suggested by Beidler. In symmetrical solutions of Krebs-Henseleit buffer, I(sc) is inhibited 30% by 10 -4 M amiloride on the mucosal side and 100% by 10 -3 M ouabain on the serosal side. These results coupled with net Cl - and Na + flux measurements show that I(sc) is due to a net Cl - efflux. With 1.0 M NaCl on the dorsal side, 10 -4 M amiloride inhibits I(sc) 84%. In contrast, when the mucosal surface is bathed in KCl (1.0 M), CsCl (1.0 M), or HCl (10 -3 M), I(sc) is insensitive to both 10 -4 M amiloride and/or 10 -3 M ouabain. These data suggest that K + , Cs + , and H + traverse the tongue through different pathways from Na + and are not energized by a Na + gradient.
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