Astringent-tasting compounds alter ion transport across isolated canine lingual epithelia

Abstract

The effects of acid and astringent compounds on ion transport across isolated canine lingual epithelia were measured in an Ussing chamber. Lowering the pH from 7.4 to 3.2 decreases ion transport, as measured by the short-circuit current ( I sc), when the dorsal surface of the tongue is bathed in 0.5 M NaCl and increases I sc when it is bathed in 0.05 M NaCl. In 0.5 M NaCl, tannic acid (0.1 M) inhibits I sc at both pH 3.2 and 7.4. At 0.05 M NaCl, pH 7.4 tannic acid also inhibits I sc. Thus, inhibition of I sc by tannic acid does not depend upon the pH, meaning that the reduction in transport arises from tannic acid. In the presence of NaCl (at both 0.05 and 0.5 M NaCl), 0.1 M AlK (SO 4) 2 or 0.1 M AlNH 4(SO 4) 2 also inhibit I sc. For these salts, the decrease in I sc arises from the aluminum ion and not from K +, NH 4 +, or SO 4 −−. Other less astringent compounds (gallic and tartaric acids) had only slight effects on I sc. The main findings of this study are that both tannic acid and the aluminum salts inhibited ion transport, likely Na + influx, via amiloride-inhibitable channels in isolated lingual epithelia. Inhibition of such Na + channels may contribute to astringent taste.