Astringent Effects of Red Wine Associated with Responses of Aquaporins Found in Human Tongue and Salivary Tissues

Aquaporin (AQP) water channels facilitate fluid transport across cell membranes, are implicated in rodent oral water sensing, and were examined in the human tongue for their modulation by mouthfeel compounds and ensuing effects on perception and saliva tribology. Immunohistochemistry demonstrated abundant AQP1 and AQP2 and moderate AQP5 in human tongue and high AQP5 in salivary gland. Trained human tasting panels evaluated astringency intensities; results correlated with wine tannin measures and inhibition of AQP1 water flux (<i>R</i>² ≥ 0.9). Wine tannin extract additions of 1 g/L reduced cell swelling -125 ± 20% (SE) (<i>P</i> < 0.0001), increased saliva-tannin friction coefficient 16.0 ± 1.9% (<i>P</i> < 0.0001) and astringency scores 17.3 ± 5.5% (<i>P</i> < 0.006). Osmotic swelling assays identified wines, red wine polyphenols, alum sulfate, and tannic acid─all archetypal astringents─as inhibitors of AQP1 and to a lesser extent AQP5. Astringent block of AQPs present in tongue and salivary gland suggests a mechanistic role of water flux in drying sensations, beyond the established changes in saliva resulting from tannin and proline-rich-protein interactions. Insights into AQPs as molecular components of mouthfeel could inform fundamental debates on how astringent phenomena arise and increase understanding of nutrient sensing and uptake as found within the digestive tract and throughout the body.