Permeability of tongue epithelium and its relation to taste.

MISTRETTA, CHARLOTTE M. Permeability of tongue epithelium and its relation to taste. Am. J. Physiol. 220(5) : 1162-l 167. 197 1 .-The permeability of rat tongue epithelium was investigated to provide information on the accessibility of free lingual nerve endings to chemical stimuli. Permeability of rat belly skin was also studied. Dorsal tongue epithelium was removed after subepithelial injection of collagenase. Abdominal skin was removed by gross dissection. The epithelium was placed in a diffusion cell and radioactive penetrants were applied to the dorsal surface. Permeability coefficients of 13 nonelectrolytes were determined according to Fick’s law. Methanol, ethanol, butanol, ethylene glycol, and propionamide penetrate the tongue and belly relatively rapidly; thiourea, acetamide, glycerol, sodium butyrate, fructose, glucose, and mannitol penetrate slowly. For the tongue and belly, an increase in penetration rate is related to an increase in the ether/water partition coefficient of the penetrant. Ethanol, a known stimulant of the trigeminal part of the lingual nerve, penetrates tongue epithelium rapidly. In general, though, tongue epithelium is as effective a barrier to chemical penetration as belly skin; the free endings of the lingual nerve are not readily accessible to chemicals.