Ion transport across lingual epithelium is modulated by chorda tympani nerve fibers.

Each chorda tympani (CT) nerve innervates taste cells in fungiform papillae on one side of the anterior two-thirds of mammalian tongues. In this study, three effects of unilateral CT transection were investigated: (1) the persistence of taste cells on the ipsilateral and contralateral sides; (2) the ability of the CT to modulate ion transport across the ipsilateral and contralateral sides of canine lingual lingual epithelia; and (3) the effect on contralateral CT responses. Unilateral transection of dog CT caused the mean number of taste buds/fungiform papilla on the ipsilateral side to decrease from five to zero by 29-30 days after surgery. Taste buds reappeared after 44 days but in reduced numbers (two taste buds/papilla). This reappearance of taste buds after 44 days is consistent with the time predicted for the CT to regenerate and reach the anterior portion of the tongue. The number of taste buds/papilla remained unchanged on the contralateral side. Measurements of the short-circuit current (Isc) across both ipsilateral and contralateral sections of isolated canine lingual epithelia were performed at various times after unilateral CT transection. Both sides responded similarly. The Isc began to decline after 3 days, reached a minimum after approximately 18 days (approximately 40% of control Isc) and increased to control values after approximately 40 days. This includes experiments performed 30 days after surgery, when no taste buds were present on the ipsilateral side and the Isc was 80% of control values. For all times after CT transection, amiloride, an epithelial Na+ channel blocker, inhibited Isc. Thus, epithelial cells in dog tongue have amiloride-inhibitable pathways. These results show that proteins involved in active Na+ transport across lingual epithelial can be modulated by CT nerve fibers.