ION-TRANSPORT ACROSS LINGUAL EPITHELIUM IS MODULATED BY CHORDA TYMPANI NERVE-FIBERS

Each chorda tympani (CT) nerve innervates taste cells in fungiform pap illae on one side of the anterior two-thirds of mammalian tongues. In this study, three effects of unilateral CT transection were investigat ed: (1) the persistence of taste cells on the ipsilateral and contrala teral sides; (2) the ability of the CT to modulate ion transport acros s the ipsilateral and contralateral sides of canine lingual lingual ep ithelia; and (3) the effect on contralateral CT responses. Unilateral transection of dog CT caused the mean number of taste buds/fungiform p apilla 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 aft er 44 days is consistent with the time predicted for the Cr to regener ate and reach the anterior portion of the tongue. The number of taste buds/papilla remained unchanged on the contralateral side. Measurement s of the short-circuit current (Isc) across both ipsilateral and contr alateral sections of isolated canine lingual epithelia were performed at various times after unilateral Cr transection. Both sides responded similarly. The Isc began to decline after 3 days, reached a minimum a fter approximately 18 days (approximately 40% of control Isc) and incr eased to control values after approximately 40 days. This includes exp eriments performed 30 days after surgery, when no taste buds were pres ent 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 amil oride-inhibitable pathways. These results show that proteins involved in active Na+ transport across lingual epithelia can be modulated by C T nerve fibers.