Epithelial modulation of afferent nerve endings: differential effects of amiloride on afferent subtypes

Mechanisms underlying the differing chemosensitivity of laryngeal afferents have not been defined. The role of airway epithelium in transducing the chemical stimuli to neural signals was investigated by using Na(+)- and Cl(-)-channel inhibitors in anesthetized spontaneously breathing cats. Single-fiber action potentials were recorded from the peripheral cut end of the superior laryngeal nerve. Luminal application of amiloride (10(-4) M), an inhibitor of epithelial Na+ channels, reduced the responsiveness of non-respiratory-modulated endings (n = 25) to distilled water (65.76 +/- 5.77 vs. 50.67 +/- 5.13 Hz; P < 0.01). Water responsiveness of these endings was unaffected by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and diphenylamine-2-carboxylate, two Cl(-)-channel blockers. Respiratory-modulated endings (water responsive, n = 8; water nonresponsive, n = 9) were unaffected by Na(+)- and Cl(-)-channel blockers. These results suggest that epithelial Na+ channels play a role in the modulation of non-respiratory-modulated laryngeal endings. The lack of an effect by amiloride on other subtypes may be due to differences in location or intrinsic properties of nerve endings. Cl- channels do not appear to play an important role in the modulation of laryngeal afferents targeted in this study.