ROLE FOR EPITHELIAL NA+ CHANNELS AND PUTATIVE NA+ H+ EXCHANGERS IN SALT TASTE TRANSDUCTION IN RATS/

The effects of the epithelial Na+ channel antagonists amiloride and be nzamil and the Na+/H+ exchange antagonist 5-(N,N-dimethyl)-amiloride ( DMA)-Cl on the integrated responses of the chorda tympani nerve to 30, 75, 150, 300, and 500 mM concentrations of NaCl, KCl, and NH4Cl were assessed in male Sprague-Dawley rats. Based on evidence from other sys tems, 1 and 25 mu M amiloride and benzamil were chosen to selectively inhibit epithelial Nat channels and 1 mu M DMA was chosen to selective ly inhibit Na+/H+ exchange; When added to stimulating salt solutions; amiloride, benzamil, and DMA were each effective in inhibiting respons es to all three salts. The degree of inhibition varied with drug, salt , and salt concentration, but not drug dose. Amiloride suppressed NaCl responses to a greater degree than KCl and NH4Cl responses, whereas D MA suppressed NH4Cl responses to a greater degree than NaCl and KCl re sponses. In all but one case (25 mu M amiloride added to KCl), drug su ppression of taste nerve responses decreased with an increase in salt concentration. The present results suggest that 1) epithelial Na+ chan nels in rat taste receptor cells may play a role in KC; and NH4Cl tast e transduction; 2) a Na+/H+ exchange protein may be present in taste r eceptor cells, representing a putative component, in addition to epith elial Na+ channels, in salt taste transduction; and 3) salt taste dete ction and transduction may depend on the utilization of a combination of common and distinct transcellular pathways.