Analysis of amiloride inhibition of chorda tympani taste response of rat to NaCl

Abstract

The kinetics of inhibition by amiloride of the integrated chorda tympani response were investigated in rats subjected to lingual stimulation with NaCl. In one series of experiments the time of exposure to amiloride was varied at fixed amiloride concentration. Exposure to 10(-4) M amiloride for 2 s reduced the response to 0.5 M NaCl by approximately 50%. The time course of recovery from amiloride inhibition was first order (relaxation time approximately equal to 4 min) for all exposure times. For exposure to 10(-4) M amiloride for less than or equal to 30 s recovery was better than 90% in 20 min. Not all of the chorda tympani response was inhibited by amiloride. With 0.5 M NaCl there was a 70% reduction in response, whereas at 0.05 M NaCl the reduction was only 30%. Parallel effects of amiloride were seen in the short-circuit current of an in vitro preparation of canine lingual epithelium. Amiloride reduced the short-circuit current by the same percentage as it inhibited the chorda tympani response. These results suggest that gustatory transduction is mediated in part by an apical membrane transport system that can be inhibited by amiloride. There exists, however, a second transducing element that is amiloride insensitive. A model is developed, assuming, in part, that the neural response reflects the flows of Na through amiloride-sensitive apical pathways.

Salt-Evoked Lingual Surface Potential in Humans

“…The electrophysiological responses evoked by Na-salts in animals are positively correlated to the concentration of the salt and are decreased by amiloride (Avenet and Lindemann 1988;DeSimone et al 1981;Gilbertson et al 1993;Simon and Garvin 1985;Ye et al 1991). Importantly, in animal studies, the salt-evoked lingual surface potential correlates well with the chorda tympani response and taste sensory activation (DeSimone and Ferrell 1985). Here, for the first time, we show measurements of the human lingual surface potential and suggest it is feasible to analyze human taste perception using noninvasive electrophysiological methods.…”

Taste discrimination between NaCl and KCl is disrupted by amiloride in inbred mice with amiloride-insensitive chorda tympani nerves

“…Thus, in contrast to the predictions based on CT recordings, discrimination in all four strains appeared to depend on the amiloride-sensitive transduction pathway, which, in the case of BALB/cByJ, 129P3/J, and DBA/2J (and perhaps C57BL/6 as well), may exist in taste buds innervated by nerves other than the CT. animal psychophysics; taste transduction; taste coding; C57BL/6; BALB/c; 129P3/J; DBA/2 THE TASTE OF SODIUM CHLORIDE appears to be transduced via at least two mechanisms, one which is selective for Na ϩ (and Li ϩ ) and is disrupted by the lingual application of the epithelial Na ϩ channel-blocker amiloride (e.g., Refs. 1,3,5,8,12,16,27, 39), and the other(s) which is amiloride-insensitive and cation nonselective (e.g., 12,17,20,22,30,[35][36][37]. In rats, electrophysiological recordings from the chorda tympani (CT) nerve have demonstrated that, when amiloride is applied to the lingual epithelium, the responsiveness of this nerve to sodium salts, but not to nonsodium salts, is markedly suppressed (e.g., Refs.…”

“…1, 3,5,8,12,16,27,39), and the other(s) which is amiloride-insensitive and cation nonselective (e.g., Refs. 6 -8, 12, 17, 20, 22, 30, 35-37).…”

Anion Size Does Not Compromise Sodium Recognition by Rats After Acute Sodium Depletion.

“…The sodium-selective ion channels, or epithelial sodium channels (ENaCs), expressed by these cells can be blocked with the drug amiloride (see Brand, Teeter, & Silver, 1985;DeSimone & Ferrell, 1985;Doolin & Gilbertson, 1993;Heck, Mierson, & DeSimone, 1984;Schiffman, Lockhead, & Maes, 1983). A second transduction pathway for sodium, the amiloride-insensitive (AI) pathway, is not sodium selective but instead appears to be activated by a variety of cations, including Na ϩ , K ϩ , and NH 4 ϩ (Brand et al, 1985;DeSimone & Ferrell, 1985;Kloub, Heck, & DeSimone, 1997;Ye, Heck, & DeSimone, 1994).…”