Size Matters: Anion Influences on Hamster Chorda Tympani Responses to Na+ Salts

Abstract

Over the past two decades, researchers have shown repeatedly that salt taste reception depends, in numerous mammals, on the passive diffusion ofNa+ ions through apical, Na+selective ion channels that can be blocked by the diuretic drug amiloride. Oral application of amiloride suppresses the sodium responsiveness of the chorda tympani nerve, which innervates taste buds in fungiform papillae on the anterior portion and in rostral foliate papillae on the sides of the mammalian tongue. Using a powerful in vivo technique that permits control of the electrical potential across the epithelium of the tongue, Ye et al. (1991) identified two topologically separate Na+ sensing mechanisms in rat fungiform papilla taste buds. Despite impressive gains in understanding Na+ sensing in the rat taste system, less is known about sodium stimulus transduction in the hamster, which is widely used in studies of gustatory neural coding. The present study used in vivo voltage clamping with simultaneous chorda tympani neurophysiology to examine sodium sensing in the intact hamster. As expected, we observed an anion influence on relative chorda tympani response magnitudes mediated through indirect anion influences on apical Na+ channel properties. The anion effect on Na+ channel properties was evident in the lower Km obtained for NaCl relative to NaGlu. Thus, our results suggest that differences in the transepithelial potentials generated by NaCl and NaGlu, which originate from differences in paracellular anion permeability, meditate stimulus-dependent modulation of apical Na+ channel affinity.