Abstract
Previous electrophysiological studies have shown that the chorda tympani nerve contains two types of NaCl-responsive fibers. One, N-type fiber, narrowly responds to NaCl and the NaCl response is strongly inhibited by amiloride, a blocker of the epithelial sodium channel (ENaC). The other type (E- or H-type) has broad responsiveness to electrolytes and shows almost no amiloride sensitivity. These fibers may receive input from amiloride sensitive and insensitive taste receptor cells. In this study, we examined NaCl responses of mouse fungiform taste cells in isolated taste bud and amiloride sensitivity of them. In our experiments, taste stimuli were applied only to the pore side of an isolated taste bud, and responses of one single cell of the bud to the stimuli were recorded from its basolateral side of the membrane as increase in firing frequency. The response to apical NaCl stimulation was recorded in some fungiform taste cells. These responses were concentration dependent. Amiloride mixed with apical NaCl solution inhibited NaCl responses in some taste cells [amiloride sensitive (AS) cells] but not in others [amiloride insensitive (AI) cells]. AI cells responded to other electrolytes such as KCl and HCl. These results suggest the existence of at least two types of NaCl sensitive cells, AS and AI cells. N- or E-type fiber may selectively innervate AS or AI cells respectively. [J Physiol Sci. 2006;56 Suppl:S183]
