A role of the epithelial sodium channel in human salt taste transduction?

Mammals perceive the five different taste qualities: bitter, sweet, umami, sour, and salty. At least two different mechanisms contribute to salt taste in rodents. One is elicited by various cations and sensitive to cetylpyridinium chloride, whereas another is selectively stimulated by Na+ and inhibited by amiloride. The latter pathway has been suggested to involve the epithelial sodium channel, ENaC. In humans, the presence of amiloride-sensitive salt taste transduction is being disputed. In this paper, we addressed the question whether ENaC may have a role in human salt taste perception. Immunohistochemistry revealed that β-, γ-, and δ-ENaC subunits are present in subsets of circumvallate and fungiform taste bud cells, whereas α-ENaC was confined to cells of circumvallate taste buds. Alpha-, β-, and γ-subunits were observed in basolateral intracellular compartments, while δ-ENaC was exclusively found in all taste pores of both types of papillae consistent with a function in taste transduction. To further assess the involvement of ENaC in salt taste transduction, we combined sensory studies and functional expression of ENaC in oocytes. With the exception of L-homoarginine, choline chloride, L-arginine, L-lysine, and L-argininyl-Larginine enhanced both salt taste perception in subjects and sodium currents recorded in αβγ- or δβγ-ENaC expressing oocytes, whereas L-glutamine did neither show salttaste- enhancing activity nor did it influence the sodium currents in the oocyte assay. Taken together, our data make ENaC an interesting molecule possibly involved in salty taste transduction.