Figure 15.

Proposed model for acid transport in fungiform TRCs and sour taste transduction in the anterior tongue. (A) Proposed acid transporters in TRC membranes. (B) An acid-induced decrease in TRC pH_i causes cell shrinkage and the activation of a flufenamic acid–sensitive shrinkage-activated nonselective cation channel that is involved in eliciting the phasic part of the CT response to acidic stimulation (P). (C) In a subset of TRCs a decrease in pH_i induces an increase in [Ca²⁺]_i that in turn activates basolateral NHE-1. Activation of NHE-1 is responsible for pH_i and cell volume recovery and for the neural adaptation (tonic response [T]) in the CT response to acid stimuli. The abbreviations used in the figure are as follows: H⁺-gated channels (HCN, hyperpolarization-activated channel; ASIC, acid-sensing ion channel; TASK-2, a two pore domain K⁺ channel); NHE-1, basolateral Na⁺-H⁺ exchanger; NHE-3, apical Na⁺-H⁺ exchanger; SANSCC, shrinkage-activated nonselective cation channel; SOC, store-operated Ca²⁺ channel; VGCC, voltage-gated Ca²⁺ channels; activation (+); Inhibition (−); increase (↑); decrease (↓). See text for details.