抄録
pH sensation is critical for nociception in sensory neurons or avoiding spoiled foods and harmful solutions. It has been reported that several TRP channels could be related to the pH sensation in mammals. We present here a recent progress in the molecular mechanisms of pH sensing through TRP channels. TRPV1 has been reported as a polymodal nociceptive receptor activated by noxious heat or acid pH. Acidic solution evoked ionic currents with a EC50 value of about pH 5.4. Extracellular protons could activate TRPV1 by increase in PO rather than by altering unitary conductance, although protons slightly reduce the amplitude of currents. Single channel currents of TRPV1 were observed by outside-out but not inside out configuration. These results suggest that protons act on amino acids in the extracellular domain of TRPV1. Recently, an acid-sensing channel complex, PKD1L3/PKD2L1, has been reported as a possible candidate for sour taste receptor. PKD2L1 (TRPP3) belongs to TRPP subfamily. In mouse tongue, PKD1L3 and PKD2L1 are co-expressed in a subset of taste receptor cells. Large currents were evoked by citric acid and HCl. PKD1L3/PKD2L1 channel complex showed a unique property named as an off-response, which implies that the channel is activated upon the removal of acid stimulus. Acid-induced responses were observed only after the removal of an acidic solution with a pH lower than 3.0. As described above, TRP channels play important roles for acid pH sensing in mammals. Furthermore, we will also mention about a recent study in which TRPA1 could be activated by alkaline pH. [J Physiol Sci. 2008;58 Suppl:S10]
