Off-response property of an acid-activated cation channel complex PKD1L3-PKD2L1.

Ligand-gated ion channels are important in sensory and synaptic transduction. The PKD1L3-PKD2L1 channel complex is a sour taste receptor candidate that is activated by acids. Here, we report that the proton-activated PKD1L3-PKD2L1 ion channels have the unique ability to be activated after the removal of an acid stimulus. We refer to this property as the off-response (previously described as a delayed response). Electrophysiological analyses show that acid-induced responses are observed only after the removal of an acid solution at less than pH 3.0. A small increase in pH is sufficient for PKD1L3-PKD2L1 channel activation, after exposure to an acid at pH 2.5. These results indicate that this channel is a new type of ion channel-designated as an 'off-channel'-which is activated during stimulus application but not gated open until the removal of the stimulus. The off-response property of PKD1L3-PKD2L1 channels might explain the physiological phenomena occurring during sour taste sensation.