| Research Abstract |
To elucidate the physiological roles of a candidate sour taste receptor, PKD1L3/PKD2L1, we generated gene knockout mice for PKD1L3 and/or PKD2L1. To investigate phenotype of these mice in taste sensation including sour taste, behavioral and electrophysiological analyses were performed. In the behavioral analyses such as two-bottle preference test and brief-access licking test, PKD1L3, PKD2L1, and double KO mice showed normal preference or avoidance behavior similar to the wild-type littermates for all the five basic taste qualities. In contrast, both whole-nerve and single-fiber chorda tympani nerve responses of PKD2L1 KO and double KO mice to sour solutions such as citric acid, HCl, and acetic acid significantly reduced compared with wild-type mice, while PKD1L3 KO mice showed normal responses. In glossopharyngeal nerve recordings, PKD1L3, PKD2L1, and double KO mice showed normal responses compared with wild-type mice. In addition, PKD1L3, PKD2L1, and double KO mice showed responses s
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imilar to wild-type mice upon stimulation with salt,sweet, bitter, and umami (savory) taste compounds. Collectively, these results demonstrate that PKD2L1 functions as a sour taste receptor in vivo and suggest that there are multiple mechanisms underlying sour taste detection such as somatosensation other than via taste buds.
We identified the N-terminal extracellular region of human PKD1L3 and the full-length of human PKD2L1. HEK 293T cells expressing human PKD2L1 and chimeric PKD1L3, which consists of the N-terminal extracellular region of human PKD1L3 and the following region of mouse PKD1L3, showed off-response upon stimulation with sour solution such as citric acid. These cells still showed robust response to sour stimuli in the presence of a taste-modifying protein, neoculin, extracted from Curculigo latifolia. These results raise the possibility that neoculin inhibits the region other than the N-terminal extracellular region of human PKD1L3. Alternatively, inhibition event occurs at the level of taste cells or taste neurons, not at the taste receptors. Less
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