Taste receptor cells express pH - sensitive leak

Two-pore domain K channels encoded by genes KCNK1-17 (K2p1-17) play important roles in regulating cell excitability. We report here that rat taste receptor cells (TRCs) highly express TASK-2 (KCNK5; K2p5.1) and to a much lesser extent TALK-1 (KCNK16; K2p16.1) and TASK-1 (KCNK3; K2p3.1) and suggest potentially important roles for these channels in setting resting membrane potentials and in sour taste transduction. Whole-cell recordings of isolated TRCs demonstrate that a leak K (Kleak) current in a subset of TRCs exhibited high sensitivity to acidic extracellular pH similar to reported properties of TASK-2 and TALK-1 channels. A drop in bath pH from 7.4 to 6 suppressed 90% of the current, resulting in membrane depolarization. K channel blockers, BaCl2 but not TEA, inhibited the current. Interestingly, resting potentials of these TRCs averaged –70 mV, which closely correlated with the amplitude of the pHsensitive Kleak, suggesting a dominant role of this conductance in setting resting potentials. RT-PCR assays followed by sequencing of PCR products showed that TASK1, TASK-2 and a functionally similar channel, TALK-1, were expressed in all three types of lingual taste buds. To verify expression of TASK channels, we labeled taste tissue with antibodies against TASK-1, TASK-2 and TASK-3. Strong labeling was seen in some TRCs with antibody against TASK-2 but not TASK-1 and TASK-3. Consistent with the immunocytochemical staining, quantitative real time PCR assays demonstrated that the message for TASK-2 was expressed at significantly higher levels (10-100X greater) than was TASK-1, TALK-1 or TASK-3. Thus, several K2P channels, and in particular TASK2, are expressed in rat TRCs where they may contribute to the establishment of resting potentials and sour reception.