title: Taste receptor cells express pH-sensitive leak K+ channels.
abstract: 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 show 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 tetraethylammonium (TEA), inhibited the current. Interestingly, resting potentials of these TRCs averaged -70 mV, which closely correlated with the amplitude of the pH-sensitive Kleak, suggesting a dominant role of this conductance in setting resting potentials. RT-PCR assays followed by sequencing of PCR products showed that TASK-1, 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 showed that the message for TASK-2 was expressed at significantly higher levels (10-100 times greater) than was TASK-1, TALK-1, or TASK-3. Thus several K2P channels, and in particular TASK-2, are expressed in rat TRCs, where they may contribute to the establishment of resting potentials and sour reception.
authors.affiliation: Cell and Developmental Biology, University of Colorado Health Sciences Center at Fitzsimons, Aurora, Colorado 80045, USA.
authors.forename: W
authors.initials: W
authors.lastname: Lin
authors.forename: C A
authors.initials: CA
authors.lastname: Burks
authors.forename: D R
authors.initials: DR
authors.lastname: Hansen
authors.forename: S C
authors.initials: SC
authors.lastname: Kinnamon
authors.forename: T A
authors.initials: TA
authors.lastname: Gilbertson
mesh_terms: D000818:Animals; D001483:Base Sequence; D019343:Citric Acid / Q000494:pharmacology; D017931:DNA Primers; D006863:Hydrogen-Ion Concentration; D015221:Potassium Channels / Q000235:genetics / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D011984:Sensory Receptor Cells / Q000502:physiology*; D013649:Taste / Q000502:physiology*; D013650:Taste Buds / Q000502:physiology*
chemical_list: D017931:DNA Primers; D015221:Potassium Channels; D019343:Citric Acid