Research ReportDye-permeable, voltage-gated channel on mouse fungiform taste bud cells

We show here the expression, permeability and pharmacology of a voltage-gated channel in certain taste bud cells (TBCs) which is known to be permeable to Lucifer Yellow CH (LY) and known to release ATP as a neurotransmitter in response to taste substances. LY dissolved in a 200 mM K+-containing solution label TBCs immunoreactive to PLCβ2, a phospholipase subtype, but not the TBC subtype immunoreactive to SNAP-25, a SNARE protein. In addition to these subtypes, LY also labelled a few of the non-immunoreactive TBCs. Monovalent and divalent anion probes with molar mass less than 1200 also label PLCβ2-immunoreactive TBCs and a few non-immunoreactive TBCs, whereas a cation probe, rhodamine B, labels the cell membrane of TBCs nonselectively and K+ independently. The number of LY-labelled TBCs is decreased by 5 μM DIDS (4,4′-diisothiocyanostilbene-2-2′disulfonate), 1 mM octanol and 10− 5 M H+, but not by 10 μM carbenoxolone, 2 mM probenecid, 10 mM TEA, or 30 μM flufenamic acid. PLCβ2-immunoreactive TBCs and a few non-immunoreactive TBCs generate a TEA-insensitive outwardly rectifying current. DIDS decreases this current in magnitude with IC50 of ~ 0.4 μM in a voltage-independent manner. Also 10− 5 M H+ and 1 mM octanol decreases the current magnitude, but 10 μM carbenoxolone and 2 mM probenecid do not. These results show that the LY-permeable channel preferably permeates anions and occurs not only on PLCβ2-immunoreactive TBCs but also on certain non-immunoreactive TBCs. Also the results show that the pharmacology of the LY-permeable channel is different from hemichannels reported. The discussion focuses on the pharmacology and the role of the LY-permeable channel.

Research highlights► The permeation limit of a voltage-gated channel that release ATP was less than 1200. ► The channel was preferably permeable to anions. ► Less than 10 μM DIDS blocked both the channel. ► The channel occurs not only on type II cells but also probably on type I cells.