Expression of calcium-activated chloride channels Ano1 and Ano2 in mouse taste cells

Abstract

Specialized Ca(2+)-dependent ion channels ubiquitously couple intracellular Ca(2+) signals to a change in cell polarization. The existing physiological evidence suggests that Ca(2+)-activated Cl(-) channels (CaCCs) are functional in taste cells. Because Ano1 and Ano2 encode channel proteins that form CaCCs in a variety of cells, we analyzed their expression in mouse taste cells. Transcripts for Ano1 and Ano2 were detected in circumvallate (CV) papillae, and their expression in taste cells was confirmed using immunohistochemistry. When dialyzed with CsCl, taste cells of the type III exhibited no ion currents dependent on cytosolic Ca(2+). Large Ca(2+)-gated currents mediated by TRPM5 were elicited in type II cells by Ca(2+) uncaging. When TRPM5 was inhibited by triphenylphosphine oxide (TPPO), ionomycin stimulated a small but resolvable inward current that was eliminated by anion channel blockers, including T16Ainh-A01 (T16), a specific Ano1 antagonist. This suggests that CaCCs, including Ano1-like channels, are functional in type II cells. In type I cells, CaCCs were prominently active, blockable with the CaCC antagonist CaCCinh-A01 but insensitive to T16. By profiling Ano1 and Ano2 expressions in individual taste cells, we revealed Ano1 transcripts in type II cells only, while Ano2 transcripts were detected in both type I and type II cells. P2Y agonists stimulated Ca(2+)-gated Cl(-) currents in type I cells. Thus, CaCCs, possibly formed by Ano2, serve as effectors downstream of P2Y receptors in type I cells. While the role for TRPM5 in taste transduction is well established, the physiological significance of expression of CaCCs in type II cells remains to be elucidated.

Ca2+-activated Cl− currents in the murine vomeronasal organ enhance neuronal spiking but are dispensable for male–male aggression

“…However, Ano2 did not co-localize with ezrin, a marker protein of microvilli of supporting cells (24). Moreover, a presence of Ano2 in supporting cells would be unexpected because to date murine Ano2 was exclusively found in neuronal cells (22,26,(41)(42)(43)(44). Hence Ano1 and Ano2 are co-expressed in microvilli of apical and basal VSNs without evidence for a preferential expression in one of these layers.…”

Calcium-Activated Chloride Channels in Newly Differentiating Mouse Lens Fiber Cells and Their Role in Volume Regulation

“…These include TRPV1 and TRPV4 channels,24–27 connexin and pannexin hemichannels,5,25 and P2Y receptors 28. Many of these channels and receptors have been reported to be involved in the activation of CaCCs in other types of cells 29–33…”

Functional expression of TMEM16A in taste bud cells

“…Multiple chloride conductances, including Ca 2+ -dependent Clcurrents, have been recorded in some taste cells (Cherkashin et al, 2016;Herness & Sun, 1999;Kim et al, 2000;McBride & Roper, 1991;Taylor & Roper, 1994;Wladkowski et al, 1998). Kim et al (2000) clearly demonstrated that a subpopulation of unidentified taste cells had Ca 2+ -activated Clcurrents and that extracellular ATP could indirectly activate these channels by intracellular Ca 2+ increase through activation of P2Y receptors.…”