Localization of Amiloride-Sensitive Sodium Current and Voltage-Gated Calcium Currents in Rat Fungiform Taste Cells

Abstract

Bigiani A, Cuoghi V. Localization of amiloride-sensitive sodium current and voltage-gated calcium currents in rat fungiform taste cells. J Neurophysiol 98: 2483-2487, 2007. First published August 8, 2007 doi:10.1152/jn.00716.2007. Recent studies have shown that taste cells transducing bitter, sweet, and umami stimuli do not possess highthreshold voltage-gated calcium channels required for synaptic transmission at conventional synapses, suggesting some sort of signal processing inside taste buds prior to the activation of nerve endings. To evaluate whether this is a general paradigm for the physiology of taste reception, we studied the transduction pathway underlying the detection of sodium ions (salty stimulus). In laboratory rodents, Na ϩ is thought to be transduced, at least in part, through amiloridesensitive sodium channels (ASSCs). Therefore we used the patchclamp techniques to analyze the occurrence pattern of amiloridesensitive sodium currents and voltage-gated calcium currents (both low-voltage-activated T-type current and high-voltage-activated Ltype current) among taste cells in rat fungiform papillae. Because taste cells turnover, we focused our attention on cells possessing large voltage-gated sodium currents, a sign of "mature" cells. We found that cells expressing functional ASSCs either did not possess any calcium currents or exhibited only T-type calcium currents, which is believed to play a role in repetitive firing. On the contrary, cells lacking functional ASSCs were endowed with L-type calcium currents, which are thought to mediate calcium influx required for neurotransmitter exocytosis. Therefore our data suggest that sodium-detecting cells are unlikely to use conventional synaptic communication to transfer taste information to nerve endings. Our findings on sodium taste detection support the recent model of taste transduction, involving separate groups of taste cells: chemosensitive cells and cells forming conventional synapses.

Oxytocin Signaling in Mouse Taste Buds

“…Yet, OXT was reported to decrease transepithelial amiloride-sensitive Na currents (ASSCs), thought to represent salt taste transduction [44]. Interestingly, salt taste detection and the underlying ASSCs may be limited to a subset of Glial-like cells [45], [46]. Consistent with this, salt-sensing taste cells were reported to be distinct from those that sense sweet, bitter, and umami stimuli (i.e.…”

Taste buds: cells, signals and synapses

“…Amiloride-sensitive Na + currents have been reported in taste bud cells that are neither type II or type III cells, based on their lack of voltage-gated currents 82 . By contrast, a report from another group demonstrated that the amiloride-blocked resting conductance was most prominent in cells that had the characteristics of type II cells 83 . Neither of these studies pinpointed the ENaC-mediated currents to cells that could be identified by type-specific molecular markers.…”

Ghrelin Is Produced in Taste Cells and Ghrelin Receptor Null Mice Show Reduced Taste Responsivity to Salty (NaCl) and Sour (Citric Acid) Tastants

“…We found co-expression of ghrelin with the ENaC α- and γ subunits and we also found reduced numbers of cells containing ENaC subunits in GHSR null mice. Taste cells expressing functional AS channels have also been shown to possess large voltage-gated sodium currents that underlie the generation of action potentials [55]. A third study has demonstrated that AS cells can generate action potentials and express ENaC subunits, suggesting that AS cells may be taste cells distinct from Type I cells without action potentials [56].…”