Regulation Of The Benzamil - insensitive Salt Taste Receptor

1 The regulation of the benzamil (Bz)-insensitive salt taste receptor was 2 investigated by intracellular Ca ([Ca]i), protein kinase C (PKC) and the Ca3 dependent serine-threonine phosphatase, calcineurin (PP2B), by monitoring chorda 4 tympani taste nerve responses to 0.1M NaCl solutions containing Bz (5x10 M) and 5 resiniferatoxin (RTX; 0-10x10 M) in Sprague-Dawley rats and in wildtype (WT) and 6 TRPV1 knockout (KO) mice. In rats and WT mice, RTX increased the NaCl+BZ chorda 7 tympani responses between 0.25x10 and 1x10 M and inhibited the responses above 8 1x10 M. Decreasing taste receptor cell [Ca]i with BAPTA loading, activation of PKC 9 with 4α-phorbol 12, 13-didecanoate (PMA) or inhibition of PP2B by cyclosporine A or 10 FK-506, enhanced the magnitude of the Bz-insensitive NaCl chorda tympani responses 11 in the presence of RTX and either minimized or completely eliminated the decrease in 12 the chorda tympani response above 1x10 M RTX. In contrast, increasing taste 13 receptor cell [Ca]i with ionomycin, inhibited Bz-insensitive NaCl chorda tympani 14 responses in the presence of RTX. No effect of the above modulators was observed on 15 the chorda tympani responses in WT mice and rats in the presence of TRPV1 blocker 16 N-(3-methoxyphenyl)-4-chlorocinnamid (SB-366791; 1x10 M) or in TRPV1 KO mice. 17 P labeling demonstrated direct phosphorylation of TRPV1 or TRPV1t in anterior 18 lingual epithelium by PMA, cyclosporin A or FK-506. PMA also enhanced the RTX19 sensitive unilateral apical Na flux in polarized fungiform taste receptor cell in vitro. We 20 conclude that TRPV1 or its variant, TRPV1t is phosphorylated and dephosphorylated by 21 PKC and PP2B, respectively, and either sensitizes or desensitizes the Bz-insensitive 22 NaCl chorda tympani responses to RTX stimulation. 23