Regulation of the Putative TRPV 1 t Salt Taste Receptor by Phosphatidylinositol 4 , 1 5 - bisphosphate

27 28 Regulation of the putative amiloride and benzamil (Bz)-insensitive TRPV1t salt 29 taste receptor by phosphatidylinositol 4, 5-bisphosphate (PIP2) was investigated by 30 monitoring chorda tympani (CT) taste nerve responses to 0.1M NaCl solutions 31 containing Bz (5x10 M; a specific ENaC blocker) and resiniferatoxin (RTX; 0-10x10 32 M; a specific TRPV1 agonist) in Sprague-Dawley rats and in wildtype (WT) and TRPV1 33 knockout (KO) mice. In rats and WT mice, RTX elicited a biphasic effect on the 34 NaCl+Bz CT response, increasing the CT response between 0.25x10 M and 1x10 M. 35 At concentrations above 1x10 M, RTX inhibited the CT response. An increase in PIP2 36 by topical lingual application of U73122 (a phospholipase C blocker) or diC8-PIP2 (a 37 short chain synthetic PIP2) inhibited the control NaCl+Bz CT response and decreased its 38 sensitivity to RTX. A decrease in PIP2 by topical lingual application of phenylarsine 39 oxide (a phosphoinositide 4 kinase blocker) enhanced the control NaCl+Bz CT 40 response, increased its sensitivity to RTX stimulation and inhibited the desensitization of 41 the CT response at RTX concentrations above 1x10 M. The ENaC-dependent NaCl 42 CT responses were not altered by changes in PIP2. An increase in PIP2 enhanced CT 43 responses to sweet (0.3M sucrose) and bitter (0.01M quinine) stimuli. RTX produced 44 the same increase in the Bz-insensitive Na response when present in salt solutions 45 containing 0.1 M NaCl+Bz, 0.1M monosodium glutamate+Bz, 0.1M NaCl+Bz+0.005M 46 SC45647 or 0.1M NaCl+Bz+0.01M quinine. No effect of RTX was observed on CT 47 responses in WT mice and rats in the presence of the TRPV1 blocker N-(348 methoxyphenyl)-4-chlorocinnamid (1x10 M) or in TRPV1 KO mice. We conclude that 49 PIP2 is a common intracellular effector for sweet, bitter, umami and TRPV1t-dependent 50 salt taste, although in the last case, PIP2 appears to directly regulate the taste receptor 51 protein itself, i.e. the TRPV1 ion channel or its taste receptor variant, TRPV1t. 52