Table 2.

Summary of the effect of various drugs that modulate PIP₂ levels in TRCs and alter the Bz-insensitive NaCl CT response

Drug	M	Intracellular Target	Number of Animals (N)
Bz	5 × 10−6	↓ ENaC	12
SB-366791	1 × 10−6	↓ TRPV1t	6
U73122	10 × 10−6 to 250 × 10−6	↓ PLC and ↑ PIP2	3
U73343	250 × 10−6	↔ PLC	3
PAO	5 × 10−6 to 50 × 10−6	↓ PI4 kinases and ↓ PIP2	8
diC8-PIP2	115 × 10−6 or 250 × 10−6	↑ PIP2	12
MSG + IMP	0.1 M + 1 × 10−3	↑ T1R1 + T1R3	3
↑ GPCRs (T2Rs, T1R1 + T1R3, T1R2 + T1R3)		↑ PLCβ2 and ↑ TRPM5	3

The GPCR associated with sweet taste (T1R2 + T1R3) was activated by adding sucrose or SC45647 to the salt mixture, the GPCR associated with umami taste (T1R1 + T1R3) was activated measuring responses to MSG and MSG + IMP, and GPCR associated with bitter taste (T2R) was activated by adding quinine to the salt mixture. Benzamil and SB were added to the salt stimuli and produced their effects on the Bz-insensitive NaCl CT responses immediately. However, all other drugs were dissolved directly in 3 ml of dimethyl sulfoxide (DMSO) and were topically applied to the tongue for at least 30 min. In some experiments, a stock solution of diC8-PIP₂ in DMSO (0.584 × 10⁻³ M) was added to 0.525 M sucrose or 0.00525 M SC45647 solution to yield a stimulating solution containing 250 × 10⁻⁶ M diC8-PIP₂ + 0.3 M sucrose or 250 × 10⁻⁶ M diC8-PIP₂ + 0.003M SC45647. Equivalent amount of DMSO was added to the rinse solution. DMSO by itself has no effect on the CT responses to salt stimuli (Lyall et al. 1999). Unless stated otherwise, all drugs were purchased from Sigma. ↑, increase; ↓, decrease; ↔, no change; Bz, benzamil (blocks Na⁺ entry through apical epithelial Na⁺ channel; ENaC); SB-366791, N-(3-methoxyphenyl)-4-chlorocinnamide (blocks Na⁺ entry through TRPV1t); U73122, 1-[6-[((17β)-3-methoxyestra-1,3,5[10]-trien-17-y)amino]hexyl]-1H-pyrrole-2,5-dione (a nonspecific blocker of phospholipase Cs (PLCs)) and blocks the hydrolysis of PIP₂ to inositol-1,4,5-trisphosphate (IP₃) + diacylglycerol (DAG) by PLC (Chuang et al. 2001; Liu et al. 2005; Prescott and Julius 2003); U73343, 1-[6-[((17β)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-2,5-pyrrolidine-dione (an inactive analog of U73122); PAO, phenylarsine oxide (a trivalent arsenic, reacts with vicinal thiol groups in proteins inhibits all isoforms of PI4 kinases and blocks the resynthesis of PIP₂ from PI (Liu and Quin 2005)); diC8-PIP₂, dioctanoyl-PIP₂ (Echelon, Salt Lake City, UT); a short-chain synthetic PIP₂ that increases PIP₂ levels in cell membranes (Liu et al. 2005); IMP, inosine-5′-monophosphate (specifically enhances CT responses to MSG); GPCRs, G-protein–coupled receptors.