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1 Physiology, Virginia Commonwealth University, Richmond, Virginia, United States
2 Richmond, Virginia, United States; Physiology, Virginia Commonwealth University, Richmond, Virginia, United States
3 R&T Sensory Research, Philip Morris, Richmond, Virginia, United States
* To whom correspondence should be addressed. E-mail: vlyall{at}vcu.edu.
The effect of nicotine on the benzamil (Bz)-insensitive (transient receptor potential vanilloid-1 variant cation channel, TRPV1t) and the Bz-sensitive (epithelial Na+ channel, ENaC) salt taste receptors and sour taste was investigated by monitoring intracellular Na+ and H+ activity (pHi) in polarized fungiform taste receptor cells (TRCs) and the chorda tympani (CT) nerve responses to NaCl, KCl and HCl. CT responses in Sprague-Dawley rats, wildtype and TRPV1 knockout (KO) mice were recorded in the presence and absence of agonists (resiniferatoxin and elevated temperature) and an antagonist (SB-366791) of TRPV1t, the ENaC blocker (Bz), and varying apical pH (pHo). At concentrations
0.015M, nicotine enhanced and
0.015M, it inhibited CT responses to KCl and NaCl. Nicotine produced maximum enhancement in the Bz-insensitive NaCl CT response between pHo 6 and 7. Resiniferatoxin and elevated temperature increased the sensitivity of the CT response to nicotine in salt-containing media, and SB-366791 inhibited these effects. TRPV1 KO mice demonstrated no Bz-insensitive CT response to NaCl and no sensitivity to nicotine, resiniferatoxin, and elevated temperature. We conclude that nicotine modulates salt responses by direct interaction with TRPV1t. At pHo
8, the apical membrane permeability of nicotine was increased significantly, resulting in increase in TRC pHi and volume, activation of ENaC, and enhancement of the Bz-sensitive NaCl CT response. At pHo
8, nicotine also inhibited the phasic component of the HCl CT response. We conclude that the effects of nicotine on ENaC and the phasic HCl CT response is due to increase in TRC pHi and volume.
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