scholarly journals Ethanol Modulates the VR-1 Variant Amiloride-insensitive Salt Taste Receptor. II. Effect on Chorda Tympani Salt Responses

2005 ◽  
Vol 125 (6) ◽  
pp. 587-600 ◽  
Author(s):  
Vijay Lyall ◽  
Gerard L. Heck ◽  
Tam-Hao T. Phan ◽  
Shobha Mummalaneni ◽  
Shahbaz A. Malik ◽  
...  

The effect of ethanol on the amiloride- and benzamil (Bz)-insensitive salt taste receptor was investigated by direct measurement of intracellular Na+ activity ([Na+]i) using fluorescence imaging in polarized fungiform taste receptor cells (TRCs) and by chorda tympani (CT) taste nerve recordings. CT responses to KCl and NaCl were recorded in Sprague-Dawley rats, and in wild-type (WT) and vanilloid receptor-1 (VR-1) knockout mice (KO). CT responses were monitored in the presence of Bz, a specific blocker of the epithelial Na+ channel (ENaC). CT responses were also recorded in the presence of agonists (resiniferatoxin and elevated temperature) and antagonists (capsazepine and SB-366791) of VR-1 that similarly modulate the Bz-insensitive VR-1 variant salt taste receptor. In the absence of mineral salts, ethanol induced a transient decrease in TRC volume and elicited only transient phasic CT responses. In the presence of mineral salts, ethanol increased the apical cation flux in TRCs without a change in volume, increased transepithelial electrical resistance across the tongue, and elicited CT responses that were similar to salt responses, consisting of both a phasic component and a sustained tonic component. At concentrations <50%, ethanol enhanced responses to KCl and NaCl, while at ethanol concentrations >50%, those CT responses were inhibited. Resiniferatoxin and elevated temperature increased the sensitivity of the CT response to ethanol in salt-containing media, and SB-366791 inhibited the effect of ethanol, resiniferatoxin, and elevated temperature on the CT responses to mineral salts. VR-1 KO mice demonstrated no Bz-insensitive CT response to NaCl and no sensitivity to ethanol. We conclude that ethanol increases salt taste sensitivity by its direct action on the Bz-insensitive VR-1 variant salt taste receptor.

2005 ◽  
Vol 125 (6) ◽  
pp. 569-585 ◽  
Author(s):  
Vijay Lyall ◽  
Gerard L. Heck ◽  
Tam-Hao T. Phan ◽  
Shobha Mummalaneni ◽  
Shahbaz A. Malik ◽  
...  

The effect of ethanol on the amiloride- and benzamil (Bz)-insensitive salt taste receptor was investigated by the measurement of intracellular Na+ activity ([Na+]i) in polarized rat fungiform taste receptor cells (TRCs) using fluorescence imaging and by chorda tympani (CT) taste nerve recordings. CT responses were monitored during lingual stimulation with ethanol solutions containing NaCl or KCl. CT responses were recorded in the presence of Bz (a specific blocker of the epithelial Na+ channel [ENaC]) or the vanilloid receptor-1 (VR-1) antagonists capsazepine or SB-366791, which also block the Bz-insensitive salt taste receptor, a VR-1 variant. CT responses were recorded at 23°C or 42°C (a temperature at which the VR-1 variant salt taste receptor activity is maximally enhanced). In the absence of permeable cations, ethanol induced a transient decrease in TRC volume, and stimulating the tongue with ethanol solutions without added salt elicited only transient phasic CT responses that were insensitive to elevated temperature or SB-366791. Preshrinking TRCs in vivo with hypertonic mannitol (0.5 M) attenuated the magnitude of the phasic CT response, indicating that in the absence of mineral salts, transient phasic CT responses are related to the ethanol-induced osmotic shrinkage of TRCs. In the presence of mineral salts, ethanol increased the Bz-insensitive apical cation flux in TRCs without a change in cell volume, increased transepithelial electrical resistance across the tongue, and elicited CT responses that were similar to salt responses, consisting of both a transient phasic component and a sustained tonic component. Ethanol increased the Bz-insensitive NaCl CT response. This effect was further enhanced by elevating the temperature from 23°C to 42°C, and was blocked by SB-366791. We conclude that in the presence of mineral salts, ethanol modulates the Bz-insensitive VR-1 variant salt taste receptor.


2010 ◽  
Vol 103 (3) ◽  
pp. 1337-1349 ◽  
Author(s):  
Vijay Lyall ◽  
Tam-Hao T. Phan ◽  
ZuoJun Ren ◽  
Shobha Mummalaneni ◽  
Pamela Melone ◽  
...  

Regulation of the putative amiloride and benzamil (Bz)-insensitive TRPV1t salt taste receptor by phosphatidylinositol 4,5-bisphosphate (PIP2) was studied by monitoring chorda tympani (CT) taste nerve responses to 0.1 M NaCl solutions containing Bz (5 × 10−6 M; a specific ENaC blocker) and resiniferatoxin (RTX; 0–10 × 10−6 M; a specific TRPV1 agonist) in Sprague-Dawley rats and in wildtype (WT) and TRPV1 knockout (KO) mice. In rats and WT mice, RTX elicited a biphasic effect on the NaCl + Bz CT response, increasing the CT response between 0.25 × 10−6 and 1 × 10−6 M. At concentrations >1 × 10−6 M, RTX inhibited the CT response. An increase in PIP2 by topical lingual application of U73122 (a phospholipase C blocker) or diC8-PIP2 (a short chain synthetic PIP2) inhibited the control NaCl + Bz CT response and decreased its sensitivity to RTX. A decrease in PIP2 by topical lingual application of phenylarsine oxide (a phosphoinositide 4 kinase blocker) enhanced the control NaCl + Bz CT response, increased its sensitivity to RTX stimulation, and inhibited the desensitization of the CT response at RTX concentrations >1 × 10−6 M. The ENaC-dependent NaCl CT responses were not altered by changes in PIP2. An increase in PIP2 enhanced CT responses to sweet (0.3 M sucrose) and bitter (0.01 M quinine) stimuli. RTX produced the same increase in the Bz-insensitive Na+response when present in salt solutions containing 0.1 M NaCl + Bz, 0.1 M monosodium glutamate + Bz, 0.1 M NaCl + Bz + 0.005 M SC45647, or 0.1 M NaCl + Bz + 0.01 M quinine. No effect of RTX was observed on CT responses in WT mice and rats in the presence of the TRPV1 blocker N-(3-methoxyphenyl)-4-chlorocinnamide (1 × 10−6 M) or in TRPV1 KO mice. We conclude that PIP2 is a common intracellular effector for sweet, bitter, umami, and TRPV1t-dependent salt taste, although in the last case, PIP2 seems to directly regulate the taste receptor protein itself, i.e., the TRPV1 ion channel or its taste receptor variant, TRPV1t.


2007 ◽  
Vol 98 (3) ◽  
pp. 1662-1674 ◽  
Author(s):  
Vijay Lyall ◽  
Tam-Hao T. Phan ◽  
Shobha Mummalaneni ◽  
Mahdis Mansouri ◽  
Gerard L. Heck ◽  
...  

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 and both wildtype and TRPV1 knockout (KO) mice were recorded in the presence and absence of agonists [resiniferatoxin (RTX) and elevated temperature] and an antagonist (SB-366791) of TRPV1t, the ENaC blocker (Bz), and varying apical pH (pHo). At concentrations <0.015 M, nicotine enhanced and at >0.015 M, it inhibited CT responses to KCl and NaCl. Nicotine produced maximum enhancement in the Bz-insensitive NaCl CT response at pHo between 6 and 7. RTX 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, RTX, 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 arise from increases in TRC pHi and volume.


1999 ◽  
Vol 277 (4) ◽  
pp. C800-C813 ◽  
Author(s):  
Vijay Lyall ◽  
Gerard L. Heck ◽  
John A. DeSimone ◽  
George M. Feldman

Osmotic effects on salt taste were studied by recording from the rat chorda tympani (CT) nerve and by measuring changes in cell volume of isolated rat fungiform taste receptor cells (TRCs). Mannitol, cellobiose, urea, or DMSO did not induce CT responses. However, the steady-state CT responses to 150 mM NaCl were significantly increased when the stimulus solutions also contained 300 mM mannitol or cellobiose, but not 600 mM urea or DMSO. The enhanced CT responses to NaCl were reversed when the saccharides were removed and were completely blocked by addition of 100 μM amiloride to the stimulus solution. Exposure of TRCs to hyperosmotic solutions of mannitol or cellobiose induced a rapid and sustained decrease in cell volume that was completely reversible, whereas exposure to hypertonic urea or DMSO did not induce sustained reductions in cell volume. These data suggest that the osmolyte-induced increase in the CT response to NaCl involves a sustained decrease in TRC volume and the activation of amiloride-sensitive apical Na+ channels.


1997 ◽  
Vol 273 (6) ◽  
pp. R1923-R1931 ◽  
Author(s):  
Robert F. Lundy ◽  
David W. Pittman ◽  
Robert J. Contreras

The effects of the epithelial Na+channel antagonists amiloride and benzamil and the Na+/H+exchange antagonist 5-( N, N-dimethyl)-amiloride (DMA)-Cl on the integrated responses of the chorda tympani nerve to 30, 75, 150, 300, and 500 mM concentrations of NaCl, KCl, and NH4Cl were assessed in male Sprague-Dawley rats. Based on evidence from other systems, 1 and 25 μM amiloride and benzamil were chosen to selectively inhibit epithelial Na+ channels and 1 μM DMA was chosen to selectively inhibit Na+/H+exchange. When added to stimulating salt solutions, amiloride, benzamil, and DMA were each effective in inhibiting responses to all three salts. The degree of inhibition varied with drug, salt, and salt concentration, but not drug dose. Amiloride suppressed NaCl responses to a greater degree than KCl and NH4Cl responses, whereas DMA suppressed NH4Cl responses to a greater degree than NaCl and KCl responses. In all but one case (25 μM amiloride added to KCl), drug suppression of taste nerve responses decreased with an increase in salt concentration. The present results suggest that 1) epithelial Na+ channels in rat taste receptor cells may play a role in KCl and NH4Cl taste transduction; 2) a Na+/H+exchange protein may be present in taste receptor cells, representing a putative component, in addition to epithelial Na+ channels, in salt taste transduction; and 3) salt taste detection and transduction may depend on the utilization of a combination of common and distinct transcellular pathways.


2002 ◽  
Vol 120 (6) ◽  
pp. 793-815 ◽  
Author(s):  
Vijay Lyall ◽  
Rammy I. Alam ◽  
Tam-Hao T. Phan ◽  
Oneal F. Russell ◽  
Shahbaz A. Malik ◽  
...  

Mixture interactions between sour and salt taste modalities were investigated in rats by direct measurement of intracellular pH (pHi) and Na+ activity ([Na+]i) in polarized fungiform taste receptor cells (TRCs) and by chorda tympani (CT) nerve recordings. Stimulating the lingual surface with NaCl solutions adjusted to pHs ranging between 2.0 and 10.3 increased the magnitude of NaCl CT responses linearly with increasing external pH (pHo). At pH 7.0, the epithelial sodium channel (ENaC) blocker, benzamil, decreased NaCl CT responses and inhibited further changes in CT responses induced by varying pHo to 2.0 or 10.3. At constant pHo, buffering NaCl solutions with potassium acetate/acetic acid (KA/AA) or HCO3−/CO2 inhibited NaCl CT responses relative to CT responses obtained with NaCl solutions buffered with HEPES. The carbonic anhydrase blockers, MK-507 and MK-417, attenuated the inhibition of NaCl CT responses in HCO3−/CO2 buffer, suggesting a regulatory role for pHi. In polarized TRCs step changes in apical pHo from 10.3 to 2.0 induced a linear decrease in pHi that remained within the physiological range (slope = 0.035; r2 = 0.98). At constant pHo, perfusing the apical membrane with Ringer's solutions buffered with KA/AA or HCO3−/CO2 decreased resting TRC pHi, and MK-507 or MK-417 attenuated the decrease in pHi in TRCs perfused with HCO3−/CO2 buffer. In parallel experiments, TRC [Na+]i decreased with (a) a decrease in apical pH, (b) exposing the apical membrane to amiloride or benzamil, (c) removal of apical Na+, and (d) acid loading the cells with NH4Cl or sodium acetate at constant pHo. Diethylpyrocarbonate and Zn2+, modification reagents for histidine residues in proteins, attenuated the CO2-induced inhibition of NaCl CT responses and the pHi-induced inhibition of apical Na+ influx in TRCs. We conclude that TRC pHi regulates Na+-influx through amiloride-sensitive apical ENaCs and hence modulates NaCl CT responses in acid/salt mixtures.


2005 ◽  
Vol 127 (1) ◽  
pp. 15-34 ◽  
Author(s):  
Vijay Lyall ◽  
Hampton Pasley ◽  
Tam-Hao T. Phan ◽  
Shobha Mummalaneni ◽  
Gerard L. Heck ◽  
...  

The relationship between cell volume and the neural response to acidic stimuli was investigated by simultaneous measurements of intracellular pH (pHi) and cell volume in polarized fungiform taste receptor cells (TRCs) using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) in vitro and by rat chorda tympani (CT) nerve recordings in vivo. CT responses to HCl and CO2 were recorded in the presence of 1 M mannitol and specific probes for filamentous (F) actin (phalloidin) and monomeric (G) actin (cytochalasin B) under lingual voltage clamp. Acidic stimuli reversibly decrease TRC pHi and cell volume. In isolated TRCs F-actin and G-actin were labeled with rhodamine phalloidin and bovine pancreatic deoxyribonuclease-1 conjugated with Alexa Fluor 488, respectively. A decrease in pHi shifted the equilibrium from F-actin to G-actin. Treatment with phalloidin or cytochalasin B attenuated the magnitude of the pHi-induced decrease in TRC volume. The phasic part of the CT response to HCl or CO2 was significantly decreased by preshrinking TRCs with hypertonic mannitol and lingual application of 1.2 mM phalloidin or 20 μM cytochalasin B with no effect on the tonic part of the CT response. In TRCs first treated with cytochalasin B, the decrease in the magnitude of the phasic response to acidic stimuli was reversed by phalloidin treatment. The pHi-induced decrease in TRC volume induced a flufenamic acid–sensitive nonselective basolateral cation conductance. Channel activity was enhanced at positive lingual clamp voltages. Lingual application of flufenamic acid decreased the magnitude of the phasic part of the CT response to HCl and CO2. Flufenamic acid and hypertonic mannitol were additive in inhibiting the phasic response. We conclude that a decrease in pHi induces TRC shrinkage through its effect on the actin cytoskeleton and activates a flufenamic acid–sensitive basolateral cation conductance that is involved in eliciting the phasic part of the CT response to acidic stimuli.


2009 ◽  
Vol 296 (4) ◽  
pp. R866-R876 ◽  
Author(s):  
Steven Zukerman ◽  
John I. Glendinning ◽  
Robert F. Margolskee ◽  
Anthony Sclafani

In addition to their well-known preference for sugars, mice and rats avidly consume starch-derived glucose polymers (e.g., Polycose). T1R3 is a component of the mammalian sweet taste receptor that mediates the preference for sugars and artificial sweeteners in mammals. We examined the role of the T1R3 receptor in the ingestive response of mice to Polycose and sucrose. In 60-s two-bottle tests, knockout (KO) mice preferred Polycose solutions (4–32%) to water, although their overall preference was lower than WT mice (82% vs. 94%). KO mice also preferred Polycose (0.5–32%) in 24-h two-bottle tests, although less so than WT mice at dilute concentrations (0.5–4%). In contrast, KO mice failed to prefer sucrose to water in 60-s tests. In 24-h tests, KO mice were indifferent to 0.5–8% sucrose, but preferred 16–32% sucrose; this latter result may reflect the post-oral effects of sucrose. Overall sucrose preference and intake were substantially less in KO mice than WT mice. However, when retested with 0.5–32% sucrose solutions, the KO mice preferred all sucrose concentrations, although they drank less sugar than WT mice. The experience-induced sucrose preference is attributed to a post-oral conditioned preference for the T1R3-independent orosensory features of the sugar solutions (odor, texture, T1R2-mediated taste). Chorda tympani nerve recordings revealed virtually no response to sucrose in KO mice, but a near-normal response to Polycose. These results indicate that the T1R3 receptor plays a critical role in the taste-mediated response to sucrose but not Polycose.


1996 ◽  
Vol 107 (4) ◽  
pp. 545-554 ◽  
Author(s):  
R E Doolin ◽  
T A Gilbertson

The role of amiloride-sensitive Na+ channels (ASSCs) in the transduction of salty taste stimuli in rat fungiform taste buds has been well established. Evidence for the involvement of ASSCs in salt transduction in circumvallate and foliate taste buds is, at best, contradictory. In an attempt to resolve this apparent controversy, we have begun to look for functional ASSCs in taste buds isolated from fungiform, foliate, and circumvallate papillae of male Sprague-Dawley rats. By use of a combination of whole-cell and nystatin-perforated patch-clamp recording, cells within the taste bud that exhibited voltage-dependent currents, reflective of taste receptor cells (TRCs), were subsequently tested for amiloride sensitivity. TRCs were held at -70 mV, and steady-state current and input resistance were monitored during superfusion of Na(+)-free saline and salines containing amiloride (0.1 microM to 1 mM). Greater than 90% of all TRCs from each of the papillae responded to Na+ replacement with a decrease in current and an increase in input resistance, reflective of a reduction in electrogenic Na+ movement into the cell. ASSCs were found in two thirds of fungiform and in one third of foliate TRCs, whereas none of the circumvallate TRCs was amiloride sensitive. These findings indicate that the mechanism for Na+ influx differs among taste bud types. All amiloride-sensitive currents had apparent inhibition constants in the submicromolar range. These results agree with afferent nerve recordings and raise the possibility that the extensive labeling of the ASSC protein and mRNA in the circumvallate papillae may reflect a pool of nonfunctional channels or a pool of channels that lacks sensitivity to amiloride.


2020 ◽  
Vol 45 (4) ◽  
pp. 249-259
Author(s):  
Enshe Jiang ◽  
Ginger D Blonde ◽  
Mircea Garcea ◽  
Alan C Spector

Abstract The chorda tympani (CT) nerve is exceptionally responsive to NaCl. Amiloride, an epithelial Na+ channel (ENaC) blocker, consistently and significantly decreases the NaCl responsiveness of the CT but not the glossopharyngeal (GL) nerve in the rat. Here, we examined whether amiloride would suppress the NaCl responsiveness of the CT when it cross-reinnervated the posterior tongue (PT). Whole-nerve electrophysiological recording was performed to investigate the response properties of the intact (CTsham), regenerated (CTr), and cross-regenerated (CT-PT) CT in male rats to NaCl mixed with and without amiloride and common taste stimuli. The intact (GLsham) and regenerated (GLr) GL were also examined. The CT responses of the CT-PT group did not differ from those of the GLr and GLsham groups, but did differ from those of the CTr and CTsham groups for some stimuli. Importantly, the responsiveness of the cross-regenerated CT to a series of NaCl concentrations was not suppressed by amiloride treatment, which significantly decreased the response to NaCl in the CTr and CTsham groups and had no effect in the GLr and GLsham groups. This suggests that the cross-regenerated CT adopts the taste response properties of the GL as opposed to those of the regenerated CT or intact CT. This work replicates the 5 decade-old findings of Oakley and importantly extends them by providing compelling evidence that the presence of functional ENaCs, essential for sodium taste recognition in regenerated taste receptor cells, depends on the reinnervated lingual region and not on the reinnervating gustatory nerve, at least in the rat.


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