A Novel Pharmacological Probe Links the Amiloride-Insensitive NaCl, KCl, and NH4Cl Chorda Tympani Taste Responses

2001 ◽  
Vol 86 (5) ◽  
pp. 2638-2641 ◽  
Author(s):  
John A. DeSimone ◽  
Vijay Lyall ◽  
Gerard L. Heck ◽  
Tam-Hao T. Phan ◽  
Rammy I. Alam ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Apical Membrane ◽  
Cetylpyridinium Chloride ◽  
Taste Receptor ◽  
Chorda Tympani ◽  
Intracellular Acidification ◽  
Cellular Origin ◽  
Receptor Cells ◽  
Nacl Concentration

Chorda tympani taste nerve responses to NaCl can be dissected pharmacologically into amiloride-sensitive and -insensitive components. It is now established that the amiloride-sensitive, epithelial sodium channel acts as a sodium-specific ion detector in taste receptor cells (TRCs). Much less is known regarding the cellular origin of the amiloride-insensitive component, but its anion dependence indicates an important role for paracellular shunts in the determination of its magnitude. However, this has not precluded the possibility that undetected apical membrane ion pathways in TRCs may also contribute to its origin. Progress toward making such a determination has suffered from lack of a pharmacological probe for an apical amiloride-insensitive taste pathway. We present data here showing that, depending on the concentration used, cetylpyridinium chloride (CPC) can either enhance or inhibit the amiloride-insensitive response to NaCl. The CPC concentration giving maximal enhancement was 250 μM. At 2 mM, CPC inhibited the entire amiloride-insensitive part of the NaCl response. The NaCl response is, therefore, composed entirely of amiloride- and CPC-sensitive components. The magnitude of the maximally enhanced CPC-sensitive component varied with the NaCl concentration and was half-maximal at [NaCl] = 62 ± 11 (SE) mM. This was significantly less than the corresponding parameter for the amiloride-sensitive component (268 ± 71 mM). CPC had similiar effects on KCl and NH4Cl responses except that in these cases, after inhibition with 2 mM CPC, a significant CPC-insensitive response remained. CPC (2 mM) inhibited intracellular acidification of TRCs due to apically presented NH4Cl, suggesting that CPC acts on an apical membrane nonselective cation pathway.

scholarly journals Modulation of Rat Chorda Tympani NaCl Responses and Intracellular Na+ Activity in Polarized Taste Receptor Cells by pH

2002 ◽  
Vol 120 (6) ◽  
pp. 793-815 ◽  
Author(s):  
Vijay Lyall ◽  
Rammy I. Alam ◽  
Tam-Hao T. Phan ◽  
Oneal F. Russell ◽  
Shahbaz A. Malik ◽  
...  
Keyword(s):  
Apical Membrane ◽  
Taste Receptor ◽  
Potassium Acetate ◽  
Chorda Tympani ◽  
Receptor Cells ◽  
Intracellular Na Activity ◽  
Taste Receptor Cells ◽  
Nerve Recordings ◽  
Acid Loading ◽  
External Ph

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.

Effects of osmolarity on taste receptor cell size and function

1999 ◽  
Vol 277 (4) ◽  
pp. C800-C813 ◽  
Author(s):  
Vijay Lyall ◽  
Gerard L. Heck ◽  
John A. DeSimone ◽  
George M. Feldman
Keyword(s):  
Cell Volume ◽  
Receptor Cell ◽  
Taste Receptor ◽  
Chorda Tympani ◽  
Taste Receptor Cell ◽  
Salt Taste ◽  
Receptor Cells ◽  
Enhanced Ct ◽  
And Function ◽  
Osmotic Effects

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.

scholarly journals Insulin activates epithelial sodium channel (ENaC) via phosphoinositide 3-kinase in mammalian taste receptor cells

2011 ◽  
Vol 300 (4) ◽  
pp. C860-C871 ◽  
Author(s):  
Arian F. Baquero ◽  
Timothy A. Gilbertson
Keyword(s):  
Sodium Channel ◽  
Taste Receptor ◽  
Epithelial Sodium Channel ◽  
Endocrine Regulation ◽  
Salt Taste ◽  
Receptor Cells ◽  
Taste Receptor Cells ◽  
Phosphoinositide 3 Kinase ◽  
20 Nm ◽  
Epithelial Sodium Channel Enac

Diabetes is a profound disease that results in a severe lack of regulation of systemic salt and water balance. From our earlier work on the endocrine regulation of salt taste at the level of the epithelial sodium channel (ENaC), we have begun to investigate the ability of insulin to alter ENaC function with patch-clamp recording on isolated mouse taste receptor cells (TRCs). In fungiform and vallate TRCs that exhibit functional ENaC currents (e.g., amiloride-sensitive Na+ influx), insulin (5–20 nM) caused a significant increase in Na+ influx at −80 mV (EC50 = 7.53 nM). The insulin-enhanced currents were inhibited by amiloride (30 μM). Similarly, in ratiometric Na+ imaging using SBFI, insulin treatment (20 nM) enhanced Na+ movement in TRCs, consistent with its action in electrophysiological assays. The ability of insulin to regulate ENaC function is dependent on the enzyme phosphoinositide 3-kinase since treatment with the inhibitor LY294002 (10 μM) abolished insulin-induced changes in ENaC. To test the role of insulin in the regulation of salt taste, we have characterized behavioral responses to NaCl using a mouse model of acute hyperinsulinemia. Insulin-treated mice show significant avoidance of NaCl at lower concentrations than the control group. Interestingly, these differences between groups were abolished when amiloride (100 μM) was added into NaCl solutions, suggesting that insulin was regulating ENaC. Our results are consistent with a role for insulin in maintaining functional expression of ENaC in mouse TRCs.

Voltage dependence of the rat chorda tympani response to Na+ salts: implications for the functional organization of taste receptor cells

1993 ◽  
Vol 70 (1) ◽  
pp. 167-178 ◽  
Author(s):  
Q. Ye ◽  
G. L. Heck ◽  
J. A. DeSimone
Keyword(s):  
Tight Junctions ◽  
Voltage Clamp ◽  
Time Course ◽  
Voltage Dependence ◽  
Functional Organization ◽  
Taste Receptor ◽  
Chorda Tympani ◽  
Lingual Epithelium ◽  
Anion Effect ◽  
Receptor Cells

1. Voltage-clamp and current-clamp data were obtained from a circumscribed region of the anterior rat lingual epithelium while simultaneously monitoring the afferent, stimulus-evoked, neural response from the same receptive field. 2. Chorda tympani (CT) responses at constant Na(+)-salt concentration were enhanced by submucosa negative voltage clamp and suppressed by positive voltage clamp. The complete CT response profile, including the time course of adaptation, was not uniquely determined by NaCl concentration alone. The response could be reproduced at different NaCl concentrations by applying a compensating voltage. 3. The form of the concentration and voltage dependence of the CT response indicates that the complete stimulus energy is the Na+ electrochemical potential difference across receptor cell apical membranes, and not Na+ concentration alone. This is the underlying principal behind the equivalence of chemical and electric taste for Na+ salts. 4. CT responses to sodium gluconate (25 and 200 mM) and 25 mM NaCl produced amiloride-insensitive components (AIC) of low magnitude. NaCl at 200 mM produced a significantly larger AIC. The AIC was voltage-clamp independent. The relative magnitude of the AIC was positively correlated with the transepithelial conductance of each salt. This suggests that the large AIC for 200 mM NaCl results from its relatively high permeability through the paracellular pathway. 5. Analysis of the CT response under voltage clamp revealed two anion effects on Na(+)-salt taste, both of which act through the paracellular shunt. 1) Anions modify the transepithelial potential (TP) across tight junctions and thereby modulate the cell receptor potential. This anion effect can be eliminated by voltage clamping the TP. 2) Sufficiently mobile anions facilitate electroneutral diffusion of Na+ salts through tight junctions. This effect is observed especially when Cl- is the anion and when the stimulus concentration favors NaCl influx, allowing Na+ to stimulate receptor cells from the submucosal side. Because the submucosal intercellular spaces are nearly isopotential regions, this effect is insensitive to voltage clamp of the TP. The large AIC associated with this anion effect is due to the low permeability of amiloride.

Amiloride Blocks Acid Responses in NaCl-Best Gustatory Neurons of the Hamster Solitary Nucleus

1998 ◽  
Vol 80 (3) ◽  
pp. 1362-1372 ◽  
Author(s):  
John D. Boughter ◽  
David V. Smith
Keyword(s):  
Citric Acid ◽  
Taste Receptor ◽  
Nerve Fibers ◽  
Chorda Tympani ◽  
Chorda Tympani Nerve ◽  
Receptor Cells ◽  
Biophysical Studies ◽  
Taste Receptor Cells ◽  
To Receive ◽  
Gustatory Neurons

Boughter, John D., Jr. and David V. Smith. Amiloride blocks acid responses in NaCl-best gustatory neurons of the hamster solitary nucleus. J. Neurophysiol. 80: 1362–1372, 1998. Biophysical studies of isolated taste receptor cells show that one mechanism of Na+ salt transduction involves the inward movement of Na+ through amiloride-blockable ion channels on the apical receptor cell membrane, which leads to a direct depolarization. Hamster taste receptor cells with amiloride-blockable Na+ responses also show an amiloride-sensitive H+ current. Thus one mechanism for the transduction of acid taste involves the amiloride-sensitive channel. We investigated the effects of amiloride on responses to acids in neurons of the nucleus of the solitary tract (NST) of the hamster. The responses of 47 NST neurons were recorded extracellularly while the anterior tongue was stimulated with solutions representing the four taste qualities (NaCl, sucrose, HCl, quinine), which were used to characterize each cell on the basis of its best stimulus. The effects of amiloride on responses to 10 mM HCl, 10 mM citric acid, 100 mM NaCl, and 100 mM sucrose were then investigated. Stimuli were presented alone for 30 s (control trials) and also presented for 10 s, followed by a mixture of the stimulus with 10 μM amiloride for 10 s, followed by the stimulus alone again for 10 s (amiloride trials). The effects of amiloride were assessed by comparing the responses of cells with the stimulus + amiloride with that of the stimulus alone. In neurons classified as NaCl-best, amiloride reversibly blocked responses to NaCl, HCl, and citric acid. In HCl-best neurons, amiloride had no effect on responses to any of these stimuli. In sucrose-best neurons, amiloride blocked the response to NaCl but not to sucrose or to either acid. These results support the hypothesis that acids are transduced by at least two different receptor mechanisms in the hamster, amiloride sensitive and amiloride insensitive. At the NST, these inputs are tightly maintained in two separate populations of neurons. Sucrose-best neurons, which show amiloride effects on NaCl but not acids, appear to receive converging inputs from both amiloride-sensitive (N-best) and amiloride-insensitive (H-best) chorda tympani nerve fibers.

Responses of gustatory cells in the nucleus of the solitary tract of the hamster after NaCl or amiloride adaptation

1996 ◽  
Vol 76 (1) ◽  
pp. 47-58 ◽  
Author(s):  
D. V. Smith ◽  
H. Liu ◽  
M. B. Vogt
Keyword(s):  
Taste Receptor ◽  
Chorda Tympani ◽  
Solitary Tract ◽  
Chorda Tympani Nerve ◽  
Receptor Cells ◽  
Human Tongue ◽  
Baseline Response ◽  
Single Nucleus ◽  
Adaptation Condition ◽  
Stimulus Classification

1. The responses of single nucleus of the solitary tract (NST) neurons in the hamster were recorded to an array of Na+ and non-Na+ stimuli under each of three adaptation conditions: distilled H2O, 0.032 M NaCl, and 10 microM amiloride. Each adapting solution flowed for 60 s before delivery of one of seven test stimuli: 0.032 M NaCl, NaNO3, and Na-gluconate, 0.1 M KCl and sucrose, 1 mM HCl, and 3 mM quinine hydrochloride (QHCl). Stimuli were dissolved in distilled H2O (H2O and NaCl adaptation conditions) or 10 microM amiloride (amiloride adaptation condition). 2. Both amiloride treatment and NaCl adaptation reduced responses to the Na+ stimuli. The effects of NaCl adaptation were generally greater than those of amiloride, and the responses to the Na+ salts were reduced by NaCl adaptation in every cell that responded to NaCl, regardless of its best-stimulus classification. Amiloride treatment suppressed the responses to Na+ salts with larger anions (NaNO3 and Na-gluconate) more than the response to NaCl. 3. Unlike amiloride treatment, NaCl adaptation also reduced responses to several non-Na+ stimuli (KCl, HCl, and QHCl). This effect occurred primarily in the NaCl-best neurons that were most highly responsive to NaCl and that showed a postexcitatory suppression after NaCl. This suppression has been observed in recordings from the chorda tympani nerve in both rats and hamsters and in taste receptor cell responses recorded in situ in the rat. If it is a receptor phenomenon, these data would imply that some NaCl-sensitive receptor cells are also responsive to these non-Na+ electrolytes. 4. The effects of amiloride on the responses to Na+ stimuli were not limited to NaCl-best neurons, but occurred in sucrose-best cells as well. These results suggest that the sucrose-best cells in the NST receive converging input from sucrose- and NaCl-best chorda tympani fibers, because there is little Na+ sensitivity in the peripheral sucrose-best fibers and the amiloride sensitivity is restricted to NaCl-best chorda tympani fibers. The responses to NaCl in the few HCl- and QHCl-best NST neurons were not affected by amiloride. 5. Rinsing the tongue with amiloride for 60 s resulted in a reduction in the baseline response rate of NST cells. This effect occurred primarily in NaCl- and sucrose-best NST neurons and implies that much of the spontaneous activity in these brain stem cells arises from amiloride-sensitive channel activity in the peripheral receptor cells. 6. The results of human psychophysical studies show very different effects of NaCl adaptation and amiloride treatment. Adaptation to NaCl produces a robust and specific reduction in the saltiness of all salts. The present results show that NaCl adaptation reduces the responses of all cells sensitive to NaCl. Treatment of the human tongue with amiloride produces a proportionately smaller reduction in the response to NaCl than it does in rodents, and it appears to have no effect on saltiness. Rather, amiloride has been shown to specifically reduce the sour side taste of NaCl, Nagluconate, and LiCl. Therefore conclusions about the effects of amiloride on taste quality based on rodent electrophysiology are questionable.

An analysis of the time course of gustatory neural adaptation in the rat

1975 ◽  
Vol 229 (4) ◽  
pp. 1134-1140 ◽  
Author(s):  
DV Smith ◽  
JW Steadman ◽  
CN Rhodine
Keyword(s):  
Transient Response ◽  
Time Course ◽  
Taste Receptor ◽  
Constant Term ◽  
Fast Time ◽  
Adaptation Process ◽  
Chorda Tympani ◽  
Chorda Tympani Nerve ◽  
Nacl Concentration ◽  
Neural Discharge

Neural responses were recorded from the rat chorda tympani nerve following stimulation of the tongue with several concentrations of NaCl. These responses were integrated using a fast time constant (47 ms), and the time course of the decline in neural discharge from the peak of the transient response was computer analyzed. The time course of the adaptation process was described by a constant term and two exponentially decaying components, which most likely reflect the existence of two separate mechanisms contributing to the adaptation process in taste. The constant term and the amplitude of the second gradual exponential decay were correlated with NaCl concentration, whereas the amplitude of the initial rapidly declining exponential component was independent of stimulus intensity. The initial transient response of the chorda tympani nerve may be a function of the rate of stimulus adsorption, whereas the gradual second decline in the neural response may reflect an adaptive mechanism of the taste receptor cell.

Functional recovery of the gustatory system after sodium deprivation during development: how much sodium and where

1990 ◽  
Vol 259 (4) ◽  
pp. R786-R791 ◽  
Author(s):  
P. Przekop ◽  
D. G. Mook ◽  
D. L. Hill
Keyword(s):  
Receptor Cell ◽  
Taste Receptor ◽  
Dietary Sodium ◽  
Chorda Tympani ◽  
Gustatory System ◽  
Chorda Tympani Nerve ◽  
Single Exposure ◽  
Multiple Generations ◽  
Receptor Cells ◽  
Taste Stimulation

Restriction of maternal dietary sodium beginning on or before embryonic day 8 and continued thereafter results in reduced taste responses of the chorda tympani nerve to NaCl in the offspring. The effects of deprivation, however, are reversible. A single ingestive bout of 30 ml isotonic NaCl was sufficient to restore normal sodium taste, and the restorative effects of the single exposure apparently persisted throughout multiple generations of taste receptor cells. Furthermore, the recovery apparently did not depend on direct receptor cell-stimulus interactions. Rats permitted to drink 30 ml of isotonic NaCl, but not allowed to retain it, did not recover normal sodium taste responses, suggesting that factors other than taste stimulation are important in the restorative effects of sodium.

scholarly journals Changes in taste receptor cell [Ca2+]i modulate chorda tympani responses to salty and sour taste stimuli

2012 ◽  
Vol 108 (12) ◽  
pp. 3206-3220 ◽  
Author(s):  
John A. DeSimone ◽  
ZuoJun Ren ◽  
Tam-Hao T. Phan ◽  
Gerard L. Heck ◽  
Shobha Mummalaneni ◽  
...  
Keyword(s):  
Apical Membrane ◽  
Receptor Cell ◽  
Imaging Techniques ◽  
Taste Receptor ◽  
Chorda Tympani ◽  
Taste Receptor Cell ◽  
Atpase Inhibitor ◽  
Acetoxymethyl Ester ◽  
Phasic Response ◽  
Sour Taste

The relationship between taste receptor cell (TRC) Ca2+ concentration ([Ca2+]i) and rat chorda tympani (CT) nerve responses to salty [NaCl and NaCl+benzamil (Bz)] and sour (HCl, CO2, and acetic acid) taste stimuli was investigated before and after lingual application of ionomycin+Ca2+, 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid acetoxymethyl ester (BAPTA-AM), U73122 (phospholipase C blocker), and thapsigargin (Ca2+-ATPase inhibitor) under open-circuit or lingual voltage-clamp conditions. An increase in TRC [Ca2+]i attenuated the tonic Bz-sensitive NaCl CT response and the apical membrane Na+ conductance. A decrease in TRC [Ca2+]i enhanced the tonic Bz-sensitive and Bz-insensitive NaCl CT responses and apical membrane Na+ conductance but did not affect CT responses to KCl or NH4Cl. An increase in TRC [Ca2+]i did not alter the phasic response but attenuated the tonic CT response to acidic stimuli. A decrease in [Ca2+]i did not alter the phasic response but attenuated the tonic CT response to acidic stimuli. In a subset of TRCs, a positive relationship between [H+]i and [Ca2+]i was obtained using in vitro imaging techniques. U73122 inhibited the tonic CT responses to NaCl, and thapsigargin inhibited the tonic CT responses to salty and sour stimuli. The results suggest that salty and sour taste qualities are transduced by [Ca2+]i-dependent and [Ca2+]i-independent mechanisms. Changes in TRC [Ca2+]i in a BAPTA-sensitive cytosolic compartment regulate ion channels and cotransporters involved in the salty and sour taste transduction mechanisms and in neural adaptation. Changes in TRC [Ca2+]i in a separate subcompartment, sensitive to inositol trisphosphate and thapsigargin but inaccessible to BAPTA, are associated with neurotransmitter release.

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