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S A Simon

Publications and source records attributed to S A Simon.

At least 91 records · Page 5Linked to original sources
PubMed1992

Astringent-tasting compounds alter ion transport across isolated canine lingual epithelia.

The effects of acid and astringent compounds on ion transport across isolated canine lingual epithelia were measured in an Ussing chamber. Lowering the pH from 7.4 to 3.2 decreases ion transport, as measured by the short-circuit current (Isc), when the dorsal surface of the tongue is bathed in 0.5 M NaCl and increases Isc when it is bathed in 0.05 M NaCl, tannic acid (0.1 M) inhibits Isc at both pH 3.2 and 7.4. At 0.05 M NaCl, pH 7.4 tannic acid also inhibits Isc. Thus, inhibition of Isc by tannic acid does not depend upon the pH, meaning that the reduction in transport arises from tannic acid. In the presence of NaCl (at both 0.05 and 0.5 M NaCl), 0.1 M AlK (SO4)2 or 0.1 M AlNH4(SO4)2 also inhibit Isc. For these salts, the decrease in Isc arises from the aluminum ion and not from K+, NH4+, or SO(4-)-. Other less astringent compounds (gallic and tartaric acids) had only slight effects on Isc. The main findings of this study are that both tannic acid and the aluminum salts inhibited ion transport, likely Na+ influx, via amiloride-inhibitable channels in isolated lingual epithelia. Inhibition of such Na+ channels may contribute to astringent taste.

Aluminum↗
PubMed1992

Modulation of the interbilayer hydration pressure by the addition of dipoles at the hydrocarbon/water interface.

The effects of the cholesterol analog 5 alpha-cholestan-3 beta-ol-6-one (6-ketocholestanol) on bilayer structure, bilayer cohesive properties, and interbilayer repulsive pressures have been studied by a combination of x-ray diffraction, pipette aspiration, and dipole potential experiments. It is found that 6-ketocholestanol, which has a similar structure to cholesterol except with a keto moiety at the 6 position of the B ring, has quite different effects than cholesterol on bilayer organization and cohesive properties. Unlike cholesterol, 6-ketocholestanol does not appreciably modify the thickness of liquid-crystalline egg phosphatidylcholine (EPC) bilayers, and causes a much smaller increase in bilayer compressibility modulus than does cholesterol. These data imply that 6-ketocholestanol has both its hydroxyl and keto moieties situated near the water-hydrocarbon interface, thus making its orientation in the bilayer different from cholesterol's. The addition of equimolar 6-ketocholestanol into EPC bilayers increases the magnitude, but not the decay length, of the exponentially decaying repulsive hydration pressure between adjacent bilayers. Incorporation of equimolar 6-ketocholestanol into EPC monolayers increases the dipole potential by approximately 300 mV. These data are consistent with our previous observation that the magnitude of the hydration pressure is proportional to the square of the dipole potential. These results mean that 6-ketocholestanol, despite its location in the bilayer hydrocarbon region, approximately 10 A from the physical edge of the bilayer, modifies the organization of interlamellar water. We argue that the incorporation of 6-ketocholestanol into EPC bilayers increases the hydration pressure, at least in part, by increasing the electric field strength in the polar head group region.

Ketocholesterols↗
PubMed1991

Surface ripples cause the large fluid spaces between gel phase bilayers containing small amounts of cholesterol.

Previous studies have found that small concentrations of cholesterol, or several other molecules such as benzene and asialoganglioside, dramatically increase the fluid separation between gel phase phosphatidylcholine bilayers. These observations can not be explained in terms of changes in the repulsive and attractive pressures known to exist between flat gel phase bilayer surfaces. We show here that the increase in fluid space occurs as a consequence of cholesterol inducing large periodic ripples in the plane of the bilayer. The analysis of Mortensen et al. (Biochim. Biophys. Acta 945, 221-245) indicates that the sides of the ripples primarily contain gel phase phosphatidylcholine, whereas the apices are enriched in cholesterol and are liquid-crystalline. We argue that the large fluid spaces can be explained by steric repulsion between adjacent bilayers caused both by thermally induced accordion-like motions of these ripples and defects in the ripple organization. In addition, ripples potentially can decrease van der Waals attraction and change hydration repulsion between bilayers.

Chemical Phenomena↗
PubMed1991

Lipid bilayer and water proton magnetization transfer: effect of cholesterol.

Magnetization transfer between macromolecules and water can be a significant factor contributing to tissue water 1H relaxation. Using saturation transfer techniques, the degree of magnetization transfer between the macromolecular matrix and bulk water 1H can be directly measured and magnetization transfer contrast (MTC) can be generated in MR images. A significant degree of MTC has been observed in tissues with high plasma membrane content such as kidney and brain. The purpose of this study was to establish whether lipid bilayers, as models for cell membranes, could exchange magnetization with the water solvent and whether this effect could contribute to MTC observed in intact tissues. Magnetization transfer was measured in aqueous dispersions of egg phosphatidylcholine (EPC) in the presence and absence of cholesterol. It was found that neither EPC bilayers nor cholesterol by themselves significantly exchanged magnetization with bulk water 1H. However, as the concentration of cholesterol was increased, the pseudo-first-order magnetization exchange rate increased to a maximum value of approximately 1 s-1. The cholesterol-induced 1H magnetization exchange may be related either to longer correlation times of the lipid or to an increase in the number of water molecules associated with the bilayer. These results indicate that EPC-cholesterol bilayers exchange 1H magnetization with bulk water. These results are consistent with lipid bilayer contributions to bulk water relaxation and MTC in intact biological tissues.

Animals↗
PubMed1991

Electrophysiological responses to non-electrolytes in lingual nerve of rat and in lingual epithelia of dog.

Epithelial and neural mechanisms underlying the trigeminal chemoreception of non-electrolytes were investigated in whole-nerve recordings from lingual nerve and in Ussing-chamber studies of isolated lingual epithelia. The non-electrolytes included menthol, amyl acetate, phenethyl alcohol, toluene, methanol, ethanol, propanol, butanol, hexanol and octanol. They produced different lingual nerve responses: methanol and ethanol only increased ongoing activity; longer-chain alcohols initially increased but then suppressed activity below baseline; phenethyl alcohol and toluene only suppressed activity. Their threshold concentrations for lingual nerve responses, with the exception of menthol, were proportional to the octanol:water partition coefficients of the stimuli. The threshold concentration for menthol was significantly lower than predicted by this coefficient. Calculation of the free energy of transfer from the threshold concentrations for the n-alcohols suggests that they undergo partition into a hydrophobic environment such as is found in lipid bilayers. Lanthanum chloride, which inhibited lingual nerve responses to hydrophilic compounds, presumably by blocking their diffusion across tight junctions, did not inhibit responses to these non-electrolytes. At high concentrations, hexanol acted as an anaesthetic in that the lingual nerve no longer responded to thermal and chemical stimuli whereas ethanol, which only increased lingual nerve activity, did not inhibit those responses. Epithelial transport, as indicated by the short-circuit current (Isc) measured across tongues bathed in symmetrical solutions of Krebs-Henseleit buffer, was reversibly inhibited by ethanol, hexanol, octanol, phenyl ethanol and menthol. The stimulus concentration necessary to inhibit 50% of the Isc decreased with increasing octanol:water partition coefficient.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1991

Trigeminal nerve responses in the rat elicited by chemical stimulation of the tongue.

Epithelial and neural mechanisms underlying trigeminal chemoreception were investigated by recording lingual nerve responses to chemical stimulation of the tongue. The chloride salts, NaCl, KCl, NH4Cl, and CaCl2, each elicited distinctly different, integrated whole-nerve responses (thresholds, 0.5-2.0 M). Incubation of the tongue with lanthanum (2.5 mM), which reduces the permeability of epithelial tight junctions, reversibly attenuated these salts responses. It did not affect neural responses to mechanical and thermal stimuli. Incubation with other established transport inhibitors--amiloride, tetra-ethyl ammonium or tetrodotoxin, had no effect on the salt responses. Acetic and hydrochloric acids (thresholds, 0.1-1.0 M), and MgCl2 and BaCl2 (greater than or equal to 0.5 M), also elicited distinctive responses. Other salts, MgSO4, Na isethionate and LaCl3 (greater than or equal to 1.0 M), and also ethanol (4 M), capsaicin (100 mM), nicotine (29.6 mM) and dextrose (0.5-2.5 M), did not elicit responses. These results indicate that ions of selected salts can diffuse through the tight junctions of the lingual epithelium to activate the trigeminal nerve, and suggest that both the cation and the anion may be important in determining if the nerves are activated and the wave-form of the responses.

Amiloride↗
PubMed1991

The hydration pressure between lipid bilayers. Comparison of measurements using x-ray diffraction and calorimetry.

The hydration pressure between dipalmitoyl phosphatidyl-N,N-dimethylethanolamine (DPPE-Me2) bilayers has been analyzed by both x-ray diffraction measurements of osmotically stressed liposomes and by differential scanning calorimetry. By the x-ray method, we obtain a magnitude (Po) and decay length (lambda) for the hydration pressure which are both quite similar to those found for bilayers of other zwitterionic lipids, such as phosphatidylcholines. That is, x-ray analysis of DPPE-Me2 in the gel phase gives lambda = 1.3 A, the same as that previously measured for the analogous gel phase lipid dipalmitoylphosphatidylcholine (DPPC), and Po = 3.9 x 10(9) dyn/cm2, which is in excellent agreement with the value of 3.6 x 10(9) dyn/cm2 calculated from the measured Volta potential of DPPE-Me2 monolayers in equilibrium with liposomes. These results indicate that the removal of one methyl group to convert DPPC to DPPE-Me2 does not markedly alter the range or magnitude of the hydration pressure. Calorimetry shows that the main gel to liquid-crystalline phase transition temperature of DPPE-Me2 is approximately constant for water contents ranging from 80 to 10 water molecules per lipid molecule, but increases monotonically with decreasing water content below 10 waters per lipid. A theoretical fit to these temperature vs. water content data predicts lambda = 6.7 A. The difference in observed values of lambda for x-ray and calorimetry measurements can be explained by effects on the thermograms of additional intra- and intermolecular interactions which occur at low water contents where apposing bilayers are in contact. We conclude that, although calorimetry provides important data on the energetics of bilayer hydration, it is difficult to obtain quantitative information on the hydration pressure from this technique.

Biophysical Phenomena↗
PubMed1990

The anion in salt taste: a possible role for paracellular pathways.

It is well established from psychophysical and electrophysiological measurements that both Na and Cl contribute to the taste response to NaCl. The contribution of Na to the NaCl response can be studied using amiloride, a drug that inhibits Na transport in taste and other epithelial cells. The pathways involved in response to Cl are less well understood. We undertook a series of experiments in the rat to determine whether tonic chorda tympani responses to NaCl are inhibited by specific inhibitors of anion transport. Whole nerve responses to NaCl were unchanged by bathing the tongue in SITS, DIDS, bumetanide, furosemide, 9-anthracene carboxylic acid, or an antibody that blocks Cl conductance pathways in many epithelia. Thus, Cl co-transporters, exchangers, and channels (at least in the apical membrane of taste cells) are probably not involved in NaCl taste responses. When other anions (acetate, isethionate, methane sulfonate, gluconate, tartrate), which are generally impermeant in other Cl-selective pathways, were substituted for Cl, the dose-response curves for the chorda tympani response were shifted toward higher concentrations than the response to NaCl, but achieved the same maximum value at sufficiently high concentrations (1.0 M Na). For all the organic Na salts, the amiloride-insensitive portion of the response was substantially less than for NaCl. Experiments with Na acetate at different pHs showed that intracellular acidification is not responsible for the differences between NaCl and organic salts of Na. One possibility which remains is that apical stimulation with these other Na salts results in a taste cell membrane potential that is hyperpolarized with respect to the membrane potential in NaCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1990

Interactions between charged, uncharged, and zwitterionic bilayers containing phosphatidylglycerol.

Pressure vs. distance relationships have been obtained for phosphatidylglycerol bilayers, in both charged and uncharged states. Water was removed from the lipid multilayers by the application of osmotic pressures in the range of 0-2.7 x 10(9) dyn/cm2, and the distance between adjacent bilayers was obtained from Fourier analysis of lamellar x-ray diffraction data. For phosphatidylglycerol bilayers made electrically neutral either by lowering the pH or by adding equimolar concentrations of the positively charged lipid stearylamine, the pressure-distance data could be fit with a single exponential. The measured decay lengths were 1.1 A at low pH and 1.5 A with stearylamine, which are similar to decay lengths of the hydration pressure found for gel phases of other neutral bilayers. In addition, the magnitude of this repulsive pressure was proportional to the square of the Volta potential (equivalent to the dipole potential for electrically neutral bilayers) measured in monolayers in equilibrium with bilayers, in agreement with results previously found for the hydration pressure between phosphatidylcholine bilayers. For charged phosphatidylglycerol bilayers, the pressure-distance relation had two distinct regions. For bilayer separations greater than 10 A, the pressure-distance data had an exponential decay length (11 A) and a magnitude consistent with that expected for electrostatic repulsion from double-layer theory. For bilayer separations of 2-10 A, the pressure decayed much more rapidly with increasing bilayer separation (decay length less than 1 A). We interpret these data at low bilayer separations in terms of a combination of hydration repulsion and steric hindrance between the lipid head groups and the sodium ions trapped between apposing bilayers.

Amines↗
PubMed1989

Range of the solvation pressure between lipid membranes: dependence on the packing density of solvent molecules.

Well-ordered multilamellar arrays of liquid-crystalline phosphatidylcholine and equimolar phosphatidylcholine-cholesterol bilayers have been formed in the nonaqueous solvents formamide and 1,3-propanediol. The organization of these bilayers and the interactions between apposing bilayer surfaces have been investigated by X-ray diffraction analysis of liposomes compressed by applied osmotic pressures up to 6 X 10(7) dyn/cm2 (60 atm). The structure of egg phosphatidylcholine (EPC) bilayers in these solvents is quite different than in water, with the bilayer thickness being largest in water, 3 A narrower in formamide, and 6 A narrower in 1,3-propanediol. The incorporation of equimolar cholesterol increases the thickness of EPC bilayers immersed in each solvent, by over 10 A in the case of 1,3-propanediol. The osmotic pressures of various concentrations of the neutral polymer poly(vinylpyrrolidone) dissolved in formamide or 1,3-propanediol have been measured with a custom-built membrane osmometer. These measurements are used to obtain the distance dependence of the repulsive solvation pressure between apposing bilayer surfaces. For each solvent, the solvation pressure decreases exponentially with distance between bilayer surfaces. However, for both EPC and EPC-cholesterol bilayers, the decay length and magnitude of this repulsive pressure strongly depend on the solvent. The decay length for EPC bilayers in water, formamide, and 1,3-propanediol is found to be 1.7, 2.4, and 2.6 A, respectively, whereas the decay length for equimolar EPC-cholesterol bilayers in water, formamide, and 1,3-propanediol is found to be 2.1, 2.9, and 3.1 A, respectively. These data indicate that the decay length is inversely proportional to the cube root of the number of solvent molecules per unit volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol↗
PubMed1989

Cholesterol modifies the short-range repulsive interactions between phosphatidylcholine membranes.

Pressure versus distance relationships have been obtained for egg phosphatidylcholine bilayers containing a range of cholesterol concentrations. Water was removed from between adjacent bilayers by the application of osmotic pressures in the range of 0.4-2600 atm (4 x 10(5)-2.6 x 10(9) dyn/cm2), and the distance between adjacent bilayers was obtained by Fourier analysis of X-ray diffraction data. For applied pressures up to about 50 atm and bilayer surface separations of 15-5 A, the incorporation of up to equimolar cholesterol has little influence on plots of pressure versus bilayer separation. However, for the higher applied pressures, cholesterol reduces the interbilayer separation distance by an amount that depends on the cholesterol concentration in the bilayer. For example, the incorporation of equimolar cholesterol reduces the distance between bilayers by as much as 6 A at an applied pressure of 2600 atm. At this applied pressure, electron density profiles show that the high-density head-group peaks from apposing bilayers have merged. This indicates that equimolar concentrations of cholesterol spread the lipid molecules apart in the plane of the bilayer enough to allow the phosphatidylcholine head groups from apposing bilayers to interpenetrate as the bilayers are squeezed together. All of these X-ray and pressure-distance data indicate that, by reducing the volume fraction of phospholipid head groups, cholesterol markedly reduces the steric repulsion between apposing bilayers but has a much smaller effect on the sum of the longer ranged repulsive hydration and fluctuation pressures. Increasing concentrations of cholesterol monotonically increase the dipole potential of egg phosphatidylcholine monolayers, from 415 mV with no cholesterol to 493 mV with equimolar cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol↗
PubMed1989

Morphology of fungiform papillae in canine lingual epithelium: location of intercellular junctions in the epithelium.

The localization and structure of intercellular junctions and barriers in the extragemmal epithelium of canine fungiform papillae were determined by using both morphological and electrophysiological methods. Gap junctions were located in all epithelial strata with the exception of the stratum corneum, suggesting that the epithelium functions as a syncytium. The extracellular space of the stratum corneum was composed of a discontinuous, three-dimensional network of tight junctions, modified desmosomes, and lamellar bodies. A zonula occludens, which stops the penetration of lanthanum, is present in the uppermost layer of the stratum granulosum. In freeze-fracture replicas, tight junctions appear as extended networks of ridges of variable thickness on the PF fracture face and complementary grooves on the EF fracture face. The relatively high resistance pathway resulting from the layers of corneocytes and networks of tight junctions and lamellar bodies in the stratum corneum is bypassed by the low-resistance pathway provided by the taste pore.

Animals↗
PubMed1989

Repulsive interactions between uncharged bilayers. Hydration and fluctuation pressures for monoglycerides.

Pressure versus distance relations have been obtained for solid (gel) and neat (liquid-crystalline) phase uncharged lipid bilayers by the use of x-ray diffraction analysis of osmotically stressed monoglyceride aqueous dispersions and multilayers. For solid phase monoelaidin bilayers, the interbilayer repulsive pressure decays exponentially from a bilayer separation of approximately 7 A at an applied pressure of 3 x 10(7) dyn/cm2 to a separation of approximately 11 A at zero applied pressure, where an excess water phase forms. The decay length is approximately 1.3 A, which is similar to the value previously measured for gel phase phosphatidylcholine bilayers. This implies that the decay length of the hydration pressure does not depend critically on the presence of zwitterionic head groups in the bilayer surface. For liquid-crystalline monocaprylin, the repulsive pressure versus distance curve has two distinct regions. In the first region, for bilayer separations of approximately 3-8 A and applied pressures of 3 x 10(8) to 4 x 10(6) dyn/cm2, the pressure decays exponentially with a decay length of approximately 1.3 A. In the second region, for bilayer separations of approximately 8-22 A and applied pressures of 4 x 10(6) to 1 x 10(5) dyn/cm2, the pressure decays much more gradually and is inversely proportional to the cube of the distance between bilayers. These data imply that two repulsive pressures operate between liquid-crystalline monocaprylin bilayers, the hydration pressure, which dominates at small (3-8 A) bilayer separations, and the fluctuation pressure, which dominates at larger bilayer separations (greater than 8 A) and strongly influences the hydration properties of the liquid-crystalline bilayers. Thus, due primarily to thermally induced fluctuations, monocaprylin bilayers imbibe considerably more water than do monoelaidin bilayers. For both monoelaidin andmonocaprylin, the measured magnitude of the hydration pressure is found to be proportional to the square of the dipole potential.

Glycerides↗
PubMed1989

Magnitude of the solvation pressure depends on dipole potential.

As polar surfaces in solvent are brought together, they experience a large repulsive interaction, termed the solvation pressure. The solvation pressure between rough surfaces, such as lipid bilayers, has been shown previously to decay exponentially with distance between surfaces. In this paper, we compare measured values of the solvation pressure between bilayers and the dipole potential for monolayers in equilibrium with bilayers. For a variety of polar solvents and lipid phases, we find a correlation between the measured solvation pressures and dipole potentials. Analysis of the data indicates that the magnitude of the solvation pressure is proportional to the square of the dipole potential. Our experiments also show that the oriented dipoles in the lipid head-group region, including those of both the lipid and solvent molecules, contribute to the dipole potential. We argue that (i) the field produced by these interfacial dipoles polarizes the interbilayer solvent molecules giving rise to the solvation pressure and (ii) both the solvation pressure and the dipole potential decay exponentially with distance from the bilayer surface, with a decay constant that depends on the packing density of the interbilayer solvent molecules (1-2 A in water). These results may have importance in cell adhesion, adsorption of proteins to membranes, characteristics of channel permeability, and the interpretation of electrokinetic experiments.

Lipid Bilayers↗
PubMed1989

The structural organization and protein composition of lens fiber junctions.

The structural organization and protein composition of lens fiber junctions isolated from adult bovine and calf lenses were studied using combined electron microscopy, immunolocalization with monoclonal and polyclonal anti-MIP and anti-MP70 (two putative gap junction-forming proteins), and freeze-fracture and label-fracture methods. The major intrinsic protein of lens plasma membranes (MIP) was localized in single membranes and in an extensive network of junctions having flat and undulating surface topologies. In wavy junctions, polyclonal and monoclonal anti-MIPs labeled only the cytoplasmic surface of the convex membrane of the junction. Label-fracture experiments demonstrated that the convex membrane contained MIP arranged in tetragonal arrays 6-7 nm in unit cell dimension. The apposing concave membrane of the junction displayed fracture faces without intramembrane particles or pits. Therefore, wavy junctions are asymmetric structures composed of MIP crystals abutted against particle-free membranes. In thin junctions, anti-MIP labeled the cytoplasmic surfaces of both apposing membranes with varying degrees of asymmetry. In thin junctions, MIP was found organized in both small clusters and single membranes. These small clusters also abut against particle-free apposing membranes, probably in a staggered or checkerboard pattern. Thus, the structure of thin and wavy junctions differed only in the extent of crystallization of MIP, a property that can explain why this protein can produce two different antibody-labeling patterns. A conclusion of this study is that wavy and thin junctions do not contain coaxially aligned channels, and, in these junctions, MIP is unlikely to form gap junction-like channels. We suggest MIP may behave as an intercellular adhesion protein which can also act as a volume-regulating channel to collapse the lens extracellular space. Junctions constructed of MP70 have a wider overall thickness (18-20 nm) and are abundant in the cortical regions of the lens. A monoclonal antibody raised against this protein labeled these thicker junctions on the cytoplasmic surfaces of both apposing membranes. Thick junctions also contained isolated clusters of MIP inside the plaques of MP70. The role of thick junctions in lens physiology remains to be determined.

Animals↗
PubMed1989

Activation by saccharides of a cation-selective pathway on canine lingual epithelium.

Responses of isolated canine lingual epithelium in an Ussing chamber to D-glucose and fructose reveal events associated with taste transduction. With the use of isotopic flux studies, together with ion substitution and pharmacological and voltage clamp measurements, it was found that the stimulation of ion transport by D-glucose arises from an increase in the influx of cations through a cation-selective pathway. This influx of cations is completely inhibited by 0.1 mM amiloride. The stimulation of transport by fructose in 0.05 M KCl and by D-glucose in 0.05 M RbCl was also inhibited by amiloride, demonstrating that the saccharide-stimulated entry pathway was specific for neither hexose sugars nor for Na. Saccharide stimulation of canine lingual epithelia does not appear to be modulated by increases in intracellular levels of adenosine 3',5'-cyclic monophosphate, guanosine 3',5'-cyclic monophosphate, or Ca. The Na that enters taste cells on saccharide stimulation exits them via the ouabain inhibitable Na+-K+-adenosinetriphosphatase located in the serosal membranes.

Amiloride↗
PubMed1988

Transport pathways in rat lingual epithelium.

Measurements of ion transport across isolated lingual epithelium of rat were correlated with electrophysiological recordings from taste nerves. At hyperosmotic concentrations of NaCl, sodium ions enter the mucosal membrane of the isolated epithelium partially through an amiloride-inhibitable pathway and exit the serosal membrane through a Na+-K+-ATPase. At hyposmotic concentrations of KCl, potassium ions enter the mucosal membrane through a K+ pathway that is inhibited by 4-aminopyridine and exit at the serosal membrane through a K+ pathway that is inhibited by BaCl2. The inhibition of sodium transport by amiloride and potassium transport by 4-aminopyridine is consistent with previously published electrophysiological recordings from the chorda tympani nerve bundle (CT) and recordings from nucleus of the solitary tract (NST) obtained here. The responses to NaCl are greater than the responses to KCl at equimolar concentrations over the entire concentration range both in epithelial and neural measurements. At hyposmotic concentrations of NaCl the epithelial responses include inward sodium and outward chloride components. Isolated rat tongue is only slightly stimulated by D-glucose or sucrose as are the CT and NTS responses. These data suggest that events in taste transduction can be understood, in part, by measuring the epithelial responses of isolated rat tongue.

4-Aminopyridine↗