The Perception of Saltiness is Eliminated by NaCl Adaptation: Implications for Gustatory Transduction and Coding

The tastes of salts to humans are complex. NaCl is the mostpurely salty of all salts, but even this stimulus tastes sweetat low concentrations and somewhat sour at mid-range intensities.Other salts taste significantly sour or bitter in addition tosalty. Previous studies have shown that the saltiness of simplehalide salts is reduced by adaptation to NaCl, suggesting thata single mechanism might be responsible for the salty tasteof these stimuli. In electrophysiological studies in rodents,the response to NaCl is reduced by application to the tongueof the Na⁺- channel blocker amiloride. Organic Na⁺ salts aremore heavily dependent on this amiloride-sensitive transductioncomponent than NaCl, and are generally less salty and more sour.In order to investigate the relationship between NaCl saltinessand that evoked by other salts, we adapted the tongue to distilledH₂O and to 0.1 M NaCl and obtained direct magnitude estimatesof the taste intensity of 15 organic and inorganic Na⁺, Li⁺,K⁺ and Ca²⁺ salts, matched for total intensity. Subjects dividedthese magnitude estimates among the component taste qualities.Adaptation to NaCl abolished the taste of NaCl and LiCl, andeliminated the saltiness of all other salts. The magnitude estimatesof the bitterness and sourness of many salts increased afterNaCI adaptation. Since recent biophysical data suggest thatadaptation in taste receptors may involve whole-cell mechanisms,we propose that saltiness is reduced by NaCl adaptation becauseit originates in the subset of taste receptors responsive toNaCl. This implies that saltiness is coded within the CNS incells whose receptive fields include the NaCl-sensitive receptorcells and that the degree to which any salt tastes salty isdetermined by its ability to drive these receptors. This modelproposes, for example, that KCl has a salty component becauseit stimulates some of the same receptor cells as NaCl, eventhough the transduction mechanisms for KCl are different thanthose engaged by NaCl. Adaptation to NaCl blocks the saltinessof KCl and other salts because they stimulate NaCl-sensitivereceptor cells. Chem. Senses 20: 545–557, 1995.     

Suppression of Bitterness by Sodium: Variation Among Bitter Taste Stimuli

Taste interactions between salts (NaCl, LiCl, KCl, L-arginine:L-asparticacid, Na-acetate and Na-gluconate) and bittertasting compounds(urea, quinine HCI, magnesium sulphate, KCI, amiloride HCI andcaffeine) were investigated. In each study binary combinationsof three or four concentrations of one bitter compound withfour concentrations (0, 0.1, 0.3 and 0.5 M) of one salt wererated for bitterness and saltiness using the method of magnitudeestimation. In most cases, perceived bitterness was suppressedby salts, although the degree of suppression varied. In general,bitterness suppression was not accompanied by an equivalentreciprocal suppression of saltiness. Only MgSO₄ and amiloridehad suppressing effects on the saltiness of NaCl at the intermediateconcentrations and no bitter compound affected the saltinessat the high concentrations of NaCl. Since salt suppressed thebitterness of urea effectively, a detailed analysis of suppressionof the bitterness of urea by different salts was conducted.Those studies indicated that the key component in this effectwas the sodium or lithium ion for two reasons: first, all threesodium salts and the lithium salt had a suppressive effect onbitterness, whereas KCl did not; secondly, the effect of a salton suppression of the bitterness of urea was independent ofits perceived saltiness; that is, NaCl, Na-acetate (which isperceived as less salty than NaCl), and Na-gluconate (whichis perceived as less salty than Na-acetate) reduced bitternesscomparably. These results suggest that there is a major peripheralcomponent to the suppression of the bitterness of urea, andperhaps other bitter tasting compounds, by sodium. Chem. Senses20: 609–623, 1995.     

Sensory irritation and taste produced by NaCl and citric acid: effects of capsaicin desensitization

Three experiments were conducted to measure the sensory irritationproduced by two prototypical gustatory stimuli: citric acidand NaCl. The stimuli were applied to the tip of the tongueon filter paper disks. The first experiment revealed that solutionsof NaCl and citric acid that produced approximately equal tastesensations also produced similar amounts of irritation; thatthe psychophysical functions for irritation were approximatelytwice as steep as the functions for taste; and that irritationgrew over time for NaCl but not for citric acid. When viewedas a percentage of the taste sensation at 25 s, NaCl irritationaveraged 23% at the lowest concentration and 70% at the highestconcentration; citric acid irritation averaged 44% at the lowestconcentration and 98% at the highest concentration. The secondexperiment investigated whether the irritation produced by thesetwo stimuli was mediated via capsaicin-sensitive (CS) fibers.The experiment included a pre-test, an irritation treatmentwith either capsaicin (a desensitizing agent) or zingerone (anon-desensitizing agent), a 15 min rest period and a post-test.Reductions in irritation and taste occurred following treatmentwith both capsaicin and zingerone. A third experiment demonstratedthat the majority of the effect of zingerone on taste and irritationwas due to a perceptual context effect. After the context effectwas taken into account, capsaicin desensitization remained significantfor both salt taste and salt irritation at the highest concentration.A similar pattern of results for citric acid suggests that bothcitric acid and NaCl produce irritation in part via CS fibers.The results are discussed in terms of the ability of subjectsto discriminate the gustatory and chemesthetic components oforal sensations and the role of salt and acid irritation inflavor perception.     

Effect of Amiloride on the Taste of NaCl, Na-gluconate and KCl in Humans: Implications for Na+ Receptor Mechanisms

Sodium-salt transduction in many species may be mediated byboth apical and submucosal ion channels on the taste receptorcell membrane. The apical ion channel is blockable by the diureticamiloride, whereas the submucosal pathway is not. Sodium saltswith small anions, such as NaCl, can stimulate submucosal aswell as apical ion channels; sodium salts with large anions,such as Na-gluconate, activate primarily the apical channels.In humans, reports on the effects of amiloride on the tasteof NaCl are conflicting and no data exist on the effects ofamiloride on organic sodium salts. In the present experiment,subjects gave magnitude estimates of the total intensity andof each of the basic taste qualtities for NaCl, Na-gluconateand KCl. Five concentrations of each of these stimuli were presentedto the anterior tongue following distilled water adaptationand after amiloride treatment. There was a significant decreasein the total taste intensity of NaCl and Na-gluconate afteramiloride, but no effect on KCl. The saltiness of all threesalts was unaffected, but amiloride decreased the preceivedsourness of the sodium salts. KCl sourness was unaffected byamiloride. There was a proportionately larger effect of amilorideon Na-gluconate than on Nacl, which is consistent with a largerrole for the apical ion channel in Na-gluconate transduction.However, an appreciable amiloride-insensitive component is presentfor both NaCl and Na-gluconate, suggesting that an amiloride-insensitivepathway also plays a role in the transduction of both sodiumsalts. These data support the hypothesis that an amiloride-sensitivetransduction component exists in humans, but suggest that itis considerably smaller than in many other species.     

THE EFFECT OF SALT REDUCTION ON TASTE PLEASANTNESS IN COOKED'BOLOGNA-TYPE'SAUSAGES

This study's objective was to study how much the salt (NaCl) content of cooked sausage can be reduced without violating the perceived taste pleasantness. The 34 assessors evaluated seven cooked sausages made with added salt concentrations of 1.05; 1.20; 1.35; 1.50; 1.65; 1.80 and 1.95%. A relative-to-standard scale was used for rating the saltiness and taste pleasantness. The saltiness and pleasantness intensity of different salt concentrations was rated against a reference sausage, which contained 1.5% added salt. A reference sample was also hidden among the samples. The assessors were able to rank sausages based on the saltiness into the right order. Based on taste pleasantness, there was no significant difference between the sausages made with 1.35; 1.50; 1.65; 1.80 or 1.95% added salt (p>0.05). Several differences were, however, detected among the saltiness levels. The results of this study suggest that it might be possible to reduce the salt content of cooked sausage to 1.35% added salt.     

Amiloride Effects on Taste Quality: Comparison of Single and Multiple Response Category Procedures

Although there is compelling evidence that amiloride reducesthe intensity of Na⁺ and Li⁺ salts in humans, its effects onsaltiness are conflicting. Many salts elicit not only a saltytaste but also one or more side tastes (sweetness, sournessor bitterness). Some studies have shown a suppression of saltinessby amiloride; others show no effect on saltiness but a significantreduction in sourness. In the experiments demonstrating a reductionof saltiness, subjects estimated only saltiness; in those showingan amiloride effect on sourness and not saltiness, subjectsestimated all qualities on each trial. The present study examinesthe role of the psychophysical method in these conflicting results.We have investigated the effects of amiloride on taste qualityby modifying only the instructions to the subjects, keepingall other variables constant. One group of subjects (intensity-only)gave magnitude estimates of the overall intensity of a LiCIconcentration series. A second group (salty-only) was instructedto estimate the saltiness of the stimuli, and a third group(sour-only) estimated their sourness. Finally, a fourth group(profile) rated all of the taste qualities on each stimuluspresentation, using a modified taste profile method. The ratingsof all groups were made comparable by the use of 0.1 mM quinine-HCIas a modulus. When subjects used only one response category,amiloride reduced their estimates (of intensity, saltiness orsourness), but if subjects attended to all four qualities, amiloridespecifically reduced the sourness of LJCI and had no significanteffect on its saltiness. Comparison of the saltiness estimatesof the salty-only group to the sum of the salty and sour estimatesof the profile group demonstrated that subjects combined thesesensations when presented with only one response alternative.To reveal the effect of amiloride on a specific quality of asalt, the psychophysical method must allow subjects to attendto all qualities on each trial. These data and previous resultssuggest that apical Na⁺ channels on the taste receptor cellmembrane mediate the sourness but not the saltiness of Na⁺ andLi⁺ salts. Chem. Senses 22: 267–275, 1997.     

Resolution of non-activated and activated androgen receptors based on differences in their hydrodynamic properties

This study shows that cytosolic androgen receptor of rat ventral prostate sediments at 10-11 S on conventional low salt sucrose density gradients (SDG), and at 4.6 S on high salt SDG, whether it is activated or not; inclusion of 10 mM Na2MoO4 in all buffers does not alter these sedimentation coefficients. In the presence of 50 mM Na2MoO4 non-activated and activated androgen receptors sediment in high salt SDG at 7-8 S and 4.6 S, respectively. Thus the presence of high concentrations of molybdate during centrifugation inhibits the KCl induced disaggregation of receptor into subunits. Similar effects are observed on Sephacryl-S200 gel filtration; in 50 mM MoO2-4 and 0.4 M KCl non-activated receptor has an estimated Stokes radius of 67 A; this value decreases to 52 A upon activation in the presence of proteolysis inhibitors; omission of molybdate during chromatography yielded 52 A and 27 A entities. Estimated mol. wts are 198,000 Daltons for the non-activated 67 A form and 98,000 Daltons for the activated 52 A receptor. Sodium molybdate (50 mM) prevents temperature (18 degrees C) and high ionic strength (0.4 M KCl) induced receptor activation. This inhibition was overcome by removing molybdate by centrifugal gel filtration, or by increasing the KCl concentration to 0.8 M. The inhibitory effects of molybdate on salt induced receptor disaggregation into activated subunits are no longer observed at pH greater than 7.4 or after chemical modification of sulfhydryl groups. Once androgen receptor has been disaggregated into its activated subunits the activated state is maintained even upon reassociation to 10-11 S aggregates in low salt. The relative concentrations of KCl and molybdate are critical; thus, 10 mM Na2MoO4/0.4 M KCl and 50 mM Na2MoO4/0.8-1.2 M KCl did not differentiate activated from non-activated androgen receptor based on their hydrodynamic properties. In the presence of 0.4 M KCl and 50 mM molybdate, however, the hydrodynamic properties of androgen receptor can be correlated with receptor activation.     

Nutrition and growth of the moderately halophilic bacteria Micrococcus morrhuae K-17 and Micrococcus luteus K-15

Chemically defined media have been developed for the growth of two moderately halophilic bacteria, Micrococcus morrhuae K-17 and Micrococcus luteus K-15. M. morrhuae K-17 grows well in a synthetic medium (SM-1) which contains a number of salts, 0.21 M KCl, 2 M NaCl, D-mannose, five vitamins and ten amino acids. The synthetic medium (SM-2) for M. luteus K-15 contains a number of salts, 0.21 M KCl, 1 M NaCl, D-fructose, nine vitamins and nine amino acids. Nutritional studies show that M. morrhuae K-17 can utilize a large number of organic compounds as carbon and energy source while the ability of M. luteus K-15 in utilizing the organic compounds is rather limited. The minimum salt requirement is 0.5 M NaCl for both strains when growth at the optimum temperature of 30 degrees C. However, this requirement can be lowered to 0.2 M in M. luteus K-15 when grown at a lower temperature of 25 degrees C. It is concluded that the ability to grow in a wider range of salt concentrations in response to temperature is species specific in moderate halophiles. The salt range for growth to occur can be extended when cells of both strains are grown in complex medium which might provide the amino acids and growth factors that cannot be synthesized by these strains at high salt concentrations.     

Interaction of the hepatic glucocorticoid-receptor complex with Affigel blue

Summary Unlike the unactivated glucocorticoid-receptor complex, the thermally activated glucocorticoid-receptor complex was able to bind to Affigel blue (a matrix previously shown to bind proteins containing a dinucleotide fold region) under low ionic conditions (0.05 M KCl). Glucocorticoid-receptor complex binding capacity to Affigel blue was enhanced by increasing salt concentration. Optimal binding was obtained at 0.15 M KCl and remained at a plateau level up to 0.4 M KCl. In contrast to Affigel blue binding, glucocorticoid-receptor complex binding to nuclei was optimum at low ionic strength buffer, declined at 0.15 M KCl and became negligible at 0.4 M KCl. Interestingly, at physiological ionic strength (0.15 M KCl) both nuclei and Affigel blue bound to the glucocorticoid-receptor complex with almost identical capacity. Glucocorticoid-receptor complexes incubated 45 min at 25 °C (activation conditions) in the presence of 10 mM molybdate were unable to bind to Affigel blue (or isolated nuclei) as expected. The results obtained suggest that Affigel blue mimics isolated nuclei in the binding of activated glucocorticoid-receptor complexes under physiological (0.15 M KCl) conditions. In addition, Affigel blue may provide a rapid and easy method to study glucocorticoid-receptor complex activation and interaction with nuclear acceptor sites.     

Reduction of saltiness and bitterness after a chlorhexidine rinse

Chronic rinsing with chlorhexidine, an oral-antiseptic, has been shown to decrease the saltiness of NaCl and the bitterness of quinine. The effect of acute chlorhexidine on taste has not been investigated. The purpose of the present study was to examine the effect of acute chlorhexidine rinses on taste intensity and quality of 11 stimuli representing sweet, salt, sour, bitter and savory. All stimuli were first matched for overall intensity so the effects of chlorhexidine would be directly comparable across compounds. As a control treatment, the bitter taste of chlorhexidine digluconate (0.12%) was matched in intensity to quinine HCl, which was found to cross-adapt the bitterness of chlorhexidine. Subjects participated in four experimental conditions: a pre-test, a quinine treatment, a chlorhexidine treatment, and a post-test condition, while rating total taste intensity and taste qualities in separate test sessions. Relative to the quinine treatment, chlorhexidine was found to decrease the salty taste of NaCl, KCl and NH4Cl, and not to significantly affect the tastes of sucrose, monosodium glutamate (MSG), citric acid, HCl and the taste of water. The bitter taste of urea, sucrose octa-acetate and quinine were suppressed after chlorhexidine rinses relative to water rinses, but were only marginally suppressed relative to quinine rinses. Potential mechanisms are discussed.     

Effects of high concentration of salts on the esterase activity and structure of a kiwifruit peptidase, actinidain

Effects of salts on the activity and stability of actinidain were examined. With increasing salt concentration up to 0.5 M, the activity (kcat/Km) for N-alpha-Cbz-L-lysine p-nitrophenyl ester decreased to 40% of that in the absence of salt. The inhibitor constant Ki of LiCl, NaCl, and KCl was 0.16-0.43 M. With 3 M KCl and NaCl, the specificity constant kcat/Km recovered to 110 and 75%, respectively. No re-activation was observed with LiCl. The inhibition and re-activation were dependent on the changes in both Km and kcat, whereas no CD change was observed. The tryptophan fluorescence of actinidain was not affected by 0-0.5 M salt, but a considerable decrease in its intensity was observed with increasing salt concentration from 0.5 to 3.0 M. These results suggest that the inhibition observed with the lower salt concentration (<0.5 M) is due to attenuation of the electrostatic interaction between the enzyme and substrate, and the higher concentration (0.5-3.0 M) induces structural change in the states of tryptophan residues, which is associated with the re-activation. Actinidain keeps considerably high activity and stability even in the presence of 3 M salts.     

Amiloride alters lick rate responses to NaCl and KCl in rats

The role-of cation channels on taste cell membranes to salttaste sensation was assessed in rats. We measured the numberof licks during multiple 10-s presentations of NaCl and KClconcentrations (0.05, 0.09, 0.16, 0.28, 0.5 M) dissolved ineither water or in 100 µM amiloride, a sodium-channelblocker. The number of licks to water and 0.3 M sucrose wasalso measured. The number of licks to NaCl was significantlylower and the number of licks to KCl was significantly higherwhen these test solutions were dissolved in amiloride than inwater. There were no differences in lick responses to waterand sucrose. These results suggest that amiloride may have alteredthe taste of NaCl and KCl. The results are discussed in relationshipto prior electrophysiological studies characterizing the effectof amiloride in blocking salt responses of the chorda tympaninerve.     

Author index

Binding of dexamethasone · receptors with isolated nuclei, DNA-cellulose and cellulose has been compared with respect to dependence on salt concentration and resistance to KCl extraction and DNAase I digestion. A solution of cytoplasmic dexamethasone-receptor complexes was prepared by the incubation of rat thymus cells with steroid at 3°C and breaking the cells by hypotonic lysis. Activation of the complexes was accomplished by warming the solution at 25°C for 15 min. Activation significantly increased the ability of dexamethasone · receptors to bind to nuclei and DNA-cellulose but not to cellulose. Dexamethasone-receptor complexes bound to nuclei at 3°C are completely resistant to extraction with 0.1 M KCl, 76% resistant to 0.2 M KCl and 20% resistant to 0.4 M KCl. Dexamethasone · receptors bound to DNA-cellulose are 45% resistant to extraction with 0.1 M and 0.2 M KCl and 29% resistant to 0.4 M KCl extraction. Cellulose-bound dexamethasone · receptors are not resistant to any of these extractions. DNAase I treatment releases 60% of the dexamethasone · receptors bound to DNA-cellulose but only 13% of those bound to nuclei, though at least 60% of the nuclear DNA is solubilized. The presence of 0.15 M KCl decreases binding of activated dexamethasone · receptors to nuclei by 73% but to DNA-cellulose by only 17%. Pretreatment of nuclei with 0.1–0.4 M KCl reduces their capacity to bind activated dexamethasone · receptors by 90% whereas similar treatment reduces the capacity of DNA-cellulose to bind dexamethasone · receptors by only 29%. Nuclei extracted with 0.1 M KCl appear to have a limited capacity to accept dexamethasone · receptors. These studies demonstrate that binding of dexamethasone · receptors to nuclei and DNA-cellulose differs by (a) the higher resistance of nuclear complexes to KCl and DNAase I treatment; (b) the much greater sensitivity of nuclei to KCl treatment.     

Effect of ionic strength on the interaction of androgens with Sertoli cell nuclei.

Only 35-50% of the label accumulated after incubation of cultured Sertoli cells with 3H-testosterone was readily extractable with 0.4 M KCl during a 1 h exposure. The degree of extractability was relatively constant over the pH range 7.0-8.5 but could be increased by prolonged (15 h) exposure. While 0.1 M KCl extracted a measurable amount of label, 0.4 M KCl was significantly more efficient. Furthermore, a higher proportion of the material extracted with 0.4 M KCl was associated with macromolecular species. After a 45 min exposure to 3H-testosterone, the nuclear fraction contained primarily labeled testosterone and its 5 alpha-reduced metabolites. The relative distribution of these metabolites between salt-resistant and readily extractable forms varied between experiments. In contrast, 3H-R1881 (17 beta-hydroxy-17-methylestra-4,9,11-trien-3-one) remained essentially intact in the nuclear fraction but also was only 35% extractable with 0.4 M KCl. In conclusion, although the quantitative aspects of salt extractability appear to depend to some extent upon the extraction conditions, it is apparent that the Sertoli cell nuclear fraction accumulates a significant amount of androgen in a form which is relatively resistant to removal with 0.4 M KCl. The biological significance of this phenomenon remains to be established.     

Ethanol modulates the VR-1 variant amiloride-insensitive salt taste receptor. II. Effect on chorda tympani salt responses

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.     

Demonstration and characterization of cytosol androgen receptor in rat exorbital lacrimal gland

The presence of a macromolecule which binds androgen with a high affinity and a low capacity was demonstrated in the cytosol of the lacrimal glands of male and female rats. Evidence was found that this macromolecule was a protein by treatment with protease, trypsin or heat. A specific 8-8.5 S peak was obtained in both sexes by glycerol gradient centrifugation in low salt condition, whereas a specific 5.2 S peak was found in high salt condition. This protein could bind to DNA-cellulose after treatment of androgen-cytosol complexes by warming (25 degrees C 15 min) or exposure under high salt (0.4 M KCl). These results suggested that this protein was an androgen receptor.     

Differential salt-induced stabilization of structure in the initial folding intermediate ensemble of barstar

The effects of two salts, KCl and MgCl(2), on the stability and folding kinetics of barstar have been studied at pH 8. Equilibrium urea unfolding curves were used to show that the free energy of unfolding, deltaG(UN), of barstar increased from a value of 4.7 kcalmol(-1) in the absence of salt to a value of 6.9 kcalmol(-1) in the presence of 1M KCl or 1M MgCl(2). For both salts, deltaG(UN) increases linearly with an increase in concentration of salt from 0M to 1M, suggesting that stabilization of the native state occurs primarily through a Hofmeister effect. Refolding kinetics were studied in detail in the presence of 1M KCl as well as in the presence of 1M MgCl(2), and it is shown that the basic folding mechanism is not altered upon addition of salt. The major effects on the refolding kinetics can be attributed to the stabilization of the initial burst phase ensemble, I(E), by salt. Stabilization of structure in I(E) by KCl causes the fluorescence properties of I(E) to change, so that there is an initial burst phase change in fluorescence at 320 nm, during refolding. The structure in I(E) is stabilized by MgCl(2), but no burst phase change in fluorescence at 320 nm is observed during refolding. The fluorescence emission spectra of I(E) show that when refolding is initiated in 1M KCl, the three tryptophan residues in I(E) are less solvent exposed than when folding is initiated in 1M MgCl(2). Stabilization of I(E) leads to an acceleration in the rate of the fast observable phase of folding by both salts, suggesting that structure of the transition state resembles that of I(E). The stabilization of I(E) by salts can be accounted for largely by the same mechanism that accounts for the stabilization of the native state of the protein, namely through the Hofmeister effect. The salts do not affect the rates of the slower phases of folding, indicating that the late intermediate ensemble, I(L), is not stabilized by salts. Stabilization of the native state results in deceleration of the fast unfolding rate, which has virtually no dependence on the concentration of KCl or MgCl(2) at high concentrations. The observation that the salt-induced stabilization of structure in I(E) is accompanied by an acceleration in the fast folding rate, suggests that I(E) is likely to be a productive on-pathway intermediate.     

Ethanol modulates the VR-1 variant amiloride-insensitive salt taste receptor. I. Effect on TRC volume and Na+ flux

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 degrees C or 42 degrees 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 degrees C to 42 degrees 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.     

Dissociation of proteins from the human 40S ribosomal subunit in a lithium chloride gradient

Human 40S ribosomal subunits were subjected to centrifugation through a 0.3–1.5 M LiCl gradient in 0.5 M KCl, 4 mM MgCl₂. Most of the proteins started to dissociate at the initial concentration of monovalent cations (0.8 M); the last to dissociate at 1.55 M salt were the core proteins S3, S5, S7, S10, S15, S16, S17, S19, S20, and S28; among these, S7, S10, S16, and S19 were the most tightly bound to 18S rRNA.     

Growth of Halotolerant Food Spoiling Yeast Debaryomyces nepalensis NCYC 3413 Under the Influence of pH and Salt

Debaryomyces nepalensis, a halotolerant food-spoiling yeast could grow in complex (YEPD) medium at different pHs ranging between 3.0 and 11.0 in the absence of salt and at pH 3.0–9.0 in the presence of different concentrations of NaCl and KCl. The specific growth rate of D. nepalensis was not affected by the initial pH of the medium in the absence of salts, whereas it was affected in the presence of salts. At 2 M NaCl and KCl, the organism exhibited a synergistic effect on pH and salt stress, which was unique in the Debaryomyces species. Irrespective of the initial pH and salt, the intracellular pH of D. nepalensis was ~7.0. Significant organic acid was produced at neutral and alkaline pH and organic acid production increased with the increase in pH and salt. Very specific organic acids are produced in the presence of NaCl and KCl. Our observation would contribute to a better understanding of the physiological phenomenon of halotolerance in D. nepalensis.