Large enhancement of canine taste responses to sugars by salts

The effects of changed ionic environments on the canine taste responses to sugars were examined by recording the activity of the chorda tympani nerve. a) The responses to various sugars were greatly enhanced by the presence of salts having monovalent cations such as Na+, K+, choline+, or Tris+. The responses to sugars were suppressed by high concentrations of salts. (b) The presence of 100 mM NaCl in fructose solution did not affect the maximal response and changed the Hill constant for the concentration-response relationship from 1.3 to 2.4. (c) CaCl2 greatly enhanced the response to fructose, while MgCl2 exhibited practically no effect. The presence of 20 mM CaCl2 in fructose solution changed the Hill constant from 1.2 to 2.4. (d) CaCl2 suppressed the responses to 0.5 M sugars except for fructose and sucrose and enhanced the responses to all sugars examined at 1 M. In the glucose response, the slope of the concentration-response curve was increased by the presence of CaCl2. Here the curve in the absence of CaCl2 intersected with that in the presence of CaCl2, indicating that CaCl2 suppressed the response to glucose of low concentrations and enhanced that of high concentrations. (e) The enhancement of the sugar responses by salts was not simply explained in terms of ionic permeability at the apical membranes of taste cells. The enhanced and suppressed effects of salts on the sugar responses were interpreted in terms of the cooperativity between receptor molecules for sugars.     

The adaptation of the frog tongue to various taste solutions: the effect on gustatory neural responses to bitter stimuli

1. After the frog tongue was adapted for 10 sec to various salts and sugars, the initial phasic component of gustatory neural responses to almost all of quinine hydrochloride (Q-HCl), quinine sulfate (Q-H2SO4). Brucine, caffeine and picric acid was suppressed. 2. Following 10 sec adaptation to acetic acid, the phasic responses to Q-HCl and Q-H2SO4 were unchanged, those to brucine and caffeine were enhanced, and that to picric acid was depressed slightly. 3. The response to any one of Q-HCl, Q-H2SO4. brucine and caffeine was suppressed after adaptation to the other three, while those to picric acid and nicotine were unchanged or enhanced after adaptation to another bitter solution.     

Physicochemical studies of taste reception. V. Suppressive effect of salts on sugar response of the frog

The model membrane composed of a Millipore filter paper and the total lipids from bovine tongue epithelium or phosphatidylcholine from egg yolk simulated well the water response of a living taste cell. The water response observed with the model membrane adapted to various salt solutions was interpreted in terms of changes in electric potential at the membrane-solution interface, i.e. the water response was attributed to the e.m.f. change produced by diffusion of the electrolytes dissolved in (or adsorbed on) the membrane surface into the bulk solution.The water response of the frog tongue was also investigated by measuring the neural response of the glossopharyngeal nerve. The results obtained were consistent with the mechanism proposed in the present paper. The response of the frog to Ca²⁺ was examined under the condition where the water response was suppressed, and it was concluded that the water response of the frog is different from the response to Ca²⁺.     

Physicochemical studies of taste reception. III. Interpretation of the water response in taste reception

The model membrane composed of a Millipore filter paper and the total lipids from bovine tongue epithelium or phosphatidylcholine from egg yolk simulated well the water response of a living taste cell. The water response observed with the model membrane adapted to various salt solutions was interpreted in terms of changes in electric potential at the membrane-solution interface, i.e. the water response was attributed to the e.m.f. change produced by diffusion of the electrolytes dissolved in (or adsorbed on) the membrane surface into the bulk solution.The water response of the frog tongue was also investigated by measuring the neural response of the glossopharyngeal nerve. The results obtained were consistent with the mechanism proposed in the present paper. The response of the frog to Ca²⁺ was examined under the condition where the water response was suppressed, and it was concluded that the water response of the frog is different from the response to Ca²⁺.     

Effect of sugars on salt reception in true slime mold Physarum polycephalum. Physicochemical interpretation of interaction between salt and sugar receptions

Interaction between salt and sugar receptions in plasmodium of Physarum polycephalum was studied by using double-chamber method. Effect of sugars on salt reception was evaluated by measuring membrane potential and the motive force of tactic movement of the slime mold, where salt concentration in one compartment was increased successively with a fixed sugar concentration. Results are summarized as follows: (1) The presence of D-glucose, D-mannose, D-maltose, or sucrose in medium led to increase of the threshold concentration Cth, for salts (chlorides and nitrates of Li, Na, K), whereas D-ribose decreased the threshold for salt reception. D-galactose showed no appreciable effect on Cth of every salt species examined. No change in Cth for salt reception was observed until concentration of sugars exceeded their respective thresholds. (2) Double logarithmic plots of Cth for salts against sugar concentration followed different straight lines for different cations, whose slopes being closely correlated with the effects of lyotropic number of anions in the absence of sugars. (3) Plots of log Cth against the reciprocal of the absolute temperature, 1/T, gave linear relations, and the slopes of the straight line became small with increase of sugar concentration above their respective thresholds. Experimental results obtained here suggest that the structure of water at the interface of cell membrane plays an indispensable role in the interaction between salt and sugar receptions.     

Consumption of sugars by Anastrepha suspensa (Diptera: Tephritidae)

We were interested in determining the feeding response of the Caribbean fruit fly, Anastrepha suspensa Loew (Diptera: Tephritidae), to various sugar concentrations to develop an improved bait for adults. We compared the consumption of 0.01-1.00 M concentrations of glucose, fructose, raffinose, and sucrose in no-choice tests for 24-h- and 6-d-old male and female flies. Sucrose was the most consumed sugar or within the most consumed group of sugars at 0.02-0.20 M concentrations. There were no differences in consumption among sugars at 0.01, 0.40, and 1.00 M. Consumption generally increased with increasing sugar concentration except that sucrose consumption peaked at 0.20 M. Twenty-four-hour females consumed less fructose than other sugars; 24-h males consumed more sucrose than fructose or raffinose, with an intermediate response to glucose. Females in the 6-d group consumed more sucrose than the other three sugars, whereas 6-d males exhibited no difference in consumption among sugars. In choice tests, flies consumed more sugar solution than water, but the difference between 0.20 M fructose and water was not significant for 24-h males or 24-h females. In choice tests between 0.20 M fructose and 0.20 M sucrose, both 24-h and 6-d females showed a preference for fructose. Males of both age classes showed no preference. These results indicate that the responses of flies to different sugars can vary by sugar, gender, and age.     

Adaptation-induced changes in sensitivity in frog olfactory receptor cells

The suction pipette technique was used to study simultaneously the odour-induced action potential and receptor current responses in frog olfactory receptor cells, which were exposed to the odour cineole for 1 s by rapidly exchanging the solution bathing their cilia. The frequency of action potential firing increased as the odour concentration was raised and saturated within a 15-fold elevation above the odour threshold, while the number of spikes fired initially grew at low-to-intermediate concentrations but then declined at higher concentrations. The receptor current response rose steadily and showed no clear sign of saturation over the 300-fold range of cineole concentration employed. The effect of adaptation on the sensitivity of olfactory receptor cells was investigated by first exposing the cell for 4 s to an adapting pre-pulse and then stimulating with a 1 s test pulse. As the pre-pulse concentration was increased, adaptation led to a progressive shift of the dose-response relationships towards higher test pulse concentrations. This resulted in a steep decline in the sensitivity of the receptor current response, combined with an even more dramatic fall in the sensitivity of the spiking responses, since the higher pre-pulse concentrations prevented the generation of action potentials at test pulse concentrations which still evoked a receptor current response.     

Sensitivity of antennal gustatory receptor neurones to aphid honeydew sugars in the carabid Anchomenus dorsalis

Using electrophysiology, the stimulating effect of 13 sugars and three sugar alcohols (each at a concentration of 100 mm ) to antennal gustatory receptor neurones (GRNs) is tested in the carabid beetle Anchomenus dorsalis (Pontoppidan, 1763) (Coleoptera, Carabidae). Maltose, sucrose, glucose and raffinose are the most stimulating sugars for the sugar‐sensitive neurone (SuN), evoking 6.7–18.6 spikes s^?1 in fed insects, whereas the others had little or no effect. The firing rate of the antennal GRNs is not affected by any of the tested sugar alcohols, dulcitol, inositol and sorbitol. Additionally, concentration/response curves for sucrose and maltose are obtained in the range 0.01–100 mm . The responses of beetles starved for 96 h to this range of sucrose are two‐ to three‐fold higher compared with those of fed beetles. The presence of a terminal α‐glucose unit is an important feature of the molecular structure determining the stimulating properties of the two disaccharides, maltose and sucrose, as well as glucose. The other monosaccharide unit of the molecule is also of great importance in determining the stimulating properties of various disaccharides. The sensitivity of the SuN to the four most prevalent aphid honeydew sugars suggests that A. dorsalis uses these chemicals as sensory cues when searching for aphids as prey.     

De-icers derived from corn steep water

Corn steep water (CSW) and other byproducts derived from fermentations and sugar productions are presently forming the base of compositions for de-icing and anti-icing materials. Since the de-icing and anti-icing values are in part a colligative property, increase in the molar concentration of ionic species has been frequently necessary to decrease further the freezing point of this byproducts stream. In the present study this has been achieved by the generation of biodegradable organic acid salts in situ, without the use of chloride or other inorganic salts, by the alkaline degradation of reducing sugars added to corn steep water, which alone is not an efficient de-icer. Reducing sugars, such as glucose, react with alkali metal hydroxides to produce principally hydroxy carboxylic acids that react with the alkali metal hydroxide to form a mixture of organic acid salts. The ionic strength of the resulting solution is increased since each sugar molecule produces nearly two acid molecules upon degradation. The ionic strength necessary to achieve the desired freezing point depression is determined by the amount and concentration of the alkali metal hydroxide used, with the necessary counter anions being derived from the degradation of the reducing sugar. The amount of the sugar used is that required to result in a near to neutral final solution. The well-known anti-corrosive property of CSW is used in the de-icer preparations, either by conducting the alkaline degradation of the sugar in this medium, or by using water for the degradation of the sugar followed by dilution of the resulting solution with CSW to adjust the viscosity of the final solution to meet the requirements for spraying. The monovalent metal hydroxides are more efficient in producing de-icer solutions than the divalent metal hydroxides.     

Enhanced permeability to sugar associated with muscle contraction. Studies of the role of Ca++

When contractures were induced in isolated frog sartorius muscles with 4 mM caffeine, there was an increase in permeability of the muscle cells to 3-methylglucose. This observation suggests that the changes in permeability to sugar that are known to occur in electrically stimulated muscles may not be intimately related to the depolarization phase of the tissue response. Contractures that were elicited by exposing the muscles to a high concentration of K+ were also associated with an increased permeability to sugar. As the concentration of 45Ca in the medium was raised, more 45Ca entered the muscles during potassium contractures, and the contractures lasted longer, in agreement with the observations of other investigators. There was also a greater change in permeability to sugar when potassium contractures were elicited in the presence of higher concentrations of Ca++. The possibility that the enhanced permeability to sugar may be related to changes in the intracellular concentration of Ca++ is discussed.     

Ion Transport in Isolated Rabbit Ileum : II. The interaction between active sodium and active sugar transport

The addition of actively transported sugars to the solution bathing the mucosal surface of an in vitro preparation of distal rabbit ileum results in a rapid increase in the transmural potential difference, the short-circuit current, and the rate of active Na transport from mucosa to serosa. These effects are dependent upon the active transport of the sugar per se and are independent of the metabolic fate of the transported sugar. Furthermore, they are inhibited both by low concentrations of phlorizin in the mucosal solution and by low concentrations of ouabain in the serosal solution. The increase in the short-circuit current, ΔI_sc, requires the presence of Na in the perfusion medium and its magnitude is a linear function of the Na concentration. On the other hand, ΔI_sc is a saturable function of the mucosal sugar concentration which is consistent with Michaelis-Menten kinetics suggesting that the increase in active Na transport is stoichiometrically related to the rate of active sugar transport. An interpretation of these findings in terms of a hypothetical model for intestinal Na and sugar transport is presented.     

Separation of two receptor sites in a single labellar sugar receptor of the flesh-fly by treatment with p-chloromercuribenzoate

A 3 min treatment of a single sugar receptor with 0·5 mM p-chloromercuribenzoate (PCMB) did not affect its response to d-fructose, but depressed completely its response to d-glucose. This is the first direct evidence of the presence of two different sites in the sugar receptor of the fly.No specific protection by d-glucose on PCMB treatment suggested that PCMB did not react at a glucose-binding site but did react at a specific site indispensable to simulation by d-glucose.Various sugars were examined and classified into two groups according to the effects of PCMB treatment on the sugar receptor. They correspond to those effective in the furanose and pyranose forms, respectively. The pyranose group was further divided into two subclasses according to the presence or absence of three successive equatorial hydroxyl groups regardless of their positions. The results are discussed in relation to the structures that are common to furanose stimulating sugars.     

Stimulation of the salt receptor of the blowfly. III. The alkali halides

Application of solutions of each of the alkali halides to the tip of a labellar sensillum of the blowfly elicited a repetitive neural discharge from the salt receptor. The records were qualitatively similar to those for NaCl. For each of the alkali chlorides and sodium halides, the shapes of the curves of the response of the salt receptor as a function of concentration were similar to that for NaCl. The alkali halides exhibited a regular pattern of relative stimulating effectiveness for the salt receptor. The effectiveness of the anions increased monotonically with atomic number. The effectiveness of the cations was greatest for potassium and declined as the atomic number was increased or decreased. This hierarchy for stimulating effectiveness was maintained at all tested molarities. The response to a mixture of two salts appeared to be an average of those to the single salts at concentrations equal to the total concentration of the mixture. Cross-adaptation was observed between the alkali halides. The results indicate that an explanation of stimulation of the salt receptor must apply to all the salts tested and that both the anion and the cation affect a salt's stimulating effectiveness.     

The radiation response of cultured mammalian V79-S171 cells exposed to a wide concentration range of sulphate salt solutions.

The radiation response of Chinese hamster cells (V79) exposed to a wide concentration range of Li2SO4, Na2SO4 or K2SO4 has been examined and compared with the radiation response of cells treated in an identical manner with LiCl, NaCl, or KCl solutions. At hypotonic salt concentrations, cells were radiosensitized by both the chloride and sulphate salts. At high salt concentrations, approximately greater than 0.9 M, a radioprotective effect was observed with both chloride and sulphate salts. At intermediate salt concentrations from about 0.2 to 0.9 M, the cells that were treated with the sulphate salt solutions were radioprotected; cells treated with chloride salt solutions were radiosensitized. The difference in radiation response was attributed to the difference in anions for the two types of salts used.     

Factors affecting the stability of dry liposomes

Previous studies have shown that liposomes can be preserved in the dry state in the presence of certain sugars, of which trehalose is particularly effective. There have been some discrepancies in results obtained by the various laboratories in which this phenomenon has been studied, both with respect to the efficacy of the sugars tested and the degree to which the dry vesicles can be stabilized. We show here that several factors that affect the stability of the dry liposomes may be responsible for the discrepancies between measurements by different laboratories. These factors include: (1) Size: small, sonicated vesicles are comparatively very unstable, and retain no more than 70% of trapped solute after drying, even in extremely high concentrations of sugars. Very large vesicles are similarly unstable. (2) Charge: a small amount of negatively charged lipid in the bilayer significantly increases stability. (3) Stabilizing sugar: the comparative efficacy of the sugar used varies with the size of the vesicles. (4) Dry-mass ratio. It is the dry-mass ratio between the stabilizing sugar and lipid that is important in the preservation during freeze-drying, not the concentration of either lipid or sugar in bulk solution.     

Selective enhancement and suppression of frog gustatory responses to amino acids

Properties of the receptor sites for L-amino acids in taste cells of the bullfrog (Rana catesbeiana) were examined by measuring the neural activities of the glossopharyngeal nerve under various conditions. (a) The frogs responded to 12 amino acids, but the responses to the amino acids varied with individual frogs under natural conditions. The frog tongues, however, exhibited similar responses after an alkaline treatment that removes Ca2+ from the tissue. The variation in the responses under natural conditions was apparently due to the variation in the amount of Ca2+ bound to the receptor membrane. (b) The responses to hydrophilic L-amino acids (glycine, L-alanine, L-serine, L- threonine, L-cysteine, and L-proline) were of a tonic type, but those to hydrophobic L-amino acids (L-valine, L-leucine, L-isoleucine, L- methionine, L-phenylalanine, and L-tyrptophan) were usually composed of both phasic and tonic components. (c) The properties of the tonic component were quite different from those of the phasic component: the tonic component was largely enhanced by the alkaline treatment and suppressed by the acidic treatment that increases binding of Ca2+ to the tissue. Also, the tonic component was suppressed by the presence of low concentrations of salts, or the action of pronase E, whereas the phasic component was unchanged under these conditions. These properties of the phasic component were quite similar to those of the response to hydrophobic substances such as quinine. These results suggest that the hydrophilic L-amino acids stimulate receptor protein(s) and that the hydrophobic L-amino acids stimulate both the receptor protein and a receptor site similar to that for quinine. (d) On the basis of the suppression of the responses to amino acids by salts, the mechanism of generation of the receptor potential is discussed.     

Cell volumes and water contents of frog muscles in solutions of permeant sugars and sugar alcohols

1. Previous work has suggested that living cells may acquire and then maintain different water contents and hence volume, in solutions containing different concentrations of solutes that are permeant to the cell membrane. Toward better understanding of this phenomenon, two hypotheses were introduced: one hypothesis is based on the membrane-pump theory; another represents an extension of the polarized multilayer theory of cell water, a part of the association-induction (AI) hypothesis. To test the different predictions of these hypotheses, the water contents of frog muscle equilibrated at 25 degrees C in solutions of different concentrations of seven pentoses, seven hexoses, seven dissacharides, two trisaccharides, and six sugar alcohols were determined. 2. The earlier finding of sustained shrinkage of muscle cells in concentrated solutions of permeant solutes was confirmed once more. 3. In equimolal solutions of sugars and sugar alcohols with different steric conformations but the same or closely similar molecular weight(s), muscles had the same or closely similar water content(s). 4. In equimolal solutions of different sugars and sugar alcohols, the equilibrium water contents of the muscles increased with decreasing molecular weights of these solutes. 5. The water contents of muscles, equilibrated in 0.4 M solutions of different sugars and sugar alcohols, are positively correlated with the equilibrium distribution coefficients (or q-values) of the sugar and sugar alcohols in the muscle cell water with a linear correlation coefficient of +0.973. 6. The relationships between the equilibrium water contents of muscles (in solutions containing different concentrations of different sugars and sugar alcohols) and the concentrations of these sugars and sugar alcohols agree in general contours with that predicted by an equation derived on the basis of the polarized multilayer theory of cell water. 7. The experimental findings described above do not agree with the prediction based on the membrane-pump hypothesis; they do agree with all four predictions of the hypothesis based on the polarized multilayer theory of cell water.     

Extra-weak chemiluminescence of drugs. VIII. Extra-weak chemiluminescence arising from the amino-carbonyl reaction

Extra-weak chemiluminescence (CL) from amino-carbonyl reactions of L-lysine with various sugars and aldehydes in aqueous solution was examined. Amongst the aldehydes and sugars tested, glycolaldehyde and D -arabinose produced the highest CL intensity. The CL of the amino-carbonyl reaction reached a maximum after about 60 minutes. The CL was pH dependent, and a linear relation between CL intensity and hydroge-ion concentration was demonstrated. Low oxygen levels inhibited CL and no CL was produced in nitrogen purged solutions. Addition of cupric or ferrous ion, decreased the CL. The involvement of free radical intermediates was demonstrated by ESR. Our findings suggest that the CL of the amino-carbonyl reaction arises from free radicals derived from melanoidines or their intermediates. CL should prove useful for evaluating the stability of crude drugs extracted from natural resources that contain various amino acid derivatives protein and sugar components.     

Water relations link carbon and oxygen isotope discrimination to phloem sap sugar concentration in Eucalyptus globulus

A strong correlation was previously observed between carbon isotope discrimination (Delta(13)C) of phloem sap sugars and phloem sap sugar concentration in the phloem-bleeding tree Eucalyptus globulus Labill. (J. Pate, E. Shedley, D. Arthur, M. Adams [1998] Oecologia 117: 312-322). We hypothesized that correspondence between these two parameters results from covarying responses to plant water potential. We expected Delta(13)C to decrease with decreasing plant water potential and phloem sap sugar concentration to increase, thereby maintaining turgor within sieve tubes. The hypothesis was tested with analyses of E. globulus trees growing on opposite ends of a rainfall gradient in southwestern Australia. The Delta(13)C of phloem sap sugars was closely related to phloem sap sugar concentration (r = -0.90, P < 0.0001, n = 40). As predicted, daytime shoot water potential was positively related to Delta(13)C (r = 0.70, P < 0.0001, n = 40) and negatively related to phloem sap sugar concentration (r = -0.86, P < 0.0001, n = 40). Additional measurements showed a strong correspondence between predawn shoot water potential and phloem sap sugar concentration measured at midday (r = -0.87, P < 0.0001, n = 30). The Delta(13)C of phloem sap sugars collected from the stem agreed well with that predicted from instantaneous measurements of the ratio of intercellular to ambient carbon dioxide concentrations on subtending donor leaves. In accordance, instantaneous ratio of intercellular to ambient carbon dioxide concentrations correlated negatively with phloem sap sugar concentration (r = -0.91, P < 0.0001, n = 27). Oxygen isotope enrichment (Delta(18)O) in phloem sap sugars also varied with phloem sap sugar concentration (r = 0.91, P < 0.0001, n = 39), consistent with predictions from a theoretical model of Delta(18)O. We conclude that drought induces correlated variation in the concentration of phloem sap sugars and their isotopic composition in E. globulus.     

The regulation of turgor pressure during sucrose mobilisation and salt accumulation by excised storage-root tissue of red beet

The changes in turgor pressure that accompany the mobilisation of sucrose and accumulation of salts by excised disks of storage-root tissue of red beet (Beta vulgaris L.) have been investigated. Disks were washed in solutions containing mannitol until all of their sucrose had disappeared and then were transferred to solutions containing 5 mol·m^-3 KCl+5 mol·m^-3 NaCl in addition to the mannitol. Changes in solute contents, osmotic pressure and turgor pressure (measured with a pressure probe) were followed. As sucrose disappeared from the tissue, reducing sugars were accumulated. For disks in 200 mol·m^-3 mannitol, the final reducing-sugar concentration equalled the initial sucrose concentration so there was no change in osmotic pressure or turgor pressure. At lower mannitol concentrations, there was a decrease in tissue osmotic pressure which was caused by a turgor-driven leakage of solutes. At concentrations of mannitol greater than 200 mol·m^-3, osmotic pressure and turgor pressure increased because reducing-sugar accumulation exceeded the initial sucrose concentration. When salts were provided they were absorbed by the tissue and reducing-sugar concentrations fell. This indicated that salts were replacing sugars in the vacuole and releasing them for metabolism. The changes in salf and sugar concentrations were not equal because there was an increase in osmotic pressure and turgor pressure. The amount of salt absorbed was not affected by the external mannitol concentration, indicating that turgor pressure did not affect this process. The implications of the results for the control of turgor pressure during the mobilisation of vacuolar sucrose are discussed.To whom correspondence should be addressed.