Cross-adaptation and molecular modeling study of receptor mechanisms common to four taste stimuli in humans

Psychophysical cross-adaptation experiments were performed with two carbohydrates, sucrose (SUC) and fructose (FRU), and two sweeteners, acesulfame-K (MOD) and dulcin (DUL). Seven subjects were asked to match concentrations that elicited the same intensity as a sucrose reference (30 g/l). Cross-adaptation levels were calculated as the ratio of isointense concentrations measured for a given stimulus before and under adaptation. On average, cross-adaptation between SUC and FRU is low and apparently reciprocal. By contrast, cross-adaptation between SUC and MOD is clearly non-reciprocal: SUC adapts MOD significantly (24%, P < 0.005), but MOD fails to adapt SUC (2%, P < 0.79). Significant and reciprocal cross-enhancement is observed between DUL and MOD (approximately -20%, P < 0.03), and also between SUC and DUL (approximately -15%, P < 0.08). In parallel, molecular modeling of the four tastants was performed in order to look for the 12 common binding motifs that were isolated on 14 other tastants in a previous study. SUC and FRU each display 10 out of the 12 binding motifs, whereas DUL and MOD only display four and five distinct motifs respectively and do not have any motif in common. Experimental cross-adaptation levels seem to correlate well with the number of motifs that molecules have in common. FRU and SUC share a majority of binding motifs and correlatively show mutual cross-adaptation. Four motifs of MOD are found among the 10 motifs of SUC, which may explain why SUC cross-adapts MOD but not vice versa. By contrast, DUL and MOD do not share any motif and do not cross- adapt. The various molecular mechanisms that may be responsible for cross-adaptation and/or cross-enhancement are discussed in light of our results.      

Location of taste buds in intact taste papillae by a selective staining method

Summary Taste buds were found to stain strongly and selectively in intact papillae with highly acidic dyes such as ponceau S. In intact tongues the taste buds in the fungiform, circumvallate and foliate papillae of the cynomolgus monkey and in the fungiform papillae of the rat as well as the taste discs in the fungiform papillae of the frog could be visualized. This method enables a rapid location and counting of taste buds in taste papillae without preparing histological sections. In cynomolgus tongue material fixed in formalin, the dyes penetrate into the buds. In fresh tongues only the taste pore region of the buds stains, which suggests that in vivo taste buds are impenetrable underneath the pore.     

Location of taste buds in intact taste papillae by a selective staining method.

Taste buds were found to stain strongly and selectively in intact papillae with highly acidic dyes such as ponceau S. In intact tongues the taste buds in the fungiform, circumvallate and foliate papillae of the cynomolgus monkey and in the fungiform papillae of the rat as well as the taste discs in the fungiform papillae of the frog could be visualized. This method enables a rapid location and counting of taste buds in taste papillae without preparing histological sections. In cynomolgus tongue material fixed in formalin, the dyes penetrate into the buds. In fresh tongues only the taste pore region of the buds stains, which suggests that in vivo taste buds are impenetrable underneath the pore.     

The Role of Perceptual and Structural Similarity in Cross-adaptation

Cross-adaptation, the decrease in sensitivity to one odorantfollowing exposure to a different odorant, is affected by odorantsimilarity, both perceptual and structural, but the preciserelationship is obscure. The present series of studies was designedto explore various aspects of perceptual and structural similarityas they relate to cross-adaptation. In Experiment 1, cross-adaptationwas assessed between androstenone and five odorants that sharea common urinous note with androstenone, but retain unique perceptualcharacteristics; only the compound judged most perceptuallysimilar to androstenone cross-adapted it. In Experiment 2, odorantsboth perceptually and structurally similar (androstenone andandrostanone) displayed significant, mutual cross-adaptation.Furthermore, magnitude estimates for androstanone were significantlyreduced following exposure to 3-methylidene-5a-androstane (3M5A),a structurally similar, perceptually odorless compound. Thisfinding appears to be the first demonstration that an odorlesscompound can affect, via cross-adaptation, the perception ofan odorous compound. Finally, in Experiment 3, significant,asymmetric cross-adaptation was observed between compounds thatare perceptually and structurally dissimilar (4-cyclohexylcyclohexanone[4-CHCH] and androstenone). These findings indicate that therole of similarity in cross-adaptation is difficult to quantifyand emphasize the numerous odorant characteristics that canaffect cross-adaptation. Chem. Senses 21: 223–237, 1996.     

Conditioned suppression as a method of detecting taste thresholds in the rat

Taste thresholds of seven male Sprague—Dawley rats (meanage 10 weeks, mean weight 250 g) were determined for four basictaste qualities: sweet, sour, salty and bitter. The method ofconditioned suppression was employed. An apparatus capable ofpresenting any one of eight separate drinking tubes during atesting session was designed. Animals were reduced to 80–85%ad lib. body weight. They were then trained to lick a sippertube through a slot in the back of an experimental chamber forpellet reinforcements. Animals progressed through a series ofreinforcement schedules starting with a fixed ratio (FR) scheduleof five licks for each reinforcement. They advanced to a variableratio (VR) schedule of reinforcement and finally a variableinterval (VI) schedule with a mean of 17.5 s was used. Whileon the VI schedule animals were trained to suppress lickingwhen any tastant other than water was presented. The first lickon any tastant was followed 10 s later by a mild electric shockif a rat made more than 20 licks on the tube in the 10-s period.Less than 20 licks on a tastant tube resulted in no shock anda 5-s time out before proceeding to the next tube. Thresholdwas determined using a suppression ratio formula. Thresholdwas defined as the 0.33 suppression ratio. Results from thisexperiment reveal mean thresholds for the seven animals as:sucrose = 2.3 mM, NaCl = 0.63 mM, quinine HCl = 0.005 mM andcitric acid = 0.085 mM.     

应用热平衡法测定玉米/大豆间作群体内作物的蒸腾量

通过田间试验采用基于热平衡法的茎流计测定玉米/大豆条带间作群体内作物的蒸腾规律.结果表明：间作群体内,玉米和大豆植株的茎流速率在晴天呈单峰曲线,在阴天则呈多峰曲线.植株的茎流受多个环境因子的影响,其中太阳辐射是影响植株茎流最主要的气象因子.玉米和大豆的单株日茎流量与多个气象因子间存在较好的相关关系,达到极显著水平.茎流观测期内（2008年6月1-30日）,间作群体内玉米植株的日均蒸腾量（1.44 mm·d^-1）为大豆（0.79 mm·d^-1）的1.8倍,玉米和大豆植株的蒸腾量分别占间作群体总蒸腾量的64%和36%.考虑到作物的茎直径和叶面积的空间变异,安装一定数量的茎流探头对于准确测定植株茎流是十分必要的.     

Eye pain with nifedipine and disturbance of taste with captopril: a mutually controlled study showing a method of postmarketing surveillance

Several notifications of eye pain and blurred vision associated with treatment with nifedipine were received by New Zealand''s Intensive Medicines Monitoring Programme. A questionnaire survey of patients taking nifedipine was undertaken to test the importance of these associations, with disturbance of taste associated with captopril taken as a methodological control. Altogether 961 patients taking nifedipine and 368 taking captopril were sent a questionnaire that asked whether any eye problems and changes in the sense of taste had occurred while they were taking the drug and whether these had resolved after treatment was stopped. Compliance was high: of 922 and 343 questionnaires that were assumed to have been delivered to patients taking nifedipine and captopril, respectively, 770 (84%) and 295 (86%) were returned satisfactorily completed. The distribution of sex was comparable in the two groups; patients taking captopril were slightly younger. Eye symptoms were reported in both groups, but eye pain was significantly more common in patients taking nifedipine (107 (14%) compared with 26 (9%) patients taking captopril). This is a new finding and may be related to ocular vasodilatation. Theoretically, glaucoma is a possible adverse reaction. Loss of taste was significantly associated with captopril, but no other disturbances of taste showed significant associations. Loss of taste persisted in 27 out of 35 patients who continued to take captopril and in three out of eight patients when the drug was withdrawn.This study showed a method of assessing early signs of adverse drug reactions, which has been used once before and identified previously unrecognised reactions.     

Oxygen consumption rate of tissue measured by a micropolarographic method

A new method for measuring the oxygen consumption rate of a sheet of homogeneous tissue is described. The method measures, by a Clark-type oxygen electrode without a membrane, the time for the tissue to consume all its dissolved oxygen. The electrode is applied to one surface of the tissue sheet and the other surface is sealed from the atmosphere by a cover slip. The consumption is calculated from an estimate of the oxygen dissolved in the tissue at the moment it is covered and the time for the oxygen tension at one surface to fall to zero. The data also yield the oxygen diffusion coefficient in the oxygen-consuming tissue.     

Predation pressure in Ugandan cotton fields measured by a sentinel prey method

Pest suppression by natural enemies is an important ecosystem service, which is a valuable resource to poor smallholders in developing countries. Diverse natural enemy assemblages of arthropod predators and parasitoids are documented in various regions in Africa, but our knowledge of their impact on herbivores in agroecosystems remains limited. We conducted experiments in cotton, Gossypium hirsutum L. (Malvaceae), under typical local agronomic practices in Uganda to assess levels of predation pressure ascribed to natural enemies. We measured predation rates on artificial caterpillars made of plasticine glued to cotton plants. Predation pressure on cotton fields varied between 1.96 and 4.1% per day, but was not significantly influenced by cotton treatments (insecticide/no insecticide, monocropping/intercropping with Phaseolus spp.). Predation pressure in non‐crop habitats adjacent to cotton fields was up to 12× higher than in the fields. Marks left on the artificial caterpillars revealed that arthropods and birds were largely accountable for predation in cotton fields, whereas arthropods and small mammals were dominant in non‐cultivated habitats.     

Cross-adaptation of Sweaty-smelling 3-methyl-2- hexenoic Acid by a Structurally-similar, Pleasant-smelling Odorant

Cross-adaptation has been interpreted as a measure of the degreeto which odors share common sensory channels. How structuralsimilarity, in the absence of perceptual similarity, influencescross-adaptation is unknown. The present study assessed cross-adaptationby structurally similar, but perceptually different, odorants.Magnitude estimates for a 10:1 mixture of (E)- and (Z)-3-methyl-2-hexenoicacid (3M2H), a principal component of human underarm odor, decreasedfollowing adaptation to a mixture of (E)- and (Z)-ethyl estersof 3M2H (EE3M2H), which possess a pleasant, fruity odor. Cross-adaptationwas asymmetric; adaptation to 3M2H did not significantly affectthe perceived intensity of EE3M2H. By contrast, there was nosignificant cross-adaptation between 3M2H and the fruity-smellingethyl esters of its homologues, 3-methyl-2-octenoic acid (EE3M20)and 3-methyl-2-pentenoic acid (EE3M2P). Similarity ratings revealedno differences among the three ethyl esters in their perceptualsimilarity to 3M2H (i.e. all were rated equally dissimilar to3M2H). Molecular modeling studies revealed no difference inthe charge distribution of these molecules. Rather, differencesin the shape and size of the hydrophobic part of the moleculemay determine the extent of cross-adaptation. These resultsdemonstrate that structurally-similar, yet perceptually-distinct,odorants may cross-adapt and suggest that the extent of cross-adaptationmay be affected by the degree of structural, as well as perceptual,similarity. Chem. Senses 20: 401–411, 1995.     

Assessment of overall metabolism inAmoeba proteus measured by a microcalorimetric method

Summary We have carried out calorimetric determinations of the overall metabolism ofAmoeba proteus. There was no significant difference in metabolic activity between cells that were starved 3, 4, and 5 days. After 7 and 10 days a significantly lower metabolism was found (p < 0.05).The mean value of heat production rate (thermal power) for the cells after 3 days starvation was found to be 0.84 ± 0.14 nW/cell. Optimal number of cells in the ampoule (1,500–4,800) was accompanied by a steady-state power-time curve. With higher cell concentrations (> 5,000) the power-time curve showed an initial peak. The fall in heat production after about 1 hour varied between 30–60%. The decrease in power value was much larger than expected from cell mortality during the calorimetric experiment.Increasing number of cells (range 1,500–10,000) in the calorimetric ampoule caused a decrease of heat production rate per cell. The correlation coefficient was r=–0.85(p < 0.001). The coefficient of variation of the method was found to be 4.8 %. It seems that the use of microcalorimetric technique can be valuable in recording metabolic events in protozoes.     

Antioxidant capacities in various animal sera as measured with multiple free-radical scavenging method

Scavenging abilities of animal sera against six reactive species (OH, O₂⁻, RO, t-BuOO, H₃C, and ¹O₂) were determined with the use of multiple free-radical scavenging (MULTIS) method. Commercially available sera from pig, horse, rabbit, Guinea pig, hamster and chicken were subjected to MULTIS analysis and the results were compared with human specimen. In general, animal sera showed lower scavenging ability against OH and RO radicals than human serum. However, it is noteworthy that rabbit and chicken sera have higher scavenging ability against O₂⁻ than others. This is consistent with the known data that superoxide dismutase levels in these sera are high. In addition, we determined the uric acid level in animal sera using the uricase-TOOS method. In chicken serum, uric acid was found to be the major effective component in RO scavenging. This paper is first to quantitatively evaluate antioxidant capacities in animal sera.     

Neurokinin B in a human pheochromocytoma measured with a specific radioimmunoassay

An N-terminally directed antiserum to neurokinin B was raised in rabbits using an immunogen prepared by coupling the free-SH group of neurokinin B extended from its C-terminus by a cysteine residue (NKB-Cys) to an -NH2 group on human serum albumin using a heterobifunctional cross-linking reagent. In radioimmunoassay with 125I-Bolton-Hunter-labelled NKB-Cys as tracer, the antiserum showed no cross-reactivity with other tachykinins. An extract of a human pheochromocytoma, previously shown to contain peptides derived from preprotachykinin A, contained NKB-LI (13 pmol/g wet weight). The retention time of tumor neurokinin on reversed-phase HPLC was the same as that of synthetic neurokinin B. Peptides with the retention times of substance P, neurokinin A, neurokinin A (3-10)-peptide and neuropeptide K were also identified in the tumor extract. NKB-LI was not detected in extracts of a further nine pheochromocytomas or in five carcinoid tumors that expressed the preprotachykinin A gene.     

Assay of glucoprotein formation from uridine diphosphate glucose by a rapid filter-paper technique.

A rapid, simple, sensitive and reproducible filter-paper assay was developed to follow the glucose transfer from uridine diphosphate [¹⁴C]glucose to protein or protein-bound oligosaccharides. This method could be useful for following the formation of any glycoprotein.Rectangles of trichloroacetic acid-treated filter paper are introduced into a test tube containing the reaction mixture. The papers are submitted to a batch washing-procedure that ensures the removal of the compounds that are not trichloroacetic acid-precipitable. After scintillation counting, the paper can be reused to study the acid lability of the glucoprotein.     

Xylem water flow in tropical vines as measured by a steady state heating method

Summary A method for determining the mass flow rate of xylem water in thin stems under natural field conditions is presented. Diurnal courses of xylem water flow and stomatal conductance of the vines Entadopsis polystachya, Cyclanthera multifoliolata, and Serjania brachycarpa were examined in a tropical deciduous forest on the west coast of Mexico. E. polystachya (leaf area 23.6 m²) had a maximum water flow rate of 6.50 kg h^-1 or 1.44 kg cm^-2 _{stem basal area} h^-1; daily water use was 2.00 kg m^-2 _{leaf area} day^-1. S. brachycarpa (leaf area 4.5 m²) and C. multifoliolata (leaf area 3.6 m²) had a maximum water flow rate of 0.72 and 0.19 kg h^-1 or 0.63 and 0.92 kg cm^-2 _{stem basal area} h^-1. Daily water use was 1.26 and 0.39 kg m^-2 _{leaf area} day^-1, respectively. The daily courses of xylem water flow were strongly influenced by the orientation of the leaf area to irradiance and its intensity. While leaves of E. polystachya had a constant high stomatal conductance during the day, S. brachycarpa had a maximum stomatal opening in the morning followed by continuous closure during the rest of the day. In contrast to the woody species, the herbaceous C. multifoliolata exhibited a strong midday depression of stomatal conductance and wilting of its leaves. The leaf biomass accounted for 8% (Entadopsis), 16% (Serjania), and 23% (Cyclanthera) of above-ground biomass. The relation of sapwood area to leaf area supplied (Huber value) was 0.19 (Entadopsis), 0.18 (Serjania), and 0.06 (Cyclanthera) cm² m^-2     

Muscarinic activation of ionic currents measured by a new whole-cell recording method

A new method is described as an alternative to whole-cell recording in order to prevent "wash-out" of the muscarinic response to acetylcholine (ACh) in rat lacrimal gland cells. The membrane of a cell-attached patch is permeabilized by nystatin in the patch pipette, thus providing electrical continuity between the pipette and the cytoplasm of the cell without the loss or alteration of cytoplasmic compounds necessary for the maintenance of the response to ACh. With normal whole-cell recording in these cells, the response to ACh, seen as the activation of Ca-activated K and Cl currents, lasts for approximately 5 min. With the nystatin method, the response is not diminished after 1 h. Nystatin, applied extracellularly, is shown to cause a rapid and reversible increase of membrane conductance to cations. In the absence of wash-out, we were able to obtain dose-response curves for the effect of ACh on Ca-activated K currents. An increase of [ACh] caused an increase in the K current, with apparent saturation at concentrations above approximately 1 microM ACh. The delay between ACh application and the activation of K current was inversely related to [ACh] and reached a minimum value of 0.7-1.0 s at high [ACh].