Eylam S, Kennedy L M
Department of Biology and Neuroscience Program, Clark University, Worcester, Massachusetts 01610, USA.
Ann N Y Acad Sci. 1998 Nov 30;855:170-4. doi: 10.1111/j.1749-6632.1998.tb10562.x.
Human psychophysical functions for sweetness are similar for sucrose and fructose, but different for glucose, and suggest different mechanisms for fructose and glucose. Drosophila behavioral and electrophysiological data are similar to the human data and indicate separate receptor cell mechanisms for the monosaccharides. Moreover, fructose 'nontasters' (NTs) and glucose NTs have been identified in two Drosophila species. Identification of human NTs would confirm separate mechanisms and could lead to identification of proteins in human sweet taste by molecular genetic techniques. To identify human NTs, we first obtained responses for sucrose, fructose and glucose from 20 subjects. They tasted seven concentrations of each sugar (2-128 mM), paired with water, and indicated the sweeter of each pair. Functions for recognition indices (RIs) (proportion of subjects recognizing the sugar as sweeter) were similar for sucrose and fructose and different for glucose; this result agrees with the previous studies and supports different mechanisms for the monosaccharides. At 128 mM, RIs for all three sugars were 1.0; this result is consistent with the monogeusia reported by Breslin et al. for concentrations higher than those tested here. Eleven rising-phase concentrations (10-35 mM fructose, 10-90 mM glucose) then were tested on 32 subjects. A statistically significant interaction indicated different regression slopes and supported different monosaccharide mechanisms. From these data, positive identification values (PIDs) (lowest concentration at which the sugar always was judged sweeter than the water) were determined for each subject. The fructose log(PID) and glucose log(PID) data were not well correlated; thus separate mechanisms were supported further. Next, NT traits were defined by log(PID)s > or = 2 SD above the mean for one sugar, while the PID for the other remained within 1 SD of the population mean log(PID). Ninety-two subjects were screened to identify 12 glucose NTs and four fructose NTs. Two glucose NTs and three average subjects were tested in six additional sessions. The NTs showed an experience-induced change: there was a statistically significant reduction of glucose PIDs, but not of fructose PIDs. No change occurred in PIDs of the average subjects for either sugar.
人类对蔗糖和果糖的甜味心理物理功能相似，但对葡萄糖则不同，这表明果糖和葡萄糖的机制不同。果蝇的行为和电生理数据与人类数据相似，表明单糖存在独立的受体细胞机制。此外，在两种果蝇物种中已鉴定出果糖“无甜味味觉者”（NTs）和葡萄糖NTs。鉴定人类NTs将证实存在独立的机制，并可能通过分子遗传学技术鉴定人类甜味中的蛋白质。为了鉴定人类NTs，我们首先从20名受试者那里获得了对蔗糖、果糖和葡萄糖的反应。他们品尝了每种糖的七种浓度（2 - 128 mM），并与水配对，指出每对中较甜的一种。识别指数（RIs）（将糖识别为较甜的受试者比例）的功能对于蔗糖和果糖相似，而对于葡萄糖则不同；这一结果与先前的研究一致，并支持单糖的不同机制。在128 mM时，所有三种糖的RIs均为1.0；这一结果与布雷斯林等人报道的高于此处测试浓度的单一味觉现象一致。然后对32名受试者测试了11个上升阶段的浓度（10 - 35 mM果糖，10 - 90 mM葡萄糖）。具有统计学意义的相互作用表明回归斜率不同，并支持不同的单糖机制。根据这些数据，为每个受试者确定了阳性识别值（PIDs）（糖始终被判定比水甜的最低浓度）。果糖的log（PID）和葡萄糖的log（PID）数据相关性不佳；因此进一步支持了独立的机制。接下来，通过一种糖的log（PID）大于或等于均值加2个标准差来定义NTs特征，而另一种糖的PID仍在总体平均log（PID）的1个标准差范围内。对92名受试者进行筛选，以鉴定出12名葡萄糖NTs和4名果糖NTs。对2名葡萄糖NTs和3名普通受试者进行了另外六次测试。NTs表现出经验诱导的变化：葡萄糖PIDs有统计学意义的降低，但果糖PIDs没有。两种糖中普通受试者的PIDs均未发生变化。
