Tsunenari T, Hayashi Y, Orita M, Kurahashi T, Kaneko A, Mori T
Research Institute for Food Science, Kyoto University, Japan.
J Gen Physiol. 1996 Dec;108(6):515-23. doi: 10.1085/jgp.108.6.515.
The chincona alkaloid quinine is known to be a bitter tasting substance for various vertebrates. We examined the effects of quinine on isolated taste receptor cells from the bullfrog (Rana catesbeiana). Membrane currents were recorded by whole-cell recording, while quinine hydrochloride was applied extracellularly from a puffer pipette. At the resting potential (-77 +/- 9 mV, mean +/- SD, n = 49 cells), taste cells generated inward currents in response to quinine stimulation (> 1 mM), indicating a depolarizing response in the taste cells. Two types of current responses were observed; a newly found quinine-activated cationic conductance and a previously reported blocking effect of quinine on K+ conductances. The cationic current was isolated from the K+ current by using a Cs(+)-containing patch pipette. The relative permeabilities (Pion) of the quinine-activated cationic conductance were: PNa/PK/PCs = 1:0.5:0.42. The quinine dose-response relation was described by the Hill equation with the K1/2 of 3.6 mM and Hill coefficient of 5.3. When extracellular [Ca2+] (1.8 mM) was reduced to nominally free, the conductance was enhanced by about sixfold. This property is consistent with observations on quinine responses recorded from the gustatory nerve, in vivo. The quinine-induced cationic current was decreased with an application of 8-bromo-cAMP. We conclude that the bitter substance quinine activates a cation channel in taste receptor cells and this channel plays an important role in bitter taste transduction.
金鸡纳生物碱奎宁是各种脊椎动物都熟知的苦味物质。我们研究了奎宁对牛蛙（Rana catesbeiana）分离出的味觉受体细胞的影响。通过全细胞记录法记录膜电流，同时用微量移液器从细胞外施加盐酸奎宁。在静息电位（-77±9 mV，平均值±标准差，n = 49个细胞）下，味觉细胞在受到奎宁刺激（>1 mM）时产生内向电流，表明味觉细胞出现去极化反应。观察到两种类型的电流反应：一种是新发现的奎宁激活的阳离子电导，另一种是先前报道的奎宁对钾离子电导的阻断作用。使用含铯（Cs⁺）的膜片钳吸管将阳离子电流与钾离子电流分离。奎宁激活的阳离子电导的相对通透性（Pion）为：PNa/PK/PCs = 1:0.5:0.42。奎宁剂量反应关系用希尔方程描述，K1/2为3.6 mM，希尔系数为5.3。当细胞外[Ca²⁺]（1.8 mM）降至名义上无钙时，电导增强约6倍。这一特性与在体情况下从味觉神经记录到的奎宁反应的观察结果一致。应用8-溴-cAMP后，奎宁诱导的阳离子电流减小。我们得出结论，苦味物质奎宁激活味觉受体细胞中的阳离子通道，该通道在苦味转导中起重要作用。
