Mechanisms of stimuli discrimination and transduction in gustatory and olfactory cells

利用味觉细胞、神经母细胞瘤和脂质体研究了味觉和嗅觉细胞对化学刺激的识别机制。在各种味觉刺激中，苦味物质吸附在细胞膜的脂质层上，导致受体电位的产生。根据受体膜脂质组成的差异，对人苯硫胺的“味觉盲”进行了检查。关于气味的识别，人们提出了各种不同的机制。许多研究者认为每种气味都存在特定的受体蛋白，但问题是动物是否对多种气味都有各自的特异性受体蛋白。我们发现神经母细胞瘤细胞和具有一定脂质成分的脂质体被各种气味剂去极化，类似于嗅觉细胞。脂质组成的变化导致对各种气味的特异性变化。目前的研究结果表明，气味识别可以通过每个细胞的受体膜的脂质组成不同来解释。利用味觉器官、神经母细胞瘤、分离的嗅觉细胞和脂质体研究了不同味觉刺激和气味刺激下膜电位变化的机制。外介质中离子与不渗透离子的交换不影响膜电位在化学刺激下的变化。脂质双层膜对苦味物质和气味物质的膜电位变化发生在膜两侧离子浓度相同的条件下，表明膜电位变化是由相边界电位的变化引起的。

The discrimination mechanisms of chemical stimuli in taste and olfactory cells were studied using taste cells, neuroblastoma and liposomes. Among various taste stimuli, bitter substances were found to adsorb on lipid layers of the membranes, which leads to generation of the receptor potentials. "Taste blind" for phenylthiocarbamide in man was examined in terms of difference in lipid composition of the receptor membranes. As for the discrimination of odorants, various mechanisms have been proposed. Many investigators have believed that there exist specific receptor protein for each odorant, but question arises whether or not animals have respective specific receptor proteins for numerous odorants. We found that neuroblastoma cells and liposomes having certain lipid compositions are depolarized by various odorants similarly to olfactory cells. Changes in the lipid composition led to changes in specificity to various odorants. The present results suggested that odorant discrimination can be explained by posturating that lipid composition of receptor membrane of each olfactory cell is different from one cell to another.The mechanisms of changes in the membrane potentials in response to various taste stimuli and odorants were examined using taste organs, neuroblastoma, isolated olfactory cells and liposomes. Exchanges of ions in external medium with impermeable ions did not affect the changes of the membrane potentials in response to chemical stimuli. The membrane potential changes of lipid bilayer membranes in response to bitter substances and odorants occurred under the conditions that ion concentration at both sides of membranes is the same, suggesting that the membrane potential changes are induced by changes in the phase boundary potentials.