Kumazawa T, Nakamura M, Kurihara K
Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Physiol Behav. 1991 May;49(5):875-81. doi: 10.1016/0031-9384(91)90197-v.
The taste responses to the "umami substances" such as monosodium glutamate (MSG), guanosine 5'-monophosphate (GMP) and inosine 5'-monophosphate (IMP) were recorded from the canine chorda tympani nerve. A large synergism was observed between MSG and the nucleotides in most mongrel dogs (type A dog). The extent of the synergism between MSG and the nucleotides was much larger than that observed in any other animal examined except for humans. No synergism was observed between the nucleotide (GMP) and stimuli other than MSG, such as NaCl, HCl, sucrose, quinine, and glycine. It was concluded that the dog is a suitable experimental animal for studies on the responses to umami substances. In order to differentiate umami and salt components in the responses to umami substances, effects of amiloride on the responses were examined. Amiloride inhibited the response to MSG, but did not inhibit the response to GMP alone or those induced by synergism between GMP and MSG. The present results favor a conclusion that GMP acts as an agonist and MSG acts as a modulator for the umami receptor in the dog. The synergism can be explained by an allosteric model where the umami receptor is assumed to have two binding sites, one for GMP and another for MSG.
从犬的鼓索神经记录了对“鲜味物质”如味精（MSG）、5'-鸟苷酸（GMP）和5'-肌苷酸（IMP）的味觉反应。在大多数杂种犬（A型犬）中，观察到味精与核苷酸之间有很大的协同作用。味精与核苷酸之间的协同程度比除人类外其他任何已检测动物中观察到的都要大得多。未观察到核苷酸（GMP）与除味精外的其他刺激物（如氯化钠、盐酸、蔗糖、奎宁和甘氨酸）之间有协同作用。得出结论，犬是研究对鲜味物质反应的合适实验动物。为了区分对鲜味物质反应中的鲜味和盐分成分，研究了氨氯地平对反应的影响。氨氯地平抑制对味精的反应，但不抑制单独对GMP的反应或由GMP与味精之间协同作用诱导的反应。目前的结果支持这样一个结论，即GMP作为犬鲜味受体的激动剂，而味精作为调节剂起作用。这种协同作用可以用变构模型来解释，在该模型中，假定鲜味受体有两个结合位点，一个用于GMP，另一个用于味精。
