Canine taste nerve responses to umami substances.
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.
Kumazawa
T
T
Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Nakamura
M
M
Kurihara
K
K
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002814:Chorda Tympani Nerve / Q000187:drug effects* / Q000502:physiology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006157:Guanosine Monophosphate / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology*; D012970:Sodium Glutamate / Q000494:pharmacology*; D013649:Taste / Q000187:drug effects* / Q000502:physiology; D013652:Taste Threshold / Q000187:drug effects / Q000502:physiology
D012965:Sodium Chloride; D000584:Amiloride; D006157:Guanosine Monophosphate; D012970:Sodium Glutamate