Responses to Monosodium Glutamate and Guanosine 5′‐Monophosphate in Rat Fungiform Taste Cellsa

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Abstract
Monosodium glutamate (MSG) elicits a unique taste sensation called umami. The umami sensation is potentiated by the presence of 5′‐ribonucleotides such as guanosine 5′‐monophosphate (5′‐GMP). We have used giga‐seal whole cell recording to examine glutamate transduction in individual cells of isolated rat fungiform taste buds. Approximately 56% of fungiform taste cells responded to bath application of glutamate. Three types of responses occurred: decrease in inward holding current; increase in inward holding current; and a biphasic response, with an increase followed by a decrease in holding current. Similar responses were observed in response to 5′‐GMP. Further, responses to 5′‐GMP may occur in cells that are glutamate‐insensitive, suggesting that different receptors mediate the transduction of glutamate and 5′‐GMP. Simultaneous bath application of glutamate and 5′‐GMP resulted in a synergistic response in some taste cells.