Citrate ions enhance taste responses to amino acids in the largemouth bass

The glossopharyngeal (IX) taste system of the largemouth bass, Micropterus salmoides, is highly selective to amino acids and is poorly responsive to trisodium citrate; however, IX taste responses to specific concentrations of L- and D-arginine and L-lysine but not L-proline were enhanced by citrate but not sodium ions. Binary mixtures of L-arginine (3 x 10(-4)M and 10(-3)M) or D-arginine (10(-3)M) + trisodium citrate (10(-3)M; pH 7-9) resulted in enhanced taste activity, whereas binary mixtures of higher concentrations (10(-2)M and 10(-1)M) of L- or D-arginine + 10(-3)M trisodium citrate were not significantly different from the response to the amino acid alone. Under continuous adaptation to 10(-3)M citrate, taste responses to L-arginine were also enhanced at the identical concentrations previously indicated, but responses to 10(-2)M and 10(-1)M L-arginine were significantly suppressed. Under continuous adaptation to 10(-2)M L-arginine, taste responses to 10(-2)M, 10(-1)M, and 10(0) M citrate were significantly enhanced. Cellular concentrations of both citrate and amino acids in prey of the carnivorous largemouth bass are sufficient for this taste-enhancing effect to occur naturally during consummatory feeding behavior. Citrate acting as a calcium chelator is presented as a possible mechanism of action for the enhancement effect.