Responses to Binary Mixtures of Amino Acids in the Facial Taste System of the Channel Catfish

Abstract

Prior studies indicated that olfactory receptor responses to mixtures of amino acids in the channel catfish, lctalurus punctatus, were enhanced only if the components bound to independent receptor sites [1,2]. Here we report the responses of 32 multiunit preparations and 55 single facial taste fibers to binary mixtures of amino acids. Tested were (a) l-alanine and l-arginine; l-alanine and l-proline; l-arginine and l-proline, and l-arginine and l-glutamate (group I), amino acids indicated to bind to independent taste receptor sites, and (b) l-alanine and glycine; l-alanine and l-methionine; l-arginine and l-alphaamino beta guanidino proprionic acid, and l-alanine and l-glutamate, amino acids indicated to bind to the same or highly cross-reactive taste receptor sites (group II). All component stimuli were adjusted in concentration to provide approximately equal response magnitude- height of integrated multiunit activity (IMA) or action potentials generated/3s of response time/single taste fiber (STF). The mixture discrimination index (MDI), defined as the response to the mixture divided by the average of the responses to the component stimuli, was calculated for each binary mixture. All group I binary mixtures resulted in enhanced taste activity [MDI: (IMA) = 1.16 ± 0.12 (SD), n = 44; (STF) = 1.17 ± 0.20 (SD); n = 116], whereas all group II binary mixtures showed no significant enhancement [MDI: (IMA) = 1.06 ± 0.15 (SD), n = 41; (STF) = 1.03 ± 0.14 (SD); n = 34]. There were no significant differences between the IMA and STF MDIs for group 1 and group 2 mixtures, respectively, nor were there differences between the MDIs of the two major fiber types, the alanine and arginine fibers [3].