Quinine suppression of single facial taste fiber responses in the channel catfish.

Two groups of single facial taste fibers that were responsive to quinine hydrochloride (QHCl) and amino acids were identified in the channel catfish, Ictalurus punctatus. Group I fibers were significantly more excited by quinine hydrochloride (QHCl) than were group II fibers. QHCl (10(-3) M), as one component in a binary mixture, suppressed taste responses of group II fibers to 10(-4) M amino acids (other component) by 61%, but did not inhibit significantly the responses to L-alanine of group I fibers. QHCl (10(-2) M) suppressed the response to 10(-4) M L-alanine of group I fibers by 58% and group II fibers to 10(-4) M L-alanine, L-arginine and L-proline by 89-100%. The suppression of amino acid responses of both groups of fibers by QHCl was reversible in subsequent testing of stimuli in the absence of QHCl. QHCl also suppressed the taste responses to other bitter stimuli [10(-3) M caffeine and 10(-2) M denatonium benzoate(DB)]; however, neither caffeine nor DB suppressed amino acid taste responses. Possible mechanisms for the suppressive effect of QHCl on taste nerve activity are discussed.