Amino acids, including neurotransmitter candidates, in a hair cell-enriched fraction from the lateral line of Xenopus laevis

A hair cell-enriched neuromast fraction from the lateral line of Xenopus laevis was compared with adjacent tactile organ and epidermis for content of primary amine-containing components. Of 32 components quantitated by cation-exchange HPLC with fluorescence detection of orthophthalaldehyde adducts, L-alpha-amino adipic acid, O-phosphoethanolamine, L-alpha-glycerophosphorylethanolamine, O-phospho-L-serine, and L-lysine were elevated in concentration in the neuromast relative to the tactile organ an/or epidermis. L-Aspartic acid, L-asparagine, L-glutamic acid, and taurine were present at higher levels in the tactile organ or epidermis than in the neuromast. Taurine was found in only trace amounts in the neuromast. The tactile organ and epidermis contained at least 3 unidentified primary amine components that were absent or reduced in amount in the neuromast. This study demonstrates that the epidermally-derived, hair cell-containing neuromast of the lateral line of Xenopus laevis is different in molecular composition from surrounding epidermally-derived tissue. Such differences may reflect specialized mechanoreceptive function.