Gustatory Responses to Organic Acids in the Yellowtail Seriola quinqneradiata.

Abstract

The stimulatory effects of a total of 24 organic acids and glycolytic and citric acid cycle inter-mediates on the taste receptors of the yellowtail Seriola quinqueradiata were studied by recording the electrical responses from the facial nerve innervating the anterior palate. The palatine receptors responded to L-lactic, DL-glyceric, pyruvic, glycolic, D-2-phosphoglyceric, oxalacetic, and propionic acids at 10-2M and pH 7.0-8.0. Their threshold was lowest for L-lactic acid, located at around 10-16M, as low as that of praline, the most potent amino acid for this fish. The thresholds of the other acids were 10-4M or higher. The fact that these acids were effective at neutral or weak alkali pHs suggests that the anion of these organic acids stimulates the receptors at this pH range. The sensitivities of single fibers to L-lactic, pyruvic, and glycolic acids were also investigated. This revealed fibers which responded well to these organic acids, but also many fibers which did not respond to them, showing the non-uniform distribution of sensitivity to these among taste units in the palatine taste system of the yellowtail.