Stimulus‐induced release of endogenous amino acids from the Xenopus laevis lateral‐line organ

Abstract

Previously, we described a method for studying stimulus‐induced release of substances from the Xenopus lateral line [Bledsoe et al., J. Acoust. Soc. Am. Suppl. 1 65, S11(A) (1979)]. To date, 13 experiments have been completed in which the release of endogenous amino acids was studied by comparing the effects of pulsatile water motion on the efflux of glutamate and aspartate from isolated skins with and without lateral‐line stitches. For a given experiment paired stitch and nonstitch skins were subjected to two. 30‐min periods of stimulation and two, 30‐min periods of no stimulation in a rotated order‐of‐occurrence. In an overall comparison of mean amino acid levels for the first and second periods of the stimulated versus nonstimulated conditions, stimulation applied to the outer skin surface caused a significant increase in glutamate and aspartate efflux from stitch (p < 0.01) and nonstitch (p < 0.01) skins. The stimulated efflux of glutamate from stitch skins was significantly greater than the stimulated efflux from nonstitch skins (p < 0.01). For aspartate efflux the between skin comparison was less clear cut with stimulation causing a significantly greater efflux from stitch skins than from nonstitch skins (p < 0.01), only when comparing the mean aspartate levels for the first periods of the stimulated versus nonstimulated conditions. Although the source and mechanisms underlying the greater stimulated efflux from stitch skins remain to be determined, the results demonstrate differences between stitch and nonstitch skins under stimulus conditions which should induce release of the afferent transmitter substance(s). [Work supported by NIH and The Kresge Foundation.]