TRANSEPIDERMAL ACCUMULATION OF NATURALLY OCCURRING AMINO ACIDS IN THE SAND DOLLAR, DENDRASTER EXCENTRICUS

¹ Department of Developmental and Cell Biology, University of California, Irvine, Irvine, California 92717

1. Influx of amino acids from dilute solution into the sand dollar, Dendraster, was measured by following the disappearance of radioactivity in the medium supplying known labeled substrates. Net flux was monitored simultaneously by following the decrease in primary amines in the medium fluorometrically. Rates of influx and net flux correspond closely at ambient concentrations greater than 5 µM.

2. Dendraster is capable of net accumulation of some of the primary amines normally found in the interstitial water of its sediment habitat.

3. A sensitive method for location of amino acids on thin layer chromatograms is described. Comparison of interstitial water before and after exposure to Dendraster shows a changed pattern of amino acids, as well as a decrease in total amino acids, which is consistent with measurements of rates of influx with single substrates.

4. Comparison of rates of influx of naturally occurring primary amines with the metabolic requirements of animals as estimated from their oxygen consumption indicates that Dendraster can acquire sufficient reduced carbon to account for its oxidative needs if its surface is exposed to naturally occurring primary amines at concentrations greater than or equal to 35 µM.

5. Primary amines in the interstitial water of sediment in the immediate vicinity of a shallow water population of Dendraster range in concentration from 17 to 244 µ (115 ± 60 µM).

6. Dendraster lives in an environment which is relatively rich in amino acids, and it possesses a transport system which can accumulate these compounds at rates sufficient to provide a significant supplement to other forms of feeding. These findings support the hypothesis that sustenance of epidermal structures of echinoids and asteroids may be relatively independent of translocation of nutrients from the digestive organs and may be based primarily on transepidermal influx of nutrients from the medium.

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