ANTENNULAR CHEMOSENSITIVITY IN THE SPINY LOBSTER,PANULIRUS ARGUS: STUDIES OF TAURINE SENSITIVE RECEPTORS

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Abstract
1. Taurine sensitive receptors in the antennules of the spiny lobster, Panulirus argus, were identified electrophysiologically. 2. Recordings from single receptors revealed a narrow and consistent specificity when tested with taurine, taurine analogs and derivatives, and structurally related compounds. 3. Taurine was the most stimulatory compound tested. Threshold concentrations for 36 individual receptors ranged from 10-8 to 10-10 M. 4. The taurine analogs, hypotaurine and β-alanine, were also very effective but the phosphonic acid analog of taurine was ineffective. 5. Regarding receptor specificity, receptor stimulation was greatest with compounds having single terminal basic (amine) and acidic groups separated by two carbon atoms. Compounds having terminal basic and acidic groups separated by three to five carbon atoms were also active. However, activity decreased with the distance of separation of charged groups. 6. Alpha-amino acids and compounds with terminal basic and acidic groups separated by only one carbon atom were virtually ineffective. 7. Receptor stimulation was markedly less with structurally related compounds that either lacked a terminal amine group, had additional amine or acidic groups, or had neutral side chains. 8. Dose/response relationships of four differentially stimulatory compounds (taurine, hypotaurine, β-alanine and υ-aminobutyric acid) applied to single receptors were compared and found to describe a series of roughly parallel lines. This implies that a less stimulatory compound effects receptor response in the same manner as a more stimulatory compound applied at a lower concentration. 9. The possible role of taurine in food finding, and the similarity of the specificity of antennular taurine receptors and taurine endoreceptors identified in various organisms are discussed.