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(88-03) Cd-Metallothionein of terrestrial pulmonates as a biomarker for metal pollution: Combining field and laboratory studies. Dallinger, Reinhard*,1, Berger, Burkhard1, Lagg, Bernhard1, Chabicovsky, Monika1, 1 Dp. of Zoology and Limnology, University of Innsbruck, Innsbruck, Austria ABSTRACT- Terrestrial pulmonates such as the helicid species Helix pomatia, Arianta arbustorum and Cepaea hortensis belong, among terrestrial invertebrates, to the most avid accumulators of Cd. This metal is assimilated by terrestrial helicids mainly via the gut and accumulates in the snail midgut gland. There, the metal is specifically sequestered by Metallothioneins (MTs). These are ubiquitous, low molecular mass proteins which can bind, by virtue of their structural features, up to seven divalent metal ions. In most animal species, MT molecules are loaded with different species of metal ions among which Cd2+ is only one. In contrast to this, a particular MT isoform in midgut gland of terrestrial helicids is specifically expressed by Cd induction, binding the major fraction of this metal entering the animal body. Because of these metal-specific features, Cd-MT of helicids has been suggested as a potential biomarker for Cd contamination in terrestrial habitats. The validity of this hypothesis was evaluated by combining field studies and laboratory experiments in which Cd-MT induction in snail midgut gland was detected by means of a metal saturation assay. In all three helicid species mentioned above, the specific Cd-MT isoform appears to be the predominant MT variant occurring after Cd exposure in vivo, independently of whether animals have attained their Cd burden under laboratory conditions or in the field. Four important features render Cd-MT induction of these species a valuable biomarker. Firstly, synthesis of the Cd-MT isoform can rapidly be induced by Cd administration, even after a short-term exposure event. Secondly, the level of Cd-MT induction in midgut gland is directly related to the metal dose administered. Thirdly, induced concentrations of Cd-MT remain persistent over extended periods of time, even if metal exposure has been ceased a long time ago. Fourthly, Cd-MT is specifically and exclusively induced in response to Cd intoxication. It is concluded that, owing to the extensive knowledge of molecular, biochemical and functional features of Cd-MT in helicids, this specific MT isoform can indeed be used as a valuable biomarker for Cd contamination in terrestrial habitats. Key words: Cadmium, Metallothionein, Biomarker, Helicidae |
