Metallothionein induction in Littorina littorea (Mollusca: Prosobranchia) on exposure to cadmium

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Abstract
Cadmium uptake, storage and metabolism has been studied in the digestive gland and remaining tissues of the intertidal gastropod Littorina littorea (L). Accumulation of cadmium was linear with time in both of these compartments in individuals exposed to a range of cadmium concentrations (4, 40 and 400 μg Cd l−1).The subcellular distribution of cadmium in the digestive gland and remaining tissues of Littorina littorea reveals that most of the metal is bound to metallothionein, even in controls, and that cadmium associated with metallothionein increases in proportion to cadmium concentrations in the surrounding water.Measurements of metallothionein, made by differential pulse polarography showed that, in the digestive gland, concentrations of this metal-binding protein are not significantly affected by cadmium exposure, while in the remaining tissues they are dose-related.The inherently high levels of metallothionein in the digestive gland of L. littorea explain the role of this tissue as a major site for cadmium storage. However, the lack of significant de novo synthesis of metallothionein in response to cadmium, together with polarographic interferences from high molecular weight thiolic proteins, reduces the value of this tissue preparation as a means of detecting sublethal responses to metals.

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