INDUCTION OF METALLOTHIONEIN SYNTHESIS IN THE GILL AND KIDNEY OF LITTORINA-LITTOREA EXPOSED TO CADMIUM

Induction of metallothionein synthesis in Littorina littorea exposed t o cadmium (400 mu g l(-1)) is tissue dependent. Concentrations of the metal-binding protein increased by a factor of four in the gills and b y a factor of three in the kidney. Gel filtration chromatography of he at-treated cytosolic extracts reveals that cadmium, accumulated in bot h the gills and the kidney, is bound principally to the newly formed m etallothionein. Cadmium saturation of the protein (at an MT:Cd molar r atio of 1:5) and the approach of steady-state condition for Cd accumul ation was indicated in the latter tissue, but there was little evidenc e for Cd equilibrium in gills. Metallothionein levels in the kidney of L. littorea can be determined on a routine basis in laboratory experi ments and in field samples by differential pulse polarography of whole -cytosol preparations: heat-treatment/centrifugation is sufficient to remove most of the interference from high-molecular-weight thiolic pro teins. In contrast, the use of gelfiltration chromatography is recomme nded alongside polarographic analysis of the gill cytosol to enable qu antification of, and compensation for, such interferences, and hence t o ensure that only metallothionein is determined. Measurements of meta llothionein induction in the kidney of Littorina may therefore prove u seful in the determination of sublethal biological response to metal c ontamination. background metallothionein concentrations of 3-4 mg g(-1 ) (measured polarographically) serve as a baseline against which sampl es from contaminated sites can be assessed.