Quantitative responses of the digestive-lysosomal system of winkles to sublethal concentrations of cadmium

The effects of the experimental exposure to sublethal concentrations of cadmium on the digestive gland lysosomal system of the marine prosobranch Littorina littorea have been studied by means of stereology in fresh frozen cryotome sections after demonstration of beta-glucuronidase activity. The volume density of secondary lysosomes was demonstrated to be independent of both the external concentration of the metal and the exposure-time. However, some punctual increases in this parameter have been related to the alternate renewal of the tissular population of this organelle. The lysosomal surface density showed a dose- and time-dependent significant decrease over the controls. The lysosomal surface to volume ratio increased over the time in the control series whilst decreased significantly in Cd-exposed animals at each sampling period. Lysosomal numerical density was strongly dependent on the external concentration of the metal, changes in this parameter showing the highest signification. It is concluded that sublethal exposure to cadmium leads to fusion of secondary lysosomes to give larger ones. This process is related to lysosomal membrane destabilisation, which could take place after the storage capacity of the organelles have been overloaded.