Effects of thermal stress and tri(n)butyl tin on anaerobic energy metabolism in Mytilus edulis

The purpose of this study was to understand the effects of tri(n)butyl tin (TBT) on anaerobic energy metabolism and whether TBT causes a lowered ability of Mytilus edulis to withstand emersion. The study design included two levels of anaerobic effect and elevated temperature. Two TBT-dosed groups of mussels (10 μg g−1 dry wt) and two control groups, were thermally stressed at 35 °C for 2 h, one TBT/control pair in air and the second TBT/control pair under nitrogen. Using an HPLC-based method, mono- and dicarboxylic acid metabolites associated with anaerobic energy metabolism were quantified before and after treatment for subsamples of all groups. TBT exposure was found to significantly increase anaerobic mortality at elevated temperatures. The rates of accumulation of the anaerobic end products succinate, lactate and propionate were greatest for the nitrogen-exposed TBT group. As an uncoupler of fumarate reductase in anaerobic energy metabolism, TBT causes lowered ATP production and a stimulation of glycogen breakdown and glycolysis consistent with the increased rate of accumulation of anaerobic end products observed in the TBT group relative to the control group. This effect is most pronounced for the strictly anaerobic nitrogen-exposed TBT group. The increased rate of lactate accumulation in the nitrogen-exposed TBT group reflects an increased glycolytic rate leading to the increased pyruvate levels observed for this group. This lowering of anaerobic metabolic efficiency is consistent with the observed lowered tolerance of emersion in TBT-exposed mussels.