Alteration of mitochondrial membrane potential (∆Ψm) and phosphatidylserine translocation as early indicators of heavy metal-induced apoptosis in the earthworm Eisenia hortensis

Abstract

The effects of the heavy metals cadmium and copper (50-500 µM) on the apoptotic events
involving changes in mitochondrial membrane potential (∆Ψm) and phosphatidylserine (PS)
translocation were investigated in the immune cells (celomocytes) of the earthworm Eisenia hortensis. Using the fluorescent probe JC-1, loss of membrane potential due to depolarization was detected in a greater proportion of cases when induced by cadmium compared to copper (58.7 % vs. 37 %) and at a lower concentration (50 µM vs. 125µM). With the use of the general caspase inhibitor Z-VAD-fmk, PS translocation detected by annexin V-FITC was found to be caspase-dependent when induced by cadmium at 125-250 µM but not at 50 µM or 500 µM; a high proportion of earthworms (60 %) exhibited inhibitory effects. Additionally, the collapse in membrane potential and PS translocation were found to strongly correlate (r > 0.5) in 89 % of cases when induced by cadmium and copper. Thus, heavy metals appear to induce death in celomocytes of E. hortensis through apoptosis by means of caspase dependent pathways.