Latent beta-glucuronidase and glucosaminidase activities have been demonstrated in small cytoplasmic particles, which may possibly be primary lysosomes, as well as some larger granules of the digestive cells of the common mussel. Latency was indicated by increased staining of these structures following incubation in buffer at pH 4.5 at 37 degrees C. The exposure of mussels to temperatures of 25-28 degrees C over a period of four days induced a significant decrease in the latency of lysosomal glucosaminidase. Thermal death produced labilization of lysosomes although selective release of hydrolase activity was indicated by the differential latency of glucosaminidase and glucuronidase. The injection of hydrocortisone induced a significant increase in latency in stressed animals, indicating that the stress response involved changes in structure and function of membranes.
ABSTRACT. Mussel hemocytes accumulate rhodamine B within their lysosomal compartment. This intracellular retention, detected and quantified by computerised confocal microscopy, is enhanced by the presence of verapamil. Study of 2 different populations showed alteration in rhodamine B retention and simultaneous differential expression levels of proteins immunorelated to the multidrug resistance (MDR) transporter in relation to their environment. Chronic exposure of animals to the Vinca antitumor alkaloid vincristine causes the hemocytes to accumulate less rhodamine B, to be more sensitive to verapamil and to express more MDR-related proteins. These data add consistency to prevlous results on multixenobiotic resistance in mussels.
Marine mussels Mytilus edulis (L.) from 3 different age/size groups were exposed for 24 h to combined hypoxia and hyperthermia (28 k 1°C) and subsequently reimmersed in seawater at 10 k 1°C. Exposure to the physical stressor induced lysosomal destabilisation and enlargement in the digestive cells of mussels of all ages. Recovery of lysosomal integrity was demonstrated after 24 h in seawater by the youngest mussels (2-4 yr) only. Levels of unsaturated neutral lipids increased in all mussels followlng exposure and was associated with enlarged lysosomes No consistent pattern or significant change was observed in lipid levels in mussels of any age during the recovery period. Levels of lipofuscin (stress pigment) in mussels exposed to hypoxia and hyperthermia and in those subsequently reunmersed in seawater did not follow any consistent pattern, but were generally much higher in the youngest n~ussels than in the older age groups. Recovery of metabolic rates to control levels was observed 12 h after reimmersion in seawater in the youngest mussels only. Metabolic rates of the 6-8 and 210 yr mussels remained elevated relative to the controls after this time. These findings indicate that the stress reaction is independent of age but that the potential for recovery of lysosomal integrity and metabolic rate is age-related.
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