Changes in protein metabolism and histology of the hepatopancreas of the snail Pila globosa (Swainson) on exposure to lethal and sublethal concentrations of Nickel

The levels of soluble and structural proteins progressively decreased over the time of exposure at 12, 24, 36 and 48 h in the hepatopancreas (HP) of snails (Pila globosa) exposed to lethal concentration (30 mg l-1) of nickel, with a corresponding increase in the levels of free amino acids (FAA) and protease activity. In snails exposed to sublethal concentration (3 mg l-1), the level of soluble proteins decreased at day 5 and increased progressively at days 10, 20 and 30, whereas the level of structural proteins increased over time of exposure from days 5 to 30. The protease activity was enhanced at days 5 and 10 (day 5 30). The FAA levels, however, decreased at all the days of exposure in the order of day 5 20 > 30. Corresponding to the protein levels, rupturing of basement membrane, tubular atrophy, cytoplasmic degeneration and cell necrosis were observed at 12 h in the hepatopancreas of snails exposed to lethal concentration. At 24 and 36 h, there was a gradual degeneration of the tubular cells and extrusion of cytoplasmic material into the haemocoelic spaces. At 48 h, further degenerative changes were noticedwith total atrophy of the digestive gland and maximum disintegration of gland tubules. In sublethal concentration at days 5 to 10, the histological section of hepatopancreas showed enlarged intertubular area filled with numerous vacuoles. At days 20 and 30, the secretary cells were conspicuous in their loci. The tubules were loose and scattered. At day 30, the structure of HP appeared almost normal. However, the number of tubules was less than that of control and their arrangement was not so compact as in the control. The observations indicated breakdown of tissue proteins in HP on exposure of snails to the lethal concentration and elevation of protein synthesis when exposed to the sublethal concentration of nickel. Similar effects were also evident from histological sections.