Effects of copper exposure on the energy metabolism in juveniles of the marine clam Mesodesma mactroides

Abstract

In freshwater osmoregulating mollusks, Cu can cause toxicity by inducing ionoregulatory disturbances.In mussels, it inhibits the activity of key enzymes involved in Na+uptake and consequently induces ionicand osmotic disturbances. In snails, Cu induces disruption of the Ca2+homeostasis leading to effects inshell deposition and snail growth. However, the mechanisms involved in Cu toxicity in osmoconformingsweater mollusks remain unclear. Recent findings from our laboratory have suggested that Cu toxicityin marine invertebrates can be associated with both ionic and respiratory disturbances. In the presentstudy, metabolic changes induced by waterborne Cu exposure were evaluated in the osmoconformingclam Mesodesma mactroides, a bivalve species widely distributed along the South American sandy beaches.Juvenile clams were kept under control conditions (no Cu addition in the water) or acutely (96 h) exposedto Cu (96-h LC10= 150 g L−1) in artificial seawater (30 ppt). ATP, protein, lipid, glycogen and glucosecontents were analyzed in gills, digestive gland, pedal muscle and hemolymph. Dinucleotide (NAD+andNADH) content was also analyzed in gills, digestive gland and pedal muscle while pyruvate and lactatecontent was determined in pedal muscle and hemolymph. In all tissues analyzed, Cu exposure did notaffect ATP content and NAD+/NADH ratio, except in the hemolymph, where a decrease in ATP content wasobserved. These findings indicate that clam cells, except those from hemolymph, were able to maintain aconstant level of free energy. A significant increase in total protein content was observed in the digestivegland, which could be a compensatory mechanism to counteract the higher level of protein oxidationpreviously observed in M. mactroides exposed to Cu under the same experimental conditions. Finally,reduced glucose content in the pedal muscle paralleled by increased lactate content in the pedal muscleand hemolymph was observed in Cu-exposed clams. Overall, these findings indicate that Cu exposure isleading to an increased reliance upon the anaerobic energy production to maintain the overall cellularATP production in the clam M. mactroides.