Bivalve Scapharca Inaequivalvis Research Articles

Cadmium accumulation and Cd-binding proteins in the bivalve Scapharca inaequivalvis

In the arcid clam, Scapharca inaequivalvis, cadmium was accumulated in the kidneys, gills, viscera, mantle, foot, muscle and red blood cells. Maximum levels were reached in the kidney (725.70 μ/g dry weight) after 4 weeks exposure to 0.5 μg Cd/ml sea-water. The accumulation was higher during the warm rather than in the cold season and in animals exposed to 0.5 as compared with 0.05 μg Cd/ml sea-water. Concentrations of zinc and copper were unaffected by cadmium treatment, whereas iron levels changed during cadmium exposure. When molluscs were returned to natural sea-water, cadmium levels fell slowly. The metal was found in the cytosolic fraction, bound to a low molecular weight ligand, shown by gel filtration to be a Cd-protein with an apparent molecular weight of 10,000 Da, possibly a metallothionein. Ion exchange chromatography of this protein isolated from the viscera revealed the presence of at least two Cd-binding isoforms; the -SH: Cd ratio of the main isoform was 2.8, the UV spectra presented a strong absorption band at 250 nm.

Hematin and sulfide removal in nemolymph of the hemoglobin-containing bivalve Scapharca inaequivalvis

Hematin and sulfide removal in nemolymph of the hemoglobin-containing bivalve Scapharca inaequivalvis

Influence of long-term hypoxia on the energy metabolism of the haemoglobin-containing bivalve Scapharca inaequivalvis: critical O2 levels for metabolic depression.

The oxygen consumption rate of Scapharca inaequivalvis measured under normoxic conditions over 48 h showed a significant daily cycle with lowest values occurring shortly after the dark period; all hypoxia exposure experiments were carried out during the declining part of the cycle. Animals were exposed to a constant level of hypoxia for a 12-h period in a series of 14 experiments, each at a different oxygen tension. The oxygen consumption was measured continuously, and the extent of accumulation of end-products (succinate and propionate), and the inhibitory effect of adenosine triphosphate on phosphofructokinase were determined at the end of exposures. All three parameters (oxygen consumption, end-product accumulation, phosphofructokinase inhibition) showed a remarkable correlation with major changes occurring between 2.5 and 1.5 ppm (7 and 4 kPa) O2. The oxygen consumption rates showed a drop to 6% of the normoxic rate, but a consistent low consumption remained below 2 ppm (5.5 kPa) which partly recovered over the 12-h exposure period by about three-fold. Succinate and propionate accumulated progressively between 2.5 and 1.5 ppm (7 and 4 kPa); at [O2] less than 1.5 ppm (4 kPa) the concentration did not increase further, indicating that anaerobic metabolism had reached a maximum. Over the same range, phosphofructokinase showed an increased sensitivity for adenosine triphosphate, the lower inhibitor concentration at 50% Vmax value pointing to depression of glycolytic rate. Despite the activation of anaerobic metabolism and the evident depression of aerobic metabolism, simple calculation demonstrates that Scapharca inaequivalvis relies mainly on aerobic metabolism even during severe hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobic metabolism of erythrocytes of the arcid clam Scapharca inaequivalvis (Bruguiere): effects of cadmium

1. 1. Anaerobic metabolism was studied in erythrocytes of the bivalve Scapharca inaequivalvis and compared with other tissue cells. In all cells aspartate reserves are utilized and alanine and succinate accumulate. 2. 2. Erythrocytes are distinct from other tissues as regards the anerobic energy supply. Phosphoarginine is not stored in the erythrocytes. The low glycogen content and the absence of glycogen phosphorylase indicate that the former cannot serve as anaerobic fuel. 3. 3. During 24 hr of anaerobiosis the energy charge in the erythrocytes decreased from 0.83 to 0.64. 4. 4. Extremely high concentrations of free β-alanine were detected in the erythrocytes. 5. 5. Plasma glucose concentration increased from 0.086 to 0.228 μmol per ml during 96 hr of anaerobiosis. 6. 6. Exposure to 50 ppb Cd during 6 weeks did not influence the energy charge during subsequent anaerobiosis, but the increase of alanine was significantly lowered.

Energy metabolism during anaerobiosis and recovery in the posterior adductor muscle of the bivalve Scapharca inaequivalvis (Bruguiere)

1. 1. In the posterior adductor muscle of Scapharca inaequivalvis both aspartate and glycogen were substrates for anaerobic metabolism. ATP and arginine phosphate only contributed to a small extent. Alanine and succinate were major end products, whereas opines were minor end products. Lactate production was not observed. 2. 2. The ATP turnover rate was reduced by a factor of 6 in the later anoxic period. Glycolysis and aspartate contributed about 90% either during the initial step or during the prolonged anoxia. 3. 3. Recovery of 24 hr was not enough for a complete restoration of energy reserves, whereas anaerobic end products were eliminated over this period. There was no strombine or lactate accumulation.