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First published online June 16, 2004
Journal of Experimental Biology 207, 2639-2648 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01054

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Cadmium effects on mitochondrial function are enhanced by elevated temperatures in a marine poikilotherm, Crassostrea virginica Gmelin (Bivalvia: Ostreidae)

I. M. Sokolova

Biology Department, University of North Carolina at Charlotte, 9201 University City Boulevard, Charlotte NC 28223, USA

View larger version (25K): [in a new window]   Fig. 1. Temperature effects on respiration rates (A), respiratory control and P/O ratio (B) of isolated oyster mitochondria. Respiration rates were measured after addition of ADP (state 3), after all ADP was used up (state 4) and in the presence of oligomycin (state 4+) in isolated oyster mitochondria at different temperatures. Respiratory control ratios were determined as the ratio of state 3 over state 4 respiration (RCR) or state 4+ respiration (RCR+) at different temperatures, and phosphorylation efficiency (ADP/O). Asterisks denote values that are significantly different from those of the respective controls measured at 15°C. Values are means ± S.E.M., N=6–8.

View larger version (26K): [in a new window]   Fig. 2. Effects of cadmium concentration on temperature dependence (Q10) of state 3 and state 4+ respiration in oyster mitochondria. Q10 of 1 indicates a complete loss of temperature dependence of mitochondrial respiration at 25–50 µmol l–1 [Cd2+].

View larger version (18K): [in a new window]   Fig. 3. Effects of cadmium concentration and temperature on state 3 respiration in isolated oyster mitochondria. Open symbols mark the values of state 3 respiration, which are significantly different from the respective controls (0 µmol l–1 of cadmium) measured at the same temperature. Values are means ± S.E.M., N=5–7.

View larger version (19K): [in a new window]   Fig. 4. Effects of cadmium concentration and temperature on (A) state 4 and (B) state 4+ respiration in isolated oyster mitochondria. Open symbols mark the values of state 4 or 4+ respiration, which are significantly different from the respective controls (0 µmol l–1 of cadmium) measured at the same temperature (P<0.05). Grey symbols mark marginally significant differences (P<0.06). Values are means ± S.E.M., N=5–7.

View larger version (31K): [in a new window]   Fig. 5. Effects of cadmium concentration and temperature on respiratory control ratios (RCR) in isolated oyster mitochondria. Asterisks mark respiratory control ratios that are significantly different from the respective controls (0 µmol l–1 of cadmium) measured at the same temperature, are marked with asterisks. Values are means ± S.E.M., N=5-7.

View larger version (22K): [in a new window]   Fig. 6. Effects of cadmium concentration on C. virginica mitochondrial volume in vitro. Changes in mitochondrial volume were monitored as a change in absorbance of mitochondrial suspension at 520 nm at 25°C after 20 min of incubation with varying concentrations of cadmium (+Cd) and after subsequent addition of ADP (+ADP). Mitochondrial swelling in hypo-osmotic medium (375 mOsm, Hyp) was used as a positive control. This method only provides qualitative data about the relative change of mitochondrial volume (swelling vs contraction). Values are means ± S.E.M., N=5.