We found that if you measure production of reactive oxygen species in the presence of cadmium, it is strongly increased, Sokolova said. Normally, the amount of oxygen that slips towards producing reactive oxygen is something like five percent in mollusks. When cadmium is present, then it is 30 percent, she noted.

In the presence of cadmium, mitochondria use nearly 30 percent of the oxygen that they consume to produce reactive oxygen species instead of using it for ATP synthesis.

The research found that the cadmium-induced increase in ROS production does not harm oyster cells when the organisms are living in temperature conditions of 20 degrees centigrade or lower, as other chemical processes in the mitochondria are able to neutralize ROS under those conditions. However, at 30 degrees centigrade the researchers found that the cleanup processes cannot cope with ROS and oxidative damage occurs.

The team detected the effect by examining the metabolic enzyme aconitase, which is susceptible to damage from ROS. In the presence of cadmium and at 30 degrees centigrade, significant quantities of the enzyme were disabled, indicating oxidative damage.

The degree of inactivation of aconitase can be used as a marker of how bad the oxidative damage is. We dont really see a lot of oxidative damage at 20 degrees, even when we see a larger amount of reactive oxidative species being produced in the presence of cadmium. This means that the anti-oxidant systems are still adequate. But at 30 degrees the same concentrations of cadmium cause extensive oxidative damage and we see it in the inactivation of aconitase.

According to Sokolova, the combined effects of temperature and heavy metal contamination on metabolic chemistry spell trouble for oysters and probabl
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Contact: James Hathaway
jbhathaw@email.uncc.edu
704-687-6675
University of North Carolina at Charlotte
13-Dec-2006