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Effect of cadmium exposure on P‐glycoprotein expression and activity in eastern oysters, Crassostrea virginica

Heavy metal pollution is a worldwide problem, and cadmium (Cd) is one of the most noxious environmental pollutants responsible for episodes of chronic poisoning in humans and posing serious threat to wildlife. One of the possible mechanisms of cell protection against Cd is an increase in expression of P‐glycoprotein (P‐gp) – an ATP‐depending pump which translocates a variety of xenobiotics out of the cell. We studied P‐gp expression and function in control and Cd exposed (50 ìg L‐1 Cd, 30 days) oysters Crassostrea virginica. Expression of P‐gp protein was significantly higher (2–2.5 fold) in cell membranes of Cd‐exposed oysters compared to the controls; no difference in P‐gp expression was observed in mitochondria of control and Cd‐exposed oysters. No difference in P‐gp mRNA expression was found between control and Cd‐exposed oysters indicating regulation at post‐transcriptional level. P‐gp activity was measured using Rhodamine B (RB) efflux assay and showed a 3.5‐7‐fold increase in P‐gP dependent RB extrusion in Cd exposed oysters. Cd exposure resulted in elevated rated of tissue MO2 by 25%. However, P‐gp inhibitors (cyclosporin A and JS‐2190) had no significant effect on tissue oxygen consumption indicating that P‐gp contribution to energy budget is negligible.