Glutathione and Metallothionein Status in an Acute Response by Mercenaria mercenaria Brown Cells to Copper in Vivo

Red glands of Mercenaria mercenaria comprise brown cells that accumulate, detoxify, and excrete copper. Brown cell involvement in metal detoxification is due in part to endogenous glutathione (GSH) and metallothionein (MT). The intent of this study was to test the hypotheses that brown cell GSH functions in protection against Cu22+ toxicity, that brown cell GSH provides the initial defense against Cu22+ prior to brown cell MT induction, and that MT variants (MTI, MTII), if present are unequal in response to Cu22+. Brown cells were analyzed for GSH and MT after 0.25, 1, 2, 3, and 4 days of treatment of Mercenaria with 0.01 and 0.05 ppm Cu22+. Glutathione initiated the brown cell acute response (within the first day of treatment) to both the 0.01 and 0.05 ppm Cu22+ treatments. Metallothionein in brown cells increased to Day 4 during treatment with 0.01 ppm Cu22+, whereas MT concentration was greatest at Day 2 after which it decreased to Day 4 with treatment of 0.05 ppm Cu22+. The change in MTII relative to its control was greater than that of MTI in the brown cell acute response to 0.01 ppm Cu22+ and also for Days 0.25 to 2 in response to the 0.05 ppm Cu22+ treatment. At Days 3 and 4 with the 0.05 ppm Cu22+ the change in MTI/MTII ratio was due to a greater change in MTI than MTII relative to their respective controls. The variants of brown cell MT appear to respond differently to Cu22+ depending on the Cu22+ treatment concentration.