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Urechis caupo is a marine worm that lives and reproduces in sediments containing a variety of potentially toxic environmental chemicals (xenobiotics). Its embryos have a multixenobiotic transporter, which is similar to the multidrug transporter in mammals, as indicated by their ability to transport a variety of moderately hydrophobic compounds such as dyes, drugs, and pesticides out of the cells. The cell membranes of the embryos contain a protein of approximately 145 kD that is immunologically related to the mammalian multidrug transport protein and that can be cross-linked by a photoactivatable substrate of the mammalian multidrug transport protein. The sediments in which the worm lives contain potential substrates for the transporter, indicating that this multixenobiotic transport activity may protect Urechis embryos from naturally occurring toxic compounds. Embryos of a sea urchin from a pristine environment do not have this transport activity and are sensitive to hydrophobic toxins. These data strongly support a role for multixenobiotic transport as a mechanism of protection from environmental toxins and indicate an unsuspected mode of protection in invertebrate embryos.

Abstract-A multixenobiotic defense mechanism similar to a P-glycoprotein multidrug transporter was characterized in the gills of the mussel Mytilus galloprovincialis from Monterey, California. Using a fluorescent dye assay, we measured multixenobiotic transport activity in individual gill cells and assessed the effects of inhibitors or competitive substrates on activity. Natural products that inhibit the mammalian transporter also affected dye transport in the mussel gill. Four moderately hydrophobic pesticides (dacthal, chlorbenside, sulfallate, and pentachlorophenol) and four highly hydrophobic xenobiotics (p,pЈ-DDT, p,pЈ-DDD, p,pЈ-DDE, and Aroclor 1254) all inhibited the efflux of dye from the gills, indicating their interaction with a multixenobiotic transport mechanism in this organism. The reactivity with these highly hydrophobic compounds seen in M. galloprovincialis differs from related transporters found in other organisms. A protein in the gill cross-reacts with antibodies directed against the mammalian multidrug transport protein. The level of protein can be assessed easily by dot blot procedures and may facilitate quantitation of protein levels in field situations.