Bivalves naturally exposed to toxic algae have mechanisms to prevent from harmful effects of diarrhetic shellfish poisoning (DSP) toxins. However, quite few studies have examined the mechanisms associated, and the information currently available is still insufficient. Multixenobiotic resistance (MXR) is ubiquitous in aquatic invertebrates and plays an important role in defense against xenobiotics. Here, to explore the roles of P-glycoprotein (P-gp) in the DSP toxins resistance in shellfish, complete cDNA of P-gp gene in the mussel Perna viridis was cloned and analyzed. The accumulation of okadaic acid (OA), a main component of DSP toxins, MXR activity and expression of P-gp in gills of P. viridis were detected after exposure to Prorocentrum lima, a dinoflagellate producing DSP toxins in the presence or absence of P-gp inhibitors PGP-4008, verapamil (VER) and cyclosporin A (CsA). The mussel P. viridis P-gp closely matches MDR/P-gp/ABCB protein from various organisms, having a typical sequence organization as full transporters from the ABCB family. After exposure to P. lima, OA accumulation, MXR activity and P-gp expression significantly increased in gills of P. viridis. The addition of P-gp-specific inhibitors PGP-4008 and VER decreased MXR activity induced by P. lima, but had no effect on the OA accumulation in gills of P. viridis. However, CsA, a broad-spectrum inhibitor of ABC transporter not only decreased MXR activity, but also increased OA accumulation in gills of P. viridis. Together with the ubiquitous presence of other ABC transporters such as MRP/ABCC in bivalves and potential compensatory mechanism in P-gp and MRP-mediated resistance, we speculated that besides P-gp, other ABC transporters, especially MRP might be involved in the resistance mechanisms to DSP toxins.
Keywords: Diarrhetic shellfish poisoning toxin; P-glycoprotein; Perna viridis; Prorocentrum lima.
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