THE MULTIXENOBIOTIC DEFENSE-MECHANISM IN MUSSELS IS INDUCED BY SUBSTRATES AND NON-SUBSTRATES - IMPLICATIONS FOR A GENERAL STRESS-RESPONSE

A multixenobiotic defense mechanism similar to the p-glycoprotein mult idrug transporter has been identified and characterized in several mar ine invertebrates. Its suggested role is protection from xenobiotics, both natural and anthropogenic. To assess whether MXR functions as a d efense mechanism against environmental toxins, studies were undertaken to determine the inducibility of the transporter by environmental tox ins. Both MXR substrates (including the pesticide chlorthal) and non-s ubstrates (including Arochlor 1254) appeared to induce MXR activity an d protein titer in the gill tissues of the mussel Mytilus californianu s. Mussels exposed for 3 days to subacute concentrations of these comp ounds showed increased ability to extrude a dye substrate from the cel ls and exhibited a stronger band at 170 kDa on a Western blot relative to animals exposed to clean sea-water. These results suggest that in mussels, MXR induction may be part of a general cellular stress respon se to organic toxins. (C) 1998 Elsevier Science Ltd. All rights reserv ed.