Effects of microcystin–LR on the expression of P-glycoprotein in Jenynsia multidentata

The multixenobiotic resistance phenomenon (MXR) related to the P-glycoprotein multidrug transporter protein (P-gp) has been identified and characterized in several aquatic organisms. In the present work, we prove the presence of a P-gp in liver, gills and brain of Jenynsia multidentata by Western Blot and RT–PCR. A 170 kDa protein has been found in liver and gills while in brain a ∼80 kDa protein has been detected. The partial nucleotide sequence obtained in this autochthonous fish showed high similarity ranging from 83% to 92% with other fishes. In addition, P-gp expression in this fish was evaluated after time and dose-dependent exposures to the cyanotoxin microcystin–LR. Individuals were exposed to MC–LR at concentrations of 2, 5 and 10 μg L−1 for 24 h and for 6, 12 and 24 h at 2 μg L−1 MC–LR. Changes in P-gp expression were observed in liver, gills and brain. However, this response was tissue specific. Only in gills of J. multidentata P-gp expression, measured either by real-time RT–PCR or Western Blot, was significantly higher compared to controls at most tested times and doses. A 3-fold increase with respect to controls was found at 12 h by RT–PCR and after 24 h by Western Blot. In dose-dependent experiments the maximum P-gp expression was observed at 2 μg L−1 MC–LR, measured by both RT–PCR and Western Blot. In the liver, P-gp protein levels were significantly increased after 24 h of exposure, at every toxin dose tested. Thus, probably longer exposures would show also significant increases in this tissue.Considering these results we can propose that P-gp belongs to the defence system involved in the response to MC–LR in J. multidentata.