Use of multidrug transporters as first lines of defense against toxins in aquatic organisms

Multidrug transporters are ATP-dependent transport proteins which efflux a variety of moderately hydrophobic compounds out of cells. This article reviews the biology and chemistry of one member of this family, the P-glycoprotein-like transporters, and the extent to which the activity of these transporters protects aquatic organisms from natural and anthropogenic toxins. Topics covered include measurement of activity, distribution in aquatic organisms, efficacy in protection from toxins, characteristics of substrates of the transporters in aquatic organisms and finally the question of induction of activity in response to toxin load in the environment. The available evidence indicates that these transporters can indeed function as a first line of defense against some toxins, but important questions remain to be answered especially relating to costs of this defense, the inducibility of the defense and whether there might be other types of transport molecules other than the P-glycoprotein example.