Algal products as naturally occurring modulators for the multidrug resistance (MDR) transporter

Extracts of various algae show modulating activity of the multidrug resistance (MDR) transporter in the mussel Mytilus californianus. Mytilus californianus is a filter feeder that removes seaweed particulates, phytoplankton and their byproducts from the water. The gills of Mytilus californianus express high MDR titer and activity possibly to provide protection from natural toxins in the diet. To test this hypothesis, extracts of various seaweeds and phytoplankton found in and around the mussel habitat were examined for presence of MDR substrates by competition assays with a fluorescent MDR substrate, rhodamine B. In mussel gills, accumulation of rhodamine was increased while dye efflux was slowed in the presence of algal extracts. Methanol extracts of the seaweeds Macrocystis pyrifera, Egregia menziesii and Phyllospadix scouleri showed modulating activity. Likewise, ethanol extracts of the neurotoxin-producing phytoplankton Alexandrium catanella and Pseudonitzchia australis showed modulating activity. These data suggest that the mussel diet contains compounds that may be MDR substrates, thus providing evidence that MDR may have evolved in response to dietary pressures. These findings also suggest that marine algae may contain compounds that are substrates for the MDR transporter in marine bivalves