In the toxic battleground of the ocean, creatures
that can cope with what their opponent throws at them are more likely to
survive. "It's a space war, and the weapons are chemicals," says
Epel, who has also found the pumps studding the flapping gills of mussels.
"Organisms use them to compete for the best real estate." The
MDR protein, he says, is a method animals have evolved to escort toxins
out of a cell. He and other researchers are finding that creatures of all
types rely on the pump as a first line of defense and it's a particularly
advantageous one at that. "MDR doesn't even let the things get in the
cell," he says.
The presence of MDR pumps in mussels might be an indicator that certain
natural and man-made chemicals are present in the sea water,Epel says. And,
in fact there may be more than previously suspected,because of the way toxins
have been traditionally measured. For more than a decade, a biomonitoring
effort called the California State Mussel Watch Program has been gauging
water pollution concentrations by measuring levels of contaminants in mussel
tissues. Mussels were thought to be ideal for the job, since they eat by
filtering water through their gills and thus have a high
exposure to whatever is in the water, says Nancy Eufemia, a graduate student
in Epel's lab. Also, they are basically stuck in place, she says, so they
can't swim away from something noxious like a fish can.
But, as it turns out, the mussels' MDR pumps allow the animals to rid
themselves of much of the toxic material they ingest, thus giving researchers
a misleadingly low reading of pollutant levels. Epel andhis group tested
eight compounds on the Program's list of common pollutants half of
them were spit right out by the MDR pump, suggesting that water levels of
some chemicals could be underestimated, Epel says.
Photo by Steve Webster