Erin Keim is a sophomore at the University of Maine. She spent her summer examining the cellular mechanisms of arsenic uptake in a model organism, Fundulus heteroclius (killifish) under the direction of Dr. Bruce Stanton. Studies on cell lines have shown that aquaglyceroporins (AQP 3, 7, 9 and 10) are permeable to water and arsenite, but little is known about the function or regulation of aquaglyceroporins in model organisms. Erin's studies revealed that plasma hypertonicity (induced by an increase in swim water salinity) reduced AQP7 gene expression in killifish gill by ~75%. Glucocorticoids had no effect on AQP7 gene expression: however, 100 ppb of arsenite up regulated AQP7 gene expression by 122%. The arsenic-induced increase in AQP7 expression is predicted to increase the body burden of arsenic in killifish exposed to this heavy metal, and since AQP7 is a water channel to also have a negative impact on water balance. Studies in progress are examining the direct role of AQP7 in mediating cellular arsenite uptake and how environmental salinity (i.e., stress) affects AQP7 expression.