Meeting Abstract
Dissolved atmospheric CO2 reacts with seawater to form carbonic acid and protons, resulting in acidification of seawater. Increased proton concentration results in dissociation of skeletal calcium carbonate, and the protonation of carbonate into bicarbonate, which is incompatible with binding to calcium to form calcium carbonate skeletons that are essential to marine life. Freshwater acidification is equally important to investigate for the animals that live there. This project examines the effects of water pH on the uptake of radioactive 45Ca by gill vesicles of a freshwater animal. River white shrimp, Penaeus setiferus, were obtained from water with a salinity of 5 ‰ and a pH of approximately 7. Partially purified plasma membrane vesicles (PMV) from shrimp gills were prepared through a homogenization and centrifugation process. Protein concentration of the vesicles was determined using a Bradford protein assay. The resulting PMV were loaded with a pH 8 mannitol buffer. PMV uptake of 45Ca at 50 µM was measured in triplicate experiments using external pH conditions in mannitol buffer adjusted to pH 8, 7, and 6 for four time periods of 1, 5, 20 and 30 minutes. Transport into gill vesicles as pmol/mg protein x min was a linear function of time and was greatest at pH 7. 45Ca uptakes at pH 6 and 8 were not significantly different from horizontal lines, suggesting that calcium transport was abolished. These tentative results suggest that environmental pH of 7, where the shrimp naturally occurs, was similar to the pH where maximum calcium uptake took place. Furthermore, small changes in environmental proton concentration may inhibit the uptake of calcium from water and potentially affect calcification in these freshwater crustaceans.
