Meeting Abstract
Atmospheric CO2 interacts with seawater to cause a decrease in oceanic pH. Lowering the pH of oceanic waters results in dissolution of the calcium carbonate exoskeletons and shells of many marine invertebrates. This study aimed at determining whether increased proton concentrations at lower pH levels lead to a decrease in calcium uptake by animal gills. Transport competition between the two cations may lead to reduced calcium availability at sites of calcification. Lobster branchiostegite epithelia were removed from both gill chambers, homogenized in hypotonic buffers, and differentially centrifuged resulting in a semi-purified pellet of plasma membrane vesicles. Vesicles were loaded with a mannitol medium at pH 7.0 and incubated for 10 min in a similar medium containing 1 mM 45CaCl2 at pH 6.0, 6.5, 7.0, 7.5, 8.0 and 8.5. 45Ca uptakes at pH 6.0, 6.5 and 7.0 were low and not significantly different from one another (p > 0.05), likely representing non-specific binding. 45Ca uptake increased significantly (p < 0.02) from pH 7.0 to 8.5 with maximal uptake at the highest pH. 45Ca uptake at pH 6.0 was a linear function of calcium concentration, suggesting increased non-specific binding with elevated 45Ca concentration. In contrast, 45Ca uptake at pH 8.0 was a biphasic function of calcium concentrations, suggesting the presence of a putative calcium transporter plus non-specific binding. Results support the presence of at least one gill branchiostegite calcium transport protein that was inhibited by increasing seawater proton concentrations.
