Effects of divalent cations on amino acid and divalent cation losses from and glycine influx into gills of freshwater bivalve molluscs Anodonta californiensis and Corbicula manilensis

Abstract

The losses of Ca 2+, Mg 2+ and primary amines from excised gills of the freshwater bivalve molluscs Anodonta californiensis and Corbicula manilensis were measured as a function of the concentration of the divalent cations Ca 2+ and Mg 2+ in the medium. The rate of loss of primary amines was reduced by the presence of Mg 2+ and more effectively by Ca 2+. This observation is consistent with the proposed role of Ca 2+ in maintaining low permeability of membranes. The losses of Ca 2+ and Mg 2+ were not affected by Mg 2+ and Ca 2+, respectively, suggesting that these cations may bind to different sites. Glycine influx into the gills of freshwater molluscs is not an active transport process. The influx of glycine is reduced by the presence of both Ca 2+ and Mg 2+, in contrast to the influx of glycine into gills of the marine bivalve mollusc Mytilus californianus, which is increased by Mg 2+ and unaffected by Ca 2+. In the case of the freshwater species, the decrease in influx with increasing Ca 2+ and Mg 2+ concentrations is probably a result of changes in the permeability of gill membranes. The difference between the effect of Ca 2+ and Mg 2+ on the uptake properties of the freshwater and marine bivalve molluscs may be related to the marine species having more polar lipids than the freshwater species.