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

The losses of Ca2+, Mg2+ and primary amines from excised gills of the fresh water bivalve molluscs Anodonta californiensis and Corbicula manilensis wer e measured as a function of the concentration of the divalent cations Ca2and Mg2+ in the medium. The rate of loss of primary amines was reduced by t he presence of Mg2+ and more effectively by Ca2+. This observation is consi stent with the proposed role of Ca2+ in maintaining low permeability of mem branes. The losses of Ca2+ and Mg2+ were not affected by Mg2+ and Ca2+, res pectively, suggesting that these cations: may bind to different sites. Glycine influx into the gills of freshwater molluscs is not an active trans port process. The influx of glycine is reduced by the presence of both Ca2 and Mg2+, in contrast to the influx of glycine into gills of the marine bi valve mollusc Mytilus californianus, which is increased by Mg2+ and unaffec ted by Ca2+. In the case of the freshwater species. the decrease in influx with increasing Ca2+ and Mg2+ concentrations is probably a result of change s in the permeability of gill membranes. The difference between the effect of Ca2+ and Mg2+ on the uptake properties of the freshwater and marine biva lve molluscs; may be related to the marine species having more polar lipids than the freshwater species. (C) 1998 Elsevier Science B.V. All rights res erved.