Patterns of uptake of dissolved amino acids in mussels (Mytilus edulis)

Abstract

Uptake of dissolved amino acids was measured in mussels adapted to 50% artificial sea water or to the sea water containing 2 mM glycine. In mussels adapted to amino-acid free sea water net uptake from μmolar solutions of glycine, glutamic acid, taurine, glutamine and tyrosine could be described by the Michaelis-Menten equation. Mussels adapted to 2 mM glycine exhibited more complex patterns of uptake that changed with time after transfer to μmolar solutions of glycine. It is suggested that the properties of the epidermal transport systems are adaptable, and that they are modified by the presence of amino acids in the medium, perhaps indirectly through changes in the concentrations of the intracellular pool of free amino acids. The uptake rates measured in mussels adapted to aminoacid free sea water express the maximum capacities for net uptake. In this state of adaptation, mussels that process the surrounding water at optimal rates may clear up to about half of the water passing the mantle cavity of amino acids present at concentrations of about 1 μM. Two thirds of 3H-taurine taken up was recovered in the gills, the remaining third was about equally distributed between the mantle and the rest of the body. There was no significant loss or redistribution of label within 24 h. It is concluded that the uptake of amino acids in the mussel gill is epidermal rather than transepidermal.