Removal of amino acid during a single passage of water across the gill of marine mussels

Abstract

AbstractThe clearance of amino acid during a single passage of inhalent water across the gills of marine mussels was studied. Samples of excurrent water were collected and analyzed for their content of 14C‐labeled amino acids and total primary amines. Comparison with concentrations measured in the ambient medium revealed that mussels are capable of removing large fractions of the amino acid present in inhalent water in a single passage across the gill surfaces. At low rates of pumping, Modiolus demissus was capable of removing 95% of the 14C‐glycine from a 1μ M solution. Efficiency of clearance of amino acid was inversely related to pumping rate; absolute rate of uptake was directly related to pumping rate. Concentration related changes in uptake rate and efficiency of clearance indicated that the effective Kt of glycine uptake by intact Mytilus californianus and Modiolus demissus is between 2 and 5μ M. These values are an order of magnitude lower than published figures for Kt of glycine uptake by preparations of isolated gill tissue from these animals. This discrepancy is probably the result of an increase in the effective thickness of unstirred layers on the surfaces of isolated gills. Net clearance of glycine by M. californianus was observed to occur from concentrations as low as 0.28μ M and, from concentrations of 1μ M and less, an average of 20% of the total primary amine offered initially as glycine was removed during a circuit of inhalent water through the animal. Hence, transepidermal transport processes for amino acids in marine mussels are adapted to function efficiently at substrate concentrations found in their normal environment, and can provide a significant supplemental input of reduced carbon and amino nitrogen for these animals.