Intestinal absorption of amino acids in fish: kinetics and interaction of the in vitro uptake of l-methionine in Atlantic salmon ( Salmo salar L.)

Abstract

The kinetics and interaction of the in vitro uptake of l-methionine were studied in the mid-intestine in Atlantic salmon by the everted sleeve method. The uptake kinetics of l-methionine alone was measured, and also how l-methionine interacted with other dietary amino acids when present in physiological concentration within the incubation medium. Knowledge of how the uptake of l-methionine is affected by other amino acids at physiological concentrations in the gut is important as methionine is considered to be the first limiting amino acid in many proteins used in fish feeds. The carrier-mediated uptake of l-methionine showed a maximum rate of transport ( V max) of 0.12 nmol mg −1 min −1 and the apparent affinity value ( K t) was estimated to be 3.0 mM l-methionine. The permeability coefficient ( P) for the nonsaturable uptake was estimated to be 0.017 nmol mg −1 min −1 mM −1. These in vitro experiments might indicate that an efficient uptake of l-methionine in a physiological mixture of all amino acids depends on a certain concentration of l-methionine in the incubation solution (2.5 mM), as methionine uptake was inhibited at lower concentrations. At higher l-methionine concentrations (10–25 mM), the uptake of l-methionine when present alone was not different from the uptake of l-methionine measured in a mixture of all amino acids. However, when the other neutral amino acids were omitted from the incubation medium, a reduced uptake of 10 and 25 mM l-methionine was found.