In vitro uptake and interaction between arginine and lysine in the intestine of Atlantic salmon (Salmo salar)

The kinetics and interactions of the in vitro uptake of the amino acids lysine and arginine were studied in the mid intestine of Atlantic salmon by the everted sleeve method. Since an imbalance of amino acids may affect feed utilisation and growth by metabolic and/or absorptive mechanisms, knowledge of the uptake dynamics of the two amino acids is relevant. The maximum rate of transport (Vmax) and apparent affinity value (Kt) for carrier-mediated arginine uptake were lower as compared to the kinetic parameters for carrier-mediated lysine uptake. Carrier-mediated arginine uptake showed a Vmax of 0.22 nmol mg-1 min-1 and a Kt of 3.5 mM, and a permeability coefficient (P) of 0.014 nmol mg-1 min-1 mM-1 for the non-saturable uptake. Carrier-mediated lysine uptake showed a Vmax of 0.50 nmol mg-1 min-1 and a Kt of 13.7 mM, and a P of 0.010 nmol mg-1 min-1 mM-1 for the non-saturable uptake. Interactions were revealed, as the total uptake of one amino acid was affected by the presence of the other amino acid in the incubation solution, suggesting that the amino acids share a common carrier. Lysine had both a stimulatory and inhibitory effect on the uptake of arginine, depending on the relative concentration of the two amino acids. Arginine had an inhibitory effect on lysine uptake, regardless of concentration.