[Various routes of L-tryptophan transport in the small intestine of the chick].

Presence of two mechanisms in the accumulation of L-tryptophan by the mucosal cells of chicken small intestine was determined in vitro: sodium-independent and sodium-dependent those, the latter being of a major importance. Analysis of the accumulation kinetics in the linear stage showed that at the replacement of sodium with potassium ions in the incubation medium, a decrease of Kt (from 4.44 mM to 1.05 mM) as well as V (from 0.78 mM/min/cm to 0.12 mM/min/cm) occurs. High level of L-threonine, L-alpha-alanine, L-valine (100 mM) considerably inhibit the accumulation of L-tryptophan from 0.24 or 2.40 mM solution, the highest inhibition (78-96%) being related to the sodium-dependent transport mechanism. No considerable changes in Kt (4.0 mM) were observed in the saturated stage of transport whereas V showed a rapid decrease (0.22 mM/min/cm). Adding of modifier 0.64 mM L-alpha-alanine was followed by the increase both in Kt (5.71 mM) and V (0.37 mM/min/cm).