L-LYSINE TRANSPORT THROUGH THE BASOLATERAL SURFACE OF OXYNTIC GLANDS AND PLASMA-MEMBRANE OF PARIETAL-CELLS ISOLATED FROM RABBIT STOMACH

L-lysine uptake was measured in isolated oxyntic glands of rabbit stom ach in both Na+-containing (1.29 +/- 0.29 nmol.mg-1.(20 s)-1) and chol ine-containing (0.93 +/- 0.15 nmol.mg-1.(20s)-1) medium. Time curves a nd concentration dependence curves showed higher uptake values in the presence of extracellular Na+. The carrier-mediated uptake of L-lysine fit the Michaelis-Menten equation for one saturable component (K(t) = 1.42 mM, Jmax = 0.16 nmol.mg-1.s-1) when sodium was replaced by choli ne in the medium. Two components are apparent when the kinetic analysi s was performed in the presence of Na+: component 1 showed lower affin ity (K(t) = 4.0 mM) than component 2 (K(t) = 0.53 mM). The transport c onstants for the Na+-independent component and for the Na+-dependent c omponent 2 (i.e. the high affinity component) are in the range describ ed for system y+ in other cells. L-lysine uptake in the choline-contai ning medium was inhibited only by cationic amino acids and histidine. In the presence of Na+, both cationic and some neutral (His, Cys, Ala, Leu, Phe) amino acids inhibited L-lysine uptake. These overall result s and the ratio of K(i) obtained for cationic and neutral amino acids suggest that at the basolateral side of the oxyntic glands cationic am ino acids transport is mediated by the system y+ and, probably, an ASC like system. The pH-insensitivity of L-lysine uptake (in the range 6. 5 to 8) supports this hypothesis. Results obtained in isolated parieta l cells suggest that L-lysine uptake would be primarily mediated by a transporter which resembles the selectivity of system b(o,+).