Barahona C, Bravo I
Departamento de Fisiología, Facultad de Ciencias Biológicas, Universidad de Concepción, Chile.
Cell Mol Biol (Noisy-le-grand). 1993 Sep;39(6):681-92.
L-lysine uptake was measured in isolated oxyntic glands of rabbit stomach in both Na(+)-containing (1.29 +/- 0.29 nmol.mg-1.(20s)-1) and choline-containing (0.93 +/- 0.15 nmol.mg-1.(20s)-1) medium. Time curves and 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 (Kt = 1.42 mM, Jmax = 0.16 nmol.mg-1.s-1) when sodium was replaced by choline in the medium. Two components are apparent when the kinetic analysis was performed in the presence of Na+: component 1 showed lower affinity (Kt = 4.0 mM) than component 2 (Kt = 0.53 mM). The transport constants for the Na(+)-independent component and for the Na(+)-dependent component 2 (i.e. the high affinity component) are in the range described for system y+ in other cells. L-lysine uptake in the choline-containing 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 results and the ratio of Ki obtained for cationic and neutral amino acids suggest that at the basolateral side of the oxyntic glands cationic amino 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 parietal cells suggest that L-lysine uptake would be primarily mediated by a transporter which resembles the selectivity of system b(o),+.
