L-lysine transport through the basolateral surface of oxyntic glands and plasma membrane of parietal cells isolated from rabbit stomach
Barahona, C.; Bravo, I.
Cellular and Molecular Biology 39(6): 681-692
1993
ISSN/ISBN: 0145-5680 PMID: 8220076 Document Number: 421586
L-lysine uptake was measured in isolated oxyntic glands of rabbit stomach in both Na+-containing (1.29 +- 0.29 nmol cntdot mg-1 cntdot (20s)-1) and choline-containing (0.93 +- 0.15 nmol cntdot mg-1 cntdot (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 (K-t = 1.42 mM, Jmax = 0.16 nmol cntdot mg-1 cntdot 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 (K-t = 4.0 mM) than component 2 (K-t = 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 K-i 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,+.