Induced Transport of Amino Acids in Rat Liver after Whole-Body γ Irradiation

Abstract

Whole-body exposure of rats to .gamma.-radiation stimulates a Na+-dependent, active transport of certain amino acids in the liver. This phenomenon was examined further using kinetic studies and the transport of various model and natural amino acids in Na+- and Na+-free media. Kinetic studies established the Vmax for AIB [.alpha.-amino isobutyric acid] transport in livers of irradiated rats to be 42.3 .+-. 5.2 .mu.mol/ml hr-1 compared with 19.5 .+-. 2.9 for liver slices from normal (unirradiated) rats. Irradiation had no effect on AIB transport in the absence of Na+. The transport of BCH (2-aminobicyclo (2,2,1) heptane-2-carboxylic acid) in vivo and in vitro, was not affected by irradiation, indicating that the L [leucine preferring] transport mechanism was not influenced. Cycloleucine and L-methionine, both transported by the A [alanine preferring] and L systems, were increased following whole-body irradiation; stimulation was observed only in the presence of Na+. Phenylalanine, leucine and histidine which showed considerable Na+-dependent transport were not stimulated. Methionine competitively inhibited all of the Na+-dependent AIB transport in liver slices from normal and irradiated rats. On the other hand, AIB only inhibited the stimulated transport of methionine. Although radiation-inducible transport of certain amino acids in rat liver is a Na+-dependent process, there exist both Na+-independent and Na+-dependent systems that are not affected.