TRANSPORT OF NONMETABOLIZABLE AMINO ACIDS IN RAT LIVER SLICES

Transport of α-amino [i-14C]isobutyric acid (AIB) by rat liver slices against a concentration gradient has been demonstrated; uptake was improved by including a preincubation step. Similarities to other systems included linearity of uptake over an extended period of time, as well as indications of saturability of the system with increasing concentrations of substrate. The transport of AIB was inhibited by anoxia and by 2,4-dinitrophenol, while glucose was without effect; inhibition also occurred in the presence of ouabain. No evidence for the active transport of AIB was seen when Na+ was totally replaced in the medium. The removal of extracellular K+ or Ca2+ markedly decreased the transport of AIB, although some uptake against a concentration gradient still occurred. The replacement of Mg2+ had little or no effect on the gradients achieved. Uptake was lower in a Krebs-Ringer phosphate than in a Krebs-Ringer bicarbonate buffer. The Na+ and K+ concentrations of slices incubated in the presence of AIB were similar to those of fresh liver. Cycloleucine was also transported against a concentration gradient but to a lesser extent than AIB. © 1969.