AIB Concentration Research Articles

Amino Acid Transport in Kidney: HETEROGENEITY OF α-AMINOISOBUTYRIC UPTAKE

Abstract 1. More than one mode of transport can be observed for concentrative uptake of α-aminoisobutyric acid (AIB) by rat kidney cortex slices when the initial concentration of AIB in the medium is varied between 0.2 and 16 mm. 2. The relative contribution from both systems to the total observed uptake at various concentrations of AIB was calculated. The Km values for the two systems were 3.87 mm and 24.8 mm. 3. Sodium-dependent inhibitory reactions influence the uptake of 0.8 mm AIB more than of 8.0 mm AIB; inhibitors affecting —SH groups have the opposite effect. 4. l-Alanine is an effective competitive inhibitor of AIB transport at high substrate concentrations; more than one Ki value for l-alanine can be derived depending on the concentration of AIB. External l-proline enhances the affinity of AIB for uptake at low substrate concentrations; an inhibitory effect is observed at high substrate concentrations. Although omission of sodium from the medium abolishes concentrative uptake of AIB at all concentrations, it is restored at low substrate concentration by the addition of 4 mm l-proline to the external sodium-free medium. l-Proline placed internally stimulates AIB accumulation at low substrate concentrations only in the presence of sodium. 5. A site at which a ternary complex between proline or sodium and the AIB-carrier complex may be formed is proposed for AIB transport at low concentrations; another system with different properties is used predominantly for AIB transport at high concentrations.

The Effect of Whole-Body X-Irradiation on Amino Acid Transport by Lymphatic Tissues

The concentration of aminoisobutyric acid (AIB) in the nonprotein fraction of the rat thymus was found to be highly influenced by irradiation. It was reciprocally and linearly related to dose up to the level of 100 r, and it could be used as an index of irradiation damage in this tissue. Both glycine and AIB were lost from the cell as a result of irradiation. In the spleen the concentration of AIB was not affected by irradiation. Glycine incorporation, however, was diminished significantly at four hours after irradiation. Thus there was no relation between the concentration of AIB and the degree of protein synthesis in the irradiated cell. Results showed that tissues other than thymus and spleen responded to irradiation with an increase in their AIB concentration. Also, there was an indication of a requirement for free amino acids during the first 24 hours after irradiation, as shown by the decreased urinary excretion of AIB. (auth)

STEROID EFFECTS ON PERMEABILITY OF RAT THYMIC LYMPHOCYTES TO ALPHA-AMINOISOBUTYRATE.

In vitro studies of the flux of α-aminoisobutyrate-1-C14 (AIB) between rat thymic lymphocytes and extracellular fluid have revealed that: a) the amino acid enters cells but is not further metabolized; b) at low concentrations, similar to those of amino acids in plasma, the net influx and efflux of AIB exhibit properties of an active process; and c) influx of AIB is inhibited, and efflux stimulated, by deoxycorticosterone (DOC), by metabolic inhibitors, and by other specific steroids. In vivo studies of the distribution of AIB between serum and tissue demonstrated that administration of DOC to adrenalectomized rats inhibited concentration of AIB by thymus, diaphragm, and skeletal muscle, augmented uptake by liver, and increased the serum level of AIB. Prior adrenalectomy of donor rats resulted in no change from normal in the in vitro capacity of thymic lymphocytes to take up AIB. There was no significant difference from normal in the in vivo concentration of AIB by thymus, liver, and skeletal muscle of adrenalectomized rats, although uptake by diaphragm was decreased compared to normal control animals.