The transport and accumulation of alpha-aminoisobutyric acid into l-strain mouse fibroblasts.

Abstract

Abstract The accumulation of isotopically labeled α-aminoisobutyric acid by L-strain fibroblasts was studied. The L cells were grown in suspension cultures, and used for these experiments during their exponential growth phase. Uptake studies were initiated in simple isotonic salt solutions. 1. 1. Maximal uptake of AIB occurred from an aqueous solution containing only Na + and K + as cations. A ratio of 136 Na + to 4 K + mequiv/l was optimal. 2. 2. The uptake of AIB was pH dependent; the highest concentration was noted at pH 8.5. 3. 3. Other ingredients in a standard tissue-culture medium such as Ca 2+ , Mg 2+ , glucose, vitamins and serum do not affect the accumulation of the amino acid. However, all of the natural l -amino acids antagonize AIB uptake. 4. 4. A mathematical assessment of the affinity constant for AIB transport by L cells was carried out in a buffer at pH 7.2 containing only Na + and K + as cations at levels which would give maximal uptake. A value of 2.8 mM was obtained. All of the amino acids appeared to competitively inhibit the uptake of AIB. It would appear from these results that all of the amino acids use common transport sites.