Details

Autor(en) / Beteiligte

• Wheeler, Frances B.
• Santora, Arthur C.
• Danner, Dean J.
• DeHaan, Robert L.
• Elsas, Louis J.

Titel

Developmental control of 2-aminoisobutyric acid transport by 7- and 14-day chick heart cell aggregates: Roles of insulin and amino acids

Ist Teil von

• Developmental biology, 1978-11, Vol.67 (1), p.73-89

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

1978

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• Cell aggregates cultured from 7-day embryonic avian heart showed a spontaneous increase in A-system 2-aminoisobutyric acid transport when placed in protein-free and amino acid-free buffer for 3 hr. The apparent V max increased from 4.0 to 9.9 nmoles/μl of intracellular fluid volume/10 min in 3 hr. l-Proline (5 m M), an amino acid transported primarily by the A system, prevented this rise, but l-phenylalanine, primarily an L-system substrate, had no effect. Actinomycin, puromycin, and cycloheximide (55 μ M) also prevented the time-dependent increase in transport. In contrast, cell aggregates cultured from 14-day embryonic heart exhibited a decrease in apparent V max during the 3-hr incubation, from 8.3 to 3.3 nmoles/μl of intracellular volume/10 min. l-Proline, but not l-phenylalanine, enhanced this decrease in A-system transport. The percentage proline inhibition of transport was reduced by actinomycin or cycloheximide (55 μ M) at both ages. Insulin stimulated A-system transport at identical half-maximal concentrations of 18 n M at 7 and 14 days of embryonic development. In the presence of cycloheximide at 7 days of age, insulin prolonged the half-life of transport activity twofold. However, at 14 days, cycloheximide reduced the insulin response by 88% [Elsas, L. J., Wheeler, F. B., Danner, D. J., and DeHaan, R. L. (1975). J. Biol. Chem. 250, 9381–9390]. l-Proline or actinomycin reduced both basal and insulin-stimulated transport by 7-day cell aggregates, but neither reduced the percentage insulin stimulation. We conclude that inherent developmental control(s), A-system amino acids, and insulin regulated the maximal velocity of A-system transport by controlling the biological turnover of transport protein(s). l-Proline decreased the existing synthesis of transport protein(s) at both ages. The predominant effect of insulin shifted from a posttranslational level at 7 days to a synthetic level by 14 days of embryonic development. Seven-day cell aggregates spontaneously increased synthesis in the absence of A-system amino acids, but 14-day cell aggregates required hormonal stimulation to shift the balance from degradation to synthesis of transport protein(s).