Amino acid uptake in the developing chick embryo heart. The effect of insulin on α-aminoisobutyric acid accumulation

Abstract

1. The uptake of (14)C-labelled alpha-aminoisobutyric acid by 5-day-old chick embryo hearts was investigated in vitro, together with the effect of insulin thereon. 2. At equilibrium the distribution ratio of this amino acid analogue between intracellular and extracellular water attained values greater than unity. Insulin enhanced the rate of alpha-aminoisobutyric acid accumulation and increased the value of its final concentration in the cell water. 3. The rate of alpha-aminoisobutyric acid accumulation and the effect of insulin on it were independent of the presence of glucose in the incubation medium. Bovine and chicken insulin were equally effective, and the action of the hormone was specifically prevented by an anti-insulin serum but not by puromycin. 4. A linear relationship was observed between the intracellular accumulation of the analogue and the logarithm of the insulin concentration in the range 50muunits-100m-units/ml. of incubation medium. 5. Evidence was obtained for the occurrence of two different transport processes for alpha-aminoisobutyric acid in the chick embryo heart: one subject to saturation and one that was not saturated by reasonable concentrations of the analogue. Insulin increased the effectiveness of the saturable component, increasing the maximal velocity of transport without altering the concentration for half-maximal velocity of transport, and decreased the contribution of the non-saturable component.

The Stimulation by Insulin of Amino Acid Uptake and Protein Synthesis in the Isolated Fetal Rat Heart

“…The insulin effect was not dependent upon the presence of glucose in the medium (table II), was dose-related (table I) and was observed at the earliest age studied (table III). Thus, the alanine recep tor, for which AIB is a model amino acid [4], appears in the fetal rat heart by at least the 16th day of gestation and is insulin-responsive at this age.…”

“…¡3-Cell granulation appears in the fetal rat pancreas at about 17 days of gestation [4]. Insulin is present in fetal sera by 18 days gestation, the earliest date at which samples can be obtained [unpublished observa tion].…”

“…When added in vitro insulin increases amino acid up take and incorporation into protein in adult rat heart preparations [8]. In the developing chick heart insulin also increases the uptake and incor poration into protein of amino acids [4].…”