Abstract

The transport and incorporation of l-leucine, l-tyrosine and α-aminoisobutyric acid into atrial strips incubated in vitro were studied. Ouabain in concentrations of 10^-4 to 10⁶ M inhibited the incorporation of leucine and tyrosine into total proteins and 700, 10,000 and 100,000 x g sediments. Calcium in concentrations of 2.5 and 5 mM increased the amount of leucine and tyrosine incorporated into total proteins as well as into all three sediments. The effect of ouabain (10^-6 M) on the incorporation of leucine was unchanged in media containing different concentrations of calcium, whereas the inhibitory effect of the same dose of ouabain on the incorporation of tyrosine was increased in the presence of higher concentrations of calcium. High concentrations of potassium in the medium (119.6 mEq/l) decreased the amount of leucine incorporated into total proteins and all three sediments. The inhibitory effect of ouabain (10^-4 M) on leucine incorporation was decreased with increasing concentrations of potassium in the medium. The transport of α-aminoisobutyric acid was inhibited by 10^-4 to 10^-7 M ouabain and by increasing concentrations of potassium, but was stimulated by higher concentrations of calcium. It seems likely that the effects of ouabain, calcium and potassium on membrane transport are primarily responsible for the observed changes in the incorporation of amino acids into atrial proteins.