The effect of insulin in vitro on the accumulation of amino acids by isolated rat diaphragm

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Abstract
The rate of penetration into isolated rat diaphragm, both ordinary "cut" preparation and "intact" preparation, of C14 present in the medium in certain [C14] amino acids has been investigated, together with the effect of insulin thereon. No important differences between the behavior of the "cut" and "intact" preparations was observed. With alanine, a-aminoisobutyric acid, glycine, leucine, lysine, ornithine and phenylalanine the ratio of concentration of radioactivity in tissue water to that in the medium exceeded unity. With glutamic acid and aspartic acid the ratio was below unity, probably because of the rapid metabolism of these amino acids in isolated rat diaphragm. The addition of insulin to the medium significantly raised the ratio for glycine and a-aminoisobutyric acid, but not for the other amino acids under study. The effect of insulin was similar whether or not glucose was added to the medium. It was abolished by anoxia and by cooling the system to 12[degree]. Under anoxic conditions, both in the presence or absence of insulin, the ratio was significantly raised by the addition of glucose to the medium. A similar effect of glucose was not seen under any other conditions studied. No substantial evidence has been obtained to suggest that insulin promotes the incorporation of amino acids into protein in isolated diaphragm by enhancing the rate of entry of amino acids into the cytoplasm of the cells from the medium.