The influx of amino acids into the heart of the rat.

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Abstract
The influx of 19 amino acids into the heart of the living rat was studied by a method specially devised for experiments under controlled conditions in vivo. When, in separate experiments, the concentration of each amino acid in turn was artificially raised in the circulation, the influx of that amino acid into the heart increased. At least 10 of these amino acids enter the heart in vivo by means of saturable carrier-mediated transport systems. The transport rates basically conform to Michaelis kinetics and the transport systems are active, i.e., energy-dependent. The amino acids studied had rates of influx into the heart which differed from each other over a range of more than 10-1, even when allowances were made for the difference in their concentration in circulating blood. These differences in influx were not related to such factors as the molecular size of the individual amino acids. The amino acids which have a high influx into the heart are mainly those which are needed either to re-synthesize contractile protein or as oxidizable substrates.