Metabolism of cardiac structural proteins in normal and hypertrophied rabbit heart.

Abstract

In an attempt to elucidate the characteristics of the metabolic response of the hypertrophying heart, the rates of amino acid incorporation into cardiac structural proteins were studied in female rabbit hearts in vivo by use of a pulse-label isotope (3H-lysine) method. Hypertrophy of the left ventricle was produced by applying mild aortic constriction. Structural proteins were separated from the heart excised 24 h after the pulse, and the rate of 3H incorporation was calculated as cpm. 3H/mg lysine of the protein. In the control (without aortic constriction), left ventricular structural proteins exhibited the following relative incorporation rate (the rate in actin being taken as 1.0): native tropomyosin, 2.79 +/- 0.38 (mean +/- SE, n = 5); 10S-actinin and alpha-actinin complex, 2.52 +/- 0.29; heavy chain of myosin, 2.09 +/- 0.25; light chain of myosin, 1.82 +/- 0.28; soluble protein, 1.79 +/- 0.30; and actin, 1.0. In the rabbits with aortic stenosis the rates of amino acid incorporation showed a striking increase up to 7 days after surgery, and declined to the control level by 1 month. Among the protein fractions, native tropomyosin and the light chain of myosin showed a much higher rate of isotopic incorporation during the earlier phase of the response. These results seem to indicate the presence of a unique pattern of metabolic response in cardiac muscle confronted with a workload.