Protein Synthesis and Amino Acid Transport in the Isolated Rabbit Right Ventricular Papillary Muscle: EFFECT OF ISOMETRIC TENSION DEVELOPMENT

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Abstract
To investigate the effects of isometric tension development on myocardial protein metabolism, 14C-phenylalanine incorporation into protein was studied in the isolated rabbit right ventricular papillary muscle. Amino acid incorporation was linear for 6 hours in resting muscles and was totally inhibited by 10-3M cycloheximide and 10-3M puromycin. Phenylalanine incorporation into total protein was unaltered by 90 minutes of isometric tension development at peak tension at stimulation rates of 30, 50, or 100/min. Significant increases were noted in muscles stimulated at 50 and 100/min for 180 minutes (P < 0.01). Electrical stimulation, in the absence of isometric tension development, was not responsible for this effect. Passive stretch also appeared to stimulate incorporation, although to a lesser degree than did active tension development. The specific activities of the intracellular phenylalanine pools were identical in control and stimulated muscles. Alpha-aminoisobutyric acid was used to evaluate the effect of tension development on myocardial amino acid transport. Enhanced transport was noted in muscles stimulated isometrically at 30, 50, or 100/min at peak tension. The increased transport ratios could not be solely attributed to active tension development since passive stretch resulted in comparable changes. This study indicates that both passive stretch and tension development are important in regulating myocardial protein synthesis.