Protein synthesis and turnover in normal and hypertrophied heart

Abstract

This review deals with some aspects of the synthesis, assembly and turnover of mitochondrial and myofibrillar proteins in normal and hypertrophied hearts. The dynamic state of the myocardium, in which intracellular proteins and organelles are constantly being destroyed and synthesized, is emphasized. In normal cardiac muscle, mitochondrial inner membrane cytochromes turn over synchronously with half-lives of 5 to 6 days. The various myofibrillar proteins also turn over; the fact that they do so with identical apparent half-lives of 8 to 10 days suggests that these proteins are assembled and degraded synchronously. In cardiac hypertrophy produced by constriction of the ascending aorta in rats, inner mitochondrial membrane cytochromes increase in parallel. Early in hypertrophy (1 day after aortic constriction) cytochrome content per gram of heart weight increases, indicating a disproportionate increase in mitochondrial cytochrome mass. By the third postoperative day there already is a decrease in cytochrome content per gram of heart weight. The increase in mitochondrial cytochrome content observed in the hypertrophied heart appears to be due to a decreased rate of cytochrome destruction as well as to an increased rate of cytochrome synthesis. The data on myosin accumulation are consistent with either decreased destruction of myosin or increased efficiency of reutilization of labeled amino acids.