DNA and protein relations in cardiomyocytes. Growth reserve in cardiac muscle

Two-wavelength scanning cytophotometry was performed for the measurement of DNA (Feulgen reaction) and total protein content (naphthol yellow S staining) in the same cardiac myocyte. A lack of proportionality between the DNA content (i.e, cell ploidy) and protein content has been detected in ventricles of normal weight in the human heart. While the ploidy classes contained ratios of 2:4:8:16:32, the ratio of the protein content was about 2:3:5:8:17. In hypertrophic left or right ventricles, the latter ratio composed a series of doubling. Owing to this additional growth, weight of muscle tissue may be increased from 30% to twice, depending on the myocyte ploidy of a given myocardium which varies from 4 to 10c on average under normal circumstances and to 30c in some cases of hypertrophy (where c is the haploid DNA content, and, accordingly, a haploid chromosome set). Thus, one of the mechanisms of cardiac hypertrophy has been revealed which comprises the first step of the growth and often the process per se. Polyploidization of cardiac myocytes and their postmitotic growth enhance the heart weight in normal circumstances and creates a growth reserve for hypertrophy under conditions of pathology in future.