Characterization of Ventricular Myocytes from the Newborn Pig Heart

The differential rate of growth of the left-ventricular free wall (LVFW) and the right-ventricular free wall (RVFW) of the newborn pig has been studied by measuring the rates of ribosome formation and protein synthesis in the isolated perfused heart. These measurements are limited by the heterogeneity of the cells and the stability of the preparation. The hypothesis of the present study was that isolated cultured myocytes would offer much less cellular heterogeneity and a more prolonged period to explore the actions of anabolic agents. The rate of [3H] phenylalanine incorporation into total protein during 24 h of culture was established as a monitor of the rate of protein synthesis in myocytes and was found to be 64 and 61% of the rates measured in the LVFW and RVFW, respectively, of the perfused heart. The relative rates of protein synthesis in LVFW and RVFW were the same in myocytes and perfused hearts. Myocytes from the LVFW had increased rates of protein synthesis after exposure to a combination of norepinephrine and propranolol or endothelin for 24 h. Exposure to endothelin for 3 days increased rates of protein synthesis to a greater extent in LVFW myocytes than in RVFW myocytes. In LVFW myocytes from enalapril-treated pigs or in LVFW myocytes exposed to 40 m KCl, angiotensin II increased the rate of protein synthesis by 14% during the third day of incubation. These studies indicated that cultured myocytes reflected the rates of protein synthesis observed in LVFW and RVFW of the perfused piglet heart. Differential effects of anα-adrenergic agonist, endothelin and angiotensin II in LVFW as compared to RVFW myocytes was observed. In each case, the response to the agonist was decreased or absent in RVFW as compared to LVFW myocytes.