An analysis of contractile proteins in developing chick heart by SDS polyacrylamide gel electrophoresis and electron microscopy.

Chick heart development was studied using transmission electron microscopy and SDS-polyacrylamide gel electrophoresis in combination with densitometry. Myosin heavy chain, alpha-actinin, actin and tropomyosin accumulations were analysed in developing hearts from preheartbeat stage 9 (Hamburger-Hamilton staging series) through 2 days after hatching. At the preheartbeat stage, electron microscopy revealed a significant number of thin filaments scattered throughout the cytoplasm of the myoblasts; however, very few thick filaments were seen. There was no obvious association between the two filament types. SDS-polyacrylamide tube gels of heart muscle homogenates demonstrated the presence of all five proteins in hearts at the preheartbeat stage. Further analyses of the proteins by gel densitometry indicated that both actin and myosin accumulated rapidly during heart development while alpha-actinin and tropomyosin levels remained relatively static. Our results show that detectable quantities of myosin heavy chain, alpha-actinin, actin and tropomyosin accumulate in myocardial cells prior to the appearance of myofibrils and initiation of the contractile function.