BASIC FIBROBLAST AND PLATELET-DERIVED GROWTH-FACTORS AS MODULATORS OFACTIN AND ALPHA-ACTININ IN CHICK MYOCARDIOCYTES DURING DEVELOPMENT

To test whether cardiac muscle is a target for regulation by peptide g rowth factors, we analyzed the effects of two growth factors on actin and alpha-actinin expression at the subcellular level. Sodium dodecyl sulfate-gel electrophoresis, Immunoblotting, and fluorescense-activate d cell sorter analysis were used to quantify the effects of basic fibr oblast growth factor and platelet-derived growth factor on cultures of chick myocardiocytes during development. Cytoplasmic and cytoskeletal concentrations of actin and alpha-actinin were dependent on the stage of embryonic development and on the type of growth factor added to th e culture. The most significant finding was the increase in actin and alpha-actinin expression in the cytoplasmic compartment after treatmen t with basic fibroblast growth factor of chick heart cells at Hamburge r and Hamilton's stage 19. At stage 39, basic fibroblast growth factor induced less marked changes in the accumulation of actin and alpha-ac tinin. Platelet-derived growth factor decreased or-actinin expression slightly in the cytoskeletal compartment in more mature stages of hear t development, Our findings support the hypothesis that basic fibrobla st growth factor plays a role in cardiomyocyte differentiation during the early stages of development.