MODULATION OF CONTRACTILE PROTEIN TROPONIN-T IN CHICK MYOCARDIAL-CELLS BY BASIC FIBROBLAST GROWTH-FACTOR AND PLATELET-DERIVED GROWTH-FACTOR DURING DEVELOPMENT

We quantified the effect of basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) on the contractile protein troponin-T (TnT) at the cellular and subcellular level in cultures of chick embryo cardiomyocytes obtained from Hamburger and Hamilton's (HH) stage 19, 29, and 39 embryos. Because expression of thin-filament molecules is considered a good marker of differentiation in muscle cell cultures, we analyzed the modifications these growth factors induced in the transcription of the gene for chick cardiac TnT. Sodium dodecyl sulfate-polyacrylamate gel electrophoresis (SDS-PAGE) and immunoblotting showed that cytoplasmic and cytoskeletal concentrations of TnT are dependent on the stage of embryonic development analyzed and on the type of growth factors added to the culture. The most significant finding was the increase in TnT expression in the cytoplasmic compartment (p < 0.001), accompanied by a slight increase in TnT mRNA, after treatment with bFGF of chick heart cells obtained at HH stage 19. At HH stage 39, bFGF induced less marked changes in the accumulation of TnT in comparison with untreated cardiomyocytes. Our findings support the hypothesis that bFGF plays a role in cardiomyocyte differentiation during early stages of development.