BEHAVIOR OF EMBRYONIC CHICK HEART-CELLS IN CULTURE .2. CELLULAR-RESPONSES TO EPIDERMAL GROWTH-FACTOR AND OTHER GROWTH SIGNALS

Muscle cell-enriched primary cell cultures were prepared from 8-day em bryonic chick heart ventricles (74% of these cells showed positive sta ining with anti-cardiac myosin antibody). To determine if Epidermal Gr owth Factor (EGF) affects cardiac muscle cells, immunostaining and aut oradiography were performed to find the Muscle Cell Labeling Index (ML I). MLI represents the proportion of cardiac myosin-positive cells tha t specifically incorporated [H-3]thymidine. The MLI for EGF-treated ce lls was 51%. Controls in Serum-free Nutrient Medium (SFNM) had a MLI o f 34.5%. Combinations of growth signals also were tested. EGF, IGF-I ( Insulin-like Growth Factor-I), or PDGF (Platelet-derived Growth Factor ) alone increased [(3H)]thymidine incorporation in the cells. Adding I GF-I or PDGF simultaneously with EGF enhanced the response of the cell s to EGF by increasing [H-3]thymidine incorporation. TGF-beta (Transfo rming Growth Factor-beta) alone was shown to have an inhibitory effect on [H-3]thymidine incorporation, and when TGF-beta was added together with EGF, it attenuated the stimulatory effect of EGF on [H-3]thymidi ne incorporation. Phorbol 12-Myristate 13-Acetate (PMA), a tumor promo ter, alone had no effect on [H-3]thymidine incorporation, but its addi tion suppressed the stimulatory effect of EGF when they were added sim ultaneously in the presence of 5% FBS. Developmental response of the h eart cells to growth signals also was tested. Heart cells from 18-day embryos were used to test the effect of insulin and EGF. Although both insulin and EGF increased [H-3]thymidine incorporation in heart cells from 8-day embryos, different responses to insulin and EGF occurred w ith heart cells from 18-day embryos. Whereas the heart cells from 18-d ay embryos still responded to EGF by increasing [H-3]thymidine incorpo ration, they did not show a response to insulin as measured by [H-3]th ymidine incorporation, suggesting that the loss of response of the hea rt cells to growth signals may occur at the receptor level. Further st udies show that EGF, TGF-alpha; aFGF, and PDGF increased the total num bers of heart cells, and that aFGF and PDGF also increased the percent ages of heart muscle cells.