To better understand the mechanisms governing the proliferation of cardiac myocytes it is important to identify the factors controlling this phenomenon, and to characterize their actions. DNA synthesis was quantified in vitro in ventricular myocytes from the adult redspotted newt,Notophthalmus viridescens. Ventricles were enzymatically separated and plated onto laminin. Myocytes were fed modified L-15 medium with 10 fetal bovine serum, and were variously treated with transforming growth factor-beta, transforming growth factor-beta combined with platelet-derived growth factor, acidic fibroblast growth factor, basic fibroblast growth factor, 12-0-tetradecanoylphorbol-13-acetate, heparin, or conditioned medium from ventricular myocytes or non-myocytes (primarily endothelial cells). With their final feeding the cells were given 1 μCi/ml of tritiated thymidine, and 24 hours later were fixed and stained. Dishes were coated with photographic emulsion, exposed, and developed. The percent of cells with labeled nuclei was determined. Experimental media that significantly increased DNA synthesis included those containing acidic fibroblast growth factor (121 of control), basic fibroblast growth factor (119 of control), 12-0-tetradecanoylphorbol-13-acetate (233 of control) and conditioned medium from ventricular myocytes (230 of control) or non-myocytes (128 of control). Media significantly inhibiting DNA synthesis were those containing heparin (31 of control), transforming growth factor-beta (38 of control), non-myocyte conditioned medium and heparin (75 of control), or transforming growth factor-beta and platelet-derived growth factor (63 of control)
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