Troponin T switching in the developing rat heart

A monoclonal antibody specific for cardiac troponin T has been used to investigate troponin changes during development in the rat heart. Specificity of the antibody was determined by immunoblot analysis with purified bovine cardiac troponin. In the rat heart, immunoblot analysis shows that anticardiac troponin T reacts with a 42.5-kDa band in fetal ventricles and with a 41-kDa band in adult ventricles. The faster migrating troponin T is present in traces in the fetal heart and increases markedly during the first 2 weeks after birth, concomitantly with the progressive decrease of the slower migrating form that is no longer detectable in the adult. The pattern of reactivity of the monoclonal antibody is not modified by alkaline phosphatase pretreatment, suggesting that the antibody is not specific for a phosphorylated epitope. Conditions known to affect cardiac myosin composition, such as hypothyroidism and hypertrophy secondary to systemic hypertension, do not change the troponin T isoform profile of adult rat ventricles. The expression and accumulation of the adult isoforms of troponin T are not suppressed by propylthiouracil treatment of pregnant and nursing rats.