Identification and distribution of the fast class of troponin T in the adult and developing avian skeletal muscle.

In the adult chicken, two groups of fast troponin T, the higher molecular weight (B1 and B2) present only in the pectoral muscle and the lower molecular weight (L1-L5) the only group present in the leg muscle, were identified by the immunoblotting procedure using monoclonal antibodies against fast skeletal troponin T. The presence of significant amounts of three major variants of leg muscle type troponin T (L3-L5), however, could also be detected in the adult chicken pectoral muscle. Although none of the antibodies cross-reacted with slow troponin T itself, the proportions of both leg and pectoral type troponin T variants belonging to the fast class varied in fast muscles that contained slow muscle fibres or fast muscles devoid of slow muscle cells. The troponin T present in the early embryonic skeletal muscles did not react with any of the antibodies raised against adult fast isoforms. The gradual expression of some of the adult isoforms of troponin T was detected at about day 13 in ovo. However, the adult isoforms did not all appear simultaneously and their full complement was not achieved until after hatching. In addition to the increased number of bands in the leg type troponin T region, the presence of two other protein bands (neonatal forms) with slower electrophoretic mobility than the other fast isoforms of troponin T, was detected in post-hatch pectoral muscle tested at 1-12 weeks of age. These neonatal forms (N1 and N2) in the pectoral muscle were undetectable at eight months of age. The presence of breast type troponin T in the leg muscle was not detected with these antibodies at any stage of development.