EXPRESSION OF CHICKEN TROPONIN-T ISOFORMS IN CULTURED MUSCLE-CELLS

Cells prepared from chicken skeletal muscles of different developmenta l stages were cultured to study their troponin T isoform expression, u sing antisera specific to tile fast- and slow-muscle-type isoforms. We found that the cultured myogenic cells from chickens and chick embryo s were classified into two types, fast type and fast/slow type in whic h fast- and slow-muscle-type isoforms were coexpressed. Cells expressi ng only slow-muscle-type troponin T isoforms could not be found. Most cells prepared from pectoralis major (fast muscle) and gastrocnemius ( mixed muscle) of 11-day old embryos belonged to the latter, with only a small fraction belonging to the former. The percentage of fast type cells in those cells prepared from pectoralis major increased along de velopment to over 90% by the 17th day of incubation, while, in the cel ls prepared from gastrocnemius, it reached a plateau of 30-40% by the 13th day of incubation. All the cells from anterior latissimus dorsi ( slow muscle) belonged to the fast/slow type. Ratios of these two types of muscle cells varied depending on their origins and stages. The in vitro expression of troponin T isoforms was different from the in vivo expression, and each muscle seems to be determined differently in the composition of cell types during the developmental course.