Titin isoforms and kinematics of fast swimming carp larvae (Cyprinus carpio L.)

Titin, a striated-muscle specific protein spanning the distance between Z- and M-lines of sarcomeres, is held responsible for developing passive tensi on and for maintaining the central position of thick filaments in contracti ng sarcomeres. Different muscles express titin isoforms of different molecu lar mass. To improve the insight in the relation between titin isoforms and kinematics of fast swimming at different ages the presence of carp larval muscle titin (Cyprinus carpio L.) was investigated and compared with data o f adult carp. Gel-electrophoresis revealed that titin isoforms were larger in adult than in larval muscle. Apparently the molecular structure of titin changed during ontogeny. A previous study showed that the size of titin is correlated with the functioning of different muscles during swimming. Fish larvae (6.5-8 mm total length), subjected to low Reynolds-number regimes d uring swimming (Re < 500), require special features to overcome frictional effects. Fibres with smaller titin isoforms require more passive tension wh en being stretched. During fast swimming of larvae, passively stretched fib res at the convex side of the body axis absorb energy, generated by activit y of fibres at the concave side, that is released in the successive opposit e bending.