Rostral–caudal variation in troponin T and parvalbumin correlates with differences in relaxation rates of cod axial muscle

Relaxation rate is an important determinant of axial muscle power production during the oscillatory contractions of undulatory locomotion. Recently, significant differences have been reported in the relaxation rates of rostral versus caudal white muscle fibers of the Atlantic cod Gadus morhua L. The present study investigates the biochemical correlates of this rostral-caudal physiological variation. Using denaturing gel electrophoresis, a series of fresh muscle samples from the dorsal epaxial muscle region was analyzed and several differences were detected. First, a gradual shift occurs in the expression of two troponin T isoforms along the length of the body. Second, rostral muscles were found to contain significantly greater amounts of parvalbumin than caudal muscles. Third, two soluble Ca(2+)-binding proteins, in addition to parvalbumin, were also detected in the rostral muscle samples yet were absent from the caudal samples. This suite of rostral-caudal variations provides a strong biochemical basis for regional differences in the relaxation rates of cod white muscle.