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 productio n during the oscillatory contractions of undulatory locomotion. Recently, s ignificant differences have been reported in the relaxation rates of rostra l versus caudal white muscle fibers of the Atlantic cod Gadus morhua L. The present study investigates the biochemical correlates of this rostral-caud al 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 par valbumin than caudal muscles. Third, two soluble Ca2+-binding proteins, in addition to parvalbumin, were also detected in the rostral muscle samples y et were absent from the caudal samples. This suite of rostral-caudal variat ions provides a strong biochemical basis for regional differences in the re laxation rates of cod white muscle.