Expression of myofibrillar proteins and parvalbumin isoforms in white muscle of dorada during development

Several polyacrylamide gel electrophoresis techniques were used to study developmental changes in myofibrillar protein composition and parvalbumin distribution in the myotomal muscle of Brycon moorei . Two myosin LC2 chains and two troponin I isoforms were successively detected. Up to four troponin T isoforms were synthesized. Slow red-muscle myofibrils from adult fish showed no common component (except actin) with larval, juvenile or adult fast white-muscle myofibrils. During growth of B. moorei , two classes of parvalbumin isoforms were sequentially expressed: larval PA I, PA IIa, and PA IIb and adult PA III. In adult fish, the content in Tn T-2 isoform decreased from the anterior to the posterior myomeres, in favour of Tn T-1 and Tn T-4. The parvalbumin content also diminished from the rostral to the caudal muscle. The fast rate of transition from larval to adult isoforms appeared to parallel the extremely fast growth of B. moorei . Sequential expression of these isoforms presumably reflected variations in the contractile properties of the muscle fibres, required by changes in physiological demands of the propulsive musculature.