PARVALBUMIN ISOTYPES IN WHITE MUSCLE FROM 3 TELEOST FISH - CHARACTERIZATION AND THEIR EXPRESSION DURING DEVELOPMENT

Parvalbumin isotypes were isolated by chromatography from trunk white muscle of rainbow trout (Oncorhynchus mykiss VV.), brown trout (Salmo trutta L.), and sea bass (Dicentrarchus labrax L.). Five, four and two components were respectively purified and physico-chemically characte rized. Expression of the various isotypes was followed in the course o f the fish development and, in adult fish, from the anterior to the po sterior myotomes. Isotype distribution varies both chronologically and spatially. In trout, parvalbumins occur around hatching; as the fish develop, transitions occur in isotype expression, PA II appearing as t he predominant larval form and PA III, IV, or V as the main adult form , as previously observed in Barbus barbus (L.). In the sea bass, the d evelopmental expression pattern is more unexpected: the synthesis of b oth isotypes (PA II and PA V) is delayed and the larval form PA II rem ains the principal isotype in adult fish. These observations indicate that the polymorphism of parvalbumins in fish constitutes a subtle mec hanism modulating the speed and power of muscle contraction. Our resul ts support the view that each isotype plays a specific role in relatio n to the muscle activity required in fish at a given developmental sta ge or a given trunk level in the adult.