CAPUTO*, N.D.*; WEAVER, F.E.; COUGHLIN, D.J.; Widener University, Chester, PA: Muscle Contraction and Troponin T Expression in Rainbow Trout Red Muscle

This study investigated how expression of the muscle protein Troponin T (TnT) relates to muscle contraction. Previous work has shown that red or aerobic muscle from the anterior of rainbow trout (Oncorhynchus mykiss) activates (generates force) more quickly than that from the posterior. TnT is the Ca2+ binding protein in muscle and, in part, regulates muscle activation. Rainbow trout express at least two forms of TnT in their aerobic or slow red muscle (S1 and S2), and the differential expression of these two forms may explain differences in contractile properties. TnT isoforms from trout muscle were identified through hydroxy-apatite chromatography of purified myofibrillar proteins followed by SDS-PAGE. Western blots employing a mammalian anti-troponin T monoclonal antibody were used to identify the isoforms of red muscle TnT from trout. The sizes determined from the blot were ~29.5 kD for TnT S1 and ~28.5 kD for TnT S2. The relative expression of the two isoforms of TnT was then examined at six longitudinal positions from each of three fish using SDS-PAGE and densitometry on the silver stained TnT bands. A significant shift in expression was detected from anterior to posterior in all three fish with TnT S1 becoming more dominant in the posterior red muscle (Kruskal-Wallis, p < 0.01). As predicted, a shift in TnT expression was associated with the decrease in activation rate along the length of the fish. Further, our results suggest that TnT S2, which is found in relatively greater abundance in the anterior muscle, is the kinetically faster form of troponin T in trout.