Meeting Abstract

P2.91  Wednesday, Jan. 5  Structural and functional changes in the Ca2+ cycling system during growth in fish white muscle KELLY, Kenneth L.*; DILLAMAN, Richard M.; KINSEY, Stephen T.; Univ. of North Carolina Wilmington klk8133@uncw.edu

Tail beat frequency in fishes decreases with increasing body length, and it follows that the rate of Ca2+ fluxes during muscle contraction-relaxation cycles decreases during growth as well. Ca2+ cycling is a reaction-diffusion process, so both the catalytic and diffusion demands are therefore relaxed during animal growth. We examined the Ca2+ cycling system during post-metamorphic growth in white muscle from black sea bass (Centropristis striata). Isolated muscle from juvenile fish had higher maximal contractile frequencies than adults. For instance, at a contractile frequency of 35 Hz, muscle from juvenile fish relaxed to 90% of peak force between contractions, whereas adults attained only 50% relaxation. The half time to relaxation was nearly two-fold greater in muscle from small fish (0.0073 s) than large fish (0.0128s) at all frequencies measured. Thus, differences in maximal tail beat frequency are an inherent property of the muscle. The higher maximal contractile frequency in juvenile fish was associated with a 2-fold higher sarcoplasmic reticulum (SR) volume density, although the SR-Ca2+ ATPase activity did not differ between size classes. Myofibrillar diameter was 25% higher in adults than in juveniles. Thus, there were increases in Ca2+ diffusion distances during animal growth but no change in the catalytic capacity of the SR-Ca2+ ATPase. In addition, the larger (kinetically slower) isoforms of parvalbumin were more prevalent in adults, while the juveniles had higher concentrations of the smaller (kinetically faster) isoform. These results suggest that Ca2+ diffusion influences changes in muscle structure during growth.