NYACK, A.C.; KINSEY, S.T.; University of North Carolina at Wilmington; University of North Carolina at Wilmington: Scaling of post-contractile phosphocreatine recovery in white muscle of black sea bass (Centropristus striata)

Most cells do not exceed sizes of about 100 μm, presumably to maintain a high cell surface area to volume ratio (SA:V) and short intracellular diffusion distances. However, white muscle fibers in adult black sea bass (Centropristus striata) attain diameters >300 μm. Large fiber diameters may accomodate more contractile mahinery, but also might compromise the rate of aerobic processes. During burst contraction in fish white muscle ATP is supplied initially by phosphocreatine (PCr) hydrolysis, which is not dependent on a high SA:V or net intracellular diffusive flux. However, the post-contractile resynthesis of PCr is tightly coupled to aerobic production of ATP, and may be influenced by fiber size. This study compared the body mass scaling of aerobic capacity (cytochrome-c oxidase (COX) activity) to that of an aerobic process (post-contractile PCr resynthesis) in the white muscle of black sea bass. It was hypothesized that the effect of intracellular diffusion would be manifested as a body mass scaling exponent that is more negative for PCr recovery than for COX activity. White muscle from C. striata ranging in mass from < 2 g to > 3500 g was fatigued ex vivo by a fused tetanus and PCr recovery was measured in perchloric acid extracts using 31P-NMR. The PCr recovery rate scaled more negatively with increasing body mass than did COX activity, suggesting that intracellular diffusive flux may limit aerobic processes in large muscle fibers.