Comparison of Ca2+ pump of sarcoplasmic reticulum in dorsal ordinary muscle between cultured red sea bream and Japanese flounder

SUMMARY: To clarify the cause of the marked difference in rigor mortis progress between cultured red sea bream and Japanese flounder, and as a part of a study program, we examined the properties of sarcoplasmic reticulum (SR), aiming at Ca2+ for both fish species. These results showed both the rigor mortis progress and caffeine contracture in cultured red sea bream was markedly faster in speed and considerably higher in the maximum level reached than that in cultured Japanese flounder. Both the Ca2+ uptake rate into SR and the Ca2+ release rate from SR were higher in cultured red sea bream than in cultured Japanese flounder. In addition, the SR Ca2+-ATPase activity was also higher in cultured red sea bream. Furthermore, the surface area percentage of SR per sarcomere was larger in cultured red sea bream than in cultured Japanese flounder. It was proposed that the differences in both biochemical properties and minute structure of SR between the two fish species may together be implicated in the marked difference in rigor mortis progress between the two fish species.