Studies on Fish Sarcoplasmic Reticulum

肌浆网是一种控制肌肉细胞内Ca~(2+)浓度的器官，存在于鱼类肌肉中。这项研究涉及几种鱼的SR的特征及其在僵直僵直进展中的可能作用。在0或10ﾟC条件下保存，用电子显微镜观察普通肌肉SR中Ca~(2+)和Gt~(2+)的变化。在0ﾟC时，SR中Ca^lt；2+&gt；消失的速度比10ﾟC时快，在0ﾟC时，SR的僵直张力发展得更快。此外，在0ﾟC.2下测得的碎裂SR对Ca^lt；2+&gt；的摄取最低。在0ﾟC的反应温度下，皱纹肌原纤维镁离子的活性低于10ﾟC时的活性，这与肌肉的放松状态相对应。由于先前的研究结果表明，在0ﾟC下，细胞内Ca~(2+)&gt；浓度迅速增加，因此在此温度下，我们测定了Ca~(2+)&lt；2+&gt；存在下的肌原纤维Mg~(2+)-ATP酶活性。该酶的活性高于10ﾟC下不含钙离子的酶活性。将鲤鱼普通肌肉中的SR进一步提纯为重、轻质SR组分。HSR组分含有许多圆形小泡，其中一些表面有足部结构。SDS-凝胶电泳法显示鲤鱼SR主要由Ca~(2+)和Gt~(2+)泵蛋白组成，其亚基相对分子质量为95,000 kDa，由70 kDa、35 kDa和10 kDa的Ca~(2+)和Gt；结合蛋白组成。穗后0ﾟC贮藏条件下，驯化到30ﾟC的鲤鱼比驯化到10ﾟC的鲤鱼僵硬进程更快。相应地，在0ﾟC的反应温度下，温驯化鲤鱼SR对Ca~(2+)的吸收低于冷驯化鲤鱼。以上结果表明，鱼类SR在僵直死亡过程中可能通过影响细胞内钙离子浓度而发挥重要作用。

Sarcoplasmic reticulum (SR) is an organ which controls muscle intracellular Ca^<2+> concentration and found in fish muscle. This study deals with characterization of SR from a few fishes and its possible role in rigor mortis progress.1. Spiked plaice was stored at 0 or 10ﾟC and examined for changes in Ca^<2+> concentration in the ordinary muscle SR by electron microscopic observation. Ca^<2+> in SR disappeared faster at 0ﾟC than at 10ﾟC with a faster development in rigor tension at 0ﾟC. In addition, fragmented SR prepared from plaice showed the lowest Ca^<2+> uptake when measured at 0ﾟC.2. Plaice myofibrillar Mg^<2+>-ATPase activity was lower at a reaction temperature of 0ﾟC than at 10ﾟC in the absence of Ca^<2+>, the condition corresponding to a relaxed state of muscle. Since the previous results suggest that intracellular Ca^<2+> concentration increases quickly when plaice is stored at 0ﾟC, myofibrillar Mg^<2+>-ATPase activity was measured at this temperature in the presence of Ca^<2+>. The activity was higher than that at 10ﾟC in the absence of Ca^<2+>.3. Fragmented SR from carp ordinary muscle was further purified into heavy and light SR fractions. HSR fraction contained many round vesicles, some of them with feet structures on the surface. SDS-gel electrophoresis revealed that carp SR was composed mainly of Ca^<2+> pump protein with a subunit molecular weight of 95,000 (95kDa) and of 70kDa, 35kDa and 10kDa Ca^<2+>-binding proteins.4. Carp acclimated to 30ﾟC was faster in rigor mortis progress than that acclimated to 10ﾟC when stored at 0ﾟC after spiking. Correspondingly, Ca^<2+> uptake by SR from warm-acclimated carp was lower at a reaction temperature of 0ﾟC than that from cold-acclimated carp.5. The above results suggest that fish SR plays an important role in rigor mortis in terms of affecting intracellular Ca^<2+> concentration after death.