Studies on Fish Sarcoplasmic Reticulum

肌浆网（SR）是控制肌肉细胞内Ca^<2+>浓度的器官，存在于鱼类肌肉中。本研究探讨了几种鱼类SR的特征及其在尸僵进展中的可能作用。将尖牙鲽在0或10‰的温度下保存，用电镜观察普通肌肉SR中Ca^<2+>浓度的变化。SR中的Ca^<2+>在0ºC时比在10ºC时消失得更快，在0ºC时严格张力的发展更快。此外，从鲽中制备的碎片SR在0‰C.2时的Ca^<2+>吸收量最低。在无Ca^<2+>的情况下，反应温度为0 C时鲽肌原纤维Mg^<2+>- atp酶活性低于反应温度为10 C时的活性。由于前人的研究结果表明，当鲽鱼储存在0ºC时，细胞内Ca^<2+>浓度迅速增加，因此在此温度下，在Ca^<2+>存在的情况下，测量了肌纤维Mg^<2+>- atp酶的活性。在不含Ca^<2+>.3的情况下，其活性高于10‰。从鲤鱼普通肌中进一步提纯成重SR和轻SR。高铁馏分含有许多圆形囊泡，其中一些表面有足状结构。SDS-gel电泳结果显示，鲤鱼SR主要由亚基分子量为95000 （95kDa）的Ca^<2+>泵蛋白和70kDa、35kDa和10kDa的Ca^<2+>结合蛋白组成。当脱粒后储存在0‰下时，30‰处理的鲫鱼比10‰处理的鲫鱼尸僵进展更快。与此相对应的是，温度为0‰时，热驯化鲤鱼SR对Ca^<2+>的吸收量低于冷驯化鲤鱼。以上结果表明，SR在影响死后细胞内Ca^<2+>浓度方面对尸僵有重要作用。

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.