McWhirter J M, Gould G W, East J M, Lee A G
Department of Biochemistry, University of Southampton, U.K.
Biochem J. 1987 Aug 1;245(3):731-8. doi: 10.1042/bj2450731.
Homogenization of muscle gives a preparation of sealed vesicles derived from the sarcoplasmic reticulum. In the presence of ATP these vesicles will initially accumulate Ca2+ from the external medium and then spontaneously release this Ca2+ in two phases, an initial slow phase and a faster second phase. By measuring ATP concentrations in parallel with measurements of external Ca2+ concentrations we have shown that the second phase of release occurs when the added ATP has been exhausted, but that the first phase of release occurs in the presence of ATP. A similar pattern of uptake and release has been observed in the presence of acetyl phosphate, showing that ADP generated by ATP hydrolysis is not essential for the release process. The temperature-dependence of both phases of release is similar to the temperature-dependence of ATPase activity. Release is dependent on pH over the same pH range as affects binding of Ca2+ to the ATPase. Therefore we propose that Ca2+ release from vesicles of sarcoplasmic reticulum actively loaded with Ca2+ is mediated by the same Ca2+ + mg2+-activated ATPase as is responsible for uptake of Ca2+.
肌肉匀浆可制备出源自肌浆网的密封囊泡制剂。在ATP存在的情况下，这些囊泡最初会从外部介质中积累Ca2+，然后分两个阶段自发释放Ca2+，一个是初始的缓慢阶段，另一个是较快的第二阶段。通过与外部Ca2+浓度测量同时测量ATP浓度，我们发现当添加的ATP耗尽时会发生第二阶段的释放，但第一阶段的释放在ATP存在时就会发生。在乙酰磷酸存在的情况下也观察到了类似的摄取和释放模式，这表明ATP水解产生的ADP对于释放过程并非必不可少。释放两个阶段的温度依赖性与ATP酶活性的温度依赖性相似。释放在与影响Ca2+与ATP酶结合的相同pH范围内依赖于pH。因此我们提出，从主动加载Ca2+的肌浆网囊泡中释放Ca2+是由与负责摄取Ca2+的相同的Ca2+ + Mg2+激活的ATP酶介导的。
