Ogawa Y, Harafuji H
Department of Pharmacology, Juntendo University School of Medicine, Tokyo.
J Biochem. 1990 Jun;107(6):887-93. doi: 10.1093/oxfordjournals.jbchem.a123143.
It has been clarified that ryanodine binds to Ca2(+)-induced Ca release channels in the open state in sarcoplasmic reticulum. While the pharmacological action of ryanodine is known to be retarded at a low temperature, the Ca-releasing action of caffeine is potentiated at a low temperature. In order to obtain deeper insight into the molecular mechanism underlying Ca-release, the effect of temperature on ryanodine binding to the heavy fraction of sarcoplasmic reticulum (HFSR) from bullfrog skeletal muscle was examined. Although Ca2+ is indispensable for ryanodine binding, Ca2+ alone cannot cause ryanodine binding in a reaction medium of a salt concentration similar to that of the sarcoplasm. In addition to Ca2+, caffeine and/or beta,gamma-methylene adenosine triphosphate (AMPOPCP) are necessary. [3H]Ryanodine binding at 25 degrees C closely paralleled the Ca release activity in respect of the Ca2(+)-dependence in the presence of caffeine and/or AMPOPCP, and the effects of inhibitors. A Scatchard plot for ryanodine binding gave a straight linear line, indicating a single class of homogeneous binding sites. At 0 degrees C, the rate of ryanodine binding decreased. Q10 being about 3 on average. The affinity for ryanodine was reduced to about half that at 25 degrees C, with no change in the maximum number of binding sites. The temperature-dependent change in apparent affinity for Ca2+ on ryanodine binding is not always consistent with that in the case of Ca-release activity. The bound ryanodine may be in an occluded state because it did not dissociate for up to 90 h at 0 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
已经明确，ryanodine可与肌浆网中处于开放状态的Ca2(+)-诱导的Ca释放通道结合。虽然已知ryanodine的药理作用在低温下会延迟，但咖啡因的Ca释放作用在低温下会增强。为了更深入地了解Ca释放的分子机制，研究了温度对ryanodine与牛蛙骨骼肌肌浆网重组分（HFSR）结合的影响。虽然Ca2+对于ryanodine结合是必不可少的，但仅Ca2+在与肌浆盐浓度相似的反应介质中不能引起ryanodine结合。除了Ca2+之外，咖啡因和/或β,γ-亚甲基三磷酸腺苷（AMPOPCP）也是必需的。在25℃下，[3H]ryanodine结合在存在咖啡因和/或AMPOPCP时在Ca2(+)-依赖性方面以及抑制剂的作用方面与Ca释放活性密切平行。ryanodine结合的Scatchard图给出一条直线，表明存在单一类别的均匀结合位点。在0℃时，ryanodine结合速率降低，平均Q10约为3。对ryanodine的亲和力降低至25℃时的约一半，结合位点的最大数量没有变化。ryanodine结合对Ca2+的表观亲和力的温度依赖性变化并不总是与Ca释放活性的情况一致。结合的ryanodine可能处于封闭状态，因为它在0℃下长达90小时都不会解离。（摘要截短至250字）
