Gilchrist J S, Belcastro A N, Katz S
Faculty of Graduate Studies, University of British Columbia, Vancouver, Canada.
J Biol Chem. 1992 Oct 15;267(29):20850-6.
The action of ryanodine upon sarcoplasmic reticulum (SR) Ca2+ handling is controversial with evidence for both activation and inhibition of SR Ca2+ release. In this study, the role of the intraluminal SR Ca2+ load was probed as a potential regulator of ryanodine-mediated effects upon SR Ca2+ release. Through dual-wavelength spectroscopy of Ca2+:antipyrylazo III difference absorbance, the intraluminal Ca2+ dependence of ryanodine and Ca(2+)-induced Ca2+ release (CICR) from skeletal SR vesicles was examined. Ryanodine addition after initiation of Ca2+ uptake (a) increased the intraluminal Ca2+ sensitivity of CICR and (b) stimulated spontaneous Ca2+ release with a delayed onset. These ryanodine effects were inversely proportional to the intraluminal Ca2+ load. Ryanodine also inhibited subsequent CICR after reaccumulation of Ca2+ released from the initial CICR. These results provide evidence that ryanodine inhibits transitions between low and high affinity Ca2+ binding states of an intraluminal Ca2+ compartment, possibly calsequestrin. Conformational transitions of calsequestrin may be reciprocally coupled to transitions between open and closed states of the Ca2+ release channel.
雷诺丁对肌浆网（SR）钙处理的作用存在争议，有证据表明它既能激活也能抑制SR钙释放。在本研究中，腔内SR钙负荷的作用被探究为雷诺丁介导的对SR钙释放影响的潜在调节因子。通过对Ca2+：安替比拉宗III差吸光度的双波长光谱法，研究了雷诺丁和钙诱导的钙释放（CICR）从骨骼肌SR囊泡中释放的腔内钙依赖性。在开始钙摄取后添加雷诺丁：（a）增加了CICR的腔内钙敏感性，并且（b）刺激了延迟开始的自发钙释放。这些雷诺丁效应与腔内钙负荷成反比。在从初始CICR释放的钙重新积累后，雷诺丁也抑制了随后的CICR。这些结果提供了证据，表明雷诺丁抑制腔内钙区室（可能是肌集钙蛋白）的低亲和力和高亲和力钙结合状态之间的转变。肌集钙蛋白的构象转变可能与钙释放通道的开放和关闭状态之间的转变相互偶联。
