Regulation of Ca2+ sparks by Ca2+ and Mg2+ in mammalian and amphibian muscle. An RyR isoform-specific role in excitation-contraction coupling?
Regulation of Ca2+ sparks by Ca2+ and Mg2+ in mammalian and amphibian muscle. An RyR isoform-specific role in excitation-contraction coupling?
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哺乳动物和两栖动物肌肉中 Ca2 和 Mg2 对 Ca2 火花的调节。
DOI：
10.1085/jgp.200409105
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
Brum,Gustavo
中科院分区：
文献类型：
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作者：
Zhou,Jingsong;Launikonis,BradleyS;Ríos,Eduardo;Brum,Gustavo
1分子生物物理和生理学系，拉什大学，芝加哥，IL 60612 2 Departamento de Biofísica，Universidad de la República，Facultad de Medicina，Montevideo，Uruguay摘要Ca 2和Mg 2是肌肉细胞内Ca 2信号传导的重要介质和调节剂。在大鼠和青蛙的单个快收缩透化纤维中，测定了胞浆[Ca 2]或[Mg 2]变化对基本Ca 2释放事件的影响，作为浓度和时间的函数。钙火花进行了鉴定，并在共聚焦图像的fluo-4荧光测量其参数。具有不同[Ca 2]或[Mg 2]的溶液在成像时快速交换。更快和空间均匀的变化[Ca 2]（达到峰值100 M）实现了光解钙NP-EGTA与激光闪光。在这两个物种中，增加胞质[Ca 2]引起了稳定的，几乎成比例增加火花频率，可逆后[Ca 2]减少。火花频率的较大变化，通常是短暂的，随后[Ca 2]在100 ms或更长的滞后后突然增加。这种延迟效应的非线性、滞后和其他特征表明，它需要SR内[Ca 2]的增加。仅在青蛙中，胞质[Ca 2]的增加往往会导致滞后后产生横向传播的火花。[Mg 2]的增加引起火花频率的下降，但具有显著的物种差异。在大鼠中，而非青蛙中，在4-40 mM [Mg 2]下观察到火花。将[Mg 2]降低到2 mM以下，这应该能够使RyR通道的激活（CICR）位点结合Ca 2，导致青蛙中火花频率的逐渐增加，但对大鼠没有影响。亚mM Mg 2的火花传播和增强是CICR的标志。它们在大鼠中的缺失表明CICR需要RyR 3旁连接簇，仅存在于青蛙中。观察到的频率火花对应于一个通道开放的概率为10 7在青蛙或10 8在大鼠。连同光释放直接诱导激活的失败，这表明原位通道的基础抑制。有人提出，这种抑制的救济可能是增加SR负载增加火花频率的机制。
1Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612 2Departamento de Biofísica, Universidad de la República, Facultad de Medicina, Montevideo, Uruguay abstract Ca2 and Mg2 are important mediators and regulators of intracellular Ca2 signaling in muscle. The effects of changes of cytosolic [Ca2] or [Mg2] on elementary Ca2 release events were determined, as functions of concentration and time, in single fast-twitch permeabilized fibers of rat and frog. Ca2 sparks were identified and their parameters measured in confocal images of fluo-4 fluorescence. Solutions with different [Ca2] or [Mg2] were rapidly exchanged while imaging. Faster and spatially homogeneous changes of [Ca2](reaching peaks 100 M) were achieved by photolysing Ca NP-EGTA with laser flashes. In both species, incrementing cytosolic [Ca2] caused a steady, nearly proportional increase in spark frequency, reversible upon [Ca2] reduction. A greater change in spark frequency, usually transient, followed sudden increases in [Ca2] after a lag of 100 ms or more. The nonlinearity, lag, and other features of this delayed effect suggest that it requires increase of [Ca2] inside the SR. In the frog only, increases in cytosolic [Ca2] often resulted, after a lag, in sparks that propagated transversally. An increase in [Mg2] caused a fall of spark frequency, but with striking species differences. In the rat, but not the frog, sparks were observed at 4–40 mM [Mg2]. Reducing [Mg2] below 2 mM, which should enable the RyR channel’s activation (CICR) site to bind Ca2, caused progressive increase in spark frequency in the frog, but had no effect in the rat. Spark propagation and enhancement by sub-mM Mg2 are hallmarks of CICR. Their absence in the rat suggests that CICR requires RyR3 para-junctional clusters, present only in the frog. The observed frequency of sparks corresponds to a channel open probability of 10 7 in the frog or 10 8 in the rat. Together with the failure of photorelease to induce activation directly, this indicates a basal inhibition of channels in situ. It is proposed that relief of this inhibition could be the mechanism by which increased SR load increases spark frequency.