Differential Ca2+ sensitivity of skeletal and cardiac muscle ryanodine receptors in the presence of calmodulin
Differential Ca2+ sensitivity of skeletal and cardiac muscle ryanodine receptors in the presence of calmodulin
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DOI：
10.1152/ajpcell.2000.279.3.c724
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发表时间：
2000-09-01
影响因子：
5.5
通讯作者：
Louis, CF
中科院分区：
文献类型：
--
作者：
Fruen, BR;Bardy, JM;Louis, CF
钙调素(CaM)激活骨骼肌Ryanodine受体钙释放通道(RyR1)。然而，CaM激活在控制骨骼肌和心脏肌浆网(SR)钙释放机制中的作用尚不清楚。在含100 nM Ca~(2+)的培养液中，CaM(1mM)可使猪骨骼肌SR囊泡的Ca-45~(2+)释放速率增加近3倍。相反，心肌SR囊泡Ca-45(2+)的释放不受CaM的影响，提示CaM激活骨骼RyR1，但不激活心脏RyR2通道异构体。CaM对RyR1的激活与[H-3]ryanodine与骨骼肌SR结合的钙敏感性增加约6倍有关，而心肌SR[H-3]ryanodine结合的钙敏感性在CaM存在和不存在的情况下相似。交联实验证实RyR1和RyR2分别是骨骼和心脏SR中主要的CaM结合蛋白，[S-35]CaM结合测定进一步表明，在微摩尔钙离子存在的情况下，CaM与这两种异构体结合类似。然而，在纳米分子钙离子中，RyR2[S-35]CaM结合的亲和力和化学计量比比RyR1降低。综上所述，我们的结果表明，CaM通过增加通道的钙敏感性来激活RyR1，并进一步表明CaM与RyR1和RyR2亚型功能相互作用的差异可能是骨骼肌和心肌细胞通道激活对钙的依赖程度不同的原因之一。
Calmodulin (CaM) activates the skeletal muscle ryanodine receptor Ca2+ release channel (RyR1) in the presence of nanomolar Ca2+ concentrations. However, the role of CaM activation in the mechanisms that control Ca2+ release from the sarcoplasmic reticulum (SR) in skeletal muscle and in the heart remains unclear. In media that contained 100 nM Ca2+, the rate of Ca-45(2+) release from porcine skeletal muscle SR vesicles was increased approximately threefold in the presence of CaM (1 mu M). In contrast, cardiac SR vesicle Ca-45(2+) release was unaffected by CaM, suggesting that CaM activated the skeletal RyR1 but not the cardiac RyR2 channel isoform. The activation of RyR1 by CaM was associated with an approximately sixfold increase in the Ca2+ sensitivity of [H-3]ryanodine binding to skeletal muscle SR, whereas the Ca2+ sensitivity of cardiac SR [H-3]ryanodine binding was similar in the absence and presence of CaM. Cross-linking experiments identified both RyR1 and RyR2 as predominant CaM binding proteins in skeletal and cardiac SR, respectively, and [S-35]CaM binding determinations further indicated comparable CaM binding to the two isoforms in the presence of micromolar Ca2+. In nanomolar Ca2+, however, the affinity and stoichiometry of RyR2 [S-35]CaM binding was reduced compared with that of RyR1. Together, our results indicate that CaM activates RyR1 by increasing the Ca2+ sensitivity of the channel, and further suggest differences in CaM's functional interactions with the RyR1 and RyR2 isoforms that may potentially contribute to differences in the Ca2+ dependence of channel activation in skeletal and cardiac muscle.