Nabhani Thomas, Zhu Xinsheng, Simeoni Ilenia, Sorrentino Vincenzo, Valdivia Héctor H, García Jesús
Department of Physiology and Biophysics, University of Illinois at Chicago College of Medicine, Chicago, Illinois 60607, USA.
Biophys J. 2002 Mar;82(3):1319-28. doi: 10.1016/S0006-3495(02)75487-8.
Most adult mammalian skeletal muscles contain only one isoform of ryanodine receptor (RyR1), whereas neonatal muscles contain two isoforms (RyR1 and RyR3). Membrane depolarization fails to evoke calcium release in muscle cells lacking RyR1, demonstrating an essential role for this isoform in excitation-contraction coupling. In contrast, the role of RyR3 is unknown. We studied the participation of RyR3 in calcium release in wild type (containing both RyR1 and RyR3 isoforms) and RyR3-/- (containing only RyR1) myotubes in the presence or absence of imperatoxin A (IpTxa), a high-affinity agonist of ryanodine receptors. IpTxa significantly increased the amplitude and the rate of release only in wild-type myotubes. Calcium currents, recorded simultaneously with the transients, were not altered with IpTxa treatment. [(3)H]ryanodine binding to RyR1 or RyR3 was significantly increased in the presence of IpTxa. Additionally, IpTxa modified the gating and conductance level of single RyR1 or RyR3 channels when studied in lipid bilayers. Our data show that IpTxa can interact with both RyRs and that RyR3 is functional in myotubes and it can amplify the calcium release signal initiated by RyR1, perhaps through a calcium-induced mechanism. In addition, our data indicate that when RyR3-/- myotubes are voltage-clamped, the effect of IpTxa is not detected because RyR1s are under the control of the dihydropyridine receptor.
大多数成年哺乳动物骨骼肌仅含有一种兰尼碱受体（RyR1）同工型，而新生肌肉含有两种同工型（RyR1和RyR3）。膜去极化无法在缺乏RyR1的肌肉细胞中引发钙释放，这表明该同工型在兴奋-收缩偶联中起关键作用。相比之下，RyR3的作用尚不清楚。我们研究了在存在或不存在兰尼碱受体的高亲和力激动剂 Imperatoxin A（IpTxa）的情况下，RyR3在野生型（同时含有RyR1和RyR3同工型）和RyR3基因敲除型（仅含有RyR1）肌管钙释放中的参与情况。IpTxa仅在野生型肌管中显著增加了释放幅度和释放速率。与瞬变同时记录的钙电流在IpTxa处理后未发生改变。在存在IpTxa的情况下，[³H]兰尼碱与RyR1或RyR3的结合显著增加。此外，在脂质双层中研究时，IpTxa改变了单个RyR1或RyR3通道的门控和电导水平。我们的数据表明，IpTxa可以与两种RyR相互作用，并且RyR3在肌管中具有功能，它可能通过钙诱导机制放大由RyR1引发的钙释放信号。此外，我们的数据表明，当对RyR3基因敲除型肌管进行电压钳制时，未检测到IpTxa的作用，因为RyR1受二氢吡啶受体的控制。
