Jiang Dawei, Chen Wenqian, Xiao Jianmin, Wang Ruiwu, Kong Huihui, Jones Peter P, Zhang Lin, Fruen Bradley, Chen S R Wayne
Libin Cardiovascular Institutes of Alberta, Department of Physiology, University of Calgary, Calgary, Alberta, Canada.
J Biol Chem. 2008 Jul 25;283(30):20813-20. doi: 10.1074/jbc.M801944200. Epub 2008 May 27.
Naturally occurring mutations in the skeletal muscle Ca(2+) release channel/ryanodine receptor RyR1 are linked to malignant hyperthermia (MH), a life-threatening complication of general anesthesia. Although it has long been recognized that MH results from uncontrolled or spontaneous Ca(2+) release from the sarcoplasmic reticulum, how MH RyR1 mutations render the sarcoplasmic reticulum susceptible to volatile anesthetic-induced spontaneous Ca(2+) release is unclear. Here we investigated the impact of the porcine MH mutation, R615C, the human equivalent of which also causes MH, on the intrinsic properties of the RyR1 channel and the propensity for spontaneous Ca(2+) release during store Ca(2+) overload, a process we refer to as store overload-induced Ca(2+) release (SOICR). Single channel analyses revealed that the R615C mutation markedly enhanced the luminal Ca(2+) activation of RyR1. Moreover, HEK293 cells expressing the R615C mutant displayed a reduced threshold for SOICR compared with cells expressing wild type RyR1. Furthermore, the MH-triggering agent, halothane, potentiated the response of RyR1 to luminal Ca(2+) and SOICR. Conversely, dantrolene, an effective treatment for MH, suppressed SOICR in HEK293 cells expressing the R615C mutant, but not in cells expressing an RyR2 mutant. These data suggest that the R615C mutation confers MH susceptibility by reducing the threshold for luminal Ca(2+) activation and SOICR, whereas volatile anesthetics trigger MH by further reducing the threshold, and dantrolene suppresses MH by increasing the SOICR threshold. Together, our data support a view in which altered luminal Ca(2+) regulation of RyR1 represents a primary causal mechanism of MH.
骨骼肌钙释放通道/雷诺丁受体RyR1的自然发生突变与恶性高热（MH）相关，MH是全身麻醉的一种危及生命的并发症。尽管长期以来人们已经认识到MH是由肌浆网中不受控制或自发的钙释放引起的，但尚不清楚MH RyR1突变如何使肌浆网易受挥发性麻醉剂诱导的自发钙释放影响。在这里，我们研究了猪的MH突变R615C（其人类等效突变也会导致MH）对RyR1通道内在特性以及在储存钙超载期间自发钙释放倾向的影响，我们将这一过程称为储存超载诱导的钙释放（SOICR）。单通道分析表明，R615C突变显著增强了RyR1的腔内钙激活。此外，与表达野生型RyR1的细胞相比，表达R615C突变体的HEK293细胞显示出较低的SOICR阈值。此外，MH触发剂氟烷增强了RyR1对腔内钙和SOICR的反应。相反，丹曲林是一种有效的MH治疗药物，它抑制了表达R615C突变体的HEK293细胞中的SOICR，但对表达RyR2突变体的细胞没有抑制作用。这些数据表明，R615C突变通过降低腔内钙激活和SOICR的阈值赋予MH易感性，而挥发性麻醉剂通过进一步降低阈值触发MH，丹曲林通过提高SOICR阈值来抑制MH。总之，我们的数据支持这样一种观点，即RyR1腔内钙调节的改变是MH的主要因果机制。
