Ta Tram Anh, Pessah Isaac N
UC Davis, Center for Children's Environmental Health, Davis, CA 95616, USA.
Neurotoxicology. 2007 Jul;28(4):770-9. doi: 10.1016/j.neuro.2006.08.007. Epub 2006 Aug 30.
Malignant hyperthermia (MH) susceptibility is conferred by inheriting one of >60 missense mutations within the highly regulated microsomal Ca(2+) channel known as ryanodine receptor type 1 (RyR1). Although MH susceptible patients lack overt clinical signs, a potentially lethal MH syndrome can be triggered by exposure to halogenated alkane anesthetics. This study compares how non-coplanar 2,2',3,5',6-pentachlorobiphenyl (PCB 95), a congener identified in environmental and human samples, alters the binding properties of [(3)H]ryanodine to RyR1 in vitro. Junctional sarcoplasmic reticulum (SR) was isolated from skeletal muscle dissected from wild type pigs ((Wt)RyR1) and pigs homozygous for MH mutation R615C ((MH)RyR1), a mutation also found in humans. Although the level of (Wt)RyR1 and (MH)RyR1 expression is the same, (MH)RyR1 shows heightened sensitivity to activation and altered regulation by physiological cations. We report here that (MH)RyR1 shows more pronounced activation by Ca(2+), and is less sensitive to channel inhibition by Ca(2+) and Mg(2+), compared to (Wt)RyR1. In a buffer containing 100nM free Ca(2+), conditions typically found in resting cells, PCB 95 (50-1000nM) enhances the activity of (MH)RyR1 whereas it has no detectable effect on (Wt)RyR1. PCB 95 (2microM) decreases channel inhibition by Mg(2+) to a greater extent in (MH)RyR1 (IC(50) increased nine-fold) compared to (Wt)RyR1 (IC(50) increased by 2.5-fold). PCB95 reduces inhibition by Ca(2+) two-fold more with (MH)RyR1 than (Wt)RyR1. Our data suggest that non-coplanar PCBs are more potent and efficacious toward (MH)RyR1 than (Wt)RyR1, and have more profound effects on its cation regulation. Considering the important roles of Ca(2+) and Mg(2+) in regulating Ca(2+) signals involving RyR channels, these data provide the first mechanistic evidence that a genetic mutation known to confer susceptibility to pharmacological agents also enhances sensitivity to an environmental contaminant.
恶性高热（MH）易感性是由遗传高度调控的微粒体钙（Ca2+）通道（称为1型兰尼碱受体（RyR1））内60多个错义突变之一引起的。尽管MH易感患者缺乏明显的临床体征，但接触卤代烷麻醉剂可能引发潜在致命的MH综合征。本研究比较了环境和人类样本中鉴定出的一种同系物——非共平面2,2',3,5',6-五氯联苯（PCB 95）如何在体外改变[3H]兰尼碱与RyR1的结合特性。从野生型猪（（Wt）RyR1）和MH突变R615C纯合猪（（MH）RyR1）（人类中也发现的一种突变）解剖的骨骼肌中分离连接肌质网（SR）。尽管（Wt）RyR1和（MH）RyR1的表达水平相同，但（MH）RyR1对激活的敏感性更高，并且生理阳离子对其调节也发生了改变。我们在此报告，与（Wt）RyR1相比，（MH）RyR1对Ca2+的激活更明显，并且对Ca2+和Mg2+介导的通道抑制不太敏感。在含有100 nM游离Ca2+的缓冲液（静息细胞中常见的条件）中，PCB 95（50 - 1000 nM）增强（MH）RyR1的活性，而对（Wt）RyR1没有可检测到的影响。与（Wt）RyR1（IC50增加2.5倍）相比，PCB 95（2 μM）在（MH）RyR1中更大程度地降低了Mg2+对通道的抑制作用（IC50增加了9倍）。与（Wt）RyR1相比，PCB95对（MH）RyR1的Ca2+抑制作用降低了两倍。我们的数据表明，非共平面多氯联苯对（MH）RyR1比（Wt）RyR1更有效，并且对其阳离子调节有更深远的影响。考虑到Ca2+和Mg2+在调节涉及RyR通道的Ca2+信号中的重要作用，这些数据提供了第一个机制证据，即已知赋予对药物易感性的基因突变也增强了对环境污染物的敏感性。
