Nelson T E, Lin M, Zapata-Sudo G, Sudo R T
Department of Anesthesia, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, North Carolina 27103, USA.
Anesthesiology. 1996 Jun;84(6):1368-79. doi: 10.1097/00000542-199606000-00013.
Dantrolene sodium (DS) is a direct-acting skeletal muscle relaxant whose only known action is to block calcium release from intracellular storage sites. The exact site of action for DS is unknown, but its efficacy in treating and preventing anesthetic-induced malignant hyperthermia (MH) is well established.
Single ryanodine (Ry1) receptor calcium release channels were incorporated into a planar lipid bilayer for electrophysiologic recording and for subsequent analysis of the channel's gating and conductance properties. The cellular effects of low DS concentrations were investigated by isometric contracture tension responses in biopsied MH human and dog muscle fascicles and in normal, single fibers from human vastus lateralis muscle.
Two concentration-dependent DS effects on the isolated Ry1 receptor were discovered, suggesting at least two different binding sites. At nanomolar concentrations, DS activated the channel by causing three-to fivefold increases in open-state probability and dwell times. At micromolar concentrations, DS first increased then reduced activity in the channels; with the dominant effect being reduced activity. A 20 nm concentration of DS produced significant contracture tension in human muscle from one MH subject and caused potentiation of twitch in muscle from another MH patient. Halothane contracture in MH dog muscle was followed by an additional increase in tension when treated with 20 nm DS. Other investigations on chemically skinned, human fibers showed that calcium loaded in the sarcoplasmic reticulum was partially released by nM DS.
The study results suggest that at least two binding sites for DS exist on the Ry1 receptor calcium channel. A low-affinity (microM) site is associated with reduced channel gating and open-state dwell time and may relate to the established pharmacologic muscle relaxant effect of DS. The proposed high-affinity (nM) DS binding site activates the channel, producing Ca2+ release to the myoplasm, which, under environmentally adverse conditions, could damage genetically predisposed MH muscle. Such a phenomenon, if it occurs in DS treated MH patients, could generate a recrudescence of the syndrome.
丹曲林钠（DS）是一种直接作用的骨骼肌松弛剂，其唯一已知作用是阻断细胞内储存部位的钙释放。DS的确切作用位点尚不清楚，但其在治疗和预防麻醉引起的恶性高热（MH）方面的疗效已得到充分证实。
将单个兰尼碱（Ry1）受体钙释放通道整合到平面脂质双分子层中，用于电生理记录以及随后对通道门控和电导特性的分析。通过对活检的MH患者和犬类肌肉束以及来自人类股外侧肌的正常单纤维进行等长收缩张力反应，研究低浓度DS的细胞效应。
发现DS对分离的Ry1受体有两种浓度依赖性效应，提示至少有两个不同的结合位点。在纳摩尔浓度下，DS通过使开放状态概率和停留时间增加三到五倍来激活通道。在微摩尔浓度下，DS首先增加然后降低通道活性；主要作用是降低活性。20纳米浓度的DS在一名MH患者的人体肌肉中产生了显著的挛缩张力，并在另一名MH患者的肌肉中引起了抽搐增强。在用20纳米DS治疗后，MH犬肌肉中的氟烷挛缩后张力进一步增加。对化学去皮的人体纤维的其他研究表明，肌浆网中加载的钙被纳摩尔浓度的DS部分释放。
研究结果表明，Ry1受体钙通道上至少存在两个DS结合位点。一个低亲和力（微摩尔）位点与通道门控减少和开放状态停留时间有关，可能与DS既定的药理肌肉松弛作用有关。提出的高亲和力（纳摩尔）DS结合位点激活通道，导致Ca2+释放到肌浆中，在环境不利条件下，这可能会损害遗传易感性的MH肌肉。如果这种现象发生在接受DS治疗的MH患者中，可能会导致综合征复发。
