Nettleton J, Castle N A, Wang G K
Department of Anesthesia Research Laboratories, Harvard Medical School, Boston, Massachusetts.
Mol Pharmacol. 1991 Mar;39(3):352-8.
The effects of clofilium on single batrachotoxin-activated Na+ channels from rabbit skeletal muscle, incorporated into planar bilayers, were studied under symmetrical 200 mM NaCl conditions. Internally applied clofilium (0.3-30 microM) induced long lasting closures, with a mean duration of approximately 450 msec at +50 mV. The fraction of time spent in the clofilium-induced closed state was concentration dependent, with an equilibrium dissociation constant (Kd) of 3.4 microM at +50 mV. Kinetic analysis showed that both open and closed time distributions were well described by single exponentials, with respective time constants of tau o and tau C. As expected for an open channel blocker, 1/tau o increased linearly with increasing clofilium concentration, whereas 1/tau c remained relatively constant. Inhibition of batrachotoxin-activated Na+ channels by clofilium exhibited a strong voltage dependence. The binding affinity of clofilium increased about 10-fold upon depolarization from -50 mV to 50 mV. Competition studies using quaternary and tertiary local anesthetics showed that clofilium and local anesthetics probably share a common receptor site located about halfway across the membrane electrical field. Together, our results demonstrate that clofilium is a potent Na+ channel blocker in bilayers and its action is similar to that of other local anesthetics characterized previously.
在对称的200 mM NaCl条件下，研究了氯非铵对整合到平面双层膜中的兔骨骼肌单个蛙毒碱激活的Na⁺通道的影响。从内部施加氯非铵（0.3 - 30 μM）会诱导通道长时间关闭，在 +50 mV时平均持续时间约为450毫秒。处于氯非铵诱导的关闭状态所花费的时间比例与浓度相关，在 +50 mV时平衡解离常数（Kd）为3.4 μM。动力学分析表明，开放时间分布和关闭时间分布都可以用单指数很好地描述，其时间常数分别为τo和τC。正如对开放通道阻滞剂所预期的那样，1/τo随氯非铵浓度的增加呈线性增加，而1/τc保持相对恒定。氯非铵对蛙毒碱激活的Na⁺通道的抑制表现出强烈的电压依赖性。从 -50 mV去极化到50 mV时，氯非铵的结合亲和力增加约10倍。使用季铵和叔胺类局部麻醉剂的竞争研究表明，氯非铵和局部麻醉剂可能共享一个位于跨膜电场大约中间位置的共同受体位点。总之，我们的结果表明，氯非铵在双层膜中是一种有效的Na⁺通道阻滞剂，其作用与先前表征的其他局部麻醉剂相似。
