ACTION POTENTIALS RECONSTRUCTED IN NORMAL AND MYOTONIC MUSCLE-FIBERS
ACTION POTENTIALS RECONSTRUCTED IN NORMAL AND MYOTONIC MUSCLE-FIBERS
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DOI：
10.1113/jphysiol.1976.sp011410
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发表时间：
1976-01-01
影响因子：
5.5
通讯作者：
MARSHALL, MW
中科院分区：
文献类型：
--
作者：
ADRIAN, RH;MARSHALL, MW
患有先天性肌强直的山羊的肌肉纤维对细胞内电流的刺激表现出特征性反应（Adrian 和 Bryant，1974）。为了测试表面氯电导降低是否可以解释这些肌强直放电，计算了模型肌纤维对长持续时间（> 100 ms）的细胞内电流的响应，假设电流施加在纤维末端，纤维具有有限长度，再生动作电位发生在横向管状系统以及表面，并且横向管状系统壁中的 K 电流提高管腔中的 K 。在缺乏关于哺乳动物肌肉中离子电流的动力学参数的信息的情况下，使用来自青蛙肌肉的数值。在使用正常表面 Cl- 电导的计算中，长期维持的电流仅给出一个动作电位。将 Cl- 电导减少到 1/2 会在电流期间产生重复点火；减少到 1/10 会在电流期间产生重复放电，并在电流结束后产生少量动作电位。从计算中消除管状 K 累积会减少数量，但不会消除施加电流结束后产生的动作电位。使用正常 Cl-电导的 1/10 计算的响应显示，如果 Na 通道的失活率降低 25%，则在恒定电流后维持放电。和以前一样，消除 K 积累会减少刺激后动作电位的数量，但并不能完全消除它们。在没有表面 Cl-电导的情况下，管状 K 积累肯定会导致膜的不稳定，但很明显，K 积累并不是强直肌纤维不稳定的唯一原因。 Na 通道的动力学很重要，但它们在正常纤维和强直纤维中是否相同尚不清楚。然而，表面 Cl-电导的存在确实稳定了纤维对恒定电流或重复刺激的响应，并且它的不存在可能是肌强直行为的充分条件。
Muscle fibers from goats with myotonia congenita show characteristic responses to stimulation with intracellular currents (Adrian and Bryant, 1974). To test whether the reduced surface chloride conductance can account for these myotonic discharges, responses of a model muscle fiber to intracellular current of long duration (> 100 ms) were calculated, assuming that the current is applied at the end of the fiber, that the fiber is of finite length, that a regenerative action potential occurs in the transverse tubular system as well as the surface, and that the K current in the wall of the transverse tubular system raises the K in the tubular lumen. In the absence of information about the kinetic parameters of the ionic currents in mammalian muscle numerical values from frog muscle were used. In calculations with a normal surface Cl- conductance, a long maintained current gives only one action potential. Reduction of the Cl- conductance to 1/2 produces repetitive firing during the current; reduction to 1/10 produces repetitive firing during and a small number of action potentials after the end of the current. Elimination of the tubular K accumulation from the calculation reduces the number but does not eliminate action potentials arising after the end of the applied current. With 1/10 of the normal Cl- conductance calculated responses show maintained firing following a constant current if the deactivating rate of the Na channels is reduced by 25%. As before, eliminating K accumulation reduces the number of post-stimulus action potentials, but it does not eliminate them altogether. In the absence of a surface Cl- conductance tubular K accumulation could certainly contribute to the instability of the membrane, but it is clear that K accumulation is not the only reason for the instability of myotonic muscle fibers. The kinetics of the Na channels are important and whether they are the same in normal and myotonic fibers is not known. Nevertheless the presence of a surface Cl- conductance does stabilize the response of a fiber to constant current or to repetitive stimulation, and its absence could be a sufficient condition for myotonic behavior.