Ruff R L
Department of Neurology, Cleveland Veterans Administration Medical Center, OH 44106, USA.
Muscle Nerve. 1996 Sep;19(9):1084-92. doi: 10.1002/(SICI)1097-4598(199609)19:9<1084::AID-MUS2>3.0.CO;2-W.
Na+ current (INa), membrane capacitance (Cm), action potential (AP) properties, and cable properties were studied on the end-plate (E), the end-plate border (EB), and extrajunctional (EJ) membrane of rat fast twitch muscle fibers. INa normalized to Cm, which is proportional to the density of Na+ channels, was the same on the E and the EB and smallest on EJ membrane. The AP threshold was lower and rate of rise of the AP was larger at the EB compared with EJ membrane. On the E and the EB, Cm and INa did not change in response to changes in fiber length. On EJ membrane, INa, Cm, and membrane cable properties changed in a manner consistent with folding and unfolding of the sarcolemma during length changes. The stiffness of the E membrane may add mechanical stability of the neuromuscular junction so that the electrical properties of the end-plate do not change with fiber length. The higher density of Na+ channels near the end-plate increases the safety factor for neuromuscular transmission by lowering the AP threshold.
在大鼠快肌纤维的终板（E）、终板边缘（EB）和接头外（EJ）膜上研究了钠离子电流（INa）、膜电容（Cm）、动作电位（AP）特性和电缆特性。归一化到Cm的INa与钠离子通道密度成正比，在E和EB上相同，在EJ膜上最小。与EJ膜相比，EB处的AP阈值较低且AP上升速率较大。在E和EB上，Cm和INa不会随纤维长度的变化而改变。在EJ膜上，INa、Cm和膜电缆特性的变化方式与长度变化期间肌膜的折叠和展开一致。E膜的刚度可能增加神经肌肉接头的机械稳定性，从而使终板的电特性不会随纤维长度而改变。终板附近较高密度的钠离子通道通过降低AP阈值增加了神经肌肉传递的安全系数。
