Ruff R L, Spiegel P
Neurology Service, Cleveland Department of Veterans Affairs Medical Center, Ohio 44106.
Am J Physiol. 1990 Dec;259(6 Pt 1):C911-9. doi: 10.1152/ajpcell.1990.259.6.C911.
Myofibrillar Ca sensitivity and single-channel acetylcholine receptor (AChR) currents were studied in garter snake (Thamnophis sirtalis sirtalis) costocutaneous muscle fibers. Nomarski optics were used to identify tonic and fast- and slow-twitch fibers. Measurements of tension generation were made using chemically skinned fibers. The maximum tensions of the three types of fibers were similar, and the fast- and slow-twitch fibers had similar Ca sensitivities. Compared with twitch fibers, tonic fibers had lower threshold Ca concentrations for tension generation and a larger range of Ca concentrations between threshold and maximum tension. The AChR channels were studied by enzymatically removing the nerve terminals and performing patch-clamp recordings on the exposed postsynaptic membrane. Twitch fibers had only one class of end-plate channel with a conductance of approximately 51 pS. Tonic fibers had two types of synaptic channels. One AChR channel in the tonic fibers resembled the type seen in twitch fibers. The other channel in tonic fibers had a smaller conductance of approximately 33 pS and resembled extrajunctional AChRs on denervated twitch fibers.
在束带蛇（Thamnophis sirtalis sirtalis）的肋皮肌纤维中研究了肌原纤维对钙的敏感性和单通道乙酰胆碱受体（AChR）电流。利用相差显微镜来识别慢肌纤维、快肌纤维和慢缩肌纤维。使用化学去膜纤维来测量张力产生。三种类型纤维的最大张力相似，快肌纤维和慢肌纤维具有相似的钙敏感性。与快、慢肌纤维相比，慢缩肌纤维产生张力的阈值钙浓度较低，且在阈值和最大张力之间的钙浓度范围更大。通过酶解法去除神经末梢并在暴露的突触后膜上进行膜片钳记录来研究AChR通道。快、慢肌纤维只有一类终板通道，电导约为51 pS。慢缩肌纤维有两种类型的突触通道。慢缩肌纤维中的一种AChR通道与快、慢肌纤维中所见的类型相似。慢缩肌纤维中的另一种通道电导较小，约为33 pS，类似于失神经支配的快、慢肌纤维上的接头外AChR。
