Mechano-receptor transduction channels in muscle spindle.

从牛蛙半腱肌分离的肌梭感觉末梢的功能被发现与末梢冷冻断裂复制品中直径大于12 nm的膜内颗粒（IMPs）的密度密切相关。大多数IMP较小（[. Itoreq.] 12 nm），其在粒度直方图中形成了不同的组。大的IMP集中在沿着轴突终末的球状区域周围。据报道，球是终端最易变形的部分，在拉伸过程中会增加体积。在坐骨神经背侧髋关节挤压后的神经再支配过程中，牵拉反应从短暂到正常模式的变化遵循与大IMP密度增加相同的时间过程，而小IMP的数量没有相关变化。在通过腱切断术缩短至控制长度的约50%持续6 - 90天或长期延长至控制长度的约130%持续8天的肌肉中，拉伸反应和大IMP的密度保持不变，但小IMP的密度在短切后增加到对照的2 - 6倍，或在延伸后降低到对照的60 - 70%。每天向蛙背淋巴囊注射蛋白质合成阻断剂放线菌素D（0.15 mg/500 g）后2天，大小IMP的密度下降至对照的50 - 60%。在第2天的拉伸反应的特征在于在动态拉伸过程中的瞬态模式，没有任何静态响应，在保持拉伸过程中，如发生完整的纺锤体。反应和IMP均在注射第3天消失。结果表明IMP的半衰期相当短。

The function of sensory endings of muscle spindles isolated from semitendinosus muscles of the bullfrog was found to be closely correlated with density of intramembrane particles (IMPs) greater then 12 nm in diameter in p-pace of freeze fracture replicas of the endings. The majority of IMPs were smaller (【.Itoreq.】 12 nm) than these,which formed a distinct group in particle size histograms. The large IMPs were concentrated around the bulb regions along the axon terminals. The bulbs have been reported be the most deformable part of the terminal and to respond with increased volume during stretch. During reinnervation after crush of the sciatic never dorsal to the hip joint, the chenge in stretch response from a transient to a normal pattern followed the same time course as the increase in the density of large IMPs, whereas there was no correlated change in the number of small IMPs. In muscles that were either shortened to approximately 50 % of control length for 6 - 90 days by tenotomy, or were chronically extended to approximately 130 % of control length for 8 days, the stretch response and the density of large IMPs remained unchanged, but the density of small IMPs increased 2 - 6 times the control after shotening or decreased to 60 - 70 % of the control after extension. The densities of large and small IMPs decreased to 50 - 60 % of the control 2 days after daily injections of a protein synthesis blocker, actinomycin D (0.15 mg/500g), into the dorsal lymphatic sac of the frogs. The stretch response at day 2 was characterized by a transient pattern during the dynamic stretch, without any static response during hold stretch such as occurs intact spindles. Both the responses and IMPs disappeared at day 3 of injection. The results suggest that the half-life of the IMPs is rather short.