Mechano-receptor transduction channels in muscle spindle.

点击翻译按钮获取中文摘要

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.