Effects of denervation and muscle inactivity on the organization of F-actin

To discriminate between the influences of a motoneuron and muscle activity on the conformation of actin filaments, the extrinsic polarized fluorescence [of rhodamine–phalloidin and N-(iodoacetylamine)-1-naphthylamine-5-sulfonic acid attached to F-actin] was measured in “ghost” fibers from intact rat soleus muscles and atrophying muscles after denervation, immobilization, or tenotomy. The results show that the conformation of F-actin changed in all the atrophying muscles, but differently. In the denervated muscle, the flexibility of the actin filaments decreased, whereas in the other experimental muscles it remained as in the intact muscle. In the denervated muscle, the mobility of the C-terminus of the actin polypeptide increased. Attachment of myosin subfragment-1 influenced the F-actin conformation differently in the denervated muscle than in the other muscles studied. These results suggest that changes in the conformation of the actin filament are induced by the lack of connection with the motoneuron rather than by muscle inactivity. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:309–317, 1988.