EFFECTS OF DENERVATION AND MUSCLE INACTIVITY ON THE ORGANIZATION OF F-ACTIN

To discriminate between the influences of a motoneuron and muscle acti vity on the conformation of actin filaments, the extrinsic polarized f luorescence [of rhodamine-phalloidin and N-(iodoacetylamine)-1-naphthy lamine-5-sulfonic acid attached to F-actin] was measured in ''ghost'' fibers from intact rat soleus muscles and atrophying muscles after den ervation, immobilization, or tenotomy. The results show that the confo rmation of F-actin changed in all the atrophying muscles, but differen tly. 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-te rminus of the actin polypeptide increased. Attachment of myosin subfra gment-1 influenced the F-actin conformation differently in the denerva ted muscle than in the other muscles studied. These results suggest th at changes in the conformation of the actin filament are induced by th e lack of connection with the motoneuron rather than by muscle inactiv ity. (C) 1998 John Wiley & Sons, Inc.