Study of the State of F-Actin in Denervated Muscle Fibre by Polarised UV Fluorescence Microscopy

In order to establish the effect of denervation on the structure of F-actin, polarisation of fluorescence of tryptophan residues of F-actin was determined in intact and denervated ghost muscle fibres (freed from myosin, troponin and tropomyosin) under various conditions. P\\, the polarisation parameter obtained by excitation of the fluorescence of tryptophan residues of F-actin by light polarised parallel to the long axis of the fibre, was found to be lower for denervated fibres than for the intact ones, i.e., P\\ (denervated) P± (intact). Moreover, solution containing adenosine triphosphate (ATP) caused an increase in P± and a decrease in P\\ of F-actin in intact fibres, and at the same time a decrease in P± and an increase in P\\ of F-actin in denervated fibres. The binding of the heavy meromyosin (FIMM) and the myosin subfragment-I (S-I) to F-actin to intact as well as to denervated fibres decreases P± and increases P\\ though to different degrees. It is supposed that denervation impairs the structure of actin in the regions in which actin-actin and actin-myosin interactions take place.