DEFINIZIONE ED INTERPRETAZIONE DI PARAMETRI FONDAMENTALI DELLA CONTRAZIONE MUSCOLARE: LA DISTRIBUZIONE DELLA LUNGHEZZA DEI FILAMENTI DI ACTINA, L’ ACCELERAZIONE DEL CARICO, LA MANOVRA DI HUXLEY-SIMMONS

The research activity reported in this thesis consists of two parts: an experimental phase and a theoretical one. In the experimental part, the changes of the macromolecular osmotic pressure associated with F-actin solutions are related to the changes of the free energy of the free actin monomers. By making use of the model of Biron et al. (Inter-filament attractions narrow the length distribution of actin filaments. Europhys. Lett. 73, 464–470, 2006), the changes of the free energy of the free actin monomers are related to the changes of the length distribution of the actin filaments. On these bases, we propose that the length distribution of the actin filaments is regulated by a) the free energy of hydrolysis of ATP b) the macromolecular osmotic pressure. In the theoretical part, we evaluate the effect of the change of the acceleration associated with the load on muscle contraction. We also consider the Huxley-Simmons manoeuvre (Huxley AF e Simmons RM. Proposed mechanism of force generation in striated muscle. Nature 233, 533-538, 1971), which consists into applying a small, very rapid, length change to a single muscle fibre in the isometric state (quick release) and to measure the subsequent rapid tension recovery at fixed sarcomere.