During the last decade, the rat mechanically skinned fibre preparation has been used with increasing frequency to investigate cellular aspects of excitation-contraction (EC)
coupling processes in mammalian skeletal muscle. The main aim of this thesis was to increase awareness of factors that affect the contractile responsiveness of rat mechanically skinned fibre preparations to T-system depolarization, a functional parameter of E-C coupling referred to, sometimes, as skinned fibre excitability. More specifically, the work presented in this thesis is concerned with the relationship between rat skinned fibre excitability and (i) developmental age, (ii) MHC composition, muscle of origin and (iii) glycogen content.