Stretch-Induced Transparency Change Associated with Cross-Bridge Deformation in Active Frog’s Muscle

Abstract

In a recent study of the transparency changes produced by stretching active frog’s muscle (Flitney & Eastwood, 1982), we identified a component of the optical signal which was associated with the extra tension generated. This was referred to as the tension-dependent transparency change, or TDC, to distinguish it from another component which appeared to be related to the change in muscle length. The amplitude of the TDC was found to vary linearly with the tension increment, Δ P, when this was made to change by altering the rest length of the muscle prior to stimulation. Since muscle stiffness (and hence, Δ P) depends upon the extent of filament overlap (see Discussion), this observation suggested to us that the TDC is generated by strain in the cross-bridges. However, for various reasons we could not exclude the possibility that the filaments themselves might be partially (or even wholly) responsible.