Axial elastic modulus as a function of relative fiber width in relaxed skinned skeletal muscle fibers

The axial elastic modulus as a function of relative fiber width was measured in relaxed skinned fiber segments from the semitendinosus muscle of the frog. Fiber width was reduced by adding the non- penetrating long-chain polymer Dextran T500 (Mm = 181,800 D) to the fiber bathing solution. The axial elastic modulus increased steeply as relative fiber width was reduced. This relationship is independent of both ionic strength and of the presence of low molecular weight fractions of dextran within the interfilament space. The observed increase in axial elastic modulus with compression may reflect an interaction between crossbridges and thin filaments, an hypothesis which is corroborated by the similarity of responses obtained from compressed fibers and from width fibers in rigor.