Sarcomere length behaviour along single frog muscle fibres at different lengths during isometric tetani

Abstract

A detailed investigation of sarcomere lengthening and shortening during fixed-end tetani has been made along frog muscle fibres stretched over a large range of sarcomere lengths. A variety of sources of error common in such measurements are quantitated and give an uncertainty in sarcomere length of about 53–62 nm. The difference in sarcomere length calculated from the left and right first orders at rest was 21 nm ±16 nm and this is suggested to be a measure of ‘Bragg artefact’. The laser diffraction measurements showed that the shortening end regions decrease in size during contraction and that the magnitude of shortening is increased at greater fibre extensions. The average length change and sarcomere length of the central and end regions was 0.10 μm (2.85 μm) and −0.37 μm (2.66 μm), respectively. The sarcomere length of the end regions at the end of creep was regularly observed to be Biophys. J. 39 (1982) 189–96) and Edman and Reggiani(J. Physiol. (Lond.) 351 (1984) 169–98), specific differences which do exist are discussed.