Force and force transients in skeletal muscle fibres of the frog skinned by freeze-drying.

A freeze-drying method is described by which single skinned skeletal muscle fibres or fibre bundles can readily be obtained. Skinned fibre segments of the ileofibularis and semitendinous muscles of the frog - activated by means of a rapid increase in the Ca-concentration - showed very stable and reproducible contractions. Complete activation occurred at a Ca-concentration of 1.6 X 10(-6) M and the mid-point of the pCa-tension curve occurred at 6.3 X 10(-7) M. Addition of phosphate (less than or equal to 10(-2) M) had a depressing effect on the speed of the Ca-activated tension development as well as on the maximum tension reached. Addition of caffeine (10(-2) M) had no effect on the tension generation, indicating that the sarcoplasmic reticulum, if present, was not active. The force responses due to rapid length changes applied to the Ca-activated fibre preparations were found to be qualitatively similar to the force responses on intact tissue. This skinning technique might be employed on human biopsies, enabling the measurement of physiological parameters such as for example force and shortening velocity.