Research Paper Volume 3, Issue 6 pp 621—634

Figure 1. Original and unfiltered recording of a SOL muscle from Wt mice illustrates robustness of our preparations as it can undergo a multitude of experimental manipulations during a prolonged protocol without signs of deterioration. (A) An entire protocol of more than 6h in duration in a soleus (SOL) muscle is shown. The experimental points shown in this record are: a) Initial equilibration period where muscle is carefully stretched; b) Force vs. frequency relationship, c) Equilibration, followed by solution change (from 2.5 mM Ca²⁺ to zero Ca²⁺ + 0.1 mM EGTA), d) Equilibration in Zero Ca²⁺, followed by change of solution back to 2.5 mM Ca²⁺, e) Recovery in 2.5 mM Ca²⁺, f) Fatiguing stimulation, g) Recovery from fatigue in the absence of caffeine, h) Recovery in the presence of 20 mM caffeine, i) After stimulation being stopped, the muscle is treated with 80 mM KCl and still produces a very large response to KCl that approximates the maximal tetanic force. Preparation produced 11 g (~107 mN) of relative force. (B) A single muscle fiber was dissected from the same intact SOL muscle shown in panel A. Single muscle fiber was the electrically stimulated with 80 Hz. and produced ~ 0.12 mN of force. The same fiber was then chemically skinned with Triton X-100 and produced a maximal contractile force of ~ 0.12 mN. From our own observations, we estimate that a SOL muscle has ~925 muscle fibers; thus, the predicted contractile force for this preparation is ~111 mN (0.12 mN/fiber × 925 = 111 mN), which is very similar to the relative force of 107 mN determined by the force calibration in our intact muscle system.