Fig. 3. Depression of force and stiffness of a maximally Ca²⁺-activated skinned anterior byssus retractor muscle (ABRM) fibre bundle by 5 µmol l^-1 blebbistatin. (A) Original recording of force and stiffness during changes of solutions as indicated. The force spikes are induced by repetitive rectangular stretches of 20 ms in duration and 0.1% L₀ in amplitude. The broken line shows an experiment at pH 7.4. The insets show experiments on another ABRM fibre bundle; here force transients were induced by rectangular length changes of 0.2% L₀ at different stages of the experiment. (B) Diagram showing the stiffness/force relationship of the experiment shown in A. Grey squares, Ca²⁺ activation; open circles, blebbistatin. (C,D) Data from similar experiments carried out at pH 7.4 (C) or in the presence of 100 µmol l^-1 cAMP and 2 µmol l^-1 cyclosporine A (CsA). Grey squares, Ca²⁺ activation; open circles, blebbistatin application.