Sarcomere length dependence of the rate of tension redevelopment and submaximal tension in rat and rabbit skinned skeletal muscle fibres

1. We examined the hypothesis that in skeletal muscle the steep relationship between twitch tension and sarcomere length (SL) within the range 2.30 to 1.85 mu m involves SL-dependent alterations in the rate of tension development. 2. In skinned preparations of both rat slow-twitch and rabbit fast-twitch skeletal muscle fibres the rate of tension redevelopment (k(tr)) at 15 degrees C was reduced at short SL (similar to 2.00 mu m) compared with a longer SL (similar to 2.30 mu m). In submaximally activated fibres, the decrease in k(tr), over this range of lengths was greater in fast-twitch fibres (38% reduction) than in slow-twitch fibres (l4% reduction). 3. Ca2+ sensitivity of tension, as assessed as the pCa (-log[Ca2+] for half-maximal activation, or pCa(50), decreased to a greater extent in rabbit fast-twitch skeletal muscle fibres than in slow-twitch fibres from both rabbit and rat when SL was reduced from similar to 2.30 to similar to 1.85 mu m. The Delta pCa(50) over this SL range was 0.24 +/- 0.07 pCa units in fast-twitch fibres from rabbit psoas muscle. The Delta pCa(30) for slow-twitch fibres from rabbit and rat soleus muscle was 0.08 +/- 0.02 and 0.10 +/- 0.04 pCa units, respectively. 4. Osmotic compression of both slow-twitch and fast-twitch fibres at a SL of 2.00 mu m increased k(tr) to values similar to those obtained at a SL of 2.30 mu m in the absence of dextran. This result indicates that the slower rate of tension redevelopment at short SL is due in large part to the increase in interfilament lattice spacing associated with shorter SL. 5. Taken together, these results suggest that length dependence of twitch tension is, in part, due to length dependence of isometric cross-bridge interaction kinetics, an effect that is mediated by length-dependent changes in interfilament lattice spacing.