Effect of temperature on cross-bridge properties in intact frog muscle fibers

It is well known that the force developed by skeletal muscles increases with temperature. Despite the work done on this subject, the mechanism of force potentiation is still debated. Most of the published papers suggest that force enhancement is due to the increase of the individual cross-bridge force. However, reports on skinned fibers and single-molecule experiments suggest that cross-bridge force is temperature independent. The effects of temperature on cross-bridge properties in intact frog fibers were investigated in this study by applying fast stretches at various tension levels (P) on the tetanus rise at 5°C and 14°C to induce cross-bridge detachment. Cross-bridge number was measured from the force (critical force, Pc) needed to detach the cross-bridge ensemble, and the average cross-bridge strain was calculated from the sarcomere elongation needed to reach Pc (critical length, Lc). Our results show that Pc increased linearly with the force developed at both temperatures, but the Pc/P ratio was con...