Temperature change does not affect force between single actin filaments and HMM from rabbit muscles

The temperature dependence of sliding force, velocity, and unbinding force was studied on actin filaments when they were placed on heavy meromyosin (HMM) attached to a glass surface. A fluorescently labeled actin filament was attached to the gelsolin-coated surface of a 1-μm polystyrene bead. The bead was trapped by optical tweezers, and HMM-actin interaction was performed at 20-35°C to examine whether force is altered by the temperature change. Our experiments demonstrate that sliding force increased moderately with temperature (Q₁₀ = 1.6 ± 0.2, ± SEM, n = 9), whereas the velocity increased significantly (Q₁₀ = 2.9 ± 0.4, n = 10). The moderate increase in force is caused by the increased number of available cross-bridges for actin interaction, because the cross-bridge number similarly increased with temperature (Q₁₀ = 1.5 ± 0.2, n = 3) when measured during rigor induction. We further found that unbinding force measured during the rigor condition did not differ with temperature. These results indicate that the amount of force each cross-bridge generates is fixed, and it does not change with temperature. We found that the above generalization was not modified in the presence of 1 mM MgADP or 8 mM phosphate.