Possibilities for Increasing Number of Cross-bridges with Temperature

The Brownian motion of the HMM molecules may release more head domains from the glass surface at higher temperature without releasing the attached end.

The increased thermal motion of the thin filament could reach a larger number of HMM molecules, thereby forming the increased number of cross-bridges at higher temperature.

The interaction between actin and myosin may be promoted at higher temperatures, because it is an endothermic reaction.

However, whether this increase in the number of available cross-bridges is a physiological phenomenon is still an open question.

Kawai, M., et al., Temperature change does not affect force between regulated actin filaments and heavy meromyosin in single-molecule experiments. J Physiol, 2006. 574(Pt 3): p. 877-87.

Temperature Change Does Not Affect Force Per Cross-Bridge

The observed cross-bridge number increased with temperature. One possibility is that the Brownian motion may release the head portion of HMM that are inadvertently stuck to the glass surface, but it leaves the C-terminus area of HMM attached to the glass surface, so that more HMM molecules become available to interact with the actin filament to generate more force at higher temperatures. However, this increase may be specific to the in vitro motility system, because the cross-bridge number is presumably maximized during the rigor induction, hence the number should not change with temperature in a physiological experiment. 

The average force per cross-bridge does not change much with temperature in the in vitro motility assay system. The HMM molecules do not change their shape much as the temperature is increased. A change in the shape would be necessary if force per crossbridge or unbinding force were to change with the temperature, because force is presumably a result of the macromolecular architecture of the HMM and actin interrelationship. 

Sliding velocity is expected to increase with the temperature. This is because the velocity is limited by one or two steps in the cross-bridge cycle, and their rate constants almost invariably increase with the temperature. 

The temperature insensitivity of the single molecular force is a fundamental property of a motor protein, and the force is associated with a particular macromolecular architecture. ( Conclusion ) 

Kawai, M., et al., Temperature change does not affect force between single actin filaments and HMM from rabbit muscles. Biophys J, 2000. 78(6): p. 3112-9.