Temperature sensitivity of force and shortening velocity in maximally activated skinned smooth muscle

We have studied the temperature dependence of isometric force, rate of force development and maximal shortening velocity (Vmax) in skinned guinea-pig taenia coli smooth muscle. To eliminate the influence of temperature on activation mechanisms, maximally thiophosphorylated preparations were used. Isometric force in the range 2-35 degrees C was maximal at 22 degrees C with a decrease of 25% at 2 degrees C and 10% at 35 degrees C. Rate of tension development from rigor after photolytic release of ATP increased four-fold between 5 degrees C and 30 degrees C. Vmax increased with a Q10 of about 2 (1.6, range 5-15 degrees C, and 2.2, range 22-30 degrees C). The temperature dependence of the rate of tension development indicates rate-limitation by transitions into force-generating states or by the hydrolysis reaction. The temperature dependence of Vmax reflects effects of temperature on reactions (e.g. the ADP-release) associated with cross-bridge detachment. The small temperature dependence of steady-state force in smooth compared with skeletal muscle suggests differences in the cross-bridge reactions controlling the number of attached force-generating states in the two muscle types.