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

Abstract

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 considerably smaller at 14°C. This means that the average force per cross bridge is greater at high temperature. This mechanism accounts for all the tetanic force enhancement. The critical length Lc was independent of the tension developed at both temperatures but was significantly lower at high temperature suggesting that cross bridges at 14°C are more strained. The increased cross-bridge strain accounts for the greater average force developed. force enhancement; fast stretches IT IS WELL KNOWN that tetanic tension in skeletal frog and mammalian muscle increases with temperature in the range 0°C to 20°C (5, 8, 9, 16 -19, 23). Most of the data in the literature indicate that the force enhancement is due to an increase of the mean force developed by the individual cross bridge without a significant change in the total number of attached bridges. It has been also reported that increase of cross-bridge force with temperature occurs at the expense of the power stroke extent, which suggests a common mechanism with force development after electrical stimulation (17). A few reports in skinned fibers (14) and single-molecule experiments (15), however, suggest that temperature increases the number of cross bridges without altering the individual cross-bridge force. From the importance of these findings for the understanding of the mechanism of force generation, we have investigated the effect of temperature on cross-bridge properties in single frog muscle fibers by using a technique recently introduced by our group (1) following Flitney and Hirst (7). This technique measures the cross-bridge number from the measurements of the critical tension (P c ) needed to forcibly detach the cross-bridge ensemble by a fast stretch. Mean sarcomere length extension is obtained from measurements of the sarcomere elongation (critical length, L c ) needed to induce the rupture of the cross-bridge ensemble. In contrast to stiffness measurements traditionally used to measure the number of cross bridges, our measurements do not need to assume...

The temperature dependence of cell mechanics measured by atomic force microscopy

“…Moreover, a temperature-induced enhancement of actomyosin activity is consistent with previous observations that temperature increases contractility in fibroblasts [46] and activates the actomyosin machinery [47–52]. Such an increase has been attributed either to an enhancement of the mean force developed by the individual actomyosin cross bridges [50–52] or to a change in the cross-bridge number [47, 49]. The parallel behaviour of G ′ and P observed here indicates that the link between both magnitudes is maintained at different temperatures.…”

Effect of Temperature on Crossbridge Force Changes during Fatigue and Recovery in Intact Mouse Muscle Fibers

“…The recovery of tension during phase 2 was much faster at 35 than at 24°C. We also found that temperature increase from 24 to 35°C did not affect fiber stiffness, indicating that tetanic force potentiation by temperature, in this range, is mainly due to the increase of the average force per crossbridge in agreement with our previous findings [19,20]. …”

“…Measurements on the same group of fibers showed that fiber stiffness at tetanus plateau did not increase significantly from 24 to 35°C, indicating that force potentiation by temperature occurred without changes in attached crossbridge number (proportional to stiffness) consistently with the idea that temperature increases the individual crossbridge force as suggested previously [19,20]. We also measured the ratio ( dl/l f )/( dp / P 0 ), defined as y 0f , which corresponds to the relative extension (% of l f ) at the tetanus plateau, of all the elastic components of the fibers: tendon, myofilament and crossbridges.…”

Effects of blebbistatin and Ca2+ concentration on force produced during stretch of skeletal muscle fibers

“…When activated muscle fibers and myofibrils are stretched at low speeds [Յ2 optimal length (L o )/s], cross bridges have to resist the opposing forces while attached to actin, which causes the force to increase in two phases: 1) a fast increase that happens over the extension of a few nanometers and subsequently 2) a slow increase or a stabilization of force (16,23,39,41,43). Rapid stretches (Ͼ10 L o /s) produce a break in the force rise also associated with the mechanical detachment of cross bridges and corresponding well to the transition in force observed during slower stretches (2,12,13). The detachment happens after the cross bridges reach a critical extension length (L c ), commonly observed in lengths between 8 and 20 nm/halfsarcomere (HS), depending on the experimental condition (16,23,39,43).…”