Tension responses to joule temperature jump in skinned rabbit muscle fibres.

Abstract

SUMMARY1. Joule temperature jumps (T-jumps) from 5-9°C up to 40°C were used to study the cross-bridge kinetics and thermodynamics in skinned rabbit muscle fibres. To produce a T-jump, an alternating current pulse was passed through a fibre 5 s after removing the activating solution (pCa -4-5) from the experimental trough. The pulse frequency was -30 kHz, amplitude < 3 kV, and duration 0-2 ms. The pulse energy liberated in the fibre was calculated using a special analog circuit and then used for estimation of the T-jump amplitude.2. The T-jump induced a tri-exponential tension transient. Phases 1 and 2 had rate constants k1 = 450-1750 s-1 and k2 = 60-250 s-1 respectively, characterizing the tension rise, whereas phase 3 had a rate constant k3 = 5-10 s-5 representing tension recovery due to the fibre cooling.3. An increase from 13 to 40°C for the final temperature achieved by the T-jump led to an increase in the amplitudes of phases 1 and 2. After T-jumps to 30-40°C during phase 1, tension increased by 50-80 %. During phase 2 an approximately 2-fold tension increase continued. Rate constants k. and k2 increased with temperature and temperature coefficients (Q1o) were 1P6 and 1-7, respectively. 4. To study which processes in the cross-bridges are involved in phases 1 and 2, a series of experiments were made where step length changes of -9 to +3 nm (hs)-1(nanometres per half-sarcomere length) were applied to the fibre 4 ms before the T-jump.5. After the step shortening, the rate constant of phase 1 increased, whereas its amplitude decreased compared to those without a length change. This indicates that phase 1 is determined by some force-generating process in the cross-bridges attached to the thin filaments. This process is, most probably, the same as that producing the early tension recovery following the length change. The enthalpy change (AH) associated with the reaction controlling this process was estimated to be positive (15-30 kJ mol').

Imaging of thermal activation of actomyosin motors

“…In muscle fibers, it was reported that force rose by a factor of 2 to 3 (9,11,12,35) between 5°C and 20°C but only by a factor of Ϸ1 (9, 12) or Ϸ1.5 (11) between 20°C and 40°C, much less than the 5-to 10-fold increase in our case. In principle, an increase in tension implies that each myosin head while attached to an actin filament exerts a larger force, and͞or that a larger number of heads are attached at any instant.…”

“…There have been several reports on the effects of temperature jumps under an optical microscope: for example, on physiological functions of muscle fibers (9)(10)(11)(12) and on phase transition phenomena in membranes of phospholipid vesicles and cells (13). To prevent thermal deterioration of biological samples, and to confirm the absence of the deterioration, it is highly desirable to restore the starting temperature as soon as the measurement is finished.…”

Use of thin filament reconstituted muscle fibres to probe the mechanism of force generation

“…2C), and "relaxation" is induced by the solution that adds 40 mM BDM to the relaxing solution and by lowering the temperature to 2°C. As it has been known for some time, active tension increases with temperature in mammalian muscles (Goldman et al 1987;Ranatunga et al 1987;Bershitsky and Tsaturyan 1992;Zhao and Kawai 1994a). Figure 2C demonstrates that the active tension is not sensitive to Ca 2+ , as expected.…”

Effects of inorganic phosphate on endothermic force generation in muscle

“…A rapid temperature jump induces a tension rise with a characteristic time-course in maximally calciumactivated muscle ¢bres and a component of it is considered to be endothermic force generation in attached crossbridges (Davis & Harrington 1987;Goldman et al 1987;Bershitsky & Tsaturyan 1992). Indeed, it has been known for nearly half a century that the active force in mammalian muscle is very temperature sensitive, increasing several-fold in warming from low (ca.…”