Table 2.
Average impact of temperature on cross-bridge dynamics parameters
| Parameter | 15°C | 20°C | 25°C | ΔA | Q10 |
|---|---|---|---|---|---|
| Tmax (mN·mm−2) | 29.1 ± 2.3 | 37.2 ± 3.1 | 40.2 ± 3.6 | 22.8 ± 2.4 | 1.4 ± 0.1 |
| Hill coefficient | 5.4 ± 0.7 | 5.5 ± 0.4 | 5.7 ± 0.5 | 4.8 ± 1.9 | 1.0 ± 0.1 |
| EC50 (μm) | 5.2 ± 0.4 | 3.8 ± 0.2 | 2.7 ± 0.1 | −55.1 ± 2.3 | 0.5 ± 0.1 |
| Amax (pmol s−1 mm−3) | 207 ± 19 | 408 ± 33 | 772 ± 70 | 87.5 ± 2.3 | 3.4 ± 0.1 |
| Tension cost (pmol s−1 mm−3) | 6.3 ± 0.6 | 9.9 ± 1.0 | 17.8 ± 1.4 | 65.7 ± 4.1 | 2.5 ± 0.1 |
| ktr−max (s−1) | 14.5 ± 0.5 | 31.4 ± 1.0 | 49.4 ± 2.2 | 85.3 ± 3.8 | 3.3 ± 0.2 |
| ktr−min (s−1) | 5.4 ± 0.5 | 9.5 ± 1.0 | 14.4 ± 1.4 | 56.8 ± 5.0 | 2.4 ± 0.1 |
| ATPase–5% tension (pmol·s−1·mm−3) | 10.0 ± 0.9 | 20.4 ± 1.7 | 36.9 ± 3.4 | 84.4 ± 3.1 | 3.3 ± 0.1 |
Tension–[Ca2+] relationships were fitted to a modified Hill equation that yielded the parameters (mean ±s.e.m.; n= 8): maximum, Ca2+ saturated tension development (Tmax), Hill coefficient, and calcium sensitivity (EC50). The maximum rates of Ca2+-activated ATP hydrolysis (Amax) and ktr−max were measured at saturating Ca2+ concentration. Tension cost was calculated from the slope of the ATPase–tension relationship obtained over a wide range of activator [Ca2+]. Rate of tension redevelopment (ktr) was estimated from a single mono-exponential fit of the tension data following a rapid release–restretch manoeuvre. ATPase–5% tension and ktr−min were estimated from their relationships as a function of Ca2+-activated tension at each temperature. Temperature dependence is indicated as the activation energy (ΔA in kJ mol−1 K−1) obtained by non-linear regression of the Arrhenius plot and as Q10 (the relative increase with a 10°C temperature increase) between 15°C and 25°C. All parameters varied significantly with temperature (P < 0.05), except the Hill coefficient.