TABLE 3.
The parameters of force production and Pi release
Summary of results from length change experiments in the presence and absence of a creatine phosphate-creatine phosphokinase ATP regenerating system. Data was analysed using the two-way analysis of variance, general linear model (Systat, Software Inc., San Jose, CA).
| Without ATP regenerating system |
With ATP regenerating system |
|||
|---|---|---|---|---|
| 32 μm Ca2+ | 1 μm Ca2+ | 32 μm Ca2+ | 1 μm Ca2+ | |
| n | 5 | 5 | 10 | 5 |
| Isometric force (kN m−2) | 49.8 ± 6.4 | 24.7 ± 4.7a | 54.0 ± 6.1 | 36.0 ± 8.4a |
| t½ (ms) | 58.2 ± 2.1 | 77.5 ± 11.7 | 65.3 ± 8.3 | 86.6 ± 12.5 |
| Stiffness (kN m−2 μm−1) | 490 ± 143 | 460 ± 162 | 325 ± 89 | 324 ± 93 |
| Peak force at end of stretch (kN m−2) | 84.3 ± 15.7 | 61.6 ± 12.9 | 80.0 ± 7.3 | 61.9 ± 15.2 |
| Force enhancement after stretch (kN m−2) | 71.7 ± 14.0 | 49.1 ± 6.7 | 69.4 ± 6.1 | 57.1 ± 11.9 |
| Force at end of release (kN m−2) | 10.9 ± 1.7 | 6.1 ± 2.4 | 14.5 ± 2.4 | 7.7 ± 2.5b |
| Isometric force after release (kN m−2) | 36.3 ± 3.0 | 16.0 ± 4.8a | 38.7 ± 3.9 | 27.2 ± 5.9b |
| t½, force redevelopment (ms) | 86.1 ± 9.5 | 127.3 ± 10.8 | 83.8 ± 9.2 | 80.2 ± 15.8c |
| ATPase rate (s−1) | ||||
| n | 5 | 5 | 4 | 3 |
| Initial (first turnover) | 15.2 ± 1.3 | 14.4 ± 1.1 | 14.7 ± 1.4 | 14.8 ± 1.4 |
| Steady state (isometric) | 8.23 ± 0.5 | 4.8 ± 0.9b | 7.5 ± 0.4 | 5.5 ± 0.4b |
| During stretch | 1.0 ± 0.9 | 1.5 ± 0.9 | 1.4 ± 1.2 | 0.3 ± 0.6 |
| After stretch | 4.7 ± 0.3 | 4.4 ± 0.5 | 4.5 ± 0.17 | 4.4 ± 0.5 |
| During release | 10.9 ± 1.5 | 7.8 ± 1.1 | 7.6 ± 0.8d | 11.0 ± 0.6d |
| End isometric | 7.8 ± 1.3 | 3.7 ± 1.1b | 6.8 ± 1.0 | 4.8 ± 0.8b |
a p < 0.01 difference between submaximal and maximal activation.
b p < 0.05 difference between submaximal and maximal activation.
c p < 0.05 difference with and without ATP regenerating system.
d Identifies a significant (p = 0.027) interaction effect of the two main factors (calcium level and ATP regeneration) on Pi release rate during the cross-bridge release phase, but there is not a clear mechanistic explanation for this minor interaction effect.