Table 2.
%α MHC | Activation level (P/P0) | kdf (s−1) | a | k1 (s−1) | b | k2 (s−1) |
---|---|---|---|---|---|---|
0 | 1.00 | 14.7 ± 1.0 | 1.00 | 15.5 ± 1.2 | — | — |
59 ± 6 | 1.00 | 25.3 ± 2.7* | 1.00 | 26.7 ± 2.9* | — | — |
100 | 1.00 | 35.4 ± 2.0** | 1.00 | 34.7 ± 2.0** | — | — |
0 | 0.53 ± 0.03 | 9.1 ± 0.8 | 0.85 ± 0.04 | 11.3 ± 0.7 | 0.15 ± 0.02 | 1.4 ± 0.3 |
59 ± 6 | 0.49 ± 0.05 | 15.5 ± 2.0* | 0.79 ± 0.06 | 16.8 ± 1.5* | 0.21 ± 0.04 | 2.2 ± 0.4* |
100 | 0.48 ± 0.02 | 23.4 ± 1.7** | 0.82 ± 0.03 | 26.9 ± 1.5** | 0.18 ± 0.02 | 3.2 ± 0.5** |
0 | 0.27 ± 0.02 | 5.1 ± 0.5 | 0.68 ± 0.03 | 8.7 ± 0.7 | 0.32 ± 0.03 | 1.0 ± 0.2 |
59 ± 6 | 0.22 ± 0.04 | 9.5 ± 0.9* | 0.63 ± 0.05 | 11.8 ± 0.9* | 0.37 ± 0.04 | 1.5 ± 0.2* |
100 | 0.23 ± 0.02 | 15.4 ± 1.5** | 0.66 ± 0.03 | 19.9 ± 1.3** | 0.34 ± 0.02 | 2.3 ± 0.4** |
Rate and amplitude data were obtained from force transients in response to stretches of 1% of muscle length at each of the indicated levels of activation (adjusted by varying free [Ca2+]). Data in each case are reported as means ±s.e.m. from 10 thyroidectomized and hyperthyroid preparations and seven euthyroid preparations. As described in the Methods, the apparent rate constants for delayed force recovery were obtained by fitting each record with a double exponential equation: y=a exp(−k1×x) +b exp(−k2×x), where a is the amplitude of the first exponential phase with rate constant k1 and b is the amplitude of the second exponential phase with rate constant k2.
Significantly different from thyroidectomized (P < 0.05)
significantly different from thyroidectomized and euthyroid (P < 0.05).