Table 2.

Apparent affinity for Ca²⁺ increases more with temperature in cardiac skinned fibres reconstituted with HcTnC D145E.

	pCa50	∆pCa50 (relative to 20–21 °C)	n Hill
WT
21 °C	5.66 ± 0.01	—	2.74 ± 0.19
15 °C	5.39 ± 0.01	−0.27	4.94 ± 0.36
25 °C	5.80 ± 0.03	0.14	2.07 ± 0.08
30°C	5.96 ± 0.04	0.30	1.65 ± 0.06
D145E
21°C	5.90 ± 0.01	—	2.73 ± 0.17
15°C	5.51 ± 0.04	−0.39	2.44 ± 0.12
25°C	6.13 ± 0.06	0.23	1.56 ± 0.08
30°C	6.42 ± 0.02	0.52	1.32 ± 0.05

The Ca²⁺ sensitivity of isometric force was measured at 15°, 25° and 30° on each fibre, after extraction of endogenous cTnC and reconstitution with recombinant HcTnC, as described in Methods. pCa₅₀ and n_Hill are from the experiments of Fig. 7a–c (n = 4–5) or (at 20–21 °C) from Landstrom et al.⁸ (n = 8). Data reported at 20–21 °C were not tested against the others. Errors are ± s.e.m.

For each protein, pCa₅₀ values at 15 °C, 25 °C and 30 °C are significantly different from each other (p ≤ 0.022). Paired t-test was used.

pCa₅₀ values at the same temperature (15 °C, 25 °C or 30 °C) are significantly different for the two proteins (p ≤ 0.01). Unpaired t-test was used.

In the last column, n _Hill values for D145E are significantly different from WT (p ≤ 0.005) at the same temperature (15 °C, 25 °C or 30 °C). Unpaired t-test was used.

In the last column, n _Hill values within each group (WT or D145E) are statistically different from each other (p ≤ 0.028). Paired t-test was used.