Table 2.

Parameter estimates of muscle fibre contractile function

	Fibres from normal mice (α-MHC)		Fibres from PTU-treated mice (β-MHC)
	α-MHC(cTnI)	α-MHC(ssTnI)	β-MHC(cTnI)	β-MHC(ssTnI)
Max Tens	43.8 ± 1.53	48.0 ± 0.76a	52.8 ± 2.37a	47.7 ± 1.56
Max ATPase	320 ± 18.6	359 ± 24.2	146 ± 5.19a	169 ± 7.73b,c
E∞	595 ± 26.8	651 ± 19.1	749 ± 32.4a	705 ± 27.4
E0/E∞	0.32 ± 0.02	0.33 ± 0.01	0.27 ± 0.01a	0.30 ± 0.01
pCa50	5.78 ± 0.01	6.11 ± 0.01a	5.85 ± 0.01a	5.90 ± 0.01b,c
nH	2.16 ± 0.09	1.80 ± 0.04a	2.46 ± 0.06a	2.62 ± 0.05c

Maximal tension production (mN mm⁻²) and rate of ATPase activity (pmol mm⁻³ s⁻¹) were measured from α-MHC and β-MHC NTG and ssTnI TG mice. E_∞ (mN mm⁻³) is the stiffness approximated at infinite frequency of chirp perturbation, and correlates with maximal tension production. E₀/E_∞ (unitless) is an approximation of the magnitude of length-mediated XB recruitment as a fraction of the number of strongly bound XB prior to perturbation. Hill's equation was fitted to pCa–tension relationships (Fig. 7) to determine parameters for myofilament Ca²⁺ sensitivity, pCa₅₀, and cooperativity, n_H. Values are means ± SEM. Number of determinants is at least 10 for each group. ^aP < 0.05 vs. α-MHC(cTnI); ^bP < 0.05 vs. β-MHC(cTnI); ^cP < 0.05 vs. α-MHC(ssTnI).