Table 1.

Maximum isometric force generation (F_max) and parameters sensitive to cross-bridge cycling kinetics as well as stiffness and y₀-values of soleus muscle fibers with myosin mutations and control fibers measured in rigor and during isometric contraction

	Mut R719W norm.	Mut R723G norm.		Mut I736T norm.		Controls norm.	Controls abs. values		Units for abs. values
		H27	H28	H19	H20		20°C	10°C
Fmax	1.43∗ ± 0.02 (14)	1.19∗ ± 0.01 (7)	1.22∗ ± 0.01 (14)	0.97 ± 0.02 (7)	1.01 ± 0.01 (20)	1.00 ± 0.01 (45)	140.86 ± 1.25 (45)	108.94 ± 5.31 (36)	kN/m2 or kPa
kredev	1.00 ± 0.05 (14)	1.11 ± 0.04 (7)	1.09 ± 0.06 (14)	0.91 ± 0.04 (7)	0.97 ± 0.03 (20)	1.00 ± 0.04 (45)	2.69 ± 0.06 (45)	0.27 ± 0.02 (36)	s−1
Fiber-ATPase	1.21∗ ± 0.02 (14)	0.97 ± 0.04 (6)	0.98 ± 0.02 (12)	0.97 ± 0.05 (6)	1.03 ± 0.03 (11)	1.00 ± 0.03 (21)	0.95§ ± 0.02 (21)	n.d.	$\frac{\text{ATP}}{\text{S}1\times \text{s}}$
vmax	1.10 ± 0.11 (6)	1.07 ± 0.04 (8)	1.17∗ ± 0.04 (9)	0.95 ± 0.04 (11)	1.00 ± 0.03 (10)	1.00 ± 0.03 (7)	3246.00 ± 86.79 (7)	329.90 ± 8.61 (10)	(nm/HS)s−1
Fiber stiffness in rigor at 5°C†	see Table 2	1.43∗ ± 0.21 (5)	1.59∗ ± 0.15 (6)	1.09 ± 0.09 (7)	1.15 ± 0.14 (10)	1.00 ± 0.15 (6)	n.d.	17.7 ± 2.7 (6)	$\frac{\text{kN}\times \text{HS}}{{\text{m}}^2\times \text{nm}}$ or kPa × HS/nm
Active fiber stiffness†	see Table 2	1.32∗ ± 0.10 (10)	1.43∗ ± 0.19 (6)	0.90 ± 0.04 (7)	0.97 ± 0.08 (11)	1.00 ± 0.13 (9)	n.d.	13.2 ± 1.7 (9)	$\frac{\text{kN}\times \text{HS}}{{\text{m}}^2\times \text{nm}}$ or kPa × HS/nm
		abs. values			abs. values
y0 (nm/HS)‡ at 10°C	see Table 2	7.70 ± 0.74 (9)	n.d.	n.d.	7.76 ± 0.44 (7)		n.d.	8.53 ± 0.42 (6)

abs., absolute; HS, half-sarcomere; n.d., not determined; norm., normalized.

Isometric force at 10°C of fibers with mutation R723G (H27) and I736T (H20) was 1.23 ± 0.05 (n = 9) times and 0.91 ± 0.08 (n = 11) times the force of control fibers, respectively. Values in parentheses indicate number of fibers studied, data are mean values ± SE. All values are normalized to control fibers that were measured in the same time period. All normalized values of F_max, k_redev, fiber-ATPase, and v_max shown here were measured at 20°C, rigor stiffness was measured at 5°C, active stiffness and y₀ were determined at 10°C.

^∗Significant changes compared to controls.

^†Fiber stiffness in rigor and isometric contraction measured at fastest speed of length change (∼3–5 × 10³ (nm/half-sarcomere)s⁻¹ for rigor and 2–5 × 10³ (nm/half-sarcomere)s⁻¹ for active stiffness).

^‡y₀ and active stiffness of the control fibers were measured on a different set of fibers with F_max = 112.95 ± 0.11 kPa.

^§ATPase activity was calculated based on ADP generated, fiber volume and an S1-content of 154 pmol S1/μL fiber volume (50).