Table 1.

SL-dependent changes in passive force, maximum Ca²⁺-activated force, pCa₅₀, n_H, and maximum rate of force redevelopment in Wt and Ho rat skinned myocardium

SL, μm	Resting Force, mN/mm2	Maximum Ca2+-Activated Force, mN/mm2	Hill Coefficient (nH)	Ca2+ Sensitivity of Force (pCa50)	Maximum Rate of Force Redevelopment (ktr, s−1)
WT (n = 13)
2.00	1.95 ± 0.25	25.99 ± 2.76	3.12 ± 0.08	5.69 ± 0.02	17.09 ± 0.97
2.35	22.64 ± 2.74*	35.23 ± 3.20*	2.71 ± 0.04*	5.81 ± 0.02*	14.96 ± 1.17*
Ho (n = 11)
2.00	1.23 ± 0.11†	16.51 ± 1.25†	2.89 ± 0.10	5.67 ± 0.01	9.28 ± 0.79†
2.35	3.68 ± 0.28*†	22.36 ± 1.70*†	2.75 ± 0.07*	5.72 ± 0.01*†	8.05 ± 0.59*†

All valuses are expressed as means ± SE, with the number of skinned trabeculae given in parentheses. Resting force was measured at pCa 9.0. Maximum force and the rate constant of force redevelopment (k_tr) were measured at pCa 4.5. pCa₅₀ and n_H values were derived by fitting the force-pCa relationships to a Hill equation. WT, wild type; Ho, homozygote.

^*Significantly different from values recorded at sarcomere length (SL) = 2.0 μm.

^†Significantly different from values recorded in WT at similar SL.