Sarcomere length-dependent Ca2+ activation in skinned rabbit psoas muscle fibers: coordinated regulation of thin filament cooperative activation and passive force

Table 2 Summary of the values of passive force, maximal active force, pCa₅₀ and Hill coefficient (n _H) in rabbit psoas muscle fibers under various conditions (see Supplementary Fig. 1)

	SL (μm)	Passive force (mN/mm²)	Maximal force (mN/mm²)	pCa₅₀	∆pCa₅₀	n _H
Control	2.0	~0	168.50 ± 7.74	5.86 ± 0.01		4.12 ± 0.12
Control	2.4	3.58 ± 0.49	191.83 ± 8.98	6.00 ± 0.01	0.15 ± 0.01	3.31 ± 0.16
+cTn	2.0	~0	145.24 ± 5.58*^,# (173.66 ± 8.49)	5.64 ± 0.04^#		3.02 ± 0.30^#
+cTn	2.4	3.19 ± 0.91	186.12 ± 7.63	5.86 ± 0.04^#	0.22 ± 0.02^#	2.19 ± 0.10^#
+sTn	2.0	~0	171.04 ± 6.44 (178.06 ± 7.59)	5.88 ± 0.01		3.94 ± 0.16
+sTn	2.4	3.78 ± 0.15	192.40 ± 7.50	6.03 ± 0.01	0.15 ± 0.01	3.41 ± 0.18

Values in the control group are the same as in those in Table 1. Maximal force was obtained by activating muscle at pCa 4.5 prior to construction of the force–pCa curve at each SL (passive force was measured just prior to activation at pCa 4.5). Numbers in parentheses indicate maximal force values obtained prior to cTn or sTn treatment (* P < 0.05 compared with the prior value). Upon SL elongation from 2.0 to 2.4 μm, maximal force was significantly (P < 0.05) increased in both cTn and sTn groups, due presumably to a change in the filament overlap (e.g., [5, 9])
^# P < 0.05 compared with the corresponding values in the control group

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