Table 4.

Measurements in skinned fibers

	NTG	NTG/PKA	β-TG	β-TG/PKA	WT:(t/t)/β	WT:(t/t)/β/PKA	AllP+:(t/t)/β	AllP+:(t/t)/β/PKA
pCa50	5.87±0.01	5.70±0.01a	5.87±0.01	5.70±0.01a	5.85±0.02	5.69±0.01a	5.88±0.01	5.69±0.01a
Hill coefficient	4.48±0.16	4.68±0.61	4.35±0.22	5.31±0.57	6.31±0.55	5.30±0.58	4.92±0.26	5.78±0.44
Maximum absolute force (μN/length)	10.16±0.23	9.59±0.29	9.46±0.32	9.04±0.36	9.42±0.24	9.01±0.11	9.71±0.19	9.33±0.12
Unloaded-shortening velocity (m.l./s)	4.24±0.09	5.67±0.27a	3.05±0.06b	4.15±0.15a,d	3.07±0.14b	4.11±0.18a,d	4.08±0.16c	4.47±0.12d
Maximum shortening velocity (m.l./s)	3.15± 0.08	4.33±0.10a	2.48±0.12b	3.4±0.23a d	2.26±0.12b	3.45±0.13a,d	3.13±0.16c	3.6±0.24d
Maximum power output (m.l./s)	0.59±0.02	0.85±0.04a	0.45±0.03b	0.67±0.02a,d	0.41±0.04b	0.64±0.02a,d	0.61±0.05c	0.67±0.02d

Contractile properties of fibers isolated from the papillary muscles of 12 week old mice.¹⁴ The unloaded shortening and maximum shortening velocities and relative power that the fibers developed were measured. To determine the effects of PKA phosphorylation on the pCa-force relationship in vitro, skinned fibers were treated with PKA after measurements of the pCa-force relationship under standard conditions. All values are expressed as mean±SE (n=6). Statistical significance was determined using the paired t-test (n=5).

^aP<0.05 versus respective untreated PKA controls

^bP<0.05 versus NTG

^cP<0.05 versus WT:(t/t)/β

^dP<0.05 versus NTG/PKA