Table 2.
Force measurements in cardiomyocytes after exchange with recombinant cTnI
| Fmax | Fpas | pCa50 | nHill | ktr-max | |
|---|---|---|---|---|---|
| 1 mg/ml cTn | |||||
| cTnI-Wt | 20.6 ± 1.7 | 3.3 ± 0.5 | 5.54 ± 0.02 | 2.6 ± 0.2 | 0.59 ± 0.04 |
| cTnI-Wt (myc) | 20.0 ± 1.8 | 3.3 ± 0.4 | 5.51 ± 0.02 | 3.0 ± 0.1 | 0.63 ± 0.03 |
| cTnI-AA (myc) | 24.6 ± 1.5 | 3.2 ± 0.2 | 5.50 ± 0.01 | 3.2 ± 0.1 | 0.59 ± 0.03 |
| cTnI-AD (myc) | 23.3 ± 1.8 | 3.3 ± 0.3 | 5.48 ± 0.01 | 3.1 ± 0.1 | 0.50 ± 0.04 |
| cTnI-DA (myc) | 22.3 ± 1.4 | 3.2 ± 0.3 | 5.51 ± 0.01 | 3.3 ± 0.1 | 0.55 ± 0.02 |
| cTnI-DD (myc) | 20.9 ± 1.3 | 3.2 ± 0.4 | 5.39 ± 0.01*** | 3.6 ± 0.3 | 0.60 ± 0.06 |
| 2 mg/ml cTn | |||||
| cTnI-AA (myc) | 24.4 ± 1.0 | 2.6 ± 0.2 | 5.48 ± 0.01 | 3.3 ± 0.2 | 0.55 ± 0.02 |
| cTnI-AD (myc) | 22.7 ± 1.2 | 3.2 ± 0.2 | 5.47 ± 0.02 | 3.0 ± 0.1 | 0.52 ± 0.04 |
Values are means ± SE. Recombinant wild-type (Wt) cTn complexes with or without the myc tag were exchanged at 1 mg/ml in two donor samples (6–8 myocytes/group). No significant differences were found in the force parameters between cTn complexes with or without the myc tag label. Myc tag-labeled cTnI mutated at Ser23 and Ser24 into alanine or aspartic acid was exchanged at 1 mg/ml (13 myocytes/cTnI mutant) in three donor samples. The midpoint of the Ca2+ sensitivity of force development (pCa50) was significantly lower in cTnI-DD compared with cTnI-AA, cTnI-AD, or cTnI-DA. Myc tag-labeled cTn-AA and cTn-AD were exchanged at 2 mg/ml (11 myocytes/cTnI mutant) in three donor samples. No significant differences were found in the maximal rate of force development (ktr-max; in s−1) at saturating Ca2+ concentration (pCa 4.5) between cTn-AA and cTn-AD (as analyzed by a Student's t-test). Fmax, maximal force (in kN/m2); Fpas, passive force (in kN/m2); nHill, Hill coefficient (steepness of the force-pCa curve).
P < 0.0001 (by one-way ANOVA followed by a Bonferroni post hoc test).