TABLE 1.
Mechanical data and contractile protein expression.
| Normal breast | Woody breast | P | |
| Optimal L/Ls | 1.34 ± 0.05(8) | 1.34 ± 0.03(8) | n.s. |
| Optimal sarcomere length, μm | 2.68 ± 0.04(5) | 2.65 ± 0.05(6) | n.s. |
| Fiber diameter, μm | 73.0 ± 1.3(8) | 88.0 ± 2.5(8) | *** |
| Maximal active tension, mN | 0.50 ± 0.08(8) | 0.73 ± 0.08(8) | n.s. |
| Maximal active stress, mN mm–2 | 116 ± 17(8) | 125 ± 19(8) | n.s. |
| Vmax, ML s–1 | 1.51 ± 0.08(4) | 1.68 ± 0.16(5) | n.s. |
| Stiffness, ML (Pa/Po)–1 | 0.036 ± 0.003(6) | 0.043 ± 0.004(6) | n.s. |
| kTR, s–1 | 19 ± 2(6) | 10 ± 1(5) | ** |
| EC50, pCa units | 5.81 ± 0.02(6) | 5.71 ± 0.03(6) | * |
| MHC, μg mg–1 wet weight | 11.0 ± 1.4(5) | 12.6 ± 1.4(6) | n.s. |
| Actin, μg mg–1 wet weight | 9.0 ± 1.3(5) | 8.8 ± 1.1(6) | n.s. |
| MHC/actin, molar ratio | 0.27 ± 0.01(5) | 0.31 ± 0.01(6) | * |
Fiber diameter, sarcomere length and active force were determined at optimal stretch (relative to slack length, L/Ls) for active force. The maximal shortening velocity (Vmax) is given in muscle length/s (ML s–1). The series elastic stiffness is given as in muscle length/relative force [ML (Pa/Po)-1] where Pa and Po are afterload and isometric force, respectively. The rate of tension development (kTR) is given in s–1. The Ca2+ concentration where half of maximal force was developed (EC50) is given in pCa units. Number of animals is given in parenthesis. Myosin heavy chain (MHC) and actin were determined using quantitative SDS-PAGE. For fiber diameter: 6–7 fibers were analyzed per animal; for optimal lengths, maximal tension and stress: 2–3 fibers per animal; for Vmax and stiffness 1 fiber per animal; for MHC and actin: a sample containing several fibers per animal, loaded in different concentrations on the same gel; for kTR, 2 fibers per animal; for EC50, 2 fiber bundles per animal. *P < 0.05, **P < 0.01, ***P < 0.001, n.s., non-significant (Student’s t-test).