Table II.
Mean Cross-sectional Areas of Muscle Fiber Types in Wild-Type and MyHC-IId Null Mice
| MyHC | Tibialis anterior | Psoas | Diaphragm | Masseter | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| w.t. | IId−/− | w.t. | IId−/− | w.t. | IId−/− | w.t. | IId−/− | |||||||||
| μm2 | μm2 | μm2 | μm2 | |||||||||||||
| IIA | 533 ± 124 | 945 ± 178* | 634 ± 120 | 906 ± 342* ‡ | 781 ± 157 | 788 ± 205 | ND | 728 ± 120‡ | ||||||||
| IIB red | 1447 ± 303 | 2606 ± 707* | 1580 ± 284 | 571 ± 200* | — | — | 1249 ± 267 | — | ||||||||
| IIB white | 1264 ± 240 | 1206 ± 265 | 1329 ± 239 | 1622 ± 370* | — | — | — | — | ||||||||
| IID | 744 ± 143 | — | 926 ± 170 | — | 1166 ± 266 | — | 742 ± 164 | — | ||||||||
| I | — | — | — | — | 730 ± 157 | 750 ± 183 | — | — | ||||||||
Cross-sectional areas were measured in muscles from wild-type (w.t.) and MyHC-IId null (IId−/−) mice (8-wk-old males). Average deviations from the mean are given. Sample sizes were as follows: w.t. TA, IIA = 111, IID = 170, IIB red = 229, IIB white = 112; IId−/− TA, IIA = 138, IIB red = 89, IIB white = 61; w.t. psoas, IIA = 92, IID = 100, IIB red = 102, IIB white = 66; IId−/− psoas, IIA = 227, IIB red = 65, IIB white = 70; w.t. diaphragm, IIA = 156, IID = 117, I = 65; IId−/− diaphragm, IIA = 233; I = 63; w.t. masseter, IIB = 50, IID = 66; IId−/− masseter, IIA = 45. Fiber areas were not determined (ND) for type IIA fibers in wild-type masseter.
P < 0.001 for the same fiber type in IId null mice compared to wild type.
No significant difference found between wild-type IID and IId null-type IIA fiber sizes.