Laidlaw D H, Callister R J, Stuart D G
Department of Biomedical Engineering/W63, Cleveland Clinic Foundation, Ohio 44195, USA.
J Morphol. 1995 Aug;225(2):193-211. doi: 10.1002/jmor.1052250205.
A description is provided of the fiber-type composition of several hindlimb muscles of the adult turtle, Pseudemys (Trachemys) scripta elegans. In addition, cross-section areas of each fiber type and an estimation of the relative (weighted) cross-section area (wCSA) occupied by the different fiber types are also provided. Seven muscles were selected for study, based on their suitability for future neurophysiological analysis as components of the segmental motor system, and on their homologies with muscles in other vertebrates. The test muscles were iliofibularis (ILF), ambiens (AMB), external gastrocnemius (EG), extensor digitorum communis (EDC), flexor digitorum longus (FDL), tibialis anterior (TA), and peroneus anterior (PA). Serial sections of these muscles were stained for myosin adenosine triphosphatase (ATPase), NADH-diaphorase, and alpha-glycerophosphate dehydrogenase (alpha-GPDH), thereby enabling fiber-type classification on the basis of indirect markers for contraction speed and oxidative (aerobic) vs. glycolytic (anaerobic) metabolism. All muscles contained three fiber types: slow oxidative (SO; possibly including some non-twitch tonic fibers); fast oxidative glycolytic (FOG); and fast glycolytic (Fg). There were at least 30% FOG and 50% FOG + Fg fibers in the seven muscles, the extreme distributions being the predominantly glycolytic ILF vs. the predominantly oxidative FDL muscle (ILF--15.5% SO, 35.2% FOG, 49.3% Fg vs. FDL--49.1% SO, 41.1% FOG, 9.8% Fg). As in other species, the test muscles exhibited varying degrees of regional concentration (compartmentalization) of the different fiber types. This feature was most striking in ILF. Pronounced compartmentalization was also observed in AMB, EG, PA, TA, and EDC, whereas the distribution of fiber types in the highly oxidative FDL was homogeneous. In five of the seven muscles, fiber size was ranked with Fg > FOG > SO. In terms of wCSA, which provides a coarse-grain measure of the different fiber types' potential contribution to whole muscle peak force, all muscles exhibited a higher Fg and lower SO contribution to cross-section area than suggested by their corresponding fiber-type composition. The largest relative increase in wCSA vs. fiber-type composition were in the ILF and AMB muscles. We conclude that the turtle hindlimb provides some interesting possibilities for testing for a division of labor among different muscles during different movements (e.g., sustained vs. ballistic), and for study of the behavior of the different fiber (and motor unit) types under normal and perturbed conditions. The relationships between the present results and previous findings on homologous muscles of the mammalian (cat, rat) and reptilian (lizard) hindlimb are discussed.
本文描述了成年红耳龟（滑龟）后肢几块肌肉的纤维类型组成。此外，还给出了每种纤维类型的横截面积，以及不同纤维类型所占相对（加权）横截面积（wCSA）的估计值。基于它们作为节段性运动系统组成部分对未来神经生理学分析的适用性，以及与其他脊椎动物肌肉的同源性，选择了七块肌肉进行研究。受试肌肉包括髂腓肌（ILF）、股直肌（AMB）、腓肠外侧肌（EG）、趾长伸肌（EDC）、趾长屈肌（FDL）、胫骨前肌（TA）和腓骨前肌（PA）。对这些肌肉的连续切片进行肌球蛋白三磷酸腺苷酶（ATPase）、NADH - 黄递酶和α - 甘油磷酸脱氢酶（α - GPDH）染色，从而能够根据收缩速度以及氧化（有氧）与糖酵解（无氧）代谢的间接标记物对纤维类型进行分类。所有肌肉都包含三种纤维类型：慢氧化型（SO；可能包括一些非抽搐性紧张性纤维）；快氧化糖酵解型（FOG）；以及快糖酵解型（Fg）。这七块肌肉中至少有30%的FOG纤维和50%的FOG + Fg纤维，极端分布情况是主要为糖酵解型的ILF肌肉与主要为氧化型的FDL肌肉（ILF——15.5% SO，35.2% FOG，49.3% Fg；FDL——49.1% SO，41.1% FOG，9.8% Fg）。与其他物种一样，受试肌肉中不同纤维类型呈现出不同程度的区域集中（分区化）。这一特征在ILF肌肉中最为显著。在AMB、EG、PA、TA和EDC肌肉中也观察到明显的分区化，而高度氧化的FDL肌肉中纤维类型的分布是均匀的。在七块肌肉中的五块中，纤维大小排序为Fg > FOG > SO。就wCSA而言，它提供了不同纤维类型对全肌峰值力潜在贡献的粗略衡量指标，所有肌肉中Fg对横截面积的贡献高于SO，且高于其相应纤维类型组成所表明的情况。wCSA相对于纤维类型组成的最大相对增加出现在ILF和AMB肌肉中。我们得出结论，龟的后肢为测试不同运动（例如持续运动与爆发性运动）过程中不同肌肉之间的分工，以及研究正常和受干扰条件下不同纤维（和运动单位）类型的行为提供了一些有趣的可能性。本文还讨论了当前结果与先前关于哺乳动物（猫、大鼠）和爬行动物（蜥蜴）后肢同源肌肉研究结果之间的关系。
