The Discipline of Physiology and the Bosch Institute, School of Medical Sciences, The University of Sydney, Sydney, New South Wales, Australia.
Invest Ophthalmol Vis Sci. 2018 Mar 1;59(3):1178-1190. doi: 10.1167/iovs.17-23102.
Extraocular muscles express 10 myosin heavy chain (MyHC) isoforms that cater for a wide range of contractile speeds. We aim to characterize the variations in MyHC expression along the length of singly (SIFs) and multiply innervated fibers (MIFs) in the orbital layer of rabbit superior rectus muscle.
Monospecific antibodies to nine MyHCs, including an anti-slow-tonic antibody characterized here were used to immunohistochemically map variations in MyHC distribution in serial sections along the muscle's full length.
The fastest MyHC, EO, is expressed at the endplate zone (EPZ) of SIFs, flanked proximally and distally by segments expressing the slower 2A, with or without embryonic MyHC. MIFs with constant diameter express α-cardiac MyHC at the EPZ, flanked by segments co-expressing α-cardiac/embryonic and possibly slow-tonic MyHCs. MIFs with varying diameter also express α-cardiac MyHC at the EPZ in their thin, central region, flanked by thin segments co-expressing α-cardiac/embryonic MyHCs, with long proximal and distal extensions of larger diameter that co-express embryonic/slow-tonic and α-cardiac or β/slow MyHCs.
Orbital fiber types express multiple MyHCs, with faster ones in SIFs, slower ones in MIFs, but all have fast EPZs and slower end segments. We hypothesize that these unique MyHC distributions enable these fibers to relax in two kinetically distinct phases while acting in an antagonistic manner during a saccade: the fast phases facilitate acceleration of eyeball rotation during agonist contraction, while the slow phases help its deceleration toward the visual target, thereby linearizing the saccade. These properties also facilitate pulley movements to implement Listing's law.
眼外肌表达 10 种肌球蛋白重链（MyHC）同工型，以适应广泛的收缩速度。我们旨在描述兔眼外直肌眶层中单根（SIFs）和多根神经支配纤维（MIFs）中 MyHC 表达的变化。
使用针对 9 种 MyHC 的单特异性抗体，包括这里描述的抗慢缩抗体，对沿肌肉全长的连续切片进行免疫组织化学定位，以描绘 MyHC 分布的变化。
最快的 MyHC，EO，表达在 SIFs 的终板区（EPZ），近端和远端两侧为表达较慢的 2A 段，伴有或不伴有胚胎 MyHC。直径恒定的 MIF 在 EPZ 表达α-心脏 MyHC，两侧为α-心脏/胚胎和可能的慢缩肌 MyHC 共表达段。直径变化的 MIF 也在其薄的中央区域的 EPZ 表达α-心脏 MyHC，两侧为薄的共表达α-心脏/胚胎 MyHC 段，近端和远端有较大直径的长延伸段，共表达胚胎/慢缩和α-心脏或β/慢 MyHC。
眶内纤维类型表达多种 MyHC，SIFs 中的更快，MIFs 中的更慢，但都有快速的 EPZ 和较慢的末端段。我们假设这些独特的 MyHC 分布使这些纤维能够在两种动力学上不同的阶段放松，同时在扫视时以拮抗的方式作用：快速阶段有助于在激动剂收缩期间加速眼球旋转，而缓慢阶段有助于其减速朝向视觉目标，从而使扫视线性化。这些特性还便于滑轮运动来实现 Listing 定律。
