Bagni M A, Cecchi G, Griffiths P J, Maéda Y, Rapp G, Ashley C C
Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze, Italy.
Biophys J. 1994 Nov;67(5):1965-75. doi: 10.1016/S0006-3495(94)80679-4.
The myosin lattice spacing of single intact muscle fibers of the frog, Rana temporaria, was studied in Ringer's solution (standard osmolarity 230 mOsm) and hyper- and hypotonic salines (1.4 and 0.8 times standard osmolarity respectively) in the relaxed state, during "fixed end" tetani, and during shortening, using synchrotron radiation. At standard tonicity, a tetanus was associated with an initial brief lattice expansion (and a small amount of sarcomere shortening), followed by a slow compression (unaccompanied by sarcomere length changes). In hypertonic saline (myosin lattice compressed by 8.1%), these spacing changes were suppressed, in hypotonic saline (lattice spacing increased by 7.5%), they were enhanced. During unloaded shortening of activated fibers, a rapid lattice expansion occurred at all tonicities, but became larger as tonicity was reduced. This expansion was caused in part by the change in length of the preparation, but also by a recoil of a stressed radial compliance associated with axial force. The lattice spacing during unloaded shortening was equal to or occasionally greater than predicted for a relaxed fiber at that sarcomere length, indicating that the lattice compression associated with activation is rapidly reversed upon loss of axial force. Lattice recompression occurred upon termination of shortening under standard and hypotonic conditions, but was almost absent under hypertonic conditions. These observations indicate that axial cross-bridge tension is associated with a compressive radial force in intact muscle fibers at full overlap; however, this radial force exhibits a much greater sensitivity to lattice spacing than does the axial force.
利用同步辐射，研究了林格氏液（标准渗透压230 mOsm）、高渗和低渗盐水（分别为标准渗透压的1.4倍和0.8倍）中处于松弛状态、“固定端”强直收缩期间以及缩短过程中，青蛙（欧洲林蛙）单个完整肌纤维的肌球蛋白晶格间距。在标准张力下，强直收缩初期晶格会短暂扩张（同时伴有少量肌节缩短），随后缓慢压缩（肌节长度无变化）。在高渗盐水中（肌球蛋白晶格压缩8.1%），这些间距变化受到抑制；在低渗盐水中（晶格间距增加7.5%），变化增强。在激活纤维的无负荷缩短过程中，所有张力下晶格都会迅速扩张，且随着张力降低扩张幅度增大。这种扩张部分是由标本长度变化引起的，也与轴向力相关的受压径向顺应性回弹有关。无负荷缩短期间的晶格间距等于或偶尔大于该肌节长度下松弛纤维的预测值，这表明与激活相关的晶格压缩在轴向力消失后会迅速逆转。在标准和低渗条件下，缩短终止时晶格会重新压缩，但在高渗条件下几乎不存在这种情况。这些观察结果表明，在完全重叠时，轴向横桥张力与完整肌纤维中的压缩径向力相关；然而，这种径向力对晶格间距的敏感性远高于轴向力。
