Danieli-Betto D, Betto R, Midrio M
Istituto di Fisiologia Umana, Università di Padova, Padua, Italy.
Pflugers Arch. 1990 Nov;417(3):303-8. doi: 10.1007/BF00370996.
We investigated the calcium sensitivity for tension generation of different fibre types and the possible correlation between calcium sensitivity and the presence of distinct regulatory protein and myosin light chain (MLC) isoforms in rat skinned skeletal muscle fibres. Fibre types 1, 2A and 2B were identified by electrophoretic analysis of myosin heavy chain (MHC) isoforms. Fibres showing more than one MHC isoform were discarded. Type 1 fibres from the soleus showed a higher pCa (-log10 [Ca], where [ ] denotes concentration) threshold and a lower slope of pCa/tension curve than type 2 extensor digitorum longus (EDL) fibres; between type 2 fibres, type 2B showed the higher slope of pCa/tension curve. Type 1 fibres from different muscles showed similar calcium sensitivities when containing only the slow set of regulatory proteins and MLC; when both slow and fast isoforms were present, calcium sensitivity shifted toward fast type fibre values. Type 2A fibres from different muscles showed a similar calcium sensitivity, independently of the set (purely fast or mixed) of regulatory proteins and MLC. It is suggested that when both fast and slow isoforms of regulatory proteins and of MLC are present in a muscle fibre, calcium sensitivity is dictated mainly by the fast isoforms.
我们研究了大鼠去皮肤骨骼肌纤维中不同纤维类型产生张力的钙敏感性，以及钙敏感性与不同调节蛋白和肌球蛋白轻链（MLC）亚型存在之间的可能相关性。通过肌球蛋白重链（MHC）亚型的电泳分析鉴定出1型、2A型和2B型纤维。显示一种以上MHC亚型的纤维被舍弃。比目鱼肌的1型纤维比2型趾长伸肌（EDL）纤维表现出更高的pCa（-log10[Ca]，其中[ ]表示浓度）阈值和更低的pCa/张力曲线斜率；在2型纤维之间，2B型显示出更高的pCa/张力曲线斜率。当仅包含慢调节蛋白和MLC组时，来自不同肌肉的1型纤维表现出相似的钙敏感性；当同时存在慢和快亚型时，钙敏感性向快型纤维值转变。来自不同肌肉的2A型纤维表现出相似的钙敏感性，与调节蛋白和MLC的组（纯快或混合）无关。有人提出，当肌肉纤维中同时存在调节蛋白和MLC的快和慢亚型时，钙敏感性主要由快亚型决定。
