Hoh Joseph F Y, Li Zhao-Bo, Qin Han, Hsu Michael K H, Rossmanith Gunther H
Discipline of Physiology and the Bosch Institute, University of Sydney, Building F13, Sydney, NSW, 2006, Australia.
J Muscle Res Cell Motil. 2007;28(6):329-41. doi: 10.1007/s10974-008-9129-x. Epub 2008 Mar 5.
Mechanical properties of the jaw-closing muscles of the cat are poorly understood. These muscles are known to differ in myosin and fibre type compositions from limb muscles. This work aims to correlate mechanical properties of single fibres in cat jaw and limb muscles with their myosin subunit compositions. The stiffness minimum frequency, f(min), which reflects isometric cross-bridge kinetics, was measured in Ca(2+)-activated glycerinated fast and slow fibres from cat jaw and limb muscles for temperatures ranging between 15 and 30 degrees C by mechanical perturbation analysis. At 15 degrees C, f(min) was 0.5 Hz for limb-slow fibres, 4-6 Hz for jaw-slow fibres, and 10-13 Hz for limb-fast and jaw-fast fibres. The activation energy for f(min) obtained from the slope of the Arrhenius plot for limb-slow fibres was 30-40% higher than values for the other three types of fibres. SDS-PAGE and western blotting using highly specific antibodies verified that limb-fast fibres contained IIA or IIX myosin heavy chain (MyHC). Jaw-fast fibres expressed masticatory MyHC while both jaw-fast and jaw-slow fibres expressed masticatory myosin light chains (MLCs). The nucleotide sequences of the 3' ends of the slow MyHC cDNAs isolated from cat masseter and soleus cDNA libraries showed identical coding and 3'-untranslated regions, suggesting that jaw-slow and limb-slow fibres express the same slow MyHC gene. We conclude that the isometric cross-bridge cycling kinetics of jaw-fast and limb-fast fibres detected by f(min) are indistinguishable in spite of differences in MyHC and light chain compositions. However, jaw-slow fibres, in which the same slow MyHCs are found in combination with MLCs of the jaw type, show enhanced cross-bridge cycling kinetics and reduced activation energy for cross-bridge detachment.
猫咬肌的力学特性目前尚不清楚。已知这些肌肉在肌球蛋白和纤维类型组成上与肢体肌肉不同。这项工作旨在将猫咬肌和肢体肌肉中单根纤维的力学特性与其肌球蛋白亚基组成联系起来。通过机械扰动分析，在15至30摄氏度的温度范围内，测量了猫咬肌和肢体肌肉中经Ca(2+)激活的甘油化快肌纤维和慢肌纤维的反映等长横桥动力学的刚度最小频率f(min)。在15摄氏度时，肢体慢肌纤维的f(min)为0.5赫兹，咬肌慢肌纤维为4至6赫兹，肢体快肌纤维和咬肌快肌纤维为10至13赫兹。从肢体慢肌纤维的阿累尼乌斯图斜率获得的f(min)的活化能比其他三种纤维类型的值高30%至40%。使用高度特异性抗体的SDS-PAGE和蛋白质印迹法证实，肢体快肌纤维含有IIA或IIX肌球蛋白重链(MyHC)。咬肌快肌纤维表达咀嚼型MyHC，而咬肌快肌纤维和咬肌慢肌纤维均表达咀嚼型肌球蛋白轻链(MLC)。从猫咬肌和比目鱼肌cDNA文库中分离出的慢肌MyHC cDNA 3'端的核苷酸序列显示编码区和3'非翻译区相同，表明咬肌慢肌纤维和肢体慢肌纤维表达相同的慢肌MyHC基因。我们得出结论，尽管MyHC和轻链组成存在差异，但通过f(min)检测到的咬肌快肌纤维和肢体快肌纤维的等长横桥循环动力学并无区别。然而，咬肌慢肌纤维中发现相同的慢肌MyHC与咬肌型MLC结合，显示出增强的横桥循环动力学和降低的横桥解离活化能。
