Abstract
In a previous study, we have developed a method to determine the diameter of single myofibrils with the accuracy of 5 nm by use of an atomic force microscope (AFM). In the present study, we applied this method to examine the diameter changes of single skeletal myofibrils under various physiological conditions.< BR >Single myofibrils were prepared by homogenizing glycerinated muscle fibers of rabbit psoas muscle. AFM measurements were made as previously. Myofibrils were fixed on the surface of cover slip coated with aminosilane. Modified AFM cantilevers, having a small glass sphere (2 μm in diameter) glued to the tip of commercial AFM cantilever, were used. The diameter of myofibrils was determined as the difference between the height at the top surface of single myofibrils and that at the surface of cover slip next to the myofibrils.< BR >The diameter of single myofibrils thus obtained was 1.129 ± 0.064 μm in a relaxed state, 1.008 ± 0.075 μm in a rigor state and 1.011 ± 0.087 μm in a contracting state. The diameter of single myofibrils was nearly constant along the fiber axis ( < ±0.06 μm ) in each state. By the addition of Dextran, the diameter of myofibrils decreased in characteristic fashions; i.e. it decreased by 44% in a relaxed state and by 22% in a rigor state, at 8% Dextran. The diameter changes of single myofibrils thus obtained were consistent with the spacing changes of the actomyosin filaments lattice of muscle fibers under comparable conditions examined by X-ray diffraction studies. [J Physiol Sci. 2007;57 Suppl:S97]
