title: Localization of the parallel elastic components in frog skinned muscle fibers studied by the dissociation of the A- and I-bands.
abstract: Localization of the parallel elastic components (PECs) in skinned muscle fibers was investigated by analyzing the change of the resting tension, which accompanies the dissociation of the A- and I-bands. The A-band was dissociated from both ends by increasing the concentration of KCl under relaxing conditions (0.09-0.54 M KCl, 4.0 mM MgATP, 1.0 mM Mg2+, 4.0 mM EGTA, pH 6.0-9.0, 20 degrees C). At sarcomere lengths greater than or equal to 3.5 microns, the length of the A-band was estimated by comparing the intensity of the first-order optical diffraction line with the results of model calculations. These results were supported by differential-interference microscopy and sodium dodecyl sulfate gel electrophoresis. It was shown that the resting tension decreased nearly in proportion to the residual length of the A-band. At sarcomere lengths less than or equal to 4.0 microns, the resting tension after the dissociation of the A-band was lowered to less than 10% of the initial value. On the other hand, at sarcomere lengths greater than or equal to 5.0 microns the resting tension after the dissociation of the A-band still showed approximately 35% of the initial value and did not change even after the I-band was dissociated by a solution containing KI. From these results, we propose that most of the PECs contributing to resting tension bind almost uniformly to the A-band and there are also PECs connecting Z-lines.
mesh_terms: D000199:Actins / Q000032:analysis; D000818:Animals; D004548:Elasticity; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology* / Q000648:ultrastructure; D009218:Myosins / Q000032:analysis; D009994:Osmolar Concentration; D011892:Rana catesbeiana; D013057:Spectrum Analysis
chemical_list: D000199:Actins; D009218:Myosins