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.

Deterioration induced by physiological concentration of calcium ions in skinned muscle fibres

“…Recently, elastic filaments have been reported to exist in sarcomeres and to connect Z-lines, or Z-line and thick filaments, bearing most of the resting tension in mechanically skinned fibres (Higuchi & Umazume, 1985). In highly-stretched muscle fibres, in which thick and thin filaments had no overlap, a decline in resting tension was observed in the present study.…”

“…If this is the case, the resting tension, which is ascribed to the force of elastic filaments connecting thick filaments to Z-lines (Higuchi & Umazume, 1985), should decline even in fibres stretched so as to abolish the overlap between thick and thin filaments. The effect of Ca 2+ was, therefore, examined in highly stretched fibres.…”

Spontaneous oscillatory contraction of sarcomeres in skeletal myofibrils

“…SPOC may be a dynamic structure that appears only in an organized system through dynamic competition between active tension developed by cross-bridges and passive tension produced by extension of the contractile system, including cross-bridges and thick and thin filaments and of passive elastic components distributed in different sarcomeres in series (Natori, 1954;Higuchi & Umazume, 1985;Magid & Law, 1985, Horowits et al, 1986.…”

Width and lattice spacing in radially compressed frog skinned muscle fibres at various pH values, magnesium ion concentrations and ionic strengths

“…It was shown by SDS-gel electrophoresis that at high F/2 myosin was selectively released from skinned fibres (Higuchi & Umazume, 1985). Therefore, this transient change of D would result from the dissociated myosin molecules diffusing from the inside to the outside of the fibre.…”

“…(1979) also studied this elastic protein and called it 'titin'. Connectin (titin) forms a network structure in the sarcoplasm and might be attached to the thick filaments (Maruyama et al, 1984;Higuchi & Umazume, 1985). Wang & Ramirez-Mitchell (1983) reported that elastic elements surrounded each myofibriI in muscle.…”