Depression of Ca2+ insensitive tension due to reduced pH in partially troponin-extracted skinned skeletal muscle fibers. |
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Authors: | J M Metzger and R L Moss |
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Affiliation: | Department of Physiology, School of Medicine, University of Wisconsin, Madison 53706. |
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Abstract: | Previous studies on skinned muscle fibers have demonstrated a direct effect of elevated levels of H+ ion to depress force production; however, the molecular basis for this effect is presently unknown. Here, whole troponin complexes were removed from skinned single fiber preparations of rat slow-twitch and fast-twitch muscles, and the effect of H+ ions on the resultant Ca2+-insensitive force was examined. The effect of H+ ions to depress force was found to be virtually identical in untreated control fibers activated in the presence of Ca2+ and in fibers activated in the absence of Ca2+ by troponin removal. Thus, the effect of H+ ions to depress force occurs at a step in activation beyond the disinhibition of the thin filament by Ca2+, probably involving reductions in the number of attached cross-bridges or in the force per attachment. |
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