title: Depression of Ca2+ insensitive tension due to reduced pH in partially troponin-extracted skinned skeletal muscle fibers.
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.
authors.affiliation: Department of Physiology, School of Medicine, University of Wisconsin, Madison 53706.
authors.forename: J M
authors.initials: JM
authors.lastname: Metzger
authors.forename: R L
authors.initials: RL
authors.lastname: Moss
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology* / Q000502:physiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D014336:Troponin / Q000502:physiology*
chemical_list: D014336:Troponin; D002118:Calcium