Journal article
Cross-bridge scheme and force per cross-bridge state in skinned rabbit psoas muscle fibers
Biophysical journal, Vol.65(2), pp.638-651
08/1993
DOI: 10.1016/S0006-3495(93)81109-3
PMCID: PMC1225766
PMID: 8218893
Abstract
The rate and association constants (kinetic constants) which comprise a seven state cross-bridge scheme were deduced by sinusoidal analysis in chemically skinned rabbit psoas muscle fibers at 20 degrees C, 200 mM ionic strength, and during maximal Ca2+ activation (pCa 4.54-4.82). The kinetic constants were then used to calculate the steady state probability of cross-bridges in each state as the function of MgATP, MgADP, and phosphate (Pi) concentrations. This calculation showed that 72% of available cross-bridges were (strongly) attached during our control activation (5 mM MgATP, 8 mM Pi), which agreed approximately with the stiffness ratio (active:rigor, 69 +/- 3%); active stiffness was measured during the control activation, and rigor stiffness after an induction of the rigor state. By assuming that isometric tension is a linear combination of probabilities of cross-bridges in each state, and by measuring tension as the function of MgATP, MgADP, and Pi concentrations, we deduced the force associated with each cross-bridge state. Data from the osmotic compression of muscle fibers by dextran T500 were used to deduce the force associated with one of the cross-bridge states. Our results show that force is highest in the AM*ADP.Pi state (A = actin, M = myosin). Since the state which leads into the AM*ADP.Pi state is the weakly attached AM.ADP.Pi state, we confirm that the force development occurs on Pi isomerization (AM.ADP.Pi --> AM*ADP.Pi). Our results also show that a minimal force change occurs with the release of Pi or MgADP, and that force declines gradually with ADP isomerization (AM*ADP -->AM.ADP), ATP isomerization (AM+ATP-->AM*ATP), and with cross-bridge detachment. Force of the AM state agreed well with force measured after induction of the rigor state, indicating that the AM state is a close approximation of the rigor state. The stiffness results obtained as functions of MgATP, MgADP, and Pi concentrations were generally consistent with the cross-bridge scheme.
Details
- Title: Subtitle
- Cross-bridge scheme and force per cross-bridge state in skinned rabbit psoas muscle fibers
- Creators
- M Kawai - Department of Anatomy, College of Medicine, University of Iowa, Iowa City 52242Y Zhao - Department of Anatomy, College of Medicine, University of Iowa, Iowa City 52242
- Resource Type
- Journal article
- Publication Details
- Biophysical journal, Vol.65(2), pp.638-651
- DOI
- 10.1016/S0006-3495(93)81109-3
- PMID
- 8218893
- PMCID
- PMC1225766
- ISSN
- 0006-3495
- eISSN
- 1542-0086
- Language
- English
- Date published
- 08/1993
- Academic Unit
- Anatomy and Cell Biology; Internal Medicine
- Record Identifier
- 9984025680102771
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