Journal article
Phosphate has dual roles in cross-bridge kinetics in rabbit psoas single myofibrils
The Journal of general physiology, Vol.153(3), p.1
03/01/2021
DOI: 10.1085/jgp.202012755
PMCID: PMC7885270
PMID: 33599680
Abstract
In this study, we aimed to study the role of inorganic phosphate (Pi) in the production of oscillatory work and cross-bridge (CB) kinetics of striated muscle. We applied small-amplitude sinusoidal length oscillations to rabbit psoas single myofibrils and muscle fibers, and the resulting force responses were analyzed during maximal Ca2+ activation (pCa 4.65) at 15°C. Three exponential processes, A, B, and C, were identified from the tension transients, which were studied as functions of Pi concentration ([Pi]). In myofibrils, we found that process C, corresponding to phase 2 of step analysis during isometric contraction, is almost a perfect single exponential function compared with skinned fibers, which exhibit distributed rate constants, as described previously. The [Pi] dependence of the apparent rate constants 2πb and 2πc, and that of isometric tension, was studied to characterize the force generation and Pi release steps in the CB cycle, as well as the inhibitory effect of Pi. In contrast to skinned fibers, Pi does not accumulate in the core of myofibrils, allowing sinusoidal analysis to be performed nearly at [Pi] = 0. Process B disappeared as [Pi] approached 0 mM in myofibrils, indicating the significance of the role of Pi rebinding to CBs in the production of oscillatory work (process B). Our results also suggest that Pi competitively inhibits ATP binding to CBs, with an inhibitory dissociation constant of ∼2.6 mM. Finally, we found that the sinusoidal waveform of tension is mostly distorted by second harmonics and that this distortion is closely correlated with production of oscillatory work, indicating that the mechanism of generating force is intrinsically nonlinear. A nonlinear force generation mechanism suggests that the length-dependent intrinsic rate constant is asymmetric upon stretch and release and that there may be a ratchet mechanism involved in the CB cycle.
Details
- Title: Subtitle
- Phosphate has dual roles in cross-bridge kinetics in rabbit psoas single myofibrils
- Creators
- Masataka Kawai - University of IowaRobert Stehle - University of CologneGabriele Pfitzer - University of CologneBogdan Iorga - University of Cologne
- Resource Type
- Journal article
- Publication Details
- The Journal of general physiology, Vol.153(3), p.1
- DOI
- 10.1085/jgp.202012755
- PMID
- 33599680
- PMCID
- PMC7885270
- NLM abbreviation
- J Gen Physiol
- ISSN
- 0022-1295
- eISSN
- 1540-7748
- Grant note
- DOI: 10.13039/100000002, name: National Institutes of Health, award: HL70041; name: Medical Faculty of the University of Cologne; name: Köln Fortune; name: ImhoffStiftung, award: 36430148/2007; name: Medical Faculty of the University of Cologne; name: Maria-Pesch Stiftung, award: 36450243/2008
- Language
- English
- Date published
- 03/01/2021
- Academic Unit
- Anatomy and Cell Biology; Internal Medicine
- Record Identifier
- 9984288822702771
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