Journal of Applied Physiology Journal of Applied Physiology
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J Appl Physiol (February 14, 2003). doi:10.1152/japplphysiol.00618.2002
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Submitted on July 9, 2002
Accepted on February 11, 2003

ATP Consumption Rate Per Cross-Bridge Depends on Myosin Heavy Chain Isoform

Young-Soo Han1, Paige C Geiger2, Mark J Cody1, Rebecca L Macken1, and Gary C Sieck2*

1 Department of Anesthesiology, Mayo Medical School, Rochester, MN, USA
2 Department of Anesthesiology, Mayo Medical School, Rochester, MN, USA; Department of Physiology & Biophysics, Mayo Medical School, Rochester, MN, USA

* To whom correspondence should be addressed. E-mail: sieck.gary{at}mayo.edu.

In the present study, we tested the hypothesis that intrinsic differences in ATP consumption rate per cross-bridge exist across rat diaphragm muscle (DIAm) fibers expressing different myosin heavy chain (MHC) isoforms. During maximum Ca2+ activation (pCa 4.0) of single, Triton-X permeabilized DIAm fibers, isometric ATP consumption rate was determined using an NADH-linked fluorometric technique. The MHC concentration in single DIAm fibers was determined by densitometric analysis of SDS-PAGE gels and comparison to a standard curve of known MHC concentrations. Isometric ATP consumption rate varied across DIAm fibers expressing different MHC isoforms, being highest in fibers expressing MHC2X (1.14 ± 0.08 nmol mm-3 s-1) and/or MHC2B(1.33 ± 0.08 nmol mm-3 s-1) followed by fibers expressing MHC2A (0.77 ± 0.11 nmol mm-3 s-1) and MHCSlow (0.46 ± 0.03 nmol mm-3 s-1). These differences in ATP consumption rate also persisted when normalized for MHC concentration in single DIAm fibers. Normalized ATP consumption rate for MHC concentration varied across DIAm fibers expressing different MHC isoforms, being highest in fibers expressing MHC2X (2.02 ± 0.19 s-1) and/or MHC2B (2.64 ± 0.15 s-1) followed by fibers expressing MHC2A (1.57 ± 0.16 s-1) and MHCSlow (0.77 ± 0.05 s-1). Based on these results, we conclude that there are intrinsic differences in ATP consumption rate per cross-bridge in DIAm fibers expressing MHC isoforms.




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