Changes in actomyosin ATP consumption rate in rat diaphragm muscle fibers during postnatal development

Gary C. Sieck, Y. S. Prakash, Young Soo Han, Yun Hua Fang, Paige C. Geiger, Wen Zhi Zhan

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Early postnatal development of rat diaphragm muscle (Diam) is marked by dramatic transitions in myosin heavy chain (MHC) isoform expression. We hypothesized that the transition from the neonatal isoform of MHC (MHCNeo) to adult fast MHC isoform expression in Diam fibers is accompanied by an increase in both the maximum velocity of the actomyosin ATPase reaction (Vmax ATPase) and the ATP consumption rate during maximum isometric activation (ATPiso). Rat Diam fibers were evaluated at postnatal days 0, 14, and 28 and in adults (day 84). Across all ages, Vmax ATPase of fibers was significantly higher than ATPiso. The reserve capacity for ATP consumption [1 - (ratio of ATPiso to Vmax ATPase)] was remarkably constant (∼55-60%) across age groups, although at day 28 and in adults the reserve capacity for ATP consumption was slightly higher for fibers expressing MHCSlow compared with fast MHC isoforms. At day 28 and in adults, both Vmax ATPase and ATPiso were lower in fibers expressing MHCSlow followed in rank order by fibers expressing MHC2A, MHC2X, and MHC2B. For fibers expressing MHCNeo, Vmax ATPase, and ATPiso were comparable to values for adult fibers expressing MHCSlow but significantly lower than values for fibers expressing fast MHC isoforms. We conclude that postnatal transitions from MHCNeo to adult fast MHC isoform expression in Diam fibers are associated with corresponding but disproportionate changes in Vmax ATPase and ATPiso.

Original languageEnglish (US)
Pages (from-to)1896-1902
Number of pages7
JournalJournal of applied physiology
Issue number5
StatePublished - May 1 2003



  • Fiber types
  • Immunohistochemistry
  • Myosin heavy chain
  • Skeletal muscle

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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