Selected Contribution: Mechanisms underlying increased force generation by rat diaphragm muscle fibers during development

• Published in: Journal of applied physiology (1985) Vol. 90; no. 1; pp. 380 - 388
• Main Authors: Geiger, Paige C., Cody, Mark J., Macken, Rebecca L., Bayrd, Megan E., Fang, Yun-Hua, Sieck, Gary C.
• Format: Journal Article
• Language: English
• Published: Bethesda American Physiological Society 01.01.2001
• Subjects: Muscular system; Rodents
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.2001.90.1.380

It has been found that maximum specific force (F max ; force per cross-sectional area) of rat diaphragm muscle doubles from birth to 84 days (adult). We hypothesize that this developmental change in F max reflects an increase in myosin heavy chain (MHC) content per half-sarcomere (an estimate of the number of cross bridges in parallel) and/or a greater force per cross bridge in fibers expressing fast MHC isoforms compared with slow and neonatal MHC isoforms (MHC slow and MHC neo , respectively). Single Triton 100-X-permeabilized fibers were activated at a pCa of 4.0. MHC isoform expression was determined by SDS-PAGE. MHC content per half-sarcomere was determined by densitometric analysis and comparison to a standard curve of known MHC concentrations. MHC content per half-sarcomere progressively increased during early postnatal development. When normalized for MHC content per half-sarcomere, fibers expressing MHC slow and coexpressing MHC neo produced less force than fibers expressing fast MHC isoforms. We conclude that lower force per cross bridge in fibers expressing MHC slow and MHC neo contributes to the lower F max seen in early postnatal development.