Force-calcium relationship depends on myosin heavy chain and troponin isoforms in rat diaphragm muscle fibers

• Published in: Journal of applied physiology (1985) 1999-11, Vol.87 (5), p.1894-1900
• Main Authors: Geiger, Paige C, Cody, Mark J, Sieck, Gary C
• Format: Article
• Language: English
• Subjects: Air breathing; Anatomy & physiology; Animals; Biological and medical sciences; Blotting, Western; Calcium; Calcium - physiology; Diaphragm - cytology; Diaphragm - metabolism; Electrophoresis, Polyacrylamide Gel; Fundamental and applied biological sciences. Psychology; Isomerism; Male; Muscle Contraction - physiology; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - physiology; Muscle Fibers, Skeletal - ultrastructure; Muscular system; Myosin Heavy Chains - biosynthesis; Myosin Heavy Chains - metabolism; Rats; Rats, Sprague-Dawley; Respiratory system: anatomy, metabolism, gas exchange, ventilatory mechanics, respiratory hemodynamics; Rodents; Troponin - biosynthesis; Troponin - metabolism; Vertebrates: respiratory system
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1999.87.5.1894

Departments of Anesthesiology and Physiology and Biophysics, Mayo Clinic and Foundation, Rochester, Minnesota 55905 The present study examined Ca 2+ sensitivity of diaphragm muscle (Dia m ) fibers expressing different myosin heavy chain (MHC) isoforms. We hypothesized that Dia m fibers expressing the MHC slow isoform have greater Ca 2+ sensitivity than fibers expressing fast MHC isoforms and that this fiber-type difference in Ca 2+ sensitivity reflects the isoform composition of the troponin (Tn) complex (TnC, TnT, and TnI). Studies were performed in single Triton-X-permeabilized Dia m fibers. The Ca 2+ concentration at which 50% maximal force was generated (pCa 50 ) was determined for each fiber. SDS-PAGE and Western analyses were used to determine the MHC and Tn isoform composition of single fibers. The pCa 50 for Dia m fibers expressing MHC slow was significantly greater than that of fibers expressing fast MHC isoforms, and this greater Ca 2+ sensitivity was associated with expression of slow isoforms of the Tn complex. However, some Dia m fibers expressing MHC slow contained the fast TnC isoform. These results suggest that the combination of TnT, TnI, and TnC isoforms may determine Ca 2+ sensitivity in Dia m fibers. myosin heavy chain; troponin; diaphragm muscle; single fibers; calcium sensitivity; cooperativity